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PubMed1979

Dysplastic enamel in odontomas.

A series of odontomas was studied by light microscopy, with special emphasis on abnormal enamel in these lesions. The findings were compared to those in amelogenesis imperfecta and in other conditions in which abnormal enamel is found. It was concluded that dysplastic enamel exhibits a number of appearances which are described in this article. A strongly basophilic laminated material was also found, often covering prismatic enamel, but it did not itself appear to be a form of enamel; its identity is not clear. Odontomas, being readily available, offer a good opportunity to study dysplastic enamel.

Dental Enamel↗

PubMed1979

Focal odontodysgenesis of the maxillary second premolars in a child.

A few months before her sixth birthday, a Caucasian girl suffered progressively worse episodes of painful, nontender, erythematous swellings of the palate lingual to apparently healthy primary second molars. Neither of the developing maxillary second premolars was discerned clearly in radiographs, but, upon surgical exploration, incomplete crowns were found in both follicles. All the other premolars appeared to be developing normally. Histologic, histochemical, and chemical analyses showed that the enamel was hypocalcified, apparently as a result of hypomaturation; the dentin was essentially normal; and morphogenesis had ceased when the heights of contour of the crowns had not yet been reached. This pattern of developmental defects differs from those of well-characterized odontogenic disorders, such as regional odontodysplasia and amelogenesis imperfecta. We suggest that focal odontodysgenesis might be an appropriate term for it. The bilateral symmetry suggests a genetic component in the etiology.

Bicuspid↗

PubMed1989

Human and mouse amelogenin gene loci are on the sex chromosomes.

Enamel is the outermost covering of teeth and is the hardest tissue in the vertebrate body. The enamel matrix is composed of enamelin and amelogenin classes of protein. We have determined the chromosomal locations for the human and mouse amelogenin (AMEL) loci using Southern blot analyses of DNA from human, mouse, or somatic cell hybrids by hybridization to a characterized mouse amelogenin cDNA. We have determined that human AMEL sequences are located on the distal short arm of the X chromosome in the p22.1----p22.3 region and near the centromere on the Y chromosome, possibly at the proximal long arm (Yq11) region. These chromosomal assignments are consistent with the hypothesis that perturbation of the amelogenin gene is involved in X-linked types of amelogenesis imperfecta, as well as with the Y-chromosomal locations for genes that participate in regulating tooth size and shape. Unlike the locus in humans, the mouse AMEL locus appears to be assigned solely to the X chromosome. Finally, together with the data on other X and Y chromosome sequences, these data for AMEL mapping support the notion of a pericentric inversion occurring in the human Y chromosome during primate evolution.

Amelogenin↗

PubMed2004

Enamel defects and Lyonization in focal dermal hypoplasia.

We report a pattern of enamel hypoplasia in focal dermal hypoplasia similar to that found in females with X-linked amelogenesis imperfecta. Three cases of focal dermal hypoplasia are described, with specific focus on the oral and dental features. In these cases the teeth all had vertical grooving with notching of the incisal or cuspal tips. Also recorded were blunt roots of taurodont form with open apices and missing teeth in 1 case. Oral papillomas were present in 2 cases. The pattern of enamel defects is attributed to Lyonization, which is consistent with the pattern of skin and bone lesions typically seen in focal dermal hypoplasia. This supports the proposal that focal dermal hypoplasia is X-linked. The authors conclude that the pattern of dental defects in focal dermal hypoplasia is consistent with Lyonization.

Anodontia↗

PubMed1995

Molecular genetic approaches to the study of human craniofacial dysmorphologies.

Craniofacial dysmorphologies are common, ranging from simple facial disfigurement to complex malformations involving the whole head. With the advent of gene mapping and cloning techniques, the genetic element of both simple and complex human craniofacial dysmorphologies can be investigated. For many of the dysmorphic syndromes, it is possible to find families that display a particular phenotype in either an autosomal dominant, recessive, or X-linked manner. This article focuses on a subgroup of craniofacial dysmorphologies, covering these three main inheritance patterns, that are being studied using molecular biology techniques: DiGeorge syndrome, Treacher Collins syndrome, Greig cephalopolysyndactyly syndrome, acrocallosal syndrome, amelogenesis imperfecta, and X-linked cleft palate with ankyloglossia. Once the mutated or deleted gene or genes for each syndrome have been cloned, patterns of normal and abnormal craniofacial development should be elucidated. This should enhance both diagnosis and treatment of these common and disfiguring disorders.

Animals↗

PubMedDate not supplied

Specialized biology from tandem beta-turns.

Diverse forms of pathologies can be derived from the lack of flexibility in tissues and the absence of required concentrations of certain types of proteins (e.g., amelogenesis imperfecta). beta-spirals using canonical proline-nucleated beta-turns in diverse proteins allow for vital functions including structural (mucin and amelogenin), respiratory (elastin), muscular (titin), and that of genetic expression (RNA polymerase II). These confer particular physical and chemical properties to proteins and therefore to the tissues in which they are found, while the pervasive presence of tandem repeats in the genome sequence indicates their importance. This paper discusses the general biomedical relevance of this structure, focusing on several proteins found in humans.

Protein Conformation↗

PubMed2001

[Dental anomalies following anticancer chemotherapy].

Chemotherapy administered during childhood may induce dental abnormalities, such as acquired amelogenesis imperfecta, microdontia, hypodontia and altered root morphology. The magnitude of the defect varies according to the cytotoxic agents, the duration of their use and the stage of tooth development at the time of chemotherapy. Patients who received high-dose chemotherapy before the age of 5 are particularly concerned. The dental supervision of these children is based upon three orthopantomograms: the first one has to be performed before starting chemotherapy and will be used as a reference; the second is done soon after the drug therapy in order to evaluate the first consequences; the third is performed after the eruption of all permanent teeth (age 12-13 in average) in order to determine the dental abnormalities. In case of hypodontia, orthodontic treatment must be considered, but it is necessary to take into account the fact that it may increase the risk of root resorption. Preventive dental care is important for these children. It involves meticulous oral hygiene and frequent dental visits to assess and maintain dental health.

Antineoplastic Agents↗

PubMed1999

Tyrosyl motif in amelogenins binds N-acetyl-D-glucosamine.

Ameloblasts secrete amelogenins on the pre-existing enamel matrix glycoproteins at the dentine-enamel junction. The hypothesis that amelogenins may interact with enamel matrix glycoproteins is tested by hemagglutination of purified, native (porcine) and recombinant murine amelogenins (rM179 and rM166) and hemagglutination inhibition with sugars. Amelogenin agglutination of murine erythrocytes was specifically inhibited by N-acetylglucosamine (GlcNAc), chitobiose, and chitotetraose and by ovalbumin with terminal GlcNAc. The GlcNAc affinity was confirmed by dosimetric binding of rM179 with [14C]GlcNAc, specific binding in relation to varying concentrations of GlcNAc, Scatchard plot analysis and competitive inhibition with cold GlcNAc. The hemagglutination activity and [14C]GlcNAc affinity were retained by the NH2-terminal tyrosine-rich amelogenin peptide (TRAP) but not by the leucine-rich amelogenin peptide, LRAP (a polypeptide sharing 33 amino acid residues of TRAP), or by the C-terminal 13 residue polypeptide of amelogenin (rM179). Since TRAP but not the 33-residue sequence of the TRAP shared by LRAP bound to [14C]GlcNAc, we inferred that the GlcNAc binding motif was located in the 13-residue tyrosyl C-terminal domain of TRAP (PYPSYGYEPMGGW), which was absent from LRAP. [14C]GlcNAc did indeed bind to this "amelogenin tyrosyl motif peptide" but not when the tyrosyl residues were substituted with phenylalanine or when the third proline was replaced by threonine. Significantly, this latter modification mimics a point mutation identified in a case of human X-linked amelogenesis imperfecta. The amelogenin tyrosyl motif peptide sequence showed a similarity to the secondary GlcNAc-binding site of wheat germ agglutinin.

Acetylglucosamine↗

PubMed2003

Amelogenin interacts with cytokeratin-5 in ameloblasts during enamel growth.

The enamel protein amelogenin binds to GlcNAc (Ravindranath, R. M. H., Moradian-Oldak, R., and Fincham, A.G. (1999) J. Biol. Chem. 274, 2464-2471) and to the GlcNAc-mimicking peptide (GMp) (Ravindranath, R. M. H., Tam, W., Nguyen, P., and Fincham, A. G. (2000) J. Biol. Chem. 275, 39654-39661). The GMp motif in the N-terminal region of the cytokeratin 14 of ameloblasts binds to trityrosyl motif peptide (ATMP) of amelogenin (Ravindranath, R. M. H., Tam, W., Bringas, P., Santos, V., and Fincham, A. G. (2001) J. Biol. Chem. 276, 36586 - 36597). K14 (Type I) pairs with K5 (Type II) in basal epithelial cells; GlcNAc-acylated K5 is identified in ameloblasts. Dosimetric analysis showed the binding affinity of amelogenin to K5 and to GlcNAc-acylated-positive control, ovalbumin. The specific binding of [3H]ATMP with K5 or ovalbumin was confirmed by Scatchard analysis. [3H]ATMP failed to bind to K5 after removal of GlcNAc. Blocking K5 with ATMP abrogates the K5-amelogenin interaction. K5 failed to bind to ATMP when the third proline was substituted with threonine, as in some cases of human X-linked amelogenesis imperfecta or when tyrosyl residues were substituted with phenylalanine. Confocal laser scan microscopic observations on ameloblasts during postnatal (PN) growth of the teeth showed that the K5-amelogenin complex migrated from the cytoplasm to the periphery (on PN day 1) and accumulated at the apical region on day 3. Secretion of amelogenin commences from day 1. K5, similar to K14, may play a role of chaperone during secretion of amelogenin. Upon secretion of amelogenin, K5 pairs with K14. Pairing of K5 and K14 commences on day 3 and ends on day 9. The pairing of K5 and K14 marks the end of secretion of amelogenin.

Amelogenin↗

PubMed2003

Resorbable plate osteosynthesis of sagittal split osteotomies with major bone movement.

This study evaluates resorbable miniplate osteosyntheses in sagittal split osteotomies with major bone repositioning. Two resorbable 2.0-mm miniplate systems, MacroSorb (Macropore, San Diego, Calif.) and PolyMax (Synthes, Oberdorf, Switzerland), were compared consecutively. Amorphous 70:30 poly-L/DL-lactide copolymer plates sustain continuous hydrolysis through water penetration into the implant body during the first 6 months in situ. This breaks copolymer chains into smaller particles, which later become degraded through phagocytotic cells. Eighteen patients, 10 women and eight men, 16 to 57 years old (average, 27 years) were examined. They had severe dysgnathia caused by congenital craniofacial malformations, systemic disorders, trauma, amelogenesis imperfecta, oligodontia, and other conditions, and they needed five 8- to 10-mm and 13 major 10- to 12-mm repositions. Twelve sagittal split osteotomies were fixed with 12 MacroSorb plates in six patients, and 24 osteotomies were filled with 32 PolyMax plates in 12 patients. Ten mandibular plate, screw, hard-tissue, and soft-tissue specimens were taken at 3, 6, 9, or 12 months postoperatively in secondary operations (e.g., dental implant placement).Follow-up ranged from 4 to 19 months; all osteosyntheses reossified. Four patients showed proximal fragments rotated up to 5 mm sagittally anteriorly and nonaligned burr holes on the postoperative radiogram, suggesting plate fractures or screw pullout. When plate fracture was noted, guided occlusion was maintained 4 weeks after surgery. Occlusal, radiologic, and skeletal results remained stable. After starting fixation with two plates on each side, no more plate fractures were seen. In three other patients, minor skeletal relapses up to 3 mm horizontally resulted. Local histologic inspection of specimens showed thorough osseous union. Screw remnants embedded in bone made screw pullout unlikely; rather, screw-head or plate fractures were found as multiple degraded particles. Microscopy showed a chronic foreign body reaction. Two patients (11 percent) developed a sterile fistula 3 and 4 months after surgery, draining implant debris. Here, the biopsies showed a granulocytic infiltrate that subsided clinically after excisional biopsy. The assignment of MacroSorb plates followed by PolyMax plates was done in an otherwise unchanged treatment protocol. Comparison of the number of patients in each group with stable osteosyntheses and regular healing showed no significant differences by Fisher's exact test (p = 0.1516); therefore, the authors focused on the combined results for both treatments. The current osteosynthesis systems showed sufficient stability for mandibular fixation after sagittal split osteotomy and repositioning more than 10 mm distant when two plates were applied to each side; however, 27 percent of patients had complications, including relapses. Disadvantages were the cost, breakability, diameter, and need to place the screws vertically to the plate, necessitating a bent instrument or transbuccal incisions.

Absorbable Implants↗

PubMed1978

Taurodontism and enamel hypomaturation associated with X-linked abnormalities.

The association of taurodontism with hypoplastic/hypomature enamel defects is presented in two cases of X-chromosome aneuploidy (47,XXY) and one of X-linked recessive Amelogenesis Imperfecta. It appears that the X-chromosome not only plays some role in tooth size the degree of taurodontism increasing with increased number of X chromosomes), but probably also plays a role in enamel maturation.

Adolescent↗

PubMed1998

DNA sequences of amelogenin genes provide clues to regulation of expression.

The amelogenins are a heterogeneous group of enamel proteins, which have an important function in enamel formation, as mutations in the amelogenin gene result in the enamel defect amelogenesis imperfecta. The cDNAs that encode murine, bovine, human, porcine, rat and opossum amelogenins have been cloned, and as many as nine alternatively spliced messages can be produced from a single primary transcript, explaining some of the protein heterogeneity. Bovine and human amelogenin genes are found on both X and Y chromosomes, and the sexually dimorphic proteins would have 87-93% identity. A comparison of genes from human, bovine and mouse indicates that they are organized into seven exons, and sequences are highly homologous among species. Bovine, murine and human upstream regions also have similarities, with consensus sequences for potential binding of transcription factors, such as AP1 and CTF/NF1. Transgenic mouse studies have shown that 2300-3500 bp of upstream region are sufficient for expression, while 900 bp are insufficient. Analysis of DNA sequence has identified (a) major homology between species for coding exons with the exception of exon 4, (b) similarities in upstream regions likely involved in tissue specific regulation of expression, and (c) sequences at the RNA splice sites which may determine exon inclusion or skipping.

Alternative Splicing↗

PubMed1991

Multiple dental developmental anomalies.

An unusual case is presented of three dental developmental anomalies, a hypomaturation-hypoplastic with taurodontism form of amelogenesis imperfecta, hypodontia of the premolars and an odontoma, occurring in an otherwise normal boy.

Abnormalities, Multiple↗

PubMed1995

Molecular biology experimental strategies for craniofacial-oral-dental dysmorphology.

This paper is a minireview of molecular biology experimental strategies for problems within craniofacial-oral-dental biology. Many of these strategies have already made remarkable contributions towards understanding the complex developmental processes associated with craniofacial biology. For example, the utilization of these strategies has resulted in the successful mapping of approximately 70 genes related to craniofacial anomalies (e.g., Pax, retinoic acid receptors, cadhedrins, aggrecan, cell adhesion molecules, substrate adhesion molecules, etc.), 30 genes related to dental tissue disorders (e.g., BMPs, bone morphogenetic proteins; dentin phosphoproteins, dentin sialoglycoproteins, enamelins, amelogenins), 20 genes related to facial clefting defects (e.g., Hox genes, transforming growth factor alpha), and 3 genes related to craniosynostosis (e.g., Msx-2). This minireview highlights selected examples of scientific progress derived from the following experimental strategies: (i) molecular approaches to the organization of the mouse and human chromosomes, with the mapping of specific gene sequences linked to human diseases (e.g., amelogenesis imperfecta, Boston type craniosynostosis, Rieger's syndrome, Treacher Collins syndrome); (ii) reverse genetic approaches for studies of gene function; (iii) homologous recombinations and the advances from "knock-out" transgenic mouse models for human craniofacial-oral-dental diseases; (iv) mutational analyses of congenital craniofacial-oral-dental dysmorphogenesis; (v) structural biology studies using computer-assisted molecular modeling for protein-protein, protein-nucleic acid and protein-inorganic interactions; (vi) computer modeling of genetic paradigms; and (vii) a cluster of newer methodologies including computer-assisted morphometry, new microinjection techniques, new cell membrane and intracellular dyes, and a number of new RNA and DNA viral constructs for the delivery of genes to enhance the resolution of cell fate maps, cell lineage studies and gene therapy approaches to human diseases.

Animals↗

PubMed1998

Identification and characterization of a cDNA for mouse ameloblastin.

Ameloblastin was first identified as one of the most abundant novel transcripts from a random screening of a rat incisor cDNA library. In situ hybridization experiments have shown ameloblastin expression to be specific to ameloblasts, with highest levels in secretory and maturation stage ameloblasts and cells of the epithelial root sheath. Ameloblastin has been identified as a candidate gene for the local hypoplastic form of autosomal dominant amelogenesis imperfecta, by virtue of it's location within the critical disease locus. The purpose of this study was to isolate a full length mouse ameloblastin cDNA and determine its temporal expression pattern during odontogenesis. A newborn mouse molar cDNA library was screened using a rat ameloblastin cDNA probe. Positive clones were confirmed by PCR analysis with ameloblastin-specific primers, and their size determined with vector-specific primers. Phage clones were rescued to phagemid using Exassist helper phage and the nucleotide sequence determined. We report here the identification of two clones, exhibiting alternative splicing of the putative open reading frame, and use of multiple polyadenylation signals. Nucleotide sequence analysis indicated a high degree of similarity to rat ameloblastin, rat amelin 1 and 2 and porcine sheathlin. Reverse transcriptase-PCR analysis using mouse first and second mandibular molar mRNA indicated initial expression at E-14. This is one day after the initial expression of tuftelin (E-13) and one day prior to that of amelogenin (E-15).

Amino Acid Sequence↗

PubMed2003

Amelogenin protein exhibits a modular design: implications for form and function.

The most abundant protein of forming enamel is amelogenin, a protein capable of self-assembly to form nanospheres. Naturally occurring mutations in the human amelogenin gene are responsible for at least some of the disease entities known collectively as amelogenesis imperfecta (AI), although it is clear that the AI phenotype may be caused by alteration to other genes responsible for the biogenesis of the enamel extracellular matrix. Mutations that create changes in the functional domains of the amelogenin protein do adversely affect enamel biomineralization. Protein engineering of amelogenin that phenocopies several of the known AI mutations exhibits defects in self-assembly. Amino acid alterations that occur within a domain of amelogenin appear to cause "mineral defects," that is to say hypocalcification of the enamel, whereas mutations that occur elsewhere in another domain of the amelogenin molecule result in "hypoplastic defects," a decrease in thickness of the enamel. However, not all patients with AI phenotypes segregate precisely into these arbitrary designations. Nonetheless, correlating the domain of the amelogenin protein that contains a specific mutation with the type of enamel structural alteration suggests a modular design for amelogenin that is corroborated by protein engineering using recombinant DNA techniques and transgenic animal studies.

Amelogenin↗

PubMed2006

Two cases of familial hypomagnesemia with hypercalciuria and nephrocalcinosis: dental findings.

BACKGROUND: The authors describe dental and periodontal conditions of two Chinese sisters affected by familial hypomagnesemia with hypercalciuria and nefrocalcinosis (FHHNC). FHHNC is a rare syndrome, genetically investigated since 1999, transmitted as an autosomal recessive disease. It is related to a mutation of PCN-1 gene which encodes for a tight junction protein named paracellin. CASE REPORT: Oral examination of two Chinese patients showed marked enamel hypoplasia, acute gingivitis and periodontal bone loss and severe malocclusion. The literature does not report previous investigations about the dental conditions of FHHNC patients. The syndrome is not definitely described from the clinical point of view. CONCLUSION: Further researches are necessary to understand the linkage between bone loss and enamel structure anomalies in FHHNC and to discover the relationships between nefrocalcinosis, hypomagnesemia, hypercalciuria and amelogenesis imperfecta.

Adolescent↗

PubMed2006

Diagnosis and treatment of molar incisor hypomineralization.

Molar incisor hypomineralization (MIH) is a relatively common condition that varies in clinical severity and can result in early loss of the permanent 6-year molars. The etiology of MIH remains unclear, and the diagnosis can be confused with more generalized enamel defects such as those that occur in amelogenesis imperfecta. The management of MIH depends largely on the severity of the enamel defect. Degrees of hypomineralization can range from mild enamel opacities to enamel that readily abrades from the tooth as it emerges into the oral cavity. Usually, severely affected molars are extremely hypersensitive, prone to rapid caries development, and can be difficult to manage in young patients. The purpose of this article is to review approaches to diagnosing and treating MIH.

Dental Enamel↗