Impact of high-concentration office-type bleaching agent on physical properties of different types of bulk-fill composites

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Methods This study used two bulk-fill composite resins, 3M Filtek Bulk-Fill (paste) and Estelite Bulk-Fill Flow (flowable). Twelve disc-shaped specimens were prepared and divided into two groups according to the type of bulk-fill materials. All samples were stored at room temperature for 24 hours with artificial saliva. Initial MH and surface SR values were measured. High-concentration office-type (HCOT) bleaching agent was applied to the samples for 30 minutes, and then the same procedure was repeated after one week. Following completion of bleaching procedures, final MH and surface SR values were evaluated. The MH values were analyzed by ANOVA and Kruskal-Wallis tests was used for SR values with a significance of 0.05. Results A statistically significant difference was found between the MH values of the groups before and after bleaching (p = 0.002). SR value of 3M Filtek Bulk-Fill was found statistically higher than Estelite Bulk-Fill Flow after or before bleaching treatment. Statistically significant difference was found SR value of 3M Filtek Bulk-Fill when compared to before and after bleaching procedures (p = 0.024). Conclusions Bleaching with high-concentration office-type material significantly reduced the MH of both bulk-fill composites. While HCOT was applied, Estelite Bulk-Fill Flow did not cause a significant change in surface SR. In contrast, the SR value of 3M Filtek Bulk-Fill was statistically higher. Therefore, if bleaching with a high-concentration office-type bleaching material is planned, it is recommended not to use 3M Filtek Bulk-Fill as a restorative material, or it may be recommended to renew existing composite resin restorations after bleaching treatment. Office bleaching carbamide peroxide bulk-fill composite resin microhardness roughness INTRODUCTION Advances in material science have enabled the use of conventional resin-based composite (RBC) materials in restorative dentistry due to their superior esthetic and physical properties ( 1 ). However, the polymerization depth of these materials is limited to 2 mm, and they must be applied using the incremental technique ( 2 ). This technique can extend the process time in deep cavities and form gaps between the composite layers ( 3 ). To overcome these challenges, manufacturers have developed a new class of composite materials known as 'bulk-fill composites' (BFCs). BFCs are designed to be applied 4–5 mm thick and undergo a single-step curing process ( 5 ). In addition to reducing the time required for the application, BFCs exhibit lower polymerization stress compared to conventional composite resins ( 5 ). Incorporating advanced-generation photoinitiators, such as Lucirin®-TPO, Ivocerin®, and RAS®, along with the translucency properties of BFCs, ensures sufficient depth polymerization ( 6 ). BFCs are categorized into two distinct classifications: flowable and paste. The composition of flowable BFCs is characterized by a reduced filler content compared to the paste-type. Flowable BFCs have weaker mechanical properties than paste-type BFCs. Therefore, their use is limited to narrow cavities ( 7 ). However, with the advancement in the composition of flowable BFCs, manufacturers assert that these composites can be utilized safely in the same cavities as paste-type composites. Nowadays, aesthetic appearance has become more important for patients. Dentists not only treat dental diseases but also care for patients' aesthetic expectations. Due to increased social interactions among individuals, bleached teeth make people feel more confident in their relationships ( 8 ). Bleaching is an oxidative reaction ( 9 ). During this procedure, carbamide peroxide (CP) and hydrogen peroxide (HP) in different concentrations are used as bleaching agents ( 10 ). With the release of free oxygen ions, bleaching occurs due to oxidation in the discolored organic tooth structure (10). Bleaching can be performed at home or in the office. Home bleaching agents have the advantages of being cheap and not needing office time ( 11 ). However, in-office bleaching treatments provide safer applications under the dentist’s control ( 12 ). SR and MH affect the longevity of restorative materials ( 10 ). Although bleaching is an effective and conservative treatment, oxidative reactions may adversely affect the physical properties of restorative materials ( 10 ). Different concentrations of bleaching agents may change the SR and MH of the dental materials ( 13 ). Increased SR can cause plaque accumulation, gingival inflammation, discoloration, microleakage, and secondary caries ( 10 ). MH is related to the physical strength and durability of materials ( 10 ). The MH of a material indicates its resistance to wear on the surface. MH is related to the durability, elasticity, plasticity, and viscosity of the material. A decrease in the material's MH may cause the restoration to fail and necessitate its replacement ( 14 ). Although the structural properties of restorative materials influence MH and SR, finishing and polishing procedures, surface treatments, and bleaching procedures also impact MH and SR ( 10 , 14 ). The effects of low-concentration home and office-type bleaching agents on resin composites were evaluated ( 15 , 16 ). Recently, HCOT bleaching agent containing 45% carbamide peroxide bleaching agent was introduced, particularly for treating intense internal discolorations, such as those caused by tetracycline. To the best of our knowledge, no study exists investigating the effect of high-concentration office-type carbamide peroxide on the MH and SR of bulk-fill composites. Therefore, this study aimed to evaluate the impact of 45% CP on the MH and SR of flowable and paste-type bulk-fill composite resin materials. The null hypothesis of this study was: There will be no significant differences between the MH and SR values ​​of different BFCs after bleaching. MATERIALS AND METHODS This study was designed as an in vitro study. Two types of A2 shade BFCs were prepared as test materials. The chemical compositions of bulk-fill composite resin materials and bleaching agents tested in the study are listed in Table 1 . Table 1 Materials used in the present study and their compositions. Type of Materials Manufacturers Compositions Paste Type Bulk-Fill Composite 3M Filtek Bulk-Fill Posterior, 3M ESPE, Germany AUDMA, UDMA, diurethane dimethacrylate, 1,12-dodecane dimethacrylate, Zirconia/ silica cluster, ytterbium trifluoride Flowable Bulk-Fill Composite Estelite Bulk-Fill Flow, Tokuyama Dental Corporation, Tokyo, Japan Bis-GMA, TEG-GMA, Bis-MPEPP, Mequinol, Dibutyl hydroxytoluene, UV absorber, Spherical silica-zirconia filler, CQ, RAP, initiator system Bleaching Agent Opalescence Quick PF 45% Ultradent, South Jordan, Utah, USA 45% carbamide peroxide, potassium nitrate, 0.11% fluoride, carbopol, glycerin AUDMA :Aromatic urethane dimethacrylate, UDMA :Diurethane dimethacrylate, Bis-GMA :Bisphenol A diglycidyl ether dimethacrylate, TEG-DMA :Triethylene glycol dimethacrylate, Bis-MPEPP :2Bis[4(methacryloxyethoxy)phenyl]propane, CQ :Camphorquinone, RAP : radical amplified photopolymerization Preparation of Samples Two types of BFCs: Flowable bulk-fill composite resin (Tokuyama Estelite Bulk-Fill, Tokuyama Dental, Tokyo, Japan) and paste-type bulk-fill composite resin (3M Filtek Bulk-Fill Posterior, 3M ESPE, Germany) were used for this study. Samples were prepared using 4 x 10 mm metal molds (n = 10). After the molds were filled with BFCs, a glass plate was placed on the Mylar strip. All samples were polymerized for 20 seconds with a light-emitting diode (LED) light cure unit (Valo Cordless, Ultradent, USA) with a 395–480 nm wavelength. Then, the samples were polished under water-cooling for 10 seconds to obtain a flat surface with 400, 800, and 1000-grain silicon carbide papers placed on a polishing device (Minitech 233, Pressi, France). Storage and thermo-aging procedure All samples were kept in dark glass bottles with artificial saliva at room temperature for 24 hours (Table 2 ). The artificial saliva solution was prepared in the Biochemistry Department of Bezmialem Vakıf University Faculty of Medicine. Using artificial saliva, all samples were then subjected to 10,000 cycles (5–55°C) with a dwell time of 30 seconds and a transfer interval of 10 seconds (SD Mechatronic, Germany). Table 2 Artificial saliva formula ( 17 ). Artificial Saliva Content Amount in 1 liter of distilled water (mmol) NaCl 4,8 KCl 137 CaCl 2 1,5 NaHCO 3 8,2 KH 2 PO 4 4 Measurement of SR After the thermo-aging procedures, the initial surface SR of all samples was measured using a conventional profilometer (MarSurf M300C, Mahr GmbH, Germany). First, the device was calibrated, and SR measurements were performed from 3 different areas of each sample. A SR value was calculated by averaging three measurements. Measurement of MH Initial MH measurements of the samples were evaluated with a MH tester (Shimadzu MH Tester HMV-2 Series, Shimadzu, Japan). A 0.2 g load was applied to each sample via the scriber tip for 5 seconds. This process was repeated at three different points on the upper surface of each sample ( 19 ). The arithmetic mean was taken, and a MH value was determined for each sample. Bleaching Procedures HCOT bleaching gel (Opalescence Quick PF 45%) (Ultradent, South Jordan, Utah, USA) was applied approximately 0.5 mm to the upper surfaces of the samples. The specimens were subjected to CP for 30 minutes, following the manufacturer's instructions ( 18 ). This procedure was then repeated after one week. After each bleaching procedure, the samples were washed with distilled water, dried using airflow and paper, and stored in an oven at 37°C in an artificial saliva solution ( 18 ). The artificial saliva solution was prepared daily during the experiment. After the bleaching procedure, final SR and MH measurements were repeated. STATISTICAL ANALYSIS Statistical analysis of the data was performed using SPSS for Windows (SPSS Inc., Chicago, IL, USA), version 20.0. Continuous variables' mean ± standard deviation (SD) values ​​were given for descriptive statistics. The equality of variances was analyzed using the Levene test, and the normality of the data was assessed with the Shapiro-Wilk test. In the MH analysis, the Wilcoxon signed-rank test was performed since the variances were not equal and the data did not show a normal distribution. The Kruskal-Wallis test was used to determine whether there was a significant difference between the groups, and the results showed a statistically significant difference (p < 0.05). The Bonferroni test was performed as a post-hoc test. The hypotheses were two-sided and were considered significant when p < 0.05. In the SR analysis, the data were found to follow a normal distribution, as indicated by the Shapiro-Wilk test. Additionally, the Levene test revealed homogeneous variances. ANOVA and the post-hoc Tukey test were used. RESULTS A statistically significant difference was observed in the surface MH of the BFCs before and after bleaching (p = 0.002). A decrease in the MH of both BFCs was observed after bleaching. This post-hoc test revealed a significant difference between all measurements (p < 0.000). Paste-type BFCs showed the highest MH value compared to flowable BFCs before and after bleaching procedures. The Ra value of the paste-type BFCs was statistically higher than that of the flowable-type BFCs after or before bleaching treatment. The Ra value of the paste-type BFCs was higher than that of the flowable-type BFCs. When the SR value before bleaching was compared with the surface SR values after bleaching, no statistically significant difference was observed in the Ra value of flowable type BFCs (p = 0.895); however, paste type BFCs was found to be statistically significant (p = 0.024), and a higher surface SR value was obtained after bleaching. MH and SR values ​​are defined in detail in Table 3 . Table 3 Comparison of VHN and Ra values ​​of bulk-fill composite resins before and after bleaching VHN values Ra values Materials Median ± Standard Deviation Median ± Standard Deviation Flowable Bulk-Fill Composite (Estelite Bulk-Fill) Before bleaching 58.98 ± 3.47 A 0.099 ± 0.032 A After bleaching 43.87 ± 2.01 B 0.099 ± 0.035 A p 0.002 0.895 Past-type Bulk-Fill Composite (3M Filtek Bulk-Fill) Before bleaching 119.53 ± 9.65 C 0.154 ± 0.025 B After bleaching 65.42 ± 5.43 D 0.168 ± 0.025 C p 0.002 0.024 There is no difference between groups having the same letters in the same column. The differences were analyzed by the Kruskal-Wallis test (p < 0.05). DISCUSSION The popularity of white teeth among people has led to a rise in bleaching procedures, which have now become a standard practice in most dental offices ( 10 ). However, due to the growing prevalence of tooth bleaching, it is imperative to consider the impact of bleaching agents on the physical properties of restorative materials. Bleaching procedures sometimes include posterior teeth depending on the smile width of the patients; therefore, BFCs, which are often used in the restoration of molars and premolars with excessive material loss, with a thickness of 4–6 mm, are minimized in this study by the incremental technique due to time loss and technical sensitivity. In Office-bleaching treatments, 25%-35% hydrogen-peroxide-containing agents are commonly used ( 19 ). In this study, it was aimed to evaluate the effect of a bleaching agent applied at a higher concentration, 45% CP, for a shorter period on the MH and SR values ​​of flowable and paste-type bulk-fill composite resin materials. The most commonly used materials for teeth bleaching are HP, CP, and sodium perborate ( 20 ). The mechanism of all bleaching agents is that HP is converted into unstable free radicals through the degradation of peroxides and the breakdown of large pigment molecules through oxidation-reduction reactions ( 21 ). Agents containing CP also initially transform into HP and perform the same reaction ( 21 ). Bleaching agents containing CP are generally preferred as home bleaching agents in low concentrations ( 22 ). However, the home bleaching procedure is associated with disadvantages, such as the long duration and the fact that it is patient-dependent and not under the control of a dentist ( 22 ). Therefore, considering its advantages, such as the ability to place the bleaching gel in a custom-made plaque and perform the bleaching process by waiting for only 30 minutes in the waiting room under the control of a dentist, high-concentration 45% office-type CP was used in this study ( 23 ). The MH of a restorative material is one of the most important factors affecting the durability of the restoration. Consequently, it is feasible to discuss a restoration that exhibits high resistance to wear, minimal deterioration, and preserved form ( 24 – 25 ). MH measurements are frequently conducted in a research to evaluate the physical properties of restorative materials in dentistry ( 24 ). It has been demonstrated that high MH values ensure restorations are durable, exhibiting resistance to deterioration when subjected to intraoral conditions. Knoop and Vickers MH measurements are generally used methods ( 25 ). Therefore, in this study, the Vickers MH test method was used. The surface SR of a restorative material has an important effect on the esthetic appearance and discoloration of the restoration, plaque accumulation, secondary caries, and gingival irritation ( 10 , 26 ). It was clearly stated that the quality of the surface is related to the clinical success of a composite restoration ( 27 ). SR values are measured using a conventional profilometer, which is easy, repeatable, and reliable ( 10 ). Bulk-fill composites are the restorative materials of choice in teeth requiringextensive restoration due to reducing polymerization shrinkage and a single application with a thickness of 4 mm. The extant literature contains only a limited number of studies on the effects of strong oxidizing agents, such as 45% CP bleaching agents, on the MH and surface SR of BFCs. To the best of our knowledge, no study has been found in the literature that compares the MH and SR of flowable and paste type BFCs with 45% CP. Therefore, the findings of the studies conducted with conventional composite resin materials containing similar inorganic and organic fillers and bleaching agents containing similar CP percentages were discussed. Similar to the present study, in a study examining the effect of 40% office-type HP and 10% CP on the SR of BFCs, it was observed that the Ra value significantly increased in the paste-type BFCs ( 28 ). In addition, regardless of the composite type, the Ra value was increased in all BFCs after the bleaching procedures, as in the present study. Some studies have been conducted on the subject of bleaching agents and their effect on the SR of composite resins. The results of these studies are inconclusive, with some reporting no effect ( 21 , 29 , 30 ) and others reporting a decrease in surface hardness values ( 31 – 33 ). In the present study, a statistically significant decrease was observed in the MH values ​​of both flowable and paste-type BFCs after bleaching procedures (p < 0.05). In contrast to the findings of our study, Yikilgan et al. reported the effects of different concentrations of CP with different periods (10% CP = 8 h per day for 14 days, 45% CP = 30 minutes for three times) on MH and SR of the TCD-containing composite and found that 45% CP did not cause any change in surface hardness ( 10 ). They stated that the reason why 45% CP did not affect the surface MH of the material may be due to the release of HP at a lower concentration (approximately 15–20%), and the composite resin containing TCD matrix was subjected to a shorter time compared to the 10% CP application. In our study, unlike the study by Yikilgan et al., the reason for the decrease in surface MH may be the subjection of the samples to thermal aging. Kamangar et al. investigated the MH after applying 15% CP and 40% HP to micro-hybrid, nanofil, and silorane-based composite resins. It was observed that the MH values of nanofil and micro-hybrid resins decreased after both bleaching applications. It was found that bleaching did not have a statistically significant effect on the surface MH of silorane-based composites (p > 0.05). They stated that the MH findings of different composite resins to which the same bleaching agent was applied may differ. They pointed out that this situation can be explained by the presence of different organic matrices and inorganic fillers (ratio and size) in the structure of each composite. Free radicals are chemical molecules that can break down polymer chains and double bonds released during bleaching and penetrate the material. It has been reported that these free radicals can destroy the structure of the composite by affecting the resin matrix and the inorganic filler-resin interface. It has been reported that the effect of bleaching on the surface MH may vary depending on the material since silorane, which does not show any change in its MH, contains silorane resin instead of Bis-GMA, unlike other materials ( 34 ). Differences in the organic matrix structure of the composites may also cause differences in MH values ​​after bleaching. The organic structures of the composite resins used in this study also differ from conventional composites. The organic structure of Estelite Bulk-Fill Flow includes Bis-GMA, TEGDMA, and Bis-MPEPP. The organic matrix structure of 3M Bulk-Fill, containing AUDMA, diurethane dimethacrylate, and 1,12-dodecane dimethacrylate, is different from Estelite Bulk-Fill Flow. Filler ratio and particle size also play an important role in the MH value. While AUDMA in 3M Bulk-Fill has a high molecular weight, which can improve MH, UDMA/TEGDMA in Estelite Bulk-Fill Flow causes low viscosity and less rigidity ( 35 ). Consequently, it can be concluded that the MH values of flowable BFCs may be more affected by the bleaching agent than paste-type BFCs. However, it was determined that an HCOT bleaching agent caused a statistically significant increase in the SR value of past-type BFC (3M Bulk-Fill, p = 0.024), and no statistically significant change was observed in the SR of the flowable BFC (Estelite Bulk-Fill Flow, p = 0.895). In the inorganic structure of flowable BFC, spherical-type silica-zirconia fillers, which are found in the ratio of 56% by volume, provide better polishing of the material and make it more resistant to abrasion. The spherical type of fillers flowable BFCs showed more resistance than paste type BFCs in terms of SR against the bleaching agent. In this study, although thermal aging was performed with artificial saliva, many other variables in the oral environment conditions could not be imitated. Furthermore, restorations in the oral environment may not be as well polished as samples prepared in vitro . Consequently, the restoration surfaces may exhibit increased SR. CONCLUSIONS Within the limitations, we concluded that; Although the bleaching process with 45% CP agent caused a significant decrease in the MH values ​​of both BFCs, no significant change was observed in the SR value of the flowable type BFCs. It has been shown that the MH value of paste-type bulk-fill composite material decreases by almost 50% after the bleaching process. Furthermore, the material displayed higher levels of SR both before and after the bleaching procedure compared to those shown by the flowable-type bulk-fill composite. Consequently, its use in the restoration of posterior teeth is not advisable if a high-concentration office-type bleaching agent will be applied. Declarations Disclosure statement No potential conflict of interest was reported by the author(s). Funding This research received no external funding. Author Contribution Conceptualization, Z.B.K. and N.D.; methodology, B.D., analysis; Z.B.K..; investigation, Z:B:K and M.K.; writing—original draft preparation, Z.B.K; writing—review and ed-iting, Z.B.K,M.K and N.D. References Dayangaç GB. Composite Resin Restorations. Hamlin NJ, Bailey C, Motyka NC, Vandewalle KS. Effect of tooth-structure thickness on light attenuation and depth of cure. 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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-6807989","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":474060787,"identity":"9bfa650f-b2ed-4253-b693-5538a8e151e9","order_by":0,"name":"Zeynep Buket Kaynar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABA0lEQVRIiWNgGAWjYBACAwY2EJUAxCBGxQGw6IEHhLQcgGs5c4CBB6QlgWgtjG0QLQz4tJhLpCU+/sCQJm/efixN8ue8O3L2YocfAm2xk9NtwK7FckbaYYMDDDmGc86kHZPm3fbMmEc6zQCoJdnY7AAOh91Ib5M4wFDBOIMhvU2acdvhxB7pBJCWA4nbcGtp/wHUYj+D/3mb5M85IC3pHwhoSTsG9H5O4gyJtGMSvA0gLTn4bbHseZYscYYhLXmGxLNka55jh415bucUHEgwwO0Xc/Y0ww8VDMm2M/jTDG/+qDksxz47ffOHDxV2cri0gAHjP0wH41E+CkbBKBgFo4AgAAAThWN6v6aWbQAAAABJRU5ErkJggg==","orcid":"","institution":"Okan University","correspondingAuthor":true,"prefix":"","firstName":"Zeynep","middleName":"Buket","lastName":"Kaynar","suffix":""},{"id":474060788,"identity":"0e37c640-6d89-4e2e-bd9d-b7ff50ba9ad0","order_by":1,"name":"Nazmiye Dönmez","email":"","orcid":"","institution":"Bolu Abant İzzet Baysal University","correspondingAuthor":false,"prefix":"","firstName":"Nazmiye","middleName":"","lastName":"Dönmez","suffix":""},{"id":474060789,"identity":"c7bb1385-aec2-43c6-aeee-d2fd2fd74bce","order_by":2,"name":"Magrur Kazak","email":"","orcid":"","institution":"Bahçeşehir University","correspondingAuthor":false,"prefix":"","firstName":"Magrur","middleName":"","lastName":"Kazak","suffix":""},{"id":474060790,"identity":"f67c419f-0aa1-4975-92e7-8cbebfedeaa2","order_by":3,"name":"Bugra Duc","email":"","orcid":"","institution":"Istanbul Medipol University","correspondingAuthor":false,"prefix":"","firstName":"Bugra","middleName":"","lastName":"Duc","suffix":""}],"badges":[],"createdAt":"2025-06-03 07:08:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6807989/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6807989/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s12903-025-06723-7","type":"published","date":"2025-09-02T15:57:02+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":90827911,"identity":"b9da52e7-1f26-4df5-bfca-f738f5af0a80","added_by":"auto","created_at":"2025-09-08 16:02:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":543671,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6807989/v1/aa5efcdc-768c-4a1d-8001-23b384213dfa.pdf"},{"id":85232802,"identity":"bbbb535e-fffc-4e7b-9e0e-addae0af8abb","added_by":"auto","created_at":"2025-06-23 16:10:29","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":1012571,"visible":true,"origin":"","legend":"","description":"","filename":"IMAGESOFGELSANDRESTORATIVEMATERIALS.docx","url":"https://assets-eu.researchsquare.com/files/rs-6807989/v1/58e3990dfb2b9a53dfc8af08.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Impact of high-concentration office-type bleaching agent on physical properties of different types of bulk-fill composites","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eAdvances in material science have enabled the use of conventional resin-based composite (RBC) materials in restorative dentistry due to their superior esthetic and physical properties (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e). However, the polymerization depth of these materials is limited to 2 mm, and they must be applied using the incremental technique (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). This technique can extend the process time in deep cavities and form gaps between the composite layers (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e). To overcome these challenges, manufacturers have developed a new class of composite materials known as 'bulk-fill composites' (BFCs). BFCs are designed to be applied 4\u0026ndash;5 mm thick and undergo a single-step curing process (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). In addition to reducing the time required for the application, BFCs exhibit lower polymerization stress compared to conventional composite resins (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). Incorporating advanced-generation photoinitiators, such as Lucirin\u0026reg;-TPO, Ivocerin\u0026reg;, and RAS\u0026reg;, along with the translucency properties of BFCs, ensures sufficient depth polymerization (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBFCs are categorized into two distinct classifications: flowable and paste. The composition of flowable BFCs is characterized by a reduced filler content compared to the paste-type. Flowable BFCs have weaker mechanical properties than paste-type BFCs. Therefore, their use is limited to narrow cavities (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e). However, with the advancement in the composition of flowable BFCs, manufacturers assert that these composites can be utilized safely in the same cavities as paste-type composites.\u003c/p\u003e \u003cp\u003eNowadays, aesthetic appearance has become more important for patients. Dentists not only treat dental diseases but also care for patients' aesthetic expectations. Due to increased social interactions among individuals, bleached teeth make people feel more confident in their relationships (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBleaching is an oxidative reaction (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e). During this procedure, carbamide peroxide (CP) and hydrogen peroxide (HP) in different concentrations are used as bleaching agents (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). With the release of free oxygen ions, bleaching occurs due to oxidation in the discolored organic tooth structure (10). Bleaching can be performed at home or in the office. Home bleaching agents have the advantages of being cheap and not needing office time (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). However, in-office bleaching treatments provide safer applications under the dentist\u0026rsquo;s control (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSR and MH affect the longevity of restorative materials (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). Although bleaching is an effective and conservative treatment, oxidative reactions may adversely affect the physical properties of restorative materials (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). Different concentrations of bleaching agents may change the SR and MH of the dental materials (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e). Increased SR can cause plaque accumulation, gingival inflammation, discoloration, microleakage, and secondary caries (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). MH is related to the physical strength and durability of materials (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). The MH of a material indicates its resistance to wear on the surface. MH is related to the durability, elasticity, plasticity, and viscosity of the material. A decrease in the material's MH may cause the restoration to fail and necessitate its replacement (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e). Although the structural properties of restorative materials influence MH and SR, finishing and polishing procedures, surface treatments, and bleaching procedures also impact MH and SR (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe effects of low-concentration home and office-type bleaching agents on resin composites were evaluated (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e). Recently, HCOT bleaching agent containing 45% carbamide peroxide bleaching agent was introduced, particularly for treating intense internal discolorations, such as those caused by tetracycline. To the best of our knowledge, no study exists investigating the effect of high-concentration office-type carbamide peroxide on the MH and SR of bulk-fill composites. Therefore, this study aimed to evaluate the impact of 45% CP on the MH and SR of flowable and paste-type bulk-fill composite resin materials. The null hypothesis of this study was: There will be no significant differences between the MH and SR values ​​of different BFCs after bleaching.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cp\u003eThis study was designed as an \u003cem\u003ein vitro\u003c/em\u003e study. Two types of A2 shade BFCs were prepared as test materials. The chemical compositions of bulk-fill composite resin materials and bleaching agents tested in the study are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMaterials used in the present study and their compositions.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eType of Materials\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eManufacturers\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCompositions\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePaste Type Bulk-Fill Composite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3M Filtek Bulk-Fill Posterior, 3M ESPE, Germany\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAUDMA, UDMA, diurethane dimethacrylate, 1,12-dodecane dimethacrylate, Zirconia/ silica cluster, ytterbium trifluoride\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlowable Bulk-Fill Composite\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEstelite Bulk-Fill Flow, Tokuyama Dental Corporation,\u003c/p\u003e \u003cp\u003eTokyo, Japan\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBis-GMA, TEG-GMA, Bis-MPEPP, Mequinol, Dibutyl hydroxytoluene, UV absorber,\u003c/p\u003e \u003cp\u003eSpherical silica-zirconia filler, CQ, RAP, initiator system\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBleaching Agent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOpalescence\u003c/p\u003e \u003cp\u003eQuick PF 45% Ultradent, South Jordan, Utah, USA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e45% carbamide peroxide, potassium nitrate, 0.11% fluoride, carbopol, glycerin\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 \u003cb\u003eAUDMA\u003c/b\u003e:Aromatic urethane dimethacrylate,\u003cb\u003eUDMA\u003c/b\u003e:Diurethane dimethacrylate,\u003cb\u003eBis-GMA\u003c/b\u003e:Bisphenol A diglycidyl ether dimethacrylate,\u003cb\u003eTEG-DMA\u003c/b\u003e:Triethylene glycol dimethacrylate,\u003c/p\u003e \u003cp\u003e \u003cb\u003eBis-MPEPP\u003c/b\u003e:2Bis[4(methacryloxyethoxy)phenyl]propane,\u003cb\u003eCQ\u003c/b\u003e:Camphorquinone,\u003cb\u003eRAP\u003c/b\u003e: radical amplified photopolymerization\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of Samples\u003c/h2\u003e \u003cp\u003eTwo types of BFCs: Flowable bulk-fill composite resin (Tokuyama Estelite Bulk-Fill, Tokuyama Dental, Tokyo, Japan) and paste-type bulk-fill composite resin (3M Filtek Bulk-Fill Posterior, 3M ESPE, Germany) were used for this study. Samples were prepared using 4 x 10 mm metal molds (n\u0026thinsp;=\u0026thinsp;10). After the molds were filled with BFCs, a glass plate was placed on the Mylar strip. All samples were polymerized for 20 seconds with a light-emitting diode (LED) light cure unit (Valo Cordless, Ultradent, USA) with a 395\u0026ndash;480 nm wavelength. Then, the samples were polished under water-cooling for 10 seconds to obtain a flat surface with 400, 800, and 1000-grain silicon carbide papers placed on a polishing device (Minitech 233, Pressi, France).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eStorage and thermo-aging procedure\u003c/h3\u003e\n\u003cp\u003eAll samples were kept in dark glass bottles with artificial saliva at room temperature for 24 hours (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The artificial saliva solution was prepared in the Biochemistry Department of Bezmialem Vakıf University Faculty of Medicine. Using artificial saliva, all samples were then subjected to 10,000 cycles (5\u0026ndash;55\u0026deg;C) with a dwell time of 30 seconds and a transfer interval of 10 seconds (SD Mechatronic, Germany).\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\u003eArtificial saliva formula (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eArtificial Saliva Content\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAmount in 1 liter of distilled water (mmol)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNaCl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4,8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKCl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e137\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCaCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1,5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNaHCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8,2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eKH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eMeasurement of SR\u003c/h3\u003e\n\u003cp\u003eAfter the thermo-aging procedures, the initial surface SR of all samples was measured using a conventional profilometer (MarSurf M300C, Mahr GmbH, Germany). First, the device was calibrated, and SR measurements were performed from 3 different areas of each sample. A SR value was calculated by averaging three measurements.\u003c/p\u003e\n\u003ch3\u003eMeasurement of MH\u003c/h3\u003e\n\u003cp\u003eInitial MH measurements of the samples were evaluated with a MH tester (Shimadzu MH Tester HMV-2 Series, Shimadzu, Japan). A 0.2 g load was applied to each sample via the scriber tip for 5 seconds. This process was repeated at three different points on the upper surface of each sample (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e). The arithmetic mean was taken, and a MH value was determined for each sample.\u003c/p\u003e\n\u003ch3\u003eBleaching Procedures\u003c/h3\u003e\n\u003cp\u003eHCOT bleaching gel (Opalescence Quick PF 45%) (Ultradent, South Jordan, Utah, USA) was applied approximately 0.5 mm to the upper surfaces of the samples. The specimens were subjected to CP for 30 minutes, following the manufacturer's instructions (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). This procedure was then repeated after one week. After each bleaching procedure, the samples were washed with distilled water, dried using airflow and paper, and stored in an oven at 37\u0026deg;C in an artificial saliva solution (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). The artificial saliva solution was prepared daily during the experiment.\u003c/p\u003e \u003cp\u003eAfter the bleaching procedure, final SR and MH measurements were repeated.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eSTATISTICAL ANALYSIS\u003c/h2\u003e \u003cp\u003eStatistical analysis of the data was performed using SPSS for Windows (SPSS Inc., Chicago, IL, USA), version 20.0. Continuous variables' mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD) values ​​were given for descriptive statistics. The equality of variances was analyzed using the Levene test, and the normality of the data was assessed with the Shapiro-Wilk test.\u003c/p\u003e \u003cp\u003eIn the MH analysis, the Wilcoxon signed-rank test was performed since the variances were not equal and the data did not show a normal distribution. The Kruskal-Wallis test was used to determine whether there was a significant difference between the groups, and the results showed a statistically significant difference (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The Bonferroni test was performed as a post-hoc test. The hypotheses were two-sided and were considered significant when p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003cp\u003eIn the SR analysis, the data were found to follow a normal distribution, as indicated by the Shapiro-Wilk test. Additionally, the Levene test revealed homogeneous variances. ANOVA and the post-hoc Tukey test were used.\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS","content":"\u003cp\u003eA statistically significant difference was observed in the surface MH of the BFCs before and after bleaching (p\u0026thinsp;=\u0026thinsp;0.002). A decrease in the MH of both BFCs was observed after bleaching. This post-hoc test revealed a significant difference between all measurements (p\u0026thinsp;\u0026lt;\u0026thinsp;0.000).\u003c/p\u003e \u003cp\u003ePaste-type BFCs showed the highest MH value compared to flowable BFCs before and after bleaching procedures.\u003c/p\u003e \u003cp\u003eThe Ra value of the paste-type BFCs was statistically higher than that of the flowable-type BFCs after or before bleaching treatment. The Ra value of the paste-type BFCs was higher than that of the flowable-type BFCs. When the SR value before bleaching was compared with the surface SR values after bleaching, no statistically significant difference was observed in the Ra value of flowable type BFCs (p\u0026thinsp;=\u0026thinsp;0.895); however, paste type BFCs was found to be statistically significant (p\u0026thinsp;=\u0026thinsp;0.024), and a higher surface SR value was obtained after bleaching.\u003c/p\u003e \u003cp\u003eMH and SR values ​​are defined in detail in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of VHN and Ra values ​​of bulk-fill composite resins before and after bleaching\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVHN values\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRa values\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMaterials\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMedian\u0026thinsp;\u0026plusmn;\u0026thinsp;Standard Deviation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMedian\u0026thinsp;\u0026plusmn;\u0026thinsp;Standard Deviation\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eFlowable Bulk-Fill Composite\u003c/p\u003e \u003cp\u003e(Estelite Bulk-Fill)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBefore bleaching\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e58.98\u0026thinsp;\u0026plusmn;\u0026thinsp;3.47\u003csup\u003eA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.099\u0026thinsp;\u0026plusmn;\u0026thinsp;0.032\u003csup\u003eA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAfter bleaching\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e43.87\u0026thinsp;\u0026plusmn;\u0026thinsp;2.01\u003csup\u003eB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.099\u0026thinsp;\u0026plusmn;\u0026thinsp;0.035\u003csup\u003eA\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003ep\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.895\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ePast-type Bulk-Fill Composite\u003c/p\u003e \u003cp\u003e(3M Filtek Bulk-Fill)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBefore bleaching\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e119.53\u0026thinsp;\u0026plusmn;\u0026thinsp;9.65\u003csup\u003eC\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.154\u0026thinsp;\u0026plusmn;\u0026thinsp;0.025\u003csup\u003eB\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAfter bleaching\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e65.42\u0026thinsp;\u0026plusmn;\u0026thinsp;5.43\u003csup\u003eD\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.168\u0026thinsp;\u0026plusmn;\u0026thinsp;0.025\u003csup\u003eC\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003ep\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.024\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 \u003cem\u003eThere is no difference between groups having the same letters in the same column.\u003c/em\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003eThe differences were analyzed by the Kruskal-Wallis test (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/em\u003e \u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThe popularity of white teeth among people has led to a rise in bleaching procedures, which have now become a standard practice in most dental offices (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). However, due to the growing prevalence of tooth bleaching, it is imperative to consider the impact of bleaching agents on the physical properties of restorative materials. Bleaching procedures sometimes include posterior teeth depending on the smile width of the patients; therefore, BFCs, which are often used in the restoration of molars and premolars with excessive material loss, with a thickness of 4\u0026ndash;6 mm, are minimized in this study by the incremental technique due to time loss and technical sensitivity.\u003c/p\u003e \u003cp\u003eIn Office-bleaching treatments, 25%-35% hydrogen-peroxide-containing agents are commonly used (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e). In this study, it was aimed to evaluate the effect of a bleaching agent applied at a higher concentration, 45% CP, for a shorter period on the MH and SR values ​​of flowable and paste-type bulk-fill composite resin materials.\u003c/p\u003e \u003cp\u003eThe most commonly used materials for teeth bleaching are HP, CP, and sodium perborate (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e). The mechanism of all bleaching agents is that HP is converted into unstable free radicals through the degradation of peroxides and the breakdown of large pigment molecules through oxidation-reduction reactions (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e). Agents containing CP also initially transform into HP and perform the same reaction (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e). Bleaching agents containing CP are generally preferred as home bleaching agents in low concentrations (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e). However, the home bleaching procedure is associated with disadvantages, such as the long duration and the fact that it is patient-dependent and not under the control of a dentist (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e). Therefore, considering its advantages, such as the ability to place the bleaching gel in a custom-made plaque and perform the bleaching process by waiting for only 30 minutes in the waiting room under the control of a dentist, high-concentration 45% office-type CP was used in this study (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe MH of a restorative material is one of the most important factors affecting the durability of the restoration. Consequently, it is feasible to discuss a restoration that exhibits high resistance to wear, minimal deterioration, and preserved form (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e). MH measurements are frequently conducted in a research to evaluate the physical properties of restorative materials in dentistry (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e). It has been demonstrated that high MH values ensure restorations are durable, exhibiting resistance to deterioration when subjected to intraoral conditions. Knoop and Vickers MH measurements are generally used methods (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e). Therefore, in this study, the Vickers MH test method was used.\u003c/p\u003e \u003cp\u003eThe surface SR of a restorative material has an important effect on the esthetic appearance and discoloration of the restoration, plaque accumulation, secondary caries, and gingival irritation (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e). It was clearly stated that the quality of the surface is related to the clinical success of a composite restoration (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e). SR values are measured using a conventional profilometer, which is easy, repeatable, and reliable (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eBulk-fill composites are the restorative materials of choice in teeth requiringextensive restoration due to reducing polymerization shrinkage and a single application with a thickness of 4 mm. The extant literature contains only a limited number of studies on the effects of strong oxidizing agents, such as 45% CP bleaching agents, on the MH and surface SR of BFCs. To the best of our knowledge, no study has been found in the literature that compares the MH and SR of flowable and paste type BFCs with 45% CP. Therefore, the findings of the studies conducted with conventional composite resin materials containing similar inorganic and organic fillers and bleaching agents containing similar CP percentages were discussed.\u003c/p\u003e \u003cp\u003eSimilar to the present study, in a study examining the effect of 40% office-type HP and 10% CP on the SR of BFCs, it was observed that the Ra value significantly increased in the paste-type BFCs (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e). In addition, regardless of the composite type, the Ra value was increased in all BFCs after the bleaching procedures, as in the present study.\u003c/p\u003e \u003cp\u003eSome studies have been conducted on the subject of bleaching agents and their effect on the SR of composite resins. The results of these studies are inconclusive, with some reporting no effect (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e) and others reporting a decrease in surface hardness values (\u003cspan additionalcitationids=\"CR32\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e). In the present study, a statistically significant decrease was observed in the MH values ​​of both flowable and paste-type BFCs after bleaching procedures (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In contrast to the findings of our study, Yikilgan et al. reported the effects of different concentrations of CP with different periods (10% CP\u0026thinsp;=\u0026thinsp;8 h per day for 14 days, 45% CP\u0026thinsp;=\u0026thinsp;30 minutes for three times) on MH and SR of the TCD-containing composite and found that 45% CP did not cause any change in surface hardness (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). They stated that the reason why 45% CP did not affect the surface MH of the material may be due to the release of HP at a lower concentration (approximately 15\u0026ndash;20%), and the composite resin containing TCD matrix was subjected to a shorter time compared to the 10% CP application. In our study, unlike the study by Yikilgan et al., the reason for the decrease in surface MH may be the subjection of the samples to thermal aging.\u003c/p\u003e \u003cp\u003eKamangar et al. investigated the MH after applying 15% CP and 40% HP to micro-hybrid, nanofil, and silorane-based composite resins. It was observed that the MH values of nanofil and micro-hybrid resins decreased after both bleaching applications. It was found that bleaching did not have a statistically significant effect on the surface MH of silorane-based composites (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). They stated that the MH findings of different composite resins to which the same bleaching agent was applied may differ. They pointed out that this situation can be explained by the presence of different organic matrices and inorganic fillers (ratio and size) in the structure of each composite. Free radicals are chemical molecules that can break down polymer chains and double bonds released during bleaching and penetrate the material. It has been reported that these free radicals can destroy the structure of the composite by affecting the resin matrix and the inorganic filler-resin interface. It has been reported that the effect of bleaching on the surface MH may vary depending on the material since silorane, which does not show any change in its MH, contains silorane resin instead of Bis-GMA, unlike other materials (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e). Differences in the organic matrix structure of the composites may also cause differences in MH values ​​after bleaching. The organic structures of the composite resins used in this study also differ from conventional composites. The organic structure of Estelite Bulk-Fill Flow includes Bis-GMA, TEGDMA, and Bis-MPEPP. The organic matrix structure of 3M Bulk-Fill, containing AUDMA, diurethane dimethacrylate, and 1,12-dodecane dimethacrylate, is different from Estelite Bulk-Fill Flow. Filler ratio and particle size also play an important role in the MH value. While AUDMA in 3M Bulk-Fill has a high molecular weight, which can improve MH, UDMA/TEGDMA in Estelite Bulk-Fill Flow causes low viscosity and less rigidity (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e). Consequently, it can be concluded that the MH values of flowable BFCs may be more affected by the bleaching agent than paste-type BFCs.\u003c/p\u003e \u003cp\u003eHowever, it was determined that an HCOT bleaching agent caused a statistically significant increase in the SR value of past-type BFC (3M Bulk-Fill, p\u0026thinsp;=\u0026thinsp;0.024), and no statistically significant change was observed in the SR of the flowable BFC (Estelite Bulk-Fill Flow, p\u0026thinsp;=\u0026thinsp;0.895). In the inorganic structure of flowable BFC, spherical-type silica-zirconia fillers, which are found in the ratio of 56% by volume, provide better polishing of the material and make it more resistant to abrasion. The spherical type of fillers flowable BFCs showed more resistance than paste type BFCs in terms of SR against the bleaching agent.\u003c/p\u003e \u003cp\u003eIn this study, although thermal aging was performed with artificial saliva, many other variables in the oral environment conditions could not be imitated. Furthermore, restorations in the oral environment may not be as well polished as samples prepared \u003cem\u003ein vitro\u003c/em\u003e. Consequently, the restoration surfaces may exhibit increased SR.\u003c/p\u003e"},{"header":"CONCLUSIONS","content":"\u003cp\u003eWithin the limitations, we concluded that;\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eAlthough the bleaching process with 45% CP agent caused a significant decrease in the MH values ​​of both BFCs, no significant change was observed in the SR value of the flowable type BFCs.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eIt has been shown that the MH value of paste-type bulk-fill composite material decreases by almost 50% after the bleaching process. Furthermore, the material displayed higher levels of SR both before and after the bleaching procedure compared to those shown by the flowable-type bulk-fill composite. Consequently, its use in the restoration of posterior teeth is not advisable if a high-concentration office-type bleaching agent will be applied.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eDisclosure statement \u003c/h2\u003e\n\u003cp\u003eNo potential conflict of interest was reported by the author(s).\u003c/p\u003e\n\u003ch2\u003eFunding \u003c/h2\u003e\n\u003cp\u003eThis research received no external funding.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization, Z.B.K. and N.D.; methodology, B.D., analysis; Z.B.K..; investigation, Z:B:K and M.K.; writing\u0026mdash;original draft preparation, Z.B.K; writing\u0026mdash;review and ed-iting, Z.B.K,M.K and N.D.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDayanga\u0026ccedil; GB. Composite Resin Restorations.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHamlin NJ, Bailey C, Motyka NC, Vandewalle KS. Effect of tooth-structure thickness on light attenuation and depth of cure. Oper Dent. 2016;41:200\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eReis AF, Vestphal M, Amaral RCD, Rodrigues JA, Roulet JF, Roscoe MG. Efficiency of polymerization of bulk-fill composite resins: A systematic review. Braz Oral Res. 2017;31:e59.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGarapati S, Das M, Mujeeb A, Dey S, Kiswe SP. Cuspal movement and microleakage in premolar teeth restored with posterior restorative materials. Int J Oral Health. 2014;6:47\u0026ndash;50.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEl-Damanhoury H, Platt J. Polymerization shrinkage stress kinetics and related properties of bulk-fill resin composites. Oper Dent. 2014;39:374\u0026ndash;82.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTerry DA, Geller W. Esthetic \u0026amp; Restorative Dentistry. Quintessence Publishing Co, Inc; 2018.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eParra Gatica E, Duran Ojeda G, Wendler M. Contemporary flowable bulk-fill resin-based composites: A systematic review. Biomater Investig Dent. 2023;10:8\u0026ndash;19.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKershaw S, Newton JT, Williams DM. The influence of tooth colour on the perceptions of personal characteristics among female dental patients: Comparisons of unmodified, decayed and \u0026lsquo;whitened\u0026rsquo; teeth. Br Dent J. 2008;204:256\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGoldberg M, Grootveld M, Lynch E. Undesirable and adverse effects of tooth-whitening products: A review. Clin Oral Investig. 2010;14:1\u0026ndash;10.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYikilgan İ, Kamak H, Akgul S, Ozcan S, Bala O. Effects of three different bleaching agents on microhardness and roughness of composite sample surfaces finished with different polishing techniques. J Clin Exp Dent. 2017;9:e460\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOzkan P, Kansu G, Ozak ST, Kurtulmus-Yilmaz S, Kansu P. Effect of bleaching agents and whitening dentifrices on the surface roughness of human teeth enamel. Acta Odontol Scand. 2013;71:488\u0026ndash;97.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKossatz S, Dalanhol AP, Cunha T, Loguercio A, Reis A. Effect of light activation on tooth sensitivity after in-office bleaching. Oper Dent. 2011;36:251\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHaywood VB, Heymann HO. Nightguard vital bleaching: How safe is it? Quintessence Int. 1991;22:515\u0026ndash;23.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlQahtani MQ. The effect of a 10% carbamide peroxide bleaching agent on the microhardness of four types of direct resin-based restorative materials. Oper Dent. 2013;38:316\u0026ndash;23.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAra\u0026uacute;jo RM, Lemes EC, Pachito RF, Feitosa FA. The impact of at-home and in-office bleaching agents on the color stability of bulk-fill composite resins. Braz Dent Sci. 2019;22:94\u0026ndash;102.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGaroushi S, Lassila L, Hatem M, Shembesh M, Baady L, Salim Z, et al. Influence of staining solutions and whitening procedures on discoloration of hybrid composite resins. Acta Odontol Scand. 2013;71:144\u0026ndash;50.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKarabulut B, Can-Karabulut DC, \u0026Ouml;zyeğin SL. Evaluation of shear bond strength values of various restorative materials applied after diode laser activated bleaching. G\u0026uuml;lhane Med J. 2010;52:172\u0026ndash;80.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKalaivani M, Prasad SD, Indumathi M, Sruthipriya M, Janani B, Pavankumar O. Influence of home bleaching regimen on microhardness and flexural strength of two contemporary composite resins: An in vitro evaluation. Eur Oral Res. 2023;57:90\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eG\u0026uuml;l P, Harorli OT, Akg\u0026uuml;l N, G\u0026uuml;ndoğdu M. Effect of different bleaching applications on the surface properties and staining susceptibility of dental composites. J Wuhan Univ Technol-Mater Sci Ed. 2016;31:677\u0026ndash;83.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eErturk-Avunduk AT, Cengiz-Yanardag E, Karakaya I. The effect of bleaching applications on stained bulk-fill resin composites. BMC Oral Health. 2022;22:392.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSilva Costa SX, Becker AB, de Souza Rastelli AN, Monteiro Loffredo LDC, de Andrade MF, Bagnato VS. Effect of four bleaching regimens on color changes and microhardness of dental nanofilled composite. Int J Dent. 2009;2009:313845.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMatis BA, Hamdan YS, Cochran MA, Eckert GJ. A clinical evaluation of a bleaching agent used with and without reservoirs. Oper Dent. 2002;27:5\u0026ndash;11.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOpalescence Quick PF. Ultradent Products. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.ultradent.com.tr/products/categories/whitening/in-office/opalescence-quick-pf\u003c/span\u003e\u003cspan address=\"https://www.ultradent.com.tr/products/categories/whitening/in-office/opalescence-quick-pf\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. Accessed 2 Jun 2025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZanolla J, Marques ABC, da Costa DC, de Souza AS, Coutinho M. Influence of tooth bleaching on dental enamel microhardness: a systematic review and meta-analysis. Aust Dent J. 2017;62(3):276\u0026ndash;82.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEsmaeili B, Abolghasemzadeh F, Gholampor A, Daryakenari G. The effect of home bleaching carbamide peroxide concentration on the microhardness of dental composite resins. Gen Dent. 2018;66(1):40\u0026ndash;4.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRodrigues CS, Mozzaquatro LR, Dala BN, Jacques LB, Mallmann A. Effect of bleaching on color stability and surface roughness of composite resins aged in staining beverage. Gen Dent. 2017;65(5):e5\u0026ndash;10.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShimane T, Endo K, Zheng JH, Yanagi T, Ohno H. Wear of opposing teeth by posterior composite resins: evaluation of newly developed wear test methods. Dent Mater J. 2010;29(6):713\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTavares BG, Fran\u0026ccedil;a FM, Basting RT, Turssi CP, Amaral FL. Effect of bleaching protocols on surface roughness and color change of high- and low-viscosity bulk-fill composite resins. Acta Odontol Latinoam. 2020;33(2):59\u0026ndash;68.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eT\u0026uuml;rker SB, Biskin T. The effect of bleaching agents on microhardness of dental aesthetic restorative materials. J Oral Rehabil. 2002;29(7):657\u0026ndash;61.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePolydorou O, Hellwig E, Auschill TM. The effect of at-home bleaching on the microhardness of six esthetic restorative materials. J Am Dent Assoc. 2007;138(7):978\u0026ndash;84.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMalkondu \u0026Ouml;, Yurdag\u0026uuml;ven H, Say EC, Kazazoğlu E, Soyman M. Effect of bleaching on microhardness of esthetic restorative materials. Oper Dent. 2011;36(2):177\u0026ndash;86.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZuryati AG, Qian OQ, Dasmawati M. Effects of home bleaching on surface hardness and surface roughness of an experimental nanocomposite. J Conserv Dent. 2013;16(4):356\u0026ndash;60.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLima DANL, De Alexandre RS, Martins ACM, Aguiar FHB, Ambrosano G, Bovi M, et al. Effect of curing lights and bleaching agents on physical properties of a hybrid composite resin. J Esthet Restor Dent. 2008;20(4):266\u0026ndash;73.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKamangar SSH, Kiakojoori K, Mirzaii M, Fard MJK. Effects of 15% carbamide peroxide and 40% hydrogen peroxide on the microhardness and color change of composite resins. J Dent (Tehran). 2014;11(2):196\u0026ndash;204.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDias MF, Esp\u0026iacute;ndola-Castro LF, Lins-Filho PC, Teixeira HM, Silva CH, Guimar\u0026atilde;es RP. Influence of different thermopolymerization methods on composite resin microhardness. J Clin Exp Dent. 2020;12(4):e335\u0026ndash;41. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4317/jced.56772\u003c/span\u003e\u003cspan address=\"10.4317/jced.56772\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"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":"Office bleaching, carbamide peroxide, bulk-fill composite resin, microhardness, roughness","lastPublishedDoi":"10.21203/rs.3.rs-6807989/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6807989/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cb\u003eBackground\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThis study investigated the effect of a 45% carbamide peroxide-containing office-type bleaching agent on the microhardness (MH) and surface roughness (SR) of flowable and paste-type bulk-fill composite resins.\u003c/p\u003e\u003cp\u003e\u003cb\u003eMethods\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThis study used two bulk-fill composite resins, 3M Filtek Bulk-Fill (paste) and Estelite Bulk-Fill Flow (flowable). Twelve disc-shaped specimens were prepared and divided into two groups according to the type of bulk-fill materials. All samples were stored at room temperature for 24 hours with artificial saliva. Initial MH and surface SR values were measured. High-concentration office-type (HCOT) bleaching agent was applied to the samples for 30 minutes, and then the same procedure was repeated after one week. Following completion of bleaching procedures, final MH and surface SR values were evaluated. The MH values were analyzed by ANOVA and Kruskal-Wallis tests was used for SR values with a significance of 0.05.\u003c/p\u003e\u003cp\u003e\u003cb\u003eResults\u003c/b\u003e\u003c/p\u003e \u003cp\u003eA statistically significant difference was found between the MH values of the groups before and after bleaching (p\u0026thinsp;=\u0026thinsp;0.002). SR value of 3M Filtek Bulk-Fill was found statistically higher than Estelite Bulk-Fill Flow after or before bleaching treatment. Statistically significant difference was found SR value of 3M Filtek Bulk-Fill when compared to before and after bleaching procedures (p\u0026thinsp;=\u0026thinsp;0.024).\u003c/p\u003e\u003cp\u003e\u003cb\u003eConclusions\u003c/b\u003e\u003c/p\u003e \u003cp\u003eBleaching with high-concentration office-type material significantly reduced the MH of both bulk-fill composites. While HCOT was applied, Estelite Bulk-Fill Flow did not cause a significant change in surface SR. In contrast, the SR value of 3M Filtek Bulk-Fill was statistically higher. Therefore, if bleaching with a high-concentration office-type bleaching material is planned, it is recommended not to use 3M Filtek Bulk-Fill as a restorative material, or it may be recommended to renew existing composite resin restorations after bleaching treatment.\u003c/p\u003e","manuscriptTitle":"Impact of high-concentration office-type bleaching agent on physical properties of different types of bulk-fill composites","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-23 16:09:07","doi":"10.21203/rs.3.rs-6807989/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-03T08:12:29+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-01T13:25:15+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-01T09:14:49+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-29T14:22:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"43784176663859481956847804038732871030","date":"2025-06-24T08:25:39+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-23T12:33:26+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"165554416743523569302600220523965134342","date":"2025-06-23T07:14:25+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"48413256684661890054526645531016764548","date":"2025-06-20T10:43:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"335074377248716285611869295111078645595","date":"2025-06-20T06:13:57+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-19T13:22:22+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-06-18T05:52:46+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-11T09:47:07+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-11T09:45:43+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Oral Health","date":"2025-06-03T07:02:03+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":"1c108cc7-46c9-4ff1-a2fa-2b0460ce07ef","owner":[],"postedDate":"June 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-09-08T15:58:58+00:00","versionOfRecord":{"articleIdentity":"rs-6807989","link":"https://doi.org/10.1186/s12903-025-06723-7","journal":{"identity":"bmc-oral-health","isVorOnly":false,"title":"BMC Oral Health"},"publishedOn":"2025-09-02 15:57:02","publishedOnDateReadable":"September 2nd, 2025"},"versionCreatedAt":"2025-06-23 16:09:07","video":"","vorDoi":"10.1186/s12903-025-06723-7","vorDoiUrl":"https://doi.org/10.1186/s12903-025-06723-7","workflowStages":[]},"version":"v1","identity":"rs-6807989","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6807989","identity":"rs-6807989","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}