Effect of preparation design on the fracture behavior of 3D-printed restorations in an in-vitro tooth wear model

Additive manufacturing technologies have introduced new nanohybrid resin composites for permanent indirect restorations. However, limited evidence exists regarding the mechanical performance of 3D-printed restorations in managing occlusal wear. This study evaluated the effect of preparation design on fracture resistance, preparation time, and failure modes of 3D-printed restorations. Forty maxillary premolars were allocated to four groups (n = 10): sound teeth (ST), overlay (OV), veneerlay (VL), and full crown (FC). Experimental groups received standardized 1.0–1.2 mm occlusal wear simulation. Restorations were designed using CAD software and fabricated with a 3D-printed nanohybrid composite (Rodin Sculpture 2.0). Cementation employed immediate dentin sealing and heated composite resin. Specimens underwent compressive fracture testing in a universal testing machine. Failure modes were categorized as catastrophic and non-catastrophic. One-way ANOVA with Tukey’s post-hoc test and Fisher’s exact test were used (α = 0.05). Preparation design significantly influenced fracture resistance (p < 0.05). OV exhibited the highest mean fracture load (1842.82 ± 560.47 N), which was significantly higher than FC (1236.79 ± 497.59 N). Preparation time increased with the invasiveness of the design (OV < VL < FC; p < 0.05). Catastrophic failures occurred most frequently in the FC group (60%) and were not observed in ST or OV. 3D-printed occlusal veneers demonstrated fracture resistance values that exceeded physiological loading, with overlays providing superior strength and the lowest risk of catastrophic failure. Conservative adhesive preparation designs should be favored over full crowns in the rehabilitation of worn dentition.