Evaluation of two instrumentation techniques and obturation methods in mandibular first premolar C- shaped canals by Micro-CT

Evaluation of two instrumentation techniques and obturation methods in mandibular first premolar C- shaped canals by Micro-CT | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Evaluation of two instrumentation techniques and obturation methods in mandibular first premolar C- shaped canals by Micro-CT Yu Zhao, Yimeng Zhang, Jiayi Shi, Li Wang, Xuekai Qi, Duohong Zou, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4167729/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Aim To investigate the effect of instrumentation using Protaper Next (PN, Dentsply Sirona, Maillefer, Ballaigues, Switzerland) and Waveone Gold (WG, Dentsply Sirona, Maillefer, Ballaigues, Switzerland) systems on the area of untouched surface (US), accumulated hard tissue debris (AHTD), and the filling ability of two obturation techniques on the percentage of void within C-shaped root canals of mandibular first premolars. Methodology: 64 mandibular first premolars with C-shaped canals were scanned, matched and assigned to 2 shaping groups (n = 32): PN and WG. Following instrumentation, specimens were randomly assigned into two obturation subgroups (n = 16): continuous wave compaction (CWC) and single-cone (SC) techniques. The US% and AHTD% after instrumentation and the vol% of void after obturation were calculated from micro-computed tomography. Data were analyzed using comparisons for two groups (PN vs WG) or two subgroups (CWC vs SC) at α = 0.05. Results For PN and WG, 18.75% and 22.69%, respectively, of the canal wall remained untouched ( p > 0.05). For both groups, the apical third had higher US% than the coronal third ( p < 0.05). Instrumentation with WG left more debris (26.48%) than PN (8.36%) in the apical 1-3mm ( p 0.05). The apical region had significantly more voids than the coronal region of the canal space in the two obturation subgroups regardless of which system was applied ( p < 0.05). Conclusions Both PN and WG systems were associated with similar US after instrumenting C-shaped canals of the mandibular first premolar. WG left significantly more AHTD compared with PN in the apical region. In PN or WG group, SC yielded similar obturation quality when compared with CWC. Both CWC and SC obturation techniques provided poorer filling quality in the apical region than in the coronal region. Clinical Significance: Micro-CT evaluation of the PN and WG shaping C-shaped canals in mandibular first premolars showed similar effects on the percentages of untouched canal wall. The PN produced less hard tissue debris in the apical regions compared with the WG. The SC yielded similar obturation quality compared with the CWC. C-shaped canal instrumentation obturation mandibular first premolar micro-CT Figures Figure 1 Figure 2 Introduction C-shaped root canal system is a complex anatomical variation of mandibular first premolars [ 1 , 2 ] , with a considerable incidence of 12.5-67.47% in Chinese population [ 3 , 4 ] . The mandibular first premolars with this special morphology usually have a deep and narrow radicular groove [ 5 ] . The buccal and lingual canals are completely or partially connected through the isthmus to form a C-shaped or semicolon shape in cross-section. This feature is more common in the middle and apical segments of the root canal, with varying degrees of curvature [ 4 ] . The presence of anatomical structures such as irregular root canal morphology, accessory canals, connecting canals, and apical deltas, may harbor soft tissue remnants or infected debris and cannot be fully contacted by instruments. Moreover, hard tissue debris during instrumentation may be packed into the irregular regions of a C-shaped canal system. The debris may hamper sealing and disinfection of the root canal system [ 6 , 7 ] . These factors compromise the outcome of mechanical and chemical debridement and pose a great challenge to endodontists. Micro-computed tomography (micro-CT) is a non-destructive, three-dimensional analytical method that permits accurate evaluation of root canal system prior and subsequent to mechanical preparation by superimposing pre- and post-instrumentation scanning data. The morphological parameters that are related to the ultimate shaping and obturation results, including changes of surface area and volume, the amount of dentine removed, untouched area, the amount and distribution of hard-tissue debris, and the volume percentage of void may be calculated and analyzed using imaging software [ 8 – 11 ] . There are a variety of NiTi machine files with different mechanisms on the market, including rotation, reciprocating, central motion or eccentric motion [ 12 ] . Protaper Next (PN, Dentsply Sirona, Maillefer, Ballaigues, Switzerland) has a unique eccentric rectangular design and a progressive and decreasing percentage taper, which help to maximize debris removal from the root canal [ 13 ] . The offset mass of rotation is more suitable for preparing irregular canals. Several studies have found that Protaper Next owned superior shaping and centering ability [ 14 , 15 ] . Protaper Next system has a similar shaping ability in long-oval canals with XP-endo Shaper system (FKG Dentaire, La Chaux-de‐Fonds, Switzerland) [ 16 ] . Waveone Gold (WG, Dentsply Sirona, Maillefer, Ballaigues, Switzerland) systems have been introduced that use the same reciprocating motion as WaveOne (WO, Dentsply Sirona, Maillefer, Ballaigues, Switzerland). WG files have an off-center, parallelogram design. The parallelogram shaped cross sections are spatially ordered in a discontinuous manner, which allows variation of the instrument’s contact [ 17 ] . WG files are manufactured using advanced heat treatment technology [ 18 , 19 ] . The manufacturer claims that the flexibility of WG is improved through this new heat treatment method. Based on the complexity and variability of the C-shaped canal anatomy in the mandibular first premolars, thoroughly removal of microorganisms is not always achievable. The surviving microorganisms must be sealed by root canal filling material, which would block microorganisms and toxins from entering the root canal system from the oral cavity [ 20 ] . Three-dimensional filling of the prepared canal is of critical importance for the success of root canal therapy. There are several ways to obturate root canals, including the lateral compaction technique, the thermos-plasticized gutta-percha obturation, the continuous wave obturation, the core-carrier technique, the single cone technique and so on. Despite a large number of accessory gutta-percha cones were inserted in C-shaped canals, the radiographic appearance was less dense than normal root canals. Previous studies showed that the quality of filling with lateral compaction technique in oval canals [ 21 ] was less reliable. The MicroSeal system is a thermomechanical filling technique that uses a lateral compaction and placement of α-gutta-percha to backfill the canal. Ordinola-Zapata found that the technique was not able to seal the C-shaped canal completely, especially the apical third [ 22 ] . Although previous studies have shown that thermos-plasticized gutta-percha was more appropriate for filling abnormal canal [ 23 ] , in the work of Soo et. al, the thermos-plasticized gutta-percha technique to fill C-shaped canal resulted in poor apical sealing but excellent adaptation in the coronal two-thirds of the canal [ 24 ] . With respect to the filling effect of the core-carrier technique in C-shaped canal obturation, data published in the literature are contradictory. Whereas the core-carrier technique was reported to be more effective when assessed by gutta-percha area than the lateral compaction and the thermos-plasticized gutta-percha obturation in this simulated C-shaped canal [ 24 ] , the result could not be validated in two more recent studies that used a similar experimental design [ 25 , 26 ] . The continuous wave compaction technique and single-cone technique are frequently used in clinical practice. The thermal gutta-percha softened in vertical compression is considered beneficial for filling complex root canals [ 27 ] . The single-cone technique gained popularity with the introduction of bioceramic sealer. iRoot SP (Innovative BioCeramix Inc, Vancouver, Canada) is a premixed bioceramic endodontic sealer which contains zirconium oxide, tricalcium silicate, dicalcium silicate, colloidal silica, calcium silicates, calcium phosphate monobasic, and calcium hydroxide, filler and thickener [ 28 ] . As an endodontic sealer, iRoot SP has many desirable properties such as biocompatibility, chemical stability, hydrophilicity, flowability, radiopacity, and slight expansive tendencies [ 29 – 32 ] . These characteristics of iRoot SP have been expected to improve the effect of root canal obturation and may allow for an enhanced seal within otherwise inaccessible canal anatomies. Recent research found that the SC technique was effective in filling mandibular molar canals, resulting in fewer voids [ 33 , 34 ] . A retrospective survey also suggested that the SC technique with bioceramic sealer achieved a success rate of 90.9% in initial treatment and retreatment [ 35 ] . Nevertheless, comprehensive knowledge on the shaping results of the aforementioned two off-center design NiTi systems and the sealing ability of the continuous wave compaction and single cone techniques in complex canal systems, such as that found in C-shaped canals of mandibular first premolars is lacking. Accordingly, the present study was designed to quantitatively evaluate the shaping properties of PN and WG instruments and the sealing ability using two obturation approaches in the C-shaped canal of mandibular first premolars. The null hypotheses tested were: 1) the PN system and the WG system produce similar morphological features after instrumentation of C-shaped canals; and 2) there is no difference between the two obturation techniques in their percentage of void. Methods and materials Specimen selection The protocol of the current study was approved by the Ethics Committee of School and Stomatology Wenzhou Medical University (WYKQ2021007). The specimens were scanned using a high-resolution micro-computed tomographic system (SkyScan 1176; Bruker-micro-CT, Kontich, Belgium) with an isotropic resolution of 17.54 µm at 90 kV, 270 µA, 0.1 mm Cu filter, and 360° rotation with a rotation step of 0.5°. The raw data was reconstructed by NRecon (v 1.6.10.4; Bruker-micro-CT, Kontich, Belgium) and was exported in TIFF format. After 3D reconstruction from the scanned data using CTAn software (v 1.20.3.0; Bruker-micro-CT, Kontich, Belgium), a total of 64 mandibular first premolars, each with a C-shaped canal system according to previously reported definition [ 36 ] , were selected and paired into 2 groups (n = 32) based on anatomical similarity to enable homogeneous specimen distribution in each group. The extracted teeth had mature apices, no fractures or cracks, no caries or calcification, and no signs of endodontically treatment. Matched standards included 3D morphology, preoperative volume and surface area of root canals. A tooth from each pair was randomly allocated to one experimental group and the group to be shaped with Protaper Next rotary files or Waveone Gold reciprocating file was determined by a coin toss. Canal instrumentation Each tooth was accessed using a diamond bur. The access cavity was filled with 1 mL of 1% NaOCl solution, and apical patency was created using a size 10 K-file (Dentsply Sirona, Maillefer, Ballaigues, Switzerland) until the file was visible at the apical foramen. The canal was irrigated with 2 mL of 1% NaOCl solution. The working length (WL) was determined as the total canal length minus 1.0 mm. Glide path preparation in both groups was developed with size 15 K-files to WL. All the canals were irrigated with 2 mL of 1% NaOCl in the two groups. Two coats of nail polish were applied to seal the apex [ 37 ] . Protaper Next (PN) group The X1(size 17/.04 taper) and X2(size 25/.06 taper) files were serially powered by the motor X-smart plus (Dentsply Sirona, Maillefer, Ballaigues, Switzerland) with parameters set at 300 rpm and torque 2.5 N /cm 2 . The instrument was used in a slow in-and-out motion of approximately 3 mm in amplitude in the apical direction, using a gentle brushing motion against the canal wall. The procedure was repeated twice until the WL was reached. Waveone Gold (WG) group Small (size 20/.07 taper) and Primary (size 25/.07 taper) files were applied in the canals with an in-and-out motion by the reciprocating “WaveOne ALL” setup of the same motor. After 3 movements of at most 3 mm amplitude in the apical direction, using a gentle brushing motion against the canal wall, the instrument was removed and cleaned with gauze. Working length was reached after 3 cycles of instrumentation used in the same fashion. The same irrigation protocol during instrumentation was used in both groups. For all specimens, the total amount of 1% NaOCl solution used in a canal was 5 mL for glide path preparation and 15 mL for shaping. During shaping, each root canal was irrigated with 2.5 mL 1% NaOCl solution when the instrument was removed from the canal and cleaned. The irrigant was delivered at a flow rate of 5 mL min − 1 with a 30-gauge needle adapted to a disposable plastic syringe. A final 1 mL sterile water rinse was used, and the canals were dried with size 25/.06 taper paper points (Dentsply Sirona, Maillefer, Ballaigues, Switzerland). The tip of needle was placed as apically as possible without binding and up to 1 mm short of the WL. A single operator with experience of PN and WG systems performed the operation in all canals. Subsequent to mechanical and chemical debridement, the access cavities were sealed with Cavition (GC Corporation, Tokyo, Japan). Micro-CT analysis All postoperative specimens were scanned with the preoperative parameter settings. The scanning data sets before and after instrumentation were co-registered using the Data Viewer (v 1.5.6.2; Bruker-micro-CT, Kontich, Belgium). The canals were segmented in the CTAn software (v 1.20.3.0; Bruker-micro-CT, Kontich, Belgium) using the 2-dimensional Otsu method. Morphologic parameters of the pre- and post-instrumentation root canal system (volume and surface area) were calculated. Information including removed dentin volume (RDV, in mm 3 ), accumulated hard tissue debris (AHTD, in mm 3 ), area of untouched surface (US, in mm 2 ), minimum mesial wall thickness (MT, in mm) and the volume void (vV, in mm 3 ) was evaluated and analyzed by CTAn, and 3D models were created in STL format by the same software. A radiopaque shadow with a density similar to dentin appeared in the radiolucent pre-operative canal images, and the percentage of this radiopaque shadow with respect to the volume of the root canal before preparation was defined as AHTD [ 37 – 39 ] . The US parameter was expressed as a percentage of the static surface voxels to the total pre-instrumentation surface voxels [ 40 , 41 ] . The two parameters of each experimental group were recorded along the total canal length, the apical (1–3 mm), middle (3–6 mm) and cervical (6–9 mm) regions. The percentage of MT thinning was calculated according to the formula: (MT B -MT A )/MT B ×100%, where MT B and MT A are the thickness of minimum mesial wall before and after instrumentation. Canal obturation The specimens after instrumentation were pair-matched in each group with respect to the 3D morphology of root canal. One tooth from each pair was randomly assigned to one of the two subgroups (n = 16) according to the obturation technique employed: Continuous wave compaction subgroup (CWC) : Each sample was filled with gutta-percha cone (25/.06) (Dentsply DeTrey GmbH, Konstanz, Germany) and AH plus sealer (Dentsply DeTrey GmbH, Konstanz, Germany). EQ-V Pack Tip (Meta Biomed Co, Cheongju-si, Chungbuk, Korea) was used to remove excess cone in the upper segment, leaving only 4-6mm within working length, and EQ-V thermal gun (Meta Biomed Co, Cheongju-si, Chungbuk, Korea) was used to backfill. Single-cone subgroup (SC) : Each sample was filled with gutta-percha cone (25/.06) and iRoot SP sealer (Innovative BioCeramix Inc, Vancouver, Canada). The upper segment was removed with EQ-V heat source, and 1mm lower the canal orifice level was retained. Each specimen was subjected to a post-obturation scan; the scanned data were used for reconstruction following the aforementioned parameters. The volume percentage of void (vol%) was calculated according to the formula: V v /(V v +V F )×100%, where V v and V F are the volume of the void after obturation and the volume of the filling material, respectively. The vol% of void in the entire canal and the different regions (i.e. coronal-third, middle-third and apical-third) of the canal were recorded. Statistical analyses The normality of all data was tested using the Shapiro-Wilk test. Tests were conducted on the change of surface area and volume, RDV, AHTD, US, MT and vol% of void. Even after multiple nonlinear transformations, the data failed to meet the normality assumption. Therefore, the statistical analyses were performed using the Wilcoxon signed-rank test. Each data set was expressed as a median and confidence interval (CI). Inter groups comparison was performed using Kruskal-Wallis analysis. ALL statistical analyses were performed using IBM SPSS v23.0 (SPSS Inc., Chicago, IL, USA). The significance level was pre-set at α = 0.05. Results Representative examples of micro-CT reconstructions of the changes in C-shaped canals of mandibular first premolars after instrumentation with the PN or WG system, and after obturation with CWC and SP are shown in Fig. 1 . Representative cross sections of hard tissue debris accumulation (orange) in post-instrumented C-shaped canals of mandibular first premolars are shown in Fig. 2 . Data derived from the coronal-third, middle-third, and apical-third regions of the canal space are illustrated in order. The pre-instrumentation surface areas (mm 2 ) and volumes (mm 3 ) were 88.68 mm 2 and 18.14 mm 3 in the PN group and 88.57 mm 2 and 18.73 mm 3 in the WG group (Table 1 ), respectively ( p > 0.05). There was no significantly difference in surface areas and volumes between the PN and WG groups before instrumentation. After instrumentation, the morphologic parameters between the two groups still had no significant difference (p > 0.05), including the increased volumes, increased surface areas, and removed dentine (Table 1 ). Table 1 Canal Volume (mm 3 ) and Surface Area (mm 2 ) before and after instrumentation using Protaper Next (PN) and Waveone Gold (WG) systems as well as the increased percentages (%) (median and confidence interval) PN WG Canal Volume Before (mm 3 ) 18.14 (15.50-20.82) 18.73 (14.67–20.45) After (mm 3 ) 20.76 (19.52–24.91) 22.56 (18.63–22.95) Canal Volume Increased (%) 10.10 (2.64–20.78) 13.65 (3.24–21.15) Canal Surface Area Before (mm 2 ) 88.68 (78.27–93.38) 88.57 (77.81–99.88) After (mm 2 ) 96.42 (90.03-107.62) 94.77 (84.84-106.85) Canal Surface Area Increased (%) 10.33 (6.05-14.00) 9.55 (4.13–12.33) There were no significant differences in any of the parameters between the Protaper Next and Waveone Gold groups ( p > 0.05). US of the entire canal was 18.75% in the PN group and 22.69% in the WG group, respectively (US shown in Table 2 ). There was no significant difference in the percentage area of untouched surface (US) between the two groups. Distributions of US from different regions of the canal space are collectively represented in Table 2 . The apical region (1–3 mm) of the canal space had significantly higher US% when compared with coronal region (6–9 mm) in the PN group ( p < 0.05); there was no significant difference between the apical region and the middle region, and between the middle region and the coronal region of the canal wall. For the WG group, the apical region had significantly higher US% than the middle region, which had significantly higher US% than the coronal region ( p < 0.05). Canal perforation was not observed in all specimens. Table 2 US (%) and AHTD (vol%) after instrumentation using Protaper Next (PN) and Waveone Gold (WG) systems in mandibular first premolars with C-shaped root canals (median and confidence interval) US(%) AHTD(%) PN WG PN WG Entire canal 18.75 (13.09–23.96) 22.69 (14.01–28.41) 1.39 (0.99–2.16) 2.15 (1.35–2.79) Apical region (1–3 mm) 35.25 (24.22–51.76) A 64.34 (39.84–74.78) A 8.36 (5.25–15.63) A * 26.48 (13.15–47.42) A * Middle region (3–6 mm) 24.97 (19.53–37.25) AB 33.63 (20.25–42.95) B 4.83 (3.36–8.46) B 5.74 (3.23–9.72) B Coronal region (6–9 mm) 16.15 (11.45–24.47) B 15.21 (6.96-22.00) C 1.64 (1.27–2.71) C 1.26 (0.72–3.41) C Asterisk (*) indicates significant difference between different instruments ( p < 0.05). Different uppercase superscripts in a single column represent significant differences among the different regions ( p < 0.05). Instrumentation of the C-shaped canals of mandibular first premolars using WG left 2.15% of the initial canal volume filled by dentin debris. In contrast, only 1.39% of the original canal volume was filled by debris in the PN group; the difference between the two groups was not statistically significant in the entire canal ( p > 0.05). For comparisons of different regions of the canal space, significant difference between the PN and WG groups could only be identified from the apical region of the canal space. For canals instrumented with the two systems, the coronal region of the canal space had significantly less debris than the middle region, which, in turn, had significantly less debris than the apical region ( p < 0.05 for all pairwise comparisons) (Table 2 ). After instrumentation, the MT was less than 0.5 mm in 65.63% (42/64) of the samples, with a minimum value of 0.14mm. The MT in the cross-section containing the C-shaped canal was thinned to varying degrees in each level of the root canal, with the most pronounced reduction in the M-1 and M level (MT shown in Table 3 ). Significant difference on the percentage of MT thinning between the PN and WG groups could not be identified in the middle regions with C-shaped morphology. Table 3 Minimum mesial wall thickness (MT) before and after preparation and the percentage of MT thinning after instrumentation using Protaper Next (PN) and Waveone Gold (WG) systems in mandibular first premolars with C-shaped root canals (median and confidence interval) Group/level n Before (mm) After (mm) Thinning (%) PN M + 1 19 0.86(0.62–1.13) 0.81(0.48–1.05) 12.0(9.5–15.8) M 23 0.68(0.60–0.88) 0.52(0.42–0.87) 22.6(10.7–33.7) M-1 29 0.68(0.60–0.78) 0.51(0.39–0.69) 21.0(7.2–35.2) AM 18 0.61(0.56–0.72) 0.52(0.45–0.57) 16.2(6.5–23.4) WG M + 1 17 0.86(0.72–1.03) 0.73(0.51–0.96) 12.3(5.0-24.1) M 22 0.71(0.62–0.86) 0.60(0.48–0.65) 15.2(5.9–23.1) M-1 23 0.61(0.59–0.71) 0.49(0.42–0.58) 19.3(6.3–30.6) AM 18 0.61(0.54–0.71) 0.50(0.48–0.64) 6.6(4.9–13.0) There was no significant difference on the degree of MT thinning in M + 1, M, M-1, AM levels after preparation between PN and WG ( p >0.05). M + 1, 1 mm above the middle of the root; M, the middle of the root; M-1, 1 mm below the middle of the root; AM, the junction of apical third and middle third of root. The vol% of void after obturation in two instrumentation groups are collectively represented in Table 4 . Irrespective of the type of file system employed for canal shaping, the two obturation protocols both produced the voids in C-shaped canals. In PN and WG group, the vol% of void had no significant difference between the CWC and SC subgroups( p > 0.05). The results about the comparisons of different regions of the canal space in two instrumentation groups were similar. The apical region had significantly more voids than the coronal region of the canal space ( p 0.05). Table 4 Volume percentage (vol%) of void after obturation using continuous wave compaction (CWC) and single cone (SC) techniques in mandibular first premolars with C-shaped root canals (median and confidence interval) PN WG CWC (%) SC (%) CWC (%) SC (%) Entire canal 5.37 (3.00-8.13) 5.46 (2.29–12.77) 4.44 (1.85–14.62) 6.57 (2.25–13.25) Apical region (1–3 mm) 18.65 (3.73–32.55) A 26.38 (3.25–30.26) A 12.11 (5.58–28.83) A 27.73 (10.46-62.00) A Middle region (3–6 mm) 7.15 (0.62–12.37) AB 5.56 (2.15–28.04) AB 3.63 (1.35–16.99) AB 10.95 (3.38–18.59) AB Coronal region (6–9 mm) 2.46 (0.81–3.76) B 1.75 (0.75–5.92) B 4.64 (0.98–9.19) B 4.26 (1.86–8.66) B No significant difference between the two filling methods when the same shaping instruments were applied ( p > 0.05). Different uppercase superscripts in a single column represent significant differences among the various regions ( p < 0.05). Discussion Anatomical complexities and high variabilities in C-shaped canal of the mandibular first premolar increase the difficulty in evaluating the instrumentation and obturation during the root canal treatment. The 64 mandibular first premolars were pre-screened before preparation using micro-CT. Based on root canal volume, surface area, and 3D C-shaped canal classification, the specimens were paired and randomly allocated into the PN and WG instrumentation groups to ensure a good uniform distribution of samples between the two groups and to reduce the risk of bias due to anatomical structures. There was no significant difference in the canal volume and surface area before and after preparation in the two instrumentation groups ( p > 0.05). After the preparation, the teeth were divided into two obturation subgroups (n = 16) in each experimental group. Statistical analysis confirmed the homogeneity of baseline parameters between the groups and improved the internal validity of this study [ 42 , 43 ] . The increase of canal surface area and volume, as well as the amount of removed dentine in the two experimental groups has no significant difference in present study. The X2 file in the PN system created a .06 taper in the apical 3 mm and ISO #25 diameter, while the Primary file in the WG system created a larger taper (.07 taper) and an equal diameter (0.25 mm) during instrumentation of the canal space. The tiny difference of taper in file design is not enough to cause the significantly different changes in canal volume and surface area, as well as dentine removal in the present study. Previous studies on mandibular second molars have shown that the wall of the C-shaped root canal was thinner on the side near the radicular groove than on the remaining sides [ 44 – 46 ] . Gu et al. [ 47 ] measured the canal wall thickness at various levels in C-shaped root canals of mandibular first premolar teeth and confirmed that the above findings were also applicable in mandibular first premolar teeth. The canal in mandibular first premolar characteristically bifurcates in the apical and middle regions to form C-shaped root canal structures [ 4 ] . The irregular morphology of C-shaped root canals is more likely to result in strip perforation during root canal preparation [ 36 , 48 ] . Our previous study revealed that the further the distance from the cemento-enamel junction, the deeper root radicular groove, the smaller the radicular groove angle, and the thinner the mesial wall. As a result, mechanical preparation of the root canal, particularly the lingual root canal and the lower segment, should be executed carefully to prevent unexpected deviation and perforation. In this study, the thickness of the mesial wall in the cross-section with C-shaped canal was measured before and after instrumentation. After cut by the two systems, the remain MT was less than 0.5 mm in 65.63% of the samples. The results supported the above-mentioned statements. Although the C-shaped morphology may occur in various levels along the root canal of mandibular first premolars, the distribution of sample size in each level is uneven. It also has been demonstrated in present study that C-shaped morphology more commonly occurred in the middle regions of the canal. Based on the fact, the degree of MT thinning between the two systems was compared in the M + 1, M, M-1, and AM levels. There was no significant difference between the two files on the degree of MT thinning, which might be accounted for the similar cross section design of the two instruments. It has been suggested that the isthmus of C-shaped canals should not be instrumented by files larger than ISO #25 to avoid perforating the canals [ 49 ] . In the present study, no perforation was observed using either X2 or Primary file in two experimental groups. However, the extreme value of MT after instrumentation was 0.14mm, which carried an extreme risk of perforation during the canal cleaning. The two experimental groups left a similar percentage of untouched surface area in the C-shaped canals of mandibular first premolars. In the PN and WG group, the untouched surface area was 18.75% and 22.69%, respectively. The results are less than those reported in previous studies about the instrumentation of the C-shaped canals in mandibular molars with different NiTi systems [ 50 – 53 ] . Although the two type teeth all possessed C-shaped canal systems, quantitative divergence between the previously-reported data and the present data may be attributed to the difference in root canal volume of different tooth types. The C-shaped canal in mandibular first premolar is relatively narrower and smaller, and therefore larger proportion canal wall would be treated by the instruments during the shaping process. Despite the innovations in designs, metallurgies, kinematics and thermal treatments, neither of the two NiTi systems were capable of completely touching the root canal walls. There were no significant differences between the mechanized preparation systems regarding the percentages of US. Several previous studies reported that untreated surface varied from 19.9–41.5% in curved mesial root canals of mandibular molars and 55.3% in distal root canals of mandibular molars after using Protaper Next [ 54 – 56 ] . Moreover, two recent studies on Waveone Gold shaping in oval-shaped canals reported that the percentage of unprepared area was 18.9–50.9% [ 56 , 57 ] . Although it has been reported that greater taper files were able to touch more canal surface [ 58 ] , the statement was not confirmed in the present study. The percentage of US remained in the apical regions of the canal space was 35.25% in PN group and 64.34% in WG group, respectively. The values of US in apical region were higher than those in coronal region in the either groups. The similar results regarding the instrumentation of C-shaped canal in mandibular molars were reported by Zhao et al. [ 50 ] . High percentages of US in the apical regions may be attributed to the complexity of apical anatomy of C-shaped canals. Factors such as the severe curved canal, the existence of accessory canals, lateral canals, intercanal communications and apical deltas [ 59 – 61 ] are likely to hamper optimal debridement of the apical region in these complicated canal systems. These findings also support the viewpoint that the irrigation and intracanal medicament plays a key role in chemo-mechanical preparation to compensate for the deficiencies of mechanical debridement [ 58 , 62 ] . Hard tissue debris, as an undesirable by-product of dentin removal during mechanical preparation [ 63 ] , was usually packed into the irregular regions of the root canal system. Some studies have found that accumulated debris in canal would compromise the effectiveness of canal irrigation or medication [ 64 ] and also block the flow of filling material [ 65 ] . Moreover, the debris contains bacteria and serves as a nidus for root canal re-infection. Paqué et al. [ 64 ] has established a method to qualitatively and quantitatively analyze the remained dentine debris in root canal system during instrumentation. In the present study, AHTD was identified in all specimens irrespective of the file system employed. There was no significant difference on AHTD in the total canal using two shaping techniques. However, the PN system produced a relatively lower percentage of AHTD in the apical regions of the canal space, when compared to the WG system. The result may be explained by the differences in movement kinematics and the tapers of the respective file systems. The kinematics of a NiTi file system may be an influential factor in debris removal. With respect to this issue, data published in the literature are contradictory. Whereas reciprocating systems were reported to produce more debris accumulation than rotary systems in the mesial root canals of mandibular molars [ 39 ] and in the C-shaped canals of mandibular molars [ 50 ] , this difference could not be validated in another study that used a similar experimental design [ 66 ] . The continuous forward motion of the rotary file enables constant exit of debris up the flute of the file, while reciprocating motion might push debris into recesses and isthmus areas [ 67 ] .The PN rotary file had an off-centered rectangular cross-section with progressive and decreasing percent taper design, superior strength and novel asymmetric rotational motion [ 68 , 69 ] for maximum debris removal [ 13 ] . These PN design features provide a wider chip space and a smaller tip taper (X1: size 17/.04 taper and X2: size 25/.06 taper), and when accompanied by rotary movement, improve debris removal from the canal system. The debris that remained in C-shaped canals of the mandibular premolars shaped by the WG system was less in the present study than the previous studies [ 39 , 66 ] . The difference may be attributed to different tooth type and irrigation protocols. Results on AHTD distribution in isolated regions were similar in the two groups. Data from the present study were consistent with those published in the literature by Zhao et al [ 50 ] who compared reciprocating and rotary techniques on a C-shaped canal in mandibular molars. The vol% was highest in apical region and lowest in coronal region. The complexity of apical anatomy in C-shaped canals and the difficulty for root canal irrigants in reaching the apical region [ 70 ] could lead to the aforementioned result. According to the available findings and the aforementioned results in the present study, no instrumentation protocol has been able to render the complex areas in C-shaped canal free of debris [ 50 , 66 , 67 ] .Therefore, a three-dimensional sealing of root canal is of critical importance for successful endodontic treatment when accumulated debris is present within the irregular areas. Several methodologies are applied to evaluate the quality of root canal filling, including: two-dimensional radiographs [ 71 ] , dye or alternative tracer leakage models [ 7 ] , the stereomicroscopic evaluation of root cross-sections [ 21 , 25 ] , and micro-CT scanning [ 72 , 73 ] .The dye penetration cannot adequately simulate true clinical conditions. The air entrapment in voids along the root canal filling will hinder the fluid dye infiltration [ 74 ] . The loss of material during sectioning and discontinuous cross sections may affect the accurate evaluation on the percentage of void [ 11 ] . Reconstructing 3D model by micro-CT scanning and imaging allows accurate assessment of canal filling outcomes. Micro-CT has the potential to differentiate filling materials, voids, and tooth structures [ 75 ] . The methodology provides a clear information about the distribution of the root filling materials, the location and volumetric measurements of internal voids along the entire root canal system. The majority of published papers on the filling quality of C-shaped canal have focused on studying mandibular molars. Due to the diversity of research methods, sample selection, and filling methods, the results on the effectiveness of C-shaped root canal filling are not completely consistent. Previous studies have demonstrated that the filling quality of C-shaped canals was unsatisfactory with the cold lateral compaction technique, the MicroSeal system, the thermos-plasticized gutta-percha obturation, and the core-carrier technique. For the significant difficulties in sample collection, the present study only evaluated the quality of obturation on the volume percentage of void after the use of SC and CWC in the C-shaped canals of mandibular first premolars. The present results showed that more voids were observed in the apical 1-3mm regions in all subgroups. The present and previous studies all indicated that the apical third of C-shaped canals was filled less completely using the cold lateral compaction, the MicroSeal, the core carrier, the CWC, and the SC technique [ 22 , 24 , 25 ] . The poor filling quality of the apical part could be caused by the irregular anatomy of the C-shaped canal. The divergent areas in the apical region of C-shaped canals are commonly unshaped, which hinders the obturating material, including gutta-percha and sealer, from flowing into the abnormalities. Although softened warm gutta-percha has excellent adaptation in the coronal two-thirds of the canal, the insufficient extension is still the main reason of the unsatisfactory apical filling [ 76 ] . Moreover, the dentine plug in the canals also serves as a barrier for the high quality apical obturation [ 77 ] . The CW technique can provide better filling of canal irregularities and lateral canals [ 23 ] , especially in the coronal regions [ 34 ] . The findings were comparable to the present study. The results may be accounted for the heated gutta-percha adapts more easily to the irregularities of the root canal during the backfilling procedure [ 78 ] . Moreover, the coronal gutta-percha receives forces more directly, optimizing filling material adaptation in this region. iRoot SP has the superior flowability and the ability to slightly expand during setting [ 79 ] . As a bioceramic material, the sealer can produce hydroxyapatite, which precipitate within the calcium silicate hydrate phase and reinforces a bond between the dentinal wall and the sealer [ 80 ] . In addition, iRoot SP displayed potent antibacterial effect against E. faecalis [ 81 ] , which might be a combination of high pH, hydrophilicity, and active calcium hydroxide release. The above-mentioned characteristics make iRoot SP a good choice as the sealer to be used in a SC technique. Regarding to the obturation quality of SC in various types canal, the studies have shown mixed results. Inan et al. [ 82 ] found the apical sealing ability of SC was comparable with that of lateral condensation and Thermafil techniques in lower premolars. Holmes et al . [ 26 ] found that the filling quality of the SC was inferior to that of cold lateral technique and superior to that of core carrier technique in the C-shaped canals. In the present study, the SC with iRoot SP sealer did not produce superior filling quality than the CWC with `AH plus sealer in the C-shaped canal of the mandibular first premolars. Other studies also suggested that the SC technique yielded similar obturation quality when compared with the continuous wave compaction technique in the curved mesial canals of the mandibular molars and the canals of the maxillary left central incisor 3D–printed replicas [ 26 , 34 , 83 ] . Aithough many studies has shown that the technique has questionable sealing ability, the simplicity is the main advantage of the SC which makes the faster canal obturation possible. Moreover, in a retrospective survey about the clinical outcome of SC technique with Bioceramic Sealer, the success rate of the initial treatment and retreatment was up to 90.9%. Therefore, the SC with iRoot SP sealer is still a viable option for the C-shaped canal obturation in mandibular first premolars. Conclusion Within the limitations of the present ex vivo study, the Protaper Next and Waveone Gold systems were associated with considerable percentages of untouched canal wall after shaping C-shaped canals in mandibular first premolars. The Protaper Next system produced less hard tissue debris in the apical regions during instrumentation compared with the Waveone Gold system. More untouched canal areas and a larger proportion of AHTD were observed in apical region of the C-shaped canals irrespective of the canal instrumentation system used. Neither of the techniques tested was capable of thoroughly sealing the C-shaped canals. More voids were remained in the apical region regardless of which system was selected to prepare and which technique was applied to obturate. The SC technique with iRoot SP yielded similar obturation quality when compared with the continuous wave compaction technique. Further studies are necessary to investigate the prognosis of the treatments performed with this technique, especially in the premolars with complex C-shaped canals anatomy. Declarations Author's Contribution YZ, YZ, DZ and YP conceived the study and designed the experiments. YZ, JS, LW and XQ collected the samples. YZ, YZ and JS performed the experiments, analyzed the data and wrote the manuscript. DZ and YP edited and approved the final manuscript. All authors contributed to the article and approved the submitted version. Conflict of interest All authors have no conflicts of interest to declare. Funding This study was supported by the National Natural Science Foundation of China (80218095). Ethics approval All procedures performed in studies involving human participants were in accordance with relevant guidelines and regulations and the ethics approval was provided by the ethical standards of the Ethics Committee of School and Stomatology Wenzhou Medical University (WYKQ2021007). 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J Oral Sci 57:361-6. https://doi.org/ 10.2334/josnusd.57.361 Veríssimo DM and do Vale MS (2006) Methodologies for assessment of apical and coronal leakage of endodontic filling materials: a critical review. J Oral Sci 48:93-98. https://doi.org/ 10.2334/josnusd.48.93 Jung M, Lommel D and Klimek J (2005) The imaging of root canal obturation using micro-CT. Int Endod J 38:617-626. https://doi.org/ 10.1111/j.1365-2591.2005.00990.x Amditis C, Blackler SM, Bryant RW and Hewitt GH (1992) The adaptation achieved by four root canal filling techniques as assessed by three methods. Aust Dent J 37:439-444. Scott AC and Vire DE (1992) An evaluation of the ability of a dentin plug to control extrusion of thermoplasticized gutta-percha. J Endod 18:52-57. https://doi.org/ 10.1016/S0099-2399(06)81370-1 Peng L, Ye L, Tan H and Zhou X (2007) Outcome of root canal obturation by warm gutta-percha versus cold lateral condensation: a meta-analysis. J Endod 33:106-9. https://doi.org/ 10.1016/j.joen.2006.09.010 Zhou HM, Shen Y, Zheng W, Li L, Zheng YF and Haapasalo M (2013) Physical properties of 5 root canal sealers. J Endod 39:1281-6. https://doi.org/ 10.1016/j.joen.2013.06.012 Yang Q, Troczynski T and Liu D-M (2002) Influence of apatite seeds on the synthesis of calcium phosphate cement. Biomaterials 23:2751-2760. Zhang H, Shen Y, Ruse ND and Haapasalo M (2009) Antibacterial activity of endodontic sealers by modified direct contact test against Enterococcus faecalis. J Endod 35:1051-5. https://doi.org/ 10.1016/j.joen.2009.04.022 Inan U, Aydin C, Tunca YM and Basak F (2009) In vitro evaluation of matched-taper single-cone obturation with a fluid filtration method. Journal (Canadian Dental Association) 75:123. Alshehri M, Alamri HM, Alshwaimi E and Kujan O (2016) Micro-computed tomographic assessment of quality of obturation in the apical third with continuous wave vertical compaction and single match taper sized cone obturation techniques. Scanning 38:352-6. https://doi.org/ 10.1002/sca.21277 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4167729","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":295206706,"identity":"80840c02-03de-4d83-beb8-c51557d4e18f","order_by":0,"name":"Yu Zhao","email":"","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"Zhao","suffix":""},{"id":295206708,"identity":"2d5064cc-6ecc-47d1-a6fb-b1c63083725a","order_by":1,"name":"Yimeng Zhang","email":"","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":false,"prefix":"","firstName":"Yimeng","middleName":"","lastName":"Zhang","suffix":""},{"id":295206710,"identity":"c567811f-4b1e-4f41-b996-6d87fc9ee5e3","order_by":2,"name":"Jiayi Shi","email":"","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":false,"prefix":"","firstName":"Jiayi","middleName":"","lastName":"Shi","suffix":""},{"id":295206712,"identity":"9cf0e4d9-dbee-4166-848a-0d186ef1e613","order_by":3,"name":"Li Wang","email":"","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Wang","suffix":""},{"id":295206713,"identity":"9d6ae3b7-effa-4726-b5ec-e0f2ca550cee","order_by":4,"name":"Xuekai Qi","email":"","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":false,"prefix":"","firstName":"Xuekai","middleName":"","lastName":"Qi","suffix":""},{"id":295206714,"identity":"e04f3b72-3a2b-4f90-8960-cdef2c26e1eb","order_by":5,"name":"Duohong Zou","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3ElEQVRIiWNgGAWjYBAC+wYGBgkGhgMQ3gcDGzuCWhiRtTDOKEhLJk0LM8+HQyAB/ICZvcfwNk/FHTlz/jVm0jYGB5gZ2A8f3YBPCxvPGWNrnjPPjC1nvDGTzjG4w8fAk5Z2A58WHokcM2netsOJG26cAWl5xswgwWOGV4sEihYLg8OMDYS0GMC1nO8xk2YgSgvPsWLLOWcOGxvcYCu27DFIS2Yj5Bf79uaNN95UHJYzOH94440ff2zs+NkPH8OrBclXGSYSIJqNOOUgwH/88QfiVY+CUTAKRsFIAgALz0vmiSMAoQAAAABJRU5ErkJggg==","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":true,"prefix":"","firstName":"Duohong","middleName":"","lastName":"Zou","suffix":""},{"id":295206715,"identity":"8dc0830b-56ab-4832-a0ac-3a4d43f1251d","order_by":6,"name":"Yihuai Pan","email":"","orcid":"","institution":"Wenzhou Medical University","correspondingAuthor":false,"prefix":"","firstName":"Yihuai","middleName":"","lastName":"Pan","suffix":""}],"badges":[],"createdAt":"2024-03-26 07:16:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4167729/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4167729/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":55567499,"identity":"a5459b23-de43-41bc-8b83-5f53e437477b","added_by":"auto","created_at":"2024-04-30 04:32:10","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":825738,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative examples of micro-CT reconstructions illustrating the changes in C-shaped canals of mandibular first premolars after instrumentation and after obturation. \u003cstrong\u003e(a)\u003c/strong\u003e Pre-instrumentation reconstructions. \u003cstrong\u003e(b)\u003c/strong\u003e Superimpositions of pre-instrumentation (red) and post-instrumentation (green) reconstructions. Red regions were untouched by instruments. \u003cstrong\u003e(c)\u003c/strong\u003e Volume of accumulated hard tissue debris (AHTD) after instrumentation (orange). \u003cstrong\u003e(d) \u003c/strong\u003eSuperimpositions of post-obturation (pink) in C-shaped canal systems. \u003cstrong\u003e(e) \u003c/strong\u003eVolume of void after obturation (blue). \u003cstrong\u003eRow A\u003c/strong\u003e: canal shaped by the PN system and obturated by CWC. \u003cstrong\u003eRow B\u003c/strong\u003e: canal shaped by the PN system and obturated by SP. \u003cstrong\u003eRow C\u003c/strong\u003e: canal shaped by the WG system and obturated by CWC. \u003cstrong\u003eRow D\u003c/strong\u003e: canal shaped by the WG system and obturated by SP).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4167729/v1/3425f7312961d77f732be18a.png"},{"id":55567498,"identity":"5f9bbce1-5720-4090-bbe2-375b8fb4c6b5","added_by":"auto","created_at":"2024-04-30 04:32:08","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":224811,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative cross sections of hard tissue debris accumulation (orange) in post-instrumented (left) C-shaped canals of mandibular first premolars. \u003cstrong\u003e(a)\u003c/strong\u003e Canal shaped by the PN system. \u003cstrong\u003e(b)\u003c/strong\u003e Canal shaped by the WG system. Top row: sections derived from the coronal-third region of the canal space. Middle row: sections derived from the middle-third region of the canal space. Bottom row: sections derived from the apical-third region of the canal space.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4167729/v1/47bd6296e6e9aae5535992c6.jpeg"},{"id":55952811,"identity":"2b8a6231-4894-470f-a118-7e1ca339ea8c","added_by":"auto","created_at":"2024-05-06 18:56:53","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1367654,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4167729/v1/2c6fa05e-02f2-4792-b845-6145d1765011.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Evaluation of two instrumentation techniques and obturation methods in mandibular first premolar C- shaped canals by Micro-CT","fulltext":[{"header":"Introduction","content":"\u003cp\u003eC-shaped root canal system is a complex anatomical variation of mandibular first premolars \u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e, with a considerable incidence of 12.5-67.47% in Chinese population \u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. The mandibular first premolars with this special morphology usually have a deep and narrow radicular groove \u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e. The buccal and lingual canals are completely or partially connected through the isthmus to form a C-shaped or semicolon shape in cross-section. This feature is more common in the middle and apical segments of the root canal, with varying degrees of curvature \u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. The presence of anatomical structures such as irregular root canal morphology, accessory canals, connecting canals, and apical deltas, may harbor soft tissue remnants or infected debris and cannot be fully contacted by instruments. Moreover, hard tissue debris during instrumentation may be packed into the irregular regions of a C-shaped canal system. The debris may hamper sealing and disinfection of the root canal system \u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e. These factors compromise the outcome of mechanical and chemical debridement and pose a great challenge to endodontists.\u003c/p\u003e \u003cp\u003eMicro-computed tomography (micro-CT) is a non-destructive, three-dimensional analytical method that permits accurate evaluation of root canal system prior and subsequent to mechanical preparation by superimposing pre- and post-instrumentation scanning data. The morphological parameters that are related to the ultimate shaping and obturation results, including changes of surface area and volume, the amount of dentine removed, untouched area, the amount and distribution of hard-tissue debris, and the volume percentage of void may be calculated and analyzed using imaging software \u003csup\u003e[\u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThere are a variety of NiTi machine files with different mechanisms on the market, including rotation, reciprocating, central motion or eccentric motion \u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e. Protaper Next (PN, Dentsply Sirona, Maillefer, Ballaigues, Switzerland) has a unique eccentric rectangular design and a progressive and decreasing percentage taper, which help to maximize debris removal from the root canal \u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e. The offset mass of rotation is more suitable for preparing irregular canals. Several studies have found that Protaper Next owned superior shaping and centering ability \u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e. Protaper Next system has a similar shaping ability in long-oval canals with XP-endo Shaper system (FKG Dentaire, La Chaux-de‐Fonds, Switzerland) \u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eWaveone Gold (WG, Dentsply Sirona, Maillefer, Ballaigues, Switzerland) systems have been introduced that use the same reciprocating motion as WaveOne (WO, Dentsply Sirona, Maillefer, Ballaigues, Switzerland). WG files have an off-center, parallelogram design. The parallelogram shaped cross sections are spatially ordered in a discontinuous manner, which allows variation of the instrument\u0026rsquo;s contact \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e. WG files are manufactured using advanced heat treatment technology \u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. The manufacturer claims that the flexibility of WG is improved through this new heat treatment method.\u003c/p\u003e \u003cp\u003eBased on the complexity and variability of the C-shaped canal anatomy in the mandibular first premolars, thoroughly removal of microorganisms is not always achievable. The surviving microorganisms must be sealed by root canal filling material, which would block microorganisms and toxins from entering the root canal system from the oral cavity \u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. Three-dimensional filling of the prepared canal is of critical importance for the success of root canal therapy. There are several ways to obturate root canals, including the lateral compaction technique, the thermos-plasticized gutta-percha obturation, the continuous wave obturation, the core-carrier technique, the single cone technique and so on. Despite a large number of accessory gutta-percha cones were inserted in C-shaped canals, the radiographic appearance was less dense than normal root canals. Previous studies showed that the quality of filling with lateral compaction technique in oval canals \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e was less reliable. The MicroSeal system is a thermomechanical filling technique that uses a lateral compaction and placement of α-gutta-percha to backfill the canal. Ordinola-Zapata found that the technique was not able to seal the C-shaped canal completely, especially the apical third \u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e. Although previous studies have shown that thermos-plasticized gutta-percha was more appropriate for filling abnormal canal \u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e, in the work of Soo et. al, the thermos-plasticized gutta-percha technique to fill C-shaped canal resulted in poor apical sealing but excellent adaptation in the coronal two-thirds of the canal \u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e. With respect to the filling effect of the core-carrier technique in C-shaped canal obturation, data published in the literature are contradictory. Whereas the core-carrier technique was reported to be more effective when assessed by gutta-percha area than the lateral compaction and the thermos-plasticized gutta-percha obturation in this simulated C-shaped canal \u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e, the result could not be validated in two more recent studies that used a similar experimental design \u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe continuous wave compaction technique and single-cone technique are frequently used in clinical practice. The thermal gutta-percha softened in vertical compression is considered beneficial for filling complex root canals \u003csup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e. The single-cone technique gained popularity with the introduction of bioceramic sealer. iRoot SP (Innovative BioCeramix Inc, Vancouver, Canada) is a premixed bioceramic endodontic sealer which contains zirconium oxide, tricalcium silicate, dicalcium silicate, colloidal silica, calcium silicates, calcium phosphate monobasic, and calcium hydroxide, filler and thickener \u003csup\u003e[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e. As an endodontic sealer, iRoot SP has many desirable properties such as biocompatibility, chemical stability, hydrophilicity, flowability, radiopacity, and slight expansive tendencies \u003csup\u003e[\u003cspan additionalcitationids=\"CR30 CR31\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e. These characteristics of iRoot SP have been expected to improve the effect of root canal obturation and may allow for an enhanced seal within otherwise inaccessible canal anatomies.\u003c/p\u003e \u003cp\u003eRecent research found that the SC technique was effective in filling mandibular molar canals, resulting in fewer voids \u003csup\u003e[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e. A retrospective survey also suggested that the SC technique with bioceramic sealer achieved a success rate of 90.9% in initial treatment and retreatment \u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e. Nevertheless, comprehensive knowledge on the shaping results of the aforementioned two off-center design NiTi systems and the sealing ability of the continuous wave compaction and single cone techniques in complex canal systems, such as that found in C-shaped canals of mandibular first premolars is lacking.\u003c/p\u003e \u003cp\u003eAccordingly, the present study was designed to quantitatively evaluate the shaping properties of PN and WG instruments and the sealing ability using two obturation approaches in the C-shaped canal of mandibular first premolars. The null hypotheses tested were: 1) the PN system and the WG system produce similar morphological features after instrumentation of C-shaped canals; and 2) there is no difference between the two obturation techniques in their percentage of void.\u003c/p\u003e"},{"header":"Methods and materials","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSpecimen selection\u003c/h2\u003e \u003cp\u003eThe protocol of the current study was approved by the Ethics Committee of School and Stomatology Wenzhou Medical University (WYKQ2021007).\u003c/p\u003e \u003cp\u003eThe specimens were scanned using a high-resolution micro-computed tomographic system (SkyScan 1176; Bruker-micro-CT, Kontich, Belgium) with an isotropic resolution of 17.54 \u0026micro;m at 90 kV, 270 \u0026micro;A, 0.1 mm Cu filter, and 360\u0026deg; rotation with a rotation step of 0.5\u0026deg;. The raw data was reconstructed by NRecon (v 1.6.10.4; Bruker-micro-CT, Kontich, Belgium) and was exported in TIFF format. After 3D reconstruction from the scanned data using CTAn software (v 1.20.3.0; Bruker-micro-CT, Kontich, Belgium), a total of 64 mandibular first premolars, each with a C-shaped canal system according to previously reported definition \u003csup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/sup\u003e, were selected and paired into 2 groups (n\u0026thinsp;=\u0026thinsp;32) based on anatomical similarity to enable homogeneous specimen distribution in each group. The extracted teeth had mature apices, no fractures or cracks, no caries or calcification, and no signs of endodontically treatment. Matched standards included 3D morphology, preoperative volume and surface area of root canals. A tooth from each pair was randomly allocated to one experimental group and the group to be shaped with Protaper Next rotary files or Waveone Gold reciprocating file was determined by a coin toss.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eCanal instrumentation\u003c/h2\u003e \u003cp\u003eEach tooth was accessed using a diamond bur. The access cavity was filled with 1 mL of 1% NaOCl solution, and apical patency was created using a size 10 K-file (Dentsply Sirona, Maillefer, Ballaigues, Switzerland) until the file was visible at the apical foramen. The canal was irrigated with 2 mL of 1% NaOCl solution. The working length (WL) was determined as the total canal length minus 1.0 mm. Glide path preparation in both groups was developed with size 15 K-files to WL. All the canals were irrigated with 2 mL of 1% NaOCl in the two groups. Two coats of nail polish were applied to seal the apex \u003csup\u003e[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eProtaper Next (PN) group\u003c/strong\u003e \u003cp\u003eThe X1(size 17/.04 taper) and X2(size 25/.06 taper) files were serially powered by the motor X-smart plus (Dentsply Sirona, Maillefer, Ballaigues, Switzerland) with parameters set at 300 rpm and torque 2.5 N /cm\u003csup\u003e2\u003c/sup\u003e. The instrument was used in a slow in-and-out motion of approximately 3 mm in amplitude in the apical direction, using a gentle brushing motion against the canal wall. The procedure was repeated twice until the WL was reached.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eWaveone Gold (WG) group\u003c/strong\u003e \u003cp\u003eSmall (size 20/.07 taper) and Primary (size 25/.07 taper) files were applied in the canals with an in-and-out motion by the reciprocating \u0026ldquo;WaveOne ALL\u0026rdquo; setup of the same motor. After 3 movements of at most 3 mm amplitude in the apical direction, using a gentle brushing motion against the canal wall, the instrument was removed and cleaned with gauze. Working length was reached after 3 cycles of instrumentation used in the same fashion.\u003c/p\u003e \u003c/p\u003e \u003cp\u003eThe same irrigation protocol during instrumentation was used in both groups. For all specimens, the total amount of 1% NaOCl solution used in a canal was 5 mL for glide path preparation and 15 mL for shaping. During shaping, each root canal was irrigated with 2.5 mL 1% NaOCl solution when the instrument was removed from the canal and cleaned. The irrigant was delivered at a flow rate of 5 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with a 30-gauge needle adapted to a disposable plastic syringe. A final 1 mL sterile water rinse was used, and the canals were dried with size 25/.06 taper paper points (Dentsply Sirona, Maillefer, Ballaigues, Switzerland). The tip of needle was placed as apically as possible without binding and up to 1 mm short of the WL. A single operator with experience of PN and WG systems performed the operation in all canals. Subsequent to mechanical and chemical debridement, the access cavities were sealed with Cavition (GC Corporation, Tokyo, Japan).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eMicro-CT analysis\u003c/h2\u003e \u003cp\u003eAll postoperative specimens were scanned with the preoperative parameter settings. The scanning data sets before and after instrumentation were co-registered using the Data Viewer (v 1.5.6.2; Bruker-micro-CT, Kontich, Belgium).\u003c/p\u003e \u003cp\u003eThe canals were segmented in the CTAn software (v 1.20.3.0; Bruker-micro-CT, Kontich, Belgium) using the 2-dimensional Otsu method. Morphologic parameters of the pre- and post-instrumentation root canal system (volume and surface area) were calculated. Information including removed dentin volume (RDV, in mm\u003csup\u003e3\u003c/sup\u003e), accumulated hard tissue debris (AHTD, in mm\u003csup\u003e3\u003c/sup\u003e), area of untouched surface (US, in mm\u003csup\u003e2\u003c/sup\u003e), minimum mesial wall thickness (MT, in mm) and the volume void (vV, in mm\u003csup\u003e3\u003c/sup\u003e) was evaluated and analyzed by CTAn, and 3D models were created in STL format by the same software. A radiopaque shadow with a density similar to dentin appeared in the radiolucent pre-operative canal images, and the percentage of this radiopaque shadow with respect to the volume of the root canal before preparation was defined as AHTD \u003csup\u003e[\u003cspan additionalcitationids=\"CR38\" citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/sup\u003e. The US parameter was expressed as a percentage of the static surface voxels to the total pre-instrumentation surface voxels \u003csup\u003e[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/sup\u003e. The two parameters of each experimental group were recorded along the total canal length, the apical (1\u0026ndash;3 mm), middle (3\u0026ndash;6 mm) and cervical (6\u0026ndash;9 mm) regions. The percentage of MT thinning was calculated according to the formula: (MT\u003csub\u003eB\u003c/sub\u003e-MT\u003csub\u003eA\u003c/sub\u003e)/MT\u003csub\u003eB\u003c/sub\u003e\u0026times;100%, where MT\u003csub\u003eB\u003c/sub\u003e and MT\u003csub\u003eA\u003c/sub\u003e are the thickness of minimum mesial wall before and after instrumentation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eCanal obturation\u003c/h2\u003e \u003cp\u003eThe specimens after instrumentation were pair-matched in each group with respect to the 3D morphology of root canal. One tooth from each pair was randomly assigned to one of the two subgroups (n\u0026thinsp;=\u0026thinsp;16) according to the obturation technique employed:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eContinuous wave compaction subgroup (CWC)\u003c/b\u003e: Each sample was filled with gutta-percha cone (25/.06) (Dentsply DeTrey GmbH, Konstanz, Germany) and AH plus sealer (Dentsply DeTrey GmbH, Konstanz, Germany). EQ-V Pack Tip (Meta Biomed Co, Cheongju-si, Chungbuk, Korea) was used to remove excess cone in the upper segment, leaving only 4-6mm within working length, and EQ-V thermal gun (Meta Biomed Co, Cheongju-si, Chungbuk, Korea) was used to backfill.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eSingle-cone subgroup (SC)\u003c/b\u003e: Each sample was filled with gutta-percha cone (25/.06) and iRoot SP sealer (Innovative BioCeramix Inc, Vancouver, Canada). The upper segment was removed with EQ-V heat source, and 1mm lower the canal orifice level was retained.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eEach specimen was subjected to a post-obturation scan; the scanned data were used for reconstruction following the aforementioned parameters. The volume percentage of void (vol%) was calculated according to the formula: V\u003csub\u003ev\u003c/sub\u003e /(V\u003csub\u003ev\u003c/sub\u003e+V\u003csub\u003eF\u003c/sub\u003e)\u0026times;100%, where V\u003csub\u003ev\u003c/sub\u003e and V\u003csub\u003eF\u003c/sub\u003e are the volume of the void after obturation and the volume of the filling material, respectively. The vol% of void in the entire canal and the different regions (i.e. coronal-third, middle-third and apical-third) of the canal were recorded.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analyses\u003c/h2\u003e \u003cp\u003eThe normality of all data was tested using the Shapiro-Wilk test. Tests were conducted on the change of surface area and volume, RDV, AHTD, US, MT and vol% of void. Even after multiple nonlinear transformations, the data failed to meet the normality assumption. Therefore, the statistical analyses were performed using the Wilcoxon signed-rank test. Each data set was expressed as a median and confidence interval (CI). Inter groups comparison was performed using Kruskal-Wallis analysis. ALL statistical analyses were performed using IBM SPSS v23.0 (SPSS Inc., Chicago, IL, USA). The significance level was pre-set at α\u0026thinsp;=\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eRepresentative examples of micro-CT reconstructions of the changes in C-shaped canals of mandibular first premolars after instrumentation with the PN or WG system, and after obturation with CWC and SP are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Representative cross sections of hard tissue debris accumulation (orange) in post-instrumented C-shaped canals of mandibular first premolars are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Data derived from the coronal-third, middle-third, and apical-third regions of the canal space are illustrated in order.\u003c/p\u003e \u003cp\u003eThe pre-instrumentation surface areas (mm\u003csup\u003e2\u003c/sup\u003e) and volumes (mm\u003csup\u003e3\u003c/sup\u003e) were 88.68 mm\u003csup\u003e2\u003c/sup\u003e and 18.14 mm\u003csup\u003e3\u003c/sup\u003e in the PN group and 88.57 mm\u003csup\u003e2\u003c/sup\u003e and 18.73 mm\u003csup\u003e3\u003c/sup\u003e in the WG group (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), respectively (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). There was no significantly difference in surface areas and volumes between the PN and WG groups before instrumentation. After instrumentation, the morphologic parameters between the two groups still had no significant difference (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05), including the increased volumes, increased surface areas, and removed dentine (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCanal Volume (mm\u003csup\u003e3\u003c/sup\u003e) and Surface Area (mm\u003csup\u003e2\u003c/sup\u003e) before and after instrumentation using Protaper Next (PN) and Waveone Gold (WG) systems as well as the increased percentages (%) (median and confidence interval)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePN\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWG\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCanal Volume\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBefore (mm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18.14 (15.50-20.82)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18.73 (14.67\u0026ndash;20.45)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter (mm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20.76 (19.52\u0026ndash;24.91)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e22.56 (18.63\u0026ndash;22.95)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCanal Volume Increased (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10.10 (2.64\u0026ndash;20.78)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e13.65 (3.24\u0026ndash;21.15)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCanal Surface Area\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBefore (mm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e88.68 (78.27\u0026ndash;93.38)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e88.57 (77.81\u0026ndash;99.88)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAfter (mm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e96.42 (90.03-107.62)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e94.77 (84.84-106.85)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCanal Surface Area Increased (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10.33 (6.05-14.00)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e9.55 (4.13\u0026ndash;12.33)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"3\"\u003eThere were no significant differences in any of the parameters between the Protaper Next and Waveone Gold groups (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eUS of the entire canal was 18.75% in the PN group and 22.69% in the WG group, respectively (US shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). There was no significant difference in the percentage area of untouched surface (US) between the two groups. Distributions of US from different regions of the canal space are collectively represented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The apical region (1\u0026ndash;3 mm) of the canal space had significantly higher US% when compared with coronal region (6\u0026ndash;9 mm) in the PN group (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05); there was no significant difference between the apical region and the middle region, and between the middle region and the coronal region of the canal wall. For the WG group, the apical region had significantly higher US% than the middle region, which had significantly higher US% than the coronal region (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Canal perforation was not observed in all specimens.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eUS (%) and AHTD (vol%) after instrumentation using Protaper Next (PN) and Waveone Gold (WG) systems in mandibular first premolars with C-shaped root canals (median and confidence interval)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eUS(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eAHTD(%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePN\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWG\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePN\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWG\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEntire canal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18.75\u003c/p\u003e \u003cp\u003e(13.09\u0026ndash;23.96)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22.69\u003c/p\u003e \u003cp\u003e(14.01\u0026ndash;28.41)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.39\u003c/p\u003e \u003cp\u003e(0.99\u0026ndash;2.16)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.15\u003c/p\u003e \u003cp\u003e(1.35\u0026ndash;2.79)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eApical region\u003c/p\u003e \u003cp\u003e(1\u0026ndash;3 mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e35.25\u003c/p\u003e \u003cp\u003e(24.22\u0026ndash;51.76) \u003csup\u003eA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e64.34\u003c/p\u003e \u003cp\u003e(39.84\u0026ndash;74.78) \u003csup\u003eA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.36\u003c/p\u003e \u003cp\u003e(5.25\u0026ndash;15.63) \u003csup\u003eA\u003c/sup\u003e*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e26.48\u003c/p\u003e \u003cp\u003e(13.15\u0026ndash;47.42) \u003csup\u003eA\u003c/sup\u003e *\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMiddle region\u003c/p\u003e \u003cp\u003e(3\u0026ndash;6 mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e24.97\u003c/p\u003e \u003cp\u003e(19.53\u0026ndash;37.25) \u003csup\u003eAB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33.63\u003c/p\u003e \u003cp\u003e(20.25\u0026ndash;42.95) \u003csup\u003eB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.83\u003c/p\u003e \u003cp\u003e(3.36\u0026ndash;8.46) \u003csup\u003eB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.74\u003c/p\u003e \u003cp\u003e(3.23\u0026ndash;9.72) \u003csup\u003eB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCoronal region\u003c/p\u003e \u003cp\u003e(6\u0026ndash;9 mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e16.15\u003c/p\u003e \u003cp\u003e(11.45\u0026ndash;24.47) \u003csup\u003eB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15.21\u003c/p\u003e \u003cp\u003e(6.96-22.00) \u003csup\u003eC\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.64\u003c/p\u003e \u003cp\u003e(1.27\u0026ndash;2.71) \u003csup\u003eC\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.26\u003c/p\u003e \u003cp\u003e(0.72\u0026ndash;3.41) \u003csup\u003eC\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eAsterisk (*) indicates significant difference between different instruments (\u003cem\u003ep\u0026thinsp;\u0026lt;\u003c/em\u003e\u0026thinsp;0.05).\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eDifferent uppercase superscripts in a single column represent significant differences among the different regions (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eInstrumentation of the C-shaped canals of mandibular first premolars using WG left 2.15% of the initial canal volume filled by dentin debris. In contrast, only 1.39% of the original canal volume was filled by debris in the PN group; the difference between the two groups was not statistically significant in the entire canal (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). For comparisons of different regions of the canal space, significant difference between the PN and WG groups could only be identified from the apical region of the canal space. For canals instrumented with the two systems, the coronal region of the canal space had significantly less debris than the middle region, which, in turn, had significantly less debris than the apical region (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 for all pairwise comparisons) (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAfter instrumentation, the MT was less than 0.5 mm in 65.63% (42/64) of the samples, with a minimum value of 0.14mm. The MT in the cross-section containing the C-shaped canal was thinned to varying degrees in each level of the root canal, with the most pronounced reduction in the M-1 and M level (MT shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Significant difference on the percentage of MT thinning between the PN and WG groups could not be identified in the middle regions with C-shaped morphology.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMinimum mesial wall thickness (MT) before and after preparation and the percentage of MT thinning after instrumentation using Protaper Next (PN) and Waveone Gold (WG) systems in mandibular first premolars with C-shaped root canals (median and confidence interval)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup/level\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBefore (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAfter (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eThinning (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePN\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eM\u0026thinsp;+\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.86(0.62\u0026ndash;1.13)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.81(0.48\u0026ndash;1.05)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12.0(9.5\u0026ndash;15.8)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.68(0.60\u0026ndash;0.88)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.52(0.42\u0026ndash;0.87)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e22.6(10.7\u0026ndash;33.7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eM-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.68(0.60\u0026ndash;0.78)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.51(0.39\u0026ndash;0.69)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e21.0(7.2\u0026ndash;35.2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.61(0.56\u0026ndash;0.72)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.52(0.45\u0026ndash;0.57)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e16.2(6.5\u0026ndash;23.4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eWG\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eM\u0026thinsp;+\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.86(0.72\u0026ndash;1.03)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.73(0.51\u0026ndash;0.96)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12.3(5.0-24.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.71(0.62\u0026ndash;0.86)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.60(0.48\u0026ndash;0.65)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e15.2(5.9\u0026ndash;23.1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eM-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.61(0.59\u0026ndash;0.71)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.49(0.42\u0026ndash;0.58)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e19.3(6.3\u0026ndash;30.6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.61(0.54\u0026ndash;0.71)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.50(0.48\u0026ndash;0.64)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e6.6(4.9\u0026ndash;13.0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eThere was no significant difference on the degree of MT thinning in M\u0026thinsp;+\u0026thinsp;1, M, M-1, AM levels after preparation between PN and WG (\u003cem\u003ep\u003c/em\u003e\u0026gt;0.05).\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eM\u0026thinsp;+\u0026thinsp;1, 1 mm above the middle of the root; M, the middle of the root; M-1, 1 mm below the middle of the root; AM, the junction of apical third and middle third of root.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe vol% of void after obturation in two instrumentation groups are collectively represented in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Irrespective of the type of file system employed for canal shaping, the two obturation protocols both produced the voids in C-shaped canals. In PN and WG group, the vol% of void had no significant difference between the CWC and SC subgroups(\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). The results about the comparisons of different regions of the canal space in two instrumentation groups were similar. The apical region had significantly more voids than the coronal region of the canal space (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05); there was no significant difference between the middle region and the apical region, as well as between the middle region and coronal region (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eVolume percentage (vol%) of void after obturation using continuous wave compaction (CWC) and single cone (SC) techniques in mandibular first premolars with C-shaped root canals (median and confidence interval)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003ePN\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eWG\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCWC (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSC (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCWC (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSC (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEntire canal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.37 (3.00-8.13)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.46 (2.29\u0026ndash;12.77)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.44 (1.85\u0026ndash;14.62)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e6.57 (2.25\u0026ndash;13.25)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eApical region\u003c/p\u003e \u003cp\u003e(1\u0026ndash;3 mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18.65 (3.73\u0026ndash;32.55) \u003csup\u003eA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26.38 (3.25\u0026ndash;30.26) \u003csup\u003eA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.11 (5.58\u0026ndash;28.83) \u003csup\u003eA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e27.73 (10.46-62.00) \u003csup\u003eA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMiddle region\u003c/p\u003e \u003cp\u003e(3\u0026ndash;6 mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7.15 (0.62\u0026ndash;12.37) \u003csup\u003eAB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.56 (2.15\u0026ndash;28.04) \u003csup\u003eAB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.63 (1.35\u0026ndash;16.99) \u003csup\u003eAB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10.95 (3.38\u0026ndash;18.59) \u003csup\u003eAB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCoronal region\u003c/p\u003e \u003cp\u003e(6\u0026ndash;9 mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.46 (0.81\u0026ndash;3.76) \u003csup\u003eB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.75 (0.75\u0026ndash;5.92) \u003csup\u003eB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.64 (0.98\u0026ndash;9.19) \u003csup\u003eB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.26 (1.86\u0026ndash;8.66) \u003csup\u003eB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eNo significant difference between the two filling methods when the same shaping instruments were applied (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eDifferent uppercase superscripts in a single column represent significant differences among the various regions (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eAnatomical complexities and high variabilities in C-shaped canal of the mandibular first premolar increase the difficulty in evaluating the instrumentation and obturation during the root canal treatment. The 64 mandibular first premolars were pre-screened before preparation using micro-CT. Based on root canal volume, surface area, and 3D C-shaped canal classification, the specimens were paired and randomly allocated into the PN and WG instrumentation groups to ensure a good uniform distribution of samples between the two groups and to reduce the risk of bias due to anatomical structures. There was no significant difference in the canal volume and surface area before and after preparation in the two instrumentation groups (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). After the preparation, the teeth were divided into two obturation subgroups (n\u0026thinsp;=\u0026thinsp;16) in each experimental group. Statistical analysis confirmed the homogeneity of baseline parameters between the groups and improved the internal validity of this study \u003csup\u003e[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe increase of canal surface area and volume, as well as the amount of removed dentine in the two experimental groups has no significant difference in present study. The X2 file in the PN system created a .06 taper in the apical 3 mm and ISO #25 diameter, while the Primary file in the WG system created a larger taper (.07 taper) and an equal diameter (0.25 mm) during instrumentation of the canal space. The tiny difference of taper in file design is not enough to cause the significantly different changes in canal volume and surface area, as well as dentine removal in the present study.\u003c/p\u003e \u003cp\u003ePrevious studies on mandibular second molars have shown that the wall of the C-shaped root canal was thinner on the side near the radicular groove than on the remaining sides \u003csup\u003e[\u003cspan additionalcitationids=\"CR45\" citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]\u003c/sup\u003e. Gu \u003cem\u003eet al.\u003c/em\u003e \u003csup\u003e[\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]\u003c/sup\u003e measured the canal wall thickness at various levels in C-shaped root canals of mandibular first premolar teeth and confirmed that the above findings were also applicable in mandibular first premolar teeth.\u003c/p\u003e \u003cp\u003eThe canal in mandibular first premolar characteristically bifurcates in the apical and middle regions to form C-shaped root canal structures \u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. The irregular morphology of C-shaped root canals is more likely to result in strip perforation during root canal preparation \u003csup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]\u003c/sup\u003e. Our previous study revealed that the further the distance from the cemento-enamel junction, the deeper root radicular groove, the smaller the radicular groove angle, and the thinner the mesial wall. As a result, mechanical preparation of the root canal, particularly the lingual root canal and the lower segment, should be executed carefully to prevent unexpected deviation and perforation.\u003c/p\u003e \u003cp\u003eIn this study, the thickness of the mesial wall in the cross-section with C-shaped canal was measured before and after instrumentation. After cut by the two systems, the remain MT was less than 0.5 mm in 65.63% of the samples. The results supported the above-mentioned statements. Although the C-shaped morphology may occur in various levels along the root canal of mandibular first premolars, the distribution of sample size in each level is uneven. It also has been demonstrated in present study that C-shaped morphology more commonly occurred in the middle regions of the canal. Based on the fact, the degree of MT thinning between the two systems was compared in the M\u0026thinsp;+\u0026thinsp;1, M, M-1, and AM levels. There was no significant difference between the two files on the degree of MT thinning, which might be accounted for the similar cross section design of the two instruments. It has been suggested that the isthmus of C-shaped canals should not be instrumented by files larger than ISO #25 to avoid perforating the canals \u003csup\u003e[\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]\u003c/sup\u003e. In the present study, no perforation was observed using either X2 or Primary file in two experimental groups. However, the extreme value of MT after instrumentation was 0.14mm, which carried an extreme risk of perforation during the canal cleaning.\u003c/p\u003e \u003cp\u003eThe two experimental groups left a similar percentage of untouched surface area in the C-shaped canals of mandibular first premolars. In the PN and WG group, the untouched surface area was 18.75% and 22.69%, respectively. The results are less than those reported in previous studies about the instrumentation of the C-shaped canals in mandibular molars with different NiTi systems \u003csup\u003e[\u003cspan additionalcitationids=\"CR51 CR52\" citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]\u003c/sup\u003e. Although the two type teeth all possessed C-shaped canal systems, quantitative divergence between the previously-reported data and the present data may be attributed to the difference in root canal volume of different tooth types. The C-shaped canal in mandibular first premolar is relatively narrower and smaller, and therefore larger proportion canal wall would be treated by the instruments during the shaping process.\u003c/p\u003e \u003cp\u003eDespite the innovations in designs, metallurgies, kinematics and thermal treatments, neither of the two NiTi systems were capable of completely touching the root canal walls. There were no significant differences between the mechanized preparation systems regarding the percentages of US. Several previous studies reported that untreated surface varied from 19.9\u0026ndash;41.5% in curved mesial root canals of mandibular molars and 55.3% in distal root canals of mandibular molars after using Protaper Next \u003csup\u003e[\u003cspan additionalcitationids=\"CR55\" citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]\u003c/sup\u003e. Moreover, two recent studies on Waveone Gold shaping in oval-shaped canals reported that the percentage of unprepared area was 18.9\u0026ndash;50.9% \u003csup\u003e[\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]\u003c/sup\u003e. Although it has been reported that greater taper files were able to touch more canal surface \u003csup\u003e[\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e]\u003c/sup\u003e, the statement was not confirmed in the present study.\u003c/p\u003e \u003cp\u003eThe percentage of US remained in the apical regions of the canal space was 35.25% in PN group and 64.34% in WG group, respectively. The values of US in apical region were higher than those in coronal region in the either groups. The similar results regarding the instrumentation of C-shaped canal in mandibular molars were reported by Zhao \u003cem\u003eet al.\u003c/em\u003e \u003csup\u003e[\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]\u003c/sup\u003e. High percentages of US in the apical regions may be attributed to the complexity of apical anatomy of C-shaped canals. Factors such as the severe curved canal, the existence of accessory canals, lateral canals, intercanal communications and apical deltas \u003csup\u003e[\u003cspan additionalcitationids=\"CR60\" citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]\u003c/sup\u003e are likely to hamper optimal debridement of the apical region in these complicated canal systems. These findings also support the viewpoint that the irrigation and intracanal medicament plays a key role in chemo-mechanical preparation to compensate for the deficiencies of mechanical debridement \u003csup\u003e[\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eHard tissue debris, as an undesirable by-product of dentin removal during mechanical preparation \u003csup\u003e[\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e]\u003c/sup\u003e, was usually packed into the irregular regions of the root canal system. Some studies have found that accumulated debris in canal would compromise the effectiveness of canal irrigation or medication \u003csup\u003e[\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e]\u003c/sup\u003e and also block the flow of filling material \u003csup\u003e[\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e]\u003c/sup\u003e. Moreover, the debris contains bacteria and serves as a nidus for root canal re-infection. Paqu\u0026eacute; \u003cem\u003eet al.\u003c/em\u003e \u003csup\u003e[\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e]\u003c/sup\u003e has established a method to qualitatively and quantitatively analyze the remained dentine debris in root canal system during instrumentation.\u003c/p\u003e \u003cp\u003eIn the present study, AHTD was identified in all specimens irrespective of the file system employed. There was no significant difference on AHTD in the total canal using two shaping techniques. However, the PN system produced a relatively lower percentage of AHTD in the apical regions of the canal space, when compared to the WG system. The result may be explained by the differences in movement kinematics and the tapers of the respective file systems.\u003c/p\u003e \u003cp\u003eThe kinematics of a NiTi file system may be an influential factor in debris removal. With respect to this issue, data published in the literature are contradictory. Whereas reciprocating systems were reported to produce more debris accumulation than rotary systems in the mesial root canals of mandibular molars \u003csup\u003e[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/sup\u003e and in the C-shaped canals of mandibular molars \u003csup\u003e[\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]\u003c/sup\u003e, this difference could not be validated in another study that used a similar experimental design \u003csup\u003e[\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e]\u003c/sup\u003e. The continuous forward motion of the rotary file enables constant exit of debris up the flute of the file, while reciprocating motion might push debris into recesses and isthmus areas \u003csup\u003e[\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e]\u003c/sup\u003e.The PN rotary file had an off-centered rectangular cross-section with progressive and decreasing percent taper design, superior strength and novel asymmetric rotational motion \u003csup\u003e[\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e, \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e]\u003c/sup\u003e for maximum debris removal \u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e. These PN design features provide a wider chip space and a smaller tip taper (X1: size 17/.04 taper and X2: size 25/.06 taper), and when accompanied by rotary movement, improve debris removal from the canal system. The debris that remained in C-shaped canals of the mandibular premolars shaped by the WG system was less in the present study than the previous studies \u003csup\u003e[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e]\u003c/sup\u003e. The difference may be attributed to different tooth type and irrigation protocols.\u003c/p\u003e \u003cp\u003eResults on AHTD distribution in isolated regions were similar in the two groups. Data from the present study were consistent with those published in the literature by Zhao \u003cem\u003eet al\u003c/em\u003e \u003csup\u003e[\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]\u003c/sup\u003e who compared reciprocating and rotary techniques on a C-shaped canal in mandibular molars. The vol% was highest in apical region and lowest in coronal region. The complexity of apical anatomy in C-shaped canals and the difficulty for root canal irrigants in reaching the apical region \u003csup\u003e[\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e]\u003c/sup\u003e could lead to the aforementioned result.\u003c/p\u003e \u003cp\u003eAccording to the available findings and the aforementioned results in the present study, no instrumentation protocol has been able to render the complex areas in C-shaped canal free of debris \u003csup\u003e[\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e, \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e, \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e]\u003c/sup\u003e.Therefore, a three-dimensional sealing of root canal is of critical importance for successful endodontic treatment when accumulated debris is present within the irregular areas.\u003c/p\u003e \u003cp\u003eSeveral methodologies are applied to evaluate the quality of root canal filling, including: two-dimensional radiographs \u003csup\u003e[\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e]\u003c/sup\u003e, dye or alternative tracer leakage models \u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e, the stereomicroscopic evaluation of root cross-sections \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e, and micro-CT scanning \u003csup\u003e[\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e, \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e]\u003c/sup\u003e.The dye penetration cannot adequately simulate true clinical conditions. The air entrapment in voids along the root canal filling will hinder the fluid dye infiltration \u003csup\u003e[\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e]\u003c/sup\u003e. The loss of material during sectioning and discontinuous cross sections may affect the accurate evaluation on the percentage of void \u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e. Reconstructing 3D model by micro-CT scanning and imaging allows accurate assessment of canal filling outcomes. Micro-CT has the potential to differentiate filling materials, voids, and tooth structures \u003csup\u003e[\u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e]\u003c/sup\u003e. The methodology provides a clear information about the distribution of the root filling materials, the location and volumetric measurements of internal voids along the entire root canal system.\u003c/p\u003e \u003cp\u003eThe majority of published papers on the filling quality of C-shaped canal have focused on studying mandibular molars. Due to the diversity of research methods, sample selection, and filling methods, the results on the effectiveness of C-shaped root canal filling are not completely consistent. Previous studies have demonstrated that the filling quality of C-shaped canals was unsatisfactory with the cold lateral compaction technique, the MicroSeal system, the thermos-plasticized gutta-percha obturation, and the core-carrier technique. For the significant difficulties in sample collection, the present study only evaluated the quality of obturation on the volume percentage of void after the use of SC and CWC in the C-shaped canals of mandibular first premolars.\u003c/p\u003e \u003cp\u003eThe present results showed that more voids were observed in the apical 1-3mm regions in all subgroups. The present and previous studies all indicated that the apical third of C-shaped canals was filled less completely using the cold lateral compaction, the MicroSeal, the core carrier, the CWC, and the SC technique \u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e. The poor filling quality of the apical part could be caused by the irregular anatomy of the C-shaped canal. The divergent areas in the apical region of C-shaped canals are commonly unshaped, which hinders the obturating material, including gutta-percha and sealer, from flowing into the abnormalities. Although softened warm gutta-percha has excellent adaptation in the coronal two-thirds of the canal, the insufficient extension is still the main reason of the unsatisfactory apical filling \u003csup\u003e[\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e]\u003c/sup\u003e. Moreover, the dentine plug in the canals also serves as a barrier for the high quality apical obturation \u003csup\u003e[\u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe CW technique can provide better filling of canal irregularities and lateral canals \u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e, especially in the coronal regions \u003csup\u003e[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e. The findings were comparable to the present study. The results may be accounted for the heated gutta-percha adapts more easily to the irregularities of the root canal during the backfilling procedure \u003csup\u003e[\u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e]\u003c/sup\u003e. Moreover, the coronal gutta-percha receives forces more directly, optimizing filling material adaptation in this region.\u003c/p\u003e \u003cp\u003eiRoot SP has the superior flowability and the ability to slightly expand during setting \u003csup\u003e[\u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e79\u003c/span\u003e]\u003c/sup\u003e. As a bioceramic material, the sealer can produce hydroxyapatite, which precipitate within the calcium silicate hydrate phase and reinforces a bond between the dentinal wall and the sealer \u003csup\u003e[\u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e80\u003c/span\u003e]\u003c/sup\u003e. In addition, iRoot SP displayed potent antibacterial effect against \u003cem\u003eE. faecalis\u003c/em\u003e \u003csup\u003e[\u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e81\u003c/span\u003e]\u003c/sup\u003e, which might be a combination of high pH, hydrophilicity, and active calcium hydroxide release. The above-mentioned characteristics make iRoot SP a good choice as the sealer to be used in a SC technique. Regarding to the obturation quality of SC in various types canal, the studies have shown mixed results. Inan \u003cem\u003eet al.\u003c/em\u003e \u003csup\u003e[\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e82\u003c/span\u003e]\u003c/sup\u003e found the apical sealing ability of SC was comparable with that of lateral condensation and Thermafil techniques in lower premolars. Holmes \u003cem\u003eet al\u003c/em\u003e. \u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e found that the filling quality of the SC was inferior to that of cold lateral technique and superior to that of core carrier technique in the C-shaped canals. In the present study, the SC with iRoot SP sealer did not produce superior filling quality than the CWC with `AH plus sealer in the C-shaped canal of the mandibular first premolars. Other studies also suggested that the SC technique yielded similar obturation quality when compared with the continuous wave compaction technique in the curved mesial canals of the mandibular molars and the canals of the maxillary left central incisor 3D\u0026ndash;printed replicas \u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e83\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eAithough many studies has shown that the technique has questionable sealing ability, the simplicity is the main advantage of the SC which makes the faster canal obturation possible. Moreover, in a retrospective survey about the clinical outcome of SC technique with Bioceramic Sealer, the success rate of the initial treatment and retreatment was up to 90.9%. Therefore, the SC with iRoot SP sealer is still a viable option for the C-shaped canal obturation in mandibular first premolars.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eWithin the limitations of the present ex vivo study, the Protaper Next and Waveone Gold systems were associated with considerable percentages of untouched canal wall after shaping C-shaped canals in mandibular first premolars. The Protaper Next system produced less hard tissue debris in the apical regions during instrumentation compared with the Waveone Gold system. More untouched canal areas and a larger proportion of AHTD were observed in apical region of the C-shaped canals irrespective of the canal instrumentation system used. Neither of the techniques tested was capable of thoroughly sealing the C-shaped canals. More voids were remained in the apical region regardless of which system was selected to prepare and which technique was applied to obturate. The SC technique with iRoot SP yielded similar obturation quality when compared with the continuous wave compaction technique. Further studies are necessary to investigate the prognosis of the treatments performed with this technique, especially in the premolars with complex C-shaped canals anatomy.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003eAuthor\u0026apos;s Contribution\u003c/p\u003e\n\u003cp\u003eYZ, YZ, DZ and YP conceived the study and designed the experiments. YZ, JS, LW and XQ collected the samples. YZ, YZ and JS performed the experiments, analyzed the data and wrote the manuscript. DZ and YP edited and approved the final manuscript. All authors contributed to the article and approved the submitted version.\u003c/p\u003e\n\u003cp\u003eConflict of interest\u003c/p\u003e\n\u003cp\u003eAll authors have no conflicts of interest to declare.\u003c/p\u003e\n\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eThis study was supported by the National Natural Science Foundation of China (80218095).\u003c/p\u003e\n\u003cp\u003eEthics approval\u003c/p\u003e\n\u003cp\u003eAll procedures performed in studies involving human participants were in accordance with relevant guidelines and regulations and the ethics approval was provided by the ethical standards of the Ethics Committee of School and Stomatology Wenzhou Medical University (WYKQ2021007).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe requirement for informed consent was waived by the Ethics Committee of School and Stomatology Wenzhou Medical University because of the retrospective nature of the study.\u003c/p\u003e\n\u003cp\u003eData availability statements\u003c/p\u003e\n\u003cp\u003eAll data generated or analyzed in this study are included in this published article.\u003c/p\u003e\n\u003cp\u003eInformed Consent statements\u003c/p\u003e\n\u003cp\u003eFor this type of study, formal consent is not required.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eKottoor J, Albuquerque D, Velmurugan N and Kuruvilla J (2013) Root anatomy and root canal configuration of human permanent mandibular premolars: a systematic review. 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Scanning 38:352-6. https://doi.org/ 10.1002/sca.21277\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"C-shaped canal, instrumentation, obturation, mandibular first premolar, micro-CT","lastPublishedDoi":"10.21203/rs.3.rs-4167729/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4167729/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eAim\u003c/h2\u003e \u003cp\u003eTo investigate the effect of instrumentation using Protaper Next (PN, Dentsply Sirona, Maillefer, Ballaigues, Switzerland) and Waveone Gold (WG, Dentsply Sirona, Maillefer, Ballaigues, Switzerland) systems on the area of untouched surface (US), accumulated hard tissue debris (AHTD), and the filling ability of two obturation techniques on the percentage of void within C-shaped root canals of mandibular first premolars.\u003c/p\u003e\u003ch2\u003eMethodology:\u003c/h2\u003e \u003cp\u003e64 mandibular first premolars with C-shaped canals were scanned, matched and assigned to 2 shaping groups (n\u0026thinsp;=\u0026thinsp;32): PN and WG. Following instrumentation, specimens were randomly assigned into two obturation subgroups (n\u0026thinsp;=\u0026thinsp;16): continuous wave compaction (CWC) and single-cone (SC) techniques. The US% and AHTD% after instrumentation and the vol% of void after obturation were calculated from micro-computed tomography. Data were analyzed using comparisons for two groups (PN vs WG) or two subgroups (CWC vs SC) at α\u0026thinsp;=\u0026thinsp;0.05.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eFor PN and WG, 18.75% and 22.69%, respectively, of the canal wall remained untouched (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). For both groups, the apical third had higher US% than the coronal third (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Instrumentation with WG left more debris (26.48%) than PN (8.36%) in the apical 1-3mm (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In PN and WG group, the vol% of void had no significant difference between the CWC and SC subgroups(\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). The apical region had significantly more voids than the coronal region of the canal space in the two obturation subgroups regardless of which system was applied (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eBoth PN and WG systems were associated with similar US after instrumenting C-shaped canals of the mandibular first premolar. WG left significantly more AHTD compared with PN in the apical region. In PN or WG group, SC yielded similar obturation quality when compared with CWC. Both CWC and SC obturation techniques provided poorer filling quality in the apical region than in the coronal region.\u003c/p\u003e\u003ch2\u003eClinical Significance:\u003c/h2\u003e \u003cp\u003eMicro-CT evaluation of the PN and WG shaping C-shaped canals in mandibular first premolars showed similar effects on the percentages of untouched canal wall. The PN produced less hard tissue debris in the apical regions compared with the WG. The SC yielded similar obturation quality compared with the CWC.\u003c/p\u003e","manuscriptTitle":"Evaluation of two instrumentation techniques and obturation methods in mandibular first premolar C- shaped canals by Micro-CT","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-30 04:31:30","doi":"10.21203/rs.3.rs-4167729/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"bb7d0b13-0e22-4532-a6bb-6b9e62455e34","owner":[],"postedDate":"April 30th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-07-06T06:44:20+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-30 04:31:30","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4167729","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4167729","identity":"rs-4167729","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}