Tooth morphogenesis and cell differentiation

Testing the patterning cascade model of cusp development in Macaca fascicularis mandibular molars

OBJECTIVE

Molar crown configuration plays an important role in systematics, and functional and comparative morphology. In particular, the number of cusps on primate molars is often used to identify fossil species and infer their phylogenetic relationships. However, this variability deserves renewed consideration as a number of studies now highlight important developmental mechanisms that may be responsible for the presence of molar cusps in some mammalian taxa. Experimental studies of rodent molars suggest that cusps form under a morphodynamic, patterning cascade model of development (PCM) that involve the iterative formation of enamel knots. This model posits that the size, shape and location of the first-forming cusps determines the presence and positioning of later-forming cusps.

DESIGN

Here we test whether variation in accessory cusp presence in 13 Macaca fascicularis mandibular second molars (M2s) is consistent with predictions of the PCM. Using micro-CT, we imaged these M2s and employed geometric morphometrics to examine whether shape variation in the enamel-dentine junction (EDJ) correlates with accessory cusp presence.

RESULTS

We find that accessory cusp patterning in macaque M2s is broadly consistent with the PCM. Molars with accessory cusps were larger in size and possessed shorter relative cusp heights compared to molars without accessory cusps. Peripheral cusp formation was also associated with more centrally positioned primary cusps, as predicted by the PCM.

CONCLUSIONS

While these results demonstrate that a patterning cascade model is broadly appropriate for interpreting cusp variation in Macaca fascicularis molars, it does not explain all manifestations of accessory cusp expression in this sample.

Development of a Thermoresponsive Core-Shell Hydrogel for Sequential Delivery of Antibiotics and Growth Factors in Regenerative Endodontics

BACKGROUND

Regenerative endodontics requires an innovative delivery system to release antibiotics/growth factors in a sequential trend. This study focuses on developing/characterizing a thermoresponsive core-shell hydrogel designed for targeted drug delivery in endodontics.

METHODS

The core-shell chitosan-alginate microparticles were prepared by electrospraying to deliver bone morphogenic protein-2 for 14 days and transforming growth factor-beta 1 (TGF-β1) for 7-14 days. Methylcellulose (MC) and gelatin were utilized to create the core-shell hydrogel to load a modified triple antibiotic combination (penicillin G/metronidazole/ciprofloxacin (PMC)) and growth factor-loaded microparticles in the shell and the core compartments, respectively. Morphological assessment, core-shell structural analysis, FTIR analysis, rheological analysis, swelling, and degradation rate studies were conducted for characterization. The viability of dental pulp stem cells (DPSCs) upon antibiotic exposure, antibacterial activity, and release studies of PMC and growth factors were investigated. Cellular studies (cell viability, alkaline phosphatase (ALP) activity, osteo/odontoblast gene expression (using Reverse transcription-polymerase chain reaction (RT-PCR)) and in vivo studies (inflammatory response and differentiation potential of the developed hydrogel by subcutaneous implantation in rats via histological examination) were assessed.

RESULTS

The hydrogel showed a porous microstructure with interconnected pores. Core-shell structure analysis confirmed the successful extrusion of the MC hydrogel to the surface. FTIR analysis revealed interactions between MC and gelatin. Rheological analysis indicated time-dependent gel formation, supporting thermosensitivity at 37 °C. Swelling occurred rapidly, and degradation reached 62.42% on day 45. Further, antibiotics exhibited no cytotoxicity on DPSCs. Sequential release of antibiotics and growth factors was observed for up to 5 and 14 d, respectively. The hydrogel showed antibacterial activity. DPSCs exhibited increased proliferation, ALP activity, and odontoblast gene expression. In vivo studies showed that the biocompatible drug-loaded hydrogel exhibited more mineralization than the control.

CONCLUSIONS

The developed core-shell hydrogel containing PMC and growth factor-loaded core-shell microparticles provided a versatile and biocompatible platform for sequential drug delivery in regenerative endodontics. The system demonstrates promising characteristics for dentin regeneration, making it a potential candidate for clinical applications.

The genetic basis of hypodontia in dental development

Dental agenesis is one of the most common developmental anomalies in humans, characterised by the developmental absence of one or more teeth. It can present as an isolated condition (non-syndromic hypodontia) or associated with a syndrome (syndromic hypodontia). This paper aims to review the genetic basis of hypodontia with reference to aetiology, classification and the subsequent clinical features.Significant progress has been made to identify the developmental basis of tooth formation, though there is still a lack of knowledge within the literature of the aetiological basis of inherited tooth loss.Gene anomalies or mutations in WNT10A, MSX1, PAX9, AXIN2 and EDA appear to be most critical during tooth development, leading to various forms of tooth agenesis.

A tooth crown morphology framework for interpreting the diversity of primate dentitions

Variation in tooth crown morphology plays a crucial role in species diagnoses, phylogenetic inference, and the reconstruction of the evolutionary history of the primate clade. While a growing number of studies have identified developmental mechanisms linked to tooth size and cusp patterning in mammalian crown morphology, it is unclear (1) to what degree these are applicable across primates and (2) which additional developmental mechanisms should be recognized as playing important roles in odontogenesis. From detailed observations of lower molar enamel-dentine junction morphology from taxa representing the major primate clades, we outline multiple phylogenetic and developmental components responsible for crown patterning, and formulate a tooth crown morphology framework for the holistic interpretation of primate crown morphology. We suggest that adopting this framework is crucial for the characterization of tooth morphology in studies of dental development, discrete trait analysis, and systematics.

Loss of Bmp2 impairs odontogenesis via dysregulating pAkt/pErk/GCN5/Dlx3/Sp7

BMP2 signaling plays a pivotal role in odontoblast differentiation and maturation during odontogenesis. Teeth lacking Bmp2 exhibit a morphology reminiscent of dentinogenesis imperfecta (DGI), associated with mutations in dentin matrix protein 1 (DMP1) and dentin sialophosphoprotein (DSPP) genes. Mechanisms by which BMP2 signaling influences expressions of DSPP and DMP1 and contributes to DGI remain elusive. To study the roles of BMP2 in dentin development, we generated Bmp2 conditional knockout (cKO) mice. Through a comprehensive approach involving RNA-seq, immunohistochemistry, promoter activity, ChIP, and Re-ChIP, we investigated downstream targets of Bmp2. Notably, the absence of Bmp2 in cKO mice led to dentin insufficiency akin to DGI. Disrupted Bmp2 signaling was linked to decreased expression of Dspp and Dmp1, as well as alterations in intracellular translocation of transcription factors Dlx3 and Sp7. Intriguingly, upregulation of Dlx3, Dmp1, Dspp, and Sp7, driven by BMP2, fostered differentiation of dental mesenchymal cells and biomineralization. Mechanistically, BMP2 induced phosphorylation of Dlx3, Sp7, and histone acetyltransferase GCN5 at Thr and Tyr residues, mediated by Akt and Erk42/44 kinases. This phosphorylation facilitated protein nuclear translocation, promoting interactions between Sp7 and Dlx3, as well as with GCN5 on Dspp and Dmp1 promoters. The synergy between Dlx3 and Sp7 bolstered transcription of Dspp and Dmp1. Notably, BMP2-driven GCN5 acetylated Sp7 and histone H3, while also recruiting RNA polymerase II to Dmp1 and Dspp chromatins, enhancing their transcriptions. Intriguingly, BMP2 suppressed the expression of histone deacetylases. we unveil hitherto uncharted involvement of BMP2 in dental cell differentiation and dentine development through pAkt/pErk42/44/Dlx3/Sp7/GCN5/Dspp/Dmp1.

Atp6i deficient mouse model uncovers transforming growth factor-β1 /Smad2/3 as a key signaling pathway regulating odontoblast differentiation and tooth root formation

The biomolecular mechanisms that regulate tooth root development and odontoblast differentiation are poorly understood. We found that Atp6i deficient mice (Atp6i-/-) arrested tooth root formation, indicated by truncated Hertwig's epithelial root sheath (HERS) progression. Furthermore, Atp6i deficiency significantly reduced the proliferation and differentiation of radicular odontogenic cells responsible for root formation. Atp6i-/- mice had largely decreased expression of odontoblast differentiation marker gene expression profiles (Col1a1, Nfic, Dspp, and Osx) in the alveolar bone. Atp6i-/- mice sample RNA-seq analysis results showed decreased expression levels of odontoblast markers. Additionally, there was a significant reduction in Smad2/3 activation, inhibiting transforming growth factor-β (TGF-β) signaling in Atp6i-/- odontoblasts. Through treating pulp precursor cells with Atp6i-/- or wild-type OC bone resorption-conditioned medium, we found the latter medium to promote odontoblast differentiation, as shown by increased odontoblast differentiation marker genes expression (Nfic, Dspp, Osx, and Runx2). This increased expression was significantly blocked by anti-TGF-β1 antibody neutralization, whereas odontoblast differentiation and Smad2/3 activation were significantly attenuated by Atp6i-/- OC conditioned medium. Importantly, ectopic TGF-β1 partially rescued root development and root dentin deposition of Atp6i-/- mice tooth germs were transplanted under mouse kidney capsules. Collectively, our novel data shows that the prevention of TGF-β1 release from the alveolar bone matrix due to OC dysfunction may lead to osteopetrosis-associated root formation via impaired radicular odontoblast differentiation. As such, this study uncovers TGF-β1 /Smad2/3 as a key signaling pathway regulating odontoblast differentiation and tooth root formation and may contribute to future therapeutic approaches to tooth root regeneration.

The Role of Cellular Metabolism in Maintaining the Function of the Dentine-Pulp Complex: A Narrative Review

The cellular metabolic processes ensure the physiological integrity of the dentine-pulp complex. Odontoblasts and odontoblast-like cells are responsible for the defence mechanisms in the form of tertiary dentine formation. In turn, the main defence reaction of the pulp is the development of inflammation, during which the metabolic and signalling pathways of the cells are significantly altered. The selected dental procedures, such as orthodontic treatment, resin infiltration, resin restorations or dental bleaching, can impact the cellular metabolism in the dental pulp. Among systemic metabolic diseases, diabetes mellitus causes the most consequences for the cellular metabolism of the dentine-pulp complex. Similarly, ageing processes present a proven effect on the metabolic functioning of the odontoblasts and the pulp cells. In the literature, several potential metabolic mediators demonstrating anti-inflammatory properties on inflamed dental pulp are mentioned. Moreover, the pulp stem cells exhibit the regenerative potential essential for maintaining the function of the dentine-pulp complex.

A Rare Incidence of Nonsyndromic Mandibular Incisor Agenesis in a Three-generation Family: Case Report and Literature Review

Hypodontia is an inherited condition involving the absence of one to six teeth. The permanent dentition is the most frequently affected; however, it may also affect the primary dentition. A congenitally missing tooth (CMT) is the most common dental abnormality, with the missing mandibular second premolar, maxillary lateral incisor, maxillary second premolar, and mandibular central incisor accounting for 90% of CMT in hypodontia studies. The etiology of CMT has been attributed to environmental and genetic contributing factors, with the latter having a strong influence. It may occur in isolation or in association with syndromes. Congenitally missing mandibular incisor is more common in the Asian population and females. Depending on the number and location of missing teeth, hypodontia may be a considerable issue for the clinician since it may impact occlusal balance, mastication, speech, and esthetics and often requires a multidisciplinary approach. Missing mandibular incisors are of particular interest to orthodontists because of the possibility of mandibular retrognathism, the potential for the development of malocclusion, and difficulty in achieving a balanced occlusion. This case report describes the skeletal and dental features of a nonsyndromic familial occurrence of missing mandibular incisors in three generations. A comprehensive literature search was also performed to review the familial cases with missing mandibular incisors.

How to cite this article

Selvaraj M, Sennimalai K, Samrit VD, et al. A Rare Incidence of Nonsyndromic Mandibular Incisor Agenesis in a Three-generation Family: Case Report and Literature Review. Int J Clin Pediatr Dent 2023;16(2):388-395.

Enamel Phenotypes: Genetic and Environmental Determinants

Dental enamel is a specialized tissue that has adapted over millions of years of evolution to enhance the survival of a variety of species. In humans, enamel evolved to form the exterior protective layer for the crown of the exposed tooth crown. Its unique composition, structure, physical properties and attachment to the underlying dentin tissue allow it to be a resilient, although not self-repairing, tissue. The process of enamel formation, known as amelogenesis, involves epithelial-derived cells called ameloblasts that secrete a unique extracellular matrix that influences the structure of the mineralizing enamel crystallites. There are over 115 known genetic conditions affecting amelogenesis that are associated with enamel phenotypes characterized by either a reduction of enamel amount and or mineralization. Amelogenesis involves many processes that are sensitive to perturbation and can be altered by numerous environmental stressors. Genetics, epigenetics, and environment factors can influence enamel formation and play a role in resistance/risk for developmental defects and the complex disease, dental caries. Understanding why and how enamel is affected and the enamel phenotypes seen clinically support diagnostics, prognosis prediction, and the selection of treatment approaches that are appropriate for the specific tissue defects (e.g., deficient amount, decreased mineral, reduced insulation and hypersensitivity). The current level of knowledge regarding the heritable enamel defects is sufficient to develop a new classification system and consensus nosology that effectively communicate the mode of inheritance, molecular defect/pathway, and the functional aberration and resulting enamel phenotype.

Odontogenic MSC Heterogeneity: Challenges and Opportunities for Regenerative Medicine

Cellular heterogeneity refers to the genetic and phenotypic differences among cells, which reflect their various fate choices, including viability, proliferation, self-renewal probability, and differentiation into different lineages. In recent years, research on the heterogeneity of mesenchymal stem cells has made some progress. Odontogenic mesenchymal stem cells share the characteristics of mesenchymal stem cells, namely, good accessibility, low immunogenicity and high stemness. In addition, they also exhibit the characteristics of vasculogenesis and neurogenesis, making them attractive for tissue engineering and regenerative medicine. However, the usage of mesenchymal stem cell subgroups differs in different diseases. Furthermore, because of the heterogeneity of odontogenic mesenchymal stem cells, their application in tissue regeneration and disease management is restricted. Findings related to the heterogeneity of odontogenic mesenchymal stem cells urgently need to be summarized, thus, we reviewed studies on odontogenic mesenchymal stem cells and their specific subpopulations, in order to provide indications for further research on the stem cell regenerative therapy.

Cytokine co-stimulation effect on odontogenic differentiation of stem cells

OBJECTIVE

The study aims to evaluate the effect of bone morphogenetic protein-2 (BMP-2) and transforming growth factor-beta 1 (TGF-β1) co-stimulation on odontogenic differentiation of human dental pulp stem cells (hDPSCs).

MATERIALS AND METHODS

The viability/proliferation of hDPSCs treated with BMP-2 (group B), TGF-β1 (group T), or BMP-2/TGF-β1 (group BT) were evaluated. The experiments on odontogenic differentiation were done for 14 days. The following subgroups were added to investigate the effect of co-stimulation with different timing: subgroup B1, TGF-β1 co-stimulation in the first week; subgroup B2, TGF-β1 co-stimulation in the second week; subgroup T1, BMP-2 co-stimulation in the first week; and subgroup T2, BMP-2 co-stimulation in the second week. The mineralization was assessed using alizarin red staining. The expression of following genes was assessed using quantitative real-time polymerase chain reaction: dentin sialophosphoprotein (DSPP), dentin matrix protein-1 (DMP1), osteopontin (OPN), and alkaline phosphatase.

RESULTS

All groups showed viability similar to the control group (P > .05). The greater mineralization was detected in B groups on day 14. The expressions of DSPP, DMP-1, and OPN increased on day 14 (P < .05). In the combination groups, the higher expressions of DSPP and DMP-1 were observed in subgroups B1 and B2 than groups B and T (P < .05).

CONCLUSIONS

BMP-2 was the key in odontogenic differentiation of hDPSCs, which was further enhanced by co-stimulation with TGF-β1. Continuous stimulation with TGFβ-1 did not improve the differentiation of hDPSCs.

CLINICAL RELEVANCE

Combined use of the BMP-2 and TGFβ-1 at the specific sequence can provide a tissue engineering approach for the future guided dentin regeneration.

Multivariate GWAS of Structural Dental Anomalies and Dental Caries in a Multi-Ethnic Cohort

Odontogenesis is a complex process, where disruption can result in dental anomalies and/or increase the risk of developing dental caries. Based on previous studies, certain dental anomalies tend to co-occur in patients, suggesting that these traits may share common genetic and etiological components. The main goal of this study was to implement a multivariate genome-wide association study approach to identify genetic variants shared between correlated structural dental anomalies and dental caries. Our cohort (N = 3,579) was derived from the Pittsburgh Orofacial Clefts Study, where multiple dental traits were assessed in both the unaffected relatives of orofacial cleft (OFC) cases (n = 2,187) and unaffected controls (n = 1,392). We identified four multivariate patterns of correlated traits in this data: tooth agenesis, impaction, and rotation (AIR); enamel hypoplasia, displacement, and rotation (HDR); displacement, rotation, and mamelon (DRM); and dental caries, tooth agenesis and enamel hypoplasia (CAH). We analyzed each of these four models using genome-wide multivariate tests of association. No genome-wide statistically significant results were found, but we identified multiple suggestive association signals (P < 10-5) near genes with known biological roles during tooth development, including ADAMTS9 and PRICKLE2 associated with AIR; GLIS3, WDR72, and ROR2 associated with HDR and DRM; ROBO2 associated with DRM; BMP7 associated with HDR; and ROBO1, SMAD2, and MSX2 associated with CAH. This is the first study to investigate genetic associations for multivariate patterns of correlated dental anomalies and dental caries. Further studies are needed to replicate these results in independent cohorts.

Transcriptional regulation of the basic helix-loop-helix factor AmeloD during tooth development

The epithelial-mesenchymal interactions are essential for the initiation and regulation of the development of teeth. Following the initiation of tooth development, numerous growth factors are secreted by the dental epithelium and mesenchyme that play critical roles in cellular differentiation. During tooth morphogenesis, the dental epithelial stem cells differentiate into several cell types, including inner enamel epithelial cells, which then differentiate into enamel matrix-secreting ameloblasts. Recently, we reported that the novel basic-helix-loop-helix transcription factor, AmeloD, is actively engaged in the development of teeth as a regulator of dental epithelial cell motility. However, the gene regulation mechanism of AmeloD is still unknown. In this study, we aimed to uncover the mechanisms regulating AmeloD expression during tooth development. By screening growth factors that are important in the early stages of tooth formation, we found that TGF-β1 induced AmeloD expression and ameloblast differentiation in the dental epithelial cell line, SF2. TGF-β1 phosphorylated ERK1/2 and Smad2/3 to induce AmeloD expression, whereas treatment with the MEK inhibitor, U0126, inhibited AmeloD induction. Promoter analysis of AmeloD revealed that the proximal promoter of AmeloD showed high activity in dental epithelial cell lines, which was enhanced following TGF-β1 stimulation. These results suggested that TGF-β1 activates AmeloD transcription via ERK1/2 phosphorylation. Our findings provide new insights into the mechanisms that govern tooth development.

Quantification of three-dimensional morphology of craniofacial mineralized tissue defects in Tgfbr2/Osx-Cre mice

Craniofacial morphology is affected by the growth, development, and three-dimensional (3D) relationship of mineralized structures including the skull, jaws, and teeth. Despite fulfilling different purposes within this region, cranial bones and tooth dentin are derived from mesenchymal cells that are affected by perturbations within the TGF-β signaling pathway. TGFBR2 encodes a transmembrane receptor that is part of the canonical, SMAD-dependent TGF-β signaling pathway and mutations within this gene are associated with Loeys-Dietz syndrome, a condition which often presents with craniofacial signs including craniosynostosis and cleft palate. To investigate the role of Tgfbr2 in immature, but committed, mineralized tissue forming cells, we analyzed postnatal craniofacial morphology in mice with conditional Tgfbr2 deletion in Osx-expressing cells. Novel application of a 3D shape-based comparative technique revealed that Tgfbr2 in Osx-expressing cells results in impaired postnatal molar root and anterior cranial growth. These findings support those from studies using similar Tgfbr2 conditional knockout models, highlight the anomalous facial and dental regions/structures using tomographic imaging-based techniques, and provide insight into the role of Tgfbr2 during postnatal craniofacial development.

Expression pattern of transcriptional enhanced associate domain family member 1 (Tead1) in developing mouse molar tooth

The Hippo pathway is essential for determining organ size by regulating cell proliferation. Previous reports have shown that impairing this pathway causes abnormal tooth development. However, the precise expression profile of the members of the transcriptional enhanced associate domain family (Tead), which are key transcription factors mediating Yap function, during tooth development is unclear. In this study, among the four isoforms of Tead (Tead1 - 4), only the expression of Tead1 mRNA was observed using semiquantitative RT- PCR in murine developing tooth germ at E16.5. The expression level of Tead1 mRNA in the excised murine mandibular molar tooth germ was significantly higher at E16.5 than at other developmental stages, as determined using quantitative PCR. We found that the mRNA expression of connective tissue growth factor (Ctgf), which is one of the Yap target genes directly controlling cell growth, changed consistently with that of Tead1 in developing molars. Fluorescent immunostaining revealed that Tead1 protein was expressed in both epithelial cells and mesenchymal cells of the dental lamina and dental epithelium, including the primary enamel knot during the cap stage. During the early bell stage (E16.5), Tead1 was expressed intensely in the inner and outer enamel epithelium, including the secondary enamel knot and the neighboring mesenchymal cells. Tead1 then specifically localized to the inner and outer enamel epithelium, which is responsible for enamel formation during the bell stage. These expression patterns were consistent with those of Yap, Taz, and Ctgf protein in developing molars. These results suggest that Tead1 acts as a mediator of the biological functions of Yap, such as the morphogenesis of cusp formation, during tooth development.

Endoscopic treatment of ectopic teeth in the maxillary sinus

Background

Ectopic teeth in maxillary sinus is rare and are usually removed via sub-labial trans-canine fossa approach (SLCFA). The aim of our study was to present our experience with extraction of ectopic teeth in the maxillary sinus via transnasal endoscopic approach (TEA).

Material and Methods

Rhinologists were asked to share their experience in the management of ectopic teeth in the maxillary sinus. Data were reviewed retrospectively.

Results

Eleven cases were reported in 10 patients from 2010 to 2019, six males and four females with a mean age of 33.5 +/-17 years (range 16 to 61). Seven patients complained of sinonasal symptoms, two were diagnosed incidentally during routine dental work-up, and one had oro-antral fistula. In eight patients, a cyst coexisted within the maxillary sinus. Teeth were located arbitrarily within the sinus. All cases were operated by TEA. One patient had self-limited periorbital emphysema, one had transient cheek numbness, and one had early post-operative bleeding that stopped after endoscopic cauterization. Long-term follow-up revealed good clinical outcomes.

Conclusions

Transnasal endoscopic removal of ectopic teeth from the maxillary sinus is a feasible and rational approach when SLCFA is contraindicated.

Key words:Ectopic teeth, dentigerous cyst, endoscopic sinus surgery, Caldwell-Luc.

RORα Regulates Odontoblastic Differentiation and Mediates the Pro-Odontogenic Effect of Melatonin on Dental Papilla Cells

Dental papilla cells (DPCs), precursors of odontoblasts, are considered promising seed cells for tissue engineering. Emerging evidence suggests that melatonin promotes odontoblastic differentiation of DPCs and affects tooth development, although the precise mechanisms remain unknown. Retinoid acid receptor-related orphan receptor α (RORα) is a nuclear receptor for melatonin that plays a critical role in cell differentiation and embryonic development. This study aimed to explore the role of RORα in odontoblastic differentiation and determine whether melatonin exerts its pro-odontogenic effect via RORα. Herein, we observed that RORα was expressed in DPCs and was significantly increased during odontoblastic differentiation in vitro and in vivo. The overexpression of RORα upregulated the expression of odontogenic markers, alkaline phosphatase (ALP) activity and mineralized nodules formation (p < 0.05). In contrast, odontoblastic differentiation of DPCs was suppressed by RORα knockdown. Moreover, we found that melatonin elevated the expression of odontogenic markers, which was accompanied by the upregulation of RORα (p < 0.001). Utilising small interfering RNA, we further demonstrated that RORα inhibition attenuated melatonin-induced odontogenic gene expression, ALP activity and matrix mineralisation (p < 0.01). Collectively, these results provide the first evidence that RORα can promote odontoblastic differentiation of DPCs and mediate the pro-odontogenic effect of melatonin.

FACEts of mechanical regulation in the morphogenesis of craniofacial structures

During embryonic development, organs undergo distinct and programmed morphological changes as they develop into their functional forms. While genetics and biochemical signals are well recognized regulators of morphogenesis, mechanical forces and the physical properties of tissues are now emerging as integral parts of this process as well. These physical factors drive coordinated cell movements and reorganizations, shape and size changes, proliferation and differentiation, as well as gene expression changes, and ultimately sculpt any developing structure by guiding correct cellular architectures and compositions. In this review we focus on several craniofacial structures, including the tooth, the mandible, the palate, and the cranium. We discuss the spatiotemporal regulation of different mechanical cues at both the cellular and tissue scales during craniofacial development and examine how tissue mechanics control various aspects of cell biology and signaling to shape a developing craniofacial organ.

HDAC6 Regulates the Fusion of Autophagosome and Lysosome to Involve in Odontoblast Differentiation

Odontoblast differentiation is an important process during tooth development in which pre-odontoblasts undergo elongation, polarization, and finally become mature secretory odontoblasts. Many factors have been found to regulate the process, and our previous studies demonstrated that autophagy plays an important role in tooth development and promotes odontoblastic differentiation in an inflammatory environment. However, it remains unclear how autophagy is modulated during odontoblast differentiation. In this study, we found that HDAC6 was involved in odontoblast differentiation. The odontoblastic differentiation capacity of human dental papilla cells was impaired upon HDAC6 inhibition. Moreover, we found that HDAC6 and autophagy exhibited similar expression patterns during odontoblast differentiation both in vivo and in vitro; the expression of HDAC6 and the autophagy related proteins ATG5 and LC3 increased as differentiation progressed. Upon knockdown of HDAC6, LC3 puncta were increased in cytoplasm and the autophagy substrate P62 was also increased, suggesting that autophagic flux was affected in human dental papilla cells. Next, we determined the mechanism during odontoblastic differentiation and found that the HDAC6 substrate acetylated-Tubulin was up-regulated when HDAC6 was knocked down, and LAMP2, LC3, and P62 protein levels were increased; however, the levels of ATG5 and Beclin1 showed no obvious change. Autophagosomes accumulated while the number of autolysosomes was decreased as determined by mRFP-GFP-LC3 plasmid labeling. This suggested that the fusion between autophagosomes and lysosomes was blocked, thus affecting the autophagic process during odontoblast differentiation. In conclusion, HDAC6 regulates the fusion of autophagosomes and lysosomes during odontoblast differentiation. When HDAC6 is inhibited, autophagosomes can't fuse with lysosomes, autophagy activity is decreased, and it leads to down-regulation of odontoblastic differentiation capacity. This provides a new perspective on the role of autophagy in odontoblast differentiation.

Simultaneous Fluorescent Identification of Odontoblasts and Ameloblasts

The tooth is mainly composed of dentin and enamel. Identification of dentin-producing odontoblasts and enamel-producing ameloblasts using reporter techniques is useful to study tooth development and regeneration with tissue engineering. Ameloblasts express Amelogenin, Ameloblastin, Enamelin, and Amelotin, whereas odontoblasts express Dentin sialophosphoprotein (Dspp) and Dentin matrix protein1 (Dmp1). Although there are several transgenic lines using promoter elements or bacterial artificial chromosomes (BACs) to label odontoblasts and ameloblasts, there is a possibility that the expression patterns vary from the endogenous genes. Here, we established 2 lines of mice where tdTomato was knocked into the second exon of X-chromosomal Amelogenin (Amelx), and green fluorescent protein (GFP) was knocked into the second exon of Dspp. tdTomato and GFP were highly expressed on secretory ameloblasts and secretory and fully differentiated odontoblasts, respectively. In addition, DSPP and AMELX were not produced in the dentin matrix and enamel matrix of Dspp^GFP/GFP and Amelx^tdTomato male mice (as representative of Amelx^tdTomato/Y hemizygous male mice), respectively. Moreover, micro-computed tomography analysis of Amelx^tdTomato male mice revealed a notable reduction in enamel volume but increased dentin mineral density. Dspp^GFP/GFP mice had reduced dentin mineral density. To identify odontoblasts and ameloblasts from developing tooth, we examined the expression of mesenchymal cell surface molecules CD90, CD166 and epithelial cell surface molecules CD49f, Epcam1 with fluorescence on odontoblasts and ameloblasts in these mice. We found that GFP⁺ odontoblasts and tdTomato⁺ ameloblasts in tooth germ from 0.5-d-old Dspp^GFP/+ mice and Amelx^tdTomato male mice were enriched in CD45^-/Ter119^-/Epcam1^-/CD90⁺/Integrin α4⁺cell fractions and CD45^-/Ter119^-/Epcam1⁺/CD49f⁺/CD147⁺ cell fractions, respectively. By using antibodies against mesenchymal and epithelial cell surface molecules and fluorescence, we can easily distinguish odontoblasts from ameloblasts and isolate each cell for further studies. These mice would serve as useful models for tooth development and regeneration as well as provide concurrent observation for the differentiation processes of odontoblasts and ameloblasts in vivo and in vitro.

Dental Pulp Mesenchymal Stem Cells as a Treatment for Periodontal Disease in Older Adults

Periodontal disease (PD) is one of the main causes of tooth loss and is related to oxidative stress and chronic inflammation. Although different treatments have been proposed in the past, the vast majority do not regenerate lost tissues. In this sense, the use of dental pulp mesenchymal stem cells (DPMSCs) seems to be an alternative for the regeneration of periodontal bone tissue. A quasi-experimental study was conducted in a sample of 22 adults between 55 and 64 years of age with PD, without uncontrolled systemic chronic diseases. Two groups were formed randomly: (i) experimental group (EG) n = 11, with a treatment based on DPMSCs; and a (ii) control group (CG) n = 11, without a treatment of DPMSCs. Every participant underwent clinical and radiological evaluations and measurement of bone mineral density (BMD) by tomography. Saliva samples were taken as well, to determine the total concentration of antioxidants, superoxide dismutase (SOD), lipoperoxides, and interleukins (IL), before and 6 months after treatment. All subjects underwent curettage and periodontal surgery, the EG had a collagen scaffold treated with DPMSCs, while the CG only had the collagen scaffold placed. The EG with DPMSCs showed an increase in the BMD of the alveolar bone with a borderline statistical significance (baseline 638.82 ± 181.7 vs. posttreatment 781.26 ± 162.2 HU, p = 0.09). Regarding oxidative stress and inflammation markers, salivary SOD levels were significantly higher in EG (baseline 1.49 ± 0.96 vs. 2.14 ± 1.12 U/L posttreatment, p < 0.05) meanwhile IL1β levels had a decrease (baseline 1001.91 ± 675.5vs. posttreatment 722.3 ± 349.4 pg/ml, p < 0.05). Our findings suggest that a DPMSCs treatment based on DPMSCs has both an effect on bone regeneration linked to an increased SOD and decreased levels of IL1β in aging subjects with PD.

FAM20B-catalyzed glycosaminoglycans control murine tooth number by restricting FGFR2b signaling

BACKGROUND

The formation of supernumerary teeth is an excellent model for studying the molecular mechanisms that control stem/progenitor cell homeostasis needed to generate a renewable source of replacement cells and tissues. Although multiple growth factors and transcriptional factors have been associated with supernumerary tooth formation, the regulatory inputs of extracellular matrix in this regenerative process remains poorly understood.

RESULTS

In this study, we present evidence that disrupting glycosaminoglycans (GAGs) in the dental epithelium of mice by inactivating FAM20B, a xylose kinase essential for GAG assembly, leads to supernumerary tooth formation in a pattern reminiscent of replacement teeth. The dental epithelial GAGs confine murine tooth number by restricting the homeostasis of Sox2(+) dental epithelial stem/progenitor cells in a non-autonomous manner. FAM20B-catalyzed GAGs regulate the cell fate of dental lamina by restricting FGFR2b signaling at the initial stage of tooth development to maintain a subtle balance between the renewal and differentiation of Sox2(+) cells. At the later cap stage, WNT signaling functions as a relay cue to facilitate the supernumerary tooth formation.

CONCLUSIONS

The novel mechanism we have characterized through which GAGs control the tooth number in mice may also be more broadly relevant for potentiating signaling interactions in other tissues during development and tissue homeostasis.

The inhibition of glycosaminoglycan incorporation influences the cell proliferation and cytodifferentiation in cultured embryonic mouse molars

The extracellular matrix (ECM) contains a variety of complex macromolecules including proteoglycans (PGs) and glycosaminoglycans (GAGs). PG consists of a protein core with covalently attached carbohydrate side chains called GAGs. Several PGs, including versican, biglycan, decorin and syndecan are involved in odontogenesis while the role of GAGs in those PGs in this process remains unclarified. The purpose of this study was to investigate the influence of GAGs on tooth development. The mandibular first molars at early bell stage were cultivated with or without 4-methylumbelliferyl-β-D-xyloside (Xyl-MU). The cultured tooth germs were metabolically labelled with [³⁵S] Na₂SO₄, then PGs in tooth germs and cultured medium were extracted separately and analyzed by gel filtration. Morphological changes were evaluated on days 2, 4, 6, and histological changes were examined by hematoxylin-eosin (HE) staining and transmission electron microscope (TEM). Related proteins and genes of cytodifferentiation were further examined by immunohistochemistry (IHC) and quantitive real-time PCR (qPCR) respectively. Meanwhile, BrdU incorporation assay was used to explore the effect of Xyl-MU on the cell proliferation of cultured tooth germs. The results demonstrated that the incorporation of GAGs to PGs in cultured tooth germs was heavily inhibited by Xyl-MU. Accompanied by the inhibition of GAGs incorporation, Xyl-MU altered tooth morphogenesis and delayed the differentiation of ameloblasts and odontoblasts. Proliferation of inner enamel epithelium (IEE) was also inhibited. Therefore, we draw a conclusion that the inhibition of GAGs incorporation influences the cell proliferation and cytodifferentiation in cultured embryonic mouse molars.

Autophagy in the dentin-pulp complex against inflammation

The dentin-pulp complex is a highly specialized tissue for protecting the dental pulp. Odontoblasts are long-lived, hard-tissue-forming cells in the dentin-pulp complex and critically involved in inflammatory responses against invading pathogens. Autophagy is a highly conserved homeostasis mechanism of living cells under various stress conditions. Growing evidence in the literature addresses the role of autophagy in odontoblast differentiation and aging. This review summarizes the current knowledge about autophagy for the dentin-pulp complex in resisting inflammation.

Bone resorption deficiency affects tooth root development in RANKL mutant mice due to attenuated IGF-1 signaling in radicular odontoblasts

The tooth root is essential for normal tooth physiological function. Studies on mice with mutations or targeted gene deletions revealed that osteoclasts (OCs) play an important role in tooth root development. However, knowledge on the cellular and molecular mechanism underlying how OCs mediate root formation is limited. During bone formation, growth factors (e.g. Insulin-like growth factor-1, IGF-1) liberated from bone matrix by osteoclastic bone resorption stimulate osteoblast differentiation. Thus, we hypothesize that OC-osteoblast coupling may also apply to OC-odontoblast coupling; therefore OCs may have a direct impact on odontoblast differentiation through the release of growth factor(s) from bone matrix, and consequently regulate tooth root formation. To test this hypothesis, we used a receptor activator of NF-κB ligand (RANKL) knockout mouse model in which OC differentiation and function was entirely blocked. We found that molar root formation and tooth eruption were defective in RANKL^-/- mice. Disrupted elongation and disorganization of Hertwig's epithelial root sheath (HERS) was observed in RANKL^-/- mice. Reduced expression of nuclear factor I C (NFIC), osterix, and dentin sialoprotein, markers essential for radicular (root) odontogenic cell differentiation indicated that odontoblast differentiation was disrupted in RANKL deficient mice likely contributing to the defect in root formation. Moreover, down-regulation of IGF/AKT/mTOR activity in odontoblast indicated that IGF signaling transduction in odontoblasts of the mutant mice was impaired. Treating odontoblast cells in vitro with conditioned medium from RANKL^-/- OCs cultured on bone slices resulted in inhibition of odontoblast differentiation. Moreover, depletion of IGF-1 in bone resorption-conditioned medium (BRCM) from wild-type (WT) OC significantly compromised the ability of WT osteoclastic BRCM to induce odontoblast differentiation while addition of IGF-1 into RANKL^-/- osteoclastic BRCM rescued impaired odontoblast differentiation, confirming that root and eruption defect in RANKL deficiency mice may result from failure of releasing of IGF-1 from bone matrix through OC bone resorption. These results suggest that OCs are important for odontoblast differentiation and tooth root formation, possibly through IGF/AKT/mTOR signaling mediated by cell-bone matrix interaction. These findings provide significant insights into regulatory mechanism of tooth root development, and also lay the foundation for root regeneration studies.

The Role of Fibroblast Growth Factors in Tooth Development and Incisor Renewal

The mineralized tissue of the tooth is composed of enamel, dentin, cementum, and alveolar bone; enamel is a calcified tissue with no living cells that originates from oral ectoderm, while the three other tissues derive from the cranial neural crest. The fibroblast growth factors (FGFs) are critical during the tooth development. Accumulating evidence has shown that the formation of dental tissues, that is, enamel, dentin, and supporting alveolar bone, as well as the development and homeostasis of the stem cells in the continuously growing mouse incisor is mediated by multiple FGF family members. This review discusses the role of FGF signaling in these mineralized tissues, trying to separate its different functions and highlighting the crosstalk between FGFs and other signaling pathways.

Inhibition of chondroitin sulfate glycosaminoglycans incorporation affected odontoblast differentiation in cultured embryonic mouse molars

Chondroitin sulfate proteoglycan (CSPG) is an important component of extracellular matrix (ECM), it is composed of a core protein and one or more chondroitin sulfate glycosaminoglycan side chains (CS-GAGs). To investigate the roles of its CS-GAGs in dentinogenesis, the mouse mandibular first molar tooth germs at early bell stage were cultivated with or without β-xyloside. As expected, the CS-GAGs were inhibited on their incorporation to CSPGs by β-xyloside, accompanied by the change of morphology of the cultured tooth germs. The histological results and the transmission electron microscopy (TEM) investigation indicated that β-xyloside exhibited obvious inhibiting effects on odontoblasts differentiation compared with the control group. Meanwhile the results of immunohistochemistry, in situ hybridization and quantitative RT-PCR for type I collagen, dentin matrix acidic phosphoprotein 1 and dentin sialophosphoprotein, the products of differentiated odontoblasts, further proved that odontoblasts differentiation was inhibited. Collagen fibers detected in TEM decreased and arranged in disorder as well. Thus we conclude that the inhibition of CS-GAGs incorporation to CSPGs can affect odontoblast differentiation in cultured embryonic mouse molars.

Nonsyndromic oligodontia : Does the Tooth Agenesis Code (TAC) enable prediction of the causative mutation?

OBJECTIVES

The literature suggests an association between phenotype and causative mutation in nonsyndromic oligodontia. Thus, the present study was designed to verify this hypothesis in a consecutive cohort of patients.

METHODS

All patients with nonsyndromic oligodontia who had been treated at the study center (Department of Orthodontics, University of Giessen, Germany) over the period 1986-2013 were contacted. Candidates were included only if at least one more family member had hypo- or oligodontia (i.e., without regard to the number of congenitally missing teeth). A total of 20 patients were included. After evaluating the dental status of each participant, the Tooth Agenesis Code (TAC) was applied. On this basis, a tentative diagnosis was made to predict which gene (MSX1, AXIN2, EDA, or PAX9) was likely to show mutation. Afterwards this hypothesis was confirmed or rejected by analyzing a saliva sample for mutation of the predicted gene. If confirmed, any available family members were also genetically analyzed.

RESULTS

Based on their TAC scores and sums, gene mutations were predicted for MXS1 in 11, AXIN2 in 3, EDA in 6, and PAX9 in none of the patients. The evaluation of MSX1 yielded variants in 4 of 11 cases, all of which were classified as nonpathogenic since they were not considered as functional mutations. The evaluation of EDA yielded a pathogenic exon-7 mutation in 2 of 6 patients, both being brothers with different TAC scores; the same mutation, which represents a novel missense mutation, was also found in other members of the same family. The evaluation of AXIN2 yielded variants in 3 of 3 cases, all of which were classified as nonpathogenic.

CONCLUSIONS

Our findings obtained in consecutive patients with nonsyndromic oligodontia did not reveal any clinically relevant associations between oligodontia phenotype (based on TAC) and causative mutations for nonsyndromic oligodontia.

Novel Mutation of the Initiation Codon of PAX9 Causes Oligodontia

Tooth development is under strict genetic control. Oligodontia is defined as the congenital absence of 6 or more permanent teeth, excluding the third molar. The occurrence of non-syndromic oligodontia is poorly understood, but in recent years several cases have been described where a single gene mutation is associated with oligodontia. Several studies have shown that MSX1 and PAX9 play a role in early tooth development. We screened one family with non-syndromic oligodontia for mutations in MSX1 and PAX9. The pedigree showed an autosomal-dominant pattern of inheritance. Direct sequencing and restriction enzyme analysis revealed a novel heterozygous A to G transition mutation in the AUG initiation codon of PAX9 in exon 1 in the affected members of the family. This is the first mutation found in the initiation codon of PAX9, and we suggest that it causes haploinsufficiency.

Prevalence of delayed tooth development and its relation to tooth agenesis in Korean children

OBJECTIVE

The aim of this study was to investigate the epidemiology of delayed tooth development (DTD) and the link between DTD and tooth agenesis (TA).

DESIGN

The dental maturity of all of the developing permanent teeth of 4611 children (2417 males and 2194 females) was evaluated from panoramic radiographs. The prevalence of DTD and TA was analyzed, and gender difference for DTS and TA was investigated. The correlation of DTD and TA was investigated in intra-fields and inter-fields.

RESULTS

The total prevalence of DTD among the 4611 children was 3.40%. The maxillary second premolar was the most frequently delayed tooth (1.02%), followed by the maxillary second molar (0.88%) and the mandibular second premolar (0.74%). DTD significantly correlated with TA in both intra-fields and inter-fields (p<0.05).

CONCLUSIONS

The field of delayed development exhibited a significant correlation with that of TA.

The Neurovascular Properties of Dental Stem Cells and Their Importance in Dental Tissue Engineering

Within the field of tissue engineering, natural tissues are reconstructed by combining growth factors, stem cells, and different biomaterials to serve as a scaffold for novel tissue growth. As adequate vascularization and innervation are essential components for the viability of regenerated tissues, there is a high need for easily accessible stem cells that are capable of supporting these functions. Within the human tooth and its surrounding tissues, different stem cell populations can be distinguished, such as dental pulp stem cells, stem cells from human deciduous teeth, stem cells from the apical papilla, dental follicle stem cells, and periodontal ligament stem cells. Given their straightforward and relatively easy isolation from extracted third molars, dental stem cells (DSCs) have become an attractive source of mesenchymal-like stem cells. Over the past decade, there have been numerous studies supporting the angiogenic, neuroprotective, and neurotrophic effects of the DSC secretome. Together with their ability to differentiate into endothelial cells and neural cell types, this makes DSCs suitable candidates for dental tissue engineering and nerve injury repair.

Progress in Bioengineered Whole Tooth Research: From Bench to Dental Patient Chair

Tooth loss is a significant health issue that affects the physiological and social aspects of everyday life. Missing teeth impair simple tasks of chewing and speaking, and can also contribute to reduced self-confidence. An emerging and exciting area of regenerative medicine based dental research focuses on the formation of bioengineered whole tooth replacement therapies that can provide both the function and sensory responsiveness of natural teeth. This area of research aims to enhance the quality of dental and oral health for those suffering from tooth loss. Current approaches use a combination of dental progenitor cells, scaffolds and growth factors to create biologically based replacement teeth to serve as improved alternatives to currently used artificial dental prosthetics. This article is an overview of current progress, challenges, and future clinical applications of bioengineered whole teeth.

Mannose 6-phosphate-dependent targeting of lysosomal enzymes is required for normal craniofacial and dental development

Mucolipidosis II (MLII) is a severe systemic genetic disorder caused by defects in mannose 6-phosphate-dependent targeting of multiple lysosomal hydrolases and subsequent lysosomal accumulation of non-degraded material. MLII patients exhibit marked facial coarseness and gingival overgrowth soon after birth, accompanied with delayed tooth eruption and dental infections. To examine the pathomechanisms of early craniofacial and dental abnormalities, we analyzed mice with an MLII patient mutation that mimic the clinical and biochemical symptoms of MLII patients. The mouse data were compared with clinical and histological data of gingiva and teeth from MLII patients. Here, we report that progressive thickening and porosity of calvarial and mandibular bones, accompanied by elevated bone loss due to 2-fold higher number of osteoclasts cause the characteristic craniofacial phenotype in MLII. The analysis of postnatal tooth development by microcomputed tomography imaging and histology revealed normal dentin and enamel formation, and increased cementum thickness accompanied with accumulation of storage material in cementoblasts of MLII mice. Massive accumulation of storage material in subepithelial cells as well as disorganization of collagen fibrils led to gingival hypertrophy. Electron and immunofluorescence microscopy, together with (35)S-sulfate incorporation experiments revealed the accumulation of non-degraded material, non-esterified cholesterol and glycosaminoglycans in gingival fibroblasts, which was accompanied by missorting of various lysosomal proteins (α-fucosidase 1, cathepsin L and Z, Npc2, α-l-iduronidase). Our study shows that MLII mice closely mimic the craniofacial and dental phenotype of MLII patients and reveals the critical role of mannose 6-phosphate-dependent targeting of lysosomal proteins for alveolar bone, cementum and gingiva homeostasis.

Structural and Morphometric Comparison of Lower Incisors in PACAP-Deficient and Wild-Type Mice

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with widespread distribution. PACAP plays an important role in the development of the nervous system, it has a trophic and protective effect, and it is also implicated in the regulation of various physiological functions. Teeth are originated from the mesenchyme of the neural crest and the ectoderm of the first branchial arch, suggesting similarities with the development of the nervous system. Earlier PACAP-immunoreactive fibers have been found in the odontoblastic and subodontoblastic layers of the dental pulp. Our previous examinations have shown that PACAP deficiency causes alterations in the morphology and structure of the developing molars of 7-day-old mice. In our present study, morphometric and structural comparison was performed on the incisors of 1-year-old wild-type and PACAP-deficient mice. Hard tissue density measurements and morphometric comparison were carried out on the mandibles and the lower incisors with micro-CT. For structural examination, Raman microscopy was applied on frontal thin sections of the mandible. With micro-CT morphometrical measurements, the size of the incisors and the relative volume of the pulp to dentin were significantly smaller in the PACAP-deficient group compared to the wild-type animals. The density of calcium hydroxyapatite in the dentin was reduced in the PACAP-deficient mice. No structural differences could be observed in the enamel with Raman microscopy. Significant differences were found in the dentin of PACAP-deficient mice with Raman microscopy, where increased carbonate/phosphate ratio indicates higher intracrystalline disordering. The evaluation of amide III bands in the dentin revealed higher structural diversity in wild-type mice. Based upon our present and previous results, it is obvious that PACAP plays an important role in tooth development with the regulation of morphogenesis, dentin, and enamel mineralization. Further studies are required to clarify the molecular background of the effects of PACAP on tooth development.

Autophagy regulates odontoblast differentiation by suppressing NF-κB activation in an inflammatory environment

Odontoblasts are derived from dental papilla mesenchymal cells and have an important role in defense against bacterial infection, whereas autophagy can recycle long-lived proteins and damaged organelles to sustain cellular homeostasis. Thus, this study explores the role of autophagy in odontoblast differentiation with lipopolysaccharide (LPS) stimulation in vitro and the colocalization of p-NF-κB and LC3 in caries teeth. The odontoblasts differentiation was enhanced through LPS stimulation, and this outcome was reflected in the increased number of mineralized nodules and alkaline phosphatase (ALP) activity. The expression levels of the autophagy markers LC3, Atg5, Beclin1 and TFE3 increased time dependently, as well along with the amount of autophagosomes and autophagy fluxes. This result suggests that autophagy was enhanced in odontoblasts cultured with mineralized-induced media containing LPS. To confirm the role of autophagy in differentiated odontoblasts with LPS stimulation, chloroquine (CQ) or rapamycin were used to either block or enhance autophagy. The number of mineralized nodules decreased when autophagy was inhibited, but this number increased with rapamycin treatment. Phosphorylated nuclear factor-κB (NF-κB) expression was negatively related to autophagy and could inhibit odontoblast differentiation. Furthermore, p-NF-κB and LC3 colocalization could be detected in cells stimulated with LPS. The nucleus translocation of p-NF-κB in odontoblasts was enhanced when autophagy was inhibited by Atg5 small interfering RNA. In addition, the colocalization of p-NF-κB and LC3 in odontoblasts and sub-odontoblastic layers was observed in caries teeth with reactionary dentin. Therefore, our findings provide a novel insight into the role of autophagy in regulating odontoblast differentiation by suppressing NF-κB activation in inflammatory environments.

Redefining the induction of periodontal tissue regeneration in primates by the osteogenic proteins of the transforming growth factor-β supergene family

The molecular bases of periodontal tissue induction and regeneration are the osteogenic proteins of the transforming growth factor-β (TGF-β) supergene family. These morphogens act as soluble mediators for the induction of tissues morphogenesis sculpting the multicellular mineralized structures of the periodontal tissues with functionally oriented ligament fibers into newly formed cementum. Human TGF-β₃ (hTGF-β₃ ) in growth factor-reduced Matrigel^® matrix induces cementogenesis when implanted in class II mandibular furcation defects surgically prepared in the non-human primate Chacma baboon, Papio ursinus. The newly formed periodontal ligament space is characterized by running fibers tightly attached to the cementoid surface penetrating as mineralized constructs within the newly formed cementum assembling and initiating within the mineralized dentine. Angiogenesis heralds the newly formed periodontal ligament space, and newly sprouting capillaries are lined by cellular elements with condensed chromatin interpreted as angioblasts responsible for the rapid and sustained induction of angiogenesis. The inductive activity of hTGF-β₃ in Matrigel^® matrix is enhanced by the addition of autogenous morcellated fragments of the rectus abdominis muscle potentially providing myoblastic, pericytic/perivascular stem cells for continuous tissue induction and morphogenesis. The striated rectus abdominis muscle is endowed with stem cell niches in para/perivascular location, which can be dominant, thus imposing stem cell features or stemness to the surrounding cells. This capacity to impose stemness is morphologically shown by greater alveolar bone induction and cementogenesis when hTGF-β₃ in Matrigel^® matrix is combined with morcellated fragments of autogenous rectus abdominis muscle. The induction of periodontal tissue morphogenesis develops as a mosaic structure in which the osteogenic proteins of the TGF-β supergene family singly, synergistically and synchronously initiate and maintain tissue induction and morphogenesis. In primates, the presence of several homologous yet molecularly different isoforms with osteogenic activity highlights the biological significance of this apparent redundancy and indicates multiple interactions during embryonic development and bone regeneration in postnatal life. Molecular redundancy with associated different biological functionalities in primate tissues may simply represent the fine-tuning of speciation-related molecular evolution in anthropoid apes at the early Pliocene boundary, which resulted in finer tuning of the bone induction cascade.

Twist1 Is Essential for Tooth Morphogenesis and Odontoblast Differentiation

Twist1 is a basic helix-loop-helix-containing transcription factor that is expressed in the dental mesenchyme during the early stages of tooth development. To better delineate its roles in tooth development, we generated Twist1 conditional knockout embryos (Twist2(Cre) (/+);Twist1(fl/fl)) by breeding Twist1 floxed mice (Twist1(fl/fl)) with Twist2-Cre recombinase knockin mice (Twist2(Cre) (/+)). The Twist2(Cre) (/+);Twist1(fl/fl) embryos formed smaller tooth germs and abnormal cusps during early tooth morphogenesis. Molecular and histological analyses showed that the developing molars of the Twist2(Cre) (/+);Twist1(fl/fl) embryos had reduced cell proliferation and expression of fibroblast growth factors 3, 4, 9, and 10 and FGF receptors 1 and 2 in the dental epithelium and mesenchyme. In addition, 3-week-old renal capsular transplants of embryonic day 18.5 Twist2(Cre) (/+);Twist1(fl/fl) molars showed malformed crowns and cusps with defective crown dentin and enamel. Immunohistochemical analyses revealed that the implanted mutant molars had defects in odontoblast differentiation and delayed ameloblast differentiation. Furthermore, in vitro ChIP assays demonstrated that Twist1 was able to bind to a specific region of the Fgf10 promoter. In conclusion, our findings suggest that Twist1 plays crucial roles in regulating tooth development and that it may exert its functions through the FGF signaling pathway.

Hypodontia prevalence and distribution pattern in a group of Qatari orthodontic and pediatric patients: A retrospective study

OBJECTIVES

The aim of this study was to investigate the prevalence and distribution of hypodontia in the permanent teeth among a group of the Qatari sample and to compare the present results with findings from other populations.

MATERIALS AND METHODS

Records of 1269 Qatari patients (674 females; mean age 11.8 ± 2.3 and 595 males; mean age 11.4 ± 2.2) which included panoramic radiographs were examined to identify hypodontia. All permanent teeth were investigated except third molars.

RESULTS

The prevalence of hypodontia was 6.2% (females 8% and males 4.2%; P < 0.05). The majority of patients had one or two missing teeth. There were no significant differences between right and left sides for any particular tooth. The most frequently missing teeth were maxillary lateral incisors (36.2%), followed by mandibular second premolar (32.6%) and maxillary second premolar (20.2%). Hypodontia was more commonly found unilaterally than bilaterally (63.2% and 44.3%; respectively).

CONCLUSIONS

The prevalence of hypodontia in a group of the Qatari population was within the average value of the majority of published studies in the literature. Hypodontia was significantly more prevalent in females. Although less prevalent, considerable cases of bilateral missing were found in the present study, which necessitates the urgent need for intervention and multi-disciplinary team approach for management.

The specific role of FAM20C in dentinogenesis

FAM20C is an evolutionarily reserved molecule highly expressed in mineralized tissues. Previously we demonstrated that Sox2-Cre;Fam20C(fl/fl) mice, in which Fam20C was ubiquitously inactivated, had dentin and enamel defects as well as hypophosphatemic rickets. We also showed that K14-Cre;Fam20C(fl/fl) mice, in which Fam20C was specifically inactivated in the epithelium, had enamel defects but lacked hypophosphatemia and defects in the bone and dentin. These results indicated that the enamel defects in the Sox2-Cre;Fam20C(fl/fl) mice were independent of dentin defects and hypophosphatemia. To determine if the dentin defects in the Sox2-Cre;Fam20C(fl/fl) mice were associated with the enamel defects and hypophosphatemia, we crossed Fam20C(fl/fl) mice with Wnt1-Cre and Osr2-Cre transgenic mice to inactivate Fam20C in the craniofacial mesenchymal cells that form dentin and alveolar bone. The resulting Wnt1-Cre;Fam20C(fl/fl) and Osr2-Cre;Fam20C(fl/fl) mice showed remarkable dentin and alveolar bone defects, while their enamel did not show apparent defects. The serum FGF23 levels in these mice were higher than normal but lower than those in the Sox2-Cre;Fam20C(fl/fl) mice; they developed a mild type of hypophosphatemia that did not cause major defects in long bones. These results indicate that the dentin defects in the Sox2-Cre;Fam20C(fl/fl) mice were independent of the enamel defects.

A pituitary homeobox 2 (Pitx2):microRNA-200a-3p:β-catenin pathway converts mesenchymal cells to amelogenin-expressing dental epithelial cells

Pitx2, Wnt/β-catenin signaling, and microRNAs (miRs) play a critical role in the regulation of dental stem cells during embryonic development. In this report, we have identified a Pitx2:β-catenin regulatory pathway involved in epithelial cell differentiation and conversion of mesenchymal cells to amelogenin expressing epithelial cells via miR-200a. Pitx2 and β-catenin are expressed in the labial incisor cervical loop or epithelial stem cell niche, with decreased expression in the differentiating ameloblast cells of the mouse lower incisor. Bioinformatics analyses reveal that miR-200a-3p expression is activated in the pre-ameloblast cells to enhance epithelial cell differentiation. We demonstrate that Pitx2 activates miR-200a-3p expression and miR-200a-3p reciprocally represses Pitx2 and β-catenin expression. Pitx2 and β-catenin interact to synergistically activate gene expression during odontogenesis and miR-200a-3p attenuates their expression and directs differentiation. To understand how this mechanism controls cell differentiation and cell fate, oral epithelial and odontoblast mesenchymal cells were reprogrammed by a two-step induction method using Pitx2 and miR-200a-3p. Conversion to amelogenin expressing dental epithelial cells involved an up-regulation of the stem cell marker Sox2 and proliferation genes and decreased expression of mesenchymal markers. E-cadherin expression was increased as well as ameloblast specific factors. The combination of Pitx2, a regulator of dental stem cells and miR-200a converts mesenchymal cells to a fully differentiated dental epithelial cell type. This pathway and reprogramming can be used to reprogram mesenchymal or oral epithelial cells to dental epithelial (ameloblast) cells, which can be used in tissue repair and regeneration studies.

Hypodontia prevalence and pattern in women with epithelial ovarian cancer

OBJECTIVE

To analyze the possible association between hypodontia and epithelial ovarian cancer (EOC), with the special interest in hypodontia pattern.

MATERIALS AND METHODS

One hundred twenty women with EOC treated at the Department of Gynecologic and Breast Oncology at the University Clinical Centre and 120 gynecologically healthy women of the same average age were reviewed for the presence and pattern of hypodontia. Collected data were analyzed for frequency, tooth type, location per jaw and side, number of missing teeth per person, and family history of hypodontia.

RESULTS

The results of the study showed prevalence of hypodontia in 19.2% of women with EOC and in 6.7% of women in the control group (P  =  .004). The most frequently missing teeth for women with EOC and women in the control group were maxillary second premolars and maxillary lateral incisors, respectively. Unilateral occurrence of hypodontia was more common than bilateral occurrence in women with EOC (P  =  .034). Of women with EOC and hypodontia, 21.7% reported a positive family history of hypodontia compared with no report in the control group of women with hypodontia (P  =  .150).

CONCLUSIONS

The results statistically support possible association between EOC and hypodontia. Because hypdontia can be recognized early in life, this finding could possibly help in earlier detection of EOC, resulting in better prognosis and treatment in earlier stages of the disease. Earlier EOC diagnosis and treatment could save many lives.

Mechanical forces induce odontoblastic differentiation of mesenchymal stem cells on three-dimensional biomimetic scaffolds

The mechanical induction of cell differentiation is well known. However, the effect of mechanical compression on odontoblastic differentiation remains to be elucidated. Thus, we first determined the optimal conditions for the induction of human dental pulp stem cells (hDPSCs) into odontoblastic differentiation in response to mechanical compression of three-dimensional (3D) scaffolds with dentinal tubule-like pores. The odontoblastic differentiation was evaluated by gene expression and confocal laser microscopy. The optimal conditions, which were: cell density, 4.0 × 10⁵ cells/cm² ; compression magnitude, 19.6 kPa; and loading time, 9 h, significantly increased expression of the odontoblast-specific markers dentine sialophosphoprotein (DSPP) and enamelysin and enhanced the elongation of cellular processes into the pores of the membrane, a typical morphological feature of odontoblasts. In addition, upregulation of bone morphogenetic protein 7 (BMP7) and wingless-type MMTV integration site family member 10a (Wnt10a) was observed. Moreover, the phosphorylation levels of mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 were also enhanced by mechanical compression, indicating the involvement of the MAPK signalling pathway. It is noteworthy that human mesenchymal stem cells (MSCs) derived from bone marrow and amnion also differentiated into odontoblasts in response to the optimal mechanical compression, demonstrating the importance of the physical structure of the scaffold in odontoblastic differentiation. Thus, odontoblastic differentiation of hDPSCs is promoted by optimal mechanical compression through the MAPK signalling pathway and expression of the BMP7 and Wnt10a genes. The 3D biomimetic scaffolds with dentinal tubule-like pores were critical for the odontoblastic differentiation of MSCs induced by mechanical compression. Copyright © 2014 John Wiley & Sons, Ltd.