The effects of buccolingual root torque on the appearance of root angulation on panoramic radiographs

Abstract

It is common practice for orthodontists to use panoramic images to assess root parallelism before, during, and after orthodontic treatment. The purpose of this laboratory study was to examine the effects of changes in buccolingual root torque on mesiodistal root angulation imaged on panoramic radiographs. Teeth investigated were maxillary lateral incisors and second premolars, and mandibular first and second premolars. By using a transparent typodont model with anatomically correct teeth (typical crown and root anatomy), root torque was progressively added to the teeth in 5° increments, totaling up to 15° of torque in each direction. Standardized digital photographs and panoramic radiographs were made after each adjustment. The photographs made from a facial perspective documented that the roots remained parallel. With each increment of change in root torque, measurement of the root apex position in a mesiodistal direction was made on the panoramic radiograph. Results showed that when torque was changed, distortion inherent to the panoramic radiograph created the appearance of mesial or distal movement of the root apices. For the premolars, adding lingual root torque (LRT) resulted in apparent increases in mesial root tip (eg, with 15° LRT, the root tips moved mesially 1.9 to 2.8 mm), whereas adding buccal root torque (BRT) resulted in apparent increases in distal root tip (eg, with 15° BRT, the root tips moved distally 2.8 to 4.4 mm). For the lateral incisors, changes in torque had a less pronounced effect on apparent root tip (eg, with 15° LRT, the root tips moved mesially 1.2 mm; with 15° BRT, the root tips moved distally 0.17 mm). The results show that changes in root torque predictably affect the appearance of root tip on panoramic radiographs. The findings suggest that if roots appear incorrectly aligned on panoramic images, the teeth in question should be carefully examined clinically (or with periapical images) to differentiate the need for appliance adjustments that alter root tip versus root torque. Am J Orthod Dentofacial Orthop 2005;127:393 0889-5406/$30.00 Copyright © 2005 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2004.07.015