Quantitative analysis of transversal dentofacial asymmetries using combined 3D jaw and face-scans: a prospective analytical cross-sectional study

The spatial position of the dentition relative to the perioral soft tissues is predominantly documented and evaluated two-dimensionally using cephalometric or photographic methods. However, objective quantitative assessment is difficult with two-dimensional imaging modalities, especially in cases of transverse asymmetries. The aim of this study was to assess the potential of three-dimensional (3D) face-jaw imaging and analysis of transverse deviations using combined 3D surface scans. Combined 3D data of the face and jaws of 76 untreated subjects were evaluated. Group A (n = 66) included patients with no evidence of tooth migration beyond the maxillary dental midline (dentMid), e.g., due to premature loss of primary teeth. The patients, whose imaging data showed tooth migration, were assigned to group B (n = 10). All 3D models were evaluated three times each by four examiners, and analysis parameters relevant to facial and dentofacial asymmetries were calculated and described. “True” landmark positions were estimated using a linear mixed-effects model. Variability of relevant results was characterized by standard deviations which were combined using a linear model. For group A, the relationship between the deviations of the dentMid and of the skeletal maxillary midline (maxMP) from the facial midline plane (facMP) was statistically evaluated by calculating the Spearman correlation coefficient. The difference between these deviations was analyzed using the Wilcoxon test. In group A, a median difference of only − 0.4 mm (range: -1.4 – +0.7 mm) was observed between dentMid and maxMP. Corresponding differences for patients assigned to group B were − 0.6 mm (-1.9 – +0.4 mm). The Spearman correlation analysis indicated a strong correlation between the two parameters (𝑟 = 0.84) and the Wilcoxon test indicated no significant difference between these deviations (p = 0.995). Our quantitative analysis of combined 3D surface scans demonstrates the wide range of the differences between dental and skeletal midline deviations in untreated individuals. The possibility to differentiate skeletal and dental aspects of midline deviations through an approach without X-rays is of particular therapeutical relevance in patients with pronounced skeletal midline deviation, to quantitatively assess the amount of dentoalveolar compensation required to align the dentMid to the facMP.