Regulation of Dental Enamel Shape and Hardness

Simmer, James P.; Papagerakis, Pétros; Smith, Charles E.; Fisher, Daniel C.; Rountrey, Adam N.; Zheng, Liwei; Hu, Jan C.‐C.

doi:10.1177/0022034510375829

Cited by 206 publications

(221 citation statements)

References 142 publications

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“…During tooth development, amelogenin and other matrix components (enamelin, ameloblastin) are deposited by enamelsecreting ameloblasts in a highly structured manner to form enamel rods that are fully mineralized during maturation, with degradation of protein components and deposition of hydroxyapatite minerals (6). Mature enamel consists of approximately 96% minerals, 3% water, and 1% organic material by weight.…”

Section: Introductionmentioning

confidence: 99%

Hair keratin mutations in tooth enamel increase dental decay risk

Duverger¹,

O’Hara²,

Shaffer³

et al. 2014

J. Clin. Invest.

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B r i e f r e p o r t5hair in the facial area upon shaving, is associated with a polymorphism (rs2232387) in the KRT75 gene and more prevalent in AfricanAmericans due to the curly nature of their hair (23). This G-to-A missense mutation (KRT75 GA or KRT75 AA genotypes) leads to an alanine-to-threonine substitution at position 161 (A161T) in a highly conserved region of the 1A α-helical segment of KRT75 ( Figure 1E). To determine whether the KRT75 A161T mutation had clinical impact on enamel function, we tested the genetic association between the KRT75 polymorphism (rs2232387) and tooth decay assessed as dental caries experience in the primary dentition of 386 children (mixed European descent, 6-12 years) and permanent dentition of 706 adults (mixed European descent, 25-50 years). The missense A allele of rs2232387, which was observed in 23% of the samples, was associated with a higher number of carious tooth surfaces in adults but not children ( Figure 1F and Supplemental Table 1).We investigated the expression pattern of KRT75 in mouse enamel organ and in mature human enamel. KRT75 was expressed by mouse ameloblasts at the secretory stage (Supplemental Figure 2A) and detected in the tufts and rod sheaths of mature human enamel ( Figure 1, B and C). Interestingly, until enamel matrix proteins were identified, enamel was thought to be a keratinized structure, like hair and nail, with an extreme degree of mineralization (18,19). Here, we show that a subset of hair keratins is expressed by ameloblasts, and we demonstrate that KRT75 is incorporated into the tufts and rod sheaths in mature enamel. Since keratins are not secreted proteins, their deposition in enamel may be related to the retention of cell fragments at the periphery of the rods (20).Mutations in hair keratins have been reported in various human pathological conditions (21, 22). Among them, pseudofolliculitis barbae, a hair disorder characterized by the formation of ingrown (F) Genetic association between the rs2232387 polymorphism and caries experience in primary and permanent dentition. Pie charts show allelic distribution of the rs2232387 polymorphism measured on 706 adults and 386 children. Graphs show measure of caries experience for each genotype: left, number of tooth surfaces with untreated decay (DS and ds); center, number of decayed, missing due to decay, and filled surfaces (DMFS and dfs); right, partial DMFS and dfs indices limited to the molars and premolars pit and fissure (PF and pf) surfaces. etched tooth samples sectioned in the plane transecting the enamel rods revealed that the distribution and characteristic keyhole shape of the rods were altered in individuals carrying the variant A allele (Figure 2A). Tufts and rod sheaths isolated from patients with the KRT75 GA or KRT75 AA genotype appeared disorganized ( Figure 2B), and the distribution pattern of KRT75 was highly disrupted ( Figure 2C). This was further corroborated by transmission electron microscopy analysis ( Figure 2D). These results suggest that epithelial hair keratins s...

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Section: Introductionmentioning

confidence: 99%

Hair keratin mutations in tooth enamel increase dental decay risk

Duverger¹,

O’Hara²,

Shaffer³

et al. 2014

J. Clin. Invest.

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“…Amelogenesis consists of secretory, transition and maturation stages (Simmer et al, 2010). During the secretory stage, ameloblasts secrete enamel proteins such as amelogenin (the most abundant enamel matrix protein; Eastoe, 1979), ameloblastin (Krebsbach et al, 1996) and enamelin (Hu et al, 1997) into the enamel matrix.…”

Section: Introductionmentioning

confidence: 99%

Critical role for αvβ6 integrin in enamel biomineralization

Mohazab

Koivisto

Jiang

et al. 2012

Journal of Cell Science

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SummaryTooth enamel has the highest degree of biomineralization of all vertebrate hard tissues. During the secretory stage of enamel formation, ameloblasts deposit an extracellular matrix that is in direct contact with the ameloblast plasma membrane. Although it is known that integrins mediate cell-matrix adhesion and regulate cell signaling in most cell types, the receptors that regulate ameloblast adhesion and matrix production are not well characterized. We hypothesized that avb6 integrin is expressed in ameloblasts where it regulates biomineralization of enamel. Human and mouse ameloblasts were found to express both b6 integrin mRNA and protein. The maxillary incisors of Itgb6 2/2 mice lacked yellow pigment and their mandibular incisors appeared chalky and rounded. Molars of Itgb6 2/2 mice showed signs of reduced mineralization and severe attrition. The mineral-to-protein ratio in the incisors was significantly reduced in Itgb6 2/2 enamel, mimicking hypomineralized amelogenesis imperfecta. Interestingly, amelogenin-rich extracellular matrix abnormally accumulated between the ameloblast layer of Itgb6 2/2 mouse incisors and the forming enamel surface, and also between ameloblasts. This accumulation was related to increased synthesis of amelogenin, rather than to reduced removal of the matrix proteins. This was confirmed in cultured ameloblast-like cells, in which avb6 integrin was not an endocytosis receptor for amelogenins, although it participated in cell adhesion on this matrix indirectly via endogenously produced matrix proteins. In summary, integrin avb6 is expressed by ameloblasts and it plays a crucial role in regulating amelogenin deposition and/or turnover and subsequent enamel biomineralization.

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“…La partie distale de ce prolongement va donner l'émail intraprismatique et la partie proximale, l'émail interprismatique ( Figure 4B-C). Au cours de la première étape de l'amélogenèse, phase sécrétoire, la production de protéines matricielles est maximale et celle des protéases, modérée [16]. Une fois l'épaisseur finale de l'émail atteinte, la phase de maturation de l'amélogenèse peut débuter.…”

Section: Les Peptides Amélairesunclassified