Background: Yusho is a disease caused by the ingestion of rice bran oil contaminated with polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs) and related compounds. Oral lesions such as oral pigmentation, anomalies of the dental root shape and deficiency of tooth germs have been observed in Yusho patients. Objective: The purpose of this study was to determine the prevalence of oral lesions, especially oral pigmentation, in Yusho patients, and also to describe the relationship between oral lesions and PCBs or PCDFs. Methods: Visual and radiographic examinations were performed on Yusho patients who visited the dentist during the annual health examination in Fukuoka prefecture. The data obtained from 1968 to 2003 were analyzed. Results: Gingival pigmentation was the most common of all types of oral pigmentation seen in Yusho patients. Of all the examined Yusho patients, the proportion who had gingival pigmentation was more than 60% during the early phase after the Yusho incident, but this value had decreased to below 30% in 1993. However, it subsequently increased again to about 50% in 2003. Yusho patients with a blood PCB pattern typical of Yusho showed the highest incidence of oral pigmentation 5 years after PCB poisoning. As time passed, however, there was no specific difference in the prevalence of oral pigmentation between any type of PCB pattern, either specific to Yusho or commonly observed in the general population. Analysis of data by three-way analysis of variance (ANOVA) in 2001 and 2002 showed that there was a close relationship between the presence of upper gingival pigmentation and blood PCDF levels. Conclusions: The prevalence of oral pigmentation still remains high even after 35 years, and PCDFs may be responsible for the presence of oral pigmentation.
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