Rotation Control of Ceramic Orthodontic Self-ligating Brackets

Objectives: Passive ceramic self-ligating brackets have been widely used by orthodontists due to their superb aesthetic appeal, ease of use, shortened chair time, good hygiene, etc. However, orthodontists are concerned about rotation control since those brackets are designed to be passive, i.e. there is a small clearance between the finishing archwire and archwire slot depth. This small clearance in-turn results into a rotation play angle between the archwire and bracket.
Rotation play angle between a 0.019”x0.025” archwire and each bracket was measured and compared for 3 types of passive ceramic self-ligating brackets from 3 different manufacturers.
Methods: Test setup and calculation of rotation play angle were published in an IADR 2017 poster (Lai, # 2015). Rotation play angle, , 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, , as shown in Figure 1. Where W is the mesial-distal width of the bracket, 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.
Results: This report presents lab test results of 3 different ceramic self-ligating bracket systems. 10 samples each of 5-8 different types of brackets were tested for each system. The calculated rotation play angles and their standard deviations are tabulated as Table 1.
Conclusions: Based on the lab testing data, Clarity ™ Ultra SL shows a small rotation play range of 1.86 degrees on average while Damon ™ Clear is 3.75 degrees and TruKlear® is 3.79 degrees using a 0.019x0.025 archwire. A rotation play angle of less than 2.5 degrees is desirable since orthodontists can discern bracket rotation misalignment down to 2.5 degrees (Lai and Mah, JCO pp. 524-528 Aug. 2009).