Comparative evaluation of two techniques for assessing internal fit of fixed dental prostheses: A randomized controlled in-vitro study

Comparative evaluation of two techniques for assessing internal fit of fixed dental prostheses: A randomized controlled in-vitro study | 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 Comparative evaluation of two techniques for assessing internal fit of fixed dental prostheses: A randomized controlled in-vitro study Khaled Jamal Alhakim, Joul Kassis, Eyad Swed This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9222477/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Objective To compare the internal fit of fixed dental prostheses using the cement replica technique and the sectioning after cementation technique assessed with an optical microscope under standardized conditions. Materials and Methods Thirty metal copings were produced on gypsum dies, which were created from impressions taken of a machined copper master abutment. Die spacer (Pico-Fit) was applied (axial and occlusal surfaces except apical 1 mm). Internal gap was first measured via cement replica technique. Subsequently, crowns were cemented with glass ionomer, sectioned, and internal gap measured under BX41 Olympus optical microscope at ×100 magnification at seven predefined sites. A paired t-tests assessed differences between the two measurement techniques utilized at (α = 0.05). Results The sectioning after cementation technique produced significantly larger internal gap measurements than the cement replica technique across all measurement sites (p < 0.05). Conclusion In this in vitro model, measurements obtained post-cementation and sectioning were more clinically representative and reliable. The internal gap values obtained from both assessment techniques were within the clinically acceptable range. internal fit die spacer optical microscopy cement replica technique fixed restorations Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The internal fit of a fixed dental restoration is a critical determinant of its clinical performance and longevity. While a perfect internal adaptation may seem ideal, in reality, a minimal, controlled gap is necessary to accommodate the luting cement, allowing proper seating, load distribution, and marginal integrity [1]. Inadequate internal adaptation can hinder excess cement escape, induce hydraulic pressure during placement [2], and compromise both marginal and internal adaptation, leading to clinical complications such as marginal gaps, occlusal discrepancies, and patient discomfort [3]. Internal fit is typically defined as the perpendicular distance from the inner surface of the restoration to the axial wall of the prepared tooth [4]. Accurate measurement of this internal gap is fundamental in evaluating the quality of the restoration, selecting fabrication techniques, and predicting long-term performance [5,6]. Several methods have been developed to assess internal adaptation, including direct visualization [7], radiographic analysis [8], profilometry [9], and silicone-based replica techniques. Among these, the cement replica technique utilising low-viscosity silicone has been widely adopted for its simplicity and non-destructive nature [10]. Alternatively, sectioning and direct examination under an optical microscope provide a more realistic simulation of clinical cementation but are more invasive [11]. This study thus designed to compare the cement replica technique with the sectioning after cementation technique in evaluating internal fit, under standardized laboratory conditions. Null hypothesis: There is no statistically significant difference in the internal fit of fixed dental restorations when measured using the cement replica technique versus the sectioning after cementation technique under standardized laboratory conditions. Materials and Methods Fabrication of master abutment: Two standardized copper dies, mimicking full crown preparations, were fabricated using an industrial CNC lathe (Model XYZ, Haas Automation Inc., USA) to replicate a maxillary first premolar prepared for a full coverage crown. Each die featured an axial wall height of 6 mm, a total occlusal convergence of 20°, and a radial shoulder finish line. A spherical notch was created on the finish line to control crown positioning and prevent rotation using a spherical diamond bur (FG 801, Komet Dental, Germany). (Fig. 1 A) Die and Crown Fabrication: Fifteen impressions of the copper dies were made using a two-step putty-wash technique with addition silicone material (Virtual XD, Ivoclar Vivadent, Liechtenstein). (Fig. 1 B) After setting, impressions were poured with Type IV dental stone (Fujirock EP, GC, Japan), producing 30 identical working dies. Then, two coats of die spacer (Pico Fit, Renfert, Hilzingen, Germany) were applied on each die using a fine brush, leaving an uncoated 1 mm band at the apical margin to ensure optimal marginal adaptation. Each coat was allowed to dry for approximately 5 minutes before the subsequent application. According to the manufacturer’s specifications, the two coats produced a uniform cement space of approximately 25–30 µm. (Fig. 1 C) After that, a Wax patterns were meticulously fabricated on the prepared gypsum dies using inlay casting wax (e.g., Inlay Wax, Kerr Corporation, Orange, CA, USA). The patterns were then sprued, invested in a phosphate-bonded investment material (e.g., Bellavest SH, BEGO, Bremen, Germany), and cast into base metal alloy copings (e.g., Ni-Cr alloy, Wiron 99, BEGO, Bremen, Germany) using the conventional lost-wax casting technique. After casting, the resulted 30 metal copings were divested, sandblasted with 50 µm aluminum oxide particles, and finished using standard laboratory rotary instruments to ensure uniform margins before subsequent evaluation. (Fig. 1 D) Cement Replica Technique: A low-viscosity blue addition silicone material (Virtual XD, Ivoclar Vivadent, Liechtenstein) was injected into the internal surface of the metal coping, which was then seated onto its corresponding copper die with finger pressure until set. Finger pressure was applied during seating in the replica procedure by an independent dental practitioner to simulate the clinical conditions of crown placement. This approach ensures uniform seating of the restoration, promotes even distribution of the impression or luting material, and prevents distortion or artificial reduction of the marginal gap that might occur with excessive or non-standardized forces [12,13]. A high-viscosity putty silicone (Virtual XD) was subsequently applied over the coping for stabilization and ease of handling. Once set, the coping and silicone block were removed, leaving a thin blue silicone layer adhered internally. (Fig. 2 A) A low-viscosity pink addition silicone material (Virtual XD) was then injected into the coping to support and bond with the blue layer, forming a unified silicone replica. After setting, the replica was removed, comprising a pink support structure with an internal blue layer representing the cement space. (Fig. 2 B)(Fig. 2 C) The replicas were carefully sectioned through their central axis using a sterile No. 11 surgical blade. The cutting was performed by a different independent dental technician with steady, controlled motions to obtain a flat and even cross-sectional surface, ensuring that the section passed precisely through the midpoint of the replica. To maintain accuracy and minimize deformation during cutting, the replicas were securely stabilized on a custom-made holder. (Fig. 2 D), then mounted onto putty silicone bases for internal gap evaluation under a light microscope (Olympus BX41, Japan). (Fig. 4 )(Fig. 5 ) Sectioning after cementation technique: The same 30 metal copings were cemented onto dies but this time (without spacer) using glass ionomer cement (GC Fuji plus, Japan) mixed per manufacturer instructions. After complete setting, each specimen was carefully positioned and marked to ensure that the longitudinal section would pass precisely through the midline of both the die and the coping. Sectioning was performed by an independent dental technician using a low-speed diamond saw (Isomet, Buehler Ltd., Lake Bluff, IL, USA) under continuous water cooling to prevent overheating and structural alteration [14–16]. Internal gaps for all specimens were measured under a BX41 Olympus light microscope (100× magnification) (Fig. 6 ) at identical seven spots (Fig. 3 ): mid buccal shoulder, mid buccal wall, buccal-occlusal angle, occlusal center, lingual-occlusal angle, mid lingual wall, mid lingual shoulder. Multiple measures per spot were averaged. Sample size calculation and statistical Analysis: The sample size was determined using G*Power software (v3.1.9.7) based on an assumed effect size of 0.45, a significance level of α = 0.05, and a study power of 80%. This calculation indicated that a minimum of 30 specimens was required for the study. Statistical analyses were conducted using SPSS v23 (IBM Corp.), with a significance level of α = 0.05 for all analyses. A Paired t-tests were performed to assess differences between the two measurement techniques utilised. Results The research sample consisted of 30 metal copings made on 30 gypsum models. Initially, the internal adaptation of the copings was measured using the cement replica technique. Then, the metal copings were bonded to gypsum models without the die spacer material, cut, and the internal adaptation was measured using a light microscope. A paired t-test was employed to determine whether there are significant differences between the means. (Table 1 ) shows the mean, standard deviation, and standard error of the internal gap for the studied samples according to the measurement location and the technique used in measuring the internal adaptation (cement replica and sectioning after cementation) techniques. Table 1 Illustrating the mean, standard deviation, and standard error of the internal gap (in microns) within the study sample, categorised by the measurement site and the technique employed for assessing internal fit. Mean N Std. Deviation Std. Error Mean Pair 1 Cement buccal 1 29.1000 10 5.42525 1.71561 Replica buccal 1 15.0000 10 2.00000 .63246 Pair 2 Cement buccal 2 31.5000 10 7.45729 2.35820 Replica buccal 2 5.1000 10 1.28668 .40689 Pair 3 Cement buccal 3 41.4000 10 7.86271 2.48641 Replica buccal 3 27.1000 10 2.07900 .65744 Pair 4 Cement occlusal 4 57.3000 10 5.35516 1.69345 Replica occlusal 4 31.0000 10 3.52767 1.11555 Pair 5 Cement lingual 5 37.1000 10 5.85852 1.85263 Replica lingual 5 28.2000 10 1.81353 .57349 Pair 6 Cement lingual 6 32.2000 10 7.26942 2.29879 Replica lingual 6 5.0000 10 .81650 .25820 Pair 7 Cement lingual 7 27.7000 10 7.61650 2.40855 Replica lingual 7 15.3000 10 1.56702 .49554 (Table 2 ) shows that the significance level is much lower than 0.05 for the difference between the means of both techniques (cement replica and sectioning after cementation) at each of the studied measurement sites (mid vestibular ridge, mid vestibular surface, vestibular occlusal line angle, mid occlusal surface, lingual occlusal line angle, mid lingual surface, mid lingual ridge). Table 2 Illustrating the outcomes of the Paired t-test for the mean differences between the two techniques (sectioning after cementation and cement replica) for each measurement point checked. Paired samples test Paired differences 95% confidence interval of the difference t df Sig. (2-tailed) Upper Pair 1 Cement buccal 1 – replica Buccal 1 18.7929 6.890 9 .000 Pair 2 Cement buccal 2 – replica Buccal 2 31.64812 11.379 9 .000 Pair 3 Cement buccal 3 – replica Buccal 3 19.92313 5.753 9 .000 Pair 4 Cement occlusal 4 – replica occlusal 4 31.32507 11.840 9 .000 Pair 5 Cement lingual 5 – replica lingual 5 13.82680 4.086 9 .003 Pair 6 Cement lingual 6 – replica lingual 6 32.50844 11.591 9 .000 Pair 7 Cement lingual 7 – replica lingual 7 18.13477 4.891 9 .001 This means that at a 95% confidence level, there are statistically significant differences in the mean internal gap (in microns) between the two techniques used to measure internal adaptation at each of the seven studied measurement sites. Internal gap values measured via sectioning after cementation technique were consistently higher than those obtained via the cement replica technique at all seven sites (p < 0.05). Detailed descriptive statistics (mean ± SD, standard error) and P-values for each site are provided in Tables 1 and 2 . Discussion Two techniques for measuring internal adaptation were studied, as the techniques used for measuring internal adaptation are limited: the cement replica and the sectioning after cementation techniques. Since these two techniques use materials with different physical properties, they are expected to behave differently under pressure. Therefore, the aim of the research was to compare these two techniques in measuring the internal adaptation of fixed restorations to determine the better technique for measuring internal adaptation. Various methods have been used to secure an internal distance for the cement, but the manual application of two layers of the separating material (pico-fit) prior to making the wax model is considered the most common and effective [17]. The metal copings were manufactured on plaster casts replicated from a copper master abutment made using an industrial lathe, with the aim of standardizing the length of the abutment, the shoulder width, and accurately adjusting the wall inclination to neutralize its effect on the research results [18,19]. Seven points were chosen to study the internal fit: two points at the midpoint of the preparation margins, two points at the midpoint of the axial walls, two points at the occlusal linear angles, and one point at the midpoint of the occlusal surface. These points are almost similar to those used by Lovgren in measuring the internal fit [20]. In the present study, internal fit measurements were performed using an optical light microscope equipped with a calibrated eyepiece micrometer (accuracy: 10 µm) at 10× magnification. Previous investigations have demonstrated that light microscopy provides measurement accuracy comparable to that of scanning electron microscopy (SEM) for evaluating crown fit, with no statistically significant differences between the two methods [21–23]. Given its reliability, lower operational complexity, and non-destructive nature, the light microscope was deemed appropriate for assessing both fabrication techniques in this study. In this study, the cement replica technique was used to assess restoration fit by measuring the thickness of a low-viscosity addition silicone layer as a surrogate for resin cement. This non-destructive, reproducible, and cost-effective method has shown measurement accuracy comparable to sectioning techniques after cementation, with no statistically significant differences in marginal or internal gaps [24]. Systematic reviews further support its validity, while noting limitations such as restricted cross-sectional analysis and possible distortion of thin silicone layers [25]. The value of the internal gap in the group where the sectioning after cementation technique was used to measure internal adaptation was significantly larger than in the group where the cement replica technique was used. This may be attributed to the difference in viscosity of both materials and the difference in the size of the atoms and molecules constituting each material. The cement used in luting has a higher viscosity and larger particle size, and thus its compressibility is lower than that of the additional soft silicone material used in the cement replica technique. Considering that the process of cementing restorations represents the clinical reality, the method of cementing crowns and then performing longitudinal sections and measuring the cement thickness with an optical microscope is the most accurate and reliable method for measuring internal adaptation. This differs from the study by Rahme and colleagues in 2008 [26], where they found that the cement replica technique is more accurate and reliable. The reason for the difference may be attributed to the type of crowns and abutments used. In Rahme's study, Procera crowns were used, and the abutments had an anatomical shape. In our study, however, the crowns were metal, and the abutments used were cylindrical with closely spaced walls and free of anatomical details. Lovgren and his colleagues [20] studied internal adaptation in 2017 using the cement matching technique for metal crowns made by three different methods. They found that metal crowns made using the lost wax technique had a larger internal gap than those made using the CAD/CAM and the laser sintering techniques. They attributed this to the fact that the lost wax technique undergoes several procedures, and each procedure can be subject to various errors, which ultimately affect the internal adaptation. The internal gap value in Lovgren's study was also significantly larger than the internal gap value in our study. This may be attributed to the fact that the abutment used in Lovgren's study had a wall inclination of 12 degrees, whereas in our study it was 20 degrees. This aligns with Fusayama's study [27], which found that increasing the preparation angle improves the fit of the restoration. The results of our study agreed with the study by Abduo and his colleagues in 2010 [28], where they assessed the fit of fixed restorations using the cement replica technique. They found that this method has its limitations and inherent errors, such as the difficulty in identifying the crown margins and finish lines, its susceptibility to tearing when removed from the crown, and the errors resulting from the trimming process, which ultimately lead to inaccurate measurements. Conclusions Within the limitation of this study we conclude that: Internal gap measurements depend significantly on the assessment technique. Sectioning and measuring cement thickness under optical microscopy yields higher and more clinically representative internal gap values. The internal gap values obtained from both assessment techniques were within the clinically acceptable range reported in the literature. Declarations Ethical approval: This study is an in vitro study, does not require ethical approval. Consent for publication: not available Competing interest: Authors declare no competing interests Acknowledgments: non Data availability: The data supporting the findings of this study are available from the corresponding author upon reasonable request. Funding: No funding was received for this study Author contributions (CRediT): JK and KA: The conception and design of the study, JK and KA: Acquisition of data, JK: Analysis and interpretation of data, KA: Drafting the article and revising it critically for important intellectual content. JK and KA: Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All authors gave their final approval and agreed to be accountable for all aspects of the work. References Kasloff Z. Casting techniques and some variables. The Journal of Prosthetic Dentistry 1961;11(3):533-36 . Pilo R, Cardash H, Baharav H, Helft M. 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Fit of titanium and a base metal alloy metal-ceramic crown. J Prosthet Dent 2000;83(3):314-8 . Lovgren N, Roxner R, Klemendz S, Larsson C. Effect of production method on surface roughness, marginal and internal fit, and retention of cobalt-chromium single crowns. J Prosthet Dent 2017;118(1):95-101 . Holmes JR, Bayne SC, Holland GA, Sulik WD. Considerations in measurement of marginal fit. The Journal of prosthetic dentistry. 1989;62(4):405-8. Groten M, Axmann D, Pröbster L, Weber H. Determination of the minimum number of marginal gap measurements required for practical in vitro testing. The Journal of prosthetic dentistry. 2000;83(1):40-9. Martins LM, Lorenzoni FC, Melo AOd, Silva LMd, Oliveira JLGd, Oliveira PCGd, et al. Internal fit of two all-ceramic systems and metal-ceramic crowns. Journal of Applied Oral Science. 2012;20:235-40. Kim D-Y, Kim E-B, Kim H-Y, Kim J-H, Kim W-C. Evaluation of marginal and internal gap of three-unit metal framework according to subtractive manufacturing and additive manufacturing of CAD/CAM systems. The journal of advanced prosthodontics. 2017;9(6):463 Di Fiore A, Zuccon A, Carraro F, Basilicata M, Bollero P, Bruno G, et al. Assessment methods for marginal and internal fit of partial crown restorations: a systematic review. Journal of Clinical Medicine. 2023;12(15):5048. Rahme HY, Tehini GE, Adib SM, Ardo AS, Rifai KT. In vitro evaluation of the "replica technique" in the measurement of the fit of Procera crowns. J Contemp Dent Pract 2008;9(2):25-32 . Fusayama T. Factors and technique of precision casting Part I. The Journal of Prosthetic Dentistry 1959;9(3):468-85 . Abduo J, Lyons K, Swain M. Fit of zirconia fixed partial denture: a systematic review. J Oral Rehabil 2010;37(11):866-76 . Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 10 May, 2026 Reviewers agreed at journal 10 May, 2026 Reviewers invited by journal 29 Apr, 2026 Editor invited by journal 10 Apr, 2026 Editor assigned by journal 26 Mar, 2026 Submission checks completed at journal 26 Mar, 2026 First submitted to journal 25 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9222477","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":632115854,"identity":"1a2d7d23-d953-4bf5-8ad2-e46072ce338e","order_by":0,"name":"Khaled Jamal Alhakim","email":"","orcid":"","institution":"Wadi International University (WIU)","correspondingAuthor":false,"prefix":"","firstName":"Khaled","middleName":"Jamal","lastName":"Alhakim","suffix":""},{"id":632115855,"identity":"faefd1f4-75d3-460d-b978-9574a00f783c","order_by":1,"name":"Joul Kassis","email":"data:image/png;base64,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","orcid":"","institution":"Damascus University","correspondingAuthor":true,"prefix":"","firstName":"Joul","middleName":"","lastName":"Kassis","suffix":""},{"id":632115856,"identity":"9afacd60-501f-4bc2-a2a1-e6ba03c11ca2","order_by":2,"name":"Eyad Swed","email":"","orcid":"","institution":"Damascus University","correspondingAuthor":false,"prefix":"","firstName":"Eyad","middleName":"","lastName":"Swed","suffix":""}],"badges":[],"createdAt":"2026-03-25 11:38:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9222477/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9222477/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108727233,"identity":"45e873e5-4813-4f9d-9268-ac03a52a4d96","added_by":"auto","created_at":"2026-05-07 17:26:46","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":695381,"visible":true,"origin":"","legend":"\u003cp\u003ethe process of die and crown fabrication\u003c/p\u003e\n\u003cp\u003eA. Copper dies\u003c/p\u003e\n\u003cp\u003eB. Impressions of the copper dies\u003c/p\u003e\n\u003cp\u003eC. Coating of die spacer the dies\u003c/p\u003e\n\u003cp\u003eD. Metal copings\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-9222477/v1/c3a50e2e853867fa3032e594.png"},{"id":108727234,"identity":"a4682746-2914-45b2-9dc5-917a7a57e430","added_by":"auto","created_at":"2026-05-07 17:26:46","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":683128,"visible":true,"origin":"","legend":"\u003cp\u003eCement Replica Technique\u003c/p\u003e\n\u003cp\u003eA. A blue silicone material into the internal surface of the metal coping\u003c/p\u003e\n\u003cp\u003eB. Injecting a pink silicone into the coping\u003c/p\u003e\n\u003cp\u003eC. A unified silicone replica\u003c/p\u003e\n\u003cp\u003eD. Replicas after being sectioned.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-9222477/v1/2bdc134d9d6d1547141a1d0c.png"},{"id":108727237,"identity":"67854e64-a7f1-4cff-9e33-9e4618fd0ddd","added_by":"auto","created_at":"2026-05-07 17:26:46","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":29494,"visible":true,"origin":"","legend":"\u003cp\u003eStudy spots\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-9222477/v1/5fb0b37dc8a0fbccb9e690d4.png"},{"id":108806997,"identity":"8b70b80b-4d36-4289-9878-dd9d90aced64","added_by":"auto","created_at":"2026-05-08 15:29:52","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":253877,"visible":true,"origin":"","legend":"\u003cp\u003eBX41 Olympus light optical microscope.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-9222477/v1/721a8f46841aea485cc3e2d7.png"},{"id":108727236,"identity":"94b863af-13e4-4d54-8a45-2e84b4fcf95c","added_by":"auto","created_at":"2026-05-07 17:26:46","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":564376,"visible":true,"origin":"","legend":"\u003cp\u003eAn illustration depicting the assessment of internal adaptation in the mid-occlusal surface area via the cement replica technique.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-9222477/v1/f440c4be18e1c3f92a252c9c.png"},{"id":108727238,"identity":"f2ca0199-3c7a-4727-b755-78faa2c8f541","added_by":"auto","created_at":"2026-05-07 17:26:47","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":338889,"visible":true,"origin":"","legend":"\u003cp\u003eAn illustration depicting the assessment of internal occlusion in the region of the linear occlusal vestibule angle utilising the light optical microscope .\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-9222477/v1/d380bfcc9d52d4b2e65b8b07.png"},{"id":108810182,"identity":"52199ff9-4935-46a1-a382-8a0413fa097d","added_by":"auto","created_at":"2026-05-08 15:57:48","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3767009,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9222477/v1/26b93cf2-76a1-4c35-9ac5-2068fbd1f645.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Comparative evaluation of two techniques for assessing internal fit of fixed dental prostheses: A randomized controlled in-vitro study","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe internal fit of a fixed dental restoration is a critical determinant of its clinical performance and longevity. While a perfect internal adaptation may seem ideal, in reality, a minimal, controlled gap is necessary to accommodate the luting cement, allowing proper seating, load distribution, and marginal integrity [1]. Inadequate internal adaptation can hinder excess cement escape, induce hydraulic pressure during placement [2], and compromise both marginal and internal adaptation, leading to clinical complications such as marginal gaps, occlusal discrepancies, and patient discomfort [3].\u003c/p\u003e \u003cp\u003eInternal fit is typically defined as the perpendicular distance from the inner surface of the restoration to the axial wall of the prepared tooth [4]. Accurate measurement of this internal gap is fundamental in evaluating the quality of the restoration, selecting fabrication techniques, and predicting long-term performance [5,6].\u003c/p\u003e \u003cp\u003eSeveral methods have been developed to assess internal adaptation, including direct visualization [7], radiographic analysis [8], profilometry [9], and silicone-based replica techniques. Among these, the cement replica technique utilising low-viscosity silicone has been widely adopted for its simplicity and non-destructive nature [10]. Alternatively, sectioning and direct examination under an optical microscope provide a more realistic simulation of clinical cementation but are more invasive [11].\u003c/p\u003e \u003cp\u003eThis study thus designed to compare the cement replica technique with the sectioning after cementation technique in evaluating internal fit, under standardized laboratory conditions.\u003c/p\u003e \u003cp\u003eNull hypothesis: There is no statistically significant difference in the internal fit of fixed dental restorations when measured using the cement replica technique versus the sectioning after cementation technique under standardized laboratory conditions.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eFabrication of master abutment:\u003c/h2\u003e \u003cp\u003eTwo standardized copper dies, mimicking full crown preparations, were fabricated using an industrial CNC lathe (Model XYZ, Haas Automation Inc., USA) to replicate a maxillary first premolar prepared for a full coverage crown. Each die featured an axial wall height of 6 mm, a total occlusal convergence of 20\u0026deg;, and a radial shoulder finish line. A spherical notch was created on the finish line to control crown positioning and prevent rotation using a spherical diamond bur (FG 801, Komet Dental, Germany). (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eDie and Crown Fabrication:\u003c/h3\u003e\n\u003cp\u003eFifteen impressions of the copper dies were made using a two-step putty-wash technique with addition silicone material (Virtual XD, Ivoclar Vivadent, Liechtenstein). (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB) After setting, impressions were poured with Type IV dental stone (Fujirock EP, GC, Japan), producing 30 identical working dies.\u003c/p\u003e \u003cp\u003eThen, two coats of die spacer (Pico Fit, Renfert, Hilzingen, Germany) were applied on each die using a fine brush, leaving an uncoated 1 mm band at the apical margin to ensure optimal marginal adaptation. Each coat was allowed to dry for approximately 5 minutes before the subsequent application. According to the manufacturer\u0026rsquo;s specifications, the two coats produced a uniform cement space of approximately 25\u0026ndash;30 \u0026micro;m. (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC) After that, a Wax patterns were meticulously fabricated on the prepared gypsum dies using inlay casting wax (e.g., Inlay Wax, Kerr Corporation, Orange, CA, USA). The patterns were then sprued, invested in a phosphate-bonded investment material (e.g., Bellavest SH, BEGO, Bremen, Germany), and cast into base metal alloy copings (e.g., Ni-Cr alloy, Wiron 99, BEGO, Bremen, Germany) using the conventional lost-wax casting technique. After casting, the resulted 30 metal copings were divested, sandblasted with 50 \u0026micro;m aluminum oxide particles, and finished using standard laboratory rotary instruments to ensure uniform margins before subsequent evaluation. (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eD)\u003c/p\u003e\n\u003ch3\u003eCement Replica Technique:\u003c/h3\u003e\n\u003cp\u003eA low-viscosity blue addition silicone material (Virtual XD, Ivoclar Vivadent, Liechtenstein) was injected into the internal surface of the metal coping, which was then seated onto its corresponding copper die with finger pressure until set. Finger pressure was applied during seating in the replica procedure by an independent dental practitioner to simulate the clinical conditions of crown placement. This approach ensures uniform seating of the restoration, promotes even distribution of the impression or luting material, and prevents distortion or artificial reduction of the marginal gap that might occur with excessive or non-standardized forces [12,13].\u003c/p\u003e \u003cp\u003eA high-viscosity putty silicone (Virtual XD) was subsequently applied over the coping for stabilization and ease of handling. Once set, the coping and silicone block were removed, leaving a thin blue silicone layer adhered internally. (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA low-viscosity pink addition silicone material (Virtual XD) was then injected into the coping to support and bond with the blue layer, forming a unified silicone replica. After setting, the replica was removed, comprising a pink support structure with an internal blue layer representing the cement space. (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB)(Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC)\u003c/p\u003e \u003cp\u003eThe replicas were carefully sectioned through their central axis using a sterile No. 11 surgical blade. The cutting was performed by a different independent dental technician with steady, controlled motions to obtain a flat and even cross-sectional surface, ensuring that the section passed precisely through the midpoint of the replica. To maintain accuracy and minimize deformation during cutting, the replicas were securely stabilized on a custom-made holder. (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD), then mounted onto putty silicone bases for internal gap evaluation under a light microscope (Olympus BX41, Japan). (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e)(Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eSectioning after cementation technique:\u003c/h3\u003e\n\u003cp\u003eThe same 30 metal copings were cemented onto dies but this time (without spacer) using glass ionomer cement (GC Fuji plus, Japan) mixed per manufacturer instructions. After complete setting, each specimen was carefully positioned and marked to ensure that the longitudinal section would pass precisely through the midline of both the die and the coping. Sectioning was performed by an independent dental technician using a low-speed diamond saw (Isomet, Buehler Ltd., Lake Bluff, IL, USA) under continuous water cooling to prevent overheating and structural alteration [14\u0026ndash;16].\u003c/p\u003e \u003cp\u003eInternal gaps for all specimens were measured under a BX41 Olympus light microscope (100\u0026times; magnification) (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) at identical seven spots (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003e): mid buccal shoulder, mid buccal wall, buccal-occlusal angle, occlusal center, lingual-occlusal angle, mid lingual wall, mid lingual shoulder. Multiple measures per spot were averaged.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eSample size calculation and statistical Analysis:\u003c/h3\u003e\n\u003cp\u003eThe sample size was determined using G*Power software (v3.1.9.7) based on an assumed effect size of 0.45, a significance level of \u003cem\u003eα\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.05, and a study power of 80%. This calculation indicated that a minimum of 30 specimens was required for the study.\u003c/p\u003e \u003cp\u003eStatistical analyses were conducted using SPSS v23 (IBM Corp.), with a significance level of \u003cem\u003eα\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.05 for all analyses. A Paired t-tests were performed to assess differences between the two measurement techniques utilised.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe research sample consisted of 30 metal copings made on 30 gypsum models. Initially, the internal adaptation of the copings was measured using the cement replica technique. Then, the metal copings were bonded to gypsum models without the die spacer material, cut, and the internal adaptation was measured using a light microscope.\u003c/p\u003e \u003cp\u003eA paired t-test was employed to determine whether there are significant differences between the means. (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) shows the mean, standard deviation, and standard error of the internal gap for the studied samples according to the measurement location and the technique used in measuring the internal adaptation (cement replica and sectioning after cementation) techniques.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eIllustrating the mean, standard deviation, and standard error of the internal gap (in microns) within the study sample, categorised by the measurement site and the technique employed for assessing internal fit.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMean\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eStd. Deviation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eStd. Error Mean\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePair 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement buccal 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29.1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.42525\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.71561\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReplica buccal 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15.0000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.00000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.63246\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePair 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement buccal 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31.5000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.45729\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.35820\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReplica buccal 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.28668\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.40689\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePair 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement buccal 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e41.4000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.86271\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.48641\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReplica buccal 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27.1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.07900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.65744\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePair 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement occlusal 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e57.3000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.35516\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.69345\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReplica occlusal 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31.0000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.52767\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.11555\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePair 5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement lingual 5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37.1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.85852\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.85263\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReplica lingual 5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28.2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.81353\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.57349\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePair 6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement lingual 6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32.2000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.26942\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.29879\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReplica lingual 6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.0000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e.81650\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.25820\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePair 7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement lingual 7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27.7000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.61650\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.40855\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eReplica lingual 7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15.3000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.56702\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.49554\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(Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) shows that the significance level is much lower than 0.05 for the difference between the means of both techniques (cement replica and sectioning after cementation) at each of the studied measurement sites (mid vestibular ridge, mid vestibular surface, vestibular occlusal line angle, mid occlusal surface, lingual occlusal line angle, mid lingual surface, mid lingual ridge).\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\u003eIllustrating the outcomes of the Paired t-test for the mean differences between the two techniques (sectioning after cementation and cement replica) for each measurement point checked.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003ePaired samples test\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" morerows=\"1\" nameend=\"c2\" namest=\"c1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePaired differences\u003c/p\u003e \u003cp\u003e95% confidence interval of the difference\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003et\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003edf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSig. (2-tailed)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUpper\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePair 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement buccal 1 \u0026ndash; replica Buccal 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18.7929\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.890\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePair 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement buccal 2 \u0026ndash; replica Buccal 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e31.64812\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11.379\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePair 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement buccal 3 \u0026ndash; replica Buccal 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e19.92313\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5.753\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePair 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement occlusal 4 \u0026ndash; replica occlusal 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e31.32507\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11.840\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePair 5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement lingual 5 \u0026ndash; replica lingual 5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e13.82680\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.086\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.003\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePair 6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement lingual 6 \u0026ndash; replica lingual 6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e32.50844\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11.591\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePair 7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement lingual 7 \u0026ndash; replica lingual 7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18.13477\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.891\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e.001\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\u003eThis means that at a 95% confidence level, there are statistically significant differences in the mean internal gap (in microns) between the two techniques used to measure internal adaptation at each of the seven studied measurement sites.\u003c/p\u003e \u003cp\u003eInternal gap values measured via sectioning after cementation technique were consistently higher than those obtained via the cement replica technique at all seven sites (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Detailed descriptive statistics (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD, standard error) and P-values for each site are provided in Tables\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eTwo techniques for measuring internal adaptation were studied, as the techniques used for measuring internal adaptation are limited: the cement replica and the sectioning after cementation techniques. Since these two techniques use materials with different physical properties, they are expected to behave differently under pressure. Therefore, the aim of the research was to compare these two techniques in measuring the internal adaptation of fixed restorations to determine the better technique for measuring internal adaptation.\u003c/p\u003e \u003cp\u003eVarious methods have been used to secure an internal distance for the cement, but the manual application of two layers of the separating material (pico-fit) prior to making the wax model is considered the most common and effective [17].\u003c/p\u003e \u003cp\u003eThe metal copings were manufactured on plaster casts replicated from a copper master abutment made using an industrial lathe, with the aim of standardizing the length of the abutment, the shoulder width, and accurately adjusting the wall inclination to neutralize its effect on the research results [18,19].\u003c/p\u003e \u003cp\u003eSeven points were chosen to study the internal fit: two points at the midpoint of the preparation margins, two points at the midpoint of the axial walls, two points at the occlusal linear angles, and one point at the midpoint of the occlusal surface. These points are almost similar to those used by Lovgren in measuring the internal fit [20].\u003c/p\u003e \u003cp\u003eIn the present study, internal fit measurements were performed using an optical light microscope equipped with a calibrated eyepiece micrometer (accuracy: 10 \u0026micro;m) at 10\u0026times; magnification. Previous investigations have demonstrated that light microscopy provides measurement accuracy comparable to that of scanning electron microscopy (SEM) for evaluating crown fit, with no statistically significant differences between the two methods [21\u0026ndash;23]. Given its reliability, lower operational complexity, and non-destructive nature, the light microscope was deemed appropriate for assessing both fabrication techniques in this study.\u003c/p\u003e \u003cp\u003eIn this study, the cement replica technique was used to assess restoration fit by measuring the thickness of a low-viscosity addition silicone layer as a surrogate for resin cement. This non-destructive, reproducible, and cost-effective method has shown measurement accuracy comparable to sectioning techniques after cementation, with no statistically significant differences in marginal or internal gaps [24]. Systematic reviews further support its validity, while noting limitations such as restricted cross-sectional analysis and possible distortion of thin silicone layers [25].\u003c/p\u003e \u003cp\u003eThe value of the internal gap in the group where the sectioning after cementation technique was used to measure internal adaptation was significantly larger than in the group where the cement replica technique was used. This may be attributed to the difference in viscosity of both materials and the difference in the size of the atoms and molecules constituting each material. The cement used in luting has a higher viscosity and larger particle size, and thus its compressibility is lower than that of the additional soft silicone material used in the cement replica technique. Considering that the process of cementing restorations represents the clinical reality, the method of cementing crowns and then performing longitudinal sections and measuring the cement thickness with an optical microscope is the most accurate and reliable method for measuring internal adaptation.\u003c/p\u003e \u003cp\u003eThis differs from the study by Rahme and colleagues in 2008 [26], where they found that the cement replica technique is more accurate and reliable. The reason for the difference may be attributed to the type of crowns and abutments used. In Rahme's study, Procera crowns were used, and the abutments had an anatomical shape. In our study, however, the crowns were metal, and the abutments used were cylindrical with closely spaced walls and free of anatomical details.\u003c/p\u003e \u003cp\u003eLovgren and his colleagues [20] studied internal adaptation in 2017 using the cement matching technique for metal crowns made by three different methods. They found that metal crowns made using the lost wax technique had a larger internal gap than those made using the CAD/CAM and the laser sintering techniques. They attributed this to the fact that the lost wax technique undergoes several procedures, and each procedure can be subject to various errors, which ultimately affect the internal adaptation.\u003c/p\u003e \u003cp\u003eThe internal gap value in Lovgren's study was also significantly larger than the internal gap value in our study. This may be attributed to the fact that the abutment used in Lovgren's study had a wall inclination of 12 degrees, whereas in our study it was 20 degrees. This aligns with Fusayama's study [27], which found that increasing the preparation angle improves the fit of the restoration.\u003c/p\u003e \u003cp\u003eThe results of our study agreed with the study by Abduo and his colleagues in 2010 [28], where they assessed the fit of fixed restorations using the cement replica technique. They found that this method has its limitations and inherent errors, such as the difficulty in identifying the crown margins and finish lines, its susceptibility to tearing when removed from the crown, and the errors resulting from the trimming process, which ultimately lead to inaccurate measurements.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eWithin the limitation of this study we conclude that:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eInternal gap measurements depend significantly on the assessment technique.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eSectioning and measuring cement thickness under optical microscopy yields higher and more clinically representative internal gap values.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe internal gap values obtained from both assessment techniques were within the clinically acceptable range reported in the literature.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eEthical approval: This study is an in vitro study, does not require ethical approval.\u003c/p\u003e\n\u003cp\u003eConsent for publication: not available\u003c/p\u003e\n\u003cp\u003eCompeting interest: Authors declare no competing interests\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAcknowledgments: non\u003c/p\u003e\n\u003cp\u003eData availability:\u0026nbsp;The data supporting the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003eFunding: No funding was received for this study\u003c/p\u003e\n\u003cp\u003eAuthor contributions (CRediT):\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eJK and KA: The conception and design of the study, JK and KA: Acquisition of data, JK: Analysis and interpretation of data, KA: Drafting the article and revising it critically for important intellectual content. JK and KA: Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All authors gave their final approval and agreed to be accountable for all aspects of the work.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eKasloff Z. Casting techniques and some variables. The Journal of Prosthetic Dentistry 1961;11(3):533-36\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003ePilo R, Cardash H, Baharav H, Helft M. Incomplete seating of cemented crowns: a literature review. The Journal of prosthetic dentistry 1988;59(4\u003cspan dir=\"RTL\"\u003e):429-33.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eJ\u0026oslash;rgensen KD. Factors affecting the film thickness of zinc phosphate cements. Acta odontologica scandinavica 1960;18(4):479-90\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eHolmes JR, Bayne SC, Holland GA, Sulik WD. Considerations in measurement of marginal fit. The Journal of prosthetic dentistry 1989;62(4):405-08\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eNakamura T, Dei N, Kojima T, Wakabayashi K. Marginal and internal fit of Cerec 3 CAD/CAM all-ceramic crowns. Int J Prosthodont 2003;16(3):244-8\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eTuntiprawon M, Wilson PR. The effect of cement thickness on the fracture strength of all-ceramic crowns. Aust Dent J 1995;40(1):17-21\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eGroten M, Girthofer S, Pr\u0026ouml;bster L. Marginal fit consistency of copy‐milled all‐ceramic\u003cspan dir=\"RTL\"\u003e \u003c/span\u003ecrowns during fabrication by light and scanning electron microscopic analysis in vitro. Journal of oral rehabilitation 1997;24(12):871-81\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eAssif D, Antopolski B, Helft M, Kaffe I. Comparison of methods of clinical evaluation of the marginal fit of complete cast gold crowns. The Journal of prosthetic dentistry 1985;54(1):20-24\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eLimkangwalmongkol P, Chiche GJ, Blatz MB. Precision of fit of two margin designs for metal-ceramic crowns. J Prosthodont 2007;16(4):233-7\u003c/li\u003e\n\u003cli\u003eIwai T, Komine F, Kobayashi K, Saito A, Matsumura H. Influence of convergence angle and cement space on adaptation of zirconium dioxide ceramic copings. Acta Odontologica Scandinavica 2008;66(4):214-18\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eOruc S, Tulunoglu Y. Fit of titanium and a base\u003cspan dir=\"RTL\"\u003e \u003c/span\u003emetal alloy metal-ceramic crown. J Prosthet Dent 2000;83(3):314-8\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eZortuk M, Bolpaca P, Kilic K, Ozdemir E, Aguloglu S. Effects of finger pressure applied by dentists during cementation of all-ceramic crowns. European journal of dentistry. 2010;4(04):383-8.\u003c/li\u003e\n\u003cli\u003eMuradov M, Ryahovsky A, Chkalin V, Karapetyan A. Study on the pressure on ceramic veneers during cementation. Stomatologiia. 2024;103(3):26-30.\u003c/li\u003e\n\u003cli\u003eFurness A, Tadros MY, Looney SW, Rueggeberg FA. Effect of bulk/incremental fill on internal gap formation of bulk-fill composites. Journal of dentistry. 2014;42(4):439-49.\u003c/li\u003e\n\u003cli\u003eZeller S, Guichet D, Kontogiorgos E, Nagy WW. Accuracy of three digital workflows for implant abutment and crown fabrication using a digital measuring technique. The Journal of Prosthetic Dentistry. 2019;121(2):276-84.\u003c/li\u003e\n\u003cli\u003eAl Maaz A, Thompson GA, Drago C, An H, Berzins D. Effect of finish line design and metal alloy on the marginal and internal gaps of selective laser melting printed copings. The Journal of Prosthetic Dentistry. 2019;122(2):143-51.\u003c/li\u003e\n\u003cli\u003eMule SA, Dange SP, Khalikar AN, Vaidya SP. Effect of Varying Layers of Two Die Spacers on Precementation Space of Full Coverage Restorations. J Indian Prosthodont Soc 2014;14(Suppl 1)\u003cspan dir=\"RTL\"\u003e:67-75.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eIwai T, Komine F, Kobayashi K, Saito A, Matsumura H. Influence of convergence angle and cement space on adaptation of zirconium dioxide ceramic copings. Acta Odontologica Scandinavica 2008;66(4):214-18\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eOruc S, Tulunoglu Y. Fit of titanium and a base\u003cspan dir=\"RTL\"\u003e \u003c/span\u003emetal alloy metal-ceramic crown. J Prosthet Dent 2000;83(3):314-8\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eLovgren N, Roxner R, Klemendz S, Larsson C. Effect of production method on surface roughness, marginal and internal fit, and retention of cobalt-chromium single crowns. J Prosthet Dent 2017;118(1):95-101\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eHolmes JR, Bayne SC, Holland GA, Sulik WD. Considerations in measurement of marginal fit. The Journal of prosthetic dentistry. 1989;62(4):405-8.\u003c/li\u003e\n\u003cli\u003eGroten M, Axmann D, Pr\u0026ouml;bster L, Weber H. Determination of the minimum number of marginal gap measurements required for practical in vitro testing. The Journal of prosthetic dentistry. 2000;83(1):40-9.\u003c/li\u003e\n\u003cli\u003eMartins LM, Lorenzoni FC, Melo AOd, Silva LMd, Oliveira JLGd, Oliveira PCGd, et al. Internal fit of two all-ceramic systems and metal-ceramic crowns. Journal of Applied Oral Science. 2012;20:235-40.\u003c/li\u003e\n\u003cli\u003eKim D-Y, Kim E-B, Kim H-Y, Kim J-H, Kim W-C. Evaluation of marginal and internal gap of three-unit metal framework according to subtractive manufacturing and additive manufacturing of CAD/CAM systems. The journal of advanced prosthodontics. 2017;9(6):463\u003c/li\u003e\n\u003cli\u003eDi Fiore A, Zuccon A, Carraro F, Basilicata M, Bollero P, Bruno G, et al. Assessment methods for marginal and internal fit of partial crown restorations: a systematic review. Journal of Clinical Medicine. 2023;12(15):5048.\u003c/li\u003e\n\u003cli\u003eRahme HY, Tehini GE, Adib SM, Ardo AS, Rifai KT. In vitro evaluation of the \u0026quot;replica technique\u0026quot; in the measurement of the fit of Procera crowns. J Contemp Dent Pract 2008;9(2):25-32\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eFusayama T. Factors and technique of precision casting Part I. The Journal of Prosthetic Dentistry 1959;9(3):468-85\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003cli\u003eAbduo J, Lyons K, Swain M. Fit of zirconia fixed\u003cspan dir=\"RTL\"\u003e \u003c/span\u003epartial denture: a systematic review. J Oral Rehabil 2010;37(11):866-76\u003cspan dir=\"RTL\"\u003e.\u003c/span\u003e\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"bmc-oral-health","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ohea","sideBox":"Learn more about [BMC Oral Health](http://bmcoralhealth.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/ohea/default.aspx","title":"BMC Oral Health","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"internal fit, die spacer, optical microscopy, cement replica technique, fixed restorations","lastPublishedDoi":"10.21203/rs.3.rs-9222477/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9222477/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjective\u003c/h2\u003e \u003cp\u003eTo compare the internal fit of fixed dental prostheses using the cement replica technique and the sectioning after cementation technique assessed with an optical microscope under standardized conditions.\u003c/p\u003e\u003ch2\u003eMaterials and Methods\u003c/h2\u003e \u003cp\u003eThirty metal copings were produced on gypsum dies, which were created from impressions taken of a machined copper master abutment. Die spacer (Pico-Fit) was applied (axial and occlusal surfaces except apical 1 mm). Internal gap was first measured via cement replica technique. Subsequently, crowns were cemented with glass ionomer, sectioned, and internal gap measured under BX41 Olympus optical microscope at \u0026times;100 magnification at seven predefined sites. A paired t-tests assessed differences between the two measurement techniques utilized at (α\u0026thinsp;=\u0026thinsp;0.05).\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThe sectioning after cementation technique produced significantly larger internal gap measurements than the cement replica technique across all measurement sites (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eIn this in vitro model, measurements obtained post-cementation and sectioning were more clinically representative and reliable. The internal gap values obtained from both assessment techniques were within the clinically acceptable range.\u003c/p\u003e","manuscriptTitle":"Comparative evaluation of two techniques for assessing internal fit of fixed dental prostheses: A randomized controlled in-vitro study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-07 17:26:42","doi":"10.21203/rs.3.rs-9222477/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"145943031670876078220102396102621465937","date":"2026-05-10T18:53:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"239487719542929250450470990520306029068","date":"2026-05-10T07:06:20+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-30T03:20:31+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-04-10T09:36:38+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-26T10:33:43+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-26T10:32:55+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Oral Health","date":"2026-03-25T11:21:35+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-oral-health","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ohea","sideBox":"Learn more about [BMC Oral Health](http://bmcoralhealth.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/ohea/default.aspx","title":"BMC Oral Health","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7b01436a-9adb-4d2a-9927-aedf4f858aa2","owner":[],"postedDate":"May 7th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewerAgreed","content":"145943031670876078220102396102621465937","date":"2026-05-10T18:53:17+00:00","index":28,"fulltext":""},{"type":"reviewerAgreed","content":"239487719542929250450470990520306029068","date":"2026-05-10T07:06:20+00:00","index":27,"fulltext":""},{"type":"reviewersInvited","content":"5","date":"2026-04-30T03:20:31+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-07T17:26:42+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-07 17:26:42","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9222477","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9222477","identity":"rs-9222477","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}