effect of internal taper of endocrown preparation on the adaptation of 3d-printed restorations

Objective: this study aimed to evaluate the influence of different internal taper angles in endocrown preparations on the marginal and internal adaptation of 3d-printed restorations.methods: three standardized mandibular first molar models were prepared with internal taper angles of 6°, 10°, and 22°. each model was scanned 12 times, and endocrown restorations were digitally designed and fabricated with a 3d printer using freeprint® temp resin. all restorations were seated by a single operator, and the adjustment time and frequency were recorded. adaptation was assessed using the replica technique, and marginal, axial, pulpal, and axio-pulpal line angle gaps were measured under a stereomicroscope. data were analyzed using one-way anova and tukey’s post-hoc test at the significance level of p<0.05.results: the pulpal gap was significantly larger in the 22° taper group compared to both the 6° (p<0.001) and 10° (p=0.001) groups. the 6° taper group exhibited significantly greater marginal misfit than the 10° (p=0.035) and 22° (p=0.021) groups. the axio-pulpal line angle misfit was significantly higher in the 22° taper group than in the 6° group (p=0.016). no significant difference was observed in axial misfit among the groups (p=0.169). notably, the 22° taper group required significantly less adjustment time and fewer adjustment attempts than the other groups (p<0.05).conclusions: all three taper angles yielded restorations with clinically acceptable adaptation. increasing the internal taper from 6° to 22° improved marginal fit and reduced clinical chairside adjustments; however, it resulted in a deterioration of pulpal adaptation.