Case-control study of oral dysplasia and risk habits among patients of a dental hospital.

Several studies have investigated risk factors for oral cancer but few have considered precancer. Records accumulated from 1975 to 1993 of dental hospital patients with histologically confirmed oral dysplasia provided the opportunity for a retrospective case-control study of the association between oral precancer and smoking tobacco and drinking alcohol. Seventy sets of case notes were available and each case was matched with records of a control subject, known to be free from dysplasia from another study, for birth date, gender and presumed ethnicity. The relative risk (OR) of having a dysplastic lesion for smokers compared with non-smokers, or ex-smokers for > 10 years, was 7.00. Logistic multiple regression revealed a dose-response relationship for tobacco dependent upon the level of cigarette consumption. Also subjects with moderate or severe dysplasia included a higher proportion of smokers than those with mild dysplasia. No overall increased risk from alcohol was found. However, the proportion of subjects who drank spirits was significantly higher among cases than controls. The study reaffirms the role of dental practitioners in identifying individuals at risk of mucosal disease, the importance of public education about the risk factors, and the necessity for counselling patients with precancerous lesions on avoiding further risk.