Inner marginal strength of CAD/CAM materials is not affected by machining protocol

PURPOSE: Here we aimed to compare two machining strategies regarding the marginal strength of CAD/CAM materials using a hoop-strength test in model sphero-cylindrical dental crowns, coupled with finite element analysis. MATERIALS AND METHODS: Five CAD/CAM materials indicated for single posterior crowns were selected, including a lithium disilicate (IPS e.max(®) CAD), a lithium (di)silicate (Suprinity(®) PC), a polymer-infiltrated ceramic scaffold (Enamic(®)), and two indirect resin composites (Grandio(®) Blocs and Lava™ Ultimate). A sphero-cylindrical model crown was built on CAD Software onto a geometrical abutment and machined using a Cerec MC XL system according to the two available protocols: rough-fast and fine-slow. Specimens were fractured using a novel hoop-strength test and analyzed using the finite element method to obtain the inner marginal strength. Data were evaluated using Weibull statistics. RESULTS: Machining strategy did not affect the marginal strength of any restorative material tested here. Ceramic materials showed a higher density of chippings in the outer margin, but this did not reduce inner marginal strength. IPS e.max(®) CAD showed the statistically highest marginal strength, and Enamic(®) and Lava™ Ultimate were the lowest. Grandio(®) Blocs showed higher performance than Suprinity(®) PC. CONCLUSIONS: The rough-fast machining strategy available in Cerec MC XL does not degrade the marginal strength of the evaluated CAD/CAD materials when compared to its fine-fast machining strategy. Depending on the material, resin composites have the potential to perform better than some glass-ceramic materials.