Purpose: When restoring hypomineralized first permanent molars, placement of cavo-surface margins can be difficult to ascertain due to uncertainty of the bonding capability of the tooth surface. The purpose of this study was to investigate the adhesion of resin composite bonded to control and hypomineralized enamel with an all-etch single-bottle adhesive or self-etching primer adhesive.
Methods: Specimens of control enamel (N=44) and hypomineralized enamel (N=45) had a 0.975-mm diameter composite rod (Filtek Supreme Universal Restorative) bonded with either 3M ESPE Single Bond or Clearfil SE Bond following manufacturers' instructions. Specimens were stressed in shear at 1 mm/min to failure (microshear bond strength). Etched enamel surfaces and enamel-adhesive interfaces were examined under scanning electron microscopy.
Results: The microshear bond strength (MPa) of resin composite bonded to hypomineralized enamel was significantly lower than for control enamel (3M ESPE Single Bond=7.08 +/- 4.90 vs 16.27 +/- 10.04; Clearfil SE Bond=10.39 +/- 7.56 vs 19.63 +/- 7.42; P=.001). Fractures were predominantly adhesive in control enamel and cohesive in hypomineralized enamel. Scotchbond etchant produced deep interprismatic and intercrystal porosity in control enamel and shallow etch patterns with minimal intercrystal porosity in hypomineralized enamel. Control enamel appeared almost unaffected by SE Primer; hypomineralized enamel showed shallow etching. The hypomineralized enamel-adhesive interface was porous with cracks in the enamel. The control enamel-adhesive interface displayed a hybrid layer of even thickness.
Conclusions: The microshear bond strength of resin composite bonded to hypomineralized enamel was significantly lower than for control enamel. This was supported by differences seen in etch patterns and at the enamel-adhesive interface.