Aim:
This study aimed to evaluate the marginal adaptation of 3D printed crowns with either horizontal or vertical margin preparations, scanned with an IOS (3Shape), showing an accuracy of 5 µm, at standardized environmental conditions.

Methods:
Two maxillary first premolar abutments were designed using CAD software, one with a horizontal preparation (Ho) and the other with a vertical preparation (Ve). Both abutments had a 5 degree angle of TOC (Total occlusal convergence); they were 3D printed in resin, and then mounted on a reference typodont. Ten crowns were fabricated for each preparation geometry using the DFAB 3D printer (DFAB CHAIRSIDE, Thiene, Italy). Cementation was simulated with polyether impression material, and then the crowns were scanned with an industrial metrological device (Atos Core 80; GOM GmbH, Germany). Finally, the scans were analyzed using a dedicated software (Geomagic Control X, Raindrop Inc., USA) to assess the marginal fit. Descriptive statistics (95% confidence interval) were calculated, and an independent samples t-test was performed at a significance level of α = 0.05 to compare differences between groups.

Results:
Mean marginal fit values for both preparation geometries were below the clinically acceptable threshold of 120 µm, with Ho at 76.83 µm and Ve at 84.37 µm. No statistically significant difference was found between the two groups (Ho p = 0.58; Ve p = 0.83).

Conclusions:
Nanocomposite crowns fabricated via 3D printing showed mean marginal discrepancies within clinically acceptable limits for both vertical and horizontal preparation geometries, with no significant difference between the two.