Shear bond strength to dentine of dental adhesives containing hydroxyapatite nano-fillers

Abstract

The aim of this study was to compare the effect of hydroxyapatite (HAP) nano-rods (HAP rods) and HAP nano-sticks (HAP sticks) added to commercial adhesives on the macro-shear bond strength (SBS) to dentine and morphology of the adhesive-dentine interface. HAP was added to Single Bond Universal (SBU, 3M ESPE) and Te-Econom Bond (TeE; Ivoclar Vivadent), in the form of water suspensions to avoid agglomeration of nano-particles and to achieve HAP concentrations of 0.5, 1.0 and 1.5 wt%. Following a 'total-etch' or a 'self-etch' protocol, the adhesives were applied to flat dentine surface of 162 intact human, third molars (N = 6/group). Composite (Z250, 3M ESPE) was built-up using a split stainless steel mould, 3 mm in diameter. SBS was tested using a universal testing machine at 1 mm/min until fracture. Data were statistically analysed using two-way and one-way analysis of variance with Tukey's post-test (alpha = 0.05). HAP(rods) had no significant effect on SBS of the tested adhesives while HAP(sticks) improved bond strength to dentine only of adhesives applied following the 'total-etch' total-etch protocol. SBS values of SBU containing 1% HAP(sticks) (15.10 +/- 2.96 MPa) and TeE containing 0.5% HAP(sticks) applied following the total-etch protocol (12.96 +/- 4.48 MPa) were higher than those of their respective control groups (10.36 +/- 2.68 and 7.97 +/- 3.64 MPa). Samples with higher SBS showed more 'mixed' failures. HAP nano-fillers may improve bond strength of total-etch adhesives without an adverse effect on adhesive dispersion on dentine and its ability to infiltrate dentinal tubules.