An epidemiological assessment of the chronological distribution of dental fluorosis in human maxillary central incisors.

The objectives of this study were: (1) to develop and test a new index, the Chronological Fluorosis Assessment (CFA) Index, for measuring variation in the chronological distribution and intensity of dental fluorosis, and (2) to determine whether the new index was sufficiently sensitive for detection of a decline in dental fluorosis corresponding to the reduction in the waterborne fluoride level in Hong Kong. According to the CFA Index, the cervical, middle, and incisal third divisions of the labial surface of a maxillary central incisor crown are each classified into one of six categories of an ordinal scale of fluorosis. Data from 1295 life-long resident Hong Kong Chinese children exposed to known water fluoride concentrations were analyzed. Fluorosis declined from incisal to cervical in 41% of cases, and a reverse gradient was apparent in 29%. Overall, fluorosis intensity was higher on incisal thirds than on both middle and cervical thirds. However, when tooth thirds were regrouped according to common 16-month developmental periods, in order to control for time-related variation in fluoride concentration, the incisal-middle difference was of reduced statistical significance, and both the incisal-cervical and the middle-cervical differences became insignificant. A regression analysis of CFA Index on cohort indicated a significant cohort-related fluorosis decrease, in relation to cervical, middle, and incisal tooth thirds. It was concluded (1) that fluorosed enamel which forms in chronological sequence tends toward a uniform intensity, and (2) that the new index was sufficiently sensitive for a decline to be measured in dental fluorosis in Hong Kong.