THIN-PLATE SPLINE ANALYSIS OF THE CRANIAL BASE IN SUBJECTS WITH CLASS-III MALOCCLUSION

The role of the cranial base in the emergence of Class III malocclusio n is not fully understood. This study determines deformations that con tribute to a Class III cranial base morphology, employing thin-plate s pline analysis on lateral cephalographs. A total of 73 children of Eur opean-American descent aged between 5 and 11 years of age with Class I II malocclusion were compared with an equivalent group of subjects wit h a normal, untreated, Class I molar occlusion. The cephalographs were traced, checked and subdivided into seven age-and sex-matched groups. Thirteen points on the crania[ base were identified and digitized. Th e datasets were scaled to an equivalent size, and statistical analysis indicated significant differences between average Class I and Class I II cranial base morphologies for each group. Thin-plate spline analysi s indicated that both affine (uniform) and non-affine transformations contribute toward the total spline for each average cranial base morph ology at each age group analysed. For non-affine transformations, Part ial warps 10, 8 and 7 had high magnitudes, indicating large-scale defo rmations affecting Bolton point, basion, pterygo-maxillare, Ricketts' point and articulare. In contrast, high eigenvalues associated with Pa rtial warps 1-3, indicating localized shape changes, were found at tub erculum sellae, sella, and the frontonasomaxillary suture. It is concl uded that large spatial-scale deformations affect the occipital comple x of the cranial base and sphenoidal region, in combination with local ized distortions at the frontonasal suture. These deformations may con tribute to reduced orthocephalization or deficient flattening of the c ranial base antero-posteriorly that, in turn, leads to the formation o f a Class III malocclusion.