Effect of repeated firing on fluorescence of porcelain-fused-to-metal porcelains.

T o simulate the bluish-white fluorescence of natural teeth under ultraviolet light,‘-’ dental manufacturers use fluorophors of proprietary composition. Uranium oxides were often used in the past in combination with cerium to impart a realistic fluorescence to dental porcelain.* Uranium is no longer used as a result of increased awareness of possible radiation effects on oral tissues.‘.” Fluorescent dental porcelains are often patented; for example, fluorescence activators for Shofu porcelain (Shofu Dental Corp., Monrovia, Calif.) include combinations of rare earths such as europium, cerium, and ytterbium.” Both natural and artificial teeth are exposed to ultraviolet (UV) light routinely. Not only does sunlight contain a significant UV component, but so do certain fluorescent lights, photoflash lights, high intensity studio lights, and entertainment lights. The bluish-white fluorescence of natural teeth is the result of a broad emission band with a diffuse peak at 410 to 420 nm when subjected to near UV excitation of approximately 340 nm (Fig. l).13 It appears that both the organic and inorganic portions of tooth structure are involved, but that for enamel the organic component predominates.‘4 In 1978, the luminescence spectra of many dental porcelains and acrylic resins commercially available were published.13 At that time, the effect of repeated firing on fluorescence was not investigated, and a clear distinction among the characteristics of opaque, body, and enamel porcelains was not made. It was felt, therefore, that a new study on presently used commercial porcelain was worthwhile.