Public Health Dispatch: Potential Risk for Lead Exposure in Dental Offices

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In December 2000, the Washington State Health Department discovered white powder that was found to be lead oxide in boxes used to store dental intraoral radiograph film. The Washington State Health Department alerted state health departments throughout the United States. Subsequently, the Wisconsin Division of Public Health (WDPH) conducted an investigation of dental offices in the state. This report summarizes the investigation, which indicated that similar storage boxes are used in Wisconsin. The findings indicate that patients are at risk for exposure to a substantial amount of lead during a dental radiograph procedure if the office stores dental film in these boxes.

During January--March 2001, radiation safety inspectors in Wisconsin visited 240 (9%) of 2,748 dental offices with radiograph equipment. Of these, 43 (18%) stored radiograph film in table-top, lead-lined boxes. Of 11 dental offices in use for >20 years, four (36%) used this storage method.

The boxes were usually made of wood and shaped like a shoe box. All boxes contained a white powder residue. A bulk sample of the residue contained 77% lead identified as lead oxide. Visits to dental offices occurred before and after a mailing had been sent by WDPH to all dental offices with radiograph equipment warning about possible lead exposure and recommending that lead-lined storage boxes be discarded. Many offices discarded the boxes before the inspection. In one office, after receiving the warning, paper was placed in the bottom of the box and film was placed on top of the paper. In another office, dental instruments had been placed in the box. Other offices used a vertical wall-mounted, lead-lined film dispensing box. Some of these boxes and the film in them also contained lead.

A mock dental radiograph procedure was performed during which wipes were placed on the tips of a dental hygienist's fingers whenever a patient's mouth was touched. Analysis of these wipe samples found 3,378µg lead that could have been transferred from the hygienist's fingers to a patient's mouth. Lead also could have been introduced directly from the film. Wipe samples of eight film packets from two dental offices that used the lead-lined storage boxes identified average lead levels of 3,352µg (range: 262µg--34,000µg). During a typical radiographic procedure, usually conducted once per year, >4 separate views are taken. When children's teeth develop to the point where adjacent teeth touch (usually age 3 years), radiographs may be taken if the dentist suspects decay.

Because of the increased susceptibility of children and the developing fetus (1), lead exposure is particularly dangerous for children and for women who are or may soon become pregnant. The approximate half-life of lead in blood is 25 days (2); as a result, the window for identifying lead exposure following dental radiographs is a few months. Health-care providers who discover high blood lead levels of unexplained origin should consider this possible route of exposure.

Advances in dental radiograph technology have reduced scatter radiation---the reason for protective boxes---making lead-lined radiograph storage boxes unnecessary. Because lead oxide cannot be removed adequately, the film packets stored in lead-lined boxes and the film packets stored in them should be discarded.

Reported by: M Chamberlain, M Bunge, W Otto, HA Anderson, MD, State Epidemiologist, Bur of Environmental Health; N McKenney, MS, W LeMay, DDS, Wisconsin Div of Public Health. Lead Poisoning Prevention Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health; and an EIS Officer, CDC.

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