Dynamic study of multi-bracket appliance using a digital image correlation method combined with three-dimensional finite element analysis : Stress distribution in the root surroundings during maxillary anterior retraction

To assess whether the force system used in orthodontic practice is appropriate, it is important to understand not only the stress distribution status in the root surroundings at the time of loading orthodontic force but also the magnitude of its stress. The aim of this study was to visualize the stress distribution status in the root surroundings during maxillary anterior retraction by means of the digital image correlation method combined with three-dimensional finite element analysis so as to solve problems such as friction and contact by the tooth and the tooth often encountered during dynamic analysis using a multi-bracket appliance. A dentition model equipped with multi-bracket appliance was prepared, then individual displaced teeth were analyzed by digital image correlation method. The loading weight showing a displacement approximately equal to the results of the amount and direction of dental displacement thus obtained was then calculated by three-dimensional finite element analysis to visualize the stress status probably generated in the root surroundings. This procedure made it possible to perform a stress analysis at the time of tooth movement by referring to the friction status between the wire and bracket as well as their contact pattern. In consequence, it was revealed that both the central and lateral incisors tended to move in an inclined manner to the palatal side while the canine and second premolar tended to move in an inclined manner to the mesial direction. It was also elucidated that a stress exceeding -1.0×10^<-2>kgf/mm^2 was produced in the compressed side in all teeth examined. From these results, it seems practicable to visualize the stress distribution in the root assuming various orthodontic forces in the future by means of the combined method used in the present study. Furthermore, preparation of a force system was also discussed by referring to the results obtained from this analysis so as to perfor m orthodontic treatment more efficiently in the future.