Effects of Shallow Retentive Designs on the Fracture Resistance of Resin Nanoceramic Overlays

Objective: This study aimed to assess the impact of two shallow retentive designs on the fracture resistance of maxillary molars restored with resin nanoceramic overlays.Material and Methods: Thirty extracted human maxillary molars were randomly divided into three groups (n=10): an intact control group and two experimental groups with different shallow retentive designs (shallow occlusal canal and shallow central dowel). All preparations included a standardized 1.5-mm occlusal reduction with additional cavity modifications according to the respective design. Overlays were fabricated using a resin nanoceramic and bonded with a dual-cured resin cement. Specimens underwent artificial aging through 5,000 thermal cycles and 120,000 mechanical loading cycles. Fracture resistance under axial compressive loading and failure modes were evaluated. Data were analyzed using one-way ANOVA and Tukey’s post hoc test (p-value=0.05).Results: No cracks or fractures were observed after the cyclic loading. The mean fracture resistance values of the shallow occlusal canal (2,742.88±354.37 N) and shallow central dowel groups (2,807.30±373.03 N) were significantly higher than the control group (2,309.33±341.67 N) (p-value