Yoon W, et al. - This research was designed to determine the effects of extraction and the number of teeth extracted on changes in occlusal function by measuring occlusal contact area and force before and after orthodontic treatment with a fixed appliance. The occlusal contact area and force demonstrated a tendency to decrease immediately after treatment and then gradually increase to pretreatment levels during the observation period. The occlusal contact area, however, did not recover fully after 2 years in the 4 premolar extraction group.