The effect of air-thinning of self-etching primer for orthodontic bonding

Objective: The purpose of this investigation was to assess the effect of air thinning of self-etching primer (SEP) on shear bond strangth of stainless steel brackets with micro-etched bases when bonded with light cured composite resin. The survival time was assessed in a ball mill and the amount of cement remaining on the enamel was assessed following bracket removal. Methods: Sixty extracted human premolars were used for bond strength testing, thirty bonded according to each bonding protocol. Shear bond strengths were asessed with Nene M3000 machine with a crosshead speed of 1mm per minute. Following debonding the adhesive remnant index(ARI) and predominant site of failure were evaluated. A further twenty premolars were used to assess survival time following one hundred hours in the ball mill; ten teeth were bonded according to each bonding protocol. Results: The difference between the mean bond strength of the two groups was insignificant (two sample t-tests p=0.33 95%CI - 0.27, 0.79) The site of failure / ARI data revealed significantly less composite remained on the teeth when the primer was air-thinned than when it was not. (ARI data chi-squared analysis p=0.001; site of failure chi-squared analysis p<0.001). No brackets failed in the survival time study after one hundred hours. Conclusions: Air-thinning of self-etching primer does not significantly affect the shear bond strength or survival time when brackets are bonded with self-etching primer. Air-thinning decreases the amount of composite remaining on the tooth surface after debonding.