The Relationship of Dental Fluorosis, Intellectual Efficiency and Working Memory in 13-15-year-olds Living in Low, Medium and High-water Fluoride Areas in Kajiado County

Abstract

Introduction: WHO recommends that water fluoride does not exceed 1.5mg/l. Intake of higher concentration has been reported to cause dental fluorosis, skeletal fluorosis and also to be a neurotoxin. Water is the primary source of fluoride to the human body. Study aim: The study aimed to determine the fluoride concentration in water, the prevalence and severity of dental fluorosis; the intellectual efficiency and working memory of children born and living in different fluoride areas and their differences and associations if any. Materials and methods: Study area and design: A cross-sectional descriptive study design was conducted in Kajiado county Kajiado North subcounty. The study was done between October 2016 and March 2017. A pilot study was done to determine the fluoride content of the water in selected areas in Kajiado North sub-county. Sampling and sample size: Seven schools were randomly selected according to fluoride content in the area of water. Two hundred and sixty-nine participants, 13-15-year-old adolescents who attended day public schools, were chosen from the three areas of high fluoride, medium fluoride and low fluoride. The areas were then divided into three of low with water fluoride ≤1.0 mg/l; medium with water fluoride ≥1.1 mg/l and ≤2.0mg/l and high fluoride with water fluoride ≥2.1mg/l none had significant heavy metal content. The fluoride in water was analysed using the specific fluoride ion-selective electrode. The use of a semi- structured questionnaire collected socio-demographic data while the Thylstrup and Fejerskov index used to determine the degree of dental fluorosis. The working memory test was done using the Weschler Intelligence Scale for Children V and the intelligence efficiency done using Wide Range Achievement Test-IV. The SPSS version 22.0 was used for data analysis and the study was conducted subject to consent from the University’s Research and Ethics Committee, Ministry of Education, Kajiado County and the guardians/parents Results: Two hundred and sixty-nine adolescents aged between 13-15 years were included in the study with one hundred and seventy-eight (66.2%) females and ninety-one (33.8%) males. The water fluoride varied from 0.8mg/l to 15.0mg/l according to the source from the school the individual attended. The household fluoride ranged from 0.5-15mg/l. The prevalence of dental fluorosis was 67.7% with household water fluoride being the most influential predictor of dental fluorosis. The mean IE of those from low water fluoride areas was 104.9+/-14.61; medium water fluoride areas were 106.3+/-13.6 while those of high water fluoride area were 97.8+/-12.5. When the household water was used to categorise, the mean IE was 107.5 for low household water fluoride and 96.2 for both medium and high household water fluoride. There was a difference in IE of adolescents living in low fluoride when compared to those living in high fluoride areas. There was no difference in means between low and medium fluoride areas. There was a difference in IE for individuals with dental fluorosis and those without; those without having higher mean IE (103.87) than those with dental fluorosis (99.044). WM for the fluoride concentrations was different from those in low water fluoride having a higher mean WM than those with high household water fluoride. Similarly, the differences in the means for working memory for the children in the medium and high fluoride areas were significant. However, a comparison in the means for working memory between the children in the low and high fluoride areas was not significant. There was a difference in working memory between populations with dental fluorosis and those without dental fluorosis. There was a significant association between prevalence and severity of dental fluorosis and the water fluoride content. Conclusion: Children who were exposed to fluoride were at the risk of developing impaired intellectual efficiency, which also affects IQ. Recommendations: water supply should be given priority by the authorities and education and awareness also given priority. More studies need to be conducted in this area. Limitations: The survey was across-sectional, and it may not be representative of the effect of fluoride on children from birth up to adolescent if it was controlled and longitudinal