Zygomatic arch interference with correct radiographic diagnosis in maxillary molar endodontics

Five hundred twenty-four periapical radiographs taken with the bisecting-angle technique were evaluated for interference of the zygomatic arch with the apical third of the roots of the first and second upper molars. The number of interferences around the second molar apices was much larger (42 percent average) than those around the first molar apices (20 percent average). For endodontic radiographic diagnosis of the upper two molars, the bisecting-angle technique has proved to be unreliable.