Measurement of three-dimensional facial changes after orthodontic extraction: a retrospective longitudinal study

This study aimed to assess the three-dimensional facial morphological changes and acquire quantitative relationship between facial landmarks and zygion point to analyze the overall facial soft tissue impact of extraction and non-extraction orthodontic treatment.

A total of 21 extraction (19.5 ± 9.2 years) and 21 non-extraction (26.2 ± 9.1 years) versus consecutive patients were enrolled. The pretreatment and posttreatment 3D facial scans were captured using the FaceSCAN3D optical system. After establishing the coordinate system and manually placing landmark, fourteen linear and twelve angular measurements were obtained. Additionally, sixteen projection distances between landmarks and the Zygion point were measured. Color-coded displacement maps were conducted through surface registration for visualization and qualitatively assessed facial changes.

In extraction group, inter-cheek width (2.60 ± 5.64 mm, P = 0.050) and mouth width (1.92 ± 3.89 mm, P = 0.040) increased, while upper lip fullness (-0.88 ± 1.11 mm, P = 0.003), lower lip fullness(-0.55 ± 1.21 mm, P = 0.050), and Li-N'-Pg' angle (-1.55 ± 1.09°, P < 0.001) decreased (T1-T0). As for quantitative measurements, the backward movement of landmarks in paranasal area (bilateral Al [nasal ala]: -1.14 ± 1.84 mm and -1.14 ± 1.47 mm, P = 0.010 and P = 0.002, respectively; bilateral Subal [subnasal ala]: -1.23 ± 2.18 mm and -1.25 ± 1.46 mm, P = 0.018 and P = 0.001, respectively) was observed. In the cheek area, significant changes were found in: left Ck-i [cheek-inner]: -1.40 ± 2.18 mm, P = 0.008; right Ck-m (cheek-middle): -2.32 ± 2.71 mm, P = 0.001), right Ck-o [cheek-outer]: -2.65 ± 4.05 mm, P = 0.007). In the lip area, changes were noted in: (bilateral Chp [chresta philtri]: P < 0.001, bilateral Ch [cheilion]: P < 0.001, Ls (labrale superius]: P = 0.002, Stm [stomion]: P < 0.001, and Li [labrale inferius]: P = 0.002. All changes observed were measured relative to the Zygion point in extraction group.

This study reveals the effects of extraction and non-extraction treatments on the lip, cheek and paranasal areas. Significant differences were found in the linear and angular measurements. The lower lip retraction was more pronounced in the extraction group. A new quantitative method for measuring facial landmarks was established. Inward and downward movement of facial landmarks was observed after extraction treatment.

The protocol of this study (PKUSSIRB-202392145) was registered at the Chinese Clinical Trial Registry (Chictr.org.cn) with the identifier ChiCTR2000034288 (01/07/2020).