Evaluation of tooth angulation measured on cone beam computed tomography and panoramic radiographs.

Abstract

Panoramic radiographs have been used for decades in the field of dentistry and in orthodontics in particular. Panoramic radiography use in orthodontics includes (but is not limited to): pre-treatment dental assessment, dental age estimation, the detection of dental anomalies, the identification of missing and impacted teeth, the prognosis for unerupted teeth, periodontal tissue assessment and pre-finishing root parallelism. The determination and validity of root position has been debated by many authors and practitioners. Knowledge regarding the production of panoramic radiographs questions whether they are the best way of judging tooth angulation. Aims: The main aim of this study was to assess dental angulation measurements generated by two panoramic x-ray machines. An attempt would be made to correct appraisal differences and, therefore, render the films more useful in providing the necessary diagnostic information to achieve optimal orthodontic treatment results. Methods: A dry human skull with an inserted typodont was imaged using two different panoramic machines in addition to a CBCT machine. Teeth within the typodont had metal markers attached to their coronal and apical ends. The markers and therefore the long axes of the teeth were identified. Teeth were divided into 5 groups (Anterior-Anterior, Anterior- Premolar, Premolar-Premolar, Premolar-Molar and Molar-Molar). The angles between adjacent teeth were measured on an “OPG extrapolation” produced by tracing markers directly on panoramic radiographs. The same measurements were performed on “Focal Trough Specific extrapolations” which were produced by applying the panoramic machine-specific focal trough around the coordinates of the coronal and apical markers. Each machine had its own “OPG extrapolation” and “Focal Trough Specific extrapolation”. The four extrapolations were compared. Results: A wide range of variation in tooth angulation was found between the measurements of each machine. For the Carestream machine, the Premolar-Molar and Molar-Molar regions were represented poorly on panoramic radiographs. While for the Vatech machine, Premolar- Premolar and Anterior-Premolar were the groups represented least accurately on the panoramic radiographs. Conclusion: Panoramic radiographs should be interpreted with caution when assessing tooth angulations. Panoramic x-ray machine manufacturers should be encouraged to provide a range of error values to help practitioners have a better understanding of the limitations of panoramic radiographic interpretation.