Impact of convergence angle of tooth preparation on the fracture resistance of incisor monolithic zirconia crowns

Purpose To evaluate the effect of convergence angles on the fracture resistance of monolithic zirconia crowns in maxillary central incisors. Materials and Methods A maxillary central incisor preparation was digitally designed with four different angles (0°, 8°, 16°, and 22°). For each group, 10 abutment teeth were manufactured using a 3D printer with photosensitive resin and positioned in a maxillary typodont model for scanning procedures. Anatomically contoured monolithic zirconia crowns were fabricated for each group ( n = 10), 40 crowns in total, using the subtractive manufacturing technique. The crowns were cemented onto their respective abutments using a self‐adhesive resin cement. Fracture resistance testing was conducted using a universal testing machine and the fracture load was recorded in Newtons (N). The obtained data were statistically analyzed using one‐way ANOVA for intergroup comparisons, and Tukey HSD post‐hoc test was applied to identify significant differences among groups ( p < 0.05). Results A statistically significant difference was found among the groups, with fracture resistance varying according to the convergence angle ( p < 0.05). Crowns with 16° angle exhibited the highest values (2897.57 N), followed by 22° (2425.58 N) and 8° (2095.76 N) groups. The lowest value was found at 0° crowns (1830.3 N). Conclusions The results indicated that the convergence angle had a significant effect on the fracture resistance of monolithic zirconia crowns. Instead of preparing parallel axial walls (0°) in central incisors, creating a tapered preparation design with different levels (8°, 16°, or 22°) increased the fracture resistance. Specifically, 16° was related to the greatest fracture resistance. However, the absence of thermocycling and fatigue testing limits the simulation of long‐term clinical performance.