Date of Award

Spring 1991

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)



First Advisor

Ferguson, Donald

Second Advisor

Dhuru, Virendra

Third Advisor

Kittleson, Russell


Long term stability of orthodontic treatment has been an ongoing problem since the inception of orthodontic therapy. Posttreatment and postretentive studies evaluating overbite, dental crowding and arch length and width reduction are abundant, but little is found in the literature regarding postretentive changes in the curve of Spee. The purpose of this study was to evaluate the changes in the curve of Spee, overbite and other mandibular dimensional changes occurring during and after orthodontic therapy. Twenty-two nonextraction cases, treated during the permanent dentition and requiring two year minimum postretention, were used for the sample. Pre, post treatment and postretention study casts were measured three dimensionally on a milling machine. Lateral cephalograms were also traced and evaluated. Paired t-tests and Pearson's correlations were used to identify statistically significant results at a probability level <.05. Results of this study indicate the following: 1) orthodontic leveling remained quite stable over time, 2) arch leveling was associated with reduction of overbite, 3) initial maximum depth of the curve was located most often just distal to the second bicuspid, moved distally during treatment just beyond the mesiobuccal cusp of the first molar and then finally returned to its original position following treatment, 4) during leveling, the cuspids became depressed, then relapsed sightly during postretention, 5) first and second bicuspids maintained stable treatment positions, 6) first molars followed an extrusive pattern during and after leveling, 7) arch length reduction and AP length reduction occurred (cuspids and molars came forward) during and after treatment, 8) expanded intercanine widths relapsed and 10) first and second bicuspids remained quite stable when expanded and leveled.



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