In vitro dentin pretreatment: surface roughness and adhesive shear bond strength

The aim was to define the morphology and roughness of dentin from different tooth areas after various pretreatments to identify the effect of hybrid layer, resin tags, and mineralised dentin surface on shear bond strength. Thirty-eight extracted molars were used, each providing two sections of cervical (c) and lateral (l) dentin. Five pretreatments were performed: A) 0.2% EDTA; B) abrasion with Al2O3 particles, 0.2% EDTA; C) 10% H3PO4; D) 10% H3PO4 and immersion in a collagenase solution; E) control: no treatment. Z100 composite resin cylinders were bonded to the specimens with All Bond 2 bonding resin and tested for shear bond strength. Twelve other specimens from each group were analysed with an optical profilometer and an atomic force microscope, and four were further examined by scanning electron microscopy (SEM). Mean shear strength values in MPa were: Ac: 8.36 +/- 4.23; Al: 8.77 +/- 3.68; Bc: 6.05 +/- 3.62; Bl: 8.39 +/- 4.60; Cc: 6.87 +/- 3.45; Cl: 9.00 +/- 5.62; Dc: 13.30 +/- 5.45; Dl: 8.44 +/- 4.47; Ec: 4.10 +/- 1.54; El: 6.09 +/- 4.34. No statistically significant difference for cervical versus lateral dentin was found within treatments except for group D. Treatments performed on lateral dentin did not differ significantly. In cervical dentin, A differed from E; C from E; and D from A, B, C and E. An increased surface roughness was found in group D. Shear bond strength to dentin did not seem to depend on a hybrid layer formation, but on the direct contact of the adhesive with the mineralised dentinal surface and partly on the orientation of the dentinal tubules.