Localised enamel hypoplasia of human deciduous canines: genotype or environment?

A discrete area of defective enamel formation that appears on the labial su rface of the crowns of deciduous canine teeth has been described in both re cent and prehistoric human populations, with reported frequencies varying f rom 1 to 45 per cent. Suggestions about the aetiology of this localized hyp oplasia range from genotypic factors to environmental conditions and system ic effects. The major aims of this study were to describe the frequency of occurrence and pattern of expression of the lesion in Australian Aboriginal and Caucasian ethnic groups, and to clarify the role of genetic factors by examining a sample of twins. The study sample consisted of dental casts of 181 pairs of Australian Cauca sian twins, 215 Aborigines and 122 Caucasian singletons, together with 253 extracted deciduous canines, Examination of dental casts and extracted teet h was undertaken under 2x magnification with emphasis being placed upon loc ation and expression of the lesion. The defect was observed in 49 per cent of twins and 44 per cent of Aborigines, but only 36 per cent of singletons. The percentages of affected teeth in each group were: 18 per cent in twins , 17 per cent in Aborigines and 13 per cent in Caucasians. A significant pr oportion of the defects occurred on the mesial aspect of the labial surface , in the middle area incisocervically, with the majority in the lower jaw. A number of significant differences in frequency were observed between grou ps, sexes, arches and sides. The results confirm some of the findings of previous studies, but also sugg est that none of environmental, genetic or systemic factors can be ruled ou t as being involved in aetiology of the defect. The higher incidence of the lesion occurring on the mesial aspect of the labial surface is suggestive of physical trauma. Also, the vulnerability of the prominent developing man dibular canine, with its thin or missing labial covering of bone, would be expected to lead to higher prevalence of the lesion in the lower jaw. Altho ugh not definitive, the results of concordance analyses in twins were sugge stive of a possible genetic predisposition in the formation of the lesion, Further research with a greater clinical orientation and emphasis on determ ining specific aetiological factors within any given environment in differe nt ethnic groups may provide better insight into the ambiguous aetiology of the hypoplastic enamel defect.