Quantitative assessment for effects of premolar extraction upon orthodontic treatment outcomes

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For eight adult females who underwent edgewise treatment with extraction and eight females who underwent the treatment with extraction of four premolars, their 3D jaw movements during gum chewing have been recorded at pre and post treatment periods. The standardized gum having known physical properties has been used for the test foods. Specifically, the analyses for the effects of orthodontic treatment on the smoothness of the jaw movement have been conducted. The smoothness of the jaw movement trajectories has been estimated by using normalized jerkcost as well as the simulation results by the minimum jerk model. The jaw movement smoothness was compared with thatdeterminedinthefemalesubjectswithacceptable goodocclusionThe present results showed significant postoperative improvement in the jaw movement smoothness in the two patient groups. As for the jaw movement smoothness for the patients treated with premolar extraction, the smoothness at the post treatment periods was not significantly different from that for the normal subjects. It is suggested that the extraction of the premolar that is often necessary for the edgewise treatment may contributes to achievement of the optimal jaw movement smoothness that is apparently seen in the control subjects