A Morphological Study on the Classification of Maxillary Dental Arches

To evaluate the morphology of dental arches, 62 (male: 36, female: 26) paired casts having normal dentitions and occlusion were selected from 396 (age: 18 to 26 years old; male: 257, female: 139) sets of dental study models. The maxillary dentitions were preliminarily classified as square, round-square, round and round V-shaped arches based on the conventional morphological descriptions. Midpoints of the incisor edge (I1(R), I1(L), I2(R), & I2(L), summits of the cuspids (CR & CL), buccal cusps of the premolars (P1(R), P1(L), P2(R), & P2L), mesial buccal cusps of the first and second molars (M1(R), M1(L), M2(R), & M2(L)), and the midpoint (A) of line I1(R)-I1(L) were designated as reference points. From A, let a vertical line intersected line M2(R)-M2(L) at reference point B. The line A-B intersected C(R)-C(L) at reference point E. We evaluated 1) the protrusion of the cuspids by (1) angle I2(R)-C(R)-P1(R) (angle R) + angle I2(L)-C(L)-P1(L) (angle L); 2) the curvature of the anterior teeth by (2) A-B/C(R)-C(L), (3) 180 degrees - angle C(R)-A-C(L), and (4) A-E/C(R)-C(L); 3) the length to width ratio of the dental arch by (5) A-B/M2(R)-M2(L); 4) the degree of roundness of the maxillary arch by estimation of (6) (rtheta5 - rtheta4)R + (rtheta5 - rtheta4)L; and 5) an item (7) for the differentiation of type I and type II round-square arches by relating the bilateral contour and position of break line P1-P2-M1-M2 (i) to line P1-M2 (ii). The data of items (1), (2), (3), (4), (5), and (6) were further standardized and summarized into three essential principal components: 1) the curvature of the anterior teeth, 2) the curvilinear contour of the dental arch, and 3) the length-to-width ratio of the dental arch. The results indicated that: 1) 60% of the maxillary dentitions were round-square arches which showed no prominent principal component; 2) square maxillary arches distinctly showed a small (1) angle R + angle L; 3) round arches were characteristic by small (6) (rtheta5 - rtheta4)R + (rtheta5 - rtheta4)L values; and 4) round V-shaped arches had large (1), (3) and (4) values.