Background: The aim of the present study was to investigate the micro-shear bond strength (µSBS) of various restorative materials applied on two different fast-setting calcium silicate-based materials and to evaluate the effect of restoration time on µSBS. Methods: A total of 180 acrylic blocks with a cavity in the center were randomly divided into 2 main groups according to the capping material to be used (Biodentine or RetroMTA). The specimens were also randomly divided into 3 groups according to the restoration time (3 min, 12 min, 24 h). After the specified waiting periods, glass hybrid material (EQUIA Forte HT), resin composite (Filtek Z550) and light-cured calcium silicate material (Theracal LC) were placed on the specimens with tygon tubes. The specimens were kept for 24 h and then subjected to µSBS test. Statistical analysis was performed by 3-way ANOVA followed by Tukey test for pairwise comparisons (α = 0.05). Results: There is a statistically significant difference (p < 0.05) between the µSBS values obtained by applying resin composite on RetroMTA after different setting times (24 h > 12 min > 3 min). The µSBS obtained for the Biodentine-resin composite at the end of the 3 min setting time is significantly lower (p < 0.05) than the µSBS values at 12 min and 24 h. For both calcium silicate cements, at the end of all time periods, the µSBS obtained when resin composite was applied at the end was higher than the other materials (p < 0.05). Conclusions: For Biodentine-resin composite bonding, the manufacturer’s recommendation of 12 min can be considered an appropriate time, whereas for RetroMTA-resin composite bonding, the µSBS increased as the waiting time increased. Regardless of the waiting time, it is recommended to prefer direct composite resin restoration over Biodentine and RetroMTA.

The temperature changes, chemical agents, and brushing activity that resin composite restorations are exposed to in the oral environment can cause changes in surface roughness. In this study, the aim was to investigate in vitro the clinical one-year surface roughness changes of different types of composites (flowable or conventional) from the same companies by subjecting them to immersion in solutions, brushing, and thermal cycling procedures to simulate intraoral conditions. Four different resin composite brands were included in the study using both their conventional (Charisma Smart, 3M Filtek Ultimate Universal, Omnichroma, Beautifil II) and flowable resin composites (Charisma Flow, 3M Filtek Ultimate Flowable, Omnichroma Flow, Beautifil Flow Plus F00), giving 4 groups with 2 types of resin composite in each. 40 samples were prepared for each group/resin type, for a total of 320 samples. After initial surface roughness measurements by a mechanical profilometer, the samples were divided into 4 subgroups (n = 10) and immersed in solutions (distilled water, tea, coffee, or wine) for 12 days. The samples were then subjected to 10,000 cycles of brushing simulation and 10,000 cycles of thermal aging. Surface roughness measurements were repeated after the procedures. For statistical analysis, the 3-way analysis of variance and the Tukey test were used (p < 0.05). It was concluded that composite groups and types had an effect on surface roughness at time t0 (p < 0.001). At time t1, the highest surface roughness value was obtained in the Beautifil-conventional interaction. When the surface roughness values between time t0 and t1 were compared, an increase was observed in the Beautifil II and Beautifil Flow Plus F00, while a decrease was observed in the other composite groups. Composite groups, types, and solutions had an effect on the surface roughness of resin composites. After aging procedures, it was concluded that the Beautifil group could not maintain the surface structure as it exceeded the threshold value of 0.2 μm for bacterial adhesion.

Background: This study aimed to evaluate the long-term color stability of single-shade composite resins when exposed to simulated intraoral conditions, including staining, brushing, and thermal cycling. Additionally, the study compared the performance of spectrophotometry and cross-polarized (CP) photography in detecting color changes, focusing on their applicability for both clinical and research purposes. Materials and methods: The study employed five single-shade composite resins (Omnichroma; OMN, Zenchroma; ZNC, Vittra APS Unique; VTR, Charisma One; CHR, and Essentia Universal; ESU) and one multi-shade composite resin (Filtek Z550: FLT) for testing. The specimens were subjected to thermal cycling, staining, and brushing to simulate intraoral conditions. Color measurements were conducted using a spectrophotometer and CP photography at the initial baseline (t₀) and following each subsequent procedure 10-day (t₁) and 1-year simulated staining, brushing and thermal cycling (t₂). Color differences (ΔE₁, ΔE₂) were calculated using the CIEDE2000 formula. Statistical analyses included Shapiro-Wilk for normality, ANOVA and paired t-tests for parametric data, and Kruskal-Wallis and Wilcoxon tests for non-parametric data. Method consistency was evaluated with the Intra-Class Correlation Coefficient (ICC) (p < 0.05). Results: All composite groups demonstrated statistically significant color changes following the simulated conditions (p < 0.001). The CHR group exhibited the highest values for both ΔE₁ and ΔE₂, indicating the greatest degree of discoloration. The FLT and ZNC groups exhibited the lowest ΔE values across methods at various time points. A positive correlation was identified between spectrophotometer and CP photography measurements for all parameters (p < 0.001), although the correlation for ΔE₁ and ΔE₂ was less robust. Conclusions: Single-shade composites display a high susceptibility to significant discoloration when subjected to simulated intraoral conditions, with CHR exhibiting the most pronounced alterations. Both spectrophotometry and CP photography were effective in assessing color stability, with CP photography offering a practical alternative for clinical settings. These findings offer insight into the aesthetic durability of single-shade composites and underscore the importance of long-term evaluations.

The degree of monomer conversion (DC) values of three different dental composites were examined using three different methods: surface microhardness (ratio of bottom/top), Fourier-transform infrared (FT-IR), and differential scanning calorimetry (DSC). Two of the dental composites included in the study were nanohybrid (Dentsply Neo Spectra ST HV and Omnichroma), and one was a microhybrid-labeled newly marketed composite containing nanoparticles (Dentac Myra). Composite discs were prepared according to the methodology for all methods and analyzed (2 mm thickness × 5 mm diameter). Surface microhardness values were measured in Vickers Hardness Number (VHN), while FT-IR and DSC values were obtained in percentage (%). Significant differences were observed in both bottom/top surface microhardness values and DC values obtained from FT-IR. However, there was no statistical difference in the ratio of bottom/top microhardness values. Neo Spectra ST HV exhibited superior performance in both microhardness and monomer conversion compared to the other two composites. Newly marketed Myra showed values close to Omnichroma. It was found that the values obtained by the DSC method were parallel to those obtained by FT-IR. In conclusion, the structure of dental composites leads to different mechanical properties. Additionally, DSC measurements and FTIR spectra were found to be complementary techniques for characterizing monomer conversion values.