3D geometric morphometric analysis of tooth shape in hypodontia

Abstract

Assessment of tooth morphology is essential in the diagnosis and management of hypodontia patients. Several techniques have been used to quantify tooth shape in hypodontia patients and these have revealed smaller tooth dimensions and anomalous tooth shapes in these patients when compared with controls. However, previous studies have mainly used 2D images and have thus provided limited information. The present study adopted a novel three-dimensional geometric morphometric technique to quantify the crown morphology and sizes of teeth of hypodontia patients and compare them with those of control patients. Allometric variations were also investigated in order to determine whether there was any association between the size and shape of teeth. Landmarks were recorded on each clinical crown of all the permanent teeth, apart from third molars, of 3D scanned study models of hypodontia and control subjects. The study sample comprised 120 hypodontia patients (40 patients with mild, 40 with moderate and 40 with severe hypodontia) and 40 age- and sex-matched controls. Procrustes superimposition was utilized to scale and superimpose the landmark coordinate data and were then subjected to principal component analysis (PCA). Subsequently, shape differences were tested statistically using multivariate statistics. Size variation was for the most part found to be significant, especially when the control subjects were compared to the hypodontia groups. The anterior teeth were more affected than the posterior. Generally speaking, the size differences became greater as the severity of the hypodontia increased. The pattern was virtually the same for both sexes. With regard to shape, most teeth were affected by the hypodontia, although the pattern was less clear. When allometry was taken into account, the pattern of size/shape relationship was found to be significant for most teeth, particularly in the anterior region, and shape differences were still significant after controlling, when possible, for allometry. It was found that the degree of variation in tooth shape was associated with the degree of severity of the hypodontia. The findings of the study therefore indicate that quantitative measurement of the tooth shape in hypodontia patients may enhance the multidisciplinary management of those patients.