Impact of Deep Margin Elevation on Fracture Resistance and Failure Mode of Different Indirect Resin-Based Composite...

To investigate the effect of deep margin elevation (DME) on the fracture resistance and fracture patterns of various indirect resin-based composite materials.

A total of 120 extracted maxillary premolars were prepared with standardized MOD onlay cavities extending 2 mm below the cementoenamel junction. Teeth were embedded in acrylic resin and randomly allocated into 10 groups (n = 12), including two controls (positive and negative) and two experimental groups with or without DME. Onlays were fabricated using four materials: Gradia Plus, Signum Ceramis, Tescera ATL, and Grandio Bloc. All restorations were cemented using adhesive protocols and subjected to thermocycling (5000 cycles, 5°C-55°C). Fracture resistance was tested using a universal testing machine. Fracture types were assessed under a stereomicroscope. Selected samples underwent scanning electron microscopy analysis. Data were statistically analyzed using Shapiro-Wilk, ANOVA, Tukey HSD, t tests, and Chi-square tests.

The highest fracture resistance was found in the intact control group and the lowest in the non-restored group. Among experimental groups, Grandio Bloc without DME showed the highest resistance, while Signum Ceramis with DME showed the lowest. DME did not significantly alter fracture resistance but significantly increased the proportion of restorable fracture types.

DME does not compromise fracture resistance but positively affects fracture patterns, promoting more repairable outcomes. Proper material and adhesive system selection remain crucial for long-term success.

Deep margin elevation enhances the restorable nature of fractures without reducing fracture resistance, offering a viable option in subgingival margin management for indirect composite restorations.