Comparison of Fracture Resistance of Three-Unit Interim Restorations Fabricated by the CAD-CAM Technology With Two Different Milling Machines and the Direct Technique by Using Different Materials.

There is a gap of information regarding the effect of type of milling machine (based on axis number) on mechanical properties of three-unit interim restorations. Thus, this study aimed to compare the fracture resistance (FR) of three-unit interim restorations fabricated by the computer-aided design/computer-aided manufacturing (CAD-CAM) technology with two different milling machines and the direct technique by using different materials. Seventy-two three-unit interim restorations were fabricated on mandibular second molar and second premolar metal dies in six groups ( = 12) according to the fabrication technique and the material used: milling groups with 4-axis (Arum) and 5-axis (Amann Girrbach) milling machines, and direct fabrication groups by using Visalys, Unifast III, Tempron, and Acropars materials. The restorations underwent thermocycling and cyclic loading, and their FR was measured. Data were analyzed by one-way ANOVA and Tukey post hoc HSD test ( = 0.05). Of the directly fabricated restorations, Visalys showed significantly higher FR than other materials ( < 0.05) while Acropars showed the lowest FR. The difference in FR between Unifast III and Tempron was not significant (=0.298). The FR of Amann Girrbach and Arum groups was not significantly different (=0.563) but their FR was significantly higher than the FR of other groups ( < 0.001). Interim restorations fabricated by CAD/CAM milling had higher FR than traditionally fabricated restorations by the direct technique. Number of axes of the milling machine had no significant effect on FR. Visalys (bis-acrylic material) showed superior results.