The uprighting effect of the Fränkel appliance on the mandibular canines and premolars during eruption.

The effect of the Fränkel (FR) appliance on the eruptive path of the mandibular canines and premolars was evaluated in patients who were monitored from 8 to 13 years of age. The sample treated with the FR appliance consisted of 84 subjects with Class I or Class II malocclusion associated with crowding in the mandibular dental arch. Twenty-seven subjects of approximately the same age and with almost an identical space deficiency in the mandibular arch not subjected to FR treatment served as a comparison group. Permanent teeth were not extracted during treatment in any of the subjects in either group. The primary criterion of patient selection was based on the availability of standardized serial lateral and posteroanterior cephalograms, permitting an exact identification of the canine and premolar contours during eruption. Increases in width between the tips of the mandibular canines and the buccal tips of the mandibular premolars during eruption were significantly greater in the FR group than in the comparison group (P less than 0.001). The expanding effect of the FR appliance was evidenced particularly in the region of the mandibular first premolars. The distance between the buccal tips of these teeth increased by an average of 3.5 mm more in the FR group than in the comparison group. Likewise, the width between the root landmarks of the first mandibular premolars increased during eruption in the FR group 2 1/2 times more than in the untreated sample, a difference that was statistically significant (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)