Relationships between facial divergence and DMD parameters

The aim of this study was to examine the relationship between facial divergence and the parameters of dentomaxillary discrepancy (DMD), in particular crowding, the curve of Spee and the position of the incisors in the sagittal dimension.

A total of 90 young adult patients was selected from among the Moroccan orthodontic population attending the dentofacial orthopedic department and satisfying the following inclusion criteria: complete permanent dentition and a skeletal class I pattern with no previous orthodontic treatment, no crossbite, no periodontal disease, no mandibular asymmetry and no condylodiscal disunion. On cephalometric tracings, measurements were made of angles FMA, Go-Gn/SN, Occ/SN in the vertical direction, and of the values I/NA et i/NB in the sagittal direction. The curve of Spee and dental crowding were assessed using the one-way ANOVA test and the Bonferroni post-hoc test. Correlation analysis was performed between divergence and the different variables measured, using SPSS software with a 0.05 significance threshold.

Patients recruited for the study had a mean age of 19.8±0.5 and were distributed as follows: 28 normodivergent, 31 hypodivergent and 31 hyperdivergent, 42 females and 48 males. Comparison showed that hypodivergent subjects had less crowding than hypo- or normodivergent individuals (P<0.05). Hypodivergent subjects had a more pronounced curve of Spee than the other two groups. This difference was not significant (P>0.05). Hyperdivergent subjects presented more labioversion and vestibular positioning of the incisors compared with the hypodivergent (P<0.05) and normodivergent (P<0.05) groups. Correlation analysis showed that crowding and the incisor positions in millimeters and in degrees were positively correlated to a moderate extent with facial divergence (r=0.3, r=0.5, r=0.4; P<0.05), while the curve of Spee was not (P>0.05). No correlation was found between age or sex and the DMD parameters (P>0.05).