The effects of different conventions regarding missing primary incisors in epidemiological studies

To assess the effects of two different conventions regarding the scoring of missing primary incisors in epidemiological studies.

During 1995/96 a sample of 5-year-old children was examined as part of the national programme of surveys coordinated by the British Association for the Study of Community Dentistry. The fate of missing incisors was recorded according to two conventions and the resulting mean dmfts and components compared.

Eight hundred and twenty-six randomly sampled 5-year-old children were examined by two trained and calibrated examiners under standardised conditions in their primary schools in North, Central and South Manchester.

The overall mean dmft was 3.40 under the new convention and 3.60 with the old, a difference of 5.6%. The mean mt was depressed by 23% from 0.86 to 0.66 under the new convention. The differential between old and new conventions increased with dmft. The district with the highest mean dmft was affected most by the application of the new convention; the mean dmft was depressed by 8.5% from 4.33 to 3.96 and the mean mt was depressed by 32% from 1.17 to 0.80. All differences were significant (P < 0.01).

A change in convention affected the results to varying degrees depending on the disease level of the population group being surveyed.