Date of Award


Document Type


Degree Name

Master of Dental Science (MDS)



Research Advisor

Edward F. Harris, Ph.D.


James L. Vaden, D.D.S., M.S. Jere L. Yates, D.D.S., M.S.


fixed, orthodontics, relapse, removable, retention, stability


Instability of the occlusion is a common problem following orthodontic treatment. The purpose of the present research was to evaluate posttreatment relapse at long-term recall (> 10 years) in cases (A) treated with temporary fixed mandibular retention plus Hawley retainers compared to (B) a similar group retained with just removable retention (standard Hawley type retainers alone). Fixed retainers were removed after having been in place for about 2.5 years. Following this period, use of removable retention was left up to the discretion of the patient in both groups. Data consisted of orthodontic records of 166 American whites, all of whom had received comprehensive orthodontic treatment, collected from multiple private practice orthodontists using conventional Edgewise mechanics. Records were analyzed at pretreatment, end of treatment, and at long-term posttreatment recall examination (mean = 16 years after treatment). The mandibular Incisor Irregularity index at recall averaged 1.9 mm in the fixed group and 2.5 mm in the Hawley-only group. This ½-mm difference is marginally significant statistically (P = 0.03), but seems trivially small clinically. A 1.0 mm change in Incisor Irregularity during treatment was shown to be associated with 0.13 mm of relapse long term. Mandibular intercanine width increased (mean = 1.2 mm) during treatment, but decreased by almost the same amount by the recall examination. Maxillary and mandibular arch widths became slightly narrower after treatment. Overbite and overjet both increased after treatment. Results of the present study seem more stable than those reported in most long-term studies; however, there is little clinical support for a fixed-retention phase given the modest (½-mm) difference in Incisor Irregularity.