Letter to the editor

Jw, Simmelink

doi:10.1002/ar.1092220215

Cited by 3 publications

(3 citation statements)

References 8 publications

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“…The argument consistently made is that the unit cell of the hydroxyapatite crystallite is hexagonal, which would predict that the external shape of the crystallite itself should reflect the shape of that unit cell (Simmelink, 1988;Warshawsky, 1988). As seen in textbook illustrations of various unit cells of crystals (Beeston, et al 1973;McKie and McKie, 1986), the hexagonal unit cell is not hexagonal, but rather a parallelepipedshaped structure with two surfaces that are rhomboidal and contain angles of 60" and 120".…”

Section: Crystallite Shape Based On Unit Cell Predictionmentioning

confidence: 99%

Organization of crystals in enamel

Warshawsky

1989

Anat. Rec.

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It has been variously suggested that the organic matrix associated with the mineral phase of enamel is present as either calcified fibrils, central dark lines, peripheral sheaths around hexagonal crystals, or organic ghosts apparently contained within crystal profiles. The most consistent findings confirm the crystal ghost conception. Grid decalcification of nearly mature sectioned enamel and staining revealed hollow, noncrystalline structures whose external measurements were statistically identical to those of the dissolved crystallites, but with internal measurements too small to accommodate the crystallites. To explain these apparent ghosts in view of the incompatibility of ghosts with crystal structure, it has been proposed that the crystallites are not hexagonal in cross-sections and the hexagonal appearance is due to projections of parallelepiped-shaped crystallite segments with cut surfaces that are rhomboidal in shape. Material on the surface of such profiles would project as if it were contained within the profile. Hexagonal forms could not be demonstrated in isolated crystallites examined by transmission electron microscopy, high-resolution scanning electron microscopy, and replicas made of the isolated crystallite preparations examined by transmission electron microscopy. Existing evidence does not rule out the possibility that the noncrystalline profiles represent stain drawn into the holes left by the dissolved crystallites as a result of high capillarity forces.

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Section: Crystallite Shape Based On Unit Cell Predictionmentioning

confidence: 99%

Organization of crystals in enamel

Warshawsky

1989

Anat. Rec.

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“…8;Warshawsky, 1987, Fig. 7), which have been interpreted as indicating the cross-sectional shape of the crystals (Daculsi and Kerebel, 1978;Nylen et al, 1963;Selvig and Halse, 1972;Simmelink, 1988). This interpretation is supported by the fact that crystal profiles with the smallest size, the sharpest outlines, and the greatest electron density (all these would be expected if the long axis of the crystal is parallel to the electron beam; Kallenbach, 1983;Simmelink, 1988) are invariably hexagonal in shape.…”

mentioning

confidence: 95%

“…A major cause of the argument over crystal shape seemed to be insufficient positive evidence, and it was thought that a careful examination and classification of crystal images would help to remedy this deficiency. The present study is based on the following considerations (Kallenbach, 1983;Simmelink, 1988). First, a perfect cross-sectional image of a crystal (exemplified in Fig.…”

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confidence: 99%

Evidence that apatite crystals of rat incisor enamel have hexagonal cross sections

Kallenbach

1990

Anat. Rec.

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Images of nearly cross sectioned enamel crystals obtained with the transmission electron microscope were examined in detail and correlated with various possible cross-sectional shapes of the crystals. The following images were seen: 1) elongated hexagons with sharp outlines, maximal density, and minimal size (type A profile); 2) elongated hexagons with one pair of long sides of high contrast, two pairs of short sides of low contrast, high density in the center of the image, and low density towards the low contrast sides (type B profile); 3) slanted hexagons with one pair of high contrast sides, two pairs of low contrast sides (one pair of long, one pair of short sides), and the density decreasing from the center towards the low contrast sides (type C profile); this profile was seen more frequently than the type B profile; and 4) octagons with low contrast edges all around, the density decreasing from the center towards the edges (type D profile). Types B, C, and D profiles were larger than type A profiles. Similar crystal images have been described in the literature. When tilting a specimen in increments of 6 degrees, the transformation of type A to type C and type C to type D profiles was observed. Many crystal images did not change their shape greatly when tilting the section through 6 degrees. No rectangular or rhomboidal profiles were seen. It is argued that types A, B, C, and D profiles cannot be generated by apatite crystals with a parallelepiped cross section. They are easily explained, however, on the basis of crystals with hexagonal cross section.

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Crystal Morphology and Decalcification Patterns Compared in Rat and Human Enamel and Synthetic Hydroxyapatite

Simmelink¹,

Abrigo²

1989

Adv Dent Res.

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The purpose of this investigation was to compare morphology and dissolution patterns by ultrastructural examination of rat and human enamel crystals as well as synthetic apatite crystals. Mature enamel crystals were of particular interest, since crystal maturation appears to be inhibited in amelogenesis imperfecta. Specimens were isolated from developing and mature rat incisor enamel. Rat enamel, mature human enamel, and synthetic apatite were thin-sectioned without decalcification and examined by transmission electron microscopy. Some sections were exposed to acid, and selected synthetic apatite sections were further treated for removal of embedding plastic, followed by vacuum-shadow-coating with carbon. Results showed that cross-sections of rat, human, and synthetic crystals had a distortion in the flattened hexagonal outline in regions where the growth of one crystal impinged on another. Crystal dissolution occurred preferentially along the c-axis, producing a central defect or hole in the crystals. Preliminary studies with weak acid on mature human enamel indicate that the relatively soluble crystal core is quickly dissolved, while the outer shell remains intact over a much longer period of time. In the mature rat and human enamel, this crystal hole formation had a consistent dimension of approximately 10-nm thickness. The crystal hole dimension was the same size as crystals that are formed during the early secretory phase in rat amelogenesis. Acid-treated synthetic apatite also showed dissolution of the crystal core along the c-axis, but dimensions of the hole were not consistent.(ABSTRACT TRUNCATED AT 250 WORDS)

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Letter to the editor

Cited by 3 publications

References 8 publications

Organization of crystals in enamel

Organization of crystals in enamel

Evidence that apatite crystals of rat incisor enamel have hexagonal cross sections

Crystal Morphology and Decalcification Patterns Compared in Rat and Human Enamel and Synthetic Hydroxyapatite

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