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 (mu TBSs) 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 mu TBS tests. Pre-treated enamel surfaces and cement-enamel interfaces were analyzed by scanning electron microscopy (SEM). Results: Phosphoric acid etching significantly increased the enamel mu TBS of GICs/RMGICs. Conditioning with the liquids of the cements produced significantly weaker or equivalent enamel mu TBS compared to the control. Regardless of etching, RMGICs yielded stronger enamel mu TBS than GICs. A visible hybrid layer was found at certain enamelcement interfaces of the etched enamels. Conclusions: Phosphoric acid etching significantly increased the enamel mu TBSs 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.