Dental arch, basal arch width and coordination analysis in skeletal Class III malocclusion

Objective To provide references for diagnosis andtreatment plan of skeletal Class Ⅲ malocclusion based on the study of dental arch widths, basal bone widths and their coordination. Methods Experimental groupconsists of 33 skeletal Class Ill malocclusion cases and control groupconsists of 47 individual normal occlusion cases. The data samples of thetwo groups were derived from Cone Beam Computed Tomography （CBCT） scans, and were used to measure dental arch widths and basalbone arch widths. The differences between the paired maxilla and mandible measurements were calculated. All the measurements and calculations were done in Mimics 10. 01. Independentsample t-testwas used to compare the two groups. Results Differences between the maxillary dental arch widths were unapparent; skeletal Class Ⅲ malocclusion had a tendency of larger mandibular dental arch widths. Maxillary basalbone archwidths of Class UI malocclusion groupwere narrower compared with normal occlusion samples. The second premolar segment was significantly narrower. Moreover, mandibular premolar and molarbasalbone arch widths of the skeletal Class Ⅲ malocclusion were significantly larger than the normal occlusion groups. Difference between maxillary and mandibular basal bone arch widths was larger in skeletal Class Ⅲ malocclusion. Difference between maxillary and mandibular dental arch widths in canine area was smaller while other dental segment width difference showed no statistical differences. Conelusions （1） In transverse dimension, maxillary basal bone arch grows insufficiently, while the mandibular basal bone archgrows excessively in skeletal class Ⅲ patients. （2） Widthdiscrepancy inskeletal class Ⅲ is at basal bonelevel. Dental arch showssome extent of compensation. Key words: Skeletal class Ⅲ malocclusion;  Dental arch width; Basal bone arch width;  CBCT