Assessing Normal Smiling Function Through 3D–3D Surfaces Registration: An Innovative Method for the Assessment of Facial Mimicry

Abstract

Smiling has a great importance, both from a functional and an aesthetic point of view. The introduction of modern 3D acquisition and elaboration methods may provide additional help in the evaluation of facial mimicry. This study aims at proposing an innovative method to assess facial and labial movements in different types of smiles. Twenty healthy subjects (10 males, 10 females, mean age 27.5 years, SD 4.5 years), were recorded through a stereophotogrammetric system in neutral position and in three types of smiles: Mona-Lisa smile, canine smile, full-denture smile. All the 3D smiling models were superimposed on the corresponding neutral one and point-to-point root mean square (RMS) differences were computed. Labial surface areas in rest position and during each smile were calculated as well, together with the percentage modification in different types of smile. RMS values (facial and labial models), labial surface areas and percentage modifications were compared through ANCOVA tests to verify possible statistically significant differences according to sex and type of smile (p < 0.05). Intercanthal labial width was considered a covariate. RMS values progressively increased from Mona-Lisa to full-denture smile; statistically significant differences were found among all types of smiles, both for facial and labial models (p < 0.05), while no statistically significant sex and sex × smile interactions were found (p > 0.05). Labial surface and percentage of modification showed statistically significant differences according to both sex and type of smile (p < 0.05). The study provides a novel contribution to the field of sexual dimorphism in smiling. Level of Evidence V This journal requires that authors assign a level of evidence to each article. For a full description of these evidence-based medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Validation of a low-cost laser scanner device for the assessment of three-dimensional facial anatomy in living subjects

“…The present study was designed to test the performances of Sense® laser scanner in all the declination of facial assessment, including not only linear and angular measurements, but also surfaces and volumes, which are acquiring a growing importance in research and clinics (Sforza et al, 2014a(Sforza et al, , 2014bGibelli et al, 2015;Ozer et al, 2016). In addition, 3D-3D pointto-point distances, calculated after registration of 3D models, were also tested, as they have had several applications in the literature (Camison et al, 2017;Gibelli et al, 2017aGibelli et al, , 2017bPucciarelli et al, 2018).…”

The Average Facial Expressions: A Range of Motion Analysis for Different Sex and Age Groups

“…Dissimilarities with those studies include that some were 2D, 23,24 some only examined subjects older than 20 years, [26][27][28][29][30][31] and none of them provided vectors of movement. [23][24][25][26][27][28][29][30][31] Only in two studies, the same expressions as in the current study were researched: the closed smile and pouting. 23,31 All other studies examined different facial exercises.…”

“…23,31 All other studies examined different facial exercises. , [24][25][26][27][28][29][30] To the best of our knowledge, the present study is the first to provide reference standards of landmark displacement in three directions for facial exercises for different young age groups.…”

“…However, a comparison between these studies and the current study is difficult to draw. Dissimilarities with those studies include that some were 2D, 23,24 some only examined subjects older than 20 years, 26–31 and none of them provided vectors of movement. 23–31 Only in two studies, the same expressions as in the current study were researched: the closed smile and pouting.…”

“…Some studies confirmed that facial movement is larger in men than in women. 23,24,[27][28][29] Others found no, or limited, sex-related differences. 26,30 It could be suggested that sexrelated differences arise from differences in facial size and shape.…”