In vitro investigation of shear bond strength of a phosphate based dentinal bonding agent

The objective with this study was to investigate how the shear bond strength of a phosphate based dentinal bonding agent is influenced by storage in saline at 37 degrees C up to 6 months. The effect of dentin bonding agent on the leachability of calcium from dentin was also determined. The results showed that the shear bond strength decreased after saline storage. After half a year, the strength was ca. 60% of the initial dry strength. The bonding agent also accelerated the leaching of calcium from the dentin discs, a finding which was explained as being a result of acidic reactions occurring at the dentin-bonding agent interface. In addition to the increased calcium leachability, the dentin bonding agent peeled off with time from the dentin discs. SEM investigation of the dentin surfaces after either shear strength determination or the film had peeled off due to water storage showed that a residual film was left on the dentin. This film, based on morphologic appearance, is most likely composed of the bonding agent but may also contain residuals of the smear layer.