Effect of finish line locations on the marginal and internal adaptations of 3D-printed interim restorations: a micro-CT evaluation

The accuracy of digital impressions is critical to the success of prosthodontic treatment, and finish line location is one of several factors reported to influence intraoral scanner (IOS) accuracy. However, evidence on whether finish line location affects the resulting marginal and internal adaptation of definitive restorations remains controversial. This study aims to evaluate how different finish line locations affect the marginal and internal adaptation of 3D-printed interim crowns produced from intraoral digital impressions. Three right maxillary first molar typodont teeth were prepared for single crowns with different finish line locations: 0.5 mm supragingival, equigingival, and 0.5 mm subgingival margins. The prepared teeth were scanned ( n = 10) using the Medit i700 intraoral scanner. Interim crowns were digitally designed, 3D-printed, and post-processed. The marginal and internal adaptation, as well as volumetric space, were analyzed using non-destructive micro-CT scanning. Then, the precision of fit measurements in the volumetric and linear aspects were assessed. Results were statistically analyzed by the Kruskal-Wallis test with Dunn’s adjustment for multiple comparisons ( p < 0.05). The marginal and internal adaptations and volumetric space values were comparable across the three finish line locations, with no statistically significant differences among groups at any measurement site ( p > 0.05). Marginal, finish line, and central fossa gaps trended slightly lower for the supragingival group, and axial wall gaps trended lowest for the equigingival group, but these differences did not reach significance ( p > 0.05). Median volumetric space was 12.67 (IQR 1.89) mm³, 12.85 (IQR 2.34) mm³, and 13.30 (IQR 2.09) mm³ for the supragingival, equigingival, and subgingival groups, respectively ( p > 0.05). Within the specific scanning and fabrication workflows tested, no statistically significant differences in the marginal and internal adaptations of the 3D-printed interim crowns were observed among the different finish line locations.