One of the goals in comprehensive orthodontic treatment is to obtain an optimal、maximun occlusion with adequate overjet and overbite. Intermaxillary tooth size discrepancy can affect the final result of orthodontic treatment and its stability. In clinic, we often can find out many patients who have teeth irregularly and malocclusion caused by intermaxillary tooth size discrepancy. Therefore, the analysis of maxillary to mandibular tooth-width ratios s one important diagnostic tool for predicting the outcome of orthodontic treatment.