Treatment effects produced by the Twin-block appliance and the FR-2 appliance of Frankel compared with an untreated Class II sample

This retrospective cephalometric study compares the treatment effects produ ced in 40 patients treated with the Twin-block appliance to those seen in a matched sample of 40 children treated with the FR-2 appliance of Frankel a nd to changes undergone in 40 untreated Class II controls from The Universi ty of Michigan Elementary and Secondary School Growth Study. The average st arting ages for the Twin-block, Frankel, and control groups were 10 years 5 months, 10 years 2 months, and 9 years 11 months, respectively. The T-2 to T-1 observation period was adjusted to an average of 16 months for all gro ups. Significant decreases in overbite and overjet were observed at the end of treatment in the Twin-block and Frankel groups. Compared with the untre ated subjects, statistically significant increases in mandibular length wer e observed in both treated groups. The Twin-block patients achieved an addi tional 3.0 mm of mandibular length, whereas the Frankel group increased 1.9 mm more than did the controls. No significant restriction of midfacial gro wth was observed in either functional appliance group relative to controls. A significant increase in lower anterior facial height was evident in both treatment groups. Vertical increase in the Twin-block patients was signifi cantly greater than in the FR-2 group. In general, more extensive dentoalve olar adaptation was observed with the tooth-borne Twin-block appliance than with the more tissue-borne FR-2 of Frankel. The Twin-block and FR-2 sample s both showed significant retroclination and extrusion (eruption) of the ma xillary incisors. The Twin-block patients also exhibited distal movement of the upper molars; however, there was no extrusion. Slight lower incisor pr oclination was noted in both treatment groups, and lower molar extrusion wa s found to be significantly greater in the Twin-block group compared with t he other 2 samples. No horizontal differences were detected in the lower mo lars among groups. The present study suggests, therefore, that Class II cor rection with the Twin-block appliance is achieved through normal growth in addition to mandibular skeletal and dentoalveolar changes. Class ii correct ion with the FR-2 is more skeletal in nature, with less dentoalveolar chang es noted.