Risk periods associated with the development of dental fluorosis in maxillary permanent central incisors:: a meta-analysis

This systematic review of the dental literature (1966-98) concerns risk periods associated with dental fluorosis in the maxillary permanent central incisors. A literature search was organized through the MedLine and the ISI databases. In addition, one unpublished paper (in manuscript) was obtained, as well as one paper published before 1966. However, out of 143 catches, only 10 studies were included in this review. The main reason for exclusions was that the data presented did not meet the criteria given for the present meta-analysis. Among the included papers, 7 pertained to subjects whose exposure to fluoride started at different ages during the enamel formation (Group 1), and 3 were based on subjects who had been exposed from birth and then experienced an abrupt reduction in daily fluoride exposure at different ages during the amelogenesis period (Group 2). The meta-analysis for Group 1 found the odds ratio (OR) for dental fluorosis in children exposed to fluoride early in life (before 2 years of age) to be 7.24 (95% CI; 4.71-11.13) as compared to children exposed later in life (after 2 years of age). The meta-analysis for the studies in Group 2 found the overall OR to be 1.88 (95% CI; 1.35-2.61) for children who had a reduction in fluoride intake after 2 years of age, as compared to individuals who experienced reduction earlier (during the first 2 years). The studies from both groups were pooled and the duration of exposure to fluoride during the first 4 years of life was the independent variable. The meta-analysis now revealed an overall OR of 5.83 (95% CI; 2.83-11.94) for long periods of fluoride exposure (>2 out of the first 4 years) versus shorter periods of exposure (<2 out of the first 4 years of life) during the enamel formation in the maxillary central incisors. Based on the findings of the meta-analysis, no specific period of enamel formation is singled out as being the most critical for the development of dental fluorosis. The duration of fluoride exposure during the amelogenesis, rather than specific risk periods, would seem to explain the development of dental fluorosis in the maxillary permanent central incisor.