Date of Award

5-2011

Document Type

Thesis

Degree Name

Master of Dental Science (MDS)

Program

Orthodontics

Research Advisor

Edward F. Harris, Ph.D.

Committee

Richard A. Williams, D.D.S., M.S. Jere L. Yates, D.D.S., M.S.

Keywords

Class II, Long-term, Stability

Abstract

Achieving long-term stability after orthodontic treatment is a major challenge for orthodontists. The previous literature shows that relapse occurs at a considerable magnitude. The purpose of the present study was to determine the amount and type of long-term, posttreatment relapse that occurs in a homogeneous group of patients treated by a single experienced orthodontist in a private practice setting. Dental casts from a sample of 30 Class II division 1 Caucasian females treated without extractions were evaluated at pretreatment (mean age = 13.1 years), posttreatment (mean age = 15.9 years) and recall (mean age = 28.3 years) to determine the nature and extent of long-term posttreatment changes. All of the subjects were treated in the private practice of a single, experienced practitioner in Southaven, MS. The dental casts were examined to investigate changes in overbite, overjet, midline deviation, buccal segment relationships, canine relationships, incisor irregularity, arch chord lengths, curve of spee, arch depths and arch widths that occurred at an average of 12 years posttreatment. Overjet increased slightly after treatment, but the mean overjet at recall examination was within acceptable limits. Overbite deepened after treatment. About 1/3 (37%) of the treatment correction in overbite was lost during the posttreatment interval. A relapse of only 37% in the present sample was more favorable than the relapse percentages reported in previous studies. Maxillary Incisor Irregularity was relatively stable (10% relapse), but 67% of treatment correction in lower incisor irregularity was lost during the recall interval. Little et al. (1981) suggested that less than 30% of cases maintain satisfactory mandibular alignment with an Irregularity Index of less than 3.5 mm at 10 years posttreatment. The present study found that 13 out of the 30 cases evaluated (43%) had Incisor Irregularity of less than 3.5 mm at the recall examination. Maxillary arch chords (1‑3 and 1‑6) were stable while mandibular 1-3 chord was unstable. Nearly all of the treatment increase in mandibular 1‑3 chord was lost during the posttreatment interval. Curve of Spee correction during treatment was stable over the long-term with less than 10% of the correction deepening over time. Although increased during treatment, maxillary arch widths were stable over the long-term. The mandibular arch widths were less stable. 50% of mandibular intercanine expansion during treatment was lost over the long-term. This was a similar finding to previous studies. Buccal segment relationship and canine relationship improved from class II toward class I during treatment and did not show relapse toward class II over the long-term. In fact, the subjects continued to grow favorably toward a more class I relationship over the long-term.

DOI

10.21007/etd.cghs.2011.0168

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