Marginal and internal adaptation and absolute marginal discrepancy of 3D-printed, milled, and prefabricated crowns for primary molar teeth: an in vitro comparative study

Background: The quality of marginal and internal adaptation plays a crucial role in the clinical longevity of pediatric crowns. This study aimed to evaluate the effect of restoration type (3D-printed, milled, and prefabricated) on the marginal and internal adaptation and absolute marginal discrepancy (AMD) values of crowns for primary molar teeth. Methods: Three restoration groups were created: 3D-printed resin, milled resin-matrix ceramic, and prefabricated zirconia crowns (n = 10 per group). A typodont tooth was prepared according to the guidelines for prefabricated zirconia crowns and scanned to design restorations. 3D-printed and milled crowns were fabricated from the same design. All crowns were cemented on standardized 3D-printed resin dies with self-adhesive resin cement. Marginal and internal adaptation and AMD values were evaluated using micro-computed tomography (micro-CT) at multiple measurement points. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey HSD tests, with statistical significance set at P < 0.05. Results: The restoration type significantly influenced the marginal and internal gap and AMD values (P < 0.05). The prefabricated crown group exhibited the highest marginal gap (233.5 +/- 33.4 mu m) and internal gap (538.6 +/- 47.4 mu m). The 3D-printed group showed the highest AMD value (299.5 +/- 70.2 mu m). The milled group demonstrated the lowest gap values, which remained within clinically acceptable limits. Conclusions: Prefabricated zirconia crowns displayed the highest marginal and internal gaps, whereas milled crowns exhibited the most favorable adaptation values within clinically acceptable limits. Given their superior adaptation, CAD-CAM-produced restorations may be a recommendable alternative for pediatric patients.