Air humidity: a detrimental factor in dentine adhesion

Successful dentine adhesion may be negatively influenced by intrinsic and extrinsic dentine wetness. Testing the influence of high humidity levels during the application of bonding systems is therefore relevant. It was the aim of this study to investigate in vitro the sensitivity to air humidity of the dentine bond strength for some commercially available bonding systems. Four bonding systems were tested in vitro on human molars at temperature/humidity levels of 25 degrees C and 40% relative humidity (RH) as well as 35 degrees C and 95% RH. Four operators each made two samples of the respective treatment combinations. After shear bond testing a three-way ANOVA was carried out. Only the factors 'material', 'humidity' as well as their interaction were statistically significant. The factor 'operator' did not exert a significant influence on the shear bond strength. For the 'clinically dry' group statistically significant differences were found between all materials (P < 0.001). In the 'high humidity' setting too, significant differences were found between materials (P < 0.001). The shear bond strength values ('high humidity') were very low (< 3 MPa) for Gluma 2000, Denthesive and Syntac, while the mean values for Scotchbond Multi-Purpose were significantly higher (12 MPa; P < 0.001). It was concluded that in general bonding systems are highly sensitive to extrinsic dentine wetness, resulting in very low adhesion values at high humidity.