Rotation Control of Orthodontic Self-ligating Brackets

Objectives: The objective of this presentation is to compare archwire rotation play angle of two different self-ligating brackets. Rotation control of an orthodontic bracket is to de-rotate a tooth to align its facial crown with the adjacent teeth. In recent years, self-ligating brackets have been extensively applied by orthodontists due to its unique features of bio-mechanics, better hygiene, aesthetics, shortened chair time, etc.
Orthodontists sometimes realize that their self-ligating brackets would not de-rotate patient’s teeth to their satisfaction due to a large rotation play angle between the bracket and finishing archwire. Rotation play angle is dictated by design of the bracket, self-ligating mechanism, clearance between the bracket and self-ligating mechanism, and manufacturing tolerances of components.
Methods: Rotation play angle, θ, of a self-ligating orthodontic bracket can be calculated by inserting a finishing 0.019”x0.025” archwire in the archwire slot and measuring the activation distance, Δ, as shown in Fig. 1, where W is the mesial-distal width of the bracket, Δ is the activation distance that the archwire displaces vertically from lowest position to that contacting the self-ligating clip or door at 0.1N of force.
This report presents lab test results of 2 different self-ligating bracket systems. 10 samples each of 8 different types of brackets were tested for each system.
Results: The calculated rotation play angles and their standard deviations based on testing are shown in Fig. 2.
Conclusions: Conclusion: Based on the lab testing data, SmartClip™ SL3 Enhanced show a small rotation play of 0.90 degree on average with a standard deviation of 0.25 degree while Damon® Q™ is 2.87 degrees with a standard deviation of 0.58 degrees using a 0.019x0.025 archwire.