A computerized cephalometric study of mandibular rotation was made of one hundred and eight patients that were treated by Drs. Ricketts and Bench of Pacific Palisades, California. These treated cases are on file at Rocky Mountain Data Systems in Sherman Oaks, California. The Ricketts computerized cephalometric analysis was utilized with each case.

Chin behavior during treatment and post-retention has always been of considerable interest to the clinical orthodontist and it was therefore decided to divide the patients into four groups according to the behavior of the chin during treatment and post-retention. Group 1 consisted of those patients that experienced a closing of the mandible during treatment and a further closing of the mandible in post-retention. Group 2 consisted of patients that manifested an opening of the bite during treatment and a closing of the mandible in post-retention. Group 3 was made up of patients in which the mandible rotated open during treatment and continued to rotate open in post-retention. Group 4 consisted of patients that experienced closure of the bite during treatment but then manifested opening of the mandible in post-retention. Opening or closing of the mandible was described in terms of the facial axis.

It was noted that although patients generally tend to experience mandibular rotation during treatment and then return to pretreatment measurements in post-retention, there is a considerable range of variation. Patients were noted to close in treatment as much as four degrees or open during treatment as much as 8.6°. Post-retention changes also exhibited a wide range of behavior with some patients exhibiting a closing of the mandible 4.3° while other patients underwent an opening of the mandible 3.6°.

Because of the recent interest and controversy regarding computers in diagnosis and prognosis it was decided to compare the actual mandibular rotation with that forecasted by the computer. The computer appears to be fairly well sensitized to mandibular rotation since it predicted significantly less mandibular rotation in Group I (close-close) as compared to the other groups.

The effects of mechanics such as intermaxillary elastics and headgear paralleled that which is reported in the literature. Age and extraction therapy versus non-extraction therapy were not significant in regard to mandibular rotation during treatment and post retention.

Composite tracings of each of the four groups revealed that the mandibular arc cephalometric measurement was significantly different in Group 1 (close-close) when compared to Group 2 (open-close). A prediction of mandibular rotation perhaps can be even further improved by lending more credence to the mandibular arc cephalometric measurement. However, it was found that in many cases the mechanics employed by the orthodontist can supersede the pretreatment mandibular arc measurement. Although the mandibular arc measurement was found to be superior to the facial axis measurement in regard to predicting chin behavior, it is unlikely that it will replace the facial axis due to it being more difficult to evaluate in a cursory manner.

LLU Discipline





Graduate School

First Advisor

Robert M. Ricketts

Second Advisor

James R. Wise

Third Advisor

J. Milford Anholm

Fourth Advisor

Steve N. Asahino

Fifth Advisor

Joseph P. Jacobs

Degree Name

Master of Science (MS)

Degree Level


Year Degree Awarded


Date (Title Page)




Library of Congress/MESH Subject Headings

Facial Bones; Orthodontic Appliances



Page Count

vi; 84

Digital Format


Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.


Loma Linda University Electronic Theses and Dissertations

Collection Website



Loma Linda University. Del E. Webb Memorial Library. University Archives