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

      Stern, Moshe; Williams, Robert E., D.M.D., M.A. (2013)
      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.
    • The Effect on Final Bond Strength of Bracket Manipulation Subsequent to Initial Positioning

      Beebe, David; Williams, Robert E., D.M.D., M.A. (2011)
      The shear bond strength of light activated orthodontic adhesives varies according to the composition of the material, placement protocol, and time prior to light curing. Manipulating brackets after their initial placement on a tooth can disrupt the adhesive's polymerization and compromise final bond strength. No previous research has investigated how a specific degree of manipulation, and the amount of time elapsed prior to curing, under specific lighting conditions, affects the orthodontic adhesives shear bond strength. Victory Series®, MBT prescription, premolar (3M Unitek, Monrovia, CA) orthodontic brackets were bonded using three different adhesives to sixty (60) bicuspids and varying the time after bracket manipulation before curing. The shear bond strength was calculated for each specimen. The brackets were debonded and the same teeth were rebonded with new, identical brackets, using the same protocol and under the same conditions. The results showed a statistically significant difference between the shear bond strength of Transbond XT and Grengloo, with Transbond XT having the highest strength. There was also a statistically significance difference in bond strength between the group cured 30 seconds after manipulation and the groups manipulated at different intervals prior to curing, with the 30 second group having the highest bond strength. This study confirms that various orthodontic adhesives have different bond strengths depending on manipulation and varying times prior to curing each adhesive.