A study on the prevalence of dental fluorosis of children after change of water in the endemic fluorosis areas in Xi'an City and influencing factors

Abstract

Objective To assess the effects of defluoridation on prevalence of children's dental fluorosis in Xi'an City and study related influencing factors. Methods In 2017, the survey results of 2013 were collected from the previous investigation of drinking water type fluorosis in Xi'an Center for Disease Control and Prevention, and villages from drinking water type fluorosis areas were divided into five groups: 0.0 -, 0.2 -, 0.5 -, 1.0 -, and ≥1.5 mg/L, according to the fluoride concentrations of water. Four villages were randomly selected from each group, a total of 20 villages were selected as the investigation sites. A cross-sectional analytical study was conducted in the 20 villages, the fluoride in drinking water, the dental fluorosis of children aged 8 - 12 years and fluoride content in urine were detected, and the survey results were compared with those of 2013. Children were divided into five groups according to urinary fluoride contents as: 0.0 - (control), 0.4 -, 0.8 -, 1.2 -, and ≥1.6 mg/L, and the logistic regression model was used to evaluate the risk of dental fluorosis. Results There were no significant differences in water fluoride content between 2013 and 2017 (P > 0.05). The rates of dental fluorosis among the study population in 2013 and 2017 were 25.35% (200/789) and 20.58% (164/797), and the difference was significant (χ2 = 5.11, P < 0.05). The prevalence rate and severity of dental fluorosis in 2013 [3.52% (9/256), 13.28% (17/128), 31.62% (43/136), 37.82%(45/119), 57.33%(86/150)] and 2017[4.02%(10/249), 11.82%(13/110), 18.05%(24/133), 29.13%(37/127), 44.94% (80/178)] were significantly increased with increase of water fluoride concentration (χ2 = 168.02, 117.83, P < 0.01). The prevalence rate of dental fluorosis was higher than 30% in the three groups with water fluoride content 0.5 -, 1.0 - and ≥1.5 mg/L in 2013, and the prevalence rates were decreased in these groups in 2017. The prevalence rate of dental fluorosis was lower than 30% in the groups with water-fluorine content of 0.5 -, 1.0 - < 1.5 mg/L, while the rate of dental fluorosis in the group with water-fluorine content of higher than 1.5 mg/L was still over 40%. The geometric mean of urinary fluoride of children in 2013 and 2017 were 1.02, 0.67 mg/L, and the difference was significant (t = 10.24, P < 0.01). There were significant differences in children urinary fluoride between water fluoride groups in 2013 and 2017 (F = 85.36, 151.14, P < 0.01). The risk of dental fluorosis increased with increase of urinary fluoride content, the odds ratio (OR) values were 5.26, 7.83 and 13.28 in the three groups with the urinary fluoride 0.8 -, 1.2 -, ≥1.6 mg/L in 2013; the OR values in 2017 were 5.18, 7.65 and 13.36, the differences were statistically significant (P < 0.05). Conclusions The situation of water fluoride and dental fluorosis are not optimistic after defluoridation of drinking water. It is necessary to reinforce the measures of water defluoridation, and carry out classified management in endemic fluorosis areas. Key words: Drinking; Fluorosis, dental; Urine