Comparison of some cephalometric distances and corresponding facial proportions with regard to heritability

Opening up on airways: the purported effect of nasorespiratory obstruction on dentofacial growth

Nasorespiratory obstruction has been purported to influence dentofacial growth adversely. This has sparked considerable debate for decades with a resurgence in interest in 'airway friendly orthodontics' among both general and specialist dental practitioners. This critical review aims to evaluate the current literature relating to two questions: does nasorespiratory obstruction alter dentofacial growth, and does early intervention targeted at alleviating nasorespiratory obstruction improve dentofacial growth? The strength of association between nasorespiratory obstruction, mouth breathing and a long face is weak. The common methodological flaws in research include unblinded and cross-sectional study designs, a lack of adequate controls, inadequate follow-up, subjective assessments and inadequate statistical power. Vertical dentofacial growth has a strong genetic influence, which implies a relatively minor contribution of environmental factors including airway obstruction. The current evidence does not support recommending procedures, such as adenotonsillectomy and maxillary expansion, with the singular aim of negating a hyperdivergent (vertical) dentofacial growth pattern. In light of low-quality evidence, both the World Health Organization guidelines and ethical principles dictate that greater emphasis is placed on avoiding harm and wastage of resources over alternative options. These findings call for quality improvement in undergraduate and postgraduate curricula and continuing professional development for health professionals.

The age distribution of facial metrics in two large Korean populations

Growth and alterations in craniofacial morphology have attracted interest in many fields of science, especially physical anthropology, genetics and forensic sciences. We performed an analysis of craniofacial morphology alterations by gender and ageing stage in Korean populations. We studied 15 facial metrics using two large Korean populations (1,926 samples from the Korea Medicine Data Center cohort and 5,643 samples from the Ansan-Ansung cohort). Among the 15 metrics, 12 showed gender differences and tended to change with age. In both of the independent populations, brow ridge height, upper lip height, nasal tip height, and profile nasal length tended to increase with age, whereas outer canthal width, right palpebral fissure height, left palpebral fissure height, right upper lip thickness, left upper lip thickness, nasal tip protrusion, facial base width, and lower facial width tended to decrease. In conclusion, our findings suggest that ageing (past 40 years of age) might affect eye size, nose length, upper lip thickness, and facial width, possibly due to loss of elasticity in the face. Therefore, these facial metric changes could be applied to individual age prediction and aesthetic facial care.

The age distribution of facial metrics in two large Korean populations

Growth and alterations in craniofacial morphology have attracted interest in many fields of science, especially physical anthropology, genetics and forensic sciences. We performed an analysis of craniofacial morphology alterations by gender and ageing stage in Korean populations. We studied 15 facial metrics using two large Korean populations (1,926 samples from the Korea Medicine Data Center cohort and 5,643 samples from the Ansan-Ansung cohort). Among the 15 metrics, 12 showed gender differences and tended to change with age. In both of the independent populations, brow ridge height, upper lip height, nasal tip height, and profile nasal length tended to increase with age, whereas outer canthal width, right palpebral fissure height, left palpebral fissure height, right upper lip thickness, left upper lip thickness, nasal tip protrusion, facial base width, and lower facial width tended to decrease. In conclusion, our findings suggest that ageing (past 40 years of age) might affect eye size, nose length, upper lip thickness, and facial width, possibly due to loss of elasticity in the face. Therefore, these facial metric changes could be applied to individual age prediction and aesthetic facial care.

Identification of five novel genetic loci related to facial morphology by genome-wide association studies

BACKGROUND

Face morphology is strongly determined by genetic factors. However, only a small number of genes related to face morphology have been identified to date. Here, we performed a two-stage genome-wide association study (GWAS) of 85 face morphological traits in 7569 Koreans (5643 in the discovery set and 1926 in the replication set).

RESULTS

In this study, we analyzed 85 facial traits, including facial angles. After discovery GWAS, 128 single nucleotide polymorphisms (SNPs) showing an association of P < 5 × 10^- 6 were selected to determine the replication of the associations, and meta-analysis of discovery GWAS and the replication analysis resulted in five genome-wide significant loci. The OSR1-WDR35 [rs7567283, G allele, beta (se) = -0.536 (0.096), P = 2.75 × 10^- 8] locus was associated with the facial frontal contour; the HOXD1-MTX2 [rs970797, A allele, beta (se) = 0.015 (0.003), P = 3.97 × 10^- 9] and WDR27 [rs3736712, C allele, beta (se) = 0.293 (0.048), P = 8.44 × 10^- 10] loci were associated with eye shape; and the SOX9 [rs2193054, C allele, beta (se) (ln-transformed) = -0.007 (0.001), P = 6.17 × 10^- 17] and DHX35 [rs2206437, A allele, beta (se) = -0.283 (0.047), P = 1.61 × 10^- 9] loci were associated with nose shape. WDR35 and SOX9 were related to known craniofacial malformations, i.e., cranioectodermal dysplasia 2 and campomelic dysplasia, respectively. In addition, we found three independent association signals in the SOX9 locus, and six known loci for nose size and shape were replicated in this study population. Interestingly, four SNPs within these five face morphology-related loci showed discrepancies in allele frequencies among ethnic groups.

CONCLUSIONS

We identified five novel face morphology loci that were associated with facial frontal contour, nose shape, and eye shape. Our findings provide useful genetic information for the determination of face morphology.

Heritability maps of human face morphology through large-scale automated three-dimensional phenotyping

The human face is a complex trait under strong genetic control, as evidenced by the striking visual similarity between twins. Nevertheless, heritability estimates of facial traits have often been surprisingly low or difficult to replicate. Furthermore, the construction of facial phenotypes that correspond to naturally perceived facial features remains largely a mystery. We present here a large-scale heritability study of face geometry that aims to address these issues. High-resolution, three-dimensional facial models have been acquired on a cohort of 952 twins recruited from the TwinsUK registry, and processed through a novel landmarking workflow, GESSA (Geodesic Ensemble Surface Sampling Algorithm). The algorithm places thousands of landmarks throughout the facial surface and automatically establishes point-wise correspondence across faces. These landmarks enabled us to intuitively characterize facial geometry at a fine level of detail through curvature measurements, yielding accurate heritability maps of the human face (www.heritabilitymaps.info).

Heritability of the Human Craniofacial Complex

Quantifying normal variation and the genetic underpinnings of anatomical structures is one of the main goals of modern morphological studies. However, the extent of genetic contributions to normal variation in craniofacial morphology in humans is still unclear. The current study addresses this gap by investigating the genetic underpinnings of normal craniofacial morphology. The sample under investigation consists of 75 linear and angular measurements spanning the entire craniofacial complex, recorded from lateral cephalographs of 1,379 participants in the Fels Longitudinal Study. Heritabilities for each trait were estimated using SOLAR, a maximum-likelihood variance components approach utilizing all pedigree information for parameter estimation. Trait means and mean effects of the covariates age, sex, age(2) , sex × age, and sex × age(2) were simultaneously estimated in the analytic models. All traits of the craniofacial complex were significantly heritable. Heritability estimates ranged from 0.10 to 0.60, with the majority being moderate. It is important to note that we found similar ranges of heritability occurring across the different functional/developmental components of the craniofacial complex, the splanchnocranium, the basicranium, and the neurocranium. This suggests that traits from different regions of the craniofacial complex are of comparable utility for the purposes of population history and phylogeny reconstruction. At the same time, this genetic influence on craniofacial morphology signals a caution to researchers of nongenetic studies to consider the implications of this finding when selecting samples for study given their project design and goals.

Heritability of Face Shape in Twins: A Preliminary Study using 3D Stereophotogrammetry and Geometric Morphometrics

INTRODUCTION

Previous research suggests that aspects of facial surface morphology are heritable. Traditionally, heritability studies have used a limited set of linear distances to quantify facial morphology and often employ statistical methods poorly designed to deal with biological shape. In this preliminary report, we use a combination of 3D photogrammetry and landmark-based morphometrics to explore which aspects of face shape show the strongest evidence of heritability in a sample of twins.

METHODS

3D surface images were obtained from 21 twin pairs (10 monozygotic, 11 same-sex dizygotic). Thirteen 3D landmarks were collected from each facial surface and their coordinates subjected to geometric morphometric analysis. This involved superimposing the individual landmark configurations and then subjecting the resulting shape coordinates to a principal components analysis. The resulting PC scores were then used to calculate rough narrow-sense heritability estimates.

RESULTS

Three principal components displayed evidence of moderate to high heritability and were associated with variation in the breadth of orbital and nasal structures, upper lip height and projection, and the vertical and forward projection of the root of the nose due to variation in the position of nasion.

CONCLUSIONS

Aspects of facial shape, primarily related to variation in length and breadth of central midfacial structures, were shown to demonstrate evidence of strong heritability. An improved understanding of which facial features are under strong genetic control is an important step in the identification of specific genes that underlie normal facial variation.

The comparison of facial estethics between orthodontically treated patients and their parents

Orthodontists emphasize the importance of facial esthetics while planning a treatment, and orthodontist state that orthodontics have more than expected effects on dentofacial esthetics. The facial esthetics of treated patients and their parents was analyzed and compared to define facial growth and to use in forensic sciences. Our study was applied to 45 orthodontic patients who were treated in our clinic and their untreated parents. The patients were divided into Classes I, II, and III groups according to their malocclusions. Pre- and posttreatment changes, pretreatment facial esthetics of the paitents and its accordance with their parents, and the calculation of heritability tests were performed. After the statistics, for pre- and posttreatment changes, all the groups except Class I revealed significant changes. There were significant correlations of patients for the heritability values and pretreatment esthetic in accordance with parents, but there were more correlations of fathers when compared to mothers. The facial esthetics in adolescences is related with so many factors, not only related with one factor. The facial esthetics in fact includes the aim of evaluation of facial properties partly or totally. Because orthodontic treatments affect facial esthetics, performing similar studies for the treatment outcomes, capabilities, and borders is important.

Human's cognitive ability to assess facial cues from photographs: a study of sexual selection in the Bolivian Amazon

BACKGROUND

Evolutionary theory suggests that natural selection favors the evolution of cognitive abilities which allow humans to use facial cues to assess traits of others. The use of facial and somatic cues by humans has been studied mainly in western industrialized countries, leaving unanswered whether results are valid across cultures.

METHODOLOGY/PRINCIPAL FINDINGS

Our objectives were to test (i) if previous finding about raters' ability to get accurate information about an individual by looking at his facial photograph held in low-income non western rural societies and (ii) whether women and men differ in this ability. To answer the questions we did a study during July-August 2007 among the Tsimane', a native Amazonian society of foragers-farmers in Bolivia. We asked 40 females and 40 males 16-25 years of age to rate four traits in 93 facial photographs of other Tsimane' males. The four traits were based on sexual selection theory, and included health, dominance, knowledge, and sociability. The rating scale for each trait ranged from one (least) to four (most). The average rating for each trait was calculated for each individual in the photograph and regressed against objective measures of the trait from the person in the photograph. We found that (i) female Tsimane' raters were able to assess facial cues related to health, dominance, and knowledge and (ii) male Tsimane' raters were able to assess facial cues related to dominance, knowledge, and sociability.

CONCLUSIONS/SIGNIFICANCE

Our results support the existence of a human ability to identify objective traits from facial cues, as suggested by evolutionary theory.

A genomewide linkage scan for quantitative trait loci influencing the craniofacial complex in baboons (Papio hamadryas spp.)

Numerous studies have detected significant contributions of genes to variation in development, size, and shape of craniofacial traits in a number of vertebrate taxa. This study examines 43 quantitative traits derived from lateral cephalographs of 830 baboons (Papio hamadryas) from the pedigreed population housed at the Southwest National Primate Research Center. Quantitative genetic analyses were conducted using the SOLAR analytic platform, a maximum-likelihood variance components method that incorporates all familial information for parameter estimation. Heritability estimates were significant and of moderate to high magnitude for all craniofacial traits. Additionally, 14 significant quantitative trait loci (QTL) were identified for 12 traits from the three developmental components (basicranium, splanchnocranium, and neurocranium) of the craniofacial complex. These QTL were found on baboon chromosomes (and human orthologs) PHA1 (HSA1), PHA 2 (HSA3), PHA4 (HSA6), PHA11 (HSA12), PHA13 (HSA2), PHA16 (HSA17), and PHA17 (HSA13) (PHA, P. hamadryas; HSA, Homo sapiens). This study of the genetic architecture of the craniofacial complex in baboons provides the groundwork needed to establish the baboon as an animal model for the study of genetic and nongenetic influences on craniofacial variation.

Heritability of facial proportions and soft-tissue profile characteristics in Turkish Anatolian siblings

INTRODUCTION

The purpose of this study was to determine the possible effects of genetic factors on facial proportions and soft-tissue profile characteristics in Turkish Anatolian siblings.

METHODS

The material consisted of lateral and posteroanterior cephalometric head radiographs of 138 siblings (70 women, 68 men) living 15 years or more in the province of Erzurum in eastern Turkey. The subjects were required to have completed their pubertal growth spurts and to have received no previous orthodontic or prosthodontic treatment. The heritability assessments of craniofacial and soft-tissue measurements were undertaken according to narrow-sense heritability. For the calculation and evaluation of heritability estimate values, the mixed-model least-squared and maximum likelihood computer program model type II was used for statistical analysis.

RESULTS

According to the narrow-sense heritability estimate values, the measurements of total depth index, soft-tissue chin thickness, soft-tissue facial angle, Merrifield angle, and Holdaway angle showed the highest heritability coefficients (P <.001). Total height index, anterior height index, facial width index, upper to lower facial height index, and lower lip-E line measurements demonstrated moderate heritability values (P<.01). The upper depth index had a low but statistically significant heritability value (P <.05). However, no statistically significant heritability coefficient in upper lip-E line measurement was found.

CONCLUSIONS

Turkish Anatolian siblings have similar facial features regarding facial proportions and soft-tissue measurements.

The use of parental data to evaluate soft tissues in an Anatolian Turkish population according to Holdaway soft tissue norms

INTRODUCTION

The relative influence of genetic and environmental factors in the etiology of malocclusion has long been a matter for discussion. The aim of this study was to compare the soft tissue structures of parents and their prepubertal, pubertal, and postpubertal offspring according to the Holdaway soft tissue norms to determine the similarity among them. Differences related to age and sex between the parents and offspring were also evaluated.

METHODS

Lateral cephalometric radiographs were used to determine the similarities in soft tissue structures in 120 families, which were divided into prepubertal (n = 40), pubertal (n = 40), and postpubertal (n = 40) groups according to the children's skeletal ages. A total of 12 variables (2 angular and 10 linear) were measured according to Holdaway's soft tissue analysis. Pairs were formed between family members (mother to son, mother to daughter, father to son, father to daughter, midparent (mean of the father's and mother's values) to son, and midparent to daughter) in each group. Descriptive statistics and multiple linear regression analysis were performed.

RESULTS

Statistically significant correlations between parents and their offspring were found. The parental data showed that a mother's genetic influence on her child's soft tissues was greater than the father's. Moreover, it was found that daughters had greater genetic influences from their parents than did sons. As age increased, the similarity was greater. Soft tissue facial angle (beta: 0.671), soft tissue chin thickness (beta: 0.549), and basic upper lip thickness (beta: 0.537) were the most similar variables between parents and their offspring.

CONCLUSIONS

A few selected cephalometric measurements of the parents might furnish important data to the clinician in predicting a child's facial growth characteristics and aging process.

Heritability of craniofacial characteristics between parents and offspring estimated from lateral cephalograms

OBJECTIVE

The purpose of the study was to estimate the heritability of different cephalometric parameters, according to lateral cephalograms, between parents and their offspring in an Icelandic population.

METHODS

The material was collected at the Faculty of Odontology, University of Iceland. The subjects were 363 children (6 years of age) and their parents. Material was also collected from the same group of children at the age of 16 years. Twenty-two reference points were identified on each cephalogram, and 33 variables were calculated, both angular and linear. Heritability was calculated at ages 6 and 16.

RESULTS

Daughters had more variables that reached the level of significance than did sons. Daughters showed similar heritability to both parents at both age levels, but more variables were highly significant ( P < or = .001) in the daughter-father groups. Sons showed stronger heritability to their mothers at both ages. The variables showing the greatest heritability were those representing the position of the lower jaw, the anterior and posterior face heights, and the cranial base dimensions. Heritability was notably low for the dental variables.

CONCLUSIONS

Genetic aberrations can be detected for complex polygenetic multifactorial traits. Cephalometric data can support predictions, and analysis of parental data could have predictive value for offspring.

Three-dimensional assessment of the relative contribution of genetics and environment to various facial parameters with the twin method

The purpose of this prospective study was to help distinguish the relative contributions of heredity and environment to the external facial features and to assess the relative strength of the genetic influence on anteroposterior and vertical facial parameters, by using 3-dimensional optical surface scanning and the inferential twin method. The subject group consisted of 10 pairs of monozygotic twins (5 male, 5 female, mean age 11.9 years), 10 pairs of same-sex dizygotic twins (3 male, 7 female, mean age 12.1 years), and 6 mixed-sex dizygotic twin pairs. Two methods of analysis were used on the 3-dimensional scans. Interlandmark measurements of 28 facial parameters were recorded, and the mean intrapair differences for each parameter were compared between the monozygotic and dizygotic groups. The second method used the analysis of surface shape for all twin pairs. This technique characterizes the face by using 9 surface shapes distinguished visually by color, allowing a qualitative description of the differences between monozygotic and dizygotic twin pairs. Analysis of the 28 facial parameters showed significant ( P< .05) genetic determination for midfacial parameters, especially left eye width, intercanthal width, nose height, and nose width. Analysis of surface shape showed the strongest genetic determination for a triangular area of the midface encompassing the orbital rims, intercanthal area, and nose. The concordance for vertical and anteroposterior facial parameters was found to be greater in monozygotic twins than in dizygotic twins. The concordance for vertical facial dimensions of the middle and lower anterior parts of the face was found to be greater than that for anteroposterior facial dimensions in monozygotic twins.

Heritability of 39 orthodontic cephalometric parameters on MZ, DZ twins and MN-paired singletons

The twin method is one of the most effective methods available for investigating genetically determined variables in orthodontics, as well as in other medical fields, depending on the variance in the shape and the size of skull and teeth, both on genetic and environmental influences. The former have been extensively evaluated and, in particular, most of the facial and dental cephalometric parameters have shown high heritability, the vertical parameters have a higher genetic control compared with the horizontal ones. Nevertheless, most of the results provided by twin research have been considered arbitrary if directly transferred to a singleton population and in further studies, including extensive analysis of the parents, familial and nutritional habits have been recommended. In this study, heritability of 39 lateral orthodontic cephalometric parameters has been estimated by both statistical method of path analysis and Dahlberg' quotient in three orthodontic samples of young monozygotic and dizygotic twins and same-sex pairs of singletons living together, matched for sex and age, to evaluate genetic versus environmental factors affecting heritability of craniofacial features in the aim to obtain results not only statistically significant but also transferrable to a singleton population. Different inheritance trends, showing the highest concordance of values between monozygotic twin pairs when compared with dizygotic twin pairs or the same-sex singletons paired group, come from the 39 selected lateral cephalometric parameters, confirming the hypothesis that strong genetic control is exerted especially on the vertical ones. Heritability seems to have more influence on anterior vertical parameters than posterior. Mandibular structure seems to be more genetically determined than mandibular size. All five Ricketts' cephalometric typological parameters confirm high heritability coefficients, the same applies to the linear horizontal McNamara's measurement and lower incisor to A-Pg line. The two tested statistical methods showed relevant concordance of results.

The use of twins in dentofacial genetic research

A literature review is given on the different results obtained with twin and family studies in relationship to the development and structure of the dentofacial complex. Recent advances in twin and family studies are mentioned. Attention is focused on functional components considered to be of primary importance in craniofacial growth.

Heritability of craniometric and occlusal variables: a longitudinal sib analysis

There has long been interest in the inheritance of malocclusion, but few studies have distinguished between skeletal (craniometric) variables and occlusal, tooth-based variables (e.g., anterior irregularity, rotations, displacements). This study was based on serial assessments of untreated persons in 30 sibships from 4 years (full deciduous dentition) to 20 years of age (full permanent dentition) in the Bolton-Brush Growth Studies of Ohio. Results define a clear dichotomy: craniometric variables (k = 29) typically show significant additive components of variance; correlations increase from age 4 to age 20; and correlations average 0.43 at adulthood. Tooth-based variables of position and relationship (k = 21) reach significance only occasionally; correlations decrease with age to the extent that few variables for subjects at age 20 have a correlation significantly different from zero. In contrast to craniometric variables, which have high heritabilities, almost all of the occlusal variability is acquired rather than inherited.