Influência do substrato no comportamento mecânico em fadiga de cerâmicas odontológicas cimentadas adesivamente

Abstract

Three studies compose this thesis that aims to evaluate the fatigue mechanical behavior of dental ceramics in relation to the different conditions of the substrate to which they were adhesively luted. In the first study, discs (n= 15; Ø= 10 mm; thickness= 0.7 mm or 1.0 mm) of two zirconia-based ceramics (ZR) were cemented on substrates of epoxy resin (ER), resin composite (RC) or metallic alloy (MA) to evaluate the influence of the elastic modulus (E) of the substrate on the fatigue behavior of two generations (2ndg and 3rdg) of ZR with different thicknesses. The specimens were submitted to an accelerated fatigue test (frequency= 20 Hz) with increasing load levels until the presence of cracks or a maximum load of 2800N. ZR cemented onto MA (higher E) presented improved results in both generations and thicknesses. 2ndg ZR had superior fatigue behavior than 3rdg ZR. Regarding the thickness, the 1.0mm specimens had improved results than the 0.7mm only for the 2ndg ZR group. In the second study, discs (n= 15; Ø= 10 mm, thickness= 1.0 mm) of ZR, feldspathic ceramic (FEL), lithium disilicate reinforced glass ceramic (LD) and polymer-infiltrated ceramic network (PICN) were adhesively cemented onto ER or MA substrates, also with the objective of evaluating the influence of the E of the substrate on the fatigue behavior of ceramic restorations. The accelerated fatigue test was performed similarly to the previous study. All the ceramics had better mechanical behavior when cemented onto MA (stiffer material), with LD presenting similar results to ZR, both superior to FEL and PICN. PICN was similar to ZR and DL when they were bonded onto a softer substrate (RC). In this condition, FEL showed lower results than the other materials. Finite Element Analysis (FEA) was performed for the first two studies, corroborating the results found in the fatigue test. The objective of the third study was to evaluate the influence of the surface treatment of the substrate on the fatigue behavior of lithium disilicate ceramics cemented onto the treated RC substrate. RC discs were made to simulate resin composite prosthetic cores and subjected to different surface treatments after the removal of temporary cement. LD discs were adhesively cemented onto the treated substrate discs, and the samples were subjected to a fatigue test (n= 15) with similar methodology to the first two studies, with the load application on the ceramic disc surface. Substrate samples were also submitted to topographic analysis, where different characteristics were found on the surface of the RC substrate, but no protocol influenced the mechanical behavior of LD. Thus, the modulus of elasticity had a positive effect on the fatigue behavior when the ceramic restorations were adhesively cemented onto stiffer substrates, while the thickness of the ceramic discs of the different generations of ZR influence only the mechanical behavior of the second generation of zirconia. The surface treatment of the substrate did not influence the mechanical behavior of the DL ceramic.