Transmission electron microscopic examination of the interface between a resin-modified glass-ionomer and Er:YAG laser-irradiated dentin.

Objective: The aim of this study was to analyze the ultrastructural characteristics of the interface between a resin-modified glass ionomer (RMGI) and Er:YAG laser-irradiated dentin. Background Data: The Er:YAG laser has been considered as a possible alternative for cavity preparation, but the interaction between glass ionomers and Er:YAG-lased dentin still needs further investigation. Materials and Methods: Five dentin surfaces were prepared by diamond bur (120,000 rpm) as controls or for Er:YAG laser irradiation (31.45 J/cm(2), 200 mJ, 10 Hz, 100 mu s). The RMGI Fuji II LC (GC) was then applied to their surfaces, which were previously conditioned with a 20% polyalkenoic acid conditioner. The samples were sealed with an unfilled resin, stored in distilled water for 1 wk at 37 degrees C, and then processed for transmission electron microscopic (TEM) examination. Results: When applied to bur-cut dentin (controls), Fuji II LC was able to partially demineralize the dentin surface, resulting in the formation of a hybrid layer, on top of which a sub-micron gel-phase was observed. In the laser-irradiated samples, the RMGI was in close contact with the irregular dentin substrate, but no hybrid layer or gel-phase formation could be detected, nor were there signs of dentin demineralization or collagen melting. Horizontal cracks were clearly seen in the sub-surface layer of dentin. Conclusion: Although presenting horizontal micro-cracks in its sub-surface, the irregular laser-irradiated dentin showed close contact with the RMGI. However, no hybrid layer or gel-phase could be detected, and there were no signs of dentin demineralization and collagen melting