Effect of reduction of phosphoric acid concentration on the shear bond strength of brackets.

The purpose of this study was to evaluate in vitro the effect of the reduction of phosphoric acid concentration on the shear bond strength of brackets to enamel. Twelve pairs of contralateral maxillary premolars were randomly divided into group 1 and group 2. Twelve additional upper premolars formed group 3. The three acid concentrations examined were 37% in group 1, 2% in group 2, and 5% in group 3. The buccal surfaces of the teeth were etched for 30 seconds, and metal brackets were bonded were Concise adhesive (3M Dental Products, St. Paul, Minn.). After storage of teeth in water at 37 degrees C for 1 week, a shear force was applied to the occlusal bracket wings in a direction parallel to the bracket base. The results showed that the mean shear bond strength after etching with 37% acid (x = 18.30 MPa) was significantly higher than that after etching with 2% acid (x = 15.28 MPa). The mean bond strength after etching with 5% acid (x = 16.49 MPa) was not significantly different from that after the use of the two other acids. The assessment of the Adhesive Remnant Index (ARI) showed that the amount of adhesive left on the teeth after debonding was smaller after etching with 2% acid than after etching with 37% acid or 5% acid. It was concluded that 2% phosphoric acid solution is appropriate for bonding of brackets. The reduced etching could be favorable in preventing enamel damage during the treatment and at the time of debonding.