WSA MODEL GRADING SYSTEM POSITIVE KEY CHARACTERISTICS Molar Relationship Angular Relationship Crown Inclination (Including proper overbite) NEGATIVE KEY CHARACTERISTICS Rotation Space Deep Curve OPTIMAL OCCLUSION GRADE +3.0 +6.0 +7.0 Fig. 4 -0.5 / rotation -0.5 / space -1.0 / deep curve +16.0 Post-treatment WSA (cast no. 26) lacking all aspects of proper Molar Relationship. Table 1 The models were also studied for proper molar rela-tionship, the absence of rotation and spaces, as well as depth of occlusal plane. Positive numerical values were assigned to the pres-ence of desirable characteristics and negative numerical values to undesirable characteristics related to the Six Keys to normal occlusion as found in the non-orthodontic normal. A numerical grading system, pertaining to the sample was devised by the author. (Table 1) The positive and negative factors of each key as it related to each study model was added and subtracted for a total point score. The models were then ranked according to score. A maximum score of posi-tive 16 represented an optimal static occlusal scheme which manifested completely the Six Keys. (Table 2) Fig. 5 Post-treatment WSA (cast no. 5) of negative maxillary Incisor Angulation. Table 2 WSA MODEL SCORE RANK ORDER SCORE +11.0 +9.5 +9.0 +8.5 +8.0 +7.5 +7.0 +6.5 +6.0 +5.5 +5.0 +4.5 +4.0 +3.5 +3.0 +2.5 +2.0 +1.5 +0.5 -0.5 -1.0 -3.5 MODEL NUMBER 12 19, 41 23, 24, 45, 47 25 10, 43 6, 46 32, 52 34, 38 42, 56 40, 44, 48 27, 36, 53 26, 51 2, 13, 16, 17, 18, 37, 54 4, 22, 35 31, 49 5, 9, 14, 21 7, 11, 55 8, 28, 29, 39 20, 30 15 1, 50 23 32 March/April 2011 JAOS This grading and ranking system was an attempt that was made to objectively assess the quality and sufficiency of the Wayland-State-of-the-Art orthodontic results as it pertained to the Six Keys. Specific models from the sample below the value score of +5.0 were chosen to represent examples of insufficiency in the individual keys to normal occlu-sion. It became evident form the selection process that the deficiency of one or more keys was predictive of other error factors. STATIC OCCLUSION Key 1. Molar Relationship (Fig. 4) The study models were analyzed for three significant characteristics of proper molar relationship totaling a positive point score of 3. A unilateral correction was assigned a half-point per characteristic. Characteristics looked for were: a)the distal surface of the distal marginal ridge of the upper first permanent molar should contact and occlude with the mesial surface of the mesial ridge of the lower second molar. b)the mesio-buccal cusp of the upper first permanent molar should fall within the groove between the mesial and middle cusps of the lower first permanent molar (Dr. Edward H. Angle’s insufficient definition of normal molar relations). c)the mesio-lingual cusp of the upper first molar should seat in the central fossa of the lower first molar.
Journal of the American Orthodontic Society March-April 2011: Page 32
