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Fluorescence in Porcelain Teeth

Porcelain was first used for teeth in dentures back in the 1850s, and since then there has been a continuing effort to fabricate porcelains for dentures and crown and bridgework to simulate the appearance of natural teeth. Achieving a fluorescent appearance in crown and bridgework or in porcelain dentures is just one way to make a dental restoration look more life-like.

It is known that natural teeth have a gleam, which is a result from natural occurring ultra violet light in the light spectrum. This phenomenon is called fluorescence. Porcelain or mineral teeth as they were called in early days of dentistry, were used for crown and bridge and denture teeth. Early porcelain did not look very realistic. It had no fluorescence. A breakthrough came when it was noted that uranium had fluorescence under ultraviolet light. A patent was granted for them in 1942, but there is mention in published scientific articles of uranium use in crown and bridge as early as 1925. The problem with the use of uranium was that it glows a dull yellow-green. This was not a very desirable look. Another breakthrough came when it was discovered that adding cesium (also radioactive) to porcelain gave it a bluish glow, and adding both these radioactive elements to porcelain gave a white glow. This was the fluorescence they had been looking for, and a patent was taken out in 1959. Uranium was so ideal for its use in porcelain fluorescence over other materials because it could survive the high heat of porcelain manufacturing.

After 10 years of use a concerned scientist published a warning of potential radiation danger. In an effort to reduce the radioactivity in crowns and dentures, the porcelain manufacturers decided to use the less radioactive depleted uranium (a nuclear industry waste product) and finally its removal entirely.

The US had eliminated the use of uranium in its dental ceramics by the early 1980s. Europe had it removed a few years earlier. In studies done of some countries in the mid -980s, it was found that crown and bridge powders still had some uranium concentrations. In a study done by Papastefanou et al (1987), measured uranium levels were found in 22 porcelain powders used in Greece.

The Nuclear Regulatory Commission set a limit of 0.05% (500 ppm uranium). Studies of porcelain have shown that they contain 0.02% or 200 ppm of uranium. The maximum range of the emitted alpha particles is only 30 micrometers and the entire dose to the oral tissue would only be received by the superficial cells of the surface, and the dose to the basal layer of the tissue would be zero.

The dental industry has also used uranium and other hazardous materials in its various acrylic tooth and denture base materials, composite materials, and dental cement. From patents in the dental industry, there is mention of the use of heavy metals such as barium, bismuth, lead, cadmium, mercury and of course uranium. Colgate holds a dental patent for a restorative composition using both thorium and tantalum. The use of thorium in medicine is one of great sadness. A thorium compound, Thorotrast, has been abandoned because it induced cancer in a number of patients.

The radioactive element radium has an even more tragic chapter in the history of radioactivity getting into the human body (The Radium Girls). In 1917, radium was used to paint the glowing dials on watches to be used by the soldiers fighting in the First World War. The watch factory workers were not informed of its danger. These girls glowed in the dark, lost all their teeth from rapid bone degeneration, and soon after all painfully died. Perhaps a caution, from the hard lessons learned from the use radioactive radium, is the reason for the discontinued use of uranium in dental porcelains.

An embarrassing, but not harmful, situation presented itself in nightclubs with the fluorescence of denture teeth and the crown and bridge restorations. Under the ultraviolet lights that are used in some clubs, the fluorescent porcelain teeth can glow embarrassingly bright.

Radioactive uranium was used to create a more natural fluorescence in dental porcelains. There may have been a small potential danger to the patient, the manufacturer, and the denturist or lab, but cancer attributed to the use of uranium has never been reported and a recall was never ordered.

Bert Rufenach’s involvement in the profession goes back to the late 1960s in his father’s commercial dental lab. He passed the RDT exams in 1977 and became a licensed denturist in 1979. He served as a director on the Denturist Association of Ontario, is the author of several articles, and has a keen interest in dentistry related to dentures from the late 1850s to the 1920s.