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Inheritance Pattern and Elemental Composition of Enamel Affected by Hypomaturation Amelogenesis Imperfecta
Abstract
Hypomaturation amelogenesis imperfecta (AI) is characterized clinically by enamel of normal thickness that is hypomineralized, mottled, and detaches easily from the underlying dentin. Autosomal dominant, autosomal recessive, X-linked, and sporadic modes of inheritance have been documented. The present study investigated the elemental composition of the enamel of teeth from individuals demonstrating clinical hypomaturation AI from families representing three of these patterns of inheritance. The aim of the study was to determine if there was any commonality in microscopic phenotype of this defect between families demonstrating the various inheritance patterns. One section from each tooth was microradiographed and then viewed in a scanning electron microscope (SEM) equipped with an ultrathin window energy-dispersive x-ray spectroscopy (EDX) detector. In the SEM, prisms and constituent crystals in discrete areas appeared to be largely obscured by an amorphous material. EDX analysis showed enamel outside these areas to have a composition indistinguishable from control teeth. However, within these affected areas there was a large increase in carbon content (up to a fivefold increase). In some teeth there was also a detectable but smaller increase in the relative amounts of nitrogen or oxygen. The results suggest the defect in these teeth with a common clinical phenotype, irrespective of the pattern of inheritance, demonstrates a commonality in microscopic phenotype. The large increase in carbon content, not matched by an equivalent increase in nitrogen or oxygen, suggests a possible increased lipid content. In those teeth with elevated nitrogen levels there may also be retained protein.
... One section in the midline was polished plano-parallel with wet 1200-grade carborundum paper to a thickness of 100-120μm, then acid etched for exactly 15 seconds with 35% phosphoric acid to remove the smear layer. The sections were then washed by dH2O to stop the acid etching and to remove any debris on the surface (Shore et al., 2002). ...
... Microstructural analysis was undertaken using a Jeol 35 SEM fitted with the Deben Genie upgrade (Deben Engineering, Debenham, UK). Elemental analysis was performed by energy dispersive X-ray spectroscopy (EDX) using a detector fitted with an ultrathin window and driven by WinEDX 3 software (Thomson Scientific, Carlton, Australia) (Shore et al., 2002). ...
... After that the sections were washed again with water for at least 1 hour and then dried overnight in a dry air vacuum. The sections were recoated with gold and scanned again across the fracture surface (Shore et al., 2002). ...
... This revealed unevenly dispersed areas with sufficiently formed enamel prisms, poorly formed prisms, and even areas of unrecognizable microstructure. According to Shore and coworkers, in hypomaturated AI with different inheritance patterns (autosomal dominant, autosomal recessive, sporadic, and X-linked) the structure and elemental composition show are similar between the samples [20]. SEM analysis revealed regions where prisms and constituent crystals appeared to be largely obscured by amorphous material, and microradiography indicated a reduced radiodensity. ...
... In the affected areas, the carbon content was increased up to fivefold. Outside these areas, the enamel composition was indistinguishable from control teeth [20]. The authors conclude that the phenotype classified clinically as hypomaturated AI is indeed associated with consistent structural and compositional defects, regardless of the mode of inheritance. ...
... Lower microhardness in AI-diagnosed enamel, in general, shows that this enamel is structurally different from healthy enamel and has a lower content of minerals and a higher content proteins and lipids. Indeed, teeth diagnosed with different types of AI have an altered structure [6,8,17,20] and impaired mineralization [5,6,17,20]. In hypomineralized areas of enamel in different AI types, the amount of Ca has been found to be lower than in normally mineralized areas [8]. ...
Amelogenesis imperfecta (AT) is an inherited tooth disorder with widely varying phenotypes. The aim of this study was to determine the microhardness and microstructure characteristics of the enamel in AT teeth. The AT phenotypes examined were hypoplastic (pitted and smooth form), hypomaturated, and hypocalcified. Six. p AT patients were diagnosed according to clinical characteristics. The microhardness of the enamel was measured on axial cuts of AI teeth acquired from the patients. The measurements were done on several sites from the enamel surface towards the dentine-enamel junction using the Vickers scale. Values of microhardness were compared to corresponding control teeth. The microstructure of AT enamel types was evaluated using scanning electron microscopy. The values of microhardness in pitted hypoplastic AT samples were, on average, lower compared to the control enamel and dropped markedly towards the dentine-enamel junction. The smooth hypoplastic enamel was not only extremely thin but also much softer than control enamel. The values for hypomaturated AT fluctuated, but the palatal sites were markedly softer than in the control tooth. Hypocalcified enamel was the softest, with values resembling those of dentin. Microstructural changes varied from altered orientation of enamel prisms in pitted hypoplastic AT to lack of normal prismatic structure and severe porosity in hypocalcified AI. The present results suggest different microhardness profiles and microstructures in each phenotype. Variations among phenotypes are expected with larger case selection in this genetically heterogeneous disease.
... Standard methods were used for tooth section (100 m) preparation from exfoliated deciduous teeth of 2 affected individuals and normal control teeth, which were then investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transverse microradiography (TMR) [Shore et al., 2002;Barron et al., 2008]. Microstructural analysis was undertaken using a Jeol 35 SEM fitted with the Deben Genie upgrade (Deben Engineering, Debenham, UK). ...
... This provides new insight into the detrimental impact on enamel formation of a FAM83H mutation. Similar observations have been reported in teeth described clinically as hypomaturation AI in non-syndromic forms (of uncertain genotype) [Wright et al., 1992;Shore et al., 2002] and in Jalili syndrome caused by mutations in CNNM4 , encoding a putative Mg 2+ transporter [Parry et al., 2009]. ...
... Accordingly, FAM83H may be involved in signal transduction or lipid metabolism. Inappropriate retention of lipid or lipid/protein complexes within the enamel matrix has been proposed as a possible mechanism central to some forms of AI clinically diagnosed as the hypomaturation subtype [Shore et al., 2002]. In the teeth presented here, the marked increase in carbon in particular may be consistent with elevated lipid content, at least in the most markedly affected areas. ...
Nonsense mutations in FAM83H are a recently described underlying cause of autosomal dominant (AD) hypocalcified amelogenesis imperfecta (AI).
This study aims to report a novel c.1374C>A p.Y458X nonsense mutation and describe the associated ultrastructural phenotype of deciduous teeth.
A family of European origin from the Iberian Peninsula with AD-inherited AI was ascertained. Family members were assessed through clinical examination and supporting investigations. Naturally exfoliated deciduous teeth from 2 siblings were investigated by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and transverse microradiography (TMR).
On clinical and radiographic investigation the appearances of the affected deciduous and permanent teeth were consistent with hypocalcified AI with small focal areas of more normal looking enamel. DNA sequencing identified a novel c.1374C>A p.Y458X FAM83H nonsense mutation in affected, but not in either unaffected family members or unrelated controls. Exfoliated teeth were characterised by substantial post-eruptive enamel loss on gross examination. Irregular, poor quality enamel prisms were observed on SEM. These were coated in amorphous material. TMR and EDX confirmed reduced mineral and increased organic content in enamel, respectively.
FAM83H nonsense mutations have recently been recognised as a cause of AD hypocalcified AI. We report a novel nonsense FAM83H mutation and describe the associated preliminary ultrastructural phenotype in deciduous teeth. This is characterised by poorly formed enamel rods with inappropriate retention of amorphous material, which is likely to represent retained organic matrix that contributes to the overall hypomineralised phenotype.
... 6,7 In addition, the microstructure of the enamel prisms in the Jalili syndrome teeth was obscured by an amorphous organic material. This appearance of the affected enamel was in many ways similar to that published previously for teeth clinically diagnosed as affected by hypomaturation AI. 15 In addition, we performed immunofluorescence on mouse retina sections and immunohistochemistry on rat incisors and confirmed Cnnm4 expression in both retina and developing teeth (Figure 4). Ameloblasts were heavily labeled during the transition and maturation phases of amelogenesis, but labeling was absent from ameloblasts during the secretion phase. ...
... 21 It is possible to envisage a role for CNNM4 B C A Figure 3. Laboratory Phenotyping of Teeth Standard methods were used for tooth-section (100 mm) preparation from Jalili syndrome teeth and normal controls for subsequent scanning electron microscopy (SEM), transverse microradiography (TMR), and energy dispersive X-ray spectroscopy (EDX). 15,37 (A) SEM: The dense, ordered rod structure of control enamel in which individual constituent hydroxyapatite crystals making up the rods can be discerned (i) contrasts with that observed in Jalili syndrome, which is characterized by incompletely formed, irregular enamel rods with detailed structure obscured by amorphous material (ii) and focal areas of more disordered enamel where the amorphous covering material is concentrated into larger, coherent areas (iii). The bar represents 10 mm. ...
Familial abnormalities of tooth biomineralisation may occur alone or in combination with other inherited abnormalities as part of syndromes. Sensory organ and tooth development are not obviously linked. Jalili Syndrome is characterised by generalised enamel defects prone to post-eruptive enamel loss consistent with a mixed Amelogenesis Imperfecta (AI) phenotype plus early onset central retinal degeneration typical of Cone Rod Dystrophy (CRD). There is an autosomal recessive pattern of inheritance. Jalili syndrome has been linked to chromosome 2q11 in a large kindred from the Gaza Strip. Objective: This study aims to describe the genetic refinement obtained through the investigation of 6 discrete families with Jalili Syndrome. Methods: Families with Jalili Syndrome originating from the Gaza Strip (2 separate pedigrees), Bosnia, Guatemala, Turkey and Iran were included. SNP chip and microsatellite marker genotyping were undertaken. Results: Genotyping confirmed linkage to chromosome 2q11 with LOD scores >2.0 in each family. Combining information from all families, the best refinement is between SNPs rs2628474 and rs1533655, an 11.64mb interval including the chromosome 2 centromere and around 60 annotated genes. There was no evidence of deletions involving one or more genes. Conclusions: Six families of diverse ethnic origins have been identified with Jalili Syndrome, characterised by AI and CRD. All families showed genetic linkage to chromosome 2q11, suggesting that Jalili syndrome is genetically homogeneous. The observation of multiple families with the same condition argues against this being due to two closely linked mutations in separate genes and favours the hypothesis that the condition is caused by mutations in a single gene essential for the development and function of both teeth and eyes. Studies are ongoing to identify the mutations responsible for this unusual combination of early-onset retinal degeneration and failure of enamel biomineralisation. Funded by the Egyptian Government (WE) and The Wellcome Trust.
... 6,7 In addition, the microstructure of the enamel prisms in the Jalili syndrome teeth was obscured by an amorphous organic material. This appearance of the affected enamel was in many ways similar to that published previously for teeth clinically diagnosed as affected by hypomaturation AI. 15 In addition, we performed immunofluorescence on mouse retina sections and immunohistochemistry on rat incisors and confirmed Cnnm4 expression in both retina and developing teeth (Figure 4). Ameloblasts were heavily labeled during the transition and maturation phases of amelogenesis, but labeling was absent from ameloblasts during the secretion phase. ...
... 21 It is possible to envisage a role for CNNM4 B C A Figure 3. Laboratory Phenotyping of Teeth Standard methods were used for tooth-section (100 mm) preparation from Jalili syndrome teeth and normal controls for subsequent scanning electron microscopy (SEM), transverse microradiography (TMR), and energy dispersive X-ray spectroscopy (EDX). 15,37 (A) SEM: The dense, ordered rod structure of control enamel in which individual constituent hydroxyapatite crystals making up the rods can be discerned (i) contrasts with that observed in Jalili syndrome, which is characterized by incompletely formed, irregular enamel rods with detailed structure obscured by amorphous material (ii) and focal areas of more disordered enamel where the amorphous covering material is concentrated into larger, coherent areas (iii). The bar represents 10 mm. ...
The combination of recessively inherited cone-rod dystrophy (CRD) and amelogenesis imperfecta (AI) was first reported by Jalili and Smith in 1988 in a family subsequently linked to a locus on chromosome 2q11, and it has since been reported in a second small family. We have identified five further ethnically diverse families cosegregating CRD and AI. Phenotypic characterization of teeth and visual function in the published and new families reveals a consistent syndrome in all seven families, and all link or are consistent with linkage to 2q11, confirming the existence of a genetically homogenous condition that we now propose to call Jalili syndrome. Using a positional-candidate approach, we have identified mutations in the CNNM4 gene, encoding a putative metal transporter, accounting for the condition in all seven families. Nine mutations are described in all, three missense, three terminations, two large deletions, and a single base insertion. We confirmed expression of Cnnm4 in the neural retina and in ameloblasts in the developing tooth, suggesting a hitherto unknown connection between tooth biomineralization and retinal function. The identification of CNNM4 as the causative gene for Jalili syndrome, characterized by syndromic CRD with AI, has the potential to provide new insights into the roles of metal transport in visual function and biomineralization.
PMID: 19200525 [PubMed - indexed for MEDLINE] PMCID: PMC2668026 Free PMC Article
... 6,7 In addition, the microstructure of the enamel prisms in the Jalili syndrome teeth was obscured by an amorphous organic material. This appearance of the affected enamel was in many ways similar to that published previously for teeth clinically diagnosed as affected by hypomaturation AI. 15 In addition, we performed immunofluorescence on mouse retina sections and immunohistochemistry on rat incisors and confirmed Cnnm4 expression in both retina and developing teeth (Figure 4). Ameloblasts were heavily labeled during the transition and maturation phases of amelogenesis, but labeling was absent from ameloblasts during the secretion phase. ...
... 21 It is possible to envisage a role for CNNM4 B C A Figure 3. Laboratory Phenotyping of Teeth Standard methods were used for tooth-section (100 mm) preparation from Jalili syndrome teeth and normal controls for subsequent scanning electron microscopy (SEM), transverse microradiography (TMR), and energy dispersive X-ray spectroscopy (EDX). 15,37 (A) SEM: The dense, ordered rod structure of control enamel in which individual constituent hydroxyapatite crystals making up the rods can be discerned (i) contrasts with that observed in Jalili syndrome, which is characterized by incompletely formed, irregular enamel rods with detailed structure obscured by amorphous material (ii) and focal areas of more disordered enamel where the amorphous covering material is concentrated into larger, coherent areas (iii). The bar represents 10 mm. ...
Autozygosity mapping and clonal sequencing of an Omani family identified mutations in the uncharacterized gene, C4orf26, as a cause of recessive hypomineralized amelogenesis imperfecta (AI), a disease in which the formation of tooth enamel fails. Screening of a panel of 57 autosomal-recessive AI-affected families identified eight further families with loss-of-function mutations in C4orf26. C4orf26 encodes a putative extracellular matrix acidic phosphoprotein expressed in the enamel organ. A mineral nucleation assay showed that the protein's phosphorylated C terminus has the capacity to promote nucleation of hydroxyapatite, suggesting a possible function in enamel mineralization during amelogenesis.
... No previous studies on this topic are to date found, why our result can not be compared with results from others. However, studying syndromes and conditions with a different aetiology than TS, such as Down's syndrome or amelogenesis imperfecta, qualitative and quantitative hard tissue aberrations have been found (217)(218). In Down's syndrome, where as in TS a prolonged cell cycle in fibroblasts is documented, enamel aberrations as less mineralised and smaller amount of enamel were found compared to controls (217). ...
... In Down's syndrome, where as in TS a prolonged cell cycle in fibroblasts is documented, enamel aberrations as less mineralised and smaller amount of enamel were found compared to controls (217). In teeth from children with X-linked amelogenesis imperfecta, an increased level of carbon together with obscured prisms and crystals were reported (218). ...
The overall aim of this thesis was to study dentofacial morphology in Turner syndrome (TS) versus controls and the influence hereupon from karyotype. One hundred thirty two TS females (5-66 years of age), from Göteborg, Uppsala and Umeå were participating. Cephalometric analysis, cast model analysis concerning palatal height, dental arch morphology and dental crown width were performed. Eighteen primary teeth were analysed in polarized light microscopy, scanning electron microscopy, microradiography and X-ray microanalysis were performed. The TS females were divided according to karyotype into: 1 45,X; 2 45,X/46,XX; 3 isochromosome; 4 other. Compared to healthy females, TS were found to have a flattened cranial base as well as small and retrognathic jaws with a posterior inclination. The maxillary dentoalveolar arch was narrower and longer, while the mandibular dental arch was wider and longer in TS compared to controls. The palatal height did not differ comparing TS and healthy females. The dental crown width was smaller in TS for both permanent and primary teeth. Aberrant elemental composition, prism pattern and lower mineral density were found in TS primary enamel compared to enamel in primary teeth from healthy girls. Turner syndrome karyotype was found having an impact on craniofacial morphology, with the mosaic 45,X/46,XX exhibiting a milder mandibular retrognathism as well as fewer cephalometric variables differing from controls compared to other karyotypes. Also for the dentoalveolar arch morphology the 45,X/46,XX group had fewer variables differing from healthy females. The isochromosome TS group exhibited the smallest dental crown width for several teeth, while 45,X/46,XX hade the largest dental crown with for some teeth and fewer teeth than both 45,X and isochromosomes that differed from controls. Thus, the mosaic 45,X/46,XX seemed to exhibit a milder phenotype, possibly due to presence of healthy 46,XX cell lines.
... Standard methods were used for tooth-section (100 μm) preparation from Jalili syndrome teeth and normal controls for subsequent scanning electron microscopy (SEM), transverse microradiography (TMR), and energy dispersive X-ray spectroscopy (EDX).15,37 ...
... In addition, the microstructure of the enamel prisms in the Jalili syndrome teeth was obscured by an amorphous organic material. This appearance of the affected enamel was in many ways similar to that published previously for teeth clinically diagnosed as affected by hypomaturation AI.15 ...
The combination of recessively inherited cone-rod dystrophy (CRD) and amelogenesis imperfecta (AI) was first reported by Jalili and Smith in 1988 in a family subsequently linked to a locus on chromosome 2q11, and it has since been reported in a second small family. We have identified five further ethnically diverse families cosegregating CRD and AI. Phenotypic characterization of teeth and visual function in the published and new families reveals a consistent syndrome in all seven families, and all link or are consistent with linkage to 2q11, confirming the existence of a genetically homogenous condition that we now propose to call Jalili syndrome. Using a positional-candidate approach, we have identified mutations in the CNNM4 gene, encoding a putative metal transporter, accounting for the condition in all seven families. Nine mutations are described in all, three missense, three terminations, two large deletions, and a single base insertion. We confirmed expression of Cnnm4 in the neural retina and in ameloblasts in the developing tooth, suggesting a hitherto unknown connection between tooth biomineralization and retinal function. The identification of CNNM4 as the causative gene for Jalili syndrome, characterized by syndromic CRD with AI, has the potential to provide new insights into the roles of metal transport in visual function and biomineralization.
... -Un émail hypomature : s'il n'y a pas de différence du ratio Ca/P comparé à l'émail sain 26,39 , l'émail atteint présente une concentration plus élevée en fluorures et en protéines 26,37 . La forte augmentation en carbone, non corrélée à celle de l'azote et de l'oxygène suggère qu'il ne s'agit pas exclusivement d'une augmentation de protéines, mais possiblement de lipides également 29 . Dans la moitié interne de l'émail apparaît souvent une zone amorphe, de radio-opacité semblable à celle de la dentine. ...
Introduction:
Bonding to enamel is a daily problem for the orthodontist. While bonding to healthy enamel is nowadays well mastered, bonding to hypomineralized enamel is much less so. The aim of this article was to help the orthodontist to optimise bonding, whatever the clinical situation.
Material and method:
Based on data from the literature, the clinical and microscopic characteristics of healthy and hypomineralised enamel, including amelogenesis imperfecta (AI), molar incisor hypomineralization (MIH), fluorosis or erosion will be described. Proposals for optimising bonding will then be identified and summarized.
Results:
Bonding to enamel is reliable, but the use of an etch-and-rinse mode (even with a universal adhesive) is recommended. For AI, MIH and fluorosis, the use of sodium hypochlorite after etching seems to significantly increase bonding. No treatment is needed for eroded enamel. However, deep resin infiltration for severe MIH or superficial resin infiltration for fluorosis would reduce the risk of enamel fracture during bracket removal.
Conclusion:
It is important to be aware of the characteristics of the dental substrate and the materials used to optimize procedures.
... Par exemple, dans le cas d'une amélogenèse imparfaite (AI) de type hypominéralisé, l'émail est caractérisé par une diminution de la minéralisation (Wright et al. 1993). Une augmentation de la teneur en carbonate a également été mise en évidence dans les AI (Shore et al. 2002, Sa et al. 2014. A contrario, Wright et al. (1993) ont trouvé des taux identiques de carbonate dans l'AI et l'émail normal (Wright et al. 1993). ...
Les diagnostics d’hypominéralisations molaire-incisive (HMI) et de colorations post-mortem de l’émail sont peu fiables et reproductibles dans des séries archéologiques. Notre guide de diagnostic a permis de distinguer les hypominéralisations de l’émail des colorations taphonomiques. L'émail hypominéralisé est caractérisé par des taux de β-carbonate plus élevés et une densité minérale plus faible. Les colorations taphonomiques présentent une concentration plus élevée en manganèse, en fer, en cuivre et en plomb, mises en évidences par des analyses en fluorescence X. Les dentures d’individus immatures issus de 21 séries archéologiques ont été examinés et comprenaient : 4 séries françaises, Sains-en-Gohelle (Pas-de-Calais), Cognac-Saint-Martin (Charente), Beauvais (Oise) et Jau-Dignac-et-Loirac (Gironde) provenant de cimetières médiévaux et post-médiévaux et 17 séries anglaises (Londres) provenant de cimetières romains, médiévaux et post-médiévaux. Nous avons dénombré 555 individus dont l’âge au décès est compris entre 5 et 19 ans et dont la datation chronologique s’étale sur une période allant du 1er au 19ème siècle. Au total, sur les 290 individus avec au moins une première molaire permanente (PMP) présente, 42 avaient au moins une opacité délimitée de l’émail sur une PMP (soit 14,5%). Parmi les 17 individus dont les dents ont été analysées, les tests statistiques n’ont mis en évidence que 9 cas de HMI, soit 52,9% de l’effectif. Une prévalence de 9,3% de HMI a été estimée dans nos séries archéologiques ce qui avoisine les prévalences connues à l’heure actuelle dans les populations du vivant en Europe. Les défauts du développement de d'émail sont souvent utilisés comme indicateurs de la santé générale dans les populations archéologiques passées. La possibilité de trouver des HMI dans des populations anciennes minimise l’importance de certaines hypothèses étiologiques contemporaines (par exemple les dérivés de dioxines, les bisphénols ou les antibiotiques) sans exclure l'aspect multifactoriel possible de l'anomalie.
... Both MIH and the hypocalcified form of AI enamel show decreased mineralisation (Wright, Duggal, Robinson, Kirkham, & Shore, 1993). Similarly, an increase of carbonate content has been determined in MIH and AI enamel (Sa et al., 2014;Shore et al., 2002). In contrast, Wright et al. (1993) reported similar carbonate content in AI and normal enamel (Wright, Duggal, Robinson, Kirkham, & Shore, 1993). ...
Objective
Molar Incisor Hypomineralisation (MIH) is a structural anomaly that affects the quality of tooth enamel and has important consequences for oral health. The developmentally hypomineralised enamel has normal thickness and can range in colour from white to yellow or brown with or without surface breakdown. The possibility of finding MIH in ‘ancient populations' could downplay several current aetiological hypotheses (e.g., dioxin derivatives, bisphenols, antibiotics) without excluding the possible multifactorial aspect of the anomaly. In an archaeological context, chemical elements contained in the burial ground can stain teeth yellow or brown and therefore might create a taphonomic bias. The purpose of the present study is to test a proposed diagnostic guide enabling determination of the pathological or taphonomic cause of enamel discolouration and defects that resemble MIH present on ‘ancient teeth'.
Design
Two sample groups including MIH discoloration (n = 12 teeth) from living patients, taphonomic discoloration (n = 9 teeth) and unknown discoloration (n = 2 teeth) from medieval specimens were tested. Three non-destructive methods—Raman spectroscopy, X-ray micro-computed tomography and X-ray fluorescence were utilised.
Results
Hypomineralised enamel has decreased mineral density (p < 0.0001) and increased phosphate/β-carbonate ratio (p < 0.01) compared to normal enamel whereas relative concentrations of manganese, copper, iron and lead are similar. In taphonomic discoloration, relative concentrations of these elements are significantly different (p < 0.05) to normal enamel whereas mineral density and Raman spectra profile are comparable.
Conclusions
Enamel hypomineralisation can be distinguished from taphonomic staining in archaeological teeth.
... However, owing to the scarcity of available enamel samples and/or the lack of appropriate technologies, hypomaturation enamel is still poorly investigated. To the best of our knowledge, a limited number of studies have simply observed the structure of hypomaturation enamel and evaluated its elemental and protein content [22,23]. Detailed is still deficient and no previous study has systematically evaluated the structural organization of hypomaturation enamel at different hierarchical levels. ...
Hypomaturation amelogenesis imperfecta is a hereditary disorder of the enamel that severely influences the function, aesthetics and psychosocial well-being of patients. In this study, we performed a thorough comparison of normal and hypomaturation enamel through a series of systematical tests on human permanent molars to understand the biomineralization process during pathological amelogenesis. The results of micro-computed tomography, scanning electron microscopy, Fourier transform infrared, Raman spectroscopy, microzone X-Ray diffraction, thermal gravimetric analysis, energy diffraction spectrum and Vickers microhardness testing together show dramatic contrasts between hypomaturation enamel and normal enamel in terms of their hierarchical structures, spectral features, crystallographic characteristics, thermodynamic behaviours, mineral distribution and mechanical property. Our current study highlights the importance of organic matrix during the amelogenesis process. It is found that the retention of organic matrix will influence the quantity, quality and distribution of mineral crystals, which will further demolish the hierarchical architecture of enamel and affect the related mechanical property. In addition, the high carbonate content in hypomaturation enamel influences the crystallinity, crystal size and solubility of hydroxyapatite crystals. These results deepen our understanding of hypomaturation enamel biomineralization during amelogenesis, explain clinical manifestations of hypomaturation enamel, provide fundamental evidence for dentists to choose optimal therapeutic strategies and lead to improved biofabrication and gene therapies.
... The mechanism by which WDR72 nonsense mutations result in hypomaturation AI is unknown, but the lack of missense mutations suggests a null phenotype due to mRNA nonsensemediated decay rather than production of stable truncated proteins. . When organic material is retained, incubation with either ␣ -chymotrypsin or lipase can be informative and reveal the enamel ultrastructure in greater detail [Shore et al., 2002]. In this study the absence of retained enamel matrix protein in affected enamel indicates that ameloblasts are able to direct degradation and removal of enamel matrix in a manner similar to that in normal teeth. ...
Mutations in WDR72 have been identified in autosomal recessive hypomaturation amelogenesis imperfecta (AI).
to describe a novel WDR72 mutation and report the ultrastructural enamel phenotype associated with a different WDR72 mutation.
A family segregating autosomal recessive hypomaturation AI was recruited, genomic DNA obtained and WDR72 sequenced. Four deciduous teeth from one individual with a previously published WDR72 mutation, extracted as part of clinical care, were subjected to scanning electron microscopy, energy-dispersive X-ray analysis and transverse microradiography.
A novel homozygous nonsense mutation, R897X, was identified in WDR72 in a family originating from Pakistan. Ultrastructural analysis of enamel from the deciduous teeth of an AI patient with the WDR72 mutation S783X revealed energy-dispersive X-ray analysis spectra with normal carbon and nitrogen peaks, excluding retention of enamel matrix protein. However, transverse microradiography values were significantly lower for affected teeth when compared to normal teeth, consistent with reduced mineralisation. On scanning electron microscopy the enamel rod form observed was normal, yet with inter-rod enamel more prominent than in controls. This appearance was unaltered following incubation with either α-chymotrypsin or lipase.
The novel WDR72 mutation described brings the total reported WDR72 mutations to four. Analyses of deciduous tooth enamel in an individual with a homozygous WDR72 mutation identified changes consistent with a late failure of enamel maturation without retention of matrix proteins. The mechanisms by which intracellular WDR72 influences enamel maturation remain unknown.
... In other conditions and syndromes, including chromosomal aberrations such as DownÕs syndrome, 22q11 deletion syndrome, and Ehlers-Danlos syndrome, in addition to amelogenisis imperfecta, qualitative and/or quantitative hard tissue changes have been published (42)(43)(44)(45). It is difficult to interpret and compare our results with previously published findings of other conditions. ...
Rizell S, Kjellberg H, Dietz W, Norén JG, Lundgren T. Altered inorganic composition of dental enamel and dentin in primary teeth from girls with Turner syndrome. Eur J Oral Sci 2010; 118: 183–190. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci
In Turner syndrome (TS) one X-chromosome is missing or defective. The amelogenin gene, located on the X-chromosome, plays a key role during the formation of dental enamel. The aim of this study was to find support for the hypothesis that impaired expression of the X-chromosome influences mineral incorporation during amelogenesis and, indirectly, during dentinogenesis. Primary tooth enamel and dentin from girls with TS were analysed and compared with the enamel and dentin of primary teeth from healthy girls. Qualitative and quantitative changes in the composition of TS enamel were found, in addition to morphological differences. Higher frequencies of subsurface lesions and rod-free zones were seen in TS enamel using polarized light microscopy. Similarly, scanning electron microscopy showed that the enamel rods from TS teeth were of atypical sizes and directions. Using X-ray microanalysis, high levels of calcium and phosphorus, and low levels of carbon, were found in both TS enamel and dentin. Using microradiography, a lower degree of mineralization was found in TS enamel. Rule induction analysis was performed to identify characteristic element patterns for TS. Low values of carbon were the most critical attributes for the outcome TS. The conclusion was that impaired expression of the X-chromosome has an impact on dental hard tissue formation.
Nanoscale chemical characterization of biominerals has been significantly improved by the use of atom probe tomography (APT). A main application is on the analysis of tooth enamel, including the alterations induced by caries processes, but limited in characterizing other diseases on human teeth. Here, we use APT to study enamel affected by amelogenesis imperfecta (AI). Our results show that APT distinguish the presence and distribution of carbon and nitrogen in AI enamel corresponding to a reported increase in protein and lipid components. Also, APT demonstrates that boundaries of apatite crystals, defined by the 3D distribution of magnesium and sodium, are disrupted in AI compared to sound enamel. In summary, our study highlights new capabilities of atom probe tomography in the analysis of biomineralized hard tissues under healthy and disease conditions.
The circularly causal orchestration of bone production and destruction is a part of the standard model of bone remodeling, but the crystallinity of the bone mineral, which naturally alternates during this process, has not had a steady place in it. Here we show that osteoclasts and osteoblasts, the cells resorbing and building bone, respectively, can sense the crystallinity of the bone mineral and adjust their activity thereto. Specifically, osteoblastic MC3T3-E1 cells secreted mineral nodules more copiously when they were brought into contact with amorphous calcium phosphate (ACP) nanoparticles than when they were challenged with their crystalline, hydroxyapatite (HAp) analogues. Moreover, the gene expressions of osteogenic markers BGLAP, ALP, BSP-1 and RUNX2 in MC3T3-E1 cells were higher in the presence of ACP than in the presence of HAp. At the same time, the dental pulp stem cells differentiated into an osteoblastic phenotype to a degree that was inversely proportional to the amount and the crystallinity of the mineral added to their cultures. In contrast, the resorption of HAp nanoparticles was more intense than the resorption of ACP, as concluded by the greater retention of the latter particles inside the osteoclastic RAW264.7 cells after 10 days of incubation and also by the time-dependent free Ca2+ concentration measurements in the cell culture media at early incubation time points (< 1 week), prior to the spontaneous crystallization of the amorphous phase. A detailed morphological, compositional and microstructural characterization of ACP and HAp is provided too and it is shown that although ACP transforms to HAp in the cell culture media, some microstructural properties are retained in the powder following this transformation, influencing the resorption rate. On the basis of these findings, a model of bone remodeling at the level of individual biogenic apatite nanoparticles was proposed, taking into account the effects of hydration and lattice strain. According to this model, apatite is a “living” mineral, undergoing fluctuations in crystallinity within a closed ossifying/resorptive feedback loop in a way that buffers against potential runaway effects. A finite degree of amorphousness of every apatite crystal in bone is seen as a vital prerequisite for a healthy, dynamic bone remodeling process and the best bone mineral, from this standpoint, is the living mineral, the one undergoing a constant process of structural change in response to biochemical stimuli thanks to its partially amorphous microstructure and unique interfacial dynamics.
Candidate genes for amelogenesis imperfecta (AI) and dentinogenesis imperfecta (DI) are located on 4q21 in humans. We tested our hypothesis that mutations in the portion of mouse chromosome 5 corresponding to human chromosome 4q21 would cause enamel and dentin abnormalities. Male C3H mice were injected with ethylnitrosourea (ENU). Within a dominant ENU mutagenesis screen, a mouse mutant was isolated with an abnormal tooth enamel (ATE) phenotype. The structure and ultrastructure of teeth were studied. The mutation was located on mouse chromosome 5 in an interval of 9 cM between markers D5Mit18 and D5Mit10. Homozygotic mutants showed total enamel aplasia with exposed dentinal tubules, while heterozygotic mutants showed a significant reduction in enamel width. Dentin of mutant mice showed a reduced content of mature collagen cross-links. We were able to demonstrate that a mutation on chromosome 5 corresponding to human chromosome 4q21 can cause amelogenesis imperfecta and changes in dentin composition.
In order to explore the possibility that phospholipids are differently expressed during the cascade of events leading to tooth formation, we decided to carry out simultaneous biochemical, histological and electron histochemical studies. High performance thin-layer chromatography and gas–liquid chromatography were used to compare the composition of embryonic mouse first molar tooth germs at day 18 of gestation (E18) and at birth (D1), erupting teeth at day 7 (D7) and erupted molars at day 21 (D21). For the latter, non-demineralized and EDTA-demineralized lipid extracts were analysed separately. Moreover, an ultrahistochemical study was carried out using the iodoplatinate reaction which retains and visualizes phospholipids. Developmentally regulated changes occurred and were closely correlated with an increase in cell membrane phospholipids. Gradual accumulation of phospholipids was identified in the extracellular matrix, at an early stage of tooth germ development within the basement membrane and later, as predentine/dentine and enamel components participating in mineralization processes. Matrix vesicles transiently present in dentine were partly responsible for the lipids that were detected. A first group of phospholipids including phosphatidylcholine as the major membrane-associated phospholipid and phosphatidylinositol as the intracellular second messenger increased by a factor of 2.3 between E18 and D21. This increase is probably associated with cell lengthening and was relatively modest compared with the higher increase detected for a second group of phospholipids, namely phosphatidylethanolamine (4.8), phosphatidylserine (5.9) and sphingomyelin (5.4). This second group of extracellular matrix-associated phospholipids constituted 68% of the demineralized lipid extract and, therefore, contributes to the mineralization of dental tissues.
Hypomaturation amelogenesis imperfecta (AI) is a hereditary condition of enamel that is presumed to result from defects during the maturation stage of enamel development. This study characterized the enamel ultrastructure and enamel crystallite morphology, as well as the distribution of organic material in enamel affected with pigmented hypomaturation AI. Enamel exhibiting autosomal recessive pigmented hypomaturation AI was sectioned or fractured and examined using light microscopy, scanning electron microscopy and transmission electron microscopy. Enamel samples were treated with 30% NaOCl or 8 M urea to remove organic components and determine the effect of deproteinization on crystallite morphology. These were compared with untreated normal enamel samples. The enamel crystallites in hypomaturation AI exhibited considerable variability in size and morphology. Examination of deproteinized tissue indicated that the AI crystallites had a thick coating, presumably of organic or partially mineralized material, which was not visible in normal enamel. The results of this investigation provide further evidence that hypomaturation AI is associated with the retention of organic material that is most probably enamel protein. Enamel protein retention is likely to be involved in the inhibition of normal crystallite growth resulting in the morphological crystallite abnormalities associated with this disorder.
Amelogenesis imperfecta is characterized by the defective formation of tooth enamel. Here we present evidence that the X-linked form of this disorder (AIH1) is caused by a structural alteration in one of the predominant proteins in enamel, amelogenin. Southern blot analysis revealed a deletion extending over 5 kb of the amelogenin gene in males with the hypomineralization form of the AIH1. Carrier females were heterozygous for the molecular defect. The deletion appears to include at least two exons of the amelogenin gene and the extent of the deletion was verified by PCR analysis. The mutation was shown to segregate with the disease among 15 analyzed individuals belonging to the same kindred. Our results link a defect in the amelogenin gene to the abnormal formation of enamel. We thus conclude that the amelogenin protein has a role in biomineralization of tooth enamel.
The mode of inheritance and the clinical manifestations of amelogenesis imperfecta (AI) were studied in 51 families from the county of Västerbotten, northern Sweden. Autosomal dominant (AD) was the most probable mode of inheritance in 33 families, but X-linked dominant (XD) inheritance was a possible alternative in one family. Autosomal recessive (AR) inheritance was found likely in 6 and X-linked recessive inheritance in 2 families. Ten probands were sporadic cases. In the families with AD inheritance, a sex difference was observed between affected and non-affected cases, with an excess of females in the affected group (p less than 0.05). In addition to the 78 index cases, 107 new cases were diagnosed. The clinical manifestations of AI observed could be divided into 2 forms, the hypoplastic form in 72% and the hypomineralization form in 28% of the individuals. AD inheritance was seen in 89% of the cases with the hypoplastic form, and in 44% of the cases with the hypomineralization form. In most families with AD or AR inheritance, each family displayed a characteristic manifestation of either hypoplastic or hypomineralization defects. In 3 families, both hypoplastic and hypomineralization forms of AI were seen. In families with X-linked inheritance, the clinical manifestation differed between females and males with males more seriously affected.
The clinical manifestations of amelogenesis imperfecta (AI) were described in 165 individuals from 51 families. The inheritance pattern for AI in these families had previously been investigated, and it was hypothesized that AI probably is solely an autosomal dominant (AD) or X-linked trait. To test this hypothesis the connection between clinical manifestation and inheritance pattern was studied. Eight different variants of AI were seen. In 33/51 families all affected individuals could be assigned to the same clinical variant. In 8/51 families those affected were assigned to different clinical variants. In the two families where an X-linked recessive (XR) inheritance pattern was found probable, the clinical manifestation differed between women and men. Except for one variant only seen as an AD trait, and the manifestation in women in families with an X-linked recessive inheritance pattern, no connection was found between a specific inheritance pattern and a specific clinical manifestation. Accordingly it seems likely that AI is solely an AD or X-linked trait. The different clinical variants observed should be regarded as a varying expressivity of the gene and in the families with X-linked inheritance probably due to lyonization. In the remaining families the modifying mechanisms are not known.
The aim of the present investigation was to determine the mineral distribution in the enamel of teeth with amelogenesis imperfecta (AI) by quantitative microradiography. A further aim was to correlate the findings to clinical manifestations and inheritance patterns for AI. Included in the study were a total of 29 teeth with AI, 28 primary and one permanent, and seven unaffected teeth, five primary and two permanent. Quantitative microradiography was applied to sagittally ground sections, 70-90 microns, of the teeth. The mineral content of the enamel, expressed as percentage by volume, was lower in most of the teeth with AI than in the unaffected teeth. The largest range for the mineral distribution was found in the enamel of the variants clinically characterized by hypomineralization. These teeth showed a mineral distribution pattern that reflected an extremely low mineral content in the bulk of the enamel. In the AI teeth clinically characterized by hypoplasia, the mineral distribution pattern was similar to that of the unaffected teeth, although with larger local variations in mineral content. Apart from the teeth connected with X-linked inheritance, no differences were found among teeth with similar clinical variants connected with different inheritance patterns.
Amelogenesis imperfecta (AI) is a group of hereditary enamel defects, characterized by large clinical diversity. On the basis of differences in clinical manifestation and inheritance pattern, 14 different subtypes have been recognized. A locus for autosomal dominant AI (ADAI) of local hypoplastic type was recently mapped to the region between D4S392 and D4S395 on the long arm of chromosome 4. To test whether the chromosome 4 locus is responsible for other forms of AI as well, a linkage study was carried out with 17 families representing at least five clinical forms of ADAI. Admixture tests for heterogeneity performed with the marker D4S2456 gave statistical support for genetic heterogeneity of ADAI with the odds 78:1. Linkage to the ADAI locus on chromosome 4q (AIH2) could only be demonstrated with families expressing the local hypoplastic type, and there was no support for heterogeneity within that group of families. Furthermore, linkage could be excluded for five families with other clinical forms of ADAI. The data therefore demonstrated that ADAI is genetically heterogeneous, and that at least two loci for it exist.
Dental enamel is a product of ameloblast cells, which secrete a mineralizing organic matrix, composed primarily of amelogenin proteins. The amelogenins are thought to be crucial for development of normal, highly mineralized enamel. The X-chromosomal amelogenin gene is a candidate gene for those cases of amelogenesis imperfecta, resulting in defective enamel, in which inheritance is X-linked. In this report, a kindred is described that has a C to A mutation resulting in a pro to thr change in exon 6 of the X-chromosomal amelogenin gene in three affected individuals, a change not found in unaffected members of the kindred. The proline that is changed by the mutation is conserved in amelogenin genes from all species examined to date.
While it is believed that proteins may protect enamel from demineralisation, recent work has indicated that such material may also hinder remineralisation. For example, albumin will inhibit apatite crystal growth in vitro and is present in carious enamel in vivo. However, it is not clear whether (1) the distribution of proteins within lesions is restricted to specific lesion zones or (2) the origin of such proteins is endogenous (i.e. as a remnant of the developmental process) or exogenous, originating in the saliva or gingival crevicular fluid. The present study used a combination of immunohistochemistry and microradiography to determine the distribution of two proteins, serum albumin and salivary amylase, within natural white-spot carious lesions in relation to specific levels of demineralisation. The results indicated that albumin is found primarily in a region of between 10 and 20% demineralisation (an area of transition between the 'dark' zone and lesion 'body'), with smaller quantities occurring in the region between 0 and 10% demineralisation and trace amounts in the zone indistinguishable from sound enamel by microradiography. A similar distribution was found for amylase in that the heaviest labelling was within the 10-20% demineralisation zone, although little if any was present in the 0-10% zone. The presence of these molecules in a region of the lesion where some potential for reprecipitation may exist will have important implications with respect to lesion progression.
Enamel protein in different types of amelogenesis imperfecta
- J T Wright
- C Robinson
- J Kirkham
Wright, J.T., Robinson, C., and Kirkham, J. (1992). " Enamel protein in different types of amelogenesis imperfecta. " In: Chemistry and Biology of Mineralised Tissues, H. Slavkin and P. Price (eds.), pp. 441–450.