Prevalence of dental fluorosis in German schoolchildren in areas with different preventive programmes.

In a retrospective study in two different regions of Germany, 1,041 fifteen-year-old pupils were examined for dental fluorosis. The adolescents had taken part in different caries prevention programmes. There were 746 subjects in the study group and 295 subjects in the control group. For each participant, specific aspects of early development, diet and fluoride exposure in group prevention programmes and at home were determined by means of questionnaires. The Thylstrup-Fejerskov index was used to classify the fluorosis scores on the buccal surfaces of teeth 11, 12, 13, 14, 15 and 16 after compressed air drying of the teeth. Binary logistic stepwise regression analyses were conducted to identify associations between fluorosis and potential influence factors. A distinction was made between early and late developing tooth parts. The significance level was set at alpha = 0.05. Fluorosis prevalence in the regions studied was 7.1 and 11.3%, respectively. The difference was not statistically significant (p = 0.052; chi square). Binary logistic stepwise regression analysis revealed that 'early start of toothbrushing' was a statistically significant predictor of dental fluorosis in the early-mineralizing enamel (OR = 1.99, p = 0.027). For the late-mineralizing enamel no single independent variable was identified as a significant predictor of dental fluorosis.

Procarbazine-induced specific-locus mutations in male mice.

Procarbazine is used in drug-combination treatment of Hodgkin's disease. The specific locus method was used to test and confirm the ability of procarbazine to induce gene mutations in pre- and post-meiotic germ cells of male mice. The lowest dose of procarbazine that significantly increased the mutation frequency in As spermatogonia over the control frequency was 400 mg/kg (P = 0.003). The corresponding dose for the post-spermatogonial germ-cell stages was 600 mg/kg (P = 0.009). The dose--response was linear for the point estimates of the mutation frequencies after treatment of As spermatogonia with 0, 200, 400 and 600 mg/kg. The point estimate of the mutation frequency at the 800 mg/kg level was one-third of that expected from a linear extrapolation. Variation in mutation rates among the 7 loci between the lowest (a locus) and the highest (p locus) was 12-fold. Only 24% of procarbazine-induced specific locus mutations in As spermatogonia were lethal in the homozygous condition. From the mutation spectra and the viability tests, it is concluded that procarbazine-induced mutations may be mainly due to base-pair changes. Procarbazine-induced specific-locus mutations fulfilled the criteria for the estimation of the doubling dose, the dose necessary to induce as many mutations as occur spontaneously. The doubling dose of procarbazine in As spermatogonia of mice was 114 mg/kg. The therapeutic dose for procarbazine is about 215 mg/kg. If man and mouse were equally sensitive, this dose would induce 1.9 times as many mutations as arise spontaneously. From the incidence of patients with Hodgkin's disease (1 : 42 000) the calculated population dose of procarbazine is 5.12 micrograms/kg. Assuming equal sensitivity between the sexes we can calculate, for an estimated number of 30 000 genes, the induction of about 22 mutations per million children due to procarbazine treatment. The same number of induced mutations can be calculated if the risk of patients is used for the estimation of the genetic hazard.