Effect of air-powder polishing on adhesion of bonding systems to tooth substrates

Abstract

Objectives. The air-powder polisher was introduced to provide a method to quickly remove stains and plaque. The purpose of this study was to evaluate what effect preparing teeth with an air-powder polisher (Air-flow 2, Shofu) has on bonding to enamel and dentin substrates. Methods. The bonding systems used in this study were one-step etching/priming systems (KBT-5, Kanebo; and Clearfil Liner Bond II, Kuraray) and a two-step etching/priming system (Superbond D-Liner Plus, Sun Medical). Bovine enamel and dentin surfaces were prepared and finished with 600-grit silicon carbide paper. Then the surfaces were either not treated (control) or air-powder polished for 15 s. A 4-mm bonding area was demarcated, and the tooth substrates were bonded with the three bonding systems according to the manufacturers' instructions. Tensile bond strengths were measured 24 h after storage in water at 37°C. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses were performed on air-powder polished specimens to determine changes in the surface morphology and detect residual material from the air-powder polisher. SEM and transmission electron microscopic (TEM) observations of the interface between the bonding resins and dentin were performed to detect variations in the hybrid layers of the control and treated specimens. Results. The results indicated that air-powder polishing did not influence the tensile bond strength to enamel, but adversely affected the tensile bond strength to dentin for the one-step systems, but not for the two-step system. Changes to the enamel surface after air-powder polishing were minimal, but an increase in surface roughness and complete removal of the smear layer were observed on dentin. SEM and TEM observations of the resin/dentin interface suggested that the air-powder polisher might cause superficial maceration of the collagen fibers on the dentin surface. This change may have decreased the ability of the etching/priming agents and bonding resin to penetrate into the dentin, which would have resulted in a poor quality hybrid layer. Significance. For those systems that contain only an acidic primer for dentin conditioning, the use of air-powder polishing for surface preparation prior to restoration of dentin margin cavities is contraindicated because of the loss of reliable bonding.