Liver cancer risk in Japanese male dentists: a long-term retrospective cohort study

It has been speculated that dentists are at high risk for occupational exposure to bloodborne viruses such as hepatitis B and hepatitis C viruses. To assess the risk of the development of liver cancer among Japanese male dentists, we conducted a retrospective cohort study on 3,314 dentists of the Osaka Dental Association who were members between 1964 and 1985, the year before HBV immunization became available. By linking to the Osaka Cancer Registry, we found that during the period of 1964-1997, 36 of the dentists were diagnosed with liver cancer over a mean follow-up of 23.6 yr. The observed number of liver cancer cases was compared with the expected number, which was calculated by multiplying the number of person-years at risk by the corresponding age- and calendar time-specific incidence rate from the Osaka Cancer Registry data. The male dentists had a significantly lower risk of developing liver cancer than the general population of Osaka (O/E=0.71, 95% CI=0.50-0.98). On subcategorical analysis by birth year or duration of follow-up, there was no significantly increased risk of developing liver cancer among the dentists. Contrary to our expectation, our findings indicate that Japanese dentists were not at increased risk of developing liver cancer compared with the general population.