Influence of self-etchant application time on bracket shear bond strength

To determine the influence of self-etching primer (SEP) application time on the shear bond strength of orthodontic brackets. Forty human molars were cleaned, mounted, and randomly divided into two groups. The same SEP, adhesive, and brackets were used in both groups. Twenty teeth were conditioned following the manufacturers' recommendations by rubbing the SEP on the enamel surface for 3 to 5 seconds. The remaining 20 teeth were conditioned using the same SEP, but the application time was increased to 15 seconds. The teeth were debonded within half an hour following initial bonding using a universal testing machine. After debonding, the amount of residual adhesive remaining on the tooth was determined. Student's t-test was used to compare the shear bond strength (SBS) of the two groups, and the chi2 test was used to compare the Adhesive Remnant Index (ARI) scores for the two adhesive systems. The mean SBS of the brackets bonded to the teeth subjected to the SEP for 3 to 5 seconds was 8.0+/-4.6 MPa and was not significantly different (t=-0.69, P=.494) from the SBS of the brackets bonded using a 15-second SEP application time (x=8.9+/-3.4 MPa). The comparisons of the ARI scores between the two groups (chi2=2.16) indicated that bracket failure mode was not significantly different (P=.340) for both groups, and most failures were at the bracket-adhesive interface. The present findings indicate that increasing the SEP application from 3 to 5 seconds to 15 seconds does not result in a significant increase in SBS.