Bonding to molars--the effect of etch time (an in vitro study)

This study evaluated the effect of etch time on the shear bond strength obtained when bonding to the buccal enamel of first molar teeth. Recently extracted first molar teeth were etched with 37 per cent phosphoric acid gel for 15, 30 and 60 seconds. Preformed cylinders of Concise composite resin were then bonded to the buccal surfaces of the molar teeth. After storage in water for 24 hours at 37 degrees C, the specimens were debonded in a direction parallel to the buccal surface. Examination of the shear bond strengths showed significant differences in shear bond strength between 15 and 30 seconds (P < 0.01) and between 15 and 60 seconds (P < 0.001). Weibull analysis revealed that the probability of bond survival increased as etch time increased, however, the difference between 30 and 60 seconds was not statistically significant. The results indicate that, despite current recommendations of a 15-second etch for premolars, canines and anterior teeth, an etching time of at least 30 seconds should be used when bonding to the buccal surfaces of first molars. A further increase in etching time to 60 seconds produces no significant increase in bond strength.