To understand the defluoridation effect in the historical severe endemic fluorosis areas of Shandong Province, and to analyze characteristics of children's dental fluorosis and related factors.

In 2015, using cross-sectional survey, 11 villages in historical severe endemic fluorosis counties were selected for water fluoride test according to previous investigation of endemic diseases in Shandong Province. In which, 4 normal water fluoride villages, 4 excessive water fluoride villages and 3 villages without water improvement were included. Dental fluorosis in children aged 7 to 12 was examined and urine fluoride was measured. Logistic regression was used to analyze the related factors affecting the detection rate of dental fluorosis.

A total of 732 children aged 7 to 12 were examined, with total detection rate of dental fluorosis 73.2% (536/732). The detection rate of dental fluorosis was 31.0% (65/210), 86.7% (176/203) and 92.5% (295/319) in the villages with normal, excessive and without water improvement villages, respectively. And the differences were statistically significant (χ²= 270.498, P < 0.01). The prevalence of dental fluorosis in girls (77.4%, 264/341) was significantly higher than that in boys (69.6%, 272/391, χ²= 5.337, P < 0.05), and the dental fluorosis prevalence in elderly group (10 - 12 years old, 76.9%, 382/497) was higher than that of younger group (7 - 9 years old, 65.5%, 154/235), the difference was statistically significant (χ²= 10.445, P < 0.05). In water fluoride normal villages, the detection rate of dental fluorosis in girls (40.0%, 36/90) was higher than that in boys (24.2%, 29/120, χ²= 6.033, P < 0.05). In water fluoride unqualified villages, the dental fluorosis prevalence rates in boys and girls were 89.7% (243/271) and 90.8% (228/251), and the difference was not statistically significant (χ²= 0.202, P > 0.05). The urinary fluoride content of children with dental fluorosis was higher than that of non-fluorosis children [(4.5 ± 2.7) vs (1.9 ± 1.5) mg/L, t=- 8.125, P < 0.01]. Logistic analysis showed that the risk of children's dental fluorosis in unqualified water fluoride village was 14.362 times high than that of normal water fluoride villages. The risk of dental fluorosis in children with high urinary fluoride was 2.497 times higher than that in normal urinary fluoride group. The risk of detecting moderate and severe fluorosis in children in the elderly group was 2.270 times higher than that in the younger group. The risk of detecting moderate and severe dental fluorosis in girls was 1.988 times higher than that in boys. The risk of detecting moderate and severe dental fluorosis in children in unqualified water fluoride villages was 49.190 times higher than that in normal water fluoride villages.

Water-quality-improvement project is an effective means to control the epidemic of dental fluorosis in children in severe fluorosis areas. Age, gender and water fluoride are influencing factors associated with dental fluorosis.

Endemic diseases; Fluorosis, dental; Urine; Water-quality-improvement project