Orthodontic residents' indications for use of the lateral TMJ tomogram and the posteroanterior cephalogram.

The purpose of this study was to determine the selection criteria used by orthodontic residents for ordering a corrected lateral tomogram (LT) of the temporomandibular joint (TMJ) and a posteroanterior cephalogram (PAC) for the diagnosis of patients needing orthodontic care. The impact of the radiographs on their treatment plans was also assessed. We conducted a study of the 144 new patients assigned to eight orthodontic residents during a two-year period. The residents responded through questionnaires describing their rationale for ordering the radiographs. A LT was ordered for twenty-eight (19 percent) of the patients. The most common reasons cited for requesting the LTs were TMJ clicking (67 percent) and pain (33 percent). The residents also perceived a need to order the LT for medico-legal protection in 85 percent of these cases. The LT tended not to have an impact on treatment planning. A PAC was ordered thirty-eight times (26 percent). The most common reasons cited by residents for ordering a PAC included clinical findings of facial asymmetry (41 percent) and maxillary airway anatomy (24 percent). Medico-legal protection was a perceived need in only 12 percent of the cases. While the PAC had no impact on treatment planning for 56 percent of the cases, they did define the transverse problems as dental or skeletal for 38 percent of the cases. Six patient traits were statistically associated with PAC requests: difficulty chewing, abnormal TMJ, TMJ clicking, facial asymmetry. crossbite, and midline discrepancy. The teaching of appropriate selection criteria for ordering these radiographs needs to be emphasized early in a resident's training.