Method: Two samples were analysed. The first sample comprised 1,454 panoramic radiographs of singleton boys and girls aged 9-10 years. The second sample comprised study models of 202 members of monozygotic and dizygotic twin pairs aged 8-11 years. Adobe Photoshop CS5 was used to construct reference lines and measure the extent of infraocclusion (in mm) of primary molars on the panoramic radiographs and on 2D images obtained from the study models. The panoramic radiographs were examined for the presence of selected dental anomalies and to assess dental development following the Demirjian and Willems systems. The twins study models were measured to assess mesiodistal crown widths.
Result: In the singleton sample there was a significant association of ectopic canines and the lateral incisor complex with infraocclusion (P<0.001), but no significant association was revealed between infraocclusion and agenesis of mandibular premolars. Dental age assessment revealed that dental development was delayed in infraocclusion patients compared to controls. The primary canines and the primary mandibular first molar were significantly smaller in size in the infraoccluded group (P<0.05).
Conclusion: A possible pleiotropic effect was reflected by the presence of other associated dental anomalies with infraocclusion. Early diagnosis of infraocclusion and associated dental anomalies should help clinicians provide better counselling for patients and care-givers and also improve clinical management.
Acknowledgements: The support of the following funding agencies is gratefully acknowledged: National Health and Medical Research Council of Australia, Australian Dental Research Foundation, and The University of Adelaide.