Effect of the buccolingual inclination of teeth on the projected mesiodistal angulation observed in panoramic radiographs

A thesis submitted to the College of Dental Medicine of Nova Southeastern University of the degree of Master of Science in Dentistry. Introduction: Panoramic radiographs are used extensively in the practice of orthodontics. They are used at the beginning of treatment to evaluate tooth presence, development and location, as well as, pathology, and the general location of anatomic structures. Panoramic radiographs are used during and after treatment to monitor those conditions as well as to assess the progress of the treatment such as the parallelism of the roots of teeth. Although the accuracy of panoramic radiographs in evaluating root parallelism has been questioned, the use of the panoramic radiographs to evaluate root parallelism is still common practice in orthodontics. Objective: To evaluate the effects the buccolingual inclination of teeth has on the projected mesiodistal angulation or root parallelism presented in panoramic radiographs. Materials and Methods: Using a dental typodonts the dentitions were bracketed using 0.022 x 0.028 ceramic brackets. The typodonts were fabricated so that between both of them the maxillary and mandibular experimental teeth from lateral incisor to second premolar were free to move about an axis surrounding the bracket and the archwire. A 0.021 x 0.025 stainless steel archwire was used to establish a standard buccolingual position for the moveable teeth. A 0.020 stainless steel archwire was then used to allow for buccolingual rotation to occur. The moveable teeth had their mesiodistal angulation and buccolingual inclination measured with a coordinate measuring machine (CMM). The teeth were positioned and measured at five degree increments in the buccolingual direction to +/- 20 degrees. At each buccolingual inclination the mesiodistal angulation was measured with the CMM. Panoramic radiographs were taken in each position. The mesiodistal angulation was then measured on the radiographs. The actual mesiodistal angulations recorded with CMM were then compared with the angulations on the panoramic radiographs. Results: A Wilcoxon sign rank test was run on the data to evaluate statistical differences. Statistically significant differences were seen at the buccolingual inclinations of +15, +20, and -20 degrees. In comparing the difference between the CMM measurements and the comparable panoramic measurements 63 percent fell outside of the clinically acceptable range of +/- 2.5 degrees. Conclusions: Caution should be taken in evaluating root parallelism with panoramic radiographs. The buccolingual inclination can affect the mesiodistal projection on panoramic radiographs. The areas of the canines and first premolars are especially susceptible to distortion