Abstract
The main aim of this study was to generate an adequate sub-phenotypic clustering model of class III skeletal malocclusion in an adult population of southern European origin. The study design was conducted in two phases, a preliminary cross-sectional study and a subsequent discriminatory evaluation by main component and cluster analysis to identify differentiated skeletal sub-groups with differentiated phenotypic characteristics. Radiometric data from 699 adult patients of southern European origin were analyzed in 212 selected subjects affected by class III skeletal malocclusion. The varimax rotation was used with Kaiser normalization, to prevent variables with more explanatory capacity from affecting the rotation. A total of 21,624 radiographic measurements were obtained as part of the cluster model generation, using a total set of 55 skeletal variables for the subsequent analysis of the major component and cluster analyses. Ten main axes were generated representing 92.7% of the total variation. Three main components represented 58.5%, with particular sagittal and vertical variables acting as major descriptors. Post hoc phenotypic clustering retrieved six clusters: C1:9.9%, C2:18.9%, C3:33%, C4:3.77%, C5:16%, and C6:16%. In conclusion, phenotypic variation was found in the southern European skeletal class III population, demonstrating the existence of phenotypic variations between identified clusters in different ethnic groups.
Highlights
Class III malocclusion has been commonly described as having a retruded or hypoplastic upper maxilla, a prognathic or hyperplastic mandible, or a combination of both[1]
Principal component analysis (PCA) enables the large number of variables used in cephalometric analysis to be reduced to fewer components, grouping the variables of greatest interaction on each a xis[9]
The number of distinguishable skeletal class III sub-phenotypes varies substantially between different studies and populations described in the literature: from seven different sub-phenotypes in Korean adults[2] to three[3,6,7] clinically distinguishable clusters in growing Caucasian patients; and four8, five[5], and 144 skeletal class III clusters (C) have been obtained via cluster analysis (CA) and described in the literature
Summary
Class III malocclusion has been commonly described as having a retruded or hypoplastic upper maxilla, a prognathic or hyperplastic mandible, or a combination of both[1]. The number of distinguishable skeletal class III sub-phenotypes varies substantially between different studies and populations described in the literature: from seven different sub-phenotypes in Korean adults[2] to three[3,6,7] clinically distinguishable clusters in growing Caucasian patients; and four8, five[5], and 144 skeletal class III clusters (C) have been obtained via cluster analysis (CA) and described in the literature These studies clearly show great variations within the same skeletal malocclusion and can be classified in different phenotypic groups with specific characteristics that differ from one ethnic group to another, and even within the same ethnic group[2,3,4,5,6,7,8,11]. Investigation is to generate an appropriate sub-phenotypic grouping of skeletal class III malocclusion in a broad adult population of southern European origin
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