Improvement of enamel bond strengths for conventional and resin-modified glass ionomers： acid-etching vs. conditioning

Objective： This study deals with the effect of phosphoric acid etching and conditioning on enamel micro-tensile bond strengths （μTBSs） of conventional and resin-modified glass ionomer cements （GICs/RMGICs）. Methods： Forty-eight bovine incisors were prepared into rectangular blocks. Highly-polished labial enamel surfaces were either acid-etched, conditioned with liquids of cements, or not further treated （control）. Subsequently, two matching pre-treated enamel surfaces were cemented together with one of four cements [two GICs： Fuji I （GC）, Ketac Cem Easymix （3M ESPE）; two RMGICs： Fuji Plus （GC）, RelyX Luting （3M ESPE）] in preparation for μTBS tests. Pre-treated enamel surfaces and cement-enamel interfaces were analyzed by scanning electron microscopy （SEM）. Results： Phosphoric acid etching significantly increased the enamel μTBS of GICs/RMGICs. Conditioning with the liquids of the cements produced significantly weaker or equivalent enamel μTBS compared to the control. Regardless of etching, RMGICs yielded stronger enamel pTBS than GICs. A visible hybrid layer was found at certain enamel- cement interfaces of the etched enamels. Conclusions： Phosphoric acid etching significantly increased the enamel μTBSs of GICs/RMGICs. Phosphoric acid etching should be recommended to etch the enamel margins before the cementation of the prostheses such as inlays and onlays, using GICs/RMGICs to improve the bond strengths. RMGICs provided stronger enamel bond strength than GICs and conditioning did not increase enamel bond strength.