Retenção de coroas de zircônia: estudo de diferentes condições de tratamento interno de coroas em zirconia e do núcleo em resina composta

Abstract

The present thesis was structured in two scientific articles that investigated the adhesion of zirconium oxide ceramic crowns. The first article aimed to evaluate different methods for silica deposition at the inner surface of Y-TZP crowns by means of a retention test. A hundred simplified full-crown preparations obtained from fiber-reinforced polymer were scanned and 100 zirconium oxide crowns with occlusal retention were machined. The preparation/crown assemblies were randomly divided in 5 groups according to the inner surface treatment: TBS – tribochemical silica coating with silica-coated alumina particles (30 μm); GHF1 – application of a thin glaze layer + hydrofluoric acid for 1 min; GHF5 – glaze application + hydrofluoric acid for 5 min; GHF15 – glaze application + hydrofluoric acid for 15 min; and Nano – silica nanofilm deposition (5 nm) via magnetron sputtering. All groups received silane coupling agent application. The preparations surfaces were etched with 10% hydrofluoric acid for 30 s and silanized. Crowns were cemented with resin cement, thermocycled (12.000 cycles; 5 / 55 °C), stored for 60 days and submitted to retention test (0.5 mm/min until failure). Retention data (MPa) were statistically analyzed by one way– ANOVA and Tukey test, as well as Weibull analysis. Failures were classified as 50C (above 50% of cement in the crown) and 50S (above 50% of cement on the substrate). TBS (5.6 ± 1.7 MPa) and Nano (5.5 ± 1 MPa) groups showed higher retention values than the other groups (p<0.0001), as well as higher characteristic strength (6.18 e 5.91, respectively). There was no difference for Weibull modulus, except for GHF1 group, which showed statistically inferior value. TBS and GHF15 presented, respectively, 60% and 70% of the failures classified as 50C, while the other groups had 50S as most part of the failures. Air-abrasion with silica-coated alumina particles and silica nanofilm deposition on the inner surface of Y-TZP crowns generated higher retention values. The second article evaluated the retention of zirconia crowns cemented to aged composite cores and prepared with burs of different grit sizes. Sixty simplified full-crown preparations were fabricated with composite resin and scanned. Sixty zirconium oxide crowns with occlusal retention were machined. The composite resin cores were stored for 120 days in humid environment at 37 °C and randomly divided in 3 groups (n=20) according to the finishing of the composite resin core: CTRL (control) – no treatment; EFB – extra-fine diamond bur (25 μm); and CB – coarse diamond bur (107 μm). Superficial grinding was performed with an adapted surveyor to standardize speed and pressure. The inner surfaces of the crowns were air-abraded with silica-coated alumina particles (30 μm) and a silane coupling agent was applied. Crowns were cemented with a self-adhesive resin cement (RelyX U200). Then, the assemblies core/crown were thermocycled (12.000 cycles; 5/55°C), stored for 120 days and submitted to retention test (0.5 mm/min until failure). Tesile date (MPa were analyzed by one way- ANOVA and Tukey test (p≤0,05), as well as Weibull analysis. Failures were classified as 50C (above 50% of cement adhered in the crown), 50S (above 50% of cement adhered on the resin substrate) and COE (cohesive failure of the core). No statistical difference was observed for the retention values (p=0.975), but the control group (CTRL) showed higher Weibull modulus. The predominant failure mode was 50S. The occurrence of cohesive failures was higher on the control group. Retention of the zirconium oxide crowns was not affected by the core roughness. It was concluded that air-abrasion followed by silane application and silica nanofilms deposition improve the retention of zircônia crowns, as well as finishing of resin cores with diamond burs does not influence the retention of zirconia crowns.