The influence of absolute humidity on shear bond adhesion

Objectives: The purpose of this study was to investigate the relationship between dentine shear bond strength, using data from experiments performed according to a standard protocol, and the absolute humidity for a new, fourth generation dentine adhesive system. Methods: Results of seven recently performed adhesion experiments using the same protocol and product were analysed. Groups of 10 human molars were each bonded in a humidity chamber. The temperature and relative humidity conditions varied from 23 to 37 °C and 30 to 95%. After bonding of the composite resin a shear bond test at a crosshead speed of 2.0 mm/min was performed. Results: The bond strength levels of the dentine adhesive system were influenced significantly by extreme temperature and humidity differences. Adhesion levels varied from 27.8 (SD 8.5) MPA to 12.8 (SD 1.4) MPA. Isobond strength curves are a good method to gain insight into the humidity sensitivity of adhesive systems. Conclusions: Results of in vitro adhesive bonding procedures for a dentine adhesive can be significantly influenced by the absolute humidity levels at which the procedures are performed. Consequently “Materials and Methods” sections of publications should refer to absolute humidity or temperature and relative humidity levels as a relevant parameter.