Objectives

To assess the linear and angular cranial base measurements (Bjork polygon) in different anteroposterior (AP) skeletal relationships using Bjork-Jarabak analysis.

Materials and Methods

Pretreatment lateral cephalograms of 288 (146 women, 142 men, mean ages 21.24 ± 2.72 years and 22.94 ± 3.28 years, respectively) adult patients were divided into Class I, II, and III skeletal relationships according to their ANB angle. Linear and angular measurements of Bjork polygon were measured and compared among different skeletal relationships. Analysis of variance was performed to detect the differences among groups. Independent-sample t-test was used to detect differences between men and women.

Results

The Class II skeletal relationship has a significantly larger saddle angle than Class III does (P < .05), whereas Class III has a significantly larger gonial angle than Class II does (P < .05). The articular angle and sum of Bjork polygon angles were not significantly different among groups (P > .05). Anterior (N-S) and posterior (S-Ar) cranial base lengths were similar in the different AP skeletal relationships (P > .05). The ramal height and body of the mandible length were significantly larger in Class III compared with Class I and II (P < .05). Women had a significantly larger articular angle than men did (P < .05), although men had significantly larger linear measurements of Bjork polygon than women did (P < .05).

Conclusions

The Class III skeletal relationship has a smaller saddle angle and larger mandibular length and gonial angle. Men have a larger cranial base and mandibular linear measurements and a smaller articular angle compared with women.

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Author notes

a

Associate Professor, Department of Orthodontics, Faculty of Dentistry, Jordan University of Science and Technology, Irbid, Jordan.

b

Specialist Orthodontist and Lecturer in Orthodontics, Department of Orthodontics, Faculty of Dentistry, Jordan University of Science and Technology, Irbid, Jordan.

c

Professor, Department of Orthodontics, Faculty of Dentistry, Jordan University of Science and Technology, Irbid, Jordan.

d

Professor, College of Dental Medicine, QU Health, Qatar University, Doha, Qatar.