Longitudinal survey of enamel defects in a cohort of New Zealand children.

Enamel defects are being used increasingly to monitor fluoride use. In New Zealand in 1982 a survey of the prevalence of enamel defects in 9-yr-old children was carried out. Children who had enamel defects on the labial surfaces of their maxillary incisors were re-examined after 3 yr together with an equal number of children without defects. The same examiner using the same examination methods and the DDE index carried out both examinations but at the second examination was unaware of the results for individual children at the first examination. There was little difference in the group prevalence of the main defect categories except for the tooth prevalence of hypoplasia. There was an increase in discolouration and hypoplasia occurring in combination with diffuse fluoride-related opacities. There was no evidence that defects had faded with time. This longitudinal survey showed that some increase in defect severity occurred over a relatively short time span in initially mild defects. In some children these changes were sufficient to cause a deterioration in tooth appearance. Age and tooth specific enamel defect data are necessary in surveys monitoring the public health use of fluoride since posteruptive changes can affect prevalence and severity.