An in vitro analysis of marginal and internal fit of 3D-printed permanent molar endocrowns with different preparation designs

Objectives The purpose of this study was to evaluate the influence of different preparation designs on the marginal and internal fit of 3D-printed permanent endocrowns. Materials and methods Typodont maxillary right first molars were prepared and divided into four groups based on different preparation designs: Group 1- butt joint with 2 mm pulp chamber depth, Group 2- butt joint with 4 mm depth, Group 3- shoulder with 2 mm depth, and Group 4- shoulder with 4 mm depth (n = 16 each). The prepared teeth were scanned and replicated as 3D-printed resin dies. Permanent endocrowns were fabricated using a ceramic-filled hybrid material and seated with light-body silicone. All restorations were rescanned, and superimposition was performed using 3D analysis software to evaluate marginal, internal, pulp chamber, and overall gaps based on multipoint measurements at standardized locations. Data were statistically analyzed using Two-Way Robust ANOVA (p < 0.05). Results No significant differences were found between preparation types and depths for internal and overall gap values (p > 0.05). However, the highest marginal gap was measured in Group 1 (0.08 mm; p = 0.017), while the largest pulp chamber gap was recorded in Group 4 (0.15 mm; p < 0.001). Conclusions A 1 mm shoulder preparation with a 2 mm pulp chamber depth demonstrated superior marginal and pulp chamber fit compared to other designs. While internal fit did not significantly vary among groups, this design showed the most consistent adaptation overall, supporting its clinical preference for 3D-printed permanent endocrowns. Clinical relevance Different preparation designs may affect the fit of endocrowns. Clinicians can prefer an endocrown preparation design of 1 mm shoulder preparation with a 2 mm pulp chamber to improve the adaptation of 3D-printed permanent endocrown restorations.