Influence of Preheating Resin Composites: A Nano CT assessment on Voids, Internal Adaptation and Post-Gel Shrinkage Strain

Influence of Preheating Resin Composites: A Nano CT assessment on Voids, Internal Adaptation and Post-Gel Shrinkage Strain | 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 Influence of Preheating Resin Composites: A Nano CT assessment on Voids, Internal Adaptation and Post-Gel Shrinkage Strain Rajaram Sundaravarathan, Venkata Suresh Venkataiah, Deepak Mehta, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4186892/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 Background Resin-based composites stand as widely employed restorative materials in the field of dentistry, owing to their superior esthetic and physicochemical properties. Nevertheless, a notable limitation of these composites is the occurrence of polymerization shrinkage, leading to stress at the interface of tooth restoration. Over time, this phenomenon may result in marginal leakage and secondary caries, thereby causing restoration failure. Objectives Our study aimed to conduct a comparative evaluation of voids, internal adaptation, and polymerization shrinkage in Class II preheated composite restorations [5 seconds vs. 20 seconds] and composites at room temperature [20 seconds], utilizing Nano CT analysis. Methods Cylindrical Class II cavities were prepared on both mesial and distal sides of Fifteen freshly extracted human maxillary premolar teeth. The specimens were then randomly allocated into three groups and restored as follows: Group 1 [Filtek Supreme XT at room temperature, photocured for 20 seconds], Group 2 [Filtek Supreme XT composite preheated to 68°C in Compex HD, photocured for 20 seconds], and Group 3 [Filtek Supreme XT composite preheated to 68°C in Compex HD, photocured for 5 seconds]. Nano CT was employed for the qualitative assessment of the samples. Statistical analysis involved the Shapiro-Wilkins test, ONE WAY ANOVA test, followed by Tukey’s HSD Post hoc analysis. Results Significantly improved outcomes were observed in preheated composite groups, irrespective of the photo curing time, when compared to the room temperature composite group in terms of polymerization shrinkage. The room temperature composite group exhibited the highest void volume and frequency among the investigated groups. Conclusions Within the constraints of the study, it can be deduced that preheating at 68°C and light curing for 5 seconds enhance internal adaptation and reduce the incidence of voids in composite restoration. Clinicians should be informed about clinical techniques that mitigate shrinkage stress to improve the durability of composite restorations. Clinicians should be informed about clinical techniques that mitigate shrinkage stress to improve the longevity of composite restorations. Preheating composites Bulk-fill composite Composite warmers Polymerization shrinkage Nano CT Figures Figure 1 Figure 2 Figure 3 1. Introduction From a scientific standpoint, composite resins emerge as the primary preference for restoring caries lesions and other defects in posterior teeth, attributed to their exceptional mechanical properties capable of enduring masticatory forces and averting restoration failure. Recent advancements have ushered in bulk-fill composite resins over the past decade, which has markedly improved the ease of use and handling of the materials [ 1 ]. Unlike traditional resin composites, bulk-fill counterparts permit application in thicker increments of up to 4 mm without compromising conversion rates or the enduring clinical efficacy of restorative materials. Several factors contribute to improving the clinical efficacy of bulk-fill composites, including lower filler concentrations enabling heightened light penetration and augmented photoactivation mediators [ 2 , 3 , 4 ]. Despite significant improvement of composite resin in their physical, compositional and mechanical properties compared to the earlier materials, volumetric shrinkage remains a notable drawback of direct resin composites. This phenomenon triggers polymerization shrinkage-stress at the tooth-restoration interface, resulting in internal stresses that may lead to patient discomfort, enamel fractures, strain at the margins, interfacial debonding, and micro leakage. Consequently, these issues contribute to secondary caries and eventually restoration failure [ 5 , 6 ]. To address these limitations, numerous clinical protocols and placement techniques have been advocated in the literature. Several approaches have been proposed to alleviate polymerization shrinkage, including employing the incremental application of the composite, incorporating low-modulus-of-elasticity liners to absorb stress, and implementing a soft-start polymerization approach [ 7 ]. However, each technique carries its own advantages and drawbacks depending on the type of resin composite used. Incremental composite application, for instance, prolongs chairside time and increases the risk of voids and gaps in the composite restorations. Similarly, applying composite liners with a low modulus of elasticity, such as flowable composite resins, may not significantly reduce stress, as noted by Braga et al [ 8 ]. Soft-start polymerization or pulse delay photoactivation techniques have not conclusively demonstrated effectiveness in reducing polymerization shrinkage. The use of reduced irradiance during photo polymerization as suggested by these techniques results in compromised conversion of the resin composites and promotes formation of linear polymeric chains which are susceptible to failure [ 9 ]. Consequently, there is a pressing need for the development of novel techniques or methodologies to effectively minimize polymerization shrinkage and its associated consequences. Recent advancements in restorative dentistry have introduced instruments capable of warming resin composites prior to application into cavity preparations. This innovative approach enhances the material handling characteristics, leading to decreased viscosity of composites, and improving marginal and internal adaptation. Moreover, pre-warming composites have been shown to greatly improve the degree of conversion before vitrification. This improvement is attributed to the enhanced monomer and increased segmental mobility of the polymerization chains when the resin is preheated, thereby delaying the onset of diffusion-controlled propagation of composites [ 10 , 11 ]. Additionally, preheated composites achieve high conversion values with relatively low irradiance, allowing for a reduction in the duration of light exposure. Despite its numerous advantages, it has been observed that the time delay between dispensing a preheated composite from its capsule or syringe and application into the cavity causes a significant decrease in its temperature [up to 400 0 C in two minutes] [ 12 , 13 ]. This temperature decrease during application affects the enhanced degree of conversion that can be achieved by photocuring of preheated composite, thus compromising the overall outcome. However, this challenge has been addressed with the introduction of advanced composite warmers such as the Compex HD gun [AdDent Inc. Danbury, CT, USA], which can transfer the restorative material directly into the prepared cavity.The Compex HD gun elevates resin composites to a maximum temperature of 68°C within one minute, thereby reducing the chair side time. Unlike traditional composite warmers, the Compex HD is a hand-held warming device capable of maintaining a constant temperature until composite is delivered into the preparation. Ergonomically designed, the Compex HD gun can dispense approximately 100 compules before requiring recharge [ 14 ]. Given these considerations, the aim of the present in-vitro study was to investigate the occurrence of voids in resin composite restorations and evaluate the internal adaptation at the tooth-restoration interface when placed in class II cavity with preheating device set at 68°C. The specimens were subjected to photo curing at 5 and 20 seconds. Subsequently, a comparative analysis was then conducted with a 20 second photo curing of room temperature bulk fill resin composite using nano computed tomography [Nano-CT] analysis. The primary null hypothesis posits that a photo curing time of either 5 or 20 seconds will not affect polymerization induced shrinkage stresses, and there will be no discernible difference in internal adaptation between the preheated resin composite groups. The secondary null hypothesis is that there will be no difference in the incidence and volume of voids between the preheated composite groups with photo curing time of 5 and 20 seconds. 2. Materials and Methods The procedural methodology of the sample preparation, accompanied by a detailed depiction of each step, is illustrated in Fig. 1 . Fifteen freshly extracted human maxillary premolar teeth of similar dimensions were used, based on the sample size calculations conducted for the study [Power of study – 90%]. The teeth sourced were extracted for Orthodontic reasons in conformity with the requirements of the Institutional Ethics Committee (IEC), Kempegowda Institute of Medical Sciences (KIMS), Bangalore, India [registration number: KIMS/IEC/D121/D/2021]. The informed consent to participate in the study was obtained from all subjects and/or their legal guardian(s). The included teeth were checked for caries, cracks or anomalies visually with 5x magnification loupes and only sound teeth were considered. The included teeth were then cleaned with a scaler and stored for one week in 0.5% chloramine T solution. Subsequently, they were stored in deionized water at a temperature of 40 C until they were used for the study. Roots were sectioned at 2 mm below the cemento-enamel junction using a low-speed diamond saw. The base of the tooth was then embedded in acrylic resin and cylindrical Class II cavities were created, measuring 3mm in both buccolingual and mesiodistal dimensions, with a depth of 2.5mm in occluso gingival direction. Butt joint margins were established on both the mesial and distal surfaces of teeth and the cervical margins of all preparations were in enamel. The cavities were prepared with a round diamond bur [ISO 001/018]. The diamonds were replaced after completing every set of five cavity preparations. The cavity dimensions were verified with a graduated periodontal probe [ 15 ]. 2.1. Restorative procedure: The prepared teeth were randomly allocated into three groups, each consisting of five teeth, resulting in a total of ten cavity samples within each group. Selective etching of enamel was performed for 15 seconds, followed by rinsing the etchant with water spray. Adhesive [Single Bond Universal, 3M ESPE] was then applied as per the manufacturer’s instructions. Subsequently, the adhesive was photo cured for 10 seconds using a LED curing light [Valo, Ultradent, USA] with a light cure intensity of 1,400 mW/cm 2 . A circumferential metal matrix [Omni matrix, Ultradent, USA] was placed and secured around the cavities. The LM Arte Solo-Posterior composite instrument was utilized to place and adapt the injected resin composite to the tooth preparation. 2.2. Nano CT protocol and interpretation The tooth samples were then scanned using the Bruker Skyscan 2214 Nano-CT imaging system [Bruker micro-CT, Kontich, Belgium]. The images were acquired at a final isotropic resolution of 1000 nm per voxel, at camera binning 1 x 1, at 80 kV accelerating voltage, 170 µA current, and with a 25-mm aluminum filter placed in front of the camera. The samples were rotated 360 degrees about the vertical axis using a step size of 0.43°, the exposure time being 1700 ms per projection. An average of 2 frames were taken, the total being 3400 ms per projection. The total scan time per sample was approximately one hour. Images were reconstructed using InstaNRecon software [Program version: 2.1.0.2], and with a filtered back-projection algorithm with ring artifact correction of 11 and beam hardening correction of 60%. A series of image processes were performed to ensure precise quantification. These include de-noising and removal of unwanted particles. This was followed by pore and filler quantification. Three-dimensional rendering was carried out in CTVox [Version 3.3 -Bruker Skyscan] [ 16 ]. 2.3. Evaluation of Internal Adaptation using Image J Software Digital sectioning of the specimen was performed to acquire 2D images in sagittal and axial slices to evaluate internal adaptation of the composites. From each sample, 15 cross sectional slices were analyzed along the occluso gingival [ 6 ], mesiodistal [ 3 ] and buccolingual direction [ 6 ], yielding 30 images for each specimen. A total of 450 slices were analyzed to evaluate volumetric polymerization shrinkage and identify voids in the specimens. The total area of the interface was calculated from the images obtained using the Image J software. Areas of improper adaptation at the composite and tooth interface were evaluated and summed up to determine the total area of lack of adaptation using the "Spline" and "Measure" tools in the Image J software. Post gel shrinkage stresses were evaluated as ratio of the area of lack of adaptation and the total area of tooth- composite interface [ 17 ]. 2.4. Evaluation of Voids using CT analyzing software The presence of voids in the composite restoration were assessed by progressively evaluating each of the axial sections obtained from Nano CT. After determining the position of voids in the axial slices, volumetric evaluation was performed. The volume of the voids was calculated in 3D by processing the images with a Gaussian low-pass filter for noise reduction and density thresholds for segmentation [ 18 ]. The slices of the specimens are evaluated to map out the regions of interest based on the differences in pixel density. The volume of the region of interest was then calculated across all specimens to determine the frequency and number of voids within each of the groups. 2.5. Statistical analysis Data was analyzed using the statistical package SPSS 26.0 [SPSS Inc., Chicago, IL] and level of significance was set at p < 0.05. Descriptive statistics was performed to assess the mean and standard deviation of the respective groups. Normality of the data was assessed using the Shapiro Wilkinson test. Since the data was following Normal distribution, Parametric tests were used for the data analysis. Inferential statistics to find out the difference between the groups was done using ONE WAY ANOVA test followed by Tukey’s HSD Post hoc analysis to find out the difference between any two groups/Intervals. 3. Results 3.1. Preheated Composites alleviates Polymerization Shrinkage Stress To assess Polymerization shrinkage stress, a total of 450 images obtained from Nano CT were selected for evaluation. The obtained images were representative of the 3D Nano CT images of the restored cavities, allowing for the evaluation of structural density differences between the composite and teeth. This distinction facilitated the assessment of the composite-tooth interface and the quality of the adaptation. The areas of lack of adaptation can be differentiated by the gap observed at the interface which appears radiolucent when compared to composite and dentin [Figure 2 A]. In group 1, larger radiolucency at tooth restoration interface was observed in Sagittal section [red arrow] and smaller radiolucency in occlusal section [Fig. 2 A, upper row]. Group 2 exhibited smaller radiolucency at tooth restoration interface in sagittal, pulpal and occlusal view [Fig. 2 A, middle row]. Conversely, Group 3, showed relatively minimal radiolucency only in the pulpal section [Fig. 2 A, Lower row]. We then quantitatively evaluated volumetric polymerization shrinkage of all the three groups using Nano CT images which are graphically presented in Fig. 2 B and values are summarized in Table 1 . Among all the groups, group 1 displayed higher Shrinkage values at gingival [1.6 ± 0.3], pulpal [3.3 ± 0.5] and sagittal [4.93 ± 0.4] section compared to groups 2 and 3. Group 2 exhibited relatively smaller shrinkage values [gingival, 1.2 ± 0.2; pulpal, 1.4 ± 0.3; sagittal, 0.9 ± 0.2], while Group 3 showed even smaller values [gingival, 1.2 ± 0.2; pulpal, 0.7 ± 0.3; sagittal, 0.4 ± 0.2]. No significant difference was observed between Group 2 and 3 at the gingival pulpal floor line angle level. However, a significant difference was noted at pulpal [p < 0.03] and sagittal [p < 0.03] sections. Overall, these findings suggest that Group 3, with preheated composite cured for 5 seconds, exhibited the least shrinkage, resulting in lower polymerization-induced stress at the tooth restoration interface. A) Three-dimensional nano CT images demonstrate the internal adaptation of bulk-fill composites at the interface of tooth restorations for groups G1 (room temperature), G2, and G3 (preheated). Images are presented in sagittal (left column) and two axial planes: pulpal floor (middle column) and gingival floor (right column). Areas of interfacial marginal gaps are indicated by red arrows. B) Graphical representation of mean volumetric shrinkage of bulk-fill composites in groups G1, G2, and G3. Significant differences were observed between most pairwise comparisons (p < 0.05), except for G2 versus G3 at the gingival floor. Table 1: Mean Post gel shrinkage values (%) based on composite temperature and exposure duration (*P<0.05 indicates statistical significance) Gingival Pulpal floor line angle Pulpal floor slice Sagittal slice Polymerization Shrinkage (%) G1 - Room temperature composite cured for 20 seconds 1.6±0.3 3.3±0.5 4.93±0.4 G2 - Preheated composite cured for 20 seconds 1.2±0.2 1.4±0.3 0.9±0.2 G3 - Preheated composite cured for 5 seconds 1.2±0.2 0.7±0.3 0.4±0.2 P VALUE 0.03* 0.0001* 0.0001* P VALUE [ TUKEY’S HSD TEST] G1 vs G2 0.04* 0.0001* 0.0001* G1 vs G3 0.04* 0.0001* 0.0001* G2 vs G3 0.99 0.03* 0.03* 3.2. Preheated Composites minimize the size and occurrence of Internal Voids We then investigated nano CT axial slices from each sample to ascertain the frequency and volume of voids in the bulk fill composite restoration within each experimental group. The results obtained provided 3D representations in axial sections, revealing areas of radiolucency, representing voids within bulk fill composite filling material. These voids were highlighted within red circles for all three groups [Figure 3 A]. Group 1 exhibited larger radiolucent areas within the filling material, as highlighted in the red circle, while minimal to no radiolucency was observed in Groups 2 and 3. Quantitative evaluation of void frequency and void volume is presented and summarized in Figs. 3 A, B and C, respectively. Group 1 displayed a higher number of voids per sample compared to Groups 2 and 3, although this difference did not reach statistical significance between any of the groups. However, the void volume in group 1 was greater [14.3] compared to group 2 [4.1] and group 3 [3.9]. This mean difference was significantly different between group 1 and 2, and group 1 and 3, but was not significant between group 2 and 3. In conclusion, the data suggest that Groups 2 and 3, with preheated composite cured for 20 and 5 seconds, respectively, exhibited a minimal number and size of voids within the bulk fill composite filling material. Table 2 Mean void volume values (%) based on composite temperature and exposure duration (*P < 0.05 indicates statistical significance). MEAN SD VOID VOLUME G1 - Room temperature composite cured for 20 seconds. 14.3 0.2 G2 - Preheated composite cured for 20 seconds. 4.1 0.3 G3 - Preheated composite cured for 5 seconds. 3.9 0.2 P VALUE [ TUKEY’S HSD TEST] G1 vs G2 0.0001* G1 vs G3 0.0001* G2 vs G3 0.40 Table 3 Mean void frequency based on composite temperature and exposure duration. (*P < 0.05 indicates statistical significance) MEAN SD VOID FREQUENCY G1 - Room temperature composite cured for 20 seconds. 4 2 G2 - Preheated composite cured for 20 seconds. 2 1 G3 - Preheated composite cured for 5 seconds. 2 1 P VALUE [ TUKEY’S HSD TEST] G1 vs G2 0.10 G1 vs G3 0.10 G2 vs G3 0.99 4. Discussion The results obtained from this study led to the rejection of the primary null hypothesis suggesting that photo curing time may not influence polymerization-induced shrinkage forces and consequently would not result in differences in internal adaptation with a short 5-second duration of light exposure. Specifically, Group 3, comprising preheated composite with a 5-second photo curing time, demonstrated superior internal adaptation compared to the other groups. However, the one objective of the secondary null hypothesis proposing no difference in the occurrence of voids among preheated groups was accepted. This conclusion was drawn as there was no statistically significant variance observed in the incidence of voids between preheated resin composites Group 2 and Group 3 [Tables 2 and 3 ]. However, the secondary objective of the same null hypothesis, suggesting no difference in the volume of voids among preheated groups, was refuted. This was evidenced by the observation that preheated composites [Groups 2 and 3] exhibited a significant disparity compared to the room temperature composites [Group 1]. Several researchers have proposed diverse strategies to mitigate the shrinkage stresses arising from high conversion rates [ 19 , 20 , 21 , 22 , 23 ]. Elhejazi et al advocated a 15 second delay after introducing preheated composite resin into the cavity before initiating photo curing [ 19 ]. They posited that this delay would still provide adequate viscosity to the preheated composite to effectively wet the cavity preparation walls, thereby ensuring marginal adaptation. Daronch et al recommended reducing the photo curing duration, contending that fewer radicals are generated due to the shortened exposure time. Consequently, this reduction leads to improved resin composite adaptation and reduced gap formation at the tooth-restoration interface [ 20 ]. In the present study, Group 3, consisting of preheated composite with a 5-second photo curing time, exhibited superior internal adaptation compared to both the 20-second photo curing time of preheated composite and the 20-second cure of room temperature composite. This finding aligns with a study conducted by Fernanda C Calheiros et al who employed a 5 second photo curing time on composite preheated to 40°C or 60°C. They reported a reduction in final stress compared to a 20-second photo curing time, along with similar or higher degrees of conversion achieved isothermally at 40°C or 60°C with a 5-second exposure compared to 20 seconds at room temperature [ 20 ]. The decreased polymerization time diminishes the accumulation of polymerization stresses, allowing for better resin composite adaptation, as evidenced in our study with Group 3, the preheated group with a 5-second photo curing duration. The difference in polymerization shrinkage values at different depths of the cavity can also be appreciated from the values in Table 1 which can be explained by the influence of proximity of the light curing unit to the resin. Our results demonstrated that polymerization shrinkage at the gingival pulpal floor interface surpasses that at the pulpal floor, attributable to the difference in the rate of polymerization and conversion to gel phase, which occurs more rapidly closer to the top of the restoration [24,25] . Regarding void formation, existing literature suggests that "voids" represent a multifactorial phenomenon[ 15 ] influenced by various factors, including placement technique and polymerization of the material. Some studies indicate that voids are more prevalent in bulk fill technique as compared to layering technique; and that there is a higher incidence of void occurrence when layering thicker increments of material as opposed to smaller increments. This phenomenon is attributed to the ease of adaptation and increased potential for void elimination when using smaller increments of resin composites [ 26 , 27 , 28 , 29 , 30 ]. In the current study, presence of voids in the composite restoration was assessed through two dimensional axial slices to determine their presence and overall volume within the restoration. Subsequent, three-dimensional evaluation of these voids, based on their location in the two-dimensional axial nano CT slices, revealed that the room temperature cured composites [Group 1] exhibited the highest number and significantly greater volume of voids compared to preheated composite [Groups 2 and 3], which underwent photo curing for 20 seconds and 5 seconds, respectively. This observation can be elucidated by the enhanced flow characteristics of resin composite when heated to 68°C, promoting homogenous distribution within the prepared cavity. Interestingly, the duration of photo curing in the preheated groups, whether for 5 seconds or 20 seconds, did not appear to significantly affect the incidence or volume of voids, as no notable difference was observed between the two preheated groups. Furthermore, the most common location for voids within the composite restorations was noted to be at the interface between the axial wall and pulpal floor across all groups. This occurrence may be attributed to cavity geometry, wherein sharp line angles present challenges for intimate adaptation of composite resin. It is suggested that the presence of rounded internal line angles may facilitate optimal adaptation of resin to the interface, thus aiding in the distribution of shrinkage stress [ 26 ]. Several researchers have indicated that bulk placement techniques yield fewer voids compared to layering methods [ 15 , 31 , 32 ]. Moreover, they have found that preheated composites exhibit significantly higher void volume compared to room temperature composites. However, these studies were performed with conventional composite warmers and they attribute the decrease in temperature and curing to the heightened incidence of voids in the composite resin. They posit that rapid temperature decrease and early vitrification, which restricts molecular mobility, hinder the diffusion of air bubbles, leading to their entrapment within the material and subsequent void formation [ 33]. In our study, there was no significant disparity in the incidence and volume of voids between the 5 and 20-second photo curing durations in the preheated composite groups. However, a higher incidence of voids was noted in the room temperature composite group without preheating. This discrepancy may be attributed to the application of preheated composite using Compex HD [AdDent Inc., Danbury CT, USA], which facilitates the direct dispensing of material into the preparation, thereby reducing time for dissipation of the temperature of the heated composite. Consequently, this process lowers the viscosity of the resin composite and promotes uniform flow, facilitating proper adaptation at the tooth-restoration interface and reducing the presence of voids in the restoration, as observed in our study. This decrease in viscosity and enhancement of wetting properties in the resin composite due to heat may mitigate gap formation in composite resin restorations. Micro CT has been widely employed for investigating and characterizing internal structures, polymerization shrinkage, and adhesion failure in dental restorative composites [ 34 , 35 ]. In our study, nano CT was utilized to assess the internal adaptation of resin composites due to its technological advancement over Micro CT, offering superior spatial resolution of up to 450 nm, surpassing the typical resolution of Micro CT systems [ 36 ]. A recent study by Haugen et al. demonstrated that nano CT could detect micro porosity in composite filling materials that were not observable in Micro CT or SEM analyses, suggesting its utility in identifying the detrimental effects of dental composites [ 36 ]. Therefore, nano CT proves to be a versatile tool for evaluating the adaptation of restorative materials to the tooth and estimating the presence of voids in 3D volumes [ 37 , 38 , 39 ]. The present study is subject to several limitations that warrant acknowledgment. For Instance, only one single brand of composite was utilized, potentially leading to variations in results when compared with other brands featuring different filler compositions. Enhancing the assessment of the degree of conversion of the composite groups using Fourier-transform infrared spectroscopy [FTIR], Differential thermal analysis [DTA] or Infrared spectroscopy would have reinforced the findings of our study. Moreover, to augment the clinical relevance of our findings, particularly concerning gap measurements at the tooth-restoration interface, further validation via high-resolution scanning electron microscopy would have been advantageous. Additionally, the results of our study, especially gap measurements at the tooth-restoration interface, would have higher clinical correlation impact, if the results were further confirmed using high resolution scanning electron microscopy. Regrettably, this avenue was not explored within the scope of our study, constituting another limitation. Despite the positive outcomes observed, the necessity for additional preclinical studies with larger sample sizes is imperative to establish a more definitive clinical correlation with the results obtained in our study. 5. Conclusions In conclusion, the investigation into the influence of preheating resin composites, as examined through Nano CT assessment on voids, internal adaptation, and post-gel shrinkage strain, yields valuable insights into the optimization of dental restoration procedures. Given the limitations of our study, it is clear that preheating bulk fill composites to 68°C and applying a 5-second light curing regimen composites can significantly impact the overall quality of dental restorations by minimizing void formation, enhancing internal adaptation to tooth structure, and reducing post-gel shrinkage strain. These findings underscore the importance of temperature management in the manipulation of resin composites during dental procedures. By understanding and leveraging the effects of preheating, clinicians can advance towards achieving superior clinical outcomes, ultimately contributing to the enhancement of patient care and satisfaction in the field of restorative dentistry. Further research and refinement of techniques in this area promise to continue elevating the standards of dental practice, ensuring the delivery of optimal and durable restorations for patients worldwide. Declarations Ethics approval statement and Consent to participate This study was approved by the Institutional Ethics Committee (IEC), Kempegowda Institute of Medical Sciences (KIMS), Bangalore, India under the registration number: KIMS/IEC/D121/D/2021. The informed consent to participate in the study was obtained from all subjects and/or their legal guardian(s). Consent to publish Not applicable. Data Availability Statement The data are available from the corresponding author upon reasonable request. Competing Interests The authors declare that they have no conflict of interest. Funding The authors receive no funding from their institutes. Acknowledgments Not applicable. Author contribution Conceptualization: S.R., D.M.; Data curation: S.R., D.M., M.R.S, A.G.; Formal analysis: D.M., N.M., V.S.; Investigation: S.S.; Methodology: R.A., D.M.; Project administration: N.M., D.M.; Resources: D.M., N.M.,V.S.; Software: S.R.; Supervision: D.M., N.M.; Validation: V.S.; Visualization: S.R., S.M., M.A.S; Writing - original draft: S.S.; Writing - review & editing: R.A., D.M., V.S. References Boaro LC, Lopes DP, de Souza AS, Nakano EL, Perez MD, Pfeifer CS, Gonçalves F. Clinical performance and chemical-physical properties of bulk fill composites resin—a systematic review and meta-analysis. Dental Materials. 2019 Oct 1;35[10]:e249-64. Ilie N, Schoner C, Bucher K, Hickel R. An in-vitro assessment of the shear bond strength of bulk-fill resin composites to permanent and deciduous teeth. 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Pre-heating of high-viscosity bulk-fill resin composites: effects on shrinkage force and monomer conversion. Journal of dentistry. 2015 Nov 1;43[11]:1358-64. Ribeiro MT, de Bragança GF, Oliveira LR, Braga SS, de Oliveira HL, Price RB, Soares CJ. Effect of preheating methods and devices on the mechanical properties, post-gel shrinkage, and shrinkage stress of bulk-fill materials. Journal of the Mechanical Behavior of Biomedical Materials. 2023 Feb 1;138:105605. Loguercio AD, Reis A, Schroeder M, Balducci I, Versluis A, Ballester RY. Polymerization shrinkage: effects of boundary conditions and filling technique of resin composite restorations. Journal of dentistry. 2004 Aug 1;32[6]:459-70. Kinomoto Y, Torii M. Photoelastic analysis of polymerization contraction stresses in resin composite restorations. Journal of dentistry. 1998 Mar 1;26[2]:165-71 Kim YS, Baek SH, Kim RJ. Effect of vibration during bulk and incremental filling on adaptation of a bulk-fill composite resin. Scientific reports. 2022 Dec 15;12[1]:21652. Malhotra, N.; Kundabala, M.; Shashirashmi, A. Strategies to overcome polymerization shrinkage–materials and techniques. A review. Dent. Update 2010, 37, 115–125. Rees, J.S.; Jagger, D.C.; Williams, D.R.; Brown, G.; Duguid, W. A reappraisal of the incremental packing technique for light cured composite resins. J. Oral Rehabil. 2004, 31, 81–84. Moore, B.K.; Platt, J.A.; Borges, G.; Chu, T.M.G.; Katsilieri, I. Depth of cure of dental resin composites: ISO 4049 depth and microhardness of types of materials and shades. Oper. Dent. 2008, 33, 408–412. Park, J.; Chang, J.; Ferracane, J.; Lee, I.B. How should composite be layered to reduce shrinkage stress: Incremental or bulk filling? Dent. Mater. 2008, 24, 1501–1505. Fronza, B.M.; Rueggeberg, F.A.; Braga, R.R.; Mogilevych, B.; Soares, L.E.S.; Martin, A.A.; Ambrosano, G.; Giannini, M. Monomer conversion, microhardness, internal marginal adaptation, and shrinkage stress of bulk-fill resin composites. Dent. Mater. 2015, 31, 1542–1551. El-Safty, S.; Akhtar, R.; Silikas, N.; Watts, D.C. Nanomechanical properties of dental resin-composites. Dent. Mater. 2012, 28, 1292–1300. Buelvas DD, Besegato JF, Vicentin BL, Jussiani EI, Hoeppner MG, Andrello AC, Di Mauro E. Impact of light-cure protocols on the porosity and shrinkage of commercial bulk fill dental resin composites with different flowability. Journal of Polymer Research. 2020 Sep;27:1-0. Kim HJ, Park SH. Measurement of the internal adaptation of resin composites using micro-CT and its correlation with polymerization shrinkage. Operative dentistry. 2014 Mar 1;39[2]:e57-70. Sampaio CS, Arias JF, Atria PJ, Cáceres E, Díaz CP, Freitas AZ, Hirata R. Volumetric polymerization shrinkage and its comparison to internal adaptation in bulk fill and conventional composites: A μCT and OCT in vitro analysis. Dental Materials. 2019 Nov 1;35[11]:1568-75. Haugen HJ, Qasim SB, Matinlinna JP, Vallittu P, Nogueira LP. Nano-CT as a tool for characterization of dental resin composites. Scientific reports. 2020 Sep 23;10[1]:15520. Ahmed HM. Nano-computed tomography: current and future perspectives. Restorative Dentistry & Endodontics. 2016 Aug 1;41[3]:236-8. Aljdaimi A, Devlin H, Dickinson M, Burnett T, Slater TJ. Micron-scale crack propagation in laser-irradiated enamel and dentine studied with nano-CT. Clinical oral investigations. 2019 May 1;23:2279-85. Sakai T, Li H, Abe T, Yamaguchi S, Imazato S. Multi-scale analysis of the influence of filler shapes on the mechanical performance of resin composites using high resolution nano-CT images. Dental Materials. 2021 Jan 1;37[1]:168-74. Additional Declarations No competing interests reported. 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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-4186892","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":287187359,"identity":"ba8c218c-bf84-4a2d-ba21-52f1ddb8a4ee","order_by":0,"name":"Rajaram Sundaravarathan","email":"","orcid":"","institution":"V. S. Dental College and Hospitals","correspondingAuthor":false,"prefix":"","firstName":"Rajaram","middleName":"","lastName":"Sundaravarathan","suffix":""},{"id":287187361,"identity":"a4857f7c-0ed8-43a0-93a6-b8413222aaa6","order_by":1,"name":"Venkata Suresh Venkataiah","email":"","orcid":"","institution":"Saveetha Dental College and Hospitals, Saveetha University","correspondingAuthor":false,"prefix":"","firstName":"Venkata","middleName":"Suresh","lastName":"Venkataiah","suffix":""},{"id":287187364,"identity":"4684ec4b-f70a-4333-bd68-9b6e8cd11833","order_by":2,"name":"Deepak Mehta","email":"","orcid":"","institution":"Saveetha Dental College and Hospitals, Saveetha University","correspondingAuthor":false,"prefix":"","firstName":"Deepak","middleName":"","lastName":"Mehta","suffix":""},{"id":287187365,"identity":"031b4ae9-622f-4167-a712-c8cd2fd84a65","order_by":3,"name":"Meena Naganath","email":"","orcid":"","institution":"V.S. Dental College","correspondingAuthor":false,"prefix":"","firstName":"Meena","middleName":"","lastName":"Naganath","suffix":""},{"id":287187367,"identity":"2d545ee6-2aa7-4422-8ab0-6ad9cc088ecf","order_by":4,"name":"Swabhaanu Manoj Sindagi","email":"","orcid":"","institution":"Center for Restorative Dentistry \u0026 Endodontics","correspondingAuthor":false,"prefix":"","firstName":"Swabhaanu","middleName":"Manoj","lastName":"Sindagi","suffix":""},{"id":287187370,"identity":"ecfbb68b-85ad-4846-b542-8ef9addd8c90","order_by":5,"name":"Ajay Guru","email":"","orcid":"","institution":"Saveetha Dental College and Hospitals, Saveetha University","correspondingAuthor":false,"prefix":"","firstName":"Ajay","middleName":"","lastName":"Guru","suffix":""},{"id":287187374,"identity":"a06536fb-31f8-493e-9eb0-b95707fde5da","order_by":6,"name":"Mohammed Rafi Shaik","email":"","orcid":"","institution":"King Saud University","correspondingAuthor":false,"prefix":"","firstName":"Mohammed","middleName":"Rafi","lastName":"Shaik","suffix":""},{"id":287187377,"identity":"91aef5cb-6dbe-47aa-8c88-6cb93b240fc9","order_by":7,"name":"Saurav Mallik","email":"","orcid":"","institution":"Harvard T. H. Chan School of Public Health","correspondingAuthor":false,"prefix":"","firstName":"Saurav","middleName":"","lastName":"Mallik","suffix":""},{"id":287187380,"identity":"c631eca5-711a-406f-852c-74220349cc35","order_by":8,"name":"Mohd Asif Shah","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA30lEQVRIie3OMQrCMBSA4SeFujxwFUrxBEJKIA4GzxIRMiuCOHZzc1YEz9DiBQIZugQ9QBfFC1RcBAeNowgNOjnkhyQk8PEC4PP9a4JzYo/XgkZqt8pNpHwjjZV7jNRfkG4anKujONDWRufXMfA4U8EprSNMhawtRMnaezmNViBppsLEQYDB8FZyMEgiBD3MFPSO9aR5rYTY845Bekd4WNK8OKYgsR9TjBhkdoqyBB0f0zizZEQTE876SEZ0rXFST4rF7nITg2Rrgl2J80G8LBZ5LYHg7UY+Xnw+n8/3S08ubkrTnLI70AAAAABJRU5ErkJggg==","orcid":"","institution":"Kardan University","correspondingAuthor":true,"prefix":"","firstName":"Mohd","middleName":"Asif","lastName":"Shah","suffix":""}],"badges":[],"createdAt":"2024-03-29 09:06:43","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4186892/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4186892/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54085605,"identity":"f9596f7e-6c12-4f99-be6c-901e7badc5a7","added_by":"auto","created_at":"2024-04-04 11:12:36","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":915923,"visible":true,"origin":"","legend":"\u003cp\u003eSequential Steps in Sample Preparation a) Illustration of the Compex HD gun. b) The Compex HD gun, pre-warmed and prepared for dispensing. c) Filtek Supreme XT composite capsule, a component of the sample. d) Standardized cavity preparation. e) Cavity preparation matrixed with Omnimatrix. f) Etching of the cavity surface. g) Application of bonding agent. h) Photocuring of bonding agent using the Valo light curing unit. i) Valo light curing unit for polymerization. j) Proper orientation of the gun relative to the cavity before composite dispensing. k) Warm composite dispensed directly into the prepared cavity. l) Condensation of composite using the LM Arte solo posterior instrument. m) Finishing of composite restorations with finishing discs.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4186892/v1/094c6d365aea80de43ef958d.png"},{"id":54085604,"identity":"2d0c2c3b-da3c-4d32-96cc-3193ccba0f4b","added_by":"auto","created_at":"2024-04-04 11:12:36","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1184964,"visible":true,"origin":"","legend":"\u003cp\u003eNano CT Analysis of Polymerization Shrinkage Stress.\u003c/p\u003e\n\u003cp\u003eA) Three-dimensional nano CT images demonstrate the internal adaptation of bulk-fill composites at the interface of tooth restorations for groups G1 (room temperature), G2, and G3 (preheated). Images are presented in sagittal (left column) and two axial planes: pulpal floor (middle column) and gingival floor (right column). Areas of interfacial marginal gaps are indicated by red arrows. B) Graphical representation of mean volumetric shrinkage of bulk-fill composites in groups G1, G2, and G3. Significant differences were observed between most pairwise comparisons (p \u0026lt; 0.05), except for G2 versus G3 at the gingival floor.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4186892/v1/feb87535b4e9abad5e1f5a38.png"},{"id":54085606,"identity":"6cfcc99d-50cb-4dc1-8ef8-844a7edbb0a8","added_by":"auto","created_at":"2024-04-04 11:12:36","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":873202,"visible":true,"origin":"","legend":"\u003cp\u003eAssessment of voids formation in the Bulkfil composite. A) Spatial distribution of voids in axially reconstructed Nano CT images for groups G1, G2, and G3. Internal voids are highlighted by red circles. B) Graphical representation comparing void frequency among the three groups. (C) Graphical illustration comparing void volume among the three groups.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4186892/v1/52225280ddccce9057d0b873.png"},{"id":65679451,"identity":"f411e69f-c00b-4c08-a6dd-ce88f245295e","added_by":"auto","created_at":"2024-10-01 08:32:35","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5192193,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4186892/v1/408f73ad-b2fc-40d7-afc9-8c84bfd56836.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Influence of Preheating Resin Composites: A Nano CT assessment on Voids, Internal Adaptation and Post-Gel Shrinkage Strain","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eFrom a scientific standpoint, composite resins emerge as the primary preference for restoring caries lesions and other defects in posterior teeth, attributed to their exceptional mechanical properties capable of enduring masticatory forces and averting restoration failure. Recent advancements have ushered in bulk-fill composite resins over the past decade, which has markedly improved the ease of use and handling of the materials [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Unlike traditional resin composites, bulk-fill counterparts permit application in thicker increments of up to 4 mm without compromising conversion rates or the enduring clinical efficacy of restorative materials. Several factors contribute to improving the clinical efficacy of bulk-fill composites, including lower filler concentrations enabling heightened light penetration and augmented photoactivation mediators [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite significant improvement of composite resin in their physical, compositional and mechanical properties compared to the earlier materials, volumetric shrinkage remains a notable drawback of direct resin composites. This phenomenon triggers polymerization shrinkage-stress at the tooth-restoration interface, resulting in internal stresses that may lead to patient discomfort, enamel fractures, strain at the margins, interfacial debonding, and micro leakage. Consequently, these issues contribute to secondary caries and eventually restoration failure [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. To address these limitations, numerous clinical protocols and placement techniques have been advocated in the literature.\u003c/p\u003e \u003cp\u003eSeveral approaches have been proposed to alleviate polymerization shrinkage, including employing the incremental application of the composite, incorporating low-modulus-of-elasticity liners to absorb stress, and implementing a soft-start polymerization approach [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, each technique carries its own advantages and drawbacks depending on the type of resin composite used. Incremental composite application, for instance, prolongs chairside time and increases the risk of voids and gaps in the composite restorations. Similarly, applying composite liners with a low modulus of elasticity, such as flowable composite resins, may not significantly reduce stress, as noted by Braga et al [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Soft-start polymerization or pulse delay photoactivation techniques have not conclusively demonstrated effectiveness in reducing polymerization shrinkage. The use of reduced irradiance during photo polymerization as suggested by these techniques results in compromised conversion of the resin composites and promotes formation of linear polymeric chains which are susceptible to failure [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Consequently, there is a pressing need for the development of novel techniques or methodologies to effectively minimize polymerization shrinkage and its associated consequences. Recent advancements in restorative dentistry have introduced instruments capable of warming resin composites prior to application into cavity preparations. This innovative approach enhances the material handling characteristics, leading to decreased viscosity of composites, and improving marginal and internal adaptation. Moreover, pre-warming composites have been shown to greatly improve the degree of conversion before vitrification. This improvement is attributed to the enhanced monomer and increased segmental mobility of the polymerization chains when the resin is preheated, thereby delaying the onset of diffusion-controlled propagation of composites [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAdditionally, preheated composites achieve high conversion values with relatively low irradiance, allowing for a reduction in the duration of light exposure. Despite its numerous advantages, it has been observed that the time delay between dispensing a preheated composite from its capsule or syringe and application into the cavity causes a significant decrease in its temperature [up to 400\u003csup\u003e0\u003c/sup\u003eC in two minutes] [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. This temperature decrease during application affects the enhanced degree of conversion that can be achieved by photocuring of preheated composite, thus compromising the overall outcome. However, this challenge has been addressed with the introduction of advanced composite warmers such as the Compex HD gun [AdDent Inc. Danbury, CT, USA], which can transfer the restorative material directly into the prepared cavity.The Compex HD gun elevates resin composites to a maximum temperature of 68\u0026deg;C within one minute, thereby reducing the chair side time. Unlike traditional composite warmers, the Compex HD is a hand-held warming device capable of maintaining a constant temperature until composite is delivered into the preparation. Ergonomically designed, the Compex HD gun can dispense approximately 100 compules before requiring recharge [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eGiven these considerations, the aim of the present in-vitro study was to investigate the occurrence of voids in resin composite restorations and evaluate the internal adaptation at the tooth-restoration interface when placed in class II cavity with preheating device set at 68\u0026deg;C. The specimens were subjected to photo curing at 5 and 20 seconds. Subsequently, a comparative analysis was then conducted with a 20 second photo curing of room temperature bulk fill resin composite using nano computed tomography [Nano-CT] analysis. The primary null hypothesis posits that a photo curing time of either 5 or 20 seconds will not affect polymerization induced shrinkage stresses, and there will be no discernible difference in internal adaptation between the preheated resin composite groups. The secondary null hypothesis is that there will be no difference in the incidence and volume of voids between the preheated composite groups with photo curing time of 5 and 20 seconds.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cp\u003eThe procedural methodology of the sample preparation, accompanied by a detailed depiction of each step, is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Fifteen freshly extracted human maxillary premolar teeth of similar dimensions were used, based on the sample size calculations conducted for the study [Power of study \u0026ndash; 90%]. The teeth sourced were extracted for Orthodontic reasons in conformity with the requirements of the Institutional Ethics Committee (IEC), Kempegowda Institute of Medical Sciences (KIMS), Bangalore, India [registration number: KIMS/IEC/D121/D/2021]. The informed consent to participate in the study was obtained from all subjects and/or their legal guardian(s). The included teeth were checked for caries, cracks or anomalies visually with 5x magnification loupes and only sound teeth were considered. The included teeth were then cleaned with a scaler and stored for one week in 0.5% chloramine T solution. Subsequently, they were stored in deionized water at a temperature of 40 C until they were used for the study.\u003c/p\u003e \u003cp\u003eRoots were sectioned at 2 mm below the cemento-enamel junction using a low-speed diamond saw. The base of the tooth was then embedded in acrylic resin and cylindrical Class II cavities were created, measuring 3mm in both buccolingual and mesiodistal dimensions, with a depth of 2.5mm in occluso gingival direction. Butt joint margins were established on both the mesial and distal surfaces of teeth and the cervical margins of all preparations were in enamel. The cavities were prepared with a round diamond bur [ISO 001/018]. The diamonds were replaced after completing every set of five cavity preparations. The cavity dimensions were verified with a graduated periodontal probe [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Restorative procedure:\u003c/h2\u003e \u003cp\u003eThe prepared teeth were randomly allocated into three groups, each consisting of five teeth, resulting in a total of ten cavity samples within each group. Selective etching of enamel was performed for 15 seconds, followed by rinsing the etchant with water spray.\u003c/p\u003e \u003cp\u003eAdhesive [Single Bond Universal, 3M ESPE] was then applied as per the manufacturer\u0026rsquo;s instructions. Subsequently, the adhesive was photo cured for 10 seconds using a LED curing light [Valo, Ultradent, USA] with a light cure intensity of 1,400 mW/cm\u003csup\u003e2\u003c/sup\u003e. A circumferential metal matrix [Omni matrix, Ultradent, USA] was placed and secured around the cavities. The LM Arte Solo-Posterior composite instrument was utilized to place and adapt the injected resin composite to the tooth preparation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Nano CT protocol and interpretation\u003c/h2\u003e \u003cp\u003eThe tooth samples were then scanned using the Bruker Skyscan 2214 Nano-CT imaging system [Bruker micro-CT, Kontich, Belgium]. The images were acquired at a final isotropic resolution of 1000 nm per voxel, at camera binning 1 x 1, at 80 kV accelerating voltage, 170 \u0026micro;A current, and with a 25-mm aluminum filter placed in front of the camera. The samples were rotated 360 degrees about the vertical axis using a step size of 0.43\u0026deg;, the exposure time being 1700 ms per projection. An average of 2 frames were taken, the total being 3400 ms per projection. The total scan time per sample was approximately one hour. Images were reconstructed using InstaNRecon software [Program version: 2.1.0.2], and with a filtered back-projection algorithm with ring artifact correction of 11 and beam hardening correction of 60%. A series of image processes were performed to ensure precise quantification. These include de-noising and removal of unwanted particles. This was followed by pore and filler quantification. Three-dimensional rendering was carried out in CTVox [Version 3.3 -Bruker Skyscan] [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Evaluation of Internal Adaptation using Image J Software\u003c/h2\u003e \u003cp\u003eDigital sectioning of the specimen was performed to acquire 2D images in sagittal and axial slices to evaluate internal adaptation of the composites. From each sample, 15 cross sectional slices were analyzed along the occluso gingival [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], mesiodistal [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] and buccolingual direction [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], yielding 30 images for each specimen. A total of 450 slices were analyzed to evaluate volumetric polymerization shrinkage and identify voids in the specimens.\u003c/p\u003e \u003cp\u003eThe total area of the interface was calculated from the images obtained using the Image J software. Areas of improper adaptation at the composite and tooth interface were evaluated and summed up to determine the total area of lack of adaptation using the \"Spline\" and \"Measure\" tools in the Image J software. Post gel shrinkage stresses were evaluated as ratio of the area of lack of adaptation and the total area of tooth- composite interface [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Evaluation of Voids using CT analyzing software\u003c/h2\u003e \u003cp\u003e The presence of voids in the composite restoration were assessed by progressively evaluating each of the axial sections obtained from Nano CT. After determining the position of voids in the axial slices, volumetric evaluation was performed. The volume of the voids was calculated in 3D by processing the images with a Gaussian low-pass filter for noise reduction and density thresholds for segmentation [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The slices of the specimens are evaluated to map out the regions of interest based on the differences in pixel density. The volume of the region of interest was then calculated across all specimens to determine the frequency and number of voids within each of the groups.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Statistical analysis\u003c/h2\u003e \u003cp\u003eData was analyzed using the statistical package SPSS 26.0 [SPSS Inc., Chicago, IL] and level of significance was set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05. Descriptive statistics was performed to assess the mean and standard deviation of the respective groups. Normality of the data was assessed using the Shapiro Wilkinson test. Since the data was following Normal distribution, Parametric tests were used for the data analysis. Inferential statistics to find out the difference between the groups was done using ONE WAY ANOVA test followed by Tukey\u0026rsquo;s HSD Post hoc analysis to find out the difference between any two groups/Intervals.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Preheated Composites alleviates Polymerization Shrinkage Stress\u003c/h2\u003e \u003cp\u003eTo assess Polymerization shrinkage stress, a total of 450 images obtained from Nano CT were selected for evaluation. The obtained images were representative of the 3D Nano CT images of the restored cavities, allowing for the evaluation of structural density differences between the composite and teeth. This distinction facilitated the assessment of the composite-tooth interface and the quality of the adaptation. The areas of lack of adaptation can be differentiated by the gap observed at the interface which appears radiolucent when compared to composite and dentin [Figure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA]. In group 1, larger radiolucency at tooth restoration interface was observed in Sagittal section [red arrow] and smaller radiolucency in occlusal section [Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA, upper row]. Group 2 exhibited smaller radiolucency at tooth restoration interface in sagittal, pulpal and occlusal view [Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA, middle row]. Conversely, Group 3, showed relatively minimal radiolucency only in the pulpal section [Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA, Lower row]. We then quantitatively evaluated volumetric polymerization shrinkage of all the three groups using Nano CT images which are graphically presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB and values are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Among all the groups, group 1 displayed higher Shrinkage values at gingival [1.6\u0026thinsp;\u003cb\u003e\u0026plusmn;\u003c/b\u003e\u0026thinsp;0.3], pulpal [3.3\u0026thinsp;\u003cb\u003e\u0026plusmn;\u003c/b\u003e\u0026thinsp;0.5] and sagittal [4.93\u0026thinsp;\u003cb\u003e\u0026plusmn;\u003c/b\u003e\u0026thinsp;0.4] section compared to groups 2 and 3. Group 2 exhibited relatively smaller shrinkage values [gingival, 1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2; pulpal, 1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3; sagittal, 0.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2], while Group 3 showed even smaller values [gingival, 1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2; pulpal, 0.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3; sagittal, 0.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2]. No significant difference was observed between Group 2 and 3 at the gingival pulpal floor line angle level. However, a significant difference was noted at pulpal [p\u0026thinsp;\u0026lt;\u0026thinsp;0.03] and sagittal [p\u0026thinsp;\u0026lt;\u0026thinsp;0.03] sections. Overall, these findings suggest that Group 3, with preheated composite cured for 5 seconds, exhibited the least shrinkage, resulting in lower polymerization-induced stress at the tooth restoration interface.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA) Three-dimensional nano CT images demonstrate the internal adaptation of bulk-fill composites at the interface of tooth restorations for groups G1 (room temperature), G2, and G3 (preheated). Images are presented in sagittal (left column) and two axial planes: pulpal floor (middle column) and gingival floor (right column). Areas of interfacial marginal gaps are indicated by red arrows. B) Graphical representation of mean volumetric shrinkage of bulk-fill composites in groups G1, G2, and G3. Significant differences were observed between most pairwise comparisons (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), except for G2 versus G3 at the gingival floor.\u003c/p\u003e \u003cp\u003e\u003cstrong\u003eTable 1:\u003c/strong\u003e Mean Post gel shrinkage values (%) based on composite temperature and exposure duration (*P\u0026lt;0.05 indicates statistical significance)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"642\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"17.601246105919003%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"36.7601246105919%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.1588785046729%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eGingival Pulpal floor line angle\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.641744548286605%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ePulpal floor slice\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.838006230529595%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;Sagittal slice\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"17.601246105919003%\" rowspan=\"3\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003ePolymerization Shrinkage (%)\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"36.7601246105919%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eG1 - Room temperature composite cured for 20 seconds\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.1588785046729%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e1.6\u0026plusmn;0.3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.641744548286605%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e3.3\u0026plusmn;0.5\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.838006230529595%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e4.93\u0026plusmn;0.4\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"44.6124763705104%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eG2 - Preheated composite cured for 20 seconds\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.251417769376182%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e1.2\u0026plusmn;0.2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.76937618147448%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e1.4\u0026plusmn;0.3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.366729678638942%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.9\u0026plusmn;0.2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"44.6124763705104%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eG3 - Preheated composite cured for 5 seconds\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.251417769376182%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e1.2\u0026plusmn;0.2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.76937618147448%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.7\u0026plusmn;0.3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.366729678638942%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.4\u0026plusmn;0.2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"54.361370716510905%\" colspan=\"2\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eP VALUE \u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.1588785046729%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.03*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.641744548286605%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.0001*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.838006230529595%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.0001*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"17.601246105919003%\" rowspan=\"3\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eP VALUE [ TUKEY\u0026rsquo;S HSD TEST]\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"36.7601246105919%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eG1 vs G2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.1588785046729%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.04*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.641744548286605%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.0001*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.838006230529595%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.0001*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"44.6124763705104%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eG1 vs G3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.251417769376182%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.04*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.76937618147448%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.0001*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.366729678638942%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.0001*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"44.6124763705104%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eG2 vs G3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.251417769376182%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.99\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.76937618147448%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.03*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.366729678638942%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.03*\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Preheated Composites minimize the size and occurrence of Internal Voids\u003c/h2\u003e \u003cp\u003eWe then investigated nano CT axial slices from each sample to ascertain the frequency and volume of voids in the bulk fill composite restoration within each experimental group. The results obtained provided 3D representations in axial sections, revealing areas of radiolucency, representing voids within bulk fill composite filling material. These voids were highlighted within red circles for all three groups [Figure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA]. Group 1 exhibited larger radiolucent areas within the filling material, as highlighted in the red circle, while minimal to no radiolucency was observed in Groups 2 and 3. Quantitative evaluation of void frequency and void volume is presented and summarized in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA, B and C, respectively. Group 1 displayed a higher number of voids per sample compared to Groups 2 and 3, although this difference did not reach statistical significance between any of the groups. However, the void volume in group 1 was greater [14.3] compared to group 2 [4.1] and group 3 [3.9]. This mean difference was significantly different between group 1 and 2, and group 1 and 3, but was not significant between group 2 and 3. In conclusion, the data suggest that Groups 2 and 3, with preheated composite cured for 20 and 5 seconds, respectively, exhibited a minimal number and size of voids within the bulk fill composite filling material.\u003c/p\u003e \u003cp\u003e \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\u003eMean void volume values (%) based on composite temperature and exposure duration (*P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 indicates statistical significance).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMEAN\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSD\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u003cb\u003eVOID\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eVOLUME\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eG1 - Room temperature composite cured for 20 seconds.\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e14.3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e0.2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eG2 - Preheated composite cured for 20 seconds.\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e4.1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e0.3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eG3 - Preheated composite cured for 5 seconds.\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e3.9\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e0.2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u003cb\u003eP VALUE \u0026nbsp;[ TUKEY\u0026rsquo;S HSD TEST]\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eG1 vs G2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.0001*\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eG1 vs G3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.0001*\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eG2 vs G3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.40\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \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\u003eMean void frequency based on composite temperature and exposure duration. (*P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 indicates statistical significance)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMEAN\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSD\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u003cb\u003eVOID\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eFREQUENCY\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eG1 - Room temperature composite cured for 20 seconds.\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e4\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eG2 - Preheated composite cured for 20 seconds.\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eG3 - Preheated composite cured for 5 seconds.\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u003cb\u003eP VALUE [ TUKEY\u0026rsquo;S HSD TEST]\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eG1 vs G2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.10\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eG1 vs G3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.10\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eG2 vs G3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e\u003cb\u003e0.99\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThe results obtained from this study led to the rejection of the primary null hypothesis suggesting that photo curing time may not influence polymerization-induced shrinkage forces and consequently would not result in differences in internal adaptation with a short 5-second duration of light exposure. Specifically, Group 3, comprising preheated composite with a 5-second photo curing time, demonstrated superior internal adaptation compared to the other groups. However, the one objective of the secondary null hypothesis proposing no difference in the occurrence of voids among preheated groups was accepted. This conclusion was drawn as there was no statistically significant variance observed in the incidence of voids between preheated resin composites Group 2 and Group 3 [Tables\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e]. However, the secondary objective of the same null hypothesis, suggesting no difference in the volume of voids among preheated groups, was refuted. This was evidenced by the observation that preheated composites [Groups 2 and 3] exhibited a significant disparity compared to the room temperature composites [Group 1].\u003c/p\u003e \u003cp\u003eSeveral researchers have proposed diverse strategies to mitigate the shrinkage stresses arising from high conversion rates [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Elhejazi et al advocated a 15 second delay after introducing preheated composite resin into the cavity before initiating photo curing [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. They posited that this delay would still provide adequate viscosity to the preheated composite to effectively wet the cavity preparation walls, thereby ensuring marginal adaptation. Daronch et al recommended reducing the photo curing duration, contending that fewer radicals are generated due to the shortened exposure time. Consequently, this reduction leads to improved resin composite adaptation and reduced gap formation at the tooth-restoration interface [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. In the present study, Group 3, consisting of preheated composite with a 5-second photo curing time, exhibited superior internal adaptation compared to both the 20-second photo curing time of preheated composite and the 20-second cure of room temperature composite. This finding aligns with a study conducted by Fernanda C Calheiros et al who employed a 5 second photo curing time on composite preheated to 40\u0026deg;C or 60\u0026deg;C. They reported a reduction in final stress compared to a 20-second photo curing time, along with similar or higher degrees of conversion achieved isothermally at 40\u0026deg;C or 60\u0026deg;C with a 5-second exposure compared to 20 seconds at room temperature [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The decreased polymerization time diminishes the accumulation of polymerization stresses, allowing for better resin composite adaptation, as evidenced in our study with Group 3, the preheated group with a 5-second photo curing duration. The difference in polymerization shrinkage values at different depths of the cavity can also be appreciated from the values in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e which can be explained by the influence of proximity of the light curing unit to the resin. Our results demonstrated that polymerization shrinkage at the gingival pulpal floor interface surpasses that at the pulpal floor, attributable to the difference in the rate of polymerization and conversion to gel phase, which occurs more rapidly closer to the top of the restoration \u003csup\u003e[24,25]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eRegarding void formation, existing literature suggests that \"voids\" represent a multifactorial phenomenon[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] influenced by various factors, including placement technique and polymerization of the material. Some studies indicate that voids are more prevalent in bulk fill technique as compared to layering technique; and that there is a higher incidence of void occurrence when layering thicker increments of material as opposed to smaller increments. This phenomenon is attributed to the ease of adaptation and increased potential for void elimination when using smaller increments of resin composites [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. In the current study, presence of voids in the composite restoration was assessed through two dimensional axial slices to determine their presence and overall volume within the restoration. Subsequent, three-dimensional evaluation of these voids, based on their location in the two-dimensional axial nano CT slices, revealed that the room temperature cured composites [Group 1] exhibited the highest number and significantly greater volume of voids compared to preheated composite [Groups 2 and 3], which underwent photo curing for 20 seconds and 5 seconds, respectively. This observation can be elucidated by the enhanced flow characteristics of resin composite when heated to 68\u0026deg;C, promoting homogenous distribution within the prepared cavity. Interestingly, the duration of photo curing in the preheated groups, whether for 5 seconds or 20 seconds, did not appear to significantly affect the incidence or volume of voids, as no notable difference was observed between the two preheated groups. Furthermore, the most common location for voids within the composite restorations was noted to be at the interface between the axial wall and pulpal floor across all groups. This occurrence may be attributed to cavity geometry, wherein sharp line angles present challenges for intimate adaptation of composite resin. It is suggested that the presence of rounded internal line angles may facilitate optimal adaptation of resin to the interface, thus aiding in the distribution of shrinkage stress [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSeveral researchers have indicated that bulk placement techniques yield fewer voids compared to layering methods [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Moreover, they have found that preheated composites exhibit significantly higher void volume compared to room temperature composites. However, these studies were performed with conventional composite warmers and they attribute the decrease in temperature and curing to the heightened incidence of voids in the composite resin. They posit that rapid temperature decrease and early vitrification, which restricts molecular mobility, hinder the diffusion of air bubbles, leading to their entrapment within the material and subsequent void formation [ 33]. In our study, there was no significant disparity in the incidence and volume of voids between the 5 and 20-second photo curing durations in the preheated composite groups. However, a higher incidence of voids was noted in the room temperature composite group without preheating. This discrepancy may be attributed to the application of preheated composite using Compex HD [AdDent Inc., Danbury CT, USA], which facilitates the direct dispensing of material into the preparation, thereby reducing time for dissipation of the temperature of the heated composite. Consequently, this process lowers the viscosity of the resin composite and promotes uniform flow, facilitating proper adaptation at the tooth-restoration interface and reducing the presence of voids in the restoration, as observed in our study. This decrease in viscosity and enhancement of wetting properties in the resin composite due to heat may mitigate gap formation in composite resin restorations.\u003c/p\u003e \u003cp\u003eMicro CT has been widely employed for investigating and characterizing internal structures, polymerization shrinkage, and adhesion failure in dental restorative composites [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. In our study, nano CT was utilized to assess the internal adaptation of resin composites due to its technological advancement over Micro CT, offering superior spatial resolution of up to 450 nm, surpassing the typical resolution of Micro CT systems [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. A recent study by Haugen et al. demonstrated that nano CT could detect micro porosity in composite filling materials that were not observable in Micro CT or SEM analyses, suggesting its utility in identifying the detrimental effects of dental composites [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Therefore, nano CT proves to be a versatile tool for evaluating the adaptation of restorative materials to the tooth and estimating the presence of voids in 3D volumes [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe present study is subject to several limitations that warrant acknowledgment. For Instance, only one single brand of composite was utilized, potentially leading to variations in results when compared with other brands featuring different filler compositions. Enhancing the assessment of the degree of conversion of the composite groups using Fourier-transform infrared spectroscopy [FTIR], Differential thermal analysis [DTA] or Infrared spectroscopy would have reinforced the findings of our study. Moreover, to augment the clinical relevance of our findings, particularly concerning gap measurements at the tooth-restoration interface, further validation via high-resolution scanning electron microscopy would have been advantageous. Additionally, the results of our study, especially gap measurements at the tooth-restoration interface, would have higher clinical correlation impact, if the results were further confirmed using high resolution scanning electron microscopy. Regrettably, this avenue was not explored within the scope of our study, constituting another limitation. Despite the positive outcomes observed, the necessity for additional preclinical studies with larger sample sizes is imperative to establish a more definitive clinical correlation with the results obtained in our study.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eIn conclusion, the investigation into the influence of preheating resin composites, as examined through Nano CT assessment on voids, internal adaptation, and post-gel shrinkage strain, yields valuable insights into the optimization of dental restoration procedures. Given the limitations of our study, it is clear that preheating bulk fill composites to 68\u0026deg;C and applying a 5-second light curing regimen composites can significantly impact the overall quality of dental restorations by minimizing void formation, enhancing internal adaptation to tooth structure, and reducing post-gel shrinkage strain. These findings underscore the importance of temperature management in the manipulation of resin composites during dental procedures. By understanding and leveraging the effects of preheating, clinicians can advance towards achieving superior clinical outcomes, ultimately contributing to the enhancement of patient care and satisfaction in the field of restorative dentistry. Further research and refinement of techniques in this area promise to continue elevating the standards of dental practice, ensuring the delivery of optimal and durable restorations for patients worldwide.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval statement and Consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eThis study was approved by the Institutional Ethics Committee (IEC), Kempegowda Institute of Medical Sciences (KIMS), Bangalore, India\u0026nbsp;under the registration number: KIMS/IEC/D121/D/2021. The informed consent to participate in the study was obtained from all subjects and/or their legal guardian(s).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to publish\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors receive no funding from their institutes.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConceptualization: S.R., D.M.; Data curation: S.R., D.M., M.R.S, A.G.; Formal analysis: D.M., N.M., V.S.; Investigation: S.S.; Methodology: R.A., D.M.; Project administration: N.M., D.M.; Resources: D.M., N.M.,V.S.; Software: S.R.; Supervision: D.M., N.M.; Validation: V.S.; Visualization: S.R., S.M., M.A.S; Writing - original draft: S.S.; Writing - review \u0026amp; editing: R.A., D.M., V.S.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col start=\"1\" type=\"1\"\u003e\n\u003cli\u003eBoaro LC, Lopes DP, de Souza AS, Nakano EL, Perez MD, Pfeifer CS, Gon\u0026ccedil;alves F. 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Journal of Esthetic and Restorative Dentistry. 2006 Nov;18[6]:340-50.\u003c/li\u003e\n\u003cli\u003eDaronch M, Rueggeberg FA, De Goes MF, Giudici R. Polymerization kinetics of pre-heated composite. Journal of Dental Research. 2006 Jan;85[1]:38-43.\u003c/li\u003e\n\u003cli\u003eMarc Geissberger, The next generation of composite warming technology. Dental Products report. 2002 July; Volume 56, Issue 7. Pg 48-49. \u003c/li\u003e\n\u003cli\u003eCorreia AM, Andrade MR, Tribst JP, Borges AL, Caneppele TM. Influence of bulk-fill restoration on polymerization shrinkage stress and marginal gap formation in class V restorations. Operative Dentistry. 2020 Jul 1;45[4]:E207-16.\u003c/li\u003e\n\u003cli\u003eHaugen HJ, Qasim SB, Matinlinna JP, Vallittu P, Nogueira LP. Nano-CT as a tool for characterization of dental resin composites. Scientific reports. 2020 Sep 23;10[1]:15520.\u003c/li\u003e\n\u003cli\u003eZeiger DN, Sun J, Schumacher GE, Lin-Gibson S. Evaluation of dental composite shrinkage and leakage in extracted teeth using X-ray microcomputed tomography. Dental Materials. 2009 Oct 1;25[10]:1213-20.\u003c/li\u003e\n\u003cli\u003eDemirel G, Baltacıoğlu İH, Kolsuz ME, Ocak M, Orhan K. Micro‐computed tomography evaluation of internal void formation of bulk‐fill resin composites in Class II restorations. Polymer Composites. 2019 Aug;40[8]:2984-92.\u003c/li\u003e\n\u003cli\u003eElhejazi AA. The effects of temperature and light intensity on the polymerization shrinkage of light-cured composite filling materials. J Contemp Dent Pract. 2006 Jul 1;7[3]:12-21.\u003c/li\u003e\n\u003cli\u003eCalheiros FC, Daronch M, Rueggeberg FA, Braga RR. Effect of temperature on composite polymerization stress and degree of conversion. Dental Materials. 2014 Jun 1;30[6]:613-8.\u003c/li\u003e\n\u003cli\u003eLangalia A, Buch A, Khamar M, Patel P. Polymerization shrinkage of composite resins: a review. J Med Dent Sci Res. 2015 Oct;2[10]:23-7.\u003c/li\u003e\n\u003cli\u003eTaub\u0026ouml;ck TT, Tarle Z, Marovic D, Attin T. Pre-heating of high-viscosity bulk-fill resin composites: effects on shrinkage force and monomer conversion. Journal of dentistry. 2015 Nov 1;43[11]:1358-64.\u003c/li\u003e\n\u003cli\u003eRibeiro MT, de Bragan\u0026ccedil;a GF, Oliveira LR, Braga SS, de Oliveira HL, Price RB, Soares CJ. Effect of preheating methods and devices on the mechanical properties, post-gel shrinkage, and shrinkage stress of bulk-fill materials. Journal of the Mechanical Behavior of Biomedical Materials. 2023 Feb 1;138:105605.\u003c/li\u003e\n\u003cli\u003eLoguercio AD, Reis A, Schroeder M, Balducci I, Versluis A, Ballester RY. Polymerization shrinkage: effects of boundary conditions and filling technique of resin composite restorations. Journal of dentistry. 2004 Aug 1;32[6]:459-70.\u003c/li\u003e\n\u003cli\u003eKinomoto Y, Torii M. Photoelastic analysis of polymerization contraction stresses in resin composite restorations. Journal of dentistry. 1998 Mar 1;26[2]:165-71\u003c/li\u003e\n\u003cli\u003eKim YS, Baek SH, Kim RJ. Effect of vibration during bulk and incremental filling on adaptation of a bulk-fill composite resin. Scientific reports. 2022 Dec 15;12[1]:21652.\u003c/li\u003e\n\u003cli\u003eMalhotra, N.; Kundabala, M.; Shashirashmi, A. Strategies to overcome polymerization shrinkage\u0026ndash;materials and techniques. A review. Dent. Update 2010, 37, 115\u0026ndash;125. \u003c/li\u003e\n\u003cli\u003eRees, J.S.; Jagger, D.C.; Williams, D.R.; Brown, G.; Duguid, W. A reappraisal of the incremental packing technique for light cured composite resins. J. Oral Rehabil. 2004, 31, 81\u0026ndash;84.\u003c/li\u003e\n\u003cli\u003eMoore, B.K.; Platt, J.A.; Borges, G.; Chu, T.M.G.; Katsilieri, I. Depth of cure of dental resin composites: ISO 4049 depth and microhardness of types of materials and shades. Oper. Dent. 2008, 33, 408\u0026ndash;412. \u003c/li\u003e\n\u003cli\u003ePark, J.; Chang, J.; Ferracane, J.; Lee, I.B. How should composite be layered to reduce shrinkage stress: Incremental or bulk filling? Dent. Mater. 2008, 24, 1501\u0026ndash;1505.\u003c/li\u003e\n\u003cli\u003eFronza, B.M.; Rueggeberg, F.A.; Braga, R.R.; Mogilevych, B.; Soares, L.E.S.; Martin, A.A.; Ambrosano, G.; Giannini, M. Monomer conversion, microhardness, internal marginal adaptation, and shrinkage stress of bulk-fill resin composites. Dent. Mater. 2015, 31, 1542\u0026ndash;1551.\u003c/li\u003e\n\u003cli\u003eEl-Safty, S.; Akhtar, R.; Silikas, N.; Watts, D.C. Nanomechanical properties of dental resin-composites. Dent. Mater. 2012, 28, 1292\u0026ndash;1300.\u003c/li\u003e\n\u003cli\u003eBuelvas DD, Besegato JF, Vicentin BL, Jussiani EI, Hoeppner MG, Andrello AC, Di Mauro E. Impact of light-cure protocols on the porosity and shrinkage of commercial bulk fill dental resin composites with different flowability. 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Restorative Dentistry \u0026amp; Endodontics. 2016 Aug 1;41[3]:236-8.\u003c/li\u003e\n\u003cli\u003eAljdaimi A, Devlin H, Dickinson M, Burnett T, Slater TJ. Micron-scale crack propagation in laser-irradiated enamel and dentine studied with nano-CT. Clinical oral investigations. 2019 May 1;23:2279-85.\u003c/li\u003e\n\u003cli\u003eSakai T, Li H, Abe T, Yamaguchi S, Imazato S. Multi-scale analysis of the influence of filler shapes on the mechanical performance of resin composites using high resolution nano-CT images. Dental Materials. 2021 Jan 1;37[1]:168-74.\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":"Preheating composites, Bulk-fill composite, Composite warmers, Polymerization shrinkage, Nano CT","lastPublishedDoi":"10.21203/rs.3.rs-4186892/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4186892/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eResin-based composites stand as widely employed restorative materials in the field of dentistry, owing to their superior esthetic and physicochemical properties. Nevertheless, a notable limitation of these composites is the occurrence of polymerization shrinkage, leading to stress at the interface of tooth restoration. Over time, this phenomenon may result in marginal leakage and secondary caries, thereby causing restoration failure.\u003c/p\u003e\u003ch2\u003eObjectives\u003c/h2\u003e \u003cp\u003eOur study aimed to conduct a comparative evaluation of voids, internal adaptation, and polymerization shrinkage in Class II preheated composite restorations [5 seconds vs. 20 seconds] and composites at room temperature [20 seconds], utilizing Nano CT analysis.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eCylindrical Class II cavities were prepared on both mesial and distal sides of Fifteen freshly extracted human maxillary premolar teeth. The specimens were then randomly allocated into three groups and restored as follows: Group 1 [Filtek Supreme XT at room temperature, photocured for 20 seconds], Group 2 [Filtek Supreme XT composite preheated to 68\u0026deg;C in Compex HD, photocured for 20 seconds], and Group 3 [Filtek Supreme XT composite preheated to 68\u0026deg;C in Compex HD, photocured for 5 seconds]. Nano CT was employed for the qualitative assessment of the samples. Statistical analysis involved the Shapiro-Wilkins test, ONE WAY ANOVA test, followed by Tukey\u0026rsquo;s HSD Post hoc analysis.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eSignificantly improved outcomes were observed in preheated composite groups, irrespective of the photo curing time, when compared to the room temperature composite group in terms of polymerization shrinkage. The room temperature composite group exhibited the highest void volume and frequency among the investigated groups.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eWithin the constraints of the study, it can be deduced that preheating at 68\u0026deg;C and light curing for 5 seconds enhance internal adaptation and reduce the incidence of voids in composite restoration. Clinicians should be informed about clinical techniques that mitigate shrinkage stress to improve the durability of composite restorations. Clinicians should be informed about clinical techniques that mitigate shrinkage stress to improve the longevity of composite restorations.\u003c/p\u003e","manuscriptTitle":"Influence of Preheating Resin Composites: A Nano CT assessment on Voids, Internal Adaptation and Post-Gel Shrinkage Strain","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-04 11:12:31","doi":"10.21203/rs.3.rs-4186892/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":"a59b29ce-add2-4441-865a-03f52eaf51a1","owner":[],"postedDate":"April 4th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-10-01T08:24:11+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-04 11:12:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4186892","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4186892","identity":"rs-4186892","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}