A post-classical theory of enamel biomineralization… and why we need one

Simmer, James P.; Richardson, Amelia S.; Hu, Yuan; Smith, Charles E.; Hu, Jan C.C.

doi:10.1038/ijos.2012.59

Cited by 94 publications

(95 citation statements)

References 88 publications

(102 reference statements)

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“…In addition, the diffusion of mineral ions from the oral environment to the enamel may decrease with an increase in the distance from the enamel surface (Park et al, 2008b;Simmer et al, 2012) because the changes in the mineral contents in the middle and the inner enamel layers are not significant between the two age groups (p40.05). As a result, there is no obvious difference in the fracture toughness of the interior enamel layers between the old and the young age groups.…”

Section: Discussionmentioning

confidence: 99%

Spatial distribution of the human enamel fracture toughness with aging

Zheng

Song

et al. 2013

Journal of the Mechanical Behavior of Biomedical Materials

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Enamel AgingMineral content a b s t r a c t A better understanding of the fracture toughness (KIC) of human enamel and the changes induced by aging is important for the clinical treatment of teeth cracks and fractures. We conducted microindentation tests and chemical content measurements on molar teeth from "young" (18≤age≤25) and "old" (55≤age) patients. The KIC and the mineral contents (calcium and phosphorus) in the outer, the middle, and the inner enamel layers within the cuspal and the intercuspal regions of the crown were measured through the Vickers toughness test and Energy Dispersive X-Ray Spectroscopy (EDS), respectively. The elastic modulus used for the KIC calculation was measured through atomic force microscope (AFM)-based nanoindentation tests. In the outer enamel layer, two direction-specific values of the KIC were calculated separately (direction I, crack running parallel to the occlusal surface; direction II, perpendicular to direction I). The mean KIC of the outer enamel layer was lower than that of the internal layers (po0.05). No other region-related differences in the mechanical properties were found in both groups. In the outer enamel layer, old enamel has a lower KIC, II and higher mineral contents than young enamel (po0.05). The enamel surface becomes more prone to cracks with aging partly due to the reduction in the interprismatic organic matrix observed with the maturation of enamel.

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Section: Discussionmentioning

confidence: 99%

Spatial distribution of the human enamel fracture toughness with aging

Zheng

Song

et al. 2013

Journal of the Mechanical Behavior of Biomedical Materials

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“…The nanoglobules are thought to do so by preferentially attaching to the lateral surfaces of the initial crystals, believed to be crystalline octacalcium phosphates (OCP) (Moradian-Oldak et al 2000;Rauth et al 2009). However, it was proposed recently that the initial long crystallite ribbons in the secretory stage consist not of crystalline but amorphous calcium phosphates (ACP) and that adsorption of amelogenins followed rather than induced the shapes of the crystals (Simmer et al 2012). A second possible function of amelogenins is that they act as a buffer to neutralize the protons that are generated during crystal formation (Smith, 1998;Smith et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Amelogenins as Potential Buffers during Secretory-stage Amelogenesis

et al. 2014

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Amelogenins are the most abundant protein species in forming dental enamel, taken to regulate crystal shape and crystal growth. Unprotonated amelogenins can bind protons, suggesting that amelogenins could regulate the pH in enamel in situ. We hypothesized that without amelogenins the enamel would acidify unless ameloblasts were buffered by alternative ways. To investigate this, we measured the mineral and chloride content in incisor enamel of amelogenin-knockout (AmelX -/-) mice and determined the pH of enamel by staining with methyl-red. Ameloblasts were immunostained for anion exchanger-2 (Ae2), a transmembrane pH regulator sensitive for acid that secretes bicarbonate in exchange for chloride. The enamel of AmelX -/-mice was 10-fold thinner, mineralized in the secretory stage 1.8-fold more than wild-type enamel and containing less chloride (suggesting more bicarbonate secretion). Enamel of AmelX -/-mice stained with methyl-red contained no acidic bands in the maturation stage as seen in wild-type enamel. Secretory ameloblasts of AmelX -/-mice, but not wild-type mice, were immunopositive for Ae2, and stained more intensely in the maturation stage compared with wild-type mice. Exposure of AmelX -/-mice to fluoride enhanced the mineral content in the secretory stage, lowered chloride, and intensified Ae2 immunostaining in the enamel organ in comparison with non-fluorotic mutant teeth. The results suggest that unprotonated amelogenins may regulate the pH of forming enamel in situ. Without amelogenins, Ae2 could compensate for the pH drop associated with crystal formation.

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“…During the secretion stage, ameloblasts secrete enamel matrix proteins (EMPs). These include amelogenin (AMEL), ameloblastin (AMBN), enamelin (ENAM), and matrix metalloproteinase 20, a calcium-dependent peptidase that cleaves newly secreted EMPs into various derivative fragments (Bartlett et al 2004;Simmer et al 2012). AMEL represents 90% of the matrix deposited, while AMBN and ENAM form the majority of the remaining 10% of the organic matrix.…”

Section: Introductionmentioning

confidence: 99%

The Importance of Serine Phosphorylation of Ameloblastin on Enamel Formation

et al. 2016

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FAM20C is a newly identified kinase on the secretory pathway responsible for the phosphorylation of serine residues in the Ser-x-Glu/pSer motifs in several enamel matrix proteins. Fam20C-knockout mice showed severe enamel defects very similar to those in the ameloblastin ( Ambn)–knockout mice, implying that phosphoserines may have a critical role in AMBN function. To test this hypothesis, we generated amelogenin ( Amel) promoter-driven Ambn-transgenic mice, in which Ser48, Ser226, and Ser227 were replaced by aspartic acid (designated as D-Tg) or alanines (designated as A-Tg). The negative charge of aspartic acid is believed to be able to mimic the phosphorylation state of serine, while alanine is a commonly used residue to substitute serine due to their similar structure. Using Western immunoblotting and quantitative polymerase chain reaction, the authors identified transgenic lines expressing transgenes somewhat higher (Tg+) or much higher (Tg++) than endogenous Ambn. The lower incisors collected from 7-d-old and 7-wk-old mice were analyzed by histology, scanning electron microscopy, immunohistochemistry, and Western immunoblotting to examine the morphology and microstructure changes in enamel, as well as the expression pattern of enamel matrix proteins. The A-Tg+ and A-Tg++ mice displayed severe enamel defects in spite of the expression level of transgenes, while the D-Tg+ and D-Tg++ mice showed minor to mild enamel defects, indicating that the D-Tg transgenes disturbed enamel formation less than the A-Tg transgenes did. Our results suggest that the phosphorylation state of serines is likely an essential component for the integrity of AMBN function.

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A post-classical theory of enamel biomineralization… and why we need one

Cited by 94 publications

References 88 publications

Spatial distribution of the human enamel fracture toughness with aging

Spatial distribution of the human enamel fracture toughness with aging

Amelogenins as Potential Buffers during Secretory-stage Amelogenesis

The Importance of Serine Phosphorylation of Ameloblastin on Enamel Formation

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