In-vitro comparison of the fracture strength of onlay restorations produced with different CAD/CAM materials

Indirect aesthetic posterior restorations are treatment options that serve as a good alternative to full crowns in posterior tooth groups where a significant amount of dental tissue has been lost. Restorations such as inlays, onlays and overlays are frequently preferred within the treatment options for restoring posterior teeth, also meeting aesthetic expectations to a large extent. The aim of our study is to investigate the fracture resistances of onlay and overlay restorations produced using different CAD/CAM materials and different preparations after thermal aging. Following the fracture resistance test, fracture types were classified, and the images obtained from the fracture surfaces under electron microscopy were evaluated. In our study, onlay and overlay restorations were produced using VarseoSmile Crown Plus, Vita Enamic, and VitaBlocs Mark Ⅱ materials. After applying thermal aging processes to the onlay and overlay restorations obtained through additive and subtractive manufacturing methods, the fracture resistances of the restorations were evaluated. The fracture surfaces were analyzed using a stereomicroscope and classified into four types. Type I indicated restoration fracture only, Type II indicated restoration and enamel fracture, Type III indicated restoration, enamel, and dentin fracture, and Type IV indicated crown-root fracture. A detailed analysis of the fracture surfaces was performed using SEM. Statistical analyses were conducted using IBM SPSS Statistics for Windows, Version 25.0 (Armonk, NY: IBM Corp.). Descriptive data were presented as mean and standard deviation values. The normality of data distribution was assessed using the Shapiro-Wilk test. Since data followed a normal distribution, two-way ANOVA and Bonferroni correction were used for comparisons between groups. A p-value of <0.05 was considered statistically significant. The highest average fracture resistance was observed in the VSC Overlay group, while the lowest fracture resistance values were found in the VBM Onlay group. The highest average fracture resistance values for onlay and overlay restoration groups were seen in the VSC groups. The effect of different materials on fracture resistance values was found to be statistically significant (p<0.05). The effects of different preparation types on fracture resistance values were also statistically significant (p<0.05).