Tooth and jaw: molecular mechanisms of patterning in the first branchial arch

No relationship found between dental fluctuating asymmetry, birthweight, and birth term in two modern North American samples

OBJECTIVE

Deciduous dental crowns primarily develop during gestation and early infancy and embody early life stress exposures. Composite measures of dental fluctuating asymmetry (DFA) generated from the deciduous teeth may therefore indicate cumulative gestational stress in developmental origins of health and disease (DOHaD) studies. This study examines whether higher composite measures of deciduous DFA are associated with low birthweight and prematurity, two aspects of birth phenotype consistently associated with increased morbidity and mortality risks in adulthood.

SUBJECTS AND METHODS

We evaluated associations between composite deciduous DFA, birthweight, and birth term in two contemporary North American samples: an autopsy sample from New Mexico (n = 94), and sample from a growth cohort study in Burlington, Ontario (n = 304). Dental metric data for each sample was collected from postmortem CT scans and dental casts, respectively. Composite DFA was estimated using buccolingual (BL) and mesiodistal (MD) crown diameters from paired deciduous teeth.

RESULTS

Contrary to expectations, the results of linear regression indicated no significant relationship between birthweight and DFA, or birth term and DFA, in either sample.

CONCLUSIONS

Deciduous DFA does not predict aspects of birth phenotype associated with gestational stress. Birthweight and birth term are plastic relative to the more developmentally stable deciduous dentition, which may only subtly embody early life stress. We suggest that deciduous DFA should be utilized with caution in DOHaD studies until its relationship with gestational stress is clarified.

Dental anomalies in craniofacial microsomia and condylo-mandibular dysplasia: A retrospective study of 103 patients

INTRODUCTION

Craniofacial microsomia (CFM) and camel-hump condylo-mandibular dysplasia (CMD) are developmental disorders affecting the mandible that share common clinical features. This study aimed to investigate and compare the dental anomalies (DA) between the two entities for differential diagnosis and to propose appropriate treatment.

METHODS

This retrospective cross-sectional study was based on panoramic radiographs of patients diagnosed with CFM or CMD. DA were evaluated using the classification reported by Bilge. Delayed tooth eruption on the affected side was noted based on a comparison with the contralateral side. Nolla's stages of tooth calcification were used to assess dental development.

RESULTS

A total of 103 patients were included, 80 subjects (77.7 %) in CFM group and 23 patients (22.3 %) in CMD group. The prevalence of DA among CFM and CMD-affected patients were 80.0 % and 95.7 %, respectively. Tooth ectopia, tooth impaction, dental development delay, and delayed tooth eruption on the affected side exhibited a significant association with the two craniofacial malformations. The overall affected teeth (molars, premolars, canines) differed between the two craniofacial malformations. Dental abnormalities such as oligodontia, hyperdontia, dentin dysplasia, and anomalies of shape were seen only in subjects affected by CFM.

CONCLUSION

DA were widely observed in patients with CFM and CMD. The global distribution of affected teeth differed between the two conditions and some DA were detected only in CFM patients. When clinical diagnosis remains uncertain, some specific radiological characteristics of DA can be used to differentiate CFM from CMD.

Dental pulp stem cells - A basic research and future application in regenerative medicine

Dental pulp is a valuable and accessible source of stem cells (DPSCs) with characteristics similar to mesenchymal stem cells. DPSCs can regenerate a range of tissues and their potential for clinical application in regenerative medicine is promising. DPSCs have been found to express low levels of Class II HLA-DR (MHC) molecules, making them potential candidates for allogeneic transplantation without matching the donor's tissue. Research on the correlation between non-coding RNAs (ncRNAs) and human dental pulp stem cells (DPSCs) provides promising insights into the use of these cells in clinical settings for a wide range of medical conditions. It is possible to use a number of ncRNAs in order to restore the functional role of downregulated ncRNAs that are correlated with osteoblastogenesis, or to suppress the functional role of overexpressed ncRNAs associated with osteoclast differentiation in some cases.

Region-specific gene expression profiling of early mouse mandible uncovered SATB2 as a key molecule for teeth patterning

Mammalian dentition exhibits distinct heterodonty, with more simple teeth located in the anterior area of the jaw and more complex teeth situated posteriorly. While some region-specific differences in signalling have been described previously, here we performed a comprehensive analysis of gene expression at the early stages of odontogenesis to obtain complete knowledge of the signalling pathways involved in early jaw patterning. Gene expression was analysed separately on anterior and posterior areas of the lower jaw at two early stages (E11.5 and E12.5) of odontogenesis. Gene expression profiling revealed distinct region-specific expression patterns in mouse mandibles, including several known BMP and FGF signalling members and we also identified several new molecules exhibiting significant differences in expression along the anterior-posterior axis, which potentially can play the role during incisor and molar specification. Next, we followed one of the anterior molecules, SATB2, which was expressed not only in the anterior mesenchyme where incisor germs are initiated, however, we uncovered a distinct SATB2-positive region in the mesenchyme closely surrounding molars. Satb2-deficient animals demonstrated defective incisor development confirming a crucial role of SATB2 in formation of anterior teeth. On the other hand, ectopic tooth germs were observed in the molar area indicating differential effect of Satb2-deficiency in individual jaw regions. In conclusion, our data provide a rich source of fundamental information, which can be used to determine molecular regulation driving early embryonic jaw patterning and serve for a deeper understanding of molecular signalling directed towards incisor and molar development.

Lepr-Expressing PDLSCs Contribute to Periodontal Homeostasis and Respond to Mechanical Force by Piezo1

Periodontium supports teeth in a mechanically stimulated tissue environment, where heterogenous stem/progenitor populations contribute to periodontal homeostasis. In this study, Leptin receptor+ (Lepr+) cells are identified as a distinct periodontal ligament stem cell (PDLSC) population by single-cell RNA sequencing and lineage tracing. These Lepr+ PDLSCs are located in the peri-vascular niche, possessing multilineage potential and contributing to tissue repair in response to injury. Ablation of Lepr+ PDLSCs disrupts periodontal homeostasis. Hyper-loading and unloading of occlusal forces modulate Lepr+ PDLSCs activation. Piezo1 is demonstrated that mediates the mechanosensing of Lepr+ PDLSCs by conditional Piezo1-deficient mice. Meanwhile, Yoda1, a selective activator of Piezo1, significantly accelerates periodontal tissue growth via the induction of Lepr+ cells. In summary, Lepr marks a unique multipotent PDLSC population in vivo, to contribute toward periodontal homeostasis via Piezo1-mediated mechanosensing.

The odontoblastic differentiation of dental mesenchymal stem cells: molecular regulation mechanism and related genetic syndromes

Dental mesenchymal stem cells (DMSCs) are multipotent progenitor cells that can differentiate into multiple lineages including odontoblasts, osteoblasts, chondrocytes, neural cells, myocytes, cardiomyocytes, adipocytes, endothelial cells, melanocytes, and hepatocytes. Odontoblastic differentiation of DMSCs is pivotal in dentinogenesis, a delicate and dynamic process regulated at the molecular level by signaling pathways, transcription factors, and posttranscriptional and epigenetic regulation. Mutations or dysregulation of related genes may contribute to genetic diseases with dentin defects caused by impaired odontoblastic differentiation, including tricho-dento-osseous (TDO) syndrome, X-linked hypophosphatemic rickets (XLH), Raine syndrome (RS), hypophosphatasia (HPP), Schimke immuno-osseous dysplasia (SIOD), and Elsahy-Waters syndrome (EWS). Herein, recent progress in the molecular regulation of the odontoblastic differentiation of DMSCs is summarized. In addition, genetic syndromes associated with disorders of odontoblastic differentiation of DMSCs are discussed. An improved understanding of the molecular regulation and related genetic syndromes may help clinicians better understand the etiology and pathogenesis of dentin lesions in systematic diseases and identify novel treatment targets.

Identification of potential key variants in mandibular premolar hypodontia through whole-exome sequencing

Determining genotype-phenotype correlations in patients with hypodontia is important for understanding disease pathogenesis, although only a few studies have elucidated it. We aimed to identify genetic variants linked to non-syndromic bilateral mandibular second premolar hypodontia in a Korean population for the first time by specifying the phenotype of hypodontia. Twenty unrelated individuals with non-syndromic bilateral mandibular second premolar hypodontia were enrolled for whole-exome sequencing. Using a tooth agenesis gene set panel consisting of 112 genes based on literature, potential candidate variants were screened through variant filtering and prioritization. We identified 13 candidate variants in 12 genes, including a stop-gain variant (c.4750C>T) in LAMA3. Through the functional enrichment analysis of the prioritized genes, several terms related to tooth development were enriched in a protein-protein interaction network of candidate genes for mandibular premolar hypodontia. The hypodontia group also had approximately 2-fold as many mutated variants in all four genes related to these key terms, which are CDH1, ITGB4, LAMA3, LAMB3, as those in the 100 healthy control group individuals. The relationship between enriched terms and pathways and mandibular premolar hypodontia was also investigated. In addition, we identified some known oligodontia variants in patients with hypodontia, strengthening the possibility of synergistic effects in other genes. This genetic investigation may be a worthwhile preliminary attempt to reveal the pathogenesis of tooth agenesis and sets a background for future studies.

Interdisciplinary orthodontics-implants management of a challenging hypodontia case complicated by a class II division 2, bimaxillary retroclination

INTRODUCTION

The case in this study had moderate hypodontia, with both lower lateral incisors and the lower-left second premolar missing. A Class II division 2 relationship with severe crowding in the upper arch and a traumatic deep bite over a skeletal I base complicated the occlusion.

MATERIALS AND METHODS

The plan was to extract the upper first premolars to relieve upper arch crowding and the lower-left impacted second premolar to preserve the bilateral class I molar relationship. A class I occlusal relationship was achieved through space opening in the lower lateral incisors region and space closure in the upper and lower premolars regions.

RESULTS

The use of orthodontic screws for bite opening and anterior segment retraction, in conjunction with bi-metric slot size selection in bracket prescription, was effective in controlling incisor inclination and interincisal angle. The use of an implant fixture before beginning the finishing stage allowed for a reduction in total treatment time and facilitated the provision of the final prosthesis before debonding the case. As a result, the patient was able to receive a satisfactory occlusion on the day of debonding.

CONCLUSION

This case of moderate hypodontia was successfully resolved by combining space closure and space opening effectively. To solve the arch problems in such Class II division 2 cases with severe crowding, extractions were required. To complete the case, this was combined with intrusive and retractive mechanics. In hypodontia cases, implants are an excellent choice for both aesthetics and functional restoration.

Sonic hedgehog signaling in craniofacial development

Mutations in SHH and several other genes encoding components of the Hedgehog signaling pathway have been associated with holoprosencephaly syndromes, with craniofacial anomalies ranging in severity from cyclopia to facial cleft to midfacial and mandibular hypoplasia. Studies in animal models have revealed that SHH signaling plays crucial roles at multiple stages of craniofacial morphogenesis, from cranial neural crest cell survival to growth and patterning of the facial primordia to organogenesis of the palate, mandible, tongue, tooth, and taste bud formation and homeostasis. This article provides a summary of the major findings in studies of the roles of SHH signaling in craniofacial development, with emphasis on recent advances in the understanding of the molecular and cellular mechanisms regulating the SHH signaling pathway activity and those involving SHH signaling in the formation and patterning of craniofacial structures.

Oral alterations in children with microcephaly associated to congenital Zika syndrome: A systematic review and meta-analyses

AIMS

To synthesize the oral alterations observed in children with microcephaly associated with congenital Zika virus syndrome (CZS), and to compare the oral alterations of these children to a normotypic healthy controls.

METHODS AND RESULTS

A search was performed in six electronic databases. Observational studies published that reported oral alterations in children with CZS were selected. Two authors independently extracted data, assessed study quality, using the Joanna Briggs Institute Critical Appraisal Checklist tools, and the certainty of evidence, using Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. Twenty-one studies were included in this systematic review and meta-analysis. The pooled crude occurrence showed 88% of increased salivation (95%CI: 82%-94%), 83% of biofilm (95%CI: 75%-91%), and 73% of bruxism (95%CI: 52%-95%). Compared to normotypic controls, children with CZS-associated microcephaly had a higher chance to have difficulty in lip sealing (OR: 18.28; 95%CI: 1.42-235.91), inadequate lingual posture at rest (OR: 13.57; 95%CI: 4.24-43.44), and delayed eruption (OR: 12.92; 95%CI: 3.42-48.78), with very low certainty.

CONCLUSION

There are several oral alterations found among children with CZS-associated microcephaly. They are more prone to present some of these alterations, such as difficulty in lip sealing, although with very low certainty of evidence.

Genetic influences on dentognathic morphology in the Jirel population of Nepal

Patterns of genetic variation and covariation impact the evolution of the craniofacial complex and contribute to clinically significant malocclusions in modern human populations. Previous quantitative genetic studies have estimated the heritabilities and genetic correlations of skeletal and dental traits in humans and nonhuman primates, but none have estimated these quantitative genetic parameters across the dentognathic complex. A large and powerful pedigree from the Jirel population of Nepal was leveraged to estimate heritabilities and genetic correlations in 62 maxillary and mandibular arch dimensions, incisor and canine lengths, and post-canine tooth crown areas (N ≥ 739). Quantitative genetic parameter estimation was performed using maximum likelihood-based variance decomposition. Residual heritability estimates were significant for all traits, ranging from 0.269 to 0.898. Genetic correlations were positive for all trait pairs. Principal components analyses of the phenotypic and genetic correlation matrices indicate an overall size effect across all measurements on the first principal component. Additional principal components demonstrate positive relationships between post-canine tooth crown areas and arch lengths and negative relationships between post-canine tooth crown areas and arch widths, and between arch lengths and arch widths. Based on these findings, morphological variation in the human dentognathic complex may be constrained by genetic relationships between dental dimensions and arch lengths, with weaker genetic correlations between these traits and arch widths allowing for variation in arch shape. The patterns identified are expected to have impacted the evolution of the dentognathic complex and its genetic architecture as well as the prevalence of dental crowding in modern human populations.

Spatiotemporal single-cell regulatory atlas reveals neural crest lineage diversification and cellular function during tooth morphogenesis

Cranial neural crest cells are an evolutionary innovation of vertebrates for craniofacial development and function, yet the mechanisms that govern the cell fate decisions of postmigratory cranial neural crest cells remain largely unknown. Using the mouse molar as a model, we perform single-cell transcriptome profiling to interrogate the cell fate diversification of postmigratory cranial neural crest cells. We reveal the landscape of transcriptional heterogeneity and define the specific cellular domains during the progression of cranial neural crest cell-derived dental lineage diversification, and find that each domain makes a specific contribution to distinct molar mesenchymal tissues. Furthermore, IGF signaling-mediated cell-cell interaction between the cellular domains highlights the pivotal role of autonomous regulation of the dental mesenchyme. Importantly, we reveal cell-type-specific gene regulatory networks in the dental mesenchyme and show that Foxp4 is indispensable for the differentiation of periodontal ligament. Our single-cell atlas provides comprehensive mechanistic insight into the cell fate diversification process of the cranial neural crest cell-derived odontogenic populations.

The association of polymorphisms in BMP2/MYO1H and skeletal Class II div.1 maxillary and mandibular dimensions. A preliminary ‘report

Introduction

The genetic impact directly or indirectly predefines maxillofacial dimensions, potentially leading to an inappropriate relationship of the jaws and subsequently skeletal malocclusion. Previous studies focused mainly on genetic polymorphisms and class III malocclusion. This study was set out to investigate the association between genetic polymorphisms in two genes BMP2 (rs235768) and MYO1H (rs11066446) with Class II division 1 malocclusion, skeletal variation in vertical plane, and maxillary and mandibular jaws length.

Subjects and methods

Sixty patients classified as Skeletal Class I (n = 30) and Class II division 1 (n = 30) were recruited. DNA was extracted from saliva and analyzed by Sanger sequencing. Lateral cephalometric radiographs were measured for the anterio-posterior relationship of maxillary and mandibular arch using digital tracing. Hardy-Weinberg equilibrium analysis of genotype frequencies was performed using Chi-square test to compare genotype distribution among groups and multiple logistic regression analysis adjusted by gender was also performed.

Results

The rs235768 polymorphism in BMP2 was associated with hypodivergent face, increased maxillary length, and decreased mandibular length. Meanwhile, the rs11066446 polymorphism in MYO1H was associated with decreased mandibular length. New polymorphism was identified in MYO1H (rs10850090) in association with decreased mandibular length.

Conclusion

A potential association between polymorpisms in BMP2 rs235768 and MOY1H rs11066446 and rs10850090 and Class II division 1 skeletal malocclusion related phenotypes exists, however, the degree of it has to be further investigated and yet to be discovered.

The effects of altered BMP4 signaling in first branchial-arch-derived murine embryonic orofacial tissues

The first branchial arch (BA1), which is derived from cranial neural crest (CNC) cells, gives rise to various orofacial tissues. Cre mice are widely used for the determination of CNC and exploration of gene functions in orofacial development. However, there is a lack of Cre mice specifically marked BA1's cells. Pax2-Cre allele was previously generated and has been widely used in the field of inner ear development. Here, by compounding Pax2-Cre and R26R-mTmG mice, we found a specific expression pattern of Pax2⁺ cells that marked BA1's mesenchymal cells and the BA1-derivatives. Compared to Pax2-Cre; R26R-mTmG allele, GFP⁺ cells were abundantly found both in BA1 and second branchial arch in Wnt1-Cre;R26R-mTmG mice. As BMP4 signaling is required for orofacial development, we over-activated Bmp4 by using Pax2-Cre; pMes-BMP4 strain. Interestingly, our results showed bilateral hyperplasia between the upper and lower teeth. We also compare the phenotypes of Wnt1-Cre; pMes-BMP4 and Pax2-Cre; pMes-BMP4 strains and found severe deformation of molar buds, palate, and maxilla-mandibular bony structures in Wnt1-Cre; pMes-BMP4 mice; however, the morphology of these orofacial organs were comparable between controls and Pax2-Cre; pMes-BMP4 mice except for bilateral hyperplastic tissues. We further explore the properties of the hyperplastic tissue and found it is not derived from Runx2⁺ cells but expresses Msx1, and probably caused by abnormal cell proliferation and altered expression pattern of p-Smad1/5/8. In sum, our findings suggest altering BMP4 signaling in BA1-specific cell lineage may lead to unique phenotypes in orofacial regions, further hinting that Pax2-Cre mice could be a new model for genetic manipulation of BA1-derived organogenesis in the orofacial region.

Heterotopic Polyodontia: Diagnosis and Surgical Removal of a Dentigerous Cyst Comprising 2 Dental Structures in a 14-Year-Old Horse

A 14-year-old American Paint Horse mare was referred for further evaluation of a firm mass with an associated draining tract at the base of the left ear suspected to be a dentigerous cyst. Approximately three months prior, the draining tract had been excised under the presumed diagnosis of an abscess with no improvement. Physical examination revealed a firm mass palpable at the base of the left ear with a draining tract that did not elicit any pain response on palpation. Digital radiographs revealed a 6x11cm mineral mass in the left temporal region. Medially, there were two projections that extended into the left temporal bone. Cone beam computed tomography (CT) showed mild thinning of the temporal bone separating the mass and the brain at the conical extension of the caudal aspect of the mass. Both structures were isolated and elevated using a combination of osteotomes, mallet, and bone rongeurs under general inhalant anesthesia with radiographs to determine complete removal. Although histopathology was declined, gross examination of both structures resembled adult molar teeth. At eight months postoperative, the owners reported that the surgical site was healed and no discharge was present. Dentigerous cysts should remain a differential for a mass with an associated draining tract at the base of the ear in horses. Practitioners should strongly consider CT when feasible for additional diagnostics in similar cases. Although benign and removal poses risk, dentigerous cysts can be surgically excised with a positive outcome.

Radiographic evaluation of dental anomalies in patients with congenital Zika virus syndrome

Numerous studies have reported abnormalities in the development of oral structures in congenital infections that also involve microcephaly. In this context, it is necessary to identify possible dental anomalies of shape and/or number in patients with Zika virus syndrome using radiography. The study population consisted of 35 children born with congenital ZIKV who underwent intraoral radiographic examinations for 24 consecutive months. A modified periapical technique was performed in an occlusal position for the maxilla and mandible. Categorical data were expressed as absolute and percentage frequencies and compared using Pearson's Chi-square test, with a 95% confidence interval. Of the entire sample, eight children (22.8%) had dental anomalies of shape and/or number, and four children (11.4%) presented with both anomalies, with agenesis of the upper and lower deciduous/permanent incisors and dental form modifications, such as microdontia and anomalous cusps. When we considered age and sex, there was no statistically significant difference between patients who presented with agenesis and those who presented with modifications. Children with congenital Zika virus syndrome were more likely to have dental modifications in the number and shape of their teeth, and it is essential to implement medium- to long-term monitoring to diagnose other possible alterations throughout the development of the mixed and permanent dentition, favoring their treatment.

Carnivoran intraspecific tooth-size variation shows heterogeneity along the tooth row and among species

Developing morphological diagnoses for fossil mammals requires an understanding of intraspecific variation in the anatomical elements under study. Dental traits along with tooth size can be informative of taxonomic identify for extinct species. However, it is unclear what selective or developmental processes are responsible for documented patterns in tooth-size variation making application to the fossil record difficult. We assessed combined species tooth-type variation and intraspecific tooth-size variation for 19 species to evaluate whether developmental controls or occlusion-driven functional demands influence carnivoran tooth-size variation. We also estimated phylogenetic signal for the coefficient of variation (CV). Combined species tooth-size variation separated by tooth type shows that canines are more variable than molars and lower premolars. We found intraspecific tooth-size variation patterns differ between species. However, comparisons of the CVs did not support the hypotheses that developmental controls or functional demands of occlusion constrain size variation in mammal teeth. Our results suggest that a combination of factors influence carnivoran tooth-size variation, such as differences in ontogeny, diet, sexual dimorphism, and evolutionary history. Patterns of carnivoran intraspecific tooth-size variation suggest a better understanding of dental size variation in extant species is essential for accurate morphological studies of fossil taxa.

Spatiotemporal cellular movement and fate decisions during first pharyngeal arch morphogenesis

Cranial neural crest (CNC) cells contribute to different cell types during embryonic development. It is unknown whether postmigratory CNC cells undergo dynamic cellular movement and how the process of cell fate decision occurs within the first pharyngeal arch (FPA). Our investigations demonstrate notable heterogeneity within the CNC cells, refine the patterning domains, and identify progenitor cells within the FPA. These progenitor cells undergo fate bifurcation that separates them into common progenitors and mesenchymal cells, which are characterized by Cdk1 and Spry2/Notch2 expression, respectively. The common progenitors undergo further bifurcations to restrict them into osteogenic/odontogenic and chondrogenic/fibroblast lineages. Disruption of a patterning domain leads to specific mandible and tooth defects, validating the binary cell fate restriction process. Different from the compartment model of mandibular morphogenesis, our data redefine heterogeneous cellular domains within the FPA, reveal dynamic cellular movement in time, and describe a sequential series of binary cell fate decision-making process.

The intraspecific diversity of tooth morphology in the large-spotted catshark Scyliorhinus stellaris: insights into the ontogenetic cues driving sexual dimorphism

Teeth in sharks are shed and replaced throughout their lifetime. Morphological dental changes through ontogeny have been identified in several species and have been correlated with shifts in diet and the acquisition of sexual maturity. However, these changes were rarely quantified in detail along multiple ontogenetic stages, which makes it difficult to infer the developmental processes responsible for the observed plasticity. In this work, we use micro-computed tomography and 3D geometric morphometrics to describe and analyze the tooth size and shape diversity across three ontogenetic stages (hatchling, juvenile, and sexually mature) in the large-spotted catshark Scyliorhinus stellaris (Linnaeus, 1758). We first describe the intra-individual variation of tooth form for each sex at each ontogenetic stage. We provide a tooth morphospace for palatoquadrate and Meckelian teeth and identify dental features, such as relative size and number of cusps, involved in the range of variation of the observed morphologies. We then use these shape data to draw developmental trajectories between ontogenetic stages and for each tooth position within the jaw to characterize ontogenetic patterns of sexual dimorphism. We highlight the emergence of gynandric heterodonty between the juvenile and mature ontogenetic stages, with mature females having tooth morphologies more similar to juveniles' than mature males that display regression in the number of accessory cusps. From these data, we speculate on the developmental processes that could account for such developmental plasticity in S. stellaris.

The effect of polyethylenglycol gel on the delivery and osteogenic differentiation of homologous tooth germ-derived stem cells in a porcine model

OBJECTIVES

The aim of this study was to investigate if bone regeneration can be promoted by homologous transplantation of STRO-1 sorted (STRO-1+) porcine tooth germ mesenchymal stem cells (TGSCs) with the combination of polyethylenglycol (PEG)-based hydrogel and biphasic calcium phosphate (BCP) scaffolds.

MATERIAL AND METHODS

TGSCs were isolated from impacted third molars of domestic pigs. Nine critical-sized defects were created as (1) untreated defect; filled with (2) autogenous bone; (3) BCP + PEG; (4) BCP + PEG + unsorted TGSCs; (5) BCP + unsorted TGSCs; (6) BCP + PEG + STRO-1-sorted TGSCs; (7) BCP + STRO-1-sorted TGSCs; (8) BCP + PEG + osteogenic induced unsorted TGSCs; and (9) BCP + PEG + osteogenic induced STRO-1-sorted TGSCs in 20 domestic pigs. CM-DiI labelling was used to track cells in vivo. Histomorphometric assessment of new bone formation was achieved by toluidine blue O staining and microradiography after 1, 2, 4 and 12 weeks posttransplantation.

RESULTS

Complete healing was achieved in all defects although defects with PEG hydrogel presented better bone formation while STRO-1+ and unsorted TGSCs showed similar ability to form new bone after 12 weeks. Transplanted cells were seen in defects where PEG hydrogel was used as carriers in contrast to defects treated with cells and only bone grafts.

CONCLUSIONS

PEG hydrogel is an efficient carrier for homologous stem cell transplantation. TGSCs are capable of promoting bone healing in critical-sized defects in combination with bone graft and PEG hydrogel.

CLINICAL RELEVANCE

This study provides information about the importance of the delivery vehicle for future translational stem cell delivery approaches.

Dental anomalies in craniofacial microsomia: A systematic review

Objective: To provide an overview on the prevalence and types of dental anomalies in patients with craniofacial microsomia (CFM). Eligibility criteria: Inclusion criteria were CFM and dental anomalies. The following data were extracted: number of patients, methodology, mean age, sex, affected side, severity of mandibular hypoplasia, dentition stage and dental anomalies. Information sources: Cochrane, EMBASE, PubMed, MEDLINE Ovid, Web of Science, CINAHL EBSCOhost and Google Scholar, searched until the 30 August 2019. Risk of bias: The quality was examined with the OCEBM Levels of Evidence. Included studies: In total, 13 papers were included: four retrospective cohort studies, four prospective cohort studies, four case‐control studies and one case series. Synthesis of results: The studies reported information on dental agenesis, delayed dental development, tooth size anomalies, tooth morphology and other dental anomalies. Description of the effect: Dental anomalies are more often diagnosed in patients with CFM than in healthy controls and occur more often on the affected than on the non‐affected side. Strengths and limitations of evidence: This is the first systematic review study on dental anomalies in CFM. However, most articles were of low quality. Interpretation: Dental anomalies are common in CFM, which might be linked to the development of CFM. The pathophysiology of CFM is not entirely clear, and further research is needed.

Clinical and x-ray oral evaluation in patients with congenital Zika Virus

OBJECTIVE

The aim of this study was to investigate possible malformations in the soft, bone and/or dental tissues in patients with congenital Zika Virus (ZIKV) by clinical and x-ray evaluation.

METHODOLOGY

Thirty children born with ZIKV and 30 children born without ZIKV (control group) were included in the study. Patients were evaluated over 24 consecutive months according to the variables: sex, age, cleft palates, soft tissue lesions, alveolar ridge hyperplasia, short labial and lingual frenums, inadequate posture of the lingual and perioral muscles at rest, micrognathia, narrow palatine vaults, changes in the teeth shape and/or number, sequence eruption, spasms, seizures and eruption delay were evaluated. Chi-square test, Student's t-test and nominal logistic regression were used (p<0.05).

RESULTS

Among the 30 babies examined, the mean age of the first dental eruption was 10.8±3.8 with almost two-thirds of the children (n=18, 60%) experiencing eruptions of their first tooth after 9 months of age, nine children (30%) had inadequate lingual posture at rest, more than half of the children (n=18, 60%) had short labial or lingual frenums. ZIKV babies showed a high prevalence of clef palate (p<0.001), inadequate lingual posture at rest (p=0.004), micrognathia (p=0.002), changes in the shape and/or number of teeth (p=0.006), alteration in sequence of dental eruption (p<0.001) and muscles spasms (p=0.002). The delay eruption was associated with inadequate lingual posture at rest (p=0.047), micrognathia (p=0.002) and changes in the shape and/or number of teeth (p=0.021). The delayed eruption (p=0.006) and narrow palatine vaults (p=0.008) were independently associated with ZIKV. Moreover, female patients showed the most narrow palatine vaults (p=0.010).

CONCLUSIONS

The children with ZIKV showed a greater tendency to have delayed eruption of the first deciduous tooth, inadequate lingual posture and short labial and lingual frenums.

The crown-root morphology of central incisors in different skeletal malocclusions assessed with cone-beam computed tomography

Background

To determine the discrepancy of crown-root morphology of central incisors among different types of skeletal malocclusion using cone-beam computed tomography (CBCT) and to provide guidance for proper torque expression of anterior teeth and prevention of alveolar fenestration and dehiscence.

Methods

In this retrospective study, a total of 108 CBCT images were obtained (ranging from 18.0 to 30.0 years, mean age 25.8 years). Patients were grouped according to routine sagittal and vertical skeletal malocclusion classification criteria. The patients in sagittal groups were all average vertical patterns, with Class I comprised 24 patients—14 females and 10 males; Class II comprised 20 patients—13 females and 7 males; and Class III comprised 22 subjects—13 females and 9 males. The patients in vertical groups were all skeletal Class I malocclusions, with low angle comprised 21 patients—12 females and 9 males; average angle comprised 24 patients; and high angle comprised 21 patients—11 females and 10 males. All the CBCT data were imported into Invivo 5.4 software to obtain a middle labio-lingual section of right central incisors. Auto CAD 2007 software was applied to measure the crown-root angulation (Collum angle), and the angle formed by a tangent to the central of the labial surface of the crown and the long axis of the crown (labial surface angle). One-way analysis of variance (ANOVA) and Scheffe’s test were used for statistical comparisons at the P < 0.05 level, and the Pearson correlation analysis was applied to investigate the association between the two measurements.

Results

The values of Collum angle and labial surface angle in maxillary incisor of Class II and mandibular incisor of Class III were significantly greater than other types of sagittal skeletal malocclusions (P < 0.05); no significant difference was detected among vertical skeletal malocclusions. Notably, there was also a significant positive correlation between the two measurements.

Conclusions

The maxillary incisor in patients with sagittal skeletal Class II malocclusion and mandibular incisor with Class III malocclusion present remarkable crown-root angulation and correspondingly considerable labial surface curvature. Equivalent deviation during bracket bonding may cause greater torque expression error and increase the risk of alveolar fenestration and dehiscence.

Expression of new genes in vertebrate tooth development and p63 signaling

BACKGROUND

p63 is an evolutionarily ancient transcription factor essential to vertebrate tooth development. Our recent gene expression screen comparing wild-type and "toothless" p63^-/- mouse embryos implicated in tooth development several new genes that we hypothesized act downstream of p63 in dental epithelium, where p63 is also expressed.

RESULTS

Via in situ hybridization and immunohistochemistry, we probed mouse embryos (embryonic days 10.5-14.5) and spotted gar fish embryos (14 days postfertilization) for these newly linked genes, Cbln1, Cldn23, Fermt1, Krt15, Pltp and Prss8, which were expressed in mouse and gar dental epithelium. Loss of p63 altered expression levels but not domains. Expression was comparable between murine upper and lower tooth organs, implying conserved gene functions in maxillary and mandibular dentitions. Our meta-analysis of gene expression databases supported that these genes act within a p63-driven gene regulatory network important to tooth development in mammals and more evolutionary ancient vertebrates (fish, amphibians).

CONCLUSIONS

Cbln1, Cldn23, Fermt1, Krt15, Pltp, and Prss8 were expressed in mouse and fish dental epithelium at placode, bud, and/or cap stages. We theorize that these genes participate in cell-cell adhesion, cell polarity, and extracellular matrix signaling to support dental epithelium integrity, folding, and epithelial-mesenchymal cross talk during tooth development.

Hedgehog signaling patterns the oral-aboral axis of the mandibular arch

Development of vertebrate jaws involves patterning neural crest-derived mesenchyme cells into distinct subpopulations along the proximal-distal and oral-aboral axes. Although the molecular mechanisms patterning the proximal-distal axis have been well studied, little is known regarding the mechanisms patterning the oral-aboral axis. Using unbiased single-cell RNA-seq analysis followed by in situ analysis of gene expression profiles, we show that Shh and Bmp4 signaling pathways are activated in a complementary pattern along the oral-aboral axis in mouse embryonic mandibular arch. Tissue-specific inactivation of hedgehog signaling in neural crest-derived mandibular mesenchyme led to expansion of BMP signaling activity to throughout the oral-aboral axis of the distal mandibular arch and subsequently duplication of dentary bone in the oral side of the mandible at the expense of tongue formation. Further studies indicate that hedgehog signaling acts through the Foxf1/2 transcription factors to specify the oral fate and pattern the oral-aboral axis of the mandibular mesenchyme.

Upper jaw development in the absence of teeth: New insights for craniodental evo-devo integration

In p63-null mice (p63^-/- ), teeth fail to form but the mandible forms normally; conversely, the upper jaw skeleton is malformed. Here we explored whether lack of dental tissues contributed to midfacial dysmorphologies in p63^-/- mice by testing if facial prominence defects appeared before odontogenesis failed. We also investigated gene dose effects by testing if one wild type (WT) p63 allele (p63^+/- ) was sufficient for normal upper jaw skeleton formation. We micro-CT scanned PFA-fixed p63^-/- , p63^+/- , and WT (p63^+/+ ) adult and embryonic mice aged E10-E14. Next, we landmarked mandibular (MdP), maxillary (MxP) and nasal prominences (NPs), and facial bones. 3D landmark data were assessed using Principal Component, Canonical Variate, Partial Least Squares, and other statistical analyses. The p63^-/- embryos showed MxP and NP malformations by E12, despite the presence of dental tissues. MdP shape was comparable among p63^-/- , p63^+/- , and p63^+/+ embryos. Upper jaw shape was comparable between p63^+/+ and p63^+/- adults. The upper jaw and its dentition both require p63 signaling, but not each other's presence, to form properly. One WT p63 allele enables normal midfacial morphogenesis; gene dose may be a target for jaw macroevolution. Jaw-specific genetic mechanisms likely integrate the evo-devo of dentitions with upper versus lower jaws.

Genetic linkage between altered tooth and eye development in lens-ablated Astyanax mexicanus

The phenotype of lens-ablated Mexican tetra (Astyanax mexicanus) compared to wild-type surface fish has been described and includes, among other effects, eye degeneration, changes in tooth number and cranial bone changes. Here, we investigate the spatiotemporal expression patterns of several key genes involved in the development of these structures. Specifically, we show that the expression of pitx2, bmp4 and shh is altered in the eye, oral jaw, nasal pit and forebrain in these lens-ablated fish. Furthermore, for the first time, we show altered pitx2 expression in the cavefish, which also has altered eye and tooth phenotypes. We thus provide evidence for a genetic linkage between the eye and tooth modules in this fish species. Furthermore, the altered pitx2 expression pattern, together with the described morphological features of the lens-ablated fish suggests that Astyanax mexicanus could be considered as an alternative teleost model organism in which to study Axenfeld-Rieger syndrome (ARS), a rare autosomal dominant developmental disorder that is associated with PITX2 and which has both ocular and non-ocular abnormalities.

MicroRNAs and the neural crest: From induction to differentiation

MicroRNAs are small noncoding RNAs that can control gene expression by base pairing to partially complementary mRNAs. Regulation by microRNAs plays essential roles in diverse biological processes such as neural crest formation during embryonic development. The neural crest is a multipotent cell population that develops from the dorsal neural fold of vertebrate embryos in order to migrate extensively and differentiate into a variety of tissues. Gene regulatory networks that coordinate neural crest cell specification and differentiation have been considerably studied so far. Although it is known that microRNAs play important roles in neural crest development, posttranscriptional regulation by microRNAs has not been deeply characterized yet. This review is focused on the microRNAs identified so far in order to regulate gene expression of neural crest cells during vertebrate development.

Coordination of bilateral tooth replacement in the juvenile gecko is continuous with in ovo patterning

We performed a test of how function impacts a genetically programmed process that continues into postnatal life. Using the dentition of the polyphyodont gecko as our model, tooth shedding was recorded longitudinally across the jaw. We compared two time periods: one in which teeth were patterned symmetrically in ovo and a later period when teeth were initiated post-hatching. By pairing shedding events on the right and left sides, we found the patterns of tooth loss are symmetrical and stable between periods, with only subtle deviations. Contralateral tooth positions shed within 3-4 days of each other in most animals (7/10). A minority of animals (3/10) had systematic tooth position shifts between right and left sides, likely due to changes in functional tooth number. Our results suggest that in addition to reproducible organogenesis of individual teeth, there is also a neotenic retention of jaw-wide dental patterning in reptiles. Finer analysis of regional asymmetries revealed changes to which contralateral position shed first, affecting up to one quarter of the jaw (10 tooth positions). Once established, these patterns were retained longitudinally. Taken together, the data support regional and global mechanisms of coordinating tooth cycling post-hatching.

AP-2α and AP-2β cooperatively orchestrate homeobox gene expression during branchial arch patterning

The evolution of a hinged moveable jaw with variable morphology is considered a major factor behind the successful expansion of the vertebrates. DLX homeobox transcription factors are crucial for establishing the positional code that patterns the mandible, maxilla and intervening hinge domain, but how the genes encoding these proteins are regulated remains unclear. Herein, we demonstrate that the concerted action of the AP-2α and AP-2β transcription factors within the mouse neural crest is essential for jaw patterning. In the absence of these two proteins, the hinge domain is lost and there are alterations in the size and patterning of the jaws correlating with dysregulation of homeobox gene expression, with reduced levels of Emx, Msx and Dlx paralogs accompanied by an expansion of Six1 expression. Moreover, detailed analysis of morphological features and gene expression changes indicate significant overlap with various compound Dlx gene mutants. Together, these findings reveal that the AP-2 genes have a major function in mammalian neural crest development, influencing patterning of the craniofacial skeleton via the DLX code, an effect that has implications for vertebrate facial evolution, as well as for human craniofacial disorders.

Homeobox genes and tooth development: Understanding the biological pathways and applications in regenerative dental science

OBJECTIVES

Homeobox genes are a group of conserved class of transcription factors that function as key regulators during the embryonic developmental processes. They act as master regulator for developmental genes, which involves coordinated actions of various auto and cross-regulatory mechanisms. In this review, we summarize the expression pattern of homeobox genes in relation to the tooth development and various signaling pathways or molecules contributing to the specific actions of these genes in the regulation of odontogenesis.

MATERIALS AND METHODS

An electronic search was undertaken using combination of keywords e.g. Homeobox genes, tooth development, dental diseases, stem cells, induced pluripotent stem cells, gene control region was used as search terms in PubMed and Web of Science and relevant full text articles and abstract were retrieved that were written in English. A manual hand search in text books were also carried out. Articles related to homeobox genes in dentistry and tissue engineering and regenerative medicine of odontogenesis were selected.

RESULTS

The possible perspective of stem cells technology in odontogenesis and subsequent analysis of gene correction pertaining to dental disorders through the possibility of induced pluripotent stem cells technology is also inferred.

CONCLUSIONS

We demonstrate the promising role of tissue engineering and regenerative medicine on odontogenesis, which can generate a new ray of hope in the field of dental science.

Detangling the evolutionary developmental integration of dentate jaws: evidence that a p63 gene network regulates odontogenesis exclusive of mandible morphogenesis

Vertebrate jaws and dentitions fit and function together, yet the genetic processes that coordinate cranial and dental morphogenesis and evolution remain poorly understood. Teeth but not jaws fail to form in the edentate p63^-/- mouse mutant, which we used here to identify genes important to odontogenesis, but not jaw morphogenesis, and that may allow dentitions to change during development and evolution without necessarily affecting the jaw skeleton. With the working hypothesis that tooth and jaw development are autonomously controlled by discreet gene regulatory networks, using gene expression microarray assays validated by quantitative reverse-transcription PCR we contrasted expression in mandibular prominences at embryonic days (E) 10-13 of mice with normal lower jaw development but either normal (p63^+/- , p63^+/+ ) or arrested (p63^-/- ) tooth development. The p63^-/- mice showed significantly different expression (fold change ≥2, ≤-2; P ≤ 0.05) of several genes. Some of these are known to help regulate odontogenesis (e.g., p63, Osr2, Cldn3/4) and/or to be targets of p63 (e.g., Jag1/2, Fgfr2); other genes have no previously reported roles in odontogenesis or the p63 pathway (e.g., Fermt1, Cbln1, Pltp, Krt8). As expected, from E10 to E13, few genes known to regulate mandible morphogenesis differed in expression between mouse strains. This study newly links several genes to odontogenesis and/or to the p63 signaling network. We propose that these genes act in a novel odontogenic network that is exclusive of lower jaw morphogenesis, and posit that this network evolved in oral, not pharyngeal, teeth.

Implications of Vertebrate Craniodental Evo-Devo for Human Oral Health

Highly processed diets eaten by postindustrial modern human populations coincide with higher frequencies of third molar impaction, malocclusion, and temporomandibular joint disorders that affect millions of people worldwide each year. Current treatments address symptoms, not causes, because the multifactorial etiologies of these three concerns mask which factors incline certain people to malocclusion, impaction, and/or joint issues. Deep scientific curiosity about the origins of jaws and dentitions continues to yield rich insights about the developmental genetic mechanisms that underpin healthy craniodental morphogenesis and integration. Mounting evidence from evolution and development (Evo-Devo) studies suggests that function is another mechanism important to healthy craniodental integration and fit. Starting as early as weaning, softer diets and thus lower bite forces appear to relax or disrupt integration of oral tissues, alter development and growth, and catalyze impaction, malocclusion, and jaw joint disorders. How developing oral tissues respond to bite forces remains poorly understood, but biomechanical feedback seems to alter balances of local bone resorption and deposition at the tooth-bone interface as well as affect tempos and amounts of facial outgrowth. Also, behavioral changes in jaw function and parafunction contribute to degeneration and pain in joint articular cartilages and masticatory muscles. The developmental genetic contribution to craniodental misfits and disorders is undeniable but still unclear; however, at present, human diet and jaw function remain important and much more actionable clinical targets. New Evo-Devo studies are needed to explain how function interfaces with craniodental phenotypic plasticity, variation, and evolvability to yield a spectrum of healthy and mismatched dentitions and jaws.

Transcriptomic signatures shaped by cell proportions shed light on comparative developmental biology

Background

Comparative transcriptomics can answer many questions in developmental and evolutionary developmental biology. Most transcriptomic studies start by showing global patterns of variation in transcriptomes that differ between species or organs through developmental time. However, little is known about the kinds of expression differences that shape these patterns.

Results

We compared transcriptomes during the development of two morphologically distinct serial organs, the upper and lower first molars of the mouse. We found that these two types of teeth largely share the same gene expression dynamics but that three major transcriptomic signatures distinguish them, all of which are shaped by differences in the relative abundance of different cell types. First, lower/upper molar differences are maintained throughout morphogenesis and stem from differences in the relative abundance of mesenchyme and from constant differences in gene expression within tissues. Second, there are clear time-shift differences in the transcriptomes of the two molars related to cusp tissue abundance. Third, the transcriptomes differ most during early-mid crown morphogenesis, corresponding to exaggerated morphogenetic processes in the upper molar involving fewer mitotic cells but more migrating cells. From these findings, we formulate hypotheses about the mechanisms enabling the two molars to reach different phenotypes. We also successfully applied our approach to forelimb and hindlimb development.

Conclusions

Gene expression in a complex tissue reflects not only transcriptional regulation but also abundance of different cell types. This knowledge provides valuable insights into the cellular processes underpinning differences in organ development. Our approach should be applicable to most comparative developmental contexts.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-017-1157-7) contains supplementary material, which is available to authorized users.

Jawbone microenvironment promotes periodontium regeneration by regulating the function of periodontal ligament stem cells

During tooth development, the jawbone interacts with dental germ and provides the development microenvironment. Jawbone-derived mesenchymal stem cells (JBMSCs) maintain this microenvironment for root and periodontium development. However, the effect of the jawbone microenvironment on periodontium tissue regeneration is largely elusive. Our previous study showed that cell aggregates (CAs) of bone marrow mesenchymal stem cells promoted periodontium regeneration on the treated dentin scaffold. Here, we found that JBMSCs enhanced not only the osteogenic differentiation of periodontal ligament stem cells (PDLSCs) but also their adhesion to titanium (Ti) material surface. Importantly, the compound CAs of PDLSCs and JBMSCs regenerated periodontal ligament-like fibers and mineralized matrix on the Ti scaffold surface, both in nude mice ectopic and minipig orthotopic transplantations. Our data revealed that an effective regenerative microenvironment, reconstructed by JBMSCs, promoted periodontium regeneration by regulating PDLSCs function on the Ti material.

Mapping the milestones in tooth regeneration: Current trends and future research

Research into finding the perfect replacement for lost dentition is an ever-evolving and rapidly advancing subject involving many scientific disciplines. The present consensus appears to be that regeneration of tooth in morphological and functional form is the ideal answer to lost tooth replacement. This article traces the milestones in this elusive search for the ultimate tooth replacement. The various research developments are highlighted that are aimed at the final goal of being able to "re-grow a natural tooth". Whole tooth regeneration is technically challenging and further research into this field of complex molecular biology, embryology, biomaterials and stem cells is required to answer the unsolved questions. However, the milestones that have been crossed in the attempts at whole tooth regeneration have been remarkable and the future is quite promising. This article highlights the noteworthy research work that is being done in the field of whole tooth regeneration with a view to not only inform the clinicians of the significant developments but also inspire them to actively participate in this rapidly evolving field.

RETRACTED: New findings for dentin sialophosphoprotein studies: Applications of purified odontoblast-like cells derived from stem cells

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Authors. After the retraction of the article [Hiyama T, Ozeki N, Mogi M, Yamaguchi H, Kawai R, Nakata K, Kondo A, Nakamura H. 2013. Matrix Metalloproteinase-3 in Odontoblastic Cells Derived from Ips Cells: Unique Proliferation Response as Odontoblastic Cells Derived from ES Cells. PLoS ONE 8(12): e83563. doi:10.1371/journal.pone.0083563] which contained fabricated/falsified data, the authors attempted to confirm original data for the results presented in their related publications. As a result, they reached a conclusion that there were no original data for the results presented in several their publications. This article was written on the basis of the seven publications retracted or to be retracted and it is no longer reliable. Reference 24: N. Ozeki, M. Mogi, R. Kawai, H. Yamaguchi, T. Hiyama, K. Nakata, H. Nakamura Mouse-induced pluripotent stem cells differentiate into odontoblast-like cells with induction of altered adhesive and migratory phenotype of integrin PLoS One, 8 (2013), p. e80026 Reference 25:R. Kawai, N. Ozeki, H. Yamaguchi, T. Tanaka, K. Nakata, M. Mogi, H. Nakamura Mouse ES cells have a potential to differentiate into odontoblast-like cells using hanging drop method Oral Dis, 20 (2014), pp. 395-403 Reference 26:N. Ozeki, M. Mogi, H. Yamaguchi, T. Hiyama, R. Kawai, N. Hase, K. Nakata, H. Nakamura, R.H. Kramer Differentiation of human skeletal muscle stem cells into odontoblasts is dependent on induction of alpha1 integrin expression J Biol Chem, 289 (2014), pp. 14380-14391 Reference 42:N. Ozeki, N. Hase, R. Kawai, H. Yamaguchi, T. Hiyama, A. Kondo, K. Nakata, M. Mogi Unique proliferation response in odontoblastic cells derived from human skeletal muscle stem cells by cytokine-induced matrix metalloproteinase-3 Exp Cell Res, 331 (2015), pp. 105-114 Reference 43: N. Ozeki, N. Hase, H. Yamaguchi, T. Hiyama, R. Kawai, A. Kondo, K. Nakata, M. Mogi Polyphosphate induces matrix metalloproteinase-3-mediated proliferation of odontoblast-like cells derived from induced pluripotent stem cells Exp Cell Res, 333 (2015), pp. 303-315 Reference 44: N. Ozeki, R. Kawai, N. Hase, T. Hiyama, H. Yamaguchi, A. Kondo, K. Nakata, M. Mogi Alpha2 integrin, extracellular matrix metalloproteinase inducer, and matrix metalloproteinase-3 act sequentially to induce differentiation of mouse embryonic stem cells into odontoblast-like Exp Cell Res, 331 (2015), pp. 21-37 Reference 45: N. Ozeki, M. Mogi, N. Hase, T. Hiyama, H. Yamaguchi, R. Kawai, A. Kondo, T. Matsumoto, K. Nakata Autophagy-related gene 5 and Wnt5 signaling pathway requires differentiation of embryonic stem cells into odontoblast-like cells Exp Cell Res, 341 (2016), pp. 92-104 All of the authors except Nobuaki Ozeki have agreed to retract the article. Nobuaki Ozeki, the corresponding author and the first author of the article, left Aichi Gakuin University in March 2018, and does not respond to co-authors inquiries. The authors deeply regret this error and any inconvenience it may have caused.

The Role of Sonic Hedgehog in Craniofacial Patterning, Morphogenesis and Cranial Neural Crest Survival

Craniofacial defects (CFD) are a significant healthcare problem worldwide. Understanding both the morphogenetic movements which underpin normal facial development, as well as the molecular factors which regulate these processes, forms the cornerstone of future diagnostic, and ultimately, preventative therapies. The soluble morphogen Sonic hedgehog (Shh), a vertebrate orthologue of Drosophila hedgehog, is a key signalling factor in the regulation of craniofacial skeleton development in vertebrates, operating within numerous tissue types in the craniofacial primordia to spatiotemporally regulate the formation of the face and jaws. This review will provide an overview of normal craniofacial skeleton development, and focus specifically on the known roles of Shh in regulating the development and progression of the first pharyngeal arch, which in turn gives rise to both the upper jaw (maxilla) and lower jaw (mandible).

What shapes the oral jaws? Accommodation of complex dentition correlates with premaxillary but not mandibular shape

BACKGROUND

Teeth are integrated into the vertebrate oral jaws to provide a functional unit for feeding, however little is known about how this integration occurs during growth and development. The purpose of this study is to identify the ontogenetic changes in oral jaw shape that are associated with the transition of the oral dentition from unicuspid teeth to multicuspid teeth. Here, we compare the shape of the occluding upper (premaxilla) and lower (mandible) jaws of the toothed Mexican tetra (Astyanax mexicanus) and the toothless (oral teeth present, pharyngeal teeth absent) zebrafish (Danio rerio) over development. Gross morphology combined with morphometric analyses were used to analyse shape changes of the occluding oral jaws in each species. Histological analyses were also used to examine the development of the mandibular symphysis.

RESULTS

The occluding edge of the premaxilla is the first region to ossify in the Mexican tetra, but the last to ossify in zebrafish. Morphometric analyses revealed that the early shape of the premaxillae (in fish younger than 8mm SL) is the same in each species but that the premaxilla shape changes significantly at larger sizes. These changes are apparent in the tooth bearing region of the Mexican tetra. The rostral region of the mandible also houses teeth, however ossification and shape in this region were surprisingly similar between species despite differences in the presence of oral dentition. Furthermore, we found that the mandibular symphysis of the Mexican tetra is composed of interdigitating bone, while the symphyseal region of the zebrafish is composed of fibrous connective tissue.

CONCLUSIONS

These differences in the jaw skeleton have likely evolved due to different feeding strategies utilised by each species. Our results show that premaxillae shape correlates strongly with the development of complex dentitions unlike in the mandible. This study provides important insights into the relationship between jaw and tooth development in bony fishes and suggests that these mechanisms may be similar amongst vertebrates.

Facioscapulohumeral muscular dystrophy (FSHD) region gene 1 (FRG1) expression and possible function in mouse tooth germ development

Abnormal expression of Facioscapulohumeral muscular dystrophy (FSHD) region gene 1 (FRG1) is involved in the pathogenesis of FSHD. FRG1 is also important for the normal muscular and vascular development. Our previous study showed that FRG1 is one of the highly expressed genes in the mandible on embryonic day 10.5 (E10.5) than on E12.0. In this study, we investigated the temporospatial expression pattern of FRG1 mRNA and protein during the development of the mouse lower first molar, and also evaluated the subcellular localization of the FRG1 protein in mouse dental epithelial (mDE6) cells. The FRG1 expression was identified in the dental epithelial and mesenchymal cells at the initiation and bud stages. It was detected in the inner enamel epithelium at the cap and early bell stages. At the late bell and root formation stages, these signals were detected in ameloblasts and odontoblasts during the formation of enamel and dentin matrices, respectively. The FRG1 protein was localized in the cytoplasm in the mouse tooth germ in vivo, while FRG1 was detected predominantly in the nucleus and faintly in the cytoplasm in mDE6 cells in vitro. In mDE6 cells treated with bone morphogenetic protein 4 (BMP4), the protein expression of FRG1 increased in cytoplasm, suggesting that FRG1 may translocate to the cytoplasm. These findings suggest that FRG1 is involved in the morphogenesis of the tooth germ, as well as in the formation of enamel and dentin matrices and that FRG1 may play a role in the odontogenesis in the mouse following BMP4 stimulation.

Bmp signaling mediates endoderm pouch morphogenesis by regulating Fgf signaling in zebrafish

The endodermal pouches are a series of reiterated structures that segment the pharyngeal arches and help pattern the vertebrate face. Multiple pathways regulate the complex process of endodermal development, including the Bone morphogenetic protein (Bmp) pathway. However, the role of Bmp signaling in pouch morphogenesis is poorly understood. Using genetic and chemical inhibitor approaches, we show that pouch morphogenesis requires Bmp signaling from 10-18 h post-fertilization, immediately following gastrulation. Blocking Bmp signaling during this window results in morphological defects to the pouches and craniofacial skeleton. Using genetic chimeras we show that Bmp signals directly to the endoderm for proper morphogenesis. Time-lapse imaging and analysis of reporter transgenics show that Bmp signaling is necessary for pouch outpocketing via the Fibroblast growth factor (Fgf) pathway. Double loss-of-function analyses demonstrate that Bmp and Fgf signaling interact synergistically in craniofacial development. Collectively, our analyses shed light on the tissue and signaling interactions that regulate development of the vertebrate face.

Prevalence and distribution of dental anomalies: a comparison between maxillary and mandibular tooth agenesis

INTRODUCTION

The aim of this study was to compare the pattern and prevalence of associated dental anomalies between maxillary and mandibular tooth agenesis (hypodontia).

METHODS

A sample of 3315 dental patients, aged 8.6 to 25.4 years, was surveyed for tooth agenesis (excluding third molars): 106 subjects were diagnosed with maxillary hypodontia (group 1) and 70 with mandibular hypodontia (group 2). Both groups were examined for the following dental anomalies: retained deciduous molars, infraocclusion of deciduous molars, impaction, microdontia of maxillary lateral incisors, supernumerary teeth, transposition, transmigration, and ectopic eruption of the permanent molars. For statistical testing, the chi-square test (P <0.05) was used to compare the occurrences of these anomalies among the groups.

RESULTS

We found that 77.5% of the patients in the mandibular hypodontia group had at least 1 dental anomaly compared with 49.5% in the maxillary hypodontia group (P <0.0001). The only dental anomaly with a significantly increased prevalence in the maxillary hypodontia group compared with the mandibular hypodontia group was microdontia of the maxillary lateral incisors (groups 1, 46.7%; group 2, 12.9%; P <0.0001). On the other hand, the prevalences of retained deciduous molars (group 1, 9.4%; group 2, 60.0%), infraoccluded deciduous molars (group 1, 0.9%; group 2, 7.1%), and impacted teeth (group 1, 22.6%; group 2, 38.6%) were significantly higher in the mandibular hypodontia group. The prevalences of supernumerary teeth, transposition, transmigration, and ectopic eruption of permanent molars were low and not significantly different between the groups.

CONCLUSIONS

Tooth agenesis isolated to the maxilla is frequently associated with microdontia of the maxillary lateral incisors, whereas tooth agenesis isolated to the mandible is frequently associated with retained deciduous molars, infraoccluded deciduous molars, and impacted teeth. The results of this study may provide additional evidence supporting the field-specific genetic control theory for dental development in both jaws.

Developmental Structural Tooth Defects in Dogs - Experience From Veterinary Dental Referral Practice and Review of the Literature

Developmental tooth abnormalities in dogs are uncommon in general veterinary practice but understanding thereof is important for optimal management in order to maintain masticatory function through preservation of the dentition. The purpose of this review is to discuss clinical abnormalities of the enamel and general anatomy of dog teeth encountered in veterinary dental referral practice and described in the literature. More than 900 referral cases are seen annually between the two referral practices. The basis of the pathogenesis, resultant clinical appearance, and the principles of management for each anomaly will be described. Future research should be aimed toward a more detailed analysis of these conditions so rarely described in the literature.