OBJECTIVES:The objective of this study was to compare the shear bond strength (SBS) of new and rebounded orthodontic brackets bonded to the buccal sound and cleaned enamel surfaces using two orthodontic adhesives: resin-modified glass-ionomer (RMGI) and resin-composite.MATERIALS AND METHODS:Forty premolars were randomly allocated into four groups, 10 teeth/group. New and rebonded brackets were bonded to sound and cleaned enamel surface, and then were subjected to thermocycling. The bond strength was determined using a universal testing machine at a crosshead speed of 1 mm/min. Remaining adhesives on enamel after bracket debonding was scored independently by two investigators who were not aware of the four different groups, using adhesive remnant index (ARI).RESULTS:There was a statistical significant difference in SBS of the four groups (P = 0.005). SBS values were significantly higher with cleaned enamel surfaces after adhesive removal compared to sound enamel. SBS was significantly higher for rebonded brackets, when compared with the new brackets. No significant difference was found between the two adhesives types. The level of agreement between the two raters was higher toward the classification of higher categories of ARI (scores 5 and 6) with agreement percentage 91.7% and 100%, respectively. There was more adhesive remained among resin-composite groups.CONCLUSIONS:The bond strength of debonded sandblasted stainless-steel brackets was higher than new brackets. Resin-composite and RMGI orthodontic adhesives used in this study exhibited sufficient SBS values for bonding brackets to sound and cleaned enamel and comparable to each other.

Objectives. The purpose of this in vitro investigation was to evaluate qualitatively the surface topography at the bracket-adhesive-enamel junction, bonded to the buccal and lingual surfaces of premolars with composite resin and resin-modified glass-ionomer orthodontic adhesives, using two methods of adhesive removal: a dental explorer and a micro brush. Methods. Forty premolar surfaces were allocated to four groups of 10/ each, 20/buccal and 20/lingual surfaces. The brackets were bonded to the surface of the enamel and any extra adhesive was removed with a dental explorer or a micro brush. Specimens were evaluated and scored by two calibrated independent raters, at the bracketadhesive-enamel junction, for adhesive overlap on the bracket, the smoothness of the surface, as well as the presence of projections and depressions, using a digital microscope. The Fisher-exact statistical test was conducted to compare the different groups. Results. Regardless of the method used to remove the adhe-sives, all groups showed partial or complete overlap of the adhesive on the bracket. No statistical difference was found between the groups for adhesive overlap (P=1.0). However, resin-modified glass-ionomer was found to be statistically significantly (P<0.05) better than composite resin in both smoothness and the lack of projections or depressions, regardless of the instrument of removal. Conclusion. Removing excess adhesive with a dental explorer or a micro brush is not an ideal method for adhesive removal, as partial or complete overlap of the adhesive on the bracket existed in all groups. On the other hand, resin-modified glassionomer was a superior material to composite resin for better smoothness and surface topography at the bracket-adhesive-enamel junction.