What's in a smile? Initial analyses of dynamic changes in facial shape and appearance

Single-level principal component analysis (PCA) and multi-level PCA (mPCA) methods are applied here to a set of (2D frontal) facial images from a group of 80 Finnish subjects (34 male; 46 female) with two different facial expressions (smiling and neutral) per subject. Inspection of eigenvalues gives insight into the importance of different factors affecting shapes, including: biological sex, facial expression (neutral versus smiling), and all other variations. Biological sex and facial expression are shown to be reflected in those components at appropriate levels of the mPCA model. Dynamic 3D shape data for all phases of a smile made up a second dataset sampled from 60 adult British subjects (31 male; 29 female). Modes of variation reflected the act of smiling at the correct level of the mPCA model. Seven phases of the dynamic smiles are identified: rest pre-smile, onset 1 (acceleration), onset 2 (deceleration), apex, offset 1 (acceleration), offset 2 (deceleration), and rest post-smile. A clear cycle is observed in standardized scores at an appropriate level for mPCA and in single-level PCA. mPCA can be used to study static shapes and images, as well as dynamic changes in shape. It gave us much insight into the question “what’s in a smile?

Genome-wide association study of primary tooth eruption identifies pleiotropic loci associated with height and craniofacial distances

Twin and family studies indicate that the timing of primary tooth eruption is highly heritable, with estimates typically exceeding 80%. To identify variants involved in primary tooth eruption we performed a population based genome-wide association study of ‘age at first tooth’ and ‘number of teeth’ using 5998 and 6609 individuals respectively from the Avon Longitudinal Study of Parents and Children (ALSPAC) and 5403 individuals from the 1966 Northern Finland Birth Cohort (NFBC1966). We tested 2,446,724 SNPs imputed in both studies. Analyses were controlled for the effect of gestational age, sex and age of measurement. Results from the two studies were combined using fixed effects inverse variance meta-analysis. We identified a total of fifteen independent loci, with ten loci reaching genome-wide significance (p<5x10−8) for ‘age at first tooth’ and eleven loci for ‘number of teeth’. Together these associations explain 6.06% of the variation in ‘age of first tooth’ and 4.76% of the variation in ‘number of teeth’. The identified loci included eight previously unidentified loci, some containing genes known to play a role in tooth and other developmental pathways, including a SNP in the protein-coding region of BMP4 (rs17563, P= 9.080x10−17). Three of these loci, containing the genes HMGA2, AJUBA and ADK, also showed evidence of association with craniofacial distances, particularly those indexing facial width. Our results suggest that the genome-wide association approach is a powerful strategy for detecting variants involved in tooth eruption, and potentially craniofacial growth and more generally organ development

Genome-Wide Association Study Reveals Multiple Loci Associated with Primary Tooth Development during Infancy

Tooth development is a highly heritable process which relates to other growth and developmental processes, and which interacts with the development of the entire craniofacial complex. Abnormalities of tooth development are common, with tooth agenesis being the most common developmental anomaly in humans. We performed a genome-wide association study of time to first tooth eruption and number of teeth at one year in 4,564 individuals from the 1966 Northern Finland Birth Cohort (NFBC1966) and 1,518 individuals from the Avon Longitudinal Study of Parents and Children (ALSPAC). We identified 5 loci at P<5×10−8, and 5 with suggestive association (P<5×10−6). The loci included several genes with links to tooth and other organ development (KCNJ2, EDA, HOXB2, RAD51L1, IGF2BP1, HMGA2, MSRB3). Genes at four of the identified loci are implicated in the development of cancer. A variant within the HOXB gene cluster associated with occlusion defects requiring orthodontic treatment by age 31 years

Sex chromosomes in human tooth root growth:radiographic studies on 47,XYY males, 46,XY females, 47,XXY males and 45,X/46,XX females

Abstract Studies on families and individuals with sex chromosome abnormalities and 46,XY females, together with molecular research, have provided proof that both X and Y chromosome genes are expressed in human tooth crown growth. The Y chromosome promotes the formation of both permanent tooth crown enamel and dentin, whereas the effect of the X chromosome is seen mainly in enamel formation. In particular, the effect of the Y chromosome on dentin formation explains the expression of sexual dimorphism in crown size. When crown growth is complete, root dentin is formed and requires proliferation of epithelial cells in Hertwig's epithelial root sheath to initiate the differentiation of root odontoblasts. These epithelial cells determine the size, shape and number of the roots. There is a clear sex difference in tooth crown sizes, men have larger teeth than women. The aim of this research was to study completed permanent tooth root lengths in individuals with sex chromosome abnormalities and 46,XY females, an approach which might also provide some clues for a further insight into the development of sexual dimorphism in human growth. The underlying hypothesis was that the effect of the X and Y chromosomes on crown growth is also expressed in root growth. The subjects were participants of L. Alvesalo's research project, Kvantti, and comprised 45,X/46,XX females, 47,XYY and 47,XXY males and female sex reversals with insensitivity to androgens (46,XY females). The root lengths were measured from dental panoramic radiographs with a sliding digital calliper. All available teeth (except third molars) with complete root formation on both sides of the jaws were measured. The results showed longer final permanent tooth root lengths in 47,XYY and 47,XXY males, while the roots in 45,X/46,XX females were shorter compared with the values of normal men and women, respectively. The root lengths of 46,XY females were longer compared to normal women and placed on a level with normal men. The root morphology did not reveal any major deviations from normal variation. In terms of population dental developmental standards it is conceivable that changes in these study groups in final size of their permanent tooth roots become evident during a period beginning eight years after birth and continuing up to the age of 14 years, at least. It became clear that the effect of the Y chromosome on tooth root growth is greater than that of the X chromosome, and this may cause the observed sexual dimorphism, males having longer roots than females. It is suggested that root growth may be affected by the same genes on the X and Y chromosomes which promote crown growth

Crown heights in the permanent teeth of 47,XXY males and 47,XXX females

Abstract Objective: Earlier results based on dental casts and radiographs have shown that additional X and Y chromosomes influence permanent and deciduous tooth crown sizes, with 47,XYY males exhibiting greater crown heights than 46,XY males. We studied here the effect of both X and Y chromosomes on tooth crown heights. Material and methods: The series consisted of 48 47,XXY males, 22 of their male relatives, and seven 47,XXX females with five female relatives. The population controls consisted of 27 males and 33 females. Measurements of all applicable teeth except for the third molars on both sides of the jaws were made on panoramic radiographs with a sliding digital calliper. Results: Apart from a few teeth, the mean crown heights in the 47,XXY males were greater than those in the male population controls, the differences being statistically significant for one tooth in the maxilla and ten teeth in the mandible. With the exception of two teeth, the 47,XXX females had taller tooth crowns than the female population controls, the differences in the two teeth being statistically significant. The 47,XXY males had greater tooth crown heights than the 47,XXX females, except in one tooth, and the differences were significant in two teeth. The tooth crown heights of the male relatives of the 47,XXY males and the female relatives of the 47,XXX females were close to those in the general population. Conclusions: The present results demonstrated the effect of additional X and Y chromosomes in increasing crown heights. The differences between the 47,XXY males and 47,XXX females indicated a stronger effect of a Y chromosome on tooth crown height than of an X chromosome

Prevalence of malocclusion traits and orthodontic treatment in a Finnish adult population

The aim of the study was to examine the prevalence of malocclusion traits and the extent of orthodontic treatment in a Finnish adult population. The study population comprised subjects (n = 1964) from the Northern Finland Birth Cohort 1966 living in the city of Oulu and within 100 km of it. A clinical oral and dental examination with registration of occlusion was carried out in 2012 in connection with a 46-year follow-up survey. Data on previous orthodontic treatment were collected based on a questionnaire. In the clinical examination, 39.5% of the subjects had at least one malocclusion trait. The most common malocclusion traits were lateral crossbite (17.9%), overbite ≥ 6 mm (11.7%) and overjet ≥ 6 mm (9.7%). Crossbite on the left premolars, negative overjet and increased overbite were found more frequently in men. The prevalence of malocclusion traits was at the same level in treated and untreated groups. Overall, 18.6% of the subjects had undergone orthodontic treatment. Women showed a significantly higher prevalence of orthodontic treatment. The most common malocclusion trait in the present study was lateral crossbite. Significant male dominance in the prevalence of malocclusion was observed, which has not been reported earlier in Finland. Orthodontic treatment of malocclusion traits was more common among females in Northern Finland. This study indicates that orthodontic treatment provided in childhood was, on average, adequate in reducing malocclusion traits to the level observed in the general population

Influence of overjet and overbite on soft tissue profile in mature adults: A cross-sectional population study

The aim of this study was to explore the association of soft tissue profile and severity of overbite and overjet in a large adult population.; The study population consisted of 1630 adults (age, 46 years; 712 men, 919 women), all part of the Northern Finland Birth Cohort 1966. A clinical examination was performed on all subjects, including recording of overjet and overbite, and digital facial (frontal and profile) photographs were obtained. A multivariate regression model was developed to study the correlation of soft tissue measurements with overjet and overbite, considering the effect of sex.; The regression model explained approximately 30% of the variability in overjet in our sample and approximately 22% of the variability in overbite. Overjet was related more significantly to upper and lower anteroposterior lip position, and upper and lower facial height (P <0.05). Overbite showed a stronger association with anteroposterior position of the lower lip, pogonion, and soft tissue B-point (P <0.05).; Soft tissue profile was weakly to moderately correlated with severity of overjet and overbite in the entire sample. However, in subjects with negative overjet (mandibular prognathism), this association was highly significant

Profile shape variation and sexual dimorphism amongst middle-aged Northern Europeans.

AIM: To explore profile shape variation in a large population of middle-aged individuals and investigate features of sexual dimorphism. MATERIALS AND METHODS: Facial profile photographs of 1776 individuals (964 females and 812 males; 46 years old), members of the Northern Finland Birth Cohort 1966 (NFBC1966), were uploaded and digitized with Viewbox software. Profile shape was defined with 47 landmarks (4 fixed and 43 sliding semi-landmarks). Digitized images were reoriented and scaled with Procrustes Superimposition, and shape variation was determined with a Principal Component Analysis. RESULTS: More than 90 per cent of profile shape variation was explained by Principal Components (PC) 1-9. PC1, explaining the largest amount of variation (33.1 per cent) described changes in facial convexity, slope of the forehead, lip, and chin protuberance. PC2 (23.1 per cent variation) was more related to vertical changes of the lower facial third and PC3 (11 per cent variation) primarily described changes in lip protrusion and nasal projection. Shape analysis showed a significant difference between the average female and the average male profile shape (P {\textless} 0.001); however, this was not evident upon visual observation. The shape variable most associated with sex was PC3 (η 2 = 0.245; P {\textless} 0.001), which described changes in lip prominence and in projection of the dorsal nasal surface. An additional discriminant analysis showed that profile shape predicted sex in 76 per cent of males and 79.6 per cent of females. CONCLUSIONS: There is significant sexual dimorphism in facial profile among middle-aged adults. Profile shape variation was associated to changes in lip protrusion, nasal protuberance, and chin projection