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ExperimentaL Oral Medicine
Published in Samuel Dreizen, Barnet M. Levy, Handbook of Experimental Stomatology, 2020
Samuel Dreizen, Barnet M. Levy
Enamel hypoplasia has been produced in experimental animals by hormone depletion (parathyroidectomy, thiouracil administration), vitamin deficiencies (vitamin D, vitamin C, vitamin B6), mineral deficiencies (magnesium, phosphorus), and by fluoride excess.127 As demonstrated by Kreshover,128 enamel hypoplasia can also be caused in developing teeth of rodents by infections that damage the ameloblasts and interfere with amelogenesis. In this study, 70 mice, 10 to 50 days old, were injected i.p. with either bovine or human type tubercle bacillus. Amount of inoculum ranged from 0.05 to 0.7 mg/100 g body weight. Serving as controls were 22 noninfected mice. The animals were sacrificed between 186 and 204 days after inoculation. The mandibles of all 92 mice were decalcified, celloidin- and paraffin-embedded, serially sectioned, and stained with hemotoxylin and eosin. In a corollary study, 14 guinea pigs were inoculated either i.p. or in the groin with human type tubercle bacillus. Inoculation doses were from 0.05 to 0.1 mg/100 g body weight. All were fed a normal diet. Time of death from either natural causes or by sacrifice was between 8 and 160 days. At necropsy, the mandibles were removed, halved, and fixed in 10% formalin. After doubleembedding (celloidin and paraffin), serial sections were prepared and stained with hematoxylin and eosin.
Odontogenic Epithelium and its Residues
Published in Roger M. Browne, Investigative Pathology of the Odontogenic Cysts, 2019
The two major classes of proteins described in the extracellular matrix of enamel from most mammalian species studied are the hydrophobic proline-, glutamine-, and histidine-rich amelogenins and the acidic serine-, glycine-, and aspartic-rich enamelins. During the secretory stage of amelogenesis in rodents and man, both the enamelins and amelogenins are secreted with the latter class of proteins constituting the major proportion of the matrix. Maturation is characterized by selective loss of amelogenins resulting in an apparent increase in enamelin concentration in the tissues. Finally, with increasing mineralization, the lower molecular weight degradation products of both classes of protein predominate.61,76 The situation in rabbit may be less complicated as it has been proposed that only enamelins are present in the developing enamel matrix.76,77 Biochemical and immunological studies in this area are thus complicated by the constantly changing proportions of amelogenins and enamelins, species differences, together with the apparent great diversity of molecular species within each family of molecules. The current situation is further complicated by recent suggestions, based on sequence homology studies, that some of the extracellular matrix proteins of enamel are related to serum albumin.78
The Cell Biology of Amelogenesis
Published in Colin Robinson, Jennifer Kirkham, Roger Shore, Dental Enamel, 2017
Ziedonis Skobe, Doris N. Stern, Kenneth S. Prostak
Amelogenesis is preceded by early events of tooth development divided into the initiation, morphogenetic, and cytodifferentiation phases.1 Teeth develop from a series of reciprocal interactions between oral epithelium and mesenchyme of the first branchial arch.2 The embryonic oral epithelium (or stomodeal ectoderm) is separated from the underlying connective tissue by a basal lamina. The first evidence of odontogenesis (the initiation phase) is the thickening of the oral epithelium, forming the primary epithelial band, which is the initial site of tooth specification.2 Increased mitotic rates in these epithelial thickenings results in a downgrowth of cells into the mesenchyme to form the dental lamina. The bud or terminus of the dental lamina gradually forms a cap-shaped epithelial structure, which surrounds condensed dental papilla mesenchyme at the sites around the arch where the teeth will form. At this stage of morphogenesis, the cap consists of an inner enamel epithelial (IEE) layer and an outer enamel epithelial (OEE) layer surrounded by a basal lamina.3'4,5 Cells of the stratum intermedium (SI) and stellate reticulum (SR) differentiate between the two layers. The edge of the cap, where the IEE and OEE meet, becomes the cervical loop, or proliferative epithelial region of the developing tooth.
Building platelet phenotypes: Diaphanous-related formin 1 (DIAPH1)-related disorder
Published in Platelets, 2022
David Rabbolini, Hai Po Helena Liang, Marie-Christine Morel-Kopp, David Connor, Shane Whittaker, Scott Dunkley, Dea Donikian, Mayuko Kondo, Walter Chen, William S Stevenson, Heather Campbell, Joanne Joseph, Christopher Ward, Timothy Brighton, Vivien M. Chen
We observed enamel hypomineralisation in both individuals with the gain-of-function DIAPH1 R1213X variant. A large number of hereditary medical conditions have been associated with amelogenesis with up or down regulation leading to developmental defects of enamel [48]. At this time it is not possible to determine if there is a definite causal relationship between the DIAPH1 R1213X variant and the observed enamel defect as mineralization is commonly related to environmental factors (nutrition, systemic illneses, premature birth, trauma, or infections). However, evaluation for this feature in future families identified with this variant will be of interest considering the importance of Rho GTPase signaling in tooth development and ameloblast differentiation [49], as well as, intriguing putative links between DIAPH1 and MMP-9 with other dynamic regulators of amelogenesis, including TGF-β [50,51].
Cone pathway dysfunction in Jalili syndrome due to a novel familial variant of CNNM4 revealed by pupillometry and electrophysiologic investigations
Published in Ophthalmic Genetics, 2022
Robert A. Hyde, Evelina Kratunova, Jason C. Park, J. Jason McAnany
AI is the dental manifestation of Jalili syndrome and its second most prominent feature (1). AI is an umbrella term that describes a group of heterogenous hereditary conditions associated with abnormal dental enamel development (35). AI typically affects both primary and permanent dentitions and can present in isolation or in conjunction with syndromic disorders (35). The enamel development (amelogenesis) is a complex process regulated by functionally diverse genes and multifaceted molecular pathways (1,35). Disturbances in the secretory stages of amelogenesis may present phenotypically with hypoplastic (thin) enamel, while errors during the stages of deposition and maturation of the enamel matrix formation may result in hypomineralized and/or hypomature (brittle, discolored) enamel (1,35). While AI can be associated with thousands of different genes and their products, the mutation of the CNNM4 in Jalili syndrome is thought to dysregulate the transport of metal ions, specifically magnesium, leading to the development of enamel structure with deficient thickness and reduced mineral content (significantly less calcium and abnormally increased magnesium) (3). In CNNM4 (-/-) mice, there is deficient dental enamel (34). All three siblings in this study showed similar anomalous tooth structure demonstrated by thin enamel and discoloration consistent with hypoplastic/ hypomineralized type AI. Anterior open bite, taurodontism and risk of spontaneous dental abscesses were also dental findings with known AI association. The dental manifestations described in this study are supported by previous literature (3,4,35).
Two siblings with Heimler syndrome caused by PEX1 variants: follow-up of ophthalmologic findings
Published in Ophthalmic Genetics, 2021
Dorien Herijgers, Ellen Denayer, Irina Balikova, Peter Witters, Julie Jacob, Ingele Casteels
Heimler syndrome was first described by Heimler et al as a combination of nail abnormalities (Beau’s lines or leukonychia), dental abnormalities, SNHL and often visual problems (1). This rare genetic diagnosis can clinically be confused with Usher syndrome since patients present with the combination of SNHL and visual loss (2). Amelogenesis imperfecta can help to differentiate between these two conditions. However, symptoms do not become apparent until eruption of the secondary dentition (3). In addition, full-field electroretinogram shows cone-rod dysfunction in Heimler syndrome whereas in Usher syndrome it shows rod – cone dysfunction. This publication describes two new cases, a brother and sister of non-consanguineous parents, with Heimler syndrome caused by a homozygous likely pathogenic variant in the PEX1 gene. So far, only 31 cases of Heimler syndrome have been published (4).