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  • Title: Long-term bond strength of restorations subjected to thermo-mechanical stresses over time.
    Author: Bedran-De-Castro AK, Pereira PN, Pimenta LA.
    Journal: Am J Dent; 2004 Oct; 17(5):337-41. PubMed ID: 15575444.
    Abstract:
    PURPOSE: To evaluate the long-term effect of thermal and mechanical cycling on dentin bond strength to cervical margins of Class II restorations. METHODS: Sixty Class II slot cavities were prepared in bovine incisors. The cavities were restored with Single Bond and Z-250 composite according to manufacturer's instructions. The teeth were then divided into two groups (n = 30): specimens that would receive thermo-mechanical load cycling (2,000 cycles 5-55 degrees C/100,000 cycles of 50 N loading) (TM) and the control (C). Fifteen specimens from each group were tested at baseline and the remaining 30 specimens were stored in distilled and deionized water at 37 degrees C and tested after 1 year. For microtensile evaluation, the restorations were sectioned perpendicular to the cervical bonded interface into 0.7 +/- 0.2 mm thick slabs. The slabs were further trimmed at the interface to 1.4 < or = 0.2 mm with a fine diamond bur to produce a cross-sectional surface area of ca. 1 mm2. Specimens were then subjected to microtensile bond testing. The bond strength data were analyzed using two-way ANOVA and Fisher's PLSD test (P < 0.05). Fracture mode analysis was performed using SEM. RESULTS: At baseline, bond strength of the TM group was significantly lower when compared to the C group (P = 0.012). However, after 1 year storage, a significant decrease in bond strength was observed for the C group compared to baseline. No significant differences were noted between the C and TM groups at 1 year. No interaction was observed between groups (C and TM) and storage time (P = 0.098). For the fracture mode evaluation, at baseline, mixed failure was predominant for the C group, and increased after TM. Decreased mixed failure was observed after 1-year storage, with a concomitant increase in interphase failure.
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