Zebrafish sp7 mutants show tooth cycling independent of attachment, eruption and poor differentiation of teeth.

The capacity to fully replace teeth continuously makes zebrafish an attractive model to explore regeneration and tooth development. The requirement of attachment bone for the appearance of replacement teeth has been hypothesized but not yet investigated. The transcription factor sp7 (osterix) is known in mammals to play an important role during odontoblast differentiation and root formation. Here we study tooth replacement in the absence of attachment bone using sp7 zebrafish mutants. We analysed the pattern of tooth replacement at different stages of development and demonstrated that in zebrafish lacking sp7, attachment bone is never present, independent of the stage of tooth development or fish age, yet replacement is not interrupted. Without bone of attachment we observed abnormal orientation of teeth, and abnormal connection of pulp cavities of predecessor and replacement teeth. Mutants lacking sp7 show arrested dentinogenesis, with non-polarization of odontoblasts and only a thin layer of dentin deposited. Osteoclast activity was observed in sp7 mutants; due to the lack of bone of attachment, remodelling was diminished but nevertheless present along the pharyngeal bone. We conclude that tooth replacement is ongoing in the sp7 mutant despite poor differentiation and defective attachment. Without bone of attachment tooth orientation and pulp organization are compromised.

Deficiency of the DSPP-cleaving enzymes meprin α and meprin ß does not result in dentin malformation in mice.

Formation of dentin requires the maturation of procollagen I and the proteolytic processing of the dentin sialophosphoprotein (DSPP). These cleavage events can be facilitated by the metalloproteinases meprin α and meprin ß as well as by bone morphogenetic protein 1 (BMP-1). All three enzymes have been shown to play important roles during collagen I maturation in vivo and their potential in cleaving DSPP was demonstrated in vitro. Hence, it has been discussed whether meprin α, meprin ß, BMP-1 or all three are crucial factors in the onset and progression of dentin-related diseases and this issue is addressed here. In this study, we compare the incisors and molars of meprin α (Mep1a -/-)- and meprin ß (Mep1b -/-)-deficient mice with wild-type (WT) controls on the macroscopic and microscopic level. The dentin was evaluated towards the bone mineral density, dentin volume, calcification and collagen matrix integrity. Using immunohistochemistry, we could identify meprin ß, BMP-1 and DSPP/DSP in the pre-dentin of WT mice. Nevertheless, no significant dentin malformation was observed in Mep1b -/- or Mep1a -/- deficient mice.

Morphological analyses and a novel de novo DLX3 mutation associated with tricho-dento-osseous syndrome in a Chinese family.

Tricho-dento-osseous (TDO) syndrome, an autosomal-dominant disorder, affects the morphological appearance of the tooth enamel, hair, and bone. Previous studies have confirmed that mutations in the DLX3 gene are responsible for TDO. In this study, we describe a Chinese patient with the typical traits of TDO - kinky hair, enamel hypoplasia, skull and jaw bones thickening, and sclerosis. Unfortunately, as a result of excessive attrition, we were unable to assess taurodontism. Examination of the tooth ground section showed a thin layer of enamel with no rods on the patient's tooth and abnormalities in Tomes' granular layer and the dentinal tubules. Scanning electron microscopy and energy-dispersive X-ray spectroscopy of the tooth enamel showed significant differences between the patient and the control individuals. A hair sample from the patient observed under a laser-scanning microscope showed longitudinal grooves in the hair shaft. Dual-energy X-ray absorptiometry measurement showed that the bone mineral density values of the patient's bones was much higher than normal. Finally, genetic analysis revealed a novel de novo missense mutation c.533A>G (p.Q178R) in the conserved homeodomain of the DLX3 gene. This DLX3 mutation is the sixth causative mutation for TDO to be identified so far.

[Late morphological teeth changes in children after chemotherapy].

BACKGROUND: Teeth changes after chemotherapy are of clinical importance, but no morphological studies were conducted on microscopic level. AIM: To assess morphological changes in teeth developing under chemotherapy. MATERIALS AND METHODS: Twenty-nine adolescents aged 13-16 years that received chemotherapy at the age of 2-13 were included in the study. Teeth morphology was evaluated by means of clinical and radiological data as well as microscopy of extracted teeth (n=13). Thirty healthy children aged 13-16 and 8 teeth extracted for orthodontic reasons served as a control. RESULTS: Chemotherapy has arresting impact on teeth development confirmed by aplasia of germs when influenced on stages I-II (p=0.0001), preliminary apexogenesis resulting in shortened roots in teeth at the later stages of growth and development (p=0.01). Enamel and dentine defects usually located in cervical area are also a specific feature, while caries incidence was not higher when compared to control group. CONCLUSION: Children receiving chemotherapy have high risk of secondary teeth loss because of germs aplasia and extraction of severely decayed teeth. Early diagnostics helps to prevent secondary deformations of dental arches by prompt prosthetic rehabilitation. Root morphology changes should be considered by root canal treatment.

[Research progress in regional odontodysplasia].

Regional odontodysplasia (ROD) is a rare localized dental developmental anomaly. The typical clinical manifestations of ROD are abnormal tooth eruption, abnormal development of enamel and dentin. The radiographic characteristic is "ghost teeth". Its etiology still remains unknown. The care and treatment of a patient with ROD needs a multidisciplinary approach. And the treatment should be taken after the assessment of each individual case of ROD. This paper reviews the definition, etiology, epidemiological features, clinical manifestations, imaging features, dental microstructure and treatment strategies of ROD to provide reference for clinical diagnosis and treatment.

Non-surgical endodontic treatment for dens invaginatus type III using cone beam computed tomography and dental operating microscope: a case report.

Dens invaginatus is a morphological abnormality of the tooth in which the coronal tooth enamel and dentin fold inwards towards the pulp cavity. Dens invaginatus type III (Oehlers: 1957) is characterized by infolding of the enamel and dentin as far as the root apex. This report describes a case of surgical and non-surgical endodontic therapy for a maxillary lateral incisor with type III dens invaginatus, necrotic pulp, and an associated large periradicular lesion. The patient was a 16-year-old man. Periapical radiographs suggested the presence of an untreated area of invagination. Cone beam computed tomography (CBCT) was then used for three-dimensional observation of the morphological details of this area. The CBCT scans revealed invagination and its relationship with the pulp chamber. A dental operating microscope was used to access two primary root canals and the area of invagination. The root canals were then localized, negotiated, enlarged, and filled with calcium hydroxide. Two months later, the canal and invagination were obturated with core-based gutta-percha (FlexPoint Neo: FP core-carrier technique) and restored. Cone beam computed tomography and microscopic techniques allow even complicated cases of dens invaginatus to be diagnosed and treated using non-surgical root canal management.

Hyperbilirubinemic stain: location and extent in dental tissues.

OBJECTIVE: The purpose of the present manuscript is to describe the location and extent of hyperbilirubinemic stain in a primary molar of a 3-year-old who was diagnosed with cystic fibrosis shortly after birth, subsequently developed liver disease and hyperbilirubinemia, and received a liver transplant at age 10-months. STUDY DESIGN: Clinical and histological assessments were performed to evaluate the location and extent of hyperbilirubinemic stain in an extracted primary molar. RESULTS: The clinical image, and macroscopic and microscopic histological examinations of a primary molar showed hyperbilirubinemic staining of enamel and of the coronal dentin that developed between birth and when the liver transplant took place, irregular dentin tubules, and an irregular cementum-dentinal junction. CONCLUSIONS: The findings of the present manuscript indicate that hyperbilirubinemc staining of primary teeth affects dental hard tissues at the time of their calcification, and the clinical picture of the stain may be related to stained enamel and/or dentin, and underlying stained dentin visible through translucent unstained enamel.

Oral features in Apert syndrome: a histological investigation.

OBJECTIVES: The number of publications on the oral features in Apert syndrome is limited. The present study investigated dental tissues in Apert syndrome histologically, to determine the nature and extent of anomalies, to provide some insight into the nature of the condition, and to explain how observed anomalies may affect the dental management of individuals with Apert syndrome. SETTING AND SAMPLE POPULATION: Extracted primary and secondary teeth were collected from patients with Apert who had attended the Australian Craniofacial Unit, Adelaide, South Australia. The total study sample comprised 13 individuals, aged from 14 to 21 , with nine men and four women. MATERIAL AND METHODS: A total of 40 teeth were available for histological examination (the number belonging to each individual varied from 2 to 5 per patient). The teeth were sectioned longitudinally, and one-half of each tooth underwent decalcification. Sections were stained with H&E for routine histological examination. Ground sections were prepared from undecalcified tooth halves. RESULTS: Histological assessment of the dental hard tissues revealed an intact enamel and dentinal structure but some irregularities were noted in the region of the dentino-enamel junction (DEJ), which could affect caries progression and also make dental management more difficult. CONCLUSION: This study identified histological anomalies of the DEJ of Apert syndrome teeth. An improved appreciation of the nature and extent of dental anomalies in Apert syndrome should assist clinicians when undertaking management of affected individuals.

Dentinogenesis imperfecta--clinical presentation and management.

UNLABELLED: Dentinogenesis imperfecta (DI) is a hereditary condition which affects the development of dentine in both the primary and permanent dentitions. Three types of DI have been described in the literature. The presentation of DI is variable, depending on the type and severity of the disease. Early intervention in the treatment of a patient with DI is extremely important both for psycho-social and for functional reasons. This paper attempts to describe the clinical presentation and management of DI, and explores its association with certain medical conditions. CLINICAL RELEVANCE: Recognition of DI is important, so that correct treatment principles may be instituted.

[An obscure anomaly: regional odontodysplasia]. / Een spookachtige afwijking: regionale odontodysplasie.

In a 3-year-old child, acute dental abscesses in combination with clinical and radiographic impressions of a number of deciduous teeth indicated regional odontodysplasia as probable diagnosis. Histological examination of the removed deciduous teeth confirmed the diagnosis. Early determination of this regional developmental anomaly in the odontogenesis is of great importance for optimal guidance of the dental care of a patient with regional odontodysplasia.

Full Mouth Rehabilitation of Two Siblings with Dentinogenesis Imperfecta Type II Using Different Treatment Modalities.

BACKGROUND: Dentinogenesis imperfecta (DGI) is a complex anomaly, not only by its structure but by treatment approach. The treatment protocol depends on the severity, behavior, and the age of the patient. CASE DESCRIPTION: This paper presents two siblings' cases of DGI type II (DGI-II) with different treatment based on the patient's clinical severity, behavior, and age (mixed versus primary dentition). The first case involves a patient in the primary dentition with severe attrition leading to a reduction in the vertical dimension of occlusion (VDO) treated by the fabrication of complete overlay dentures. The second case involves a patient in the early mixed dentition treated with restorations and extractions. CONCLUSION: Full mouth rehabilitation in the two patients dramatically improves function, aesthetics, and proved to be a significant psychological boost to the patient's well-being. PRACTICAL IMPLICATIONS: Early diagnosis and a multidisciplinary approach for patients with DGI to preserve the remaining teeth and rehabilitation for their function and aesthetics are essential for obtaining a favorable prognosis.

Disruption of Nfic causes dissociation of odontoblasts by interfering with the formation of intercellular junctions and aberrant odontoblast differentiation.

We reported previously that Nfic-deficient mice exhibit short and abnormal molar roots and severely deformed incisors. The objective of this study is to address the mechanisms responsible for these changes using morphological, IHC, and RT-PCR analysis. Nfic-deficient mice exhibited aberrant odontoblasts and abnormal dentin formation in molar roots and the labial crown analog of incisors. The most striking changes observed in these aberrant odontoblasts were the loss of intercellular junctions and the decreased expression of ZO-1 and occludin. As a result, they became dissociated, had a round shape, and lost their cellular polarity and arrangement as a sheet of cells. Furthermore, the dissociated odontoblasts became trapped in dentin-like mineralized tissue, resembling osteodentin in the overall morphology. These findings suggest that loss of the Nfic gene interferes with the formation of intercellular junctions that causes aberrant odontoblast differentiation and abnormal dentin formation. Collectively, these changes in odontoblasts contributed to development of molars with short and abnormal roots in Nfic-deficient mice.

Aberrant cementum phenotype associated with the hypophosphatemic hyp mouse.

BACKGROUND: Cementogenesis is sensitive to altered local phosphate levels; thus, we hypothesized a cementum phenotype, likely of decreased formation, would be present in the teeth of X-linked hypophosphatemic (Hyp) mice. Mutations in the phosphate-regulating gene with homologies to endopeptidases on the X chromosome (Phex) cause X-linked hypophosphatemia, characterized by rickets, osteomalacia, and hypomineralized dentin formation, a phenotype recapitulated in the Hyp mouse homolog. Here, we report a developmental study of tooth root formation in Hyp mouse molars, focusing on dentin and cementum. METHODS: Light and transmission electron microscopy were used to study molar tissues from wild-type (WT) and Hyp mice. Demineralized and hematoxylin and eosin-stained tissues at developmental stages 23 to 96 days postcoital (dpc) were examined by light microscopy. Immunohistochemistry methods were used to detect bone sialoprotein (BSP) distribution in Hyp and WT mouse molar tissues, and transmission electron microscopy was used to study similar molar tissues in the non-demineralized state. RESULTS: Dentin in Hyp mice exhibited mineralization defects by 33 dpc, as expected, but this defect was partially corrected by 96 dpc. In support of our hypothesis, a cementum phenotype was detected using a combination of immunohistochemistry and transmission electron microscopy, which included thinner BSP-positive staining within the cementum, discontinuous mineralization, and a globular appearance compared to WT controls. CONCLUSION: Mutations in the phosphate-regulating Phex gene of the Hyp mouse resulted in defective cementum development.

Regional odontodysplasia in early childhood: a clinical and histological study.

Regional odontodysplasia (RO) is a rare disorder of dental development. The affected teeth are clinically hypoplastic and hypocalcified, presenting a ghost-like appearance radiographically. The aim of this work was to report a clinical case of a child with both primary and permanent dentition affected by RO. The conducted therapy was based on a conservative approach, which consisted of follow-up clinical evaluations of the anomalous teeth. However, the endodontic treatment of the primary incisors failed. Then, the chosen option for patient rehabilitation became extraction followed by removable of prosthesis confection. The extracted teeth were processed for histological analysis. In spite of the uncertain prognosis, but taking into account the psychological aspects of the patient, a conservative approach in an attempt to maintain those viable teeth in the oral cavity should be established.

Transgenic overexpression of gremlin results in developmental defects in enamel and dentin in mice.

Bone morphogenetic proteins (BMPs) and BMP antagonists play a crucial role in the regulation of tooth development. One of the BMP extracellular antagonists, gremlin, is a highly conserved 20.7-kDa glycoprotein. Previously, researchers reported that transgenic mice overexpressing gremlin under the control of the osteocalcin promoter (gremlin OE) exhibit a skeletal phenotype and tooth fragility. To further define the tooth phenotype, teeth and surrounding supporting tissues, obtained from gremlin OE at ages of 4 weeks, 2 months, and 4 months, were examined. The histological results demonstrate that gremlin OE exhibit an enlarged pulp chamber with ectopic calcification and thinner dentin and enamel compared with wild-type control. In vitro studies using murine pulp cells revealed that gremlin inhibited BMP-4 mediated induction of Dspp. These data provide evidence that balanced interactions between BMP agonists/antagonists are required for proper development of teeth and surrounding tissues. It is clear that these interactions require further investigation to better define the mechanisms controlling tooth root formation (pulp, dentin, cementum, and surrounding tissue) to provide the information needed to successfully regenerate these tissues.

Mouse models of tooth abnormalities.

Tooth number is abnormal in about 20% of the human population. The most common defect is agenesis of the third molars, followed by loss of the lateral incisors and loss of the second premolars. Tooth loss appears as both a feature of multi-organ syndromes and as a non-syndromic isolated character. Apart from tooth number, abnormalities are also observed in tooth size, shape, and structure. Many of the genes that underlie dental defects have been identified, and several mouse models have been created to allow functional studies to understand, in greater detail, the role of particular genes in tooth development. The ability to manipulate the mouse embryo using explant culture and genome targeting provides a wealth of information that ultimately may pave the way for better diagnostics, treatment or even cures for human dental disorders. This review aims to summarize recent knowledge obtained in mouse models, which can be used to gain a better understanding of the molecular basis of human dental abnormalities.

Effect of acid etching time on bond strength of an etch-and-rinse adhesive to primary tooth dentine affected by amelogenesis imperfecta.

BACKGROUND: Dentine affected by amelogenesis imperfecta (AI) is histologically altered following loss of the hypoplastic enamel and becomes hypermineralized, which would make bonding less predictable. AIM: This study examined the effect of etching time on the microtensile bond strength (microTBS) to AI-affected primary dentine. DESIGN: Flat coronal dentine surface was obtained from extracted AI-affected and noncarious primary molars. Teeth were etched either for 15 or for 30 s using 34% phosphoric acid. Prime & Bond NT (Dentsply De Trey), an etch-and-rinse adhesive, was applied to dentine surfaces, air-dried and light-cured, followed by composite build-ups. The bonded teeth were sectioned into beams of 0.8 mm(2) and stressed to failure under tension. Representative fractured beams from each group were examined under scanning electron microscopy. RESULTS: The extended etching time had an adverse effect on the microTBS for the normal dentine, while no significant difference was found for AI-affected dentine. When the AI-affected dentine was etched for 30 s, the fracture occurred in the demineralized dentine at the base of the hybrid layer. CONCLUSION: Bonding to AI-affected dentine compromised the bonding of the etch-and-rinse adhesive. The bonding could not be improved by increasing etching time.

Dentinogenesis imperfecta: a review and case report of a family over four generations.

Dentinogenesis imperfecta (DGI) is one of the most common hereditary disorders of dentin formation. It follows an autosomal dominant pattern of transmission, affecting both the formation and mineralization of dentin. Either or both primary and permanent dentition is affected by it. This paper briefly reviews the manifestations of DGI Type II (DGI1) and presents a case report of a family affected with DGI1 over four generations.

Whole exome sequencing identifies an AMBN missense mutation causing severe autosomal-dominant amelogenesis imperfecta and dentin disorders.

Tooth development is a complex process that involves precise and time-dependent orchestration of multiple genetic, molecular, and cellular interactions. Ameloblastin (AMBN, also named "amelin" or "sheathlin") is the second most abundant enamel matrix protein known to have a key role in amelogenesis. Amelogenesis imperfecta (AI [MIM: 104500]) refers to a genetically and phenotypically heterogeneous group of conditions characterized by inherited developmental enamel defects. The hereditary dentin disorders comprise a variety of autosomal-dominant genetic symptoms characterized by abnormal dentin structure affecting either the primary or both the primary and secondary teeth. The vital role of Ambn in amelogenesis has been confirmed experimentally using mouse models. Only two cases have been reported of mutations of AMBN associated with non-syndromic human AI. However, no AMBN missense mutations have been reported to be associated with both human AI and dentin disorders. We recruited one kindred with autosomal-dominant amelogenesis imperfecta (ADAI) and dentinogenesis imperfecta/dysplasia characterized by generalized severe enamel and dentin defects. Whole exome sequencing of the proband identified a novel heterozygous C-T point mutation at nucleotide position 1069 of the AMBN gene, causing a Pro to Ser mutation at the conserved amino acid position 357 of the protein. Exfoliated third molar teeth from the affected family members were found to have enamel and dentin of lower mineral density than control teeth, with thinner and easily fractured enamel, short and thick roots, and pulp obliteration. This study demonstrates, for the first time, that an AMBN missense mutation causes non-syndromic human AI and dentin disorders.

Microdontia after chemotherapy in a patient treated for neuroblastoma: Histopathological findings.

Microdontia is one of the late effects of antineoplastic therapy in children. This study is based on the comparative histological examination of abnormal, peg-shaped premolars, erupted in a patient treated for neuroblastoma, and of non-affected teeth, extracted in a healthy child. Apart from the size, the teeth vary in tissue morphology. The number of dentinal tubules, dependent on the number of odontoblasts, is smaller in the microdontal sample when observation in the same-sized field of view is conducted. Moreover, the youngest, more than 100-micrometer-thick layer of the microdontal dentin seems to be the secondary dentin, with crispy-shaped tubules and empty spaces between them. No irregular dentin is deposited in the samples of physiologically developed teeth. The structure of cementum is different as well. Unlike regularly shaped premolars, in which typical 2-layer tissue is seen, in sections of microdontal teeth, only acellular tissue with cementoblasts overlying its surface is present. Thorough analysis of drug administration effects, which are visible in microscopic sections, and of time of anticancer treatment could provide insight into the developmental mechanisms of tooth germ formation.