The Effect of Bracket Manipulation at Various Time Intervals on Final Bond Strength of Three Orthodontic Adhesives

Abstract

Introduction: Adhesive bond strength is an essential component for the success of orthodontic treatment and it is important to understand what factors can affect its clinical effectiveness. The primary purpose of this study was to attempt to establish clear parameters for the effect that manipulation at various time intervals will have on the final bond strength of orthodontic adhesives. The secondary goal was to evaluate the characteristics of three adhesives (Transbond Plus, Grengloo, and Light-Bond) and test the effect that bracket manipulation at various time intervals will have on their final bond strength. Methods: Sixty (60) extracted human premolar teeth with intact buccal surfaces were collected and stored in a plastic tube containing distilled water. Prior to data collection, all teeth were mounted in acrylic filled plastic tubing. Each tooth was marked with black permanent marker 10 degrees from the midpoint/cusp tip using a 10 degree angular wedge. This mark established the amount each bracket would be turned after the allotted time interval had passed. The buccal surface of each tooth was cleaned with pumice, and etched for 30seconds. Each tooth was lightly coated with Assure Universal Bonding Resin® primer and a Victory Series®, MBT prescription; premolar bracket was bonded using one of the adhesives being tested. The brackets were then manipulated at various time intervals (30sec, 2min, 3min, and 4min) and then cured. After 24 hours in a controlled environment the shear bond strengths of the adhesives were tested using an Instron® universal testing machine. Results: There was a statistically significant difference between the shear bond strengths of Grengloo, Lightbond, and Transbond, with Transbond having stronger bond strength than either of the other adhesives. There was no statistically significant difference in shear bond strength between Grengloo and Light Bond. An observed power of 0.872 was found for this data. There was a difference approaching significance (F=2.45, p=0.071), between the different times elapsed prior to bracket manipulation and curing. In general the bond strength decreased as more time elapsed prior to bracket manipulation and curing. There was no significant interaction (F=0.55, p=0.771), between the types of adhesive and the times prior to curing. Conclusion: 1) There is no statistically significant decrease in bond strength of the adhesives tested as time elapsed (30 seconds, 2 minutes, 3 minutes, 4 minutes) prior to bracket manipulation. 2) All time intervals had clinically acceptable bond strength. The difference in bond strength between 30 seconds and 4 minutes was approaching significance. If a larger sample size is tested, 4 minutes might be found as the threshold for significant decrease in bond strength. 3) Transbond Plus had statistically significant higher bond strength (32% and 35% greater) than Light Bond and Grengloo. The difference in bond strength between Light Bond and Grengloo was not statistically significant.