[The inaccuracy of the panoramic radiograph as a tool to determine tooth inclination]

The panoramic radiograph is one of the most common radiographs in orthodontics. It is sometimes used as an aid for the decision which teeth should be extracted as part of the individual treatment plan. When treating patients with clear plates (for example, Invisalign), it is very important to know the inclination direction of the involved teeth. Tipping is more predictable and it takes less time than bodily movement. The objective of this paper is to demonstrate the limitations of the panoramic radiograph in the decision making process related extraction in orthodontics. An eleven years old girl with lower anterior crowding of about 5 mm was examined prior to her orthodontic treatment. One possible treatment plan, in order to relieve the crowding, was to extract two lower bicuspids. The other treatment plan was to extract one lower incisor. Clinically, both cuspids were acutely tipped mesially, but were imaged uprighted and parallel to their adjacent teeth in the panoramic radiograph. In order to better understand the cuspids position, a model of the lower arch was prepared, with a similar malocclusion demonstrated by the patient. In the model, the cuspids' metal teeth, invested in wax, were mesially angulated. A panoramic radiograph of the model was then taken. The radiograph of the model shows a parallel position of the incisors, the cuspids and the bicuspids, exactly as was shown in the patient's radiograph. It has been demonstrated that there is a discrepancy between the actual position of the teeth and roots and their position in the panoramic radiograph, especially in the mesiodistal angulation. It was concluded that we should be very cautious when trying to interpret the panoramic radiograph as a tool for root parallelism, and remember the inherent image distortions. This is especially true before deciding which teeth will be extracted, on the basis of "incorrect" tooth angulation.