Técnicas de recobrimento cerâmico de infraestruturas de Y-TZP: influência no comportamento mecânico

Abstract

The present study, divided in two articles, aimed to evaluate the influence of veneering ceramic techniques on the mechanical behavior of bilayer ceramic with Y-TZP frameworks. The first paper assessed the effect of the veneering method on the flexural strength and load to failure of Y-TZP by means of a systematic review and meta-analysis. Searches were performed on PubMed/MEDLINE, Web of Science (Core Collection), Scopus and Embase. From 3242 identified articles, 241 were selected for full-text analysis from titles and abstracts reviewing, according to pre-determined eligibility criteria. Thirty-three papers were included in the systematic review, from which 32 were considered in the meta-analyses. A manual search of the included studies did not retrieve additional studies. The control (hand-layered) was compared with pressed, fused and cemented veneering. Considering flexural strength, the meta-analysis comparing hand-layered and pressed methods did not show statistical difference and the two studies evaluating cemented method showed contradictory results, in which one of them favored the hand-layered and the other one favored the cemented technique. Regarding failure load, three meta-analyses were performed: one comparing hand-layered and pressed, one by subgroups for the fused technique in comparison with hand-layered and the other comparing cemented and hand-layered techniques. The results showed statistical equivalence between control and pressed and between control and cemented methods, but fused method with particle-filled glass ceramics was statistically superior to control. It was concluded that fused method with particle-filled glass ceramics represents and appropriate alternative for Y-TZP veneering. The second paper investigated the effect of the veneering technique (fused and cemented) and the side under tension on the fatigue strength of veneered Y-TZP in comparison with monolithic Y-TZP. Discs were fabricated according to the groups: Z: monolithic zirconia, F-FT: fused method with framework under tension, F-VT: fused with veneer under tension, C-FT: cemented method with framework under tension and C-VT: cemented with veneer under tension. Fatigue strength test (n=20) was performed in water using the staircase approach with piston-on-three ball design at 20 Hz and 750.000 cycles, as well as finite element analysis. There was statistical difference among all groups. Fatigue strength means were: Z: 413,92 MPa, F-FT: 345,15 MPa, C-FT: 315,04 MPa, F-VT: 185,18 MPa and C-VT: 96,5 MPa. Finite element analysis predicted values were similar to experimental values. It was concluded that monolithic Y-TZP has higher fatigue strength than the other methods and that the material under tension affects fatigue strength, as well as the fused technique presents higher fatigue strength than the cemented technique.