Principal component analysis of mandibular dental arches

Objectives: This study was undertaken to find objective criteria for morphological evaluation of mandibular dental arches. Methods: 53 paired casts having normal dentition and occlusion were selected from 396 sets of dental study models. The mandibular dentitions were preliminarily classification of square, round-square, round and round V-shaped arches with reference to the Thompson's morphological description. We determined midpoints of the incisal ridge of the incisors (I1_R, I1_L, I2_R & I2_L), cusp tips of the canines (C_R & C_L), summits of buccal cusps of the premolars (P1_R, P1_L, P2_R & P2_L), summits of mesiobuccal cusps of the molars (M1_R, M1_L, M2_R & M2_L) and the midpoint A of line (I1_R-I1_L). Point B is defined as the intersection of the vertical line from point A with the line (M2_R-M2_L). Point E is the intersection of (A-B) with (C_R-C_L). The midpoint of line (M2_R-M2_L) was point O. We also determined the relation of the contour and position of line (P1-P2-M1-M2) to line (P1-M2). Seven items were developed and analysed with reference to the correlation matrix of the variables. Results: Round arches were not found. We observed significant differences between the round V-shaped arches and the other types of arch by evaluating curvature of anterior teeth and degree of roundness of the arch. No significant differences of each arch type were found in protrusion of cuspids and length-to-width ratio of the dental arch. Conclusion: Six selected items were summarized into three principal components. The first principal component showed the curvature of anterior teeth, the second principal component represented the curvilinear contour of the dental arch, and the third principal component indicated length-to-width ratio of the dental arch. The first and second principal components are essential in classification of mandibular dental arches.