Abstract
Aims: To identify the cephalometric features of three skeletal jaw relations (Class I, II and III). Materials and methods: one hundred thirty four students were selected aged 12–15 years from secondary schools in Mosul City, 45 with Class I normal occlusion as control, 44 with Class II malocclusion and 45 with Class III malocclusion, after taking the lateral cephalometric radiographs according to ANB angle. A 20 variables (12 angular and 8 linear) were used in this study to correlate these variables in the three skeletal Classes. Results: No significant sex differences were observed for the majority of angular and linear measurements for the three skeletal types. Anterior cranial base length (S–N) and saddle angle (NSAr) didn’t show significant difference among the three skeletal Classes, the posterior cranial base (S–Ar) was shorter in Class III which indicate the anterior articulation of the mandible. The length of maxillary base (ANS–PNS) was longer in Class II than Class I and III which lead to maxillary prognathism. The body length of the mandible (Go– Pog),effective mandibular length (Ar–Gn) and lower anterior face height was significantly longer in Class III which lead to mandibular prognathism. The SNA angle was significantly smaller in Class III than in the others. SNB and SNPog angles were larger in Class III followed by Class I and then Class II. The gonial angle (Ar–Go– Me) was larger in Class III which acts to increase mandibular effective length. The (N–A–Pog) showed as convex in Class II and concave in Class III. (The U1–PP) angle was larger in Class II followed by Class I and then by Class III. The (L1–MP) angle in Class II and III was significantly smaller than in Class I. Conclusion: Most of the angular and linear measurements indicated that the skeletal differences between the Class I, Class II and Class III are concentrated with in the maxillary and mandibular bases in both the anteroposterior and vertical dimensions and their type of articulation. The dental measurements appear to be compensated with that of skeletal one. Also these variables showed no significant sex differences in the majority of their measurements
Highlights
It was found that point of the differences between Class II, Class I and Class III was accounted by systemical variation in a coherent set of midface and cranial base dimensions
No sex differences were seen in the majority of the linear and angular measurements except for SAr distance in Class
While for the angular measurements, U1–PP in Class III was higher in males and SN–MP in Class II was higher in females,(Fig. 2, 3 and 4)
Summary
It was found that point of the differences between Class II, Class I and Class III was accounted by systemical variation in a coherent set of midface and cranial base dimensions. These variation were in harmony with each other; the cranial base angle (Ba–S–N) closed and the legs (S–N) and (S–Ba) shortened systemically from Class II over Class I, to Class III. As for sagittal measurements, TMJ position was more posterior in skeletal Class II when compared with skeletal Class III.[2]. It is unclear whether malocclusion characterized by jaw discrepancy is caused by variations in mandibular position, mandibular size, or a combination of the two.
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