The metal/tissue interface effect in irradiation of the oral cavity

Metal dental prostheses or overlays may lead to increased mucosal reactions of adjacent tissue surfaces during intensive irradiation of the oral cavity. The dosimetry of this phenomenon was investigated by irradiating dental phantoms with 4-and 6-MeV photons. Gold and amalgam interfaces may produce local mucosal doses as high as 150-170% depending on the beam geometry, but doses of 111-126% for gold crowns and about 109-118% for amalgam fillings were found for opposed-beam configurations. 2-4 mm of tissue-equivalent absorber is sufficient to re-establish a homogeneous dose distribution and should be employed throughout therapy whenever dental extraction is unwarranted. The radiobiological exaggeration of the interface effect in treatment with opposed beams using one field per day is discussed.