Towards a Better Understanding of the Adhesion Mechanism of Resin-modified Glass-ionomers by Bonding to Differently Prepared Dentin

Objectives: The purpose of this study was to evaluate the bonding effectiveness of a resin-modified glass-ionomer (RMGI) to differently prepared dentin and how this restorative material interacts with these distinct substrates. Also the potential adhesion-promoting role of a polyalkenoic-acid conditioner was assessed.

Methods: Forty-eight dentin surfaces were prepared from sound human molars and randomly distributed among 6 experimental groups. Fuji II LC (GC) was applied on bur-cut (100 μm diamond), fractured and Er:YAG laser-irradiated (200mJ, 10Hz, 31.4J/cm(2)) dentin with or without the beforehand application of the aqueous polyalkenoic-acid conditioner, Cavity Conditioner (GC). After 7 days of storage in water at 37 °C, specimens were prepared for microtensile bond strength testing (μTBS), as well as for TEM characterization of the resultant RMGI-dentin interface. Statistical analysis of the μTBS results was performed using ANOVA and Tukey's test (p<0.05).

Results: The use of conditioner resulted in a significantly higher bond strength only when dentin was prepared by diamond bur (p<0.05). Laser irradiation induced micro-cracks on the dentin surface and led to the lowest bond strength, irrespective of the use of conditioner (p<0.05). Fuji II LC was able to partially demineralise (up to 2.0μm) and infiltrate bur-cut and fractured dentin, but no evident interaction was observed at the interface between the RMGI and laser-irradiated dentin.

Conclusions: Laser-induced surface modifications impaired the interaction of the RMGI with dentin, thereby negatively influencing its bonding effectiveness. The use of a polyalkenoic-acid conditioner remains crucial for the RMGI to bond effectively to bur-cut dentin.