The effect of pre-cure bracket movement on shear bond strength during placement of orthodontic brackets, an in vitro study

BACKGROUND: The purpose of this study was to determine the influence of linear and rotational pre-cure bracket displacement during the bonding procedure on shear bond strength (SBS) of orthodontic brackets. MATERIAL AND METHODS: Stainless steel orthodontic premolar brackets were bonded to the buccal surfaces of 50 human pre-molars with a conventional two-step bonding protocol. Extracted human pre-molars were divided into 5 groups (n=10/group). In the Control Group, the brackets were bonded with no pre-cure bracket displacement or rotation. The Rotation Group was bonded with 45 degrees of pre-cure rotation. The Displacement Group was bonded with 2mm pre-cure linear displacement. The Rotation-Displacement Group was bonded with pre-cure movements of 45º counter-clockwise rotation and 2mm displacement. The Slippage Group was bonded with 2mm each of mesial and distal pre-cure linear displacement. Photo-activation was carried out on the lateral sides of the bracket. Shear debonding force was measured, 24 hours after initial bonding, with an Instron universal testing machine using a knife-edged chisel. Data was analyzed using one-way ANOVA test. Adhesive Remnant Index (ARI) was scored under 15x magnification. The ARI data was analyzed using the Chi-square test (p -value < 0.05) RESULTS: No statistically significant differences were detected among the control and experimental groups (p = 0.331). The rotation and displacement group showed the highest mean SBS than all other groups. Mean SBS for all groups were above the clinically acceptable range. No statistically significant differences were detected in ARI scores among groups (p = 0.071). CONCLUSIONS: Linear and rotational pre-cure bracket displacements do not appear to effect the shear bond strength of orthodontic brackets. Key words:Shear bond strength, orthodontic bracket, displacement, rotation, adhesive remnant index, pre-cure movement.