Effect of the region of the CAD/CAM block on the flexural strength and structural reliability of restorative materials.

Abstract

The aim of the study was to evaluate whether the region (internal or external) of the CAD/CAM block influences the mechanical performance of restorative materials. Blocks of different CAD/CAM materials (Composites: KAV - Katana Avencia; LULT - LULT Ultimate; Ceramics: ENAM - Vita Enamic; NICE - N!CE; EMP - IPS Empress CAD; VMII - Vita Mark II; EMAX - IPS e.max CAD) were selected, and direct resin composite blocks (APX - Clearfil AP-X; FSUP - Filtek Supreme) were built using the incremental technique on a mold from one of the CAD/CAM blocks. All blocks were sectioned into bar-shaped specimens (1 × 1 × 14 mm), which were separated into two groups according to the region of the block (inside or outside). 3-point bending tests were performed following ISO 6872:2015 and flexural strength data were analyzed using one-way ANOVA and Bonferroni post-hoc tests (p < 0.05). Weibull module and characteristic strength were also calculated. In general, the mean flexural strength values were not statistically different (p > 0.05) between the inside and outside regions of each material, except for LULT (inside > outside) and EMAX (outside > inside). Comparing the materials, a similar strength (only discrete variations) was observed for inside, outside or merged (inside and outside data assembled together) regions: EMAX > KAV = LULT > NICE = APX > EMP = ENAM = VMII ≥ FSUP (merged condition). Characteristic strength at 63.2% failure probability and at 5% failure probability generally corroborates such observations. There were no statistical differences for Weibull module data (inside, outside, or merged), except for KAV and NICE (outside > inside). Thus, the region from where the restoration is milled within the CAD/CAM block generally does not influence the mechanical performance hereof (flexural strength, failure probability, risk of premature failures, and mechanical reliability) of the material, except for LULT and EMAX.