Bonding amalgam to enamel: shear bond strength and SEM morphology

Most studies of amalgam bonding have used dentin as the substrate. There is little data on bonding to enamel.

This study evaluated the shear bond strength of amalgam to enamel with the use of 3 resin cements, 1 resin-modified glass ionomer lining cement, and 2 dentin bonding agents.

Sixty bovine teeth were trimmed to expose a flat enamel surface and randomly assigned to 6 test groups of 10 specimens each. A single-plane lap shear test assembly was used. The enamel surfaces were treated with either Amalgambond Plus (group I, control), 2 coats of Amalgambond Plus (group II), light-polymerized Panavia F followed by an additional coat of autopolymerized Panavia F (group III), light-polymerized Fuji Lining LC followed by an additional coat of acid-base set Fuji Lining LC (group IV), Clearfil SE Bond followed by an additional coat of autopolymerized Panavia F (group V), or Single Bond followed by an additional coat of autopolymerized RelyX ARC (group VI). Freshly mixed amalgam was condensed against the treated enamel surfaces. Shear bond strengths for each group were compared with 1-way ANOVA and post hoc Duncan's test (P=.05). Fracture modes were examined visually. SEM observations of the fractured enamel surfaces, interfacial morphology, and conditioned enamel surfaces for each group were performed.

Low bond strengths of 1.2 and 1.6 MPa were obtained in groups VI and I, respectively. The dual application of materials in all remaining groups resulted in higher bond strengths that ranged from 14.2 to 15.7 MPa. SEM illustrations revealed various degrees of intermingling between the adhesive material and amalgam. The conditioned enamel surfaces were morphologically varied according to conditioning solution.

In this in vitro study, with the exception of group VI, the dual application of either adhesive resins or resin-modified glass ionomer resulted in satisfactory bond strengths of amalgam to enamel (up to 16 MPa).