Date of Award

5-2008

Document Type

Thesis

Degree Name

Master of Dental Science (MDS)

Program

Orthodontics

Research Advisor

Edward Harris, Ph.D.

Committee

Frank Marlin Grimes, D.D.S., M.S. Joe L. Wasson, D.D.S., M.S.

Abstract

Early or two-phase orthodontic treatment of Class II malocclusions is a debated topic in orthodontic circles primarily because the benefits of early intervention have not been consistently reproduced among researchers. The present study was a retrospective analysis of cephalograms from patients with Class II, division 1 malocclusions at the start of treatment. These were 50 consecutively treated youths who received phase 1 (early) treatment with a Bionator appliance and later treatment with full appliances (all treated by a single clinician). The comparison group consisted subjects treated in a single phase with fixed Edgewise appliances only. Importantly, subjects in the two samples were matched, on a one-to-one basis, for demographic and cephalometric variables (ANB, SNA, SNB, NAP, FMA) to ensure comparability in the nature and severity of the malocclusions. The key question was whether the cephalometric results at the end of treatment were comparable between groups. Two-phase subjects were treated on average 1.4 years longer than the one-phase group, though this measure of clock time may obscure the greater ease of treatment chair side. Neither of out two integumental variables (Z angle, E plane) differed statistically, but two key skeletal variables did differ, namely ANB and NAP. ANB was significantly smaller ( = 2.6°) in the two-phase group than in the one-phase group ( = 3.7°), and NAP averaged 2.7º in the two-phase group compared to a mean of 4.8º in the one-phase group. Consequently, the two-phase group was discernibly more orthognathic at the end of treatment, with most of the correction coming from mandibular growth rather than maxillary restriction. None of the dental variables differed statistically except the position of the maxillary incisors which were slightly more proclined in the two-phase group, and this was due to operator preference. The two-phase subjects had a lower rate of premolar extraction (12% vs 84%) than the one-phase subjects. Overall, the two-phase group achieved a better bony facial profile, with the majority of the skeletal and dental correction occurring during the first phase of treatment. These favorable results contrast with published randomized clinical trials, possibly because of differences in patient selection and appliance design. Our results do support the value of early intervention, though it is not known whether the statistically significant improvements in the facial profile are large enough to be perceptible to the patient and parents.

DOI

10.21007/etd.cghs.2008.0278

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