The addition of nanostructured hydroxyapatite to an experimental adhesive resin

Objectives: Was produced nanostructured hydroxyapatite (HA(nano)) and evaluated the influence of its incorporation in an adhesive resin. Methods: HA(nano) was produced by a flame-based process and was characterized by scanning electron microscopy. The surface area, particle size, micro-Raman and cytotoxicity were evaluated. The organic phase was formulated by mixing 50 wt.% Bis-GMA, 25 wt.% TEGDMA, and 25 wt.% HEMA. HA(nano) was added at seven different concentrations: 0; 0.5; 1; 2; 5; 10 and 20 wt.%. Adhesive resins with hydroxyapatite incorporation were evaluated for their radiopacity, degree of conversion, flexural strength, softening in solvent and microshear bond strength. The data were analyzed by one-way ANOVA and Tukey's post hoc test (alpha = 0.05), except for softening in solvent (paired t-test) and cytotoxicity (two-way ANOVA and Bonferroni). Results: HA(nano) presented 15.096 m(2)/g of specific surface area and a mean size of 26.7 nm. The radiopacity values were not different from those of 1-mm aluminium. The degree of conversion ranged from 52.2 to 63.8%. The incorporation of HA(nano) did not influence the flexural strength, which ranged from 123.3 to 143.4 MPa. The percentage of reduction of the microhardness after immersion in the solvent became lower as the HA(nano) concentration increased. The addition of 2% nanostructured hydroxyapatite resulted in a higher value of microshear bond strength than the control group (p < 0.05). Conclusions: The incorporation of 2% of nanostructured hydroxyapatite into an adhesive resin presented the best results. Clinical significance: The incorporation of nanostructured hydroxyapatite increases the adhesive properties and may be a promising filler for adhesive resin. (C) 2013 Elsevier Ltd. All rights reserved.