Defining new dental phenotypes using 3-D image analysis to enhance discrimination and insights into biological processes

New Approach to Dental Morphometric Research Based on 3D Imaging Techniques

Recent progress in imaging and image processing techniques has provided for improvements in odontological research in a variety of aspects. Thus, the presented method has been developed precisely in order to assess metrically 3D reconstructions of teeth. Rapidly and accurately obtained data of a wide range and appropriate density are sufficient enough for morphometric studies rather than tooth size assessments which are inherent to conventional techniques. The main contributions providing for holistic and objective morphometric analysis of teeth are the following: (1) interpretation of basic dental morphological features; (2) automated of orientational coordinate system setup based on tooth surface analysis; (3) new tooth morphometric parameters which could not be obtained through application of conventional odontometric techniques; (4) methodological novelty for automated odontomorphometric analysis pipeline. Application of tomographic imaging, which has been used for obtaining 3D models, expands the proposed method potential further through providing detailed and comprehensive reconstructions of teeth. The current study was conducted on unique material from the archaeological site of Sunghir related to the Upper Palaeolithic period. Metric assessments of external and internal morphological layers of teeth were performed in common orientation and sectioning. The proposed technique allowed more profound analysis of Sunghirian teeth which date back to the times of modern human morphology formation.

Inter-Operator Reliability of Dental Morphometric Measurements

Background: Measurement-based studies are prone to measurement errors, which occur at the same operator or between different operators during repeated measurements of the same sample.

Aim of the study: To assess the inter-operator reliability of morphometric measurements using a bidimensional image analysis method.

Material and methods: Eight study models have been selected, images of teeth and models were taken from vestibular and occlusal view. The following parameters were measured individually by three, previously trained operators: mesio-distal, occluso-gingival, and vestibulo-oral dimensions, vestibular and occlusal area, depth of palatal arch, arch breadth, arch circumference, and arch length. Intraclass correlation coefficients were calculated for each measurement.

Results: The reliability of the measurements showed high degrees, all values being higher than 0.8.

Conclusions: Dental morphometric measurements done by 2D image analysis can be performed by multiple operators with an excellent reliability.

Facial Anthropometric Norms among Kosovo - Albanian Adults

Background

The development of an anthropometric craniofacial database is a necessary multidisciplinary proposal.

Aim

The aim of this study was to establish facial anthropometric norms and to investigate into sexual dimorphism in facial variables among Kosovo Albanian adults.

Materials and Methods

The sample included 204 students of Dental School, Faculty of Medicine, University of Pristina. Using direct anthropometry, a series of 8 standard facial measurements was taken on each subject with digital caliper with an accuracy of 0.01 mm (Boss, Hamburg-Germany). The normative data and percentile rankings were calculated. Gender differences in facial variables were analyzed using t- test for independent samples (p<0.05). The index of sexual dimorphism (ISD) and percentage of sexual dimorphism were calculated for each facial measurement.

Results: N

ormative data for all facial anthropometric measurements in males were higher than in females. Male average norms compared with the female average norms differed significantly from each other (p>0.05).The highest index of sexual dimorphism (ISD) was found for the lower facial height 1.120, for which the highest percentage of sexual dimorphism, 12.01%., was also found. The lowest ISD was found for intercanthal width, 1.022, accompanied with the lowest percentage of sexual dimorphism, 2.23%.

Conclusion

The obtained results have established the facial anthropometric norms among Kosovo Albanian adults. Sexual dimorphism has been confirmed for each facial measurement.

Anthropometric Study of Three-Dimensional Facial Morphology in Malay Adults

OBJECTIVES

To establish the three-dimensional (3D) facial soft tissue morphology of adult Malaysian subjects of the Malay ethnic group; and to determine the morphological differences between the genders, using a non-invasive stereo-photogrammetry 3D camera.

MATERIAL AND METHODS

One hundred and nine subjects participated in this research, 54 Malay men and 55 Malay women, aged 20-30 years old with healthy BMI and with no adverse skeletal deviation. Twenty-three facial landmarks were identified on 3D facial images captured using a VECTRA M5-360 Head System (Canfield Scientific Inc, USA). Two angular, 3 ratio and 17 linear measurements were identified using Canfield Mirror imaging software. Intra- and inter-examiner reliability tests were carried out using 10 randomly selected images, analyzed using the intra-class correlation coefficient (ICC). Multivariate analysis of variance (MANOVA) was carried out to investigate morphologic differences between genders.

RESULTS

ICC scores were generally good for both intra-examiner (range 0.827-0.987) and inter-examiner reliability (range 0.700-0.983) tests. Generally, all facial measurements were larger in men than women, except the facial profile angle which was larger in women. Clinically significant gender dimorphisms existed in biocular width, nose height, nasal bridge length, face height and lower face height values (mean difference > 3mm). Clinical significance was set at 3mm.

CONCLUSION

Facial soft tissue morphological values can be gathered efficiently and measured effectively from images captured by a non-invasive stereo-photogrammetry 3D camera. Adult men in Malaysia when compared to women had a wider distance between the eyes, a longer and more prominent nose and a longer face.

Comparison of the total length and areas of upper central incisors between males and females using computer-assisted morphometry

The determination of measurements of teeth facilitates various procedures in dentistry. The purpose of this study was to evaluate the total length and the area of the non-extracted upper central incisors (UCI). Periapical radiographies of 42 UCI were placed over a lighted box. The outlines of the teeth and the pulp cavity were traced onto sheets and then measured using an image analyzer. The area of the upper left central incisor tooth (tooth 21) was statistically significantly larger in males than in females (p = 0.02). The total length of the right UCI was similar to that of the left one. This study demonstrates that computer-assisted morphometry is an important tool for the evaluation of the total length and areas of teeth and their pulp cavities. The significantly larger area of tooth 21 in males compared to females has anthropomorphic and clinical implications.

Genetic, Epigenetic, and Environmental Influences on Dentofacial Structures and Oral Health: Ongoing Studies of Australian Twins and Their Families

The Craniofacial Biology Research Group in the School of Dentistry at The University of Adelaide is entering an exciting new phase of its studies of dental development and oral health in twins and their families. Studies of the teeth and faces of Australian twins have been continuing for nearly 30 years, with three major cohorts of twins recruited over that time, and currently we are working with twins aged 2 years old to adults. Cross-sectional data and records relating to teeth and faces of twins are available for around 300 pairs of teenage twins, as well as longitudinal data for 300 pairs of twins examined at three different stages of development, once with primary teeth, once at the mixed dentition stage, and then again when the permanent teeth had emerged. The third cohort of twins comprises over 600 pairs of twins recruited at around birth, together with other family members. The emphasis in this third group of twins has been to record the timing of emergence of the primary teeth and also to sample saliva and dental plaque to establish the timing of colonization of decay-forming bacteria in the mouth. Analyses have confirmed that genetic factors strongly influence variation in timing of primary tooth emergence. The research team is now beginning to carry out clinical examinations of the twins to see whether those who become colonized earlier with decay-forming bacteria develop dental decay at an earlier age. By making comparisons within and between monozygotic (MZ) and dizygotic (DZ) twin pairs and applying modern molecular approaches, we are now teasing out how genetic, epigenetic, and environmental factors interact to influence dental development and also oral health.

Three-dimensional analysis of tooth dimensions in the MSX1-missense mutation

OBJECTIVES

A novel, 3D technique to measure the differences in tooth crown morphology between the MSX1 cases and non-affected controls was designed to get a better understanding of dental phenotype-genotype associations.

MATERIALS AND METHODS

Eight Dutch subjects from a single family with tooth agenesis, all with an established nonsense mutation c.332 C > A, p. Ser 111 Stop in exon 1 of MSX1, were compared with unaffected controls regarding several aspects of tooth crown morphology of incisor and molar teeth. A novel method of quantitative three-dimensional analysis was used to detect differences.

RESULTS

Statistically significant shape differences were observed for the maxillary incisor in the MSX1 family compared with the controls on the following parameters: surface area, buccolingual dimension, squareness, and crown volume (P ≤ 0.002). Molar crown shape was unaffected.

CONCLUSIONS

A better understanding of dental phenotype-genotype associations may contribute to earlier diagnosis of some multiple-anomaly congenital syndromes involving dental anomalies.

CLINICAL RELEVANCE

A "shape database" that includes associated gene mutations resulting from developmental syndromes may facilitate the genetic identification of hypodontia cases.

Phenotype-genotype correlations in mouse models of amelogenesis imperfecta caused by Amelx and Enam mutations

Mutations in human and in mouse orthologous genes Amelx and Enam result in a diverse range of enamel defects. In this study we aimed to investigate the phenotype-genotype correlation between the mutants and the wild-type controls in mouse models of amelogenesis imperfecta using novel measurement approaches. Ten hemi-mandibles and incisors were dissected from each group of Amelx(WT), Amelx(X/Y64H), Amelx(Y/Y64H), Amelx(Y64H/Y64H), and Enam(WT), Enam(Rgsc395) heterozygous and Enam(Rgsc395) homozygous mice. Their macro-morphology, colour and micro-topography were assessed using bespoke 2D and 3D image analysis systems and customized colour and whiteness algorithms. The novel methods identified significant differences (p ≤ 0.05) between the Amelx groups for mandible and incisor size and enamel colour and between the Enam groups for incisor size and enamel colour. The Amelx(WT) mice had the largest mandibles and incisors, followed in descending order of size by the Amelx(X/Y64H), Amelx(Y/Y64H) and Amelx(Y64H/Y64H) mice. Within the Enam groups the Enam(WT) incisors were largest and the Enam(Rgsc395) heterozygous mice were smallest. The effect on tooth morphology was also reflected by the severity of the enamel defects in the colour and whiteness assessment. Amelogenin affected mandible morphology and incisor enamel formation, while enamelin only affected incisors, supporting the multifunctional role of amelogenin. The enamelin mutation was associated with earlier forming enamel defects. The study supported the critical involvement of amelogenin and enamelin in enamel mineralization.

Stereophotogrammetric analysis of nasolabial morphology among Asian Malays: influence of age and sex

OBJECTIVE

It is clear that population-specific norms should be used when planning plastic and reconstructive surgery for selected patients. In this study, we aimed to generate nasal and labial reference values by applying a stereophotogrammetric technique. A further aim was to investigate the effect of sexual dimorphism, age-related changes, and the interrelation between nasal and labial morphology.

DESIGN

Cross-sectional study.

SETTING

The data were collected from different locations on the Malaysian peninsula.

PARTICIPANTS

A total of 276 Asian Malays (138 males and 138 females) were included in this study, and a three-dimensional system was used for capturing data. The sample was divided into three age groups: 13 to 14, 15 to 17, and 18 to 36 years.

MAIN OUTCOME MEASURE(S)

Twenty-five dimensions of the nose and lips were measured and analyzed separately in males and females.

RESULTS

Significant differences between males and females were identified in 11 distances, and significant effects of age were found in most of the dimensions (p < .05). Significant correlations between the nasal and labial dimensions were recorded, particularly between lateral lip height and width of the ala insertion. A principal component analysis showed interrelationships between the nasal width distances and upper lip height.

CONCLUSION

This study has provided a new three-dimensional database for nose and lip morphology in Malays and demonstrated patterns of variation that can be used by surgeons to make comparisons within and between different human populations and also to develop treatment plans for their patients.

Multilevel complex interactions between genetic, epigenetic and environmental factors in the aetiology of anomalies of dental development

Dental anomalies are caused by complex interactions between genetic, epigenetic and environmental factors during the long process of dental development. This process is multifactorial, multilevel, multidimensional and progressive over time. In this paper the evidence from animal models and from human studies is integrated to outline the current position and to construct and evaluate models, as a basis for future work. Dental development is multilevel entailing molecular and cellular interactions which have macroscopic outcomes. It is multidimensional, requiring developments in the three spatial dimensions and the fourth dimension of time. It is progressive, occurring over a long period, yet with critical stages. The series of interactions involving multiple genetic signalling pathways are also influenced by extracellular factors. Interactions, gradients and spatial field effects of multiple genes, epigenetic and environmental factors all influence the development of individual teeth, groups of teeth and the dentition as a whole. The macroscopic, clinically visible result in humans is a complex unit of four different tooth types formed in morphogenetic fields, in which teeth within each field form directionally and erupt at different times, reflecting the spatio-temporal control of development. Even when a specific mutation of a single gene or one major environmental insult has been identified in a patient with a dental anomaly, detailed investigation of the phenotype often reveals variation between affected individuals in the same family, between dentitions in the same individual and even between different teeth in the same dentition. The same, or closely similar phenotypes, whether anomalies of tooth number or structure, may arise from different aetiologies: not only mutations in different genes but also environmental factors may result in similar phenotypes. Related to the action of a number of the developmental regulatory genes active in odontogenesis, in different tissues, mutations can result in syndromes of which dental anomalies are part. Disruption of the antagonistic balance between developmental regulatory genes, acting as activators or inhibitors can result in dental anomalies. There are critical stages in the development of the individual tooth germs and, if progression fails, the germ will not develop further or undergoes apoptosis. The reiterative signalling patterns over time during the sequential process of initiation and morphogenesis are reflected in the clinical association of anomalies of number, size and form and the proposed models. An initial step in future studies is to combine the genetic investigations with accurate recording and measurement of the phenotype. They also need to collate findings at each level and exploit the accurate definition of both human and murine phenotypes now possible.

Morphogenetic fields within the human dentition: a new, clinically relevant synthesis of an old concept

This paper reviews the concept of morphogenetic fields within the dentition that was first proposed by Butler (Butler PM. Studies of the mammalian dentition. Differentiation of the post-canine dentition. Proc Zool Soc Lond B 1939;109:1–36), then adapted for the human dentition by Dahlberg (Dahlberg AA. The changing dentition of man. J Am Dent Assoc 1945;32:676–90; Dahlberg AA. The dentition of the American Indian. In: Laughlin WS, editor. The Physical Anthropology of the American Indian. New York: Viking Fund Inc.; 1951. p. 138–76). The clone theory of dental development, proposed by Osborn (Osborn JW. Morphogenetic gradients: fields versus clones. In: Butler PM, Joysey KA, editors Development, function and evolution of teeth. London: Academic Press, 1978. p. 171–201), is then considered before these two important concepts are interpreted in the light of recent findings from molecular, cellular, genetic and theoretical and anthropological investigation. Sharpe (Sharpe PT. Homeobox genes and orofacial development. Connect Tissue Res 1995;32:17–25) put forward the concept of an odontogenic homeobox code to explain how different tooth classes are initiated in different parts of the oral cavity in response to molecular cues and the expression of specific groups of homeobox genes. Recently, Mitsiadis and Smith (Mitsiadis TA, Smith MM. How do genes make teeth to order through development? J Exp Zool (Mol Dev Evol) 2006; 306B:177–82.) proposed that the field, clone and homeobox code models could all be incorporated into a single model to explain dental patterning. We agree that these three models should be viewed as complementary rather than contradictory and propose that this unifying view can be extended into the clinical setting using findings on dental patterning in individuals with missing and extra teeth. The proposals are compatible with the unifying aetiological model developed by Brook (Brook AH. A unifying aetiological explanation for anomalies of tooth number and size. Archs Oral Biol 1984;29:373–78) based on human epidemiological and clinical findings. Indeed, this new synthesis can provide a sound foundation for clinical diagnosis, counselling and management of patients with various anomalies of dental development as well as suggesting hypotheses for future studies.