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 (C_R & C_L), buccal cusps of the premolars (P1_R, P1_L, P2_R, & P2_L), mesial buccal cusps of the first and second molars (M1_R, M1_L, M2_R, & M2_L), and the midpoint (A) of line I1R-I1L 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 (∠R) + angle I2_L-C_L-P1_L (∠L); 2) the curvature of the anterior teeth by ② A-B/C_R-C_L, ③ 180°C∠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 (rθ₅ - rθ₄)_R - (rθ₅ - rθ₄)_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 ∠R - ∠L; 3) round arches were characteristic by small ⑥ (rθ₅ - rθ₄) + (rθ₅ - rθ₄)_L values; and 4) round V-shaped arches had large ②, ③ and ④ values.