Aim: The major goal of the orthodontic treatment is the stability in the long term. For stability, maintaining the arch form during orthodontic treatment is one of the determinants. The aim of this study is to investigate the arch form changes during and after treatment according to the pretreatment, posttreatment, postretention orthodontic casts and the occlusal images of these orthodontic casts of extraction and nonextraction cases.
Material and Methods: For this purpose, images of the occlusal surfaces of upper and lower orthodontic casts taken from 70 adults of 38 extraction and 32 nonextraction were transfered to computer environment, Matlab 7.0 ® ( The MathWorks, Inc.) and the curves of the arch forms were drawed by using fourth order polynomial function, then the correlation of pretreatment-posttreatment, posttreatment -postretention curves were evaluated.
Conclusions: The results of this study indicates that; 1) During orthodontic treatment, maxillary arch form is maintained as compared with mandibular arch form. 2) In the postretention period, more relapse is seen in the mandibular arch form of nonextraction group. 3) There is no significant difference in performing the orthontic treament compatible with the pretreatment arch form, maintaning the arch form in the postretention period between extraction and nonextraction groups.