Considerations in determining the FS-T index

Background: Dental caries experience is traditionally recorded using the decayed (D), missing (M) and filled (F), DMF-T index. It has been suggested that this method of summating caries experience gives inadequate weight to sound (S) teeth, and the FS-T (filled and sound) index has been proposed as a measure of functional status, in estimating the impact of caries. Previous studies have assumed 28 teeth in estimating the FS-T index. Objectives: In 12 years olds, to compare; (1) the FS-T index estimated as (FS-T=28-DM), (2) the FS-T index calculated on the basis of clinical examination and (3) the worst third FS-T, with DMFT in comparing local health boards (LHBs) in Wales. Methods: Data from the 2001 BASCD survey of 7,412 twelve year-olds in Wales were used in this analysis. Results: The mean DMFT was 1.31 and ranged from 0.97-1.79 in Cardiff and Carmarthenshire respectively. The mean FS-T estimated was 27.28 (range 27.67-26.93). However, using clinical examination data the FS-T was 23.82 (range 24.64-22.98). The FS-T (clinical) for the worst third of the population was 19.39 (range 20.91-17.59). Marked differences in rank order (up to 10 places) were observed when the 22 LHBs were ranked according to FS-T estimated and FS-T clinical. This can be accounted for by the fact that in Wales overall, just 27.5% of children had 28 teeth, the proportion of children with a complete dentition ranged from 19.8-35.7% in different LHBs. This may reflect earlier eruption of teeth in high caries areas (due to early primary tooth loss) or possible extraction for orthodontic purposes in more affluent localities. Conclusion: In Welsh 12 year-olds, assuming 28 teeth present in estimating FS-T scores, overestimates the functional dentition. FS-T indices should therefore be based on clinical examination derived data. The support of the Wales Assembly Government is acknowledged gratefully.