Effect of different surface treatments and resin cements on bond strength and fatigue failure load of a glass ceramic:

Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPqThe aim of the present study was to evaluate the effect of different surface treatments and resin cements on bond strength and mechanical behavior of a zirconia reinforced lithium silicate ceramic (ZLS). For the micro-shear bond strength test, the ZLS blocks were cut into rectangular (1 × 14 × 12 mm) slices, embedded in acrylic resin and divided according to the study factors (n = 36): “surface treatment” (hydrofluoric acid etching 5%- HF; application of a self-etching primer- EP and sandblasting with silica coated aluminum oxide particles- SB) and “resin cements” (MDP-free cement - nMDP; MDP-containing cement - MDP; and self-adhesive cement - SA). After the surface treatments, the different cements were applied inside starch tubes on the ceramic and photopolymerized. Twenty-four hours after the cementation, all specimens were thermocycled (5-55°C, 5,000 cycles). Subsequently, the wire-loop micro-shear test was carried out. Statistical analysis was performed using Kruskal-Wallis and post-hoc Dunn tests. For the fatigue test, ceramic discs (diameter- Ø = 10 mm, thickness = 1.5 mm) and discs of dentin analog material (Ø = 10 mm, thickness = 20 mm) were made and divided according to the factors of the study (n = 15) described above. The discs were cemented, thermocycled and submitted to the fatigue test (Step-wise), starting with a load of 400N at a frequency of 20Hz for 10,000 cycles for step, plus 100N for step. Statistical analysis was performed using Kaplan-Meier and Mantel-Cox (Log Rank) tests (p < 0.05). For the bond strength test, considering the type of surface treatment, the HF and the EP provided higher values of bond strength with the self-adhesive cement, and the SB with the conventional resin cement and the self-adhesive cement. Considering the type of cement, the MDP-free conventional one showed better results with the HF or SB treatments and the MDP-containing and the self-adhesive cements performed better results with HF etching. Regarding the fatigue test, the surface treatment with hydrofluoric acid and ceramic primer showed values of load and number of cycles for failure statistically similar and higher than the sandblasting, regardless of the type of cement. When only the surface treatment was considered, the best cement for hydrofluoric acid and sandblast surface treatments was self-adhesive cement. There was no difference between the cements for the ceramic treatment with the self-etching primer.O objetivo do presente estudo foi avaliar o efeito de diferentes tratamentos de superfície e cimentos resinosos na resistência de união e no comportamento mecânico de uma cerâmica a base de silicato de lítio reforçada por zircônia. Para o teste de resistência de união ao microcisalhamento, blocos de cerâmica (18 × 14 × 12) foram cortados em fatias de formato retangular (1 × 14 × 12 mm), embutidos em resina acrílica e divididos de acordo com os fatores do estudo (n = 36) “tratamento de superfície” (condicionamento com ácido fluorídrico 5%- HF; aplicação de primer autocondicionante- EP; e jateamento com óxido de alumínio revestido por sílica- SB) e “cimentos resinosos” (cimento convencional sem MDP - nMDP; cimento convencional com MDP- MDP; e cimento autoadesivo- SA). Após os respectivos tratamentos de superfície, os cimentos foram aplicados dentro de matrizes de tubos de amido sobre a cerâmica e fotopolimerizados. Esperou-se 24 horas e realizou-se a termociclagem (5-55°C; 5 mil ciclos) de todos os espécimes. Posteriormente, foi realizado o teste de microcisalhamento pela técnica do fio (wire-loop). Os dados foram submetidos aos testes de Kruskal-Wallis e posthoc Dunn. Para o teste de fadiga foram confeccionados discos cerâmicos (diâmetro (Ø)= 10 mm, espessura= 1,5 mm) e de material análogo de dentina (Ø= 10 mm, espessura= 2,0 mm), os quais foram divididos de acordo com os fatores do estudo (n=15) acima descritos. Todos os discos foram cimentados, termociclados e submetidos ao teste de fadiga (Step-wise) iniciando com uma carga de 400N, à uma frequência de 20Hz por 10.000 ciclos por etapa, com acréscimo de 100N por etapa. A análise estatística foi realizada com testes de Kaplan-Meier e Mantel-Cox (Log Rank) (p