Fixed orthodontic treatment is based on effective bonding of bracket to enamel surface. During orthodontic therapy, load is applied on bracket slot by orthodontic wire, and then it is transferred to adhesive layer and enamel surface (state I). After the completion of treatment period, orthodontic brackets are debonded by load application on the incisal region of bracket-adhesive interface (state II).

In order to compare the diversity in stress distribution pattern of these two states, micro CT images of maxillary premolar tooth and bracket were transformed to STL files and imported to Hypermesh software to create high quality 3D finite element models. Space between enamel and bracket was filled with orthodontic adhesive material which sets to 0.2 mm at thickest region. Mechanical property was assigned to each layer and appropriate boundary conditions were applied. By using a load distributing element RBE3, firstly 150 N shear load was applied on the bracket slot to simulate bracket-adhesive-tooth system of state I and secondly the same load was applied on the incisal area of bracket and bracket-adhesive bonding to simulate bracket-adhesive-tooth system of state II.

Generated stresses on the bracket, the adhesive and the tooth in both systems were obtained and compared to each other. The Findings of this study, reveal that the effect of bonding loads was directly transform to the adhesive layer and the enamel surface; hence, treatment period would decrease.

Alternatively, debonding loads would bring about higher stresses on the bracket and facilitate debonding action.

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