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

Abstract

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.