Aspectos mecânicos e topográficos relacionados às características de superfície e adesivas de diferentes cerâmicas odontológicas

Abstract

The present thesis composes four scientific articles that evaluate the mechanical characteristics of dental ceramics related to their microstructural and adhesive characteristics after bonding and aging. The first study shows the mechanical behavior to fatigue and impact test of five ceramics (feldspathic, lithium disilicate, lithium silicate, polymer infiltrated ceramic network, and zirconia) when polished and when submitted to CAD/CAM (Computer- Aided Design/Computer-Aided Manufacturing) milling simulation (as-milled). Specimens of each material were prepared for fatigue (12×12×1.2mm3, n=15, Stepwise) and impact (15×10×2mm3; n=15) tests, and were polished (sandpaper #2500-grit) or ground (sandpaper #60-grit) simulating CAD/CAM. Analysis of roughness, topography, fractography, finite elements and Pearson correlation (roughness vs. impact and fatigue data) were performed. Greater roughness was generally correlated with material lower resistance to fatigue and impact. Simulation of CAD/CAM milling significantly increased the materials roughness and reduced fatigue performance and impact resistance. The second article investigated the effect of etching a feldspathic ceramic with hydrofluoric acid (HF: HF10%/1min) and thermocycling (Tc:5-55°C/12,000 cycles) on its fatigue failure load when cemented to the dentin-like material (G10) using two different cements. Ceramic specimens (Ø=10mm; thickness=1mm) and G10 (Ø=10mm; thickness=2.5mm) were prepared and divided according to three factors: HF (without; with), cement (self-adhesive- RelyX U200, conventional- Multilink Automix), Tc (without; with). The Staircase fatigue test (n=20; 250,000 cycles;20Hz), the contact angle, topography and fractography analyses were performed. The HF plus the silane application provided greater wettability to the ceramic, but without improving the fatigue data. When the ceramic was conditioned with HF there was significant mechanical reduction after thermocycling, regardless of the cement. The last two articles aimed to investigate the effect of different cementation protocols on the fatigue strength of a monolithic zirconia cemented on G10 with and without aging. The zirconia (Ø=10mm; thickness=0.7mm) and G10 (Ø=10mm; thickness=2.8mm) specimens presented equal dimensions in both works. In the first, the zirconia was sandblasted (45μm aluminum oxide) and cemented in G10 with four different cements [ionomeric, self-adhesive resin cement, conventional resin cement with monomer-phosphate (MDP) in the primer, and conventional resin cement with MDP in the cement] and the fatigue test (n=20; Staircase) was performed. The ionomeric cement resulted in a lower fatigue resistance, and the conventional resin cement with MDP in the primer performed better. Tc did not reduce fatigue load values. In the last article, the fatigue resistance of monolithic zirconia was evaluated under three factors: zirconia treatment (AO-sandblasting with aluminum oxide or TTtribochemical treatment); conventional resin cement (without or with MDP); aging (without or with: Tc + 60 days in water). Cementation (zirconia/G10), aging and the fatigue test (n=20; Staircase) were performed. The fatigue performance of specimens sandblasted with AO and cemented with MDP-containing cement was significantly reduced after aging. In the works involving cementation, the fractographic analyses detected that all failures (as radial cracks) had origin in the ceramics’ intaglio surface. It is concluded that the roughness, surface treatment, cementation system and aging can influence the mechanical behavior of dental ceramics.