Mod cavity restorations with excessive material loss: Comparison of marginal adaptation and fracture strength of new generation resin materials

Aim: The aim of this study was to evaluate the before and after aging marginal adaptation and post-aging fracture strength of new generation restorative materials used for the restoration of class II MOD cavities in molar teeth with excessive material loss. Significance: Direct composite restorations have a very important place in contemporary dentistry. However, restoration fractures, discolorations, and tooth-filling separations in clinical practice limit the effectiveness of these restorations. This study will compare materials that promise high strength and longevity in clinical practice, and contribute to the literature with the data obtained. Materials and Methods: In this study, 65 extracted human mandibular molar teeth were used. Teeth were randomly divided into 5 groups (n=13) as control (no procedure) and four different restorative materials (G-aenial Posterior, G-aenial Universal Injectable, EverX Flow, EverX Posterior). Except for the control group, mesio-occluso-distal (MOD) cavities with 5mm vertical depth and 2.5mm buccal-lingual wall thickness were prepared. After the applications of universal adhesive agent (G-premio Bond (GC, Tokyo Japan)), to the cavity surfaces roughened with the selective-etch method, the teeth were restored with composite resin materials according to the manufacturer's instructions. Then, the samples were aged in thermal cycling and chewing simulators. The samples were examined with SEM at 150X magnification before and after aging to evaluate marginal adaptation. After aging, the samples were subjected to fracture strength test with Universal Testing Machine (Instron. Canton, MA, USA) and the deformation and fracture values were recorded. The data obtained from the marginal adaptation analysis were analyzed with two-way ANOVA, and the data obtained after the fracture test were analyzed with one-way ANOVA. Between-group comparisons were made with Tukey's multiple comparison test. The restorability of the fractured samples was analyzed with the Chi-square test (p<0.05). Results: Significant difference were observed in the marginal adaptation analyses of the different types of composite resins used before and after aging (p<0.05). According to the fracture test results, EverX Flow showed significantly higher strength than G-aenial Universal Injectable composite resin (p<0.05). According to the fracture type analysis, the most restorable fracture was seen in EverX Posterior and the least restorable fracture was seen in G-aenial Posterior, but this was not statistically significant (p>0.05). Conclusion: The fiber-reinforced flowable composite resin used in the study showed better fracture strength than other composite resins. The choice of composite resin material has a significant effect on marginal adaptation but no significant effect on fracture type. The use of fiber-reinforced materials in composite resin restorations of molar MOD cavities with excessive material loss significantly increases the compressive strength. Keywords: Fracture strength, marginal adaptation, bulkfill composite, fiber reinforced composite, SEM