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.

Abstract

Long-term posttreatment cephalometric changes from late adolescence into early adulthood were analyzed in this study. Lateral cephalometric radiographs from a sample of 30 Class II division 1 Caucasian females treated without extractions were evaluated at posttreatment (mean age = 15.9 years) and recall (mean age = 28.3 years). All of the subjects were treated in the private practice of a single, experienced practitioner. The cephalograms were examined to investigate changes in the cranial base, midface, maxilla, mandible, maxillomandibular relationships, dental relationships, and the soft tissue profile that occurred at an average of 12.4 years posttreatment. Descriptive and inferential statistics were calculated to see whether the posttreatment changes were statistically significantly different from zero.

Significant posttreatment change (P < 0.0001) occurred for most skeletal measurements, and this was primarily attributed to late adolescent growth. Total mandibular length increased (Cd‑Gn) by 6.6 mm on average, and total downward and forward directional growth of the maxilla (Se‑A) was 4.3 mm on average. Overall, late mandibular growth after adolescence exceeded late growth in the maxilla by nearly twice as much, which was confirmed by an increase in SNA Angle by approximately 0.4 degrees and an increase in SNB Angle by approximately 0.8 degrees. Upper Anterior Facial Height increased by 3.1 mm, and Lower Anterior Facial Height increased by 4.3 mm, making the total increase in the vertical dimension of the anterior face greater than 7 mm.

Dentally, the upper and lower incisors experienced significant uprighting after treatment, which was confirmed by decreases in U1‑SN, U1‑NA, IMPA, and L1‑NB angles. Overbite and overjet increased by 0.9 mm and 1.0 mm, respectively. Maxillary and mandibular arch lengths decreased by 1.2 mm and 1.7 mm, respectively, and this was associated with mesial movement of the maxillary and mandibular first molars.

Soft tissue profiles became progressively more flattened after treatment. This was disclosed by an increase in Z Angle by 4.5 degrees and increased retrusion of the upper and lower lips relative to the E Plane. The nose and soft tissue chin continued to grow forward after treatment (NaPerp‑Pr increased by 1.9 mm and W point‑Pg' increased by 1.5 mm). The upper and lower lips drooped inferiorly by 1.7 mm and 2.3 mm, respectively.

DOI

10.21007/etd.cghs.2011.0256

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