Transferability of the PRS estimates for height and BMI obtained from the European ethnic groups to the Western Russian populations.

Genetic data plays an increasingly important role in modern medicine. Decrease in the cost of sequencing with subsequent increase in imputation accuracy, and the accumulation of large amounts of high-quality genetic data enable the creation of polygenic risk scores (PRSs) to perform genotype-phenotype associations. The accuracy of phenotype prediction primarily depends on the overall trait heritability, Genome-wide association studies cohort size, and the similarity of genetic background between the base and the target cohort. Here we utilized 8,664 high coverage genomic samples collected across Russia by "Evogen", a Russian biomedical company, to evaluate the predictive power of PRSs based on summary statistics established on cohorts of European ancestry for basic phenotypic traits, namely height and BMI. We have demonstrated that the PRSs calculated for selected traits in three distinct Russian populations, recapitulate the predictive power from the original studies. This is evidence that GWAS summary statistics calculated on cohorts of European ancestry are transferable onto at least some ethnic groups in Russia.

An exploration of adolescent facial shape changes with age via multilevel partial least squares regression.

BACKGROUND AND OBJECTIVES: Multilevel statistical models represent the existence of hierarchies or clustering within populations of subjects (or shapes in this work). This is a distinct advantage over single-level methods that do not. Multilevel partial-least squares regression (mPLSR) is used here to study facial shape changes with age during adolescence in Welsh and Finnish samples comprising males and females. METHODS: 3D facial images were obtained for Welsh and Finnish male and female subjects at multiple ages from 12 to 17 years old. 1000 3D points were defined regularly for each shape by using "meshmonk" software. A three-level model was used here, including level 1 (sex/ethnicity); level 2, all "subject" variations excluding sex, ethnicity, and age; and level 3, age. The mathematical formalism of mPLSR is given in an Appendix. RESULTS: Differences in facial shape between the ages of 12 and 17 predicted by mPLSR agree well with previous results of multilevel principal components analysis (mPCA); buccal fat is reduced with increasing age and features such as the nose, brow, and chin become larger and more distinct. Differences due to ethnicity and sex are also observed. Plausible simulated faces are predicted from the model for different ages, sexes and ethnicities. Our models provide good representations of the shape data by consideration of appropriate measures of model fit (RMSE and R2). CONCLUSIONS: Repeat measures in our dataset for the same subject at different ages can only be modelled indirectly at the lowest level of the model at discrete ages via mPCA. By contrast, mPLSR models age explicitly as a continuous covariate, which is a strong advantage of mPLSR over mPCA. These investigations demonstrate that multivariate multilevel methods such as mPLSR can be used to describe such age-related changes for dense 3D point data. mPLSR might be of much use in future for the prediction of facial shapes for missing persons at specific ages or for simulating shapes for syndromes that affect facial shape in new subject populations.

Multilevel principal components analysis of three-dimensional facial growth in adolescents.

BACKGROUND AND OBJECTIVES: The study of age-related facial shape changes across different populations and sexes requires new multivariate tools to disentangle different sources of variations present in 3D facial images. Here we wish to use a multivariate technique called multilevel principal components analysis (mPCA) to study three-dimensional facial growth in adolescents. METHODS: These facial shapes were captured for Welsh and Finnish subjects (both male and female) at multiple ages from 12 to 17 years old (i.e., repeated-measures data). 1000 "dense" 3D points were defined regularly for each shape by using a deformable template via "meshmonk" software. A three-level model was used here, namely: level 1 (sex/ethnicity); level 2, all "subject" variations excluding sex, ethnicity, and age; and level 3, age. The technicalities underpinning the mPCA method are presented in Appendices. RESULTS: Eigenvalues via mPCA predicted that: level 1 (ethnicity/sex) contained 7.9% of variation; level 2 contained 71.5%; and level 3 (age) contained 20.6%. The results for the eigenvalues via mPCA followed a similar pattern to those results of single-level PCA. Results for modes of variation made sense, where effects due to ethnicity, sex, and age were reflected in modes at appropriate levels of the model. Standardised scores at level 1 via mPCA showed much stronger differentiation between sex and ethnicity groups than results of single-level PCA. Results for standardised scores from both single-level PCA and mPCA at level 3 indicated that females had different average "trajectories" with respect to these scores than males, which suggests that facial shape matures in different ways for males and females. No strong evidence of differences in growth patterns between Finnish and Welsh subjects was observed. CONCLUSIONS: mPCA results agree with existing research relating to the general process of facial changes in adolescents with respect to age quoted in the literature. They support previous evidence that suggests that males demonstrate larger changes and for a longer period of time compared to females, especially in the lower third of the face. These calculations are therefore an excellent initial test that multivariate multilevel methods such as mPCA can be used to describe such age-related changes for "dense" 3D point data.

Centre of resistance and centre of rotation of a tooth: experimental determination, computer simulation and the effect of tissue nonlinearity.

The centre of resistance and centre of rotation of a tooth are key concepts in orthodontics. Determining the coordinates of these points is essential for planning orthodontic tooth movement. The paper proposes a procedure for experimental determination of the two centres, verifies a previously developed mathematical theory through computer simulations and evaluates the effect of nonlinearity of the periodontal ligament on the parameters related to the centres. The paper relies on the mathematical theory of a rigid body embedded in an elastic medium, physical experiment, finite element method and a simple nonlinear theory of the tooth. The concept of the centre of resistance requires a revision if nonlinearity is taken into account.

Comparison between landmark and surface-based three-dimensional analyses of facial asymmetry in adults.

BACKGROUND/OBJECTIVES: To collect the reference values for facial asymmetry in adults using landmark and surface-based three-dimensional analyses and to compare their diagnostic abilities. MATERIALS AND METHODS: Laser scans were taken from 85 British Caucasians, 29 males (23.9±5.7 years, range 19-44) and 56 females (28.1±9.5 years, range 19-54), students and staff of the Cardiff Dental Hospital, and three orthodontic patients with marked facial asymmetry. An asymmetry index (AI) was measured for 14 landmarks. The surface-to-surface average distance between the best-fit registered original and mirror scans (ADom) was measured for the whole face and six regions. Non-parametric descriptive statistics was used to obtain the reference values, and Mann-Whitney U-test was used for gender comparison. P values less than 0.05 were considered significant. Patients' values were compared to the reference values by calculating the corresponding percentiles. RESULTS: The lowest AI was found for 'pronasale' in males [median 0.1 (interquartile range 0.0-0.3) mm] and the highest for 'cheilion' [3.5 (2.4-5.0) mm] in females. The ADom for the whole face was 0.7 (0.5-0.9) mm in males and 0.6 (0.5-0.7) mm in females and regionally between 0.4 (0.3-0.6) mm and 0.8 (0.4-1.2) mm. In orthodontic patients, AI did not always reveal asymmetry in a particular coordinate plane, and surface-based analysis was favourable in regions underrepresented by landmarks. CONCLUSIONS: Facial asymmetry can be accurately quantified using landmark- and surface-based approaches. The latter offers a more comprehensive analysis of the face.

Determining normal and abnormal lip shapes at border positions for use as a longitudinal surgical outcome measure.

Objective measures of facial movement are important for interventions where surgical repositioning of facial structures can influence soft tissue mobility and include the management of patients with cleft lip, facial nerve palsy and orthognathic surgery. As such, the aim of this study is to present a method for determining the outcome of surgical procedures on lip shape during speech. A control group (CG) of 115 average subjects and 30 patients with a Class 3 malocclusion requiring bimaxillary surgery performed four reproducible verbal utterances during image capture using a non-invasive, three-dimensional (3D) motion scanner (3dMDFace™ Dynamic System). Landmark coordinates around the lips of the 3D facial shells were extracted and subjected to discriminant analysis and principal component analysis to statistically differentiate lip shapes between the CG and the patient group (PG) pre- and post-surgery. Pre-surgically, the PG showed statistically significant differences in lip shape during speech in the lateral and vertical dimensions, preferring a wider, shorter lip shape when compared with the CG for all the utterances. The shape differences normalised towards the CG post-surgery. The method presented utilises pre-existing statistical shape analyses and can be reproduced in the clinical setting to provide a diagnostic and functional outcome tool. In this example, correction of the Class 3 skeletal disproportions appeared to normalise lip shape during speech.

Three-dimensional analysis of facial shape and symmetry in twins using laser surface scanning.

OBJECTIVES: Three-dimensional analysis of facial shape and symmetry in twins. SETTING AND SAMPLE POPULATION: Faces of 37 twin pairs [19 monozygotic (MZ) and 18 dizygotic (DZ)] were laser scanned at the age of 15 during a follow-up of the Avon Longitudinal Study of Parents and Children (ALSPAC), South West of England. MATERIAL AND METHODS: Facial shape was analysed using two methods: 1) Procrustes analysis of landmark configurations (63 x, y and z coordinates of 21 facial landmarks) and 2) three-dimensional comparisons of facial surfaces within each twin pair. Monozygotic and DZ twins were compared using ellipsoids representing 95% of the variation in landmark configurations and surface-based average faces. Facial symmetry was analysed by superimposing the original and mirror facial images. RESULTS: Both analyses showed greater similarity of facial shape in MZ twins, with lower third being the least similar. Procrustes analysis did not reveal any significant difference in facial landmark configurations of MZ and DZ twins. The average faces of MZ and DZ males were coincident in the forehead, supraorbital and infraorbital ridges, the bridge of the nose and lower lip. In MZ and DZ females, the eyes, supraorbital and infraorbital ridges, philtrum and lower part of the cheeks were coincident. Zygosity did not seem to influence the amount of facial symmetry. Lower facial third was the most asymmetrical. CONCLUSION: Three-dimensional analyses revealed differences in facial shapes of MZ and DZ twins. The relative contribution of genetic and environmental factors is different for the upper, middle and lower facial thirds.

Assessment of facial asymmetry in growing subjects with a three-dimensional laser scanning system.

OBJECTIVES: To evaluate facial asymmetry in growing subjects with no malocclusion on three-dimensional laser facial scans. SETTING AND SAMPLE POPULATION: Twenty-seven healthy Caucasian children (15 boys and 12 girls, aged 5.4 ± 0.3 years) in the primary dentition without malocclusion were randomly selected from a local kindergarten in Slovenia. MATERIAL AND METHODS: Surface facial images were obtained using a three-dimensional laser scanning system at baseline and at 18, 30, 42 and 54 months of follow-up. Facial asymmetry was assessed quantitatively by measuring the average distance between facial image and mirrored image. Further, the percentage of asymmetry was calculated as the percentage of image to mirrored image not coinciding within 0.5 mm. Qualitative assessment was performed on colour deviation maps by recording the predominant side of the face for the upper, middle and lower parts of the face separately. Nonparametric tests were used for data analysis. RESULTS: No face was perfectly symmetric. The average distance between the mirrored images for the whole face ranged 0.22-0.85 mm and the percentage of asymmetry 7.8-66.9. There were no significant gender differences (p > 0.05), and no significant change was found over the observed period. The upper part of the face was the least asymmetric, while the lower and middle parts showed similar degrees of asymmetry. CONCLUSION: Facial asymmetry is already present at an early developmental stage and does not show any tendency to increase or decrease with growth in the pre-pubertal period.

Statistical modelling of lip movement in the clinical context.

OBJECTIVE: To establish three-dimensional (3D) reference data on average lip movement in normal healthy subjects using statistical shape analysis techniques. SETTING AND SAMPLE POPULATION: School of Dentistry and Cardiff School of Computer Science, Cardiff University, United Kingdom. One hundred and fifteen white subjects. MATERIAL AND METHODS: Subjects performed four reproducible verbal gestures (puppy, rope, baby and bob) in a normal relaxed manner, which were captured using a non-invasive, 3D motion scanner (3dMDFace™ Dynamic System). Six landmarks were manually placed around the lips of the 3D facial shells showing maximum lip displacement. Generalized procrustes analysis followed by principal component analysis was applied to the landmark coordinates to characterize lip movement for each word. RESULTS: The first four principal components (PCs) describe the majority of variation in lip movement for the four words involving a complex interaction of lip movements in three dimensions. Bilateral landmarks were paired within PCs showing that movement was largely symmetrical. Female resting lip shape was narrower and shorter in height than males. During motion, females preferred a more protrusive articulation than males. CONCLUSION: Statistical shape analysis techniques can be used to characterize lip movement during articulation. Data from this study can act as a reference for average lip movement to compare similar population groups.

Reproducibility of facial soft tissue landmarks on 3D laser-scanned facial images.

BACKGROUND: The three-dimensional (3D) measuring technology is useful to inspect facial shape in three planes of space (X, Y, and Z). Recent work has been directed to analyse craniofacial morphology using facial soft tissue landmarks to identify facial differences among population. The reproducibility of facial landmarks is almost necessary to ensure accurate 3D facial measurements. OBJECTIVE: The aim of this study is to assess the reproducibility of facial soft tissue landmarks using laser-scan 3D imaging technology. SUBJECTS AND METHODS: Facial landmarks were assessed for 30 15(1/2)-year-old British-Caucasian children (15 males and 15 females). The sample was recruited from the Avon Longitudinal Study of Parents and Children (ALSPAC). The 3D facial images were acquired for each subject using two high-resolution Konica/Minolta laser scanners. Twenty-one facial landmarks (63 X, Y, and Z coordinates) were identified and recorded on each 3D facial image by two examiners. The reproducibility of landmarks identification at 2-week interval was assessed for one of the examiners (intra-examiner). In addition, the reproducibility of landmarks was assessed between the two examiners (inter-examiner). Using Bland-Altman plots, both intra- and inter-examiner assessments had evaluated landmarks reproducibility in three dimensions for the sample divided by gender. The reproducibility of the 3D-coordinates for each landmark was considered under three categories (< 0.5 mm, < 1 mm, and >1 mm) for both intra- and inter-examiner reproducibility assessments. RESULTS: The distribution of coordinates at the three levels of reproducibility show the following percentages: intra-examiner: < 0.5 mm (38%), < 1 mm (51%), >1 mm (11%); inter-examiner: < 0.5 mm (35%), < 1 mm (48%), >1 mm (17%). Generally, 10 landmarks were reproducible to less than 1 mm for both intra- and inter-examiner reproducibility assessments. The Labiale Superius was the most reproducible and Palebrale Superius was the least reproducible landmark. Some landmarks showed greater reliability in certain planes of space; the Glabella was more reliable in the Z than the Y axis. Gender differences were found; Subnasale was more reproducible in the Y-axis in males compared with females. CONCLUSIONS: The reproducibility of facial landmarks should be considered in the three planes of space. The majority of X-Y-Z coordinates taken to the 21 facial landmarks were reproducible to < 1 mm which is clinically acceptable. The accuracy of landmarks identification ranged from 0.39 to 1.49 mm. The reliability in identification depends on the clarity and definition of each landmark as well as gender characteristics. The different landmarks reproducibility should be considered when evaluating changes related to growth and healthcare interventions.

A three-dimensional look for facial differences between males and females in a British-Caucasian sample aged 151/2 years old.

BACKGROUND: Optical surface scanning accurately records the three-dimension (3D) shape of the face non-invasively. Many software programs have been developed to process and analyze the 3D data, enabling the clinicians to create average templates for groups of subjects to provide a comparison of facial shape. OBJECTIVE: Differences in facial morphology of males and females were identified using a laser scan imaging technology. SUBJECTS AND METHODS: This study was undertaken on 380 British-Caucasian children aged 15 and a half year old, recruited from the Avon Longitudinal Study of Parents and Children (ALSPAC). 3D facial images were obtained for each individual using two high resolution Konica/Minolta laser scanners. The scan quality was assessed and any unsuitable scans were excluded from the study. Average facial templates were created for males and females, and a registration technique was used to superimpose the facial shells of males and females so that facial differences can be quantified. RESULTS: Thirty unsuitable scans were excluded from the study. The final sample consisted of 350 subjects (166 females, 184 males). Females tend to have more prominent eyes and cheeks in relation to males with a maximum difference of 2.4 mm. Males tend to have more prominent noses and mouths with a maximum difference of 2.7 mm. About 31% of the facial shells match exactly (no difference), mainly in the forehead and chin regions of the face. CONCLUSIONS: Differences in facial morphology can be accurately quantified and visualized using 3D imaging technology. This method of facial assessment can be recommended and applied for future research studies to assess facial soft tissue changes because of growth or healthcare intervention.

Facial templates: a new perspective in three dimensions.

PURPOSE: This paper describes the use of adult facial template in gender-specific facial analysis. SUBJECTS AND METHODS: Eighty adults, mean age 24.5, were selected for the study. Laser-scanned images of the subjects were obtained under a reproducible and controlled environment with two Minolta Vivid 900 (Osaka, Japan) optical laser-scanning devices assembled as a stereo-pair. A set of left and right scanned images was taken for each subject and each scan took an average of 2.5 s. These scanned images were processed and merged to form a composite three-dimensional soft tissue reproduction of the subjects using commercially available reverse modelling software. The differences in facial morphology were measured using shell deviation colour maps. The facial template was used to compare differences between males vs. females groups and two subjects with facial disproportions. RESULTS: The difference between the male and female facial templates was 1.28 +/- 1.02 mm. The areas of greatest deviation were at the nasal, zygomatic area and lower jaw line. The results of the surface deviation maps between the templates and subjects with facial disproportion showed that the results could be applied for orthodontic diagnosis. CONCLUSIONS: The construction of the adult facial templates provides an interesting perspective into measuring changes in groups of patients and also acts as a useful template for the comparison of skeletal disproportion.

A new method for the 3D measurement of postoperative swelling following orthognathic surgery.

OBJECTIVE: To describe a new method for measuring facial swelling following orthognathic surgery using a 3D laser-scanning device. DESIGN: Prospective clinical trial. Setting and Sample Population -- University Dental Hospital, Wales College of Medicine, Biology Life and Health Sciences. Three subjects requiring bi-maxillary orthognathic surgery were recruited for the study. EXPERIMENTAL VARIABLES: Laser-scanned images of the subjects were obtained under a reproducible and controlled environment with two Minolta Vivid 900 (Osaka, Japan) optical laser-scanning devices assembled as a stereo-pair. A set of left and right scanned images was taken for each subject and each scan took an average of 2.5 s. 3D laser scans were recorded over six time periods (T1 -- pre-surgical scan, postoperatively: T2 -- 1 day, T3 -- 1 week, T4 -- 1 month, T5 -- 3 months and T6 -- 6 months). OUTCOME MEASURE: Facial scans from different time periods were overlaid onto the baseline (T6) facial scan to determine the reduction and changes in swelling following orthognathic surgery. RESULTS: The results showed that swelling could be accurately quantified following surgery. Furthermore, there was a significant reduction in the amount of swelling 1 month postoperatively. Furthermore, the facial morphology returned to approximately 90% of the baseline facial scan at 3 months. CONCLUSION: The 3D laser-scanning device and the method described was a reliable and accurate measure of facial swelling following surgery.

The investigation of the changing facial appearance of identical twins employing a three-dimensional laser imaging system.

OBJECTIVE: An investigation to determine the changing facial appearance of identical twins. DESIGN: Clinical study. MATERIALS AND METHODS: Two Minolta Vivid 900 3D optical laser scanners were placed as a stereo pair to capture the soft tissues of a pair of identical twins. Each scan took approximately 2.5 s. The scanned whole faces were superimposed to determine changes in facial morphologies at different time intervals. OUTCOME MEASURES: The shell deviations between left and right scans of each patient were recorded and analysed for differences. Furthermore, final merged faces were overlaid to determine the changes in facial morphology over time. RESULTS: The results showed that changes in height and weight correlated with changes in facial morphology. CONCLUSION: The 3D laser scanning device is a clinically useful tool in the study of facial growth and facial morphology in a pair of twins.

The feasibility of measuring three-dimensional facial morphology in children.

OBJECTIVE: An investigation to determine the feasibility of measuring soft tissue morphology in children using a three-dimensional laser-scanning device. DESIGN: Prospective clinical trial. SETTING AND SAMPLE POPULATION: University of Wales, College of Medicine and one secondary school in the South Wales region. Sixty live subjects (30 adults, 30 children) were recruited in the study. EXPERIMENTAL VARIABLES: Laser scanned images of the subjects were obtained under a reproducible and controlled environment with two Minolta Vivid 900 (Osaka, Japan) optical laser-scanning devices assembled as a stereo-pair. A set of left and right scanned images was taken for each subject and each scan took an average of 2.5 s. These scanned images were processed and merged to form a composite three-dimensional soft tissue reproduction of the subjects using commercially available reverse modelling software. OUTCOME MEASURE: The shell deviations between left and right scan of each patient were recorded and analysed for differences. These differences determined whether the subjects could remain still during the time of the scans. RESULTS: The results showed that the mean differences between shell deviations for the adult scans and children scans were 0.25 +/- 0.09 and 0.30 +/- 0.09 mm, respectively. Paired t-tests showed that the mean error between subject groups was 0.05 +/- 0.15 mm indicating that there was no difference between the two subject groups (p = 0.18). CONCLUSION: The technique as described is clinically reproducible for children and adults and can be used for studies assessing facial changes due to growth or clinical intervention.