Radiographic evaluation of mandibular asymmetry in twins with III skeletal class

Aim: this study aims to evaluate mandibular deviation or asimmetries in couples of twins who have a skeletal III class through measurements made on frontal telecranium in postero-anterior projection. Methods: twins with skeletal III class were selected because literature reports that patients with skeletal III class are more predisposed to mandibular asimmetry. Frontal telecranium in postero-anterior projection of 4 couples of twins were analyzed thanks to the permission of AAOF Craniofacial Growth Legacy Collection and Forsyth Institute. RX were all taken before the beginning of an orthodontic treatment. Measurements used were: distance between GA, AG and PM; GA/AG ratio; distance between GA and AG’s perpendicular projections on MP (Mid-plane). Results: 3 of the 4 couples analyzed had a GA/AG ratio less than 1, so there was a left transverse deviation. The other couple instead had a GA/AG ratio higher than 1, so a right transverse deviation. Every twin in each couple had a deviation on the same side (left or right). 3 of the 4 couples presented a normal range of vertical asymmetry (0+/-2 mm). The other couple had higher asymmetry respectively of 10 and 5 mm, both of them on the left. Conclusions: despite a poor sample, all couples of twins had concordant transversal and vertical asymmetries. Other studies should be taken to validate this analysis.