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PubMed1997

The protein composition of normal and developmentally defective enamel.

The development of human enamel involves a complex series of events including the secretion and degradation of a unique extracellular matrix. Ameloblasts progress through a succession of cellular phenotypes executing specialized secretory and regulatory functions. When performing optimally, ameloblasts produce a highly structured and mineralized tissue. Given the elaborate developmental events required for normal enamel formation, it is not surprising that a variety of enamel malformations arise from defects in matrix synthesis, secretion and extracellular processing. Normal matrix secretion and post-secretory processing by ameloblasts can be affected by a variety of hereditary and environmental conditions. These disturbances can result in an abnormal amount and/or composition of matrix proteins, and subsequently, an altered enamel structure and/or mineral content. For example, abnormal matrix removal during enamel maturation apparently contributes to hypomineralization associated with dental fluorosis. Incomplete matrix removal can also occur in several different forms of the hereditary condition amelogenesis imperfects. Specific types of this condition can have retention of substantial enamel protein (e.g. 5% by weight) that is, at least in part, composed of amelogenin and/or its breakdown products. Characterization of the enamel proteins in teeth affected by developmental disturbances can provide insight into the pathogenesis and normal formation of this highly specialized tissue.

Adult↗
PubMed1994

Deciduous enamel defects in low-birth-weight children: correlated X-ray microtomographic and backscattered electron imaging study of hypoplasia and hypomineralization.

Enamel does not remodel, and disturbances occurring during development may remain in the tooth as a permanent record of the upset. Mineralization in prenatal and postnatal deciduous enamel was studied in the shed deciduous incisors of low-birth-weight (LBW: < 2kg) children. The specific objective was to gain further insight into the mechanism of formation of developmental defects of enamel. Sections at a resolution of 22-40 microns were reconstructed using X-ray microtomography (microCT) giving absolute measurements of linear absorption coefficient for AgK alpha radiation. Detail to ca. 1 micron resolution was obtained using automated, digital backscattered electron (BSE) imaging of PMMA-embedded material. Matching the histograms of BSE and microCT images made possible the calibration of the mean atomic number-dependent signal in the BSE images. The comparison of abnormal, affected enamel regions and post-recovery, normal, unaffected regions could be made in the same teeth, since these zones were easily recognized from the distribution of hypoplasia and hypomineralization. The microCT values, converted to calculated mineral densities, ranged from 2.3 g cm-3 to 2.6 g cm-3 in LBW hypoplastic, and between 2.65 and 2.78 g cm-3 in control primary enamel and post-defect, post-natal LBW enamel. Hypoplasia with or without minimal hypomineralization indicated recovery of the ameloblasts in the maturation phase. Disturbance during late matrix formation and early maturation resulted in hypoplasia and hypomineralization.

Child, Preschool↗
PubMed1978

Enamel defects.

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Amelogenesis Imperfecta↗
PubMed2003

Insights from stable light isotopes on enamel defects and weaning in Pliocene herbivores.

A high prevalence of enamel hypoplasia in several herbivores from the early Pliocene Langebaanweg locality, South Africa, indicates general systemic stress during the growing years of life. The presence of several linear enamel hypoplasias per tooth crown in many teeth further suggest that these stress events may be episodic. The delta18O values along tooth crowns of mandibular second molars of Sivatherium hendeyi (Artiodactyla, Giraffidae) were used to investigate the cause of the stress events in this tooth type. Results show that weaning in this fossil giraffid occurred at a similar ontogenetic age to that in extant giraffes, and that the observed enamel hypoplasia towards the base of this tooth type manifested post-weaning. Further, high-resolution oxygen isotope analyses across S. hendeyi third molars suggest that the entire development of defective tooth crowns occurred under conditions of increased aridity in which the cool, rainy part of the seasonal cycle was missing. The high prevalence of this defect in many herbivores suggests that climatic conditions were not favourable. This study reiterates the value of stable isotope analyses in determining both the behaviour of fossil animals and the environmental conditions that prevailed during tooth development.

Animals↗
PubMed2000

Microabrasion of teeth with discoloration resembling hypomaturation enamel defects: four-year follow up.

Microabrasion with 18% HCl and pumice to remove enamel dysmineralization and improve esthetics is an accepted and effective treatment. This technique can probably be extended even to generalized defects resembling hypomaturation amelogenesis imperfecta that appear on all erupted teeth. Five children aged 9 to 11 with two types of enamel-hypomaturation probably due to developmental defects were treated successfully by microabrasion, with marked improvement of the discoloration. The patients were followed for up to four years. During this period, no tooth-sensitivity or staining was noted. The teeth looked healthier and shinier.

Amelogenesis Imperfecta↗
PubMed1997

Molecular biology of hereditary enamel defects.

Amelogenesis imperfecta is a disfiguring inherited condition affecting tooth enamel. X-Linked and autosomal dominant and recessive inheritance patterns occur. X-Linked amelogenesis imperfecta has been studied extensively at the molecular level. Linkage analysis has shown that there is genetic hetetogeneity in X-linked amelogenesis imperfecta with two identified loci: AIH1 and AIH3. The AIH1 locus corresponds to the location of the amelogenin gene on the distal short arm of the X chromosome; various mutations in the amelogenin gene have been found in families with X-linked amelogenesis imperfecta. The AIH3 locus maps to the Xq24-q27.1 region on the long arm of the X chromosome. Linkage to the long arm of chromosome 4 has been established in three families with autosomal dominant amelogenesis imperfecta. There is as yet no published evidence for genetic heterogeneity in autosomal dominant amelogenesis imperfecta as in X-linked amelogenesis imperfecta. Candidate genes for autosomal dominant amelogenesis imperfecta include tuftelin (1q), albumin (4q) and ameloblastin (4q) but the involvement of these genes in the disease has yet to be demonstrated. In view of the variable clinical appearances within families with autosomal dominant amelogenesis imperfecta and X-linked amelogenesis imperfecta, together with the finding that different X-linked amelogenesis imperfecta phenotypes result from mutations within the same gene, an alternative classification based on the molecular defect and mode of inheritance rather than phenotype has been proposed.

Amelogenesis Imperfecta↗
PubMed2003

Novel ENAM mutation responsible for autosomal recessive amelogenesis imperfecta and localised enamel defects.

The genetic basis of non-syndromic autosomal recessive forms of amelogenesis imperfecta (AI) is unknown. To evaluate five candidate genes for an aetiological role in AI. In this study 20 consanguineous families with AI were identified in whom probands suggested autosomal recessive transmission. Family members were genotyped for genetic markers spanning five candidate genes: AMBN and ENAM (4q13.3), TUFT1 (1q21), MMP20 (11q22.3-q23), and KLK4 (19q13). Genotype data were evaluated to identify homozygosity in affected individuals. Mutational analysis was by genomic sequencing. Homozygosity linkage studies were consistent for localisation of an AI locus in three families to the chromosome 4q region containing the ENAM gene. ENAM sequence analysis in families identified a 2 bp insertion mutation that introduced a premature stop codon in exon 10. All three probands were homozygous for the same g.13185_13186insAG mutation. These probands presented with a generalised hypoplastic AI phenotype and a class II openbite malocclusion. All heterozygous carriers of the g.13185_13186insAG mutation had localised hypoplastic enamel pitting defects, but none had AI or openbite. The phenotype associated with the g.13185_13186insAG ENAM mutation is dose dependent such that ARAI with openbite malocclusion segregates as a recessive trait, and enamel pitting as a dominant trait.

Amelogenesis Imperfecta↗
PubMed2005

Tooth enamel defects in mice with a deletion at the Arhgap 6/Amel X locus.

The amelogenin proteins regulate enamel mineral formation in the developing tooth. The human AMELX gene, which encodes the amelogenin proteins, is located within an intron of the Arhgap 6 gene. ARHGAP 6 encodes a Rho GAP, which regulates activity of Rho A, a small G protein involved in intracellular signal transduction. Mice were generated in which the entire ARHGAP 6 gene was deleted by Cre-mediated recombination, which also removed the nested Amel X gene. Enamel from these mice appeared chalky white, and the molars showed excessive wear. The enamel layer was hypoplastic and non-prismatic, whereas other dental tissues had normal morphology. This phenotype is similar to that reported for Amel X null mice, which have a short deletion that removed the region surrounding the translation initiation site, and resembles some forms of X-linked amelogenesis imperfecta in humans. Analysis of the enamel from the Arhgap 6/Amel X-deleted mice verifies that the Amel X gene is nested within the murine Arhgap 6 gene and shows that removal of the entire Amel X gene leads to a phenotype similar to the earlier Amel X null mouse results, in which no amelogenin protein was detected. However, an unusual layer of aprismatic enamel covers the enamel surface, which may be related to the 1.1-Mb deletion, which included Arhgap 6 in these mice.

Amelogenesis Imperfecta↗
PubMed2002

Development of enamel defects in rat mandibular incisor after thyro-parathyroidectomy.

Previous studies with scanning electron microscopy (SEM) demonstrated the presence of small hypoplastic defects in the incisal third of incisors and deep hypoplasia in the apical third of the incisors after thyro-parathyroidectomy in the rat. These studies provided a morphological description of the defects, but uncertainty remained concerning their development throughout amelogenesis. The aim of the present investigation was to study, with SEM operated in the backscattered mode, the development of the hypoplastic defects, from the beginning of the secretion to the end of the maturation zone of the enamel, in the lower incisor of thyroparathyroidectomized rats. The results of the present study showed that the large and small defects developed are separate entities that do not develop into the other. The distribution of large defects might be linked to a reduction of the eruption rate in these rats. The pathogenesis of these defects needs further investigation.

Animals↗
PubMed2003

Deciduous dentition and enamel defects.

Two hundred eighty children including wellnourished, malnourished and infants with intrauterine growth retardation (IUGR) were examined for dental eruption and enamel hypoplasia. In malnourished and IUGR children eruption of teeth was delayed. The prevalence of enamel hypoplsia in wellnourished children was 20% being significantly higher in females as compared to males in age group 1-2 years. Enamel hypoplasia was seen in 36.6% malnourished subjects. Breast-feeding was protective against enamel hypoplasia.

Dental Enamel Hypoplasia↗