Deformations of the midfacial complex in twins with orofacial clefts.

OBJECTIVE To investigate the craniofacial morphology in twins with cleft lip and/or palate (OFC) and localize differences, compared with noncleft (NC) twins. DESIGN Retrospective study. SETTING School of Dentistry, University of Michigan. SAMPLE Posteroanterior cephalographs of 32 pairs of dizygotic, concordant, like-sexed twins. The NC group consisted of 20 pairs of noncleft twins. The cleft twin (CT) group consisted of 12 pairs of concordant twins (both exhibited OFC). MAIN OUTCOME MEASURES Changes in linear distances, differences in form difference matrices, and visualization of deformations of thin-plate spline (TPS) transformation grids. RESULTS Linear analysis indicated significant reductions in interorbital distance ( approximately 12%; p <.01) and reduced maxillary heights ( approximately 27%; p <.001) in CTs. Euclidean distance matrix analysis strongly supported these findings, confirmed that the form matrices were significantly different (p <.05), and indicated relative decreases in internasal width ( approximately 12%) and maxillary base width ( approximately 10%). The TPS analysis produced a transformation grid that showed superoinferior compression, suggesting that OFC is associated with a downward displacement of the nasomaxillary complex as well as distortion in the region of the maxillary base. CONCLUSIONS Twins with orofacial clefts differ from their unaffected counterparts by a midfacial skeletal morphology characterized by decreases in interorbital and internasal widths and relatively shorter maxillary basal heights and widths. Although most of these differences appear to be due to compression and regionalized deformation, the resultant inferior displacement of the medial region of the midface concomitant with horizontal widening in the presumptive palatal region may be a development model associated with OFC.