Abstract:

Objective  To study 13 different cephalometric measurements of the anteroposterior jaw relationship in Angle Class Ⅱ division 1 statistically and geometrically, and to discuss the effects of various factors on this relationship, and then to choose the most adequate measurements. Methods  120 patients with skeletal malocclusion Angle Class Ⅱ division 1 were selected. The samples consisted of 60 men and 60 women between 20 to 28 years of age. Lateral cephalometric radiograph for each patient was taken in natural head posture by the same operator. A wire plumb line and suspended weight recorded the true vertical on each radiograph. The subject was then asked to determine the self-balanced position of the head. After determining the self-balanced neutral position, the subject was asked to look into his/her own eyes in the mirror. ANB angle, A-B plane angle, Wits appraisal, AF-BF distance, AXB angle, AB/SN4 distance, AB/PP distance, AXD angle, AD/SN distance, SGn/AB angle, APDI, FABA angle, beta angle and AB/HP distance were measured. Coefficient correlations among measurements were tabulated to determine which combination would produce a higher value. Fuzzy grouping analysis was made. Results  Statistically significant and highly correlated relationships was found among many measurements except Wits appraisal and SGn/AB angle. The thirteen measurements could be divided into five clusters. Conclusion  The cephalometric measurements except Wits appraisal and SGn/AB angle can be used to evaluate anteroposterior jaw relationship. The AB/SN4 distance is the most adequate measurements. ANB angle, A-B plane angle, AF-BF distance, AXB angle, AB/PP distance, APDI, FABA angle and beta angle are similar in describing anteroposterior apical base relationship in Angle Class Ⅱ division 1 patients.

Key words: Angle Class Ⅱ division 1, anteroposterior base relationship, cephalometrics, reliability evaluation