Maxillomandibular arch width differences at centers of resistance in skeletal Class III

Abstract

Introduction : The aim of this study were : (1) to compare the transverse dimensions and maxillomandibular transverse relationships between untreated normal occlusion and Class III groups, (2) to compare the basal arch dimensions between measured at CT scans and at casts, and (3) to find the possible transverse basal arch dimensions to establish normal occlusion in each tooth area.

Materials and Methods : The casts and 3D CT data of 30 normal occlusion and 30 skeletal Class III subjects requiring orthognathic surgery were selected. Using the casts, the dental arch widths (DAW) were measured at the respective cusp tips and the basal arch widths (BAW [cast]) were measured the distance between the points at the mucogingival junction (MGJ) above the respective cusp tips. The basal arch widths from the CT scans (BAW [CT]) were measured at the estimated centers of resistance (CR) at either furcation or one third of root length. The dimensions and maxillomandibular differences were analyzed.

Results : In contrast to the similarity in DAWs between two groups, the maxillary BAW [CT]s except at the 2nd molar and all maxillary BAW [cast]s in Class III malocclusion were significantly smaller than those of normal occlusion group. All mandibular BAW [CT]s of Class III group were significantly greater than those of normal occlusion group. None of mandibular BAW [cast]s showed statistically significant differences between two groups. The maxillomandibular BAW differences on both CT and cast showed significant differences in all transverse measurements between two groups. Correlation analysis represented significant correlation between BAW [CT] variables and BAW [cast] variables.

Conclusions : The results indicated possible basal transverse discrepancy and transverse dental compensation in the skeletal Class III subjects. Correlation analysis represented significant correlation between BAW [CT] variables and BAW [cast] variables. The 1st molar BAW [CT] differences of -0.39 ± 1.87 mm, BAW [cast] differences of 5.15 ± 2.56 mm in normal occlusion were obtained to represent optimal maxillomandibular transverse difference at the basal bone level.