Tensile strength and microhardness of treated human dentin

Objectives. To determine the ultimate tensile strength and Knoop hardness of mineralized, EDTA-treated, sodium hypochlorite (NaOCl)-treated, EDTA-treated resin-infiltrated, and NaOCl-treated resin-infiltrated dentin. Methods. Dumbell-shaped specimens with a cross-sectional area of 0.5 mm2 were prepared from the crowns of extracted human third molars. Specimens were randomly assigned to the following experimental groups: (1) mineralized dentin; (2) 0.5 M EDTA-demineralized dentin, pH 7/5 days; (3) 5% NaOCl-deproteinized dentin/2 days; (4) EDTA-treated, Single Bond resin-infiltrated dentin; (5) NaOCl-treated, Single Bond resin-infiltrated dentin. All specimens were tested in tension in a Vitrodyne testing machine at 0.6 mm/min. Knoop microhardness was measured on the fractured edges of specimens in groups 1, 3, 4, and 5. Results were analyzed by ANOVA and SNK tests (p<0.05). Results. Both EDTA and NaOCl treatments caused significant reductions in the tensile strength and microhardness of mineralized dentin (p<0.05), with the largest reductions observed after NaOCl treatment (p<0.05). Resin infiltration of treated dentin resulted in moderate increase of its tensile strength and microhardness, however, the original mineralized values were not recovered (p<0.05). Significance. Whenever dentin surfaces are treated with EDTA or NaOCl prior to a clinical bonding procedure, clinicians must be aware that a weak layer may be present at the interface, which may lead to premature failures of resin/dentin bonds.