Genetics or Environment? A Twin-Method Study of Malocclusions

Objectives: Twin studies that use monozygotic and dizygotic pairs have proven valuable in studies of malocclusion etiologies. The differences in monozygotic twins (Mz) depend on environmental activity, whereas differences in dizygotic twins (Dz) can be due to either environmental or genetic factors. Within-pair Mz twins' considerable concordance testifies to substantial influence through heredity. However, comparable Mz and Dz concordances suggest strong environmental factors. As more frequent within-pair Dz concordances occur, there are stronger claims for environmental influence. Aim: to assess malocclusions susceptible to orthodontic prophylaxis by using the twin-method of analysis. Methods: a comparative analysis of malocclusion was performed in monozygotic and dizygotic twins [164 twin-couples: 90 Mz ¨C 50 males (Mz°á) , 40 females (Mz°â) and 73 Dz couples with 46 male (Dz°á) and 28 female (Dz°â)]. 98% of the zygotic twin-status certainty was assigned using serologic and morphological criteria together with dermatoglyphs. The Allen equation was applied for calculation of the hereditary coefficient for a given malocclusion. Significance established at p<0.05 was used to analyze the data. Results: different distribution of within-pair malocclusions depended upon the gender of the individuals,: nevertheless, the differences with statistical significance occurred only in Class II males and females and males with crossbites. High frequency of within-pair malocclusion similarity (80 ¨C 94%) characterized all groups except the Dz °á where the magnitude was two times less. The differing distribution of the dentoalveolar discrepancies was of statistical significance (p>0.05). The frequency of within-pair similarity equaled 100% in Mz patients, while only 57% was found in Dz°â. The hereditary coefficient had low or negative values - only in males did the examined values exceed 10%. Conclusion: This investigation discovered that environmental factors account for more malocclusions than previously believed. This discovery encourages early intervention to intercept, disrupt and diminish the effects of malocclusions.