Effect of Composite Resin Preheating on Microleakage in Class V Restorations

Effect of Composite Resin Preheating on Microleakage in Class V Restorations | 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 Effect of Composite Resin Preheating on Microleakage in Class V Restorations Nasrin Tayebghasemi, Nastaran Dabiri Shahabi, Ladan Ranjbar Omrani, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7013471/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 Introduction: Microleakage around restorative margins has always been a concern in various clinical conditions. To reduce the effects of microleakage in restorations, various techniques such as composite preheating and immediate or delayed curing are utilized. However, limited and contradictory studies have been conducted on the effect of preheating on microleakage and marginal adaptation of Class V composite restorations. Therefore, this study aimed to evaluate the effect of preheating on microleakage in Class V restorations and to compare it with the standard technique (sandwich technique). Materials and Methods: This experimental study included fifty healthy premolar teeth, on which Class V cavities were prepared on the buccal and lingual surfaces. The samples were then divided into four groups, each consisting of 25 teeth. The first group (G1, control) was restored with composite resin. In the second group (G2), cavities were restored with composite resin preheated to 68°C. The third group (G3) had cavities restored with composite resin preheated to 68°C, followed by delayed curing for 15 seconds. In the fourth group (G4), cavities were restored using the sandwich technique (RMGI + composite). After thermocycling, the teeth were immersed in a methylene blue solution for 24 hours. The samples were then sectioned buccolingually, and microleakage was assessed under a stereomicroscope. The findings were analyzed using the Kruskal-Wallis and Mann-Whitney tests. Results: The average microleakage on the gingival side was highest in group G4 (2.44±1.16) and lowest in group G3 (0.32±0.63). A statistically significant difference in average microleakage was observed between the groups (p<0.001). The Mann-Whitney test results indicated statistically significant differences between all pairwise group comparisons, except between G1 and G3 (p<0.001). Conclusion: Preheating improves the adaptation of composite resin and reduces microleakage. The use of an RMGI liner did not reduce microleakage. Delayed curing diminishes the positive effects of preheating on microleakage. microleakage preheating marginal adaptation composite resin gap Figures Figure 1 Figure 2 Figure 3 Introduction Dental composites are widely used as restorative materials due to their numerous advantages, including biocompatibility, excellent aesthetics, preservation of maximum dental tissue, adhesion to teeth, and mercury-free construction ( 1 – 3 ). However, composite resins still present certain limitations ( 4 ). Issues such as high viscosity, polymerization shrinkage, low durability, and strength make composite application and adaptation within dental cavities challenging, thus limiting their use in some clinical situations ( 3 , 5 ). The weak bond between dentin and restorative materials, coupled with polymerization shrinkage, leads to the formation of gaps, which in turn result in microleakage. Microleakage allows the penetration of oral microorganisms, saliva, and chemicals between the restorative material and the tooth structure (6–8). This phenomenon is considered a primary factor contributing to clinical complications of composite fillings, such as postoperative sensitivity, pulp inflammation, discoloration, recurrent caries, and even restoration failure ( 5 , 7 , 8 , 9 ). To mitigate microleakage and improve the marginal fit of composites, various methods have been proposed, including the use of flowable liners ( 9 , 10 ), application of Resin Modified Glass Ionomer (RMGI) liners beneath the main restoration (sandwich technique) ( 11 , 12 ), and the preheating method ( 13 ). However, studies by Sabatini and dos Santos did not demonstrate a significant reduction in microleakage after applying the preheating technique ( 8 , 14 ). On the other hand, Wagner et al. found that preheating resulted in the lowest microleakage at cervical margins, while delayed curing increased microleakage compared to both the flowable liner and preheating groups ( 15 ). Despite these findings, the effect of preheating on microleakage and marginal adaptation in Class V composite restorations remains insufficiently explored, with limited and sometimes contradictory results. The aim of this study is to evaluate the effect of preheating on microleakage in Class V composite restorations and compare it with the standard and widely recommended sandwich technique in vitro. Materials and Methods Sample Size Calculation To determine the required sample size, the study by Soliman et al. ( 6 ) was used as a reference. With a confidence level of 95% and a power of 80%, the required sample size for each group was 25, resulting in a total of 100 prepared cavities. Data Collection In this study, 50 sound human premolar teeth, extracted for orthodontic reasons and free of decay, were selected. The teeth were cleaned and disinfected with thymol solution and stored in distilled water at room temperature until the start of the experiment. A total of 100 standard Class V cavities were prepared on the buccal and lingual surfaces of the teeth using a diamond cylinder bur (HEICO SWISS), with dimensions of 3 mm x 2 mm x 2 mm in depth. The marginal area of the cavity was positioned 1 mm below the cementoenamel junction (CEJ). After every five teeth, the bur was replaced to ensure consistency. Group Division and Restoration Procedure The samples were randomly divided into four groups, and composite restorations were performed using Filtek Z250 composite (3M ESPE, USA) and Clearfil SE Bond adhesive (Kuraray, Japan) as follows: Group A (Control) : The enamel margins of the cavities were etched with 37% phosphoric acid for 20 seconds, rinsed with water, and dried with cotton. Following the manufacturer’s instructions, the primer was applied to all cavity surfaces for 20 seconds, then air-dried gently. Bonding agent was applied, followed by air-drying using a dental unit air syringe under mild pressure. Finally, the composite was incrementally placed and cured for 20 seconds with a D.LUX light cure unit (Diadent, South Korea) according to the manufacturer's instructions. Group B : In this group, the composite was heated to 68°C using a hot water bath in the composite tube heads. The heated composite was then placed into an injection gun, and the cavities were restored following the same procedure as Group A. Group C : Similar to Group B, the composite was heated to 68°C and used for restoration. The difference in this group was that the composite curing was delayed by 15 seconds after cavity filling. Group D (Sandwich Technique) : In this group, a thin layer (approximately 1 mm) of RMGI (Ionoseal, Voco, Germany) was applied under the restorative composite and cured for 20 seconds. Following acid etching and bonding procedures, the composite was applied as in Group A. Thermocycling and Dye Penetration After the restorations were completed, all specimens were polished. The samples were placed in distilled water until the thermocycling process, which simulated oral conditions. The thermocycling was performed between 5°C and 55°C for 500 cycles (1 minute per cycle). After thermocycling, the teeth were sealed with two layers of nail polish, covering all areas except for 1 mm around the restoration site. In addition to nail polish, adhesive wax was applied to the tooth apices to ensure proper sealing. The dye penetration technique was used to assess microleakage, chosen for its simplicity, low cost, speed, minimal need for specialized laboratory equipment, and the ability to perform quantitative measurements ( 16 , 17 ). Methylene blue solution was selected for dye penetration due to its similar molecular size to bacterial products, such as butyric acid ( 17 ). The samples were immersed in a 0.5% methylene blue solution for 24 hours, then rinsed gently under water. Afterward, the teeth were sectioned buccolingually using a diamond disc. Microleakage was assessed under a stereomicroscope at 40x magnification, using the following grading criteria: Grade 0 : No dye penetration Grade 1 : Dye penetration less than or equal to half of the occlusal/gingival wall Grade 2 : Dye penetration over half of the occlusal/gingival wall Grade 3 : Dye penetration into the axial wall Data Analysis Descriptive statistics, including frequency distributions and percentages, were used to analyze the data. Given the non-normal distribution of the data, non-parametric tests such as the Kruskal-Wallis and Mann-Whitney tests were applied for comparisons. The data were analyzed using SPSS-21 software, and a significance level of p < 0.05 was considered for all tests. Results This in vitro study was conducted on 50 healthy human teeth, from which 100 cavities were prepared and restored using four different methods. Normality tests (Kolmogorov-Smirnov and Shapiro-Wilk) were performed to assess the distribution of the data across the four study groups. The results indicated that the data did not follow a normal distribution, particularly according to the Shapiro-Wilk test, which is recommended for smaller sample sizes. Consequently, non-parametric statistical methods were used for subsequent comparisons (Table 1 ). Table 1 Assessing the distribution normality of measured parameters for the groups to be studied Group Kolmogorov-Smirnov Shapiro-Wilk Statistic df Sig. Statistic Df Sig. Microleakage_OCC Control 0.476 25 0.001> 0.515 25 0.001> Sandwich 0.539 25 0.001> 0.203 25 0.001> Preheating 0.539 25 0.001> 0.203 25 0.001> Preheating&Delay 0.451 25 0.001> 0.561 25 0.001> Microleakage_Gin Control 0.304 25 0.001> 0.797 25 0.001> Sandwich 0.486 25 0.001> 0.505 25 0.001> Preheating 0.455 25 0.001> 0.566 25 0.001> Preheating&Delay 0.273 25 0.001> 0.766 25 0.001> The results of the Kruskal-Wallis test for the average microleakage of restored cavities on the occlusal surfaces showed that the highest average microleakage was found in the Preheating & Delay group (0.48 ± 0.96), while the lowest was observed in the Preheating group (0.04 ± 0.20). However, the comparison between the groups did not yield a statistically significant difference (p = 0.065) (Table 2). Table 2 Comparison of the mean microleakage of restored cavities on the occlusal side for the groups to be studied Group Mean Std. Deviation Minimum Maximum p-value Control 0.44 0.96 0 3 Sandwich 0.12 0.60 0 3 Preheating 0.04 0.20 0 1 0.065 Preheating&Delay 0.48 0.96 0 3 For the gingival surface, the highest average microleakage was found in the Sandwich group (2.44 ± 1.16), and the lowest was in the Preheating group (0.32 ± 0.63). The mean comparison between the groups indicated a statistically significant difference (p < 0.001) (Table 3). Table 3 Comparison of the mean microleakage of restored cavities on the gingival side for the groups to be studied Group Mean Std. Deviation Minimum Maximum p-value Control 1.24 1.13 0 3 Sandwich 2.44 1.16 0 3 Preheating 0.32 0.63 0 2 0.001> Preheating&Delay 0.84 1.03 0 3 To further investigate the differences, the Mann-Whitney test was performed to compare the groups with each other. The results were as follows: A statistically significant difference was observed between the Control (room temperature) and Sandwich groups (p < 0.001). A statistically significant difference was found between the Control and Preheating groups (p < 0.001). No statistically significant difference was found between the Control and Preheating & Delay groups (p = 0.164). A significant difference was observed in mean microleakage between the Sandwich and Preheating groups (p < 0.001). A statistically significant difference was found between the Sandwich and Preheating & Delay groups (p < 0.001). There was a statistically significant difference in microleakage between the Preheating and Preheating & Delay groups (p = 0.038). (Data not shown) Discussion Composite resins have been widely used in dentistry for many years. However, most studies report that their lifespan remains less than optimal ( 18 ). Microleakage is considered the primary factor contributing to the failure of composite restorations ( 19 ). One of the major challenges in restorative dentistry is preventing microleakage, especially in cervical lesions ( 20 ). This study was conducted to investigate the effect of composite preheating on reducing microleakage in these areas. Various techniques have been employed to evaluate the seal of restorations, with the dye penetration method being one of the most commonly used ( 16 , 21 ). A 2023 systematic review indicated that hybrid resin composite restorations were less prone to failure in Class V restorations compared to conventional Glass Ionomer Cement (GIC) and Resin Modified Glass Ionomer Cement (RMGIC) ( 22 ). In the present study, composite restorations served as the control group. Our study revealed that the microleakage rate at the occlusal surfaces was significantly lower than that at the gingival surfaces across all groups. This observation is consistent with the findings of previous studies by Goda et al., Akarsu et al., and Moustafa et al. ( 23 – 25 ). Interestingly, no significant difference was observed in the occlusal microleakage rates across the various groups. A major challenge when working with high-viscosity composites is their inability to adequately adapt to the cavity walls, often due to air bubbles. Preheating the composite has been suggested as a solution to this issue. Heating lowers the viscosity of the composite, improving the polymerization process by increasing the conversion of radicals, thereby enhancing the composite's fit with the cavity walls ( 2 , 26 ). Our results demonstrated that preheating the composite significantly reduced gingival microleakage, with the preheated group showing the least leakage, followed by the preheating and delayed curing group. The control group and the sandwich technique group exhibited higher microleakage rates. The study by Goda et al. (2023) found that thermocycling of preheated nanofilled composites resulted in more microleakage compared to thermocycling of preheated bulk-filled composites. Additionally, Moustafa et al. (2020) reported that although no technique produced gap-free margins, preheating flowable bulk-fill composites preserved marginal integrity and reduced microleakage better than other methods ( 24 ). Our findings align with a systematic review by Lopes et al., which concluded that preheating composite resins reduces viscosity and enhances mechanical and physical properties ( 27 ). Several studies have suggested that elevated temperatures expedite the return of composites to their original shape, which may cause separation from the cavity if delayed curing is employed. This effect may explain the increased microleakage observed in the preheating and delayed curing group compared to the preheating-only group ( 6 , 15 ). This factor could be responsible for the difference in results between these two groups in our study. In contrast to our findings, studies by Nabil et al. (2022), Soliman et al. (2016), and Sabatini et al. (2010) did not observe significant differences in microleakage between heated and control groups ( 6 ). In this study, to explore this hypothesis, we included a delayed curing group in which composite was not cured immediately after placement. Our results indicated that this delay led to increased microleakage, likely due to the viscoelastic behavior of the composite and its tendency to separate from the cavity when delayed curing occurred. Supporting our findings, Didron et al. (2013) and Feros-Salgado et al. (2010) reported that preheating composites up to 60°C increased polymerization contraction stress and significantly reduced microleakage at the cervical margin ( 4 , 28 ). Although preheating improves polymerization and radical conversion, it can also increase composite viscosity during curing, potentially leading to higher microleakage. However, this phenomenon was not observed in our study. Water absorption, which causes composite swelling, has been proposed as a factor that may compensate for the initial shrinkage during polymerization ( 8 ). In our study, the samples were kept in water after restoration, which may have contributed to the reduced microleakage observed in the preheating groups. The C-factor, which refers to the ratio of bonded to unbonded surfaces during restoration, is another important factor influencing composite shrinkage during polymerization. A reduction in the C-factor can decrease shrinkage stress. To minimize this factor, we used an incremental restoration technique, which has been shown to reduce shrinkage ( 29 ). The type of composite also plays a role; in this study, Filtek Z250, with 82% mineral filler content, was used. Higher mineral filler content generally leads to reduced shrinkage ( 1 , 8 ). Interestingly, the sandwich technique, which incorporates an RMGI liner, exhibited the highest microleakage in our study. This was unexpected, as it was anticipated that the RMGI liner, known for its moisture tolerance, would improve adaptation between the restoration and cavity walls, thus reducing microleakage. RMGI liners are believed to mitigate polymerization shrinkage stresses by reducing the C-factor ( 30 ). Additionally, the slower setting reaction of RMGI allows it to better accommodate contraction stresses during polymerization ( 21 ). However, contrary to this hypothesis, RMGI did not reduce microleakage in our study. Several studies have reported similar results, indicating that RMGI liners do not effectively reduce microleakage compared to the control group ( 31 – 37 ). Nematollahi et al. (2017) conducted a study on microleakage in Class V restorations using different techniques and found no significant difference between RMGI-lined restorations and the control group. The absence of mechanical loading and thermocycling in our study may explain the similar microleakage results observed with the sandwich technique and the control group ( 30 , 38 ). Additionally, Gowda et al. (2015) found that the sandwich technique with RMGI exhibited higher microleakage, attributing this to the different rates of polymerization shrinkage between RMGI and composite, leading to gaps at the RMGI-tooth interface ( 36 ). Furthermore, RMGI's lower elasticity and higher rigidity can cause bond failure during curing, especially in response to thermal expansion and shrinkage stresses. For staining, methylene blue was used due to its ability to penetrate through materials like glass ionomer. Previous studies using methylene blue have shown varying rates of dye penetration, which could be influenced by the real gaps between the restoration and tooth structure (39, 40). Finally, the type of bonding system used may also influence the results. In this study, Clearfil SE Bond, a two-step self-etch adhesive, was employed. This adhesive contains 10-MDP, a monomer known for its hydrophobic properties and ability to form a stable chemical bond with hydroxyapatite in dentin ( 41 , 42 ). This bond is less susceptible to hydrolytic degradation compared to other self-etch adhesives, which may have contributed to the relatively low microleakage observed in our study. Conclusion The results of the present study indicate that preheating the composite significantly improves its adaptation to the cavity walls and reduces microleakage. However, delaying the curing of the preheated composite appears to diminish its positive effects on microleakage. Contrary to some previous studies, the use of an RMGI liner and the sandwich technique did not lead to a reduction in microleakage in this study. Further research, including mechanical loading and longer-term evaluations, is needed to confirm these findings and explore the impact of different factors on microleakage and restoration longevity. Declarations Acknowledgements Not applicable. Clinical trial number Not applicable. Funding There was no Funding. Ethics declarations Our study adhered to the Declaration of Helsinki. Ethics approval and consent to participate The protocol for this study was approved by the Ethics Committee of Tehran University of Medical Sciences under the code IR.UMSU.REC.1397.154, and all requirements were met. Informed consent to participate was obtained from all of the participants in the study. Consent for publication Not applicable. Competing interests The authors declare no competing interests. Consent to Publish declaration not applicable. References Mohammadi N, Jafari-Navimipour E, Kimyai S, Ajami A-A, Bahari M, Ansarin M, Ansarin M. 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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-7013471","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":492382586,"identity":"2055c549-3fe5-4dd4-8bef-70ce405dc742","order_by":0,"name":"Nasrin Tayebghasemi","email":"","orcid":"","institution":"Iran Urmia, Restorative Specialist","correspondingAuthor":false,"prefix":"","firstName":"Nasrin","middleName":"","lastName":"Tayebghasemi","suffix":""},{"id":492382591,"identity":"f932ba97-5b78-46ac-885c-4eab5aa55c0b","order_by":1,"name":"Nastaran Dabiri Shahabi","email":"","orcid":"","institution":"Department of Restorative Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.","correspondingAuthor":false,"prefix":"","firstName":"Nastaran","middleName":"Dabiri","lastName":"Shahabi","suffix":""},{"id":492382594,"identity":"770f7bf9-08d0-4c3e-b9ce-88599c17a704","order_by":2,"name":"Ladan Ranjbar Omrani","email":"","orcid":"","institution":"Department of Restorative Dentistry, School of Dentistry, Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran.","correspondingAuthor":false,"prefix":"","firstName":"Ladan","middleName":"Ranjbar","lastName":"Omrani","suffix":""},{"id":492382596,"identity":"3d6b967a-2c8b-47e3-8774-a2ad561e860c","order_by":3,"name":"Mahboobeh Mahmood","email":"","orcid":"","institution":"Department of Restorative Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.","correspondingAuthor":false,"prefix":"","firstName":"Mahboobeh","middleName":"","lastName":"Mahmood","suffix":""},{"id":492382597,"identity":"27e1d834-f207-4c59-ac80-836f1fb7333c","order_by":4,"name":"Marzieh Arjmandzadeh","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwElEQVRIiWNgGAWjYFCCBDaGBAYGORDzwANStBiDtSQQrQUIEhvAbGI0mLMnP3vwcM/h9Plhhx8CbbGT020goMWy55m5QcKzw7kbb6cZALUkG5sdIKDF4EaCmUTCAaCW2QkgLQcStxHWkv4NpCXdcHb6B2K15IBtSZCXziHWljNvyg0SDqQbbpDOKTiQYECMX46nb3v444C1vPzs9M0fPlTYyRHUAgXNDAZglQbEKQeBOgb5BuJVj4JRMApGwQgDAKGFTGY8QZfpAAAAAElFTkSuQmCC","orcid":"","institution":"Department of Pediatric Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.","correspondingAuthor":true,"prefix":"","firstName":"Marzieh","middleName":"","lastName":"Arjmandzadeh","suffix":""}],"badges":[],"createdAt":"2025-06-30 18:38:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7013471/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7013471/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":87927179,"identity":"16b68043-8874-42f8-a6da-4dd5ad2fde81","added_by":"auto","created_at":"2025-07-30 12:48:29","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":22511,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the mean microleakage on the occlusal side between the groups to be studied\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7013471/v1/4a013fe9f6442e98bdcdbdee.jpg"},{"id":87927935,"identity":"640471fd-4806-40cf-b182-745104bc9f0e","added_by":"auto","created_at":"2025-07-30 12:56:29","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":24568,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the mean microleakage on the gingival side between the groups to be studied\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7013471/v1/9cbe1b2b6068218280ba7f92.jpg"},{"id":87927181,"identity":"e58c84d1-886c-4e1b-bfb8-1d4e5d786d4d","added_by":"auto","created_at":"2025-07-30 12:48:29","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":588726,"visible":true,"origin":"","legend":"\u003cp\u003eThe code of each sample\u003c/p\u003e","description":"","filename":"Picture3.png","url":"https://assets-eu.researchsquare.com/files/rs-7013471/v1/c778fbcc290e3d583a697c56.png"},{"id":89704858,"identity":"f584e7f6-aa0b-4e55-b468-a6781744d729","added_by":"auto","created_at":"2025-08-22 22:46:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1091281,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7013471/v1/12778ad1-a23d-4747-b30b-fc16dad08d09.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of Composite Resin Preheating on Microleakage in Class V Restorations","fulltext":[{"header":"Introduction","content":"\u003cp\u003eDental composites are widely used as restorative materials due to their numerous advantages, including biocompatibility, excellent aesthetics, preservation of maximum dental tissue, adhesion to teeth, and mercury-free construction (\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e). However, composite resins still present certain limitations (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e). Issues such as high viscosity, polymerization shrinkage, low durability, and strength make composite application and adaptation within dental cavities challenging, thus limiting their use in some clinical situations (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe weak bond between dentin and restorative materials, coupled with polymerization shrinkage, leads to the formation of gaps, which in turn result in microleakage. Microleakage allows the penetration of oral microorganisms, saliva, and chemicals between the restorative material and the tooth structure (6\u0026ndash;8). This phenomenon is considered a primary factor contributing to clinical complications of composite fillings, such as postoperative sensitivity, pulp inflammation, discoloration, recurrent caries, and even restoration failure (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eTo mitigate microleakage and improve the marginal fit of composites, various methods have been proposed, including the use of flowable liners (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e), application of Resin Modified Glass Ionomer (RMGI) liners beneath the main restoration (sandwich technique) (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e), and the preheating method (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e). However, studies by Sabatini and dos Santos did not demonstrate a significant reduction in microleakage after applying the preheating technique (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e). On the other hand, Wagner et al. found that preheating resulted in the lowest microleakage at cervical margins, while delayed curing increased microleakage compared to both the flowable liner and preheating groups (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eDespite these findings, the effect of preheating on microleakage and marginal adaptation in Class V composite restorations remains insufficiently explored, with limited and sometimes contradictory results. The aim of this study is to evaluate the effect of preheating on microleakage in Class V composite restorations and compare it with the standard and widely recommended sandwich technique in vitro.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003e\u003cb\u003eSample Size Calculation\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTo determine the required sample size, the study by Soliman et al. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e) was used as a reference. With a confidence level of 95% and a power of 80%, the required sample size for each group was 25, resulting in a total of 100 prepared cavities.\u003c/p\u003e\u003cp\u003e\u003cb\u003eData Collection\u003c/b\u003e\u003c/p\u003e\u003cp\u003eIn this study, 50 sound human premolar teeth, extracted for orthodontic reasons and free of decay, were selected. The teeth were cleaned and disinfected with thymol solution and stored in distilled water at room temperature until the start of the experiment.\u003c/p\u003e\u003cp\u003eA total of 100 standard Class V cavities were prepared on the buccal and lingual surfaces of the teeth using a diamond cylinder bur (HEICO SWISS), with dimensions of 3 mm x 2 mm x 2 mm in depth. The marginal area of the cavity was positioned 1 mm below the cementoenamel junction (CEJ). After every five teeth, the bur was replaced to ensure consistency.\u003c/p\u003e\u003cp\u003e\u003cb\u003eGroup Division and Restoration Procedure\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe samples were randomly divided into four groups, and composite restorations were performed using Filtek Z250 composite (3M ESPE, USA) and Clearfil SE Bond adhesive (Kuraray, Japan) as follows:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup A (Control)\u003c/b\u003e:\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eThe enamel margins of the cavities were etched with 37% phosphoric acid for 20 seconds, rinsed with water, and dried with cotton. Following the manufacturer\u0026rsquo;s instructions, the primer was applied to all cavity surfaces for 20 seconds, then air-dried gently. Bonding agent was applied, followed by air-drying using a dental unit air syringe under mild pressure. Finally, the composite was incrementally placed and cured for 20 seconds with a D.LUX light cure unit (Diadent, South Korea) according to the manufacturer's instructions.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup B\u003c/b\u003e:\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eIn this group, the composite was heated to 68\u0026deg;C using a hot water bath in the composite tube heads. The heated composite was then placed into an injection gun, and the cavities were restored following the same procedure as Group A.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup C\u003c/b\u003e:\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eSimilar to Group B, the composite was heated to 68\u0026deg;C and used for restoration. The difference in this group was that the composite curing was delayed by 15 seconds after cavity filling.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGroup D (Sandwich Technique)\u003c/b\u003e:\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eIn this group, a thin layer (approximately 1 mm) of RMGI (Ionoseal, Voco, Germany) was applied under the restorative composite and cured for 20 seconds. Following acid etching and bonding procedures, the composite was applied as in Group A.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eThermocycling and Dye Penetration\u003c/b\u003e\u003c/p\u003e\u003cp\u003eAfter the restorations were completed, all specimens were polished. The samples were placed in distilled water until the thermocycling process, which simulated oral conditions. The thermocycling was performed between 5\u0026deg;C and 55\u0026deg;C for 500 cycles (1 minute per cycle). After thermocycling, the teeth were sealed with two layers of nail polish, covering all areas except for 1 mm around the restoration site. In addition to nail polish, adhesive wax was applied to the tooth apices to ensure proper sealing.\u003c/p\u003e\u003cp\u003eThe dye penetration technique was used to assess microleakage, chosen for its simplicity, low cost, speed, minimal need for specialized laboratory equipment, and the ability to perform quantitative measurements (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). Methylene blue solution was selected for dye penetration due to its similar molecular size to bacterial products, such as butyric acid (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe samples were immersed in a 0.5% methylene blue solution for 24 hours, then rinsed gently under water. Afterward, the teeth were sectioned buccolingually using a diamond disc. Microleakage was assessed under a stereomicroscope at 40x magnification, using the following grading criteria:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGrade 0\u003c/b\u003e: No dye penetration\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGrade 1\u003c/b\u003e: Dye penetration less than or equal to half of the occlusal/gingival wall\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGrade 2\u003c/b\u003e: Dye penetration over half of the occlusal/gingival wall\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eGrade 3\u003c/b\u003e: Dye penetration into the axial wall\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eData Analysis\u003c/h2\u003e\u003cp\u003eDescriptive statistics, including frequency distributions and percentages, were used to analyze the data. Given the non-normal distribution of the data, non-parametric tests such as the Kruskal-Wallis and Mann-Whitney tests were applied for comparisons. The data were analyzed using SPSS-21 software, and a significance level of p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered for all tests.\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eThis in vitro study was conducted on 50 healthy human teeth, from which 100 cavities were prepared and restored using four different methods.\u003c/p\u003e\n\u003cp\u003eNormality tests (Kolmogorov-Smirnov and Shapiro-Wilk) were performed to assess the distribution of the data across the four study groups. The results indicated that the data did not follow a normal distribution, particularly according to the Shapiro-Wilk test, which is recommended for smaller sample sizes. Consequently, non-parametric statistical methods were used for subsequent comparisons (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAssessing the distribution normality of measured parameters for the groups to be studied\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd colspan=\"3\" rowspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eGroup\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" align=\"left\"\u003e\n \u003cp\u003eKolmogorov-Smirnov\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"6\" align=\"left\"\u003e\n \u003cp\u003eShapiro-Wilk\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eStatistic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003edf\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSig.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eStatistic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003eDf\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSig.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\" rowspan=\"4\" align=\"left\"\u003e\n \u003cp\u003eMicroleakage_OCC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.476\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.515\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003eSandwich\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.539\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.203\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003ePreheating\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.539\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.203\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003ePreheating\u0026amp;Delay\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.451\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.561\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\" rowspan=\"4\" align=\"left\"\u003e\n \u003cp\u003eMicroleakage_Gin\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.304\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.797\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003eSandwich\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.486\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.505\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003ePreheating\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.455\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.566\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003ePreheating\u0026amp;Delay\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.273\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.766\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003eThe results of the Kruskal-Wallis test for the average microleakage of restored cavities on the occlusal surfaces showed that the highest average microleakage was found in the Preheating \u0026amp; Delay group (0.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.96), while the lowest was observed in the Preheating group (0.04\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20). However, the comparison between the groups did not yield a statistically significant difference (p\u0026thinsp;=\u0026thinsp;0.065) (Table 2).\u0026nbsp;\u003c/p\u003e\n \u003ctable id=\"Tab2\" style=\"width: 393px;\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eComparison of the mean microleakage of restored cavities on the occlusal side for the groups to be studied\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 123.125px;\" colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003eGroup\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 29px;\" align=\"left\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 93.6343px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eStd. Deviation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65.5556px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eMinimum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68.6921px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eMaximum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55.9954px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 123.125px;\" colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 29px;\" align=\"left\"\u003e\n \u003cp\u003e0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 93.6343px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65.5556px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68.6921px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55.9954px;\" colspan=\"2\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 123.125px;\" colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003eSandwich\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 29px;\" align=\"left\"\u003e\n \u003cp\u003e0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 93.6343px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65.5556px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68.6921px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55.9954px;\" colspan=\"2\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 123.125px;\" colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003ePreheating\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 29px;\" align=\"left\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 93.6343px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65.5556px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68.6921px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55.9954px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.065\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 123.125px;\" colspan=\"3\" align=\"left\"\u003e\n \u003cp\u003ePreheating\u0026amp;Delay\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 29px;\" align=\"left\"\u003e\n \u003cp\u003e0.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 93.6343px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65.5556px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68.6921px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55.9954px;\" colspan=\"2\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eFor the gingival surface, the highest average microleakage was found in the Sandwich group (2.44\u0026thinsp;\u0026plusmn;\u0026thinsp;1.16), and the lowest was in the Preheating group (0.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.63). The mean comparison between the groups indicated a statistically significant difference (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) (Table\u0026nbsp;3).\u0026nbsp;\u003c/p\u003e\n\u003ctable id=\"Tab3\" style=\"width: 392.857px;\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eComparison of the mean microleakage of restored cavities on the gingival side for the groups to be studied\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 113.16px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eGroup\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 29px;\" align=\"left\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\" align=\"left\"\u003e\n \u003cp\u003eStd. Deviation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 50px;\" align=\"left\"\u003e\n \u003cp\u003eMinimum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 53px;\" align=\"left\"\u003e\n \u003cp\u003eMaximum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\" align=\"left\"\u003e\n \u003cp\u003ep-value\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 113.16px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eControl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 29px;\" align=\"left\"\u003e\n \u003cp\u003e1.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\" align=\"left\"\u003e\n \u003cp\u003e1.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 50px;\" align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 53px;\" align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 113.16px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eSandwich\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 29px;\" align=\"left\"\u003e\n \u003cp\u003e2.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\" align=\"left\"\u003e\n \u003cp\u003e1.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 50px;\" align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 53px;\" align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 113.16px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003ePreheating\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 29px;\" align=\"left\"\u003e\n \u003cp\u003e0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\" align=\"left\"\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 50px;\" align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 53px;\" align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\" align=\"left\"\u003e\n \u003cp\u003e0.001\u0026gt;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 113.16px;\" colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003ePreheating\u0026amp;Delay\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 29px;\" align=\"left\"\u003e\n \u003cp\u003e0.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 78px;\" align=\"left\"\u003e\n \u003cp\u003e1.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 50px;\" align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 53px;\" align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 41px;\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eTo further investigate the differences, the Mann-Whitney test was performed to compare the groups with each other. The results were as follows:\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003e\n \u003cp\u003eA statistically significant difference was observed between the Control (room temperature) and Sandwich groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003eA statistically significant difference was found between the Control and Preheating groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003eNo statistically significant difference was found between the Control and Preheating \u0026amp; Delay groups (p\u0026thinsp;=\u0026thinsp;0.164).\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003eA significant difference was observed in mean microleakage between the Sandwich and Preheating groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003eA statistically significant difference was found between the Sandwich and Preheating \u0026amp; Delay groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003eThere was a statistically significant difference in microleakage between the Preheating and Preheating \u0026amp; Delay groups (p\u0026thinsp;=\u0026thinsp;0.038). (Data not shown)\u003c/p\u003e\n \u003c/li\u003e\n\u003c/ul\u003e"},{"header":"Discussion","content":"\u003cp\u003eComposite resins have been widely used in dentistry for many years. However, most studies report that their lifespan remains less than optimal (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). Microleakage is considered the primary factor contributing to the failure of composite restorations (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e). One of the major challenges in restorative dentistry is preventing microleakage, especially in cervical lesions (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e). This study was conducted to investigate the effect of composite preheating on reducing microleakage in these areas.\u003c/p\u003e\u003cp\u003eVarious techniques have been employed to evaluate the seal of restorations, with the dye penetration method being one of the most commonly used (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e). A 2023 systematic review indicated that hybrid resin composite restorations were less prone to failure in Class V restorations compared to conventional Glass Ionomer Cement (GIC) and Resin Modified Glass Ionomer Cement (RMGIC) (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e). In the present study, composite restorations served as the control group.\u003c/p\u003e\u003cp\u003eOur study revealed that the microleakage rate at the occlusal surfaces was significantly lower than that at the gingival surfaces across all groups. This observation is consistent with the findings of previous studies by Goda et al., Akarsu et al., and Moustafa et al. (\u003cspan additionalcitationids=\"CR24\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e). Interestingly, no significant difference was observed in the occlusal microleakage rates across the various groups.\u003c/p\u003e\u003cp\u003eA major challenge when working with high-viscosity composites is their inability to adequately adapt to the cavity walls, often due to air bubbles. Preheating the composite has been suggested as a solution to this issue. Heating lowers the viscosity of the composite, improving the polymerization process by increasing the conversion of radicals, thereby enhancing the composite's fit with the cavity walls (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e). Our results demonstrated that preheating the composite significantly reduced gingival microleakage, with the preheated group showing the least leakage, followed by the preheating and delayed curing group. The control group and the sandwich technique group exhibited higher microleakage rates.\u003c/p\u003e\u003cp\u003eThe study by Goda et al. (2023) found that thermocycling of preheated nanofilled composites resulted in more microleakage compared to thermocycling of preheated bulk-filled composites. Additionally, Moustafa et al. (2020) reported that although no technique produced gap-free margins, preheating flowable bulk-fill composites preserved marginal integrity and reduced microleakage better than other methods (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e). Our findings align with a systematic review by Lopes et al., which concluded that preheating composite resins reduces viscosity and enhances mechanical and physical properties (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eSeveral studies have suggested that elevated temperatures expedite the return of composites to their original shape, which may cause separation from the cavity if delayed curing is employed. This effect may explain the increased microleakage observed in the preheating and delayed curing group compared to the preheating-only group (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). This factor could be responsible for the difference in results between these two groups in our study.\u003c/p\u003e\u003cp\u003eIn contrast to our findings, studies by Nabil et al. (2022), Soliman et al. (2016), and Sabatini et al. (2010) did not observe significant differences in microleakage between heated and control groups (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e). In this study, to explore this hypothesis, we included a delayed curing group in which composite was not cured immediately after placement. Our results indicated that this delay led to increased microleakage, likely due to the viscoelastic behavior of the composite and its tendency to separate from the cavity when delayed curing occurred.\u003c/p\u003e\u003cp\u003eSupporting our findings, Didron et al. (2013) and Feros-Salgado et al. (2010) reported that preheating composites up to 60\u0026deg;C increased polymerization contraction stress and significantly reduced microleakage at the cervical margin (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e). Although preheating improves polymerization and radical conversion, it can also increase composite viscosity during curing, potentially leading to higher microleakage. However, this phenomenon was not observed in our study.\u003c/p\u003e\u003cp\u003eWater absorption, which causes composite swelling, has been proposed as a factor that may compensate for the initial shrinkage during polymerization (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e). In our study, the samples were kept in water after restoration, which may have contributed to the reduced microleakage observed in the preheating groups.\u003c/p\u003e\u003cp\u003eThe C-factor, which refers to the ratio of bonded to unbonded surfaces during restoration, is another important factor influencing composite shrinkage during polymerization. A reduction in the C-factor can decrease shrinkage stress. To minimize this factor, we used an incremental restoration technique, which has been shown to reduce shrinkage (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e). The type of composite also plays a role; in this study, Filtek Z250, with 82% mineral filler content, was used. Higher mineral filler content generally leads to reduced shrinkage (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eInterestingly, the sandwich technique, which incorporates an RMGI liner, exhibited the highest microleakage in our study. This was unexpected, as it was anticipated that the RMGI liner, known for its moisture tolerance, would improve adaptation between the restoration and cavity walls, thus reducing microleakage. RMGI liners are believed to mitigate polymerization shrinkage stresses by reducing the C-factor (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e). Additionally, the slower setting reaction of RMGI allows it to better accommodate contraction stresses during polymerization (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e). However, contrary to this hypothesis, RMGI did not reduce microleakage in our study.\u003c/p\u003e\u003cp\u003eSeveral studies have reported similar results, indicating that RMGI liners do not effectively reduce microleakage compared to the control group (\u003cspan additionalcitationids=\"CR32 CR33 CR34 CR35 CR36\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e). Nematollahi et al. (2017) conducted a study on microleakage in Class V restorations using different techniques and found no significant difference between RMGI-lined restorations and the control group. The absence of mechanical loading and thermocycling in our study may explain the similar microleakage results observed with the sandwich technique and the control group (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAdditionally, Gowda et al. (2015) found that the sandwich technique with RMGI exhibited higher microleakage, attributing this to the different rates of polymerization shrinkage between RMGI and composite, leading to gaps at the RMGI-tooth interface (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e). Furthermore, RMGI's lower elasticity and higher rigidity can cause bond failure during curing, especially in response to thermal expansion and shrinkage stresses.\u003c/p\u003e\u003cp\u003eFor staining, methylene blue was used due to its ability to penetrate through materials like glass ionomer. Previous studies using methylene blue have shown varying rates of dye penetration, which could be influenced by the real gaps between the restoration and tooth structure (39, 40).\u003c/p\u003e\u003cp\u003eFinally, the type of bonding system used may also influence the results. In this study, Clearfil SE Bond, a two-step self-etch adhesive, was employed. This adhesive contains 10-MDP, a monomer known for its hydrophobic properties and ability to form a stable chemical bond with hydroxyapatite in dentin (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e). This bond is less susceptible to hydrolytic degradation compared to other self-etch adhesives, which may have contributed to the relatively low microleakage observed in our study.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe results of the present study indicate that preheating the composite significantly improves its adaptation to the cavity walls and reduces microleakage. However, delaying the curing of the preheated composite appears to diminish its positive effects on microleakage. Contrary to some previous studies, the use of an RMGI liner and the sandwich technique did not lead to a reduction in microleakage in this study. Further research, including mechanical loading and longer-term evaluations, is needed to confirm these findings and explore the impact of different factors on microleakage and restoration longevity.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003eClinical trial number\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere was no Funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOur study adhered to the Declaration of Helsinki.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe \u0026nbsp;protocol \u0026nbsp;for \u0026nbsp;this \u0026nbsp;study \u0026nbsp;was \u0026nbsp;approved \u0026nbsp;by \u0026nbsp;the \u0026nbsp;Ethics Committee of Tehran University of Medical Sciences under the code IR.UMSU.REC.1397.154, and \u0026nbsp;all requirements \u0026nbsp;were \u0026nbsp;met.\u003c/p\u003e\n\u003cp\u003eInformed consent to participate was obtained from all of the participants in the study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003enot applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMohammadi N, Jafari-Navimipour E, Kimyai S, Ajami A-A, Bahari M, Ansarin M, Ansarin M. 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Effect of cavity preparation techniques and different preheating procedures on microleakage of class V resin restorations. Eur J dentistry. 2012;6(1):87.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEman M, Soliman ILE, Adel A, Kamar A. Effect of Preheating on Microleakage and Microhardness of Composite resin(an in vitro study). Alexandria Dent J. 2016;41:4\u0026ndash;11.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJacob G, Goud KM. A comparative study on microleakage of two low shrinkage composite materials in Class II cavities: A stereomicroscopic analysis. J Conservative Dentistry: JCD. 2023;26(1):83.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSabatini C, Blunck U, Denehy G, Munoz C. Effect of pre-heated composites and flowable liners on Class II gingival margin gap formation. Oper Dent. 2010;35(6):663\u0026ndash;71.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHilton TJ, Ferracane JL, Broome JC. Summitt's fundamentals of operative dentistry: a contemporary approach. 4th ed. Quintessence Publishing Company Incorporated; 2013.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBonilla E, Stevenson R, Caputo A, White S. Microleakage resistance of minimally invasive Class I flowable composite restorations. Oper Dent. 2012;37(3):290\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChuang S, Jin Y, Liu J, Chang C, Shieh D. Influence of flowable composite lining thickness on Class II composite restorations. Operative Dentistry-University Washington-. 2004;29:301\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLabella R, Lambrechts P, Van Meerbeek B, Vanherle G. Polymerization shrinkage and elasticity of flowable composites and filled adhesives. Dent Mater. 1999;15(2):128\u0026ndash;37.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHilton TJ, Ferracane JL, Broome JC, Santos Jd, Summitt JB. Summitt's fundamentals of operative dentistry: a contemporary approach. (No Title). 2013.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003edos Santos RA, Lima A, Soares G, Ambrosano G, Marchi G, Lovadino J, Aguiar F. Effect of preheating resin composite and light-curing units on the microleakage of Class II restorations submitted to thermocycling. Oper Dent. 2011;36(1):60\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWagner W, Aksu M, Neme A, Linger J, Pink F, Walker S. Effect of pre-heating resin composite on restoration microleakage. Oper Dent. 2008;33(1):72\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGupta SK, Gupta J, Saraswathi V, Ballal V, Acharya SR. Comparative evaluation of microleakage in Class V cavities using various glass ionomer cements: An in vitro study. J Interdisciplinary Dentistry. 2012;2(3):164.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAnjum S, Malik A, Sharma S. Evaluation of Microleakage in Class V Restorations with Three different Adhesive Systems. J Contemp Dent Pract. 2017;18(6):497\u0026ndash;500.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFerracane J. Models of caries formation around dental composite restorations. J Dent Res. 2017;96(4):364\u0026ndash;71.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBansal D, Mahajan M. Comparative evaluation of different periods of enamel microabrasion on the microleakage of class V resin-modified glass ionomer and compomer restorations: An In vitro study. Indian J Dent Res. 2017;28(6):675.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eManhart J, Garcı́a-Godoy F, Hickel R. Direct posterior restorations: clinical results and new developments. Dent Clin. 2002;46(2):303\u0026ndash;39.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003e\u0026Ouml;zcan S, YIKILGAN İ, Bala O, \u0026Uuml;\u0026Ccedil;TAŞLI MB, \u0026Ouml;m\u0026uuml;rl\u0026uuml; H. The effect of different liners on the microleakege of class II restorations after thermocyclign and occlusal loading. 2013.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePilcher L, Pahlke S, Urquhart O, O\u0026rsquo;Brien KK, Dhar V, Fontana M, et al. Direct materials for restoring caries lesions: Systematic review and meta-analysis\u0026mdash;a report of the American Dental Association Council on Scientific Affairs. The Journal of the American Dental Association; 2023.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAkarsu S, Atasoy S. Comparison of Microleakage in Class V Restorations Using Different Composite Resins and Techniques. J Dent Mater Techniques. 2021;10(4).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMoustafa MN, El-Fattah A, Wegdan M, Al-Abbassy FH. Effect of composite preheating and placement techniques on marginal integrity of class V restorations. 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Composite pre-heating: effects on marginal adaptation, degree of conversion and mechanical properties. Dent Mater. 2010;26(9):908\u0026ndash;14.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChandrasekhar V, Rudrapati L, Badami V, Tummala M. Incremental techniques in direct composite restoration. J conservative dentistry. 2017;20(6):386\u0026ndash;91.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNematollahi H, Bagherian A, Ghazvini K, Esmaily H, Mehr MA. Microbial microleakage assessment of class V cavities restored with different materials and techniques: A laboratory study. Dent Res J. 2017;14(5):344.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLokhande NA, Padmai AS, Rathore VPS, Shingane S, Jayashankar D, Sharma U. Effectiveness of flowable resin composite in reducing microleakage\u0026ndash;An in vitro study. J Int oral health: JIOH. 2014;6(3):111.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSadeghi M, Lynch C. The effect of flowable materials on the microleakage of Class II composite restorations that extend apical to the cemento-enamel junction. Oper Dent. 2009;34(3):306\u0026ndash;11.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLeevailoj C, Cochran M, Matis B, Moore B, Platt J. Microleakage of posterior packable resin composites with and without flowable liners. Oper Dent. 2001;26(3):302\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMajety KK, Pujar M. In vitro evaluation of microleakage of class II packable composite resin restorations using flowable composite and resin modified glass ionomers as intermediate layers. J conservative dentistry: JCD. 2011;14(4):414.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYazici A, Baseren M, Dayangac B. The effect of flowable resin composite on microleakage in class V cavities. Oper Dent. 2003;28(1):42\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBore Gowda V, Sreenivasa Murthy B, Hegde S, Venkataramanaswamy SD, Pai VS, Krishna R. Evaluation of gingival microleakage in Class II composite restorations with different lining techniques: An in vitro study. Scientifica. 2015;2015.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eArslan S, Demirbuga S, Ustun Y, Dincer AN, Canakci BC, Zorba YO. The effect of a new-generation flowable composite resin on microleakage in Class V composite restorations as an intermediate layer. J conservative dentistry: JCD. 2013;16(3):189.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMoazzami S, Sarabi N, Hajizadeh H, Majidinia S, Li Y, Meharry M, Shahrokh H. Efficacy of four lining materials in sandwich technique to reduce microleakage in class II composite resin restorations. Oper Dent. 2014;39(3):256\u0026ndash;63.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eXie H, Zhang F, Wu Y, Chen C, Liu W. Dentine bond strength and microleakage of flowable composite, compomer and glass ionomer cement. Aust Dent J. 2008;53(4):325\u0026ndash;31.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYavuz I, Aydin A. New method for measurement of surface areas of microleakage at the primary teeth by biomolecule characteristics of methilene blue. Biotechnol Biotechnol Equip. 2005;19(1):181\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMotevaselian F, Yassine E, Mirzaee M, Kharazifard MJ, Heydari S, Shafiee M. In Vitro Microleakage of Class V Composite Restorations in Use of Three Adhesive Systems. J Islamic Dent Association Iran. 2016;28(1):14\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAnsari ZJ, Panahandeh N, Shafiei ZST, Baghban AA. Effect of self-etching adhesives on the bond strength of glass-ionomer cements. J dentistry (Tehran Iran). 2014;11(6):680.\u003c/span\u003e\u003c/li\u003e\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":"microleakage, preheating, marginal adaptation, composite resin, gap","lastPublishedDoi":"10.21203/rs.3.rs-7013471/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7013471/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eIntroduction:\u003c/strong\u003e Microleakage around restorative margins has always been a concern in various clinical conditions. To reduce the effects of microleakage in restorations, various techniques such as composite preheating and immediate or delayed curing are utilized. However, limited and contradictory studies have been conducted on the effect of preheating on microleakage and marginal adaptation of Class V composite restorations. Therefore, this study aimed to evaluate the effect of preheating on microleakage in Class V restorations and to compare it with the standard technique (sandwich technique).\u003cbr\u003e\n\u003cstrong\u003eMaterials and Methods:\u003c/strong\u003e This experimental study included fifty healthy premolar teeth, on which Class V cavities were prepared on the buccal and lingual surfaces. The samples were then divided into four groups, each consisting of 25 teeth. The first group (G1, control) was restored with composite resin. In the second group (G2), cavities were restored with composite resin preheated to 68°C. The third group (G3) had cavities restored with composite resin preheated to 68°C, followed by delayed curing for 15 seconds. In the fourth group (G4), cavities were restored using the sandwich technique (RMGI + composite). After thermocycling, the teeth were immersed in a methylene blue solution for 24 hours. The samples were then sectioned buccolingually, and microleakage was assessed under a stereomicroscope. The findings were analyzed using the Kruskal-Wallis and Mann-Whitney tests.\u003cbr\u003e\n\u003cstrong\u003eResults:\u003c/strong\u003e The average microleakage on the gingival side was highest in group G4 (2.44±1.16) and lowest in group G3 (0.32±0.63). A statistically significant difference in average microleakage was observed between the groups (p\u0026lt;0.001). The Mann-Whitney test results indicated statistically significant differences between all pairwise group comparisons, except between G1 and G3 (p\u0026lt;0.001).\u003cbr\u003e\n\u003cstrong\u003eConclusion:\u003c/strong\u003e Preheating improves the adaptation of composite resin and reduces microleakage. The use of an RMGI liner did not reduce microleakage. Delayed curing diminishes the positive effects of preheating on microleakage.\u003c/p\u003e","manuscriptTitle":"Effect of Composite Resin Preheating on Microleakage in Class V Restorations","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-30 12:48:24","doi":"10.21203/rs.3.rs-7013471/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":"f0b1c588-2696-4dac-afd1-ab110b865dce","owner":[],"postedDate":"July 30th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-08-22T22:38:05+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-30 12:48:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7013471","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7013471","identity":"rs-7013471","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}