Effects of orthodontic ligation methods on treating dental crowding

Objectives: The purpose of this study was to evaluate the stress distribution produced in the dentoalveloar system when using different ligation method or different wire material to subside mandibular dental crowding. Methods: Photoelastic models of alveolar process, with ivory-colored resin teeth, were fabricated using epoxy resin. The teeth were arranged with various degrees of crowding. In addition, teeth arrangements with neighboring teeth existed or not were also simulated. To understand the effect of ligation method on the outcome of orthodontic treatment in subsiding dental crowding, stress distributions at bone/root interface were recorded and compared between traditional ligation method and lingual approaching method (LAM) in combination with superelastic archwire. For all the tests, the effect of wire pattern was also taken into consideration. Before and after simulated treatment, the models were recorded photographically using circular polariscope technique. Results: In our quantity results, mainly lateral stress produced on the other two teeth in stead of stress focussed in the most crowded tooth was observed in the LAM model without neighboring teeth added(with highest fringe order = 1.8), compared to the result of traditional methods (with highest fringe order = 0.9). And less lateral stress was found in both group with neighboring existed. However, no obvious difference in the stress distribution was found when the archwire material was altered. On the other hand, our results demonstrated that, compared with light archwire, the stress was more focused on the apical and coronal portion of root surface in the case of using larger dimensional archwire. Conclusion: Our results showed that photoelastic method can be a useful and efficient tool for the biomechanical evaluation of orthodontic treatment. Furthermore, lingual approaching method (LAM) in combination with superelastic archwire may offer some benefit in the early stage of orthodontic treatment.