Discussion
SLS, IMPACTION
The pilot study is exploratory in methodological feasibility of facial soft tissue volume measurement and rationality of experimental design for the preparation of further research. A non-randomized, non-blind, and self-controlled clinical trial was conducted to measure the 3D soft and hard tissue changes of the human face after ipsilateral wisdom teeth removal.It was found that the HTV on the extraction side decreased by 2.33 ± 0.46ml at T2. There was no obvious correlation between the HTVC and the STVC. The pilot study has not distinguished third molars impaction types. Due to the classification of the impacted wisdom teeth may influence the quantity of bone removal, the variation may influence the HTV decrease.The paired t-test showed no significant difference in the shape (µ, SD, RMS) or volume (STVC) between the extraction side and the non-extraction side. Interestingly, extraction of wisdom teeth may result in a decrease of STV on the extraction side in a short time (the STV decreased by 1.396ml (P < 0.05) between T0 toT1), which return to the T0 level (P > 0.05)) in a long time (the STV increased by 1.753ml (P = 0.05) between T1 and T2). There is no such change on the non-extraction side. However, statistical significance does not imply clinical significance. The reproducibility of FaceScan SLS system applied to real person in buccal region is 0.4195 mm with 95%CI (0.3960, 0.4429) mm, P < 0.05 [The great thickness of buccal soft tissue and the prominent bone support around the buccal area may be the essential reasons why the deep-seated HTVC does not reveal on the surface. A study investigated the tissue response of defined amounts of filler material injected into facial fat compartments using the surface-volume coefficient (the surface volume change observed divides the actual injection volume) as outcome variables [From the perspective of methodology: The projection method is appropriate for small facial soft tissue volume change measurement and is reproducible. It can be applied to other facial regions, such as the nose, paranasal area, upper lip, lower lip, and chin (the coronal plane can be used as the reference plane). It provides a new, feasible and detailed method for orthodontics, orthognathic surgery, plastic surgery, and other disciplines concerned with facial morphological changes.The main disadvantage of the SLS is that the reliability is significantly influenced by the facial soft tissue variability in vivo. One case of the unqualified facial scan was excluded in this study, which may be due to mandibular position variation or SLS quality defects. This suggests that even with the standardized procedure [The limitations of this study are the sample size was small and the third molars were not classified by impact types or bone removal quantity. Although the standardized procedure [