Marginal adaptation and fracture resistance of milled and 3D-printed CAD/CAM hybrid materials of dental crowns with various occlusal thicknesses

Purpose To evaluate the marginal adaptation and fracture resistance of three computeraideddesign/computer-assisted manufacturing hybrid dental materials with different occlusal thicknesses.Methods Ninety single-molar crowns were digitally fabricated using a milled hybrid nanoceramic (Cerasmart, CE), polymer-infiltrated ceramic network (PICN, Vita Enamic, VE), and 3D-printed materials (Varseosmile, VS) with occlusal thicknesses of 0.8, 1, and 1.5 mm (10 specimens/group). Anatomical 3D-printed resin dies (Rigid 10K) were used as supporting materials. A CEREC MCX milling unit and a DLP-based 3D printer, Freeform Pro 2, were utilized to produce the crown samples. Before and After cementation with self-adhesive resin cement, the marginal adaptation, absolutemarginal discrepancy (AMD), and marginal gap (MG) were assessed using micro-CT scanning. Fracture resistance was evaluated using a universal testing machine. The number of fractured crowns and the maximum fracture values (N) were recorded. Datawere statistically analyzed using both one- and two-way ANOVA, followed by Tukey’s honestly significant difference (HSD) test. Results: For all occlusal thicknesses, the VS crowns demonstrated the lowest AMD and MG distances, significantly different from those of the other two milling groups(P<0.05), whereas CE and VE did not differ significantly (P>0.05). All VS crowns were fractured using the lowest loading forces (1480.3±226.1 to 1747.2±108.7 N). No CE and 1 and 1.5 mm VE crowns fractured under a 2000 N maximum load.Conclusions All hybrid-material crowns demonstrated favorable marginal adaptation withina clinically acceptable range, with 3D printing yielding superior results to milling. All materials could withstand normal occlusal force even with a 0.8 mm occlusal thickness.