Bond Durability and Film Thickness of Luting Cement to Ceramic

Objectives: To evaluate the effect of thermocycling (TC) on the microtensile bond strength (µTBS) of two luting agents (LAs) to feldspathic ceramic and measure the film thickness (FT) of the LAs. The null hypotheses were that the µTBS decrease after TC and that the different LAs have different FT. Methods: For µTBS test, sixteen blocks (6.4x6.4x4.8mm) were fabricated using a feldspathic ceramic (Vita VM7), etched with 10% hydrofluoric acid (60 s), rinsed with air-water spray (60 s), air-dried and cleaned ultrasonically in distilled water (5 min). Silane was applied with a microbrush. The ceramic blocks were divided into two groups (N=8), according the type of LAs: Gr1: resin cement (Variolink II), Gr2: flowable resin (Filtek Z350). The blocks were positioned in their individual silicone molds and the LAs applied on the treated surfaces. The ceramic-cement blocks were stored in distilled water (370C; 24h) prior to sectioning. After blocks sectioning, the microsticks (bonded area: 1 mm2) of each block were divided into two storage conditions: dry (D) and TC (6.000 cycles; 5°/55°C). The µTBS was evaluated using a universal testing machine (EMIC) (1 mm/min). The data were submitted to two -way ANOVA and Tukey's test (5%). For the FT test (ISO 4049), 0.05 mL of each LA (N=8) was pressed between 2 Mylar-covered glass plates (15 kg) for 180 s, light polymerized and measured using a digital paquimeter. The data were submitted to one-way ANOVA test. Results: The µTBS mean (MPa) were: dry condition (Gr1:15±4.3; Gr2:13.1±5.5) and after TC (Gr1:21.2±9.3; Gr2:20.7±7.2). It was not observed influence of the LAs on the µTBS (p=0.4467). However, the TC effected significantly the µTBS (p= 0.0001). The LAs presented similar FT (p=0.1203): Variolink II- 0.05±0.01mm; Filtek-0.04±0.003mm). The null hypotheses were rejected. Conclusions: The LAs presented similar FT and µTBS results, in dry and TC conditions.