A Controlled Study of Enamel Hypoplasia in Twins

METHODS: This case control study (n=128) included twins (n=88) and singletons (n= 40) aged 2-4 years. Medical and social histories were obtained, and the teeth were examined for enamel defects using the modified Developmental Defects of Enamel Index.

RESULTS: The prevalence of EH by teeth was 21% in monozygotic twins (MZ), 22% in dizygotic twins (DZ), and 15% in singleton controls. Significant differences in prevalence were observed between twins and singletons (p<0.05), but differences between MZ and DZ were not statistically significant. EH was noted most frequently in primary second molars (44%), followed by first molars (35%), canines (12%), central incisors (6%) and lateral incisors (3%). There were no significant variations in distribution of EH among the subgroups. Environmental risk factors contributing to increased EH prevalence in twins are likely to be neonatal intubation (twins 35% vs singletons 12%, p<0.05), neonatal complications (twins 65% vs singletons 33%, p<0.05), lower birth weight (twins 2.35kg vs singletons 3.47kg, p<0.05) and shorter gestational age (twins 35.3 weeks vs singletons 38.3 weeks, p<0.05). Further support for the role of environmental factors may be seen in the case of EH on the labial aspects of the primary canine, where there were no significant differences in site concordance within the MZ pairs compared with DZ pairs.

CONCLUSIONS: EH prevalence was significantly higher in twins compared to singletons but no differences were found between MZ and DZ twins.

This project was supported by the Australian Dental Research Foundation and the Dental Board of Queensland. Key words: ENAMEL HYPOPLASIA, TWINS, PRIMARY DENTITION, RISK FACTORS