RESUMO
Background To obtain prolonged clinical success with composite restorations, better bonding of resin to the tooth substrate is crucial. Aim The study was aimed to evaluate the microtensile bond strength (µTBS) of bulk-fill composite resin restorations when bonded to a cavity previously restored with amalgam, comparing with that of freshly prepared dentin. Materials and method Mesio-occlusal cavity preparations were done on 80 extracted human mandibular molars with a buccolingual width of 4 mm and a 1.5 mm axial depth by placing the gingival seat 0.5 mm coronal to the cementoenamel junction (CEJ) and were restored with fine-grain amalgam alloy. After thermocycling, the amalgam restorations were removed. Disto-occlusal cavities with similar dimensions of mesial cavities were prepared, and both the proximal surfaces were filled with bulk-fill composite using either etch-and-rinse or self-etch adhesives. Following thermomechanical cyclic loading, all the teeth were sectioned for µTBS testing. Bond strength data expressed in megapascals (MPa) were subjected to statistical analyses using analysis of variance (ANOVA) and Tukey's multiple post-hoc tests. Results The total-etch adhesive exhibited statistically higher bond strength values to both dentin substrates compared to self-etch adhesives (p<0.05). Failure mode analysis reported more of adhesive failures. Conclusion The µTBS of bulk-fill composite resin restorations bonded to a cavity previously restored with amalgam was significantly lower than that of freshly prepared dentin. Total-etch adhesives bond strength was higher than self-etch adhesives to both the substrates tested.
RESUMO
AIM: The aim is to assess and compare the mineral gain and penetration depth of hydroxyapatite and silica nanoparticle infiltrates into artificially created erosive lesions of enamel and dentin. MATERIALS AND METHODS: Sixty extracted human molars were sectioned to obtain enamel and dentin samples (n = 60 each). They were demineralized using citric and formic acid, respectively, to create erosive lesions on enamel and dentin surfaces. Samples were assigned into nanohydroxyapatite (nHA) or nanosilica groups (n = 30 each) according to the infiltrant used. Half of the enamel and dentin samples in each group (n = 15) were analyzed after erosive attack for mineral loss, after infiltrant application for mineral gain, using energy-dispersive X-ray spectroscopy. In another half of the enamel and dentin samples (n = 15), the penetration depth of the nanoinfiltrants was analyzed using confocal microscopy. STATISTICAL ANALYSIS: To compare the overall mineral gain between groups, a dependent t-test was applied. The intergroup comparisons were made using one-way ANOVA followed by Tukey post hoc test for pairwise comparisons for both penetration depth and mineral gain. The significance level was set to P ≤ 0.05. RESULTS: The mineral gain in enamel was not statistically different between nHA and nanosilica infiltrants (P = 0.9950). nHA infiltrated dentin showed significantly more mineral gain (P = 0.0001) than nanosilica infiltrant. The depth of penetration of the nHA in enamel was statistically greater than that of nanosilica, but in dentin, the difference was not significant. CONCLUSION: nHA infiltrant performed better in mineral gain, and penetrated deeper into the demineralized erosive lesions, compared to nanosilica infiltrant in both enamel and dentin. The highest mineral precipitation and deeper penetration into both demineralized enamel and dentin was observed with nHA infiltrant compared to (as against) nanosilica infiltrant.
