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(1) Background: Hypodontia has a multifactorial aetiology, in which genetic factors are a major component. Associated with this congenital absence, the formed teeth may show differences in size and shape, which may vary with the specific genetic variants and with the location of the missing teeth. The aims of the present study were to investigate a specific variant of MSX1, derive morphometric tooth measurements in a sample of patients with isolated maxillary lateral incisor agenesis and matched controls, and model the findings. (2) Methods: Genotyping of the MSX1 rs8670 genetic variant and morphometric measurements with a 2D image analysis method were performed for 26 hypodontia patients and 26 matched controls. (3) Results: The risk of upper lateral incisor agenesis was 6.9 times higher when the T allele was present. The morphometric parameters showed significant differences between hypodontia patients and controls and between the unilateral and bilateral agenesis cases. The most affected crown dimension in the hypodontia patients was the bucco-lingual dimension. In crown shape there was significant variation the Carabelli trait in upper first molars. (4) Conclusions: The MSX1 rs8670 variant was associated with variations in morphological outcomes. The new findings for compensatory interactions between the maxillary incisors indicate that epigenetic and environmental factors interact with this genetic variant. A single-level directional complex interactive network model incorporates the variations seen in this study. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate whether the genetic, epigenetic and environmental factors that give rise to supernumeraries in the maxillary incisor region and larger dimensions of the adjacent maxillary incisors are also associated with variations in the morphology of the mandibular incisors. If so, this would contribute to understanding the distribution and interactions of factors during dental development and how these can be modelled. The sample consisted of 34 patients with supernumerary teeth in the maxillary anterior region, matched for gender, age and White Caucasian ethnicity with 34 control subjects. The average ages of the supernumerary and control groups were 12.8 and 12.2 years, respectively. Study models of all subjects were constructed and imaged using a previously validated system. Using custom software, each of the mandibular incisor teeth were measured to obtain 17 parameters from the labial view and 17 from the occlusal view. Principal component analysis (PCA) was used to summarize the measurements into a smaller set representing distinct features of the clinical crowns, followed by a comparison between the supernumerary and control groups using 2-way ANOVA. Seven factors of tooth size of the mandibular central incisors and six factors of the mandibular lateral incisors were identified as major features of the clinical crowns. All parameters of both mandibular incisors were greater in the supernumerary group than in the control, with three of these, located in the incisal and cervical regions of the mandibular lateral incisors, being statistically significantly larger. The findings of this study indicate that the aetiological factors associated with supernumerary teeth in the maxillary anterior region also affect tooth crown dimensions of mandibular incisors. This new evidence enhances several models of the interactions of genetic, epigenetic and environmental components of dental development and supports a multi-model approach to increase understanding of this process and its variations. [ABSTRACT FROM AUTHOR]

Background: Chemotherapy treatment of cancer in children can influence formation of normal tissues, leading to irreversible changes in their structure and function. Tooth formation is susceptible to several types of chemotherapy that induce irreversible changes in the structure of enamel, dentin and dental root morphology. These changes can make the teeth more prone to fracture or to caries when they have erupted. Recent studies report successful treatment of brain tumors with the alkylating drug temozolomide (TMZ) in combination with veliparib (VLP) in a glioblastoma in vivo mouse model. Whether these drugs also affect tooth formation is unknown. Aim: In this study the effect of TMZ/VLP on incisor formation was investigated in tissue sections of jaws from mice and compared with mice not treated with these drugs. Materials and method: The following aspects were studied using immunohistochemistry of specific protein markers including: (1) proliferation (by protein expression of proliferation marker Ki67) (2) a protein involved in paracellular ion transport (expression of tight junction (TJ) protein claudin-1) and (3) in transcellular passage of ions across the dental epithelium (expression of Na+, K+ 2Cl- cotransporter/NKCC1). Results: Chemotherapy with TMZ/VLP strongly reduced immunostaining for claudin-1 in distal parts of maturation ameloblasts. No gross changes were found in the treated mice, either in cell proliferation in the dental epithelium at the cervical loop or in the immunostaining pattern for NKCC1 in (non-ameloblastic) dental epithelium. The salivary glands in the treated mice contained strongly reduced immunostaining for NKCC1 in the basolateral membranes of acinar cells. Discussion/Conclusions: Based on the reduction of claudin-1 immunostaining in ameloblasts, TMZ/VLP may potentially influence forming enamel by changes in the structure of TJs structures in maturation ameloblasts, structures that are crucial for the selective passage of ions through the intercellular space between neighboring ameloblasts. The strongly reduced basolateral NKCC1 staining seen in fully-grown salivary glands of TMZ/VLP-treated mice suggests that TMZ/VLF could also influence ion transport in adult saliva by the salivary gland epithelium. This may cause treated children to be more susceptible to caries. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Two metaphors are presented to highlight concepts that could lead to a paradigm shift in dental studies of twins. The first, derived from the Song of Solomon in the Bible, refers to teeth as being twins. This viewpoint emphasises that each tooth should be viewed as a paired structure, not only with its antimere (within the same arch) but also with its isomer (in the opposing arch). The other metaphor provided by Waddington in 1957 is visual and involves 'an epigenetic landscape' that represents the processes of decision-making by cells during development. It likens the different stages of cellular decision-making to a ball rolling down an undulating landscape of interconnecting hills and valleys. This viewpoint helps to explain how distinct differences in dental phenotypes may arise both within and between monozygotic (MZ) co-twins due to relatively minor temporospatial effects during development. Measurements of maximum mesiodistal diameters of teeth in a pair of MZ twins, using calipers and also cllls2D and 3D imaging systems, have demonstrated that differences in dental crown size occur between antimeric pairs and between corresponding teeth of MZ co-twins. By defining new dental phenotypes that provide more comprehensive descriptions of tooth size and shape, and by drawing on the metaphors described, we are confident of providing new insights into the reasons for observed similarities and differences within, and between, the dentitions of twins. Our approaches will focus on multivariate analyses that take into account the paired arrangement of teeth and also explore epigenetic, as well as genetic and environmental, sources of variation. [ABSTRACT FROM AUTHOR]

Background: Three-dimensional measurement of dental morphology is providing new variables and shape information not available previously, and the reliability of these data has proved to be substantial. Accurate superimposition of 2D and 3D data-sets has several applications in dental research when making comparisons of similar structures. For example, two data-sets of the same object can be superimposed to highlight differences apparent in limited region(s) of the tooth crown. When significant regions represented by the two data-sets are identical, registration of the images can be achieved by standard superimposition methods. However, for comparisons of crown morphologies between monozygotic and dizygotic co-twins, the data sets are similar but not identical so a new approach to superimposition has been developed. Aim: To develop a non 'best fit' (Synetic) method for the 3D superimposition of non-similar objects that forms one comparable interface providing enhanced methodology for the analysis of differences within the dentition of twins. Method: A minimised least-squares registration approach is followed by diffusion based registration to provide global minimisation between points that is not based on a best fit algorithm. This process is linear and therefore the method ensures uniqueness of the superimposition. Results: Initial results indicate a reliable method producing only one output as opposed to best fit approaches that may generate a different output each time. Conclusion: Diffusion-based registration offers a more reliable approach to superimposing non-identical objects, such as the tooth crowns of monozygotic co-twins, than conventional best fit methods. [ABSTRACT FROM AUTHOR]

Mutations in the amelogenin gene, AMGX, are known to cause X-linked amelogenesis imperfecta (AIH1). We have used DNA single-strand conformational polymorphism analysis and DNA sequencing to diagnose this disorder unequivocally in two related boys aged 3 and 7 years, respectively, from a family in which an existing mutation in the amelogenin gene is segregating. [ABSTRACT FROM AUTHOR]

The article discusses various reports on the clinical aspects of dental morphology published within the issue, including one comparing the dental morphology of twins, another on the application of a novel superimposition technique to morphology data derived from measurement of the dental study models of monozygotic co-twins, as well as a report on the modifying effects of the familial genetic contribution in Turner (XO) syndrome.

Abstract: Objective: To assess the reproducibility of a mobile non-contact camera-based digital imaging system (DIS) for measuring tooth colour under in vitro and in vivo conditions. Methods: One in vitro and two in vivo studies were performed using a mobile non-contact camera-based digital imaging system. In vitro study: two operators used the DIS to image 10 dry tooth specimens in a randomised order on three occasions. In vivo study 1: 25 subjects with two natural, normally aligned, upper central incisors had their teeth imaged using the DIS on four consecutive days by one operator to measure day-to-day variability. On one of the four test days, duplicate images were collected by three different operators to measure inter- and intra-operator variability. In vivo study 2: 11 subjects with two natural, normally aligned, upper central incisors had their teeth imaged using the DIS twice daily over three days within the same week to assess day-to-day variability. Three operators collected images from subjects in a randomised order to measure inter- and intra-operator variability. Results: Subject-to-subject variability was the largest source of variation within the data. Pairwise correlations and concordance coefficients were >0.7 for each operator, demonstrating good precision and excellent operator agreement in each of the studies. Intraclass correlation coefficients (ICCs) for each operator indicate that day-to-day reliability was good to excellent, where all ICC''s where >0.75 for each operator. Conclusion: The mobile non-contact camera-based digital imaging system was shown to be a reproducible means of measuring tooth colour in both in vitro and in vivo experiments. [Copyright &y& Elsevier]

Summary: Objective:: Fluctuating dental asymmetry as an indication of the effect of environmental insults during tooth development requires further investigation. The aim of this study was to assess asymmetry in tooth crown dimension for the increased range of parameters possible with image analysis compared to previous manual measurements. Methods:: Study models of 25 male and 25 female white Caucasian subjects were measured from buccal and occlusal views to determine mesio-distal, bucco-lingual, occluso-gingival and tooth surface area dimensions using image analysis. Method errors were assessed by the repeatability coefficient RC and asymmetry assessed calculating intra-class correlation coefficients between pairs of antimere teeth. Results:: The method errors calculated using RC were small. There was a high degree of symmetry with correlation coefficients with a range of 0.67–0.96 for linear measurements and 0.80–0.97 for tooth surface areas. No significant differences were found between the genders or between the upper and lower jaws. Asymmetry tended to follow a pattern in morphogenic tooth fields with the mesial tooth showing greater symmetry than the more distal. There were differences in the degree of symmetry among the variables measured with the mesio-distal dimension showing the greatest symmetry. Conclusions:: This new technique was reliable and readily applicable, providing also a greater range of measurements. While the asymmetry generally followed a similar pattern to earlier manual studies, there were variations in the degree of symmetry between different parameters. [Copyright &y& Elsevier]

• A shape classification model based on quasi-conformal theory is proposed. • The surface geometry, anatomical landmarks and curvature differences of the shapes are all taken into account in our proposed method. • The classification accuracy for teeth with respect to ancestry and gender is significantly improved by our proposed method. Shape analysis is important in anthropology, bioarchaeology and forensic science for interpreting useful information from human remains. In particular, teeth are morphologically stable and hence well-suited for shape analysis. In this work, we propose a framework for tooth morphometry using quasi-conformal theory. Landmark-matching Teichmüller maps are used for establishing a 1-1 correspondence between tooth surfaces with prescribed anatomical landmarks. Then, a quasi-conformal statistical shape analysis model based on the Teichmüller mapping results is proposed for building a tooth classification scheme. We deploy our framework on a dataset of human premolars to analyze the tooth shape variation among genders and ancestries. Experimental results show that our method achieves much higher classification accuracy with respect to both gender and ancestry when compared to the existing methods. Furthermore, our model reveals the underlying tooth shape difference between different genders and ancestries in terms of the local geometric distortion and curvatures. In particular, our experiment suggests that the shape difference between genders is mostly captured by the conformal distortion but not the curvatures, while that between ancestries is captured by both of them. [ABSTRACT FROM AUTHOR]