Influence of filler addition to bonding agents on shear bond strength to bovine dentin

The purpose of this study was to investigate the influence of adding filler particles to a bonding agent on dentin bond strength and of the temperature change during curing in order to determine the optimum filler level for an experimental bonding agent.

Experimental light-cured bonding agents with microfiller (average size: 0.05 micrometers) content of 0, 10, 20, 30, 40, 50, 60, and 70 wt% were used with the Imperva Bond / Lite-Fil II A (Shofu) restorative material. Bovine incisors were mounted in self-cured resin, and the facial surfaces were prepared with 600-grit SiC paper. After dentin surface pretreatment with dentin primer, experimental bonding agents were applied to the dentin surface and bonded with resin composite. Ten samples per test group were stored in 37 degrees C water for 24 h, then shear tested at 1.0 mm/min. The temperature change of the bonding agent was monitored during the exthothermic polymerization reaction according to the method of ISO standard #4049. The peak temperature and the time required to reach peak temperature were recorded.

Bond strength to dentin and the temperature change were greatly affected by the filler level. Maximum dentin bond strength (14.3 +/- 2.3 MPa) was obtained with a filler level of 10 wt% and decreased with filler level higher than 30 wt% (10.4 +/- 1.7 MPa - 5.3 +/- 2.6 MPa). Peak temperature decreased and the time required to reach peak temperature increased with the higher filler levels. There were strong correlations between the bond strength and temperature change of experimental bonding agents.

The initial setting behavior of bonding agents containing filler particles may be one of the important factors influencing dentin bond strength. When bonding agents with filler particles are used, it is important to determine if optimum filler levels exist in order to optimize the dentin bond strength.