TEM Observations on the Ameloblast/Enamel Interface in the Rat Incisor

Risnes, Steinar; Septier, D.; Periere, Gilles Deville De; Goldberg, Michel

doi:10.1080/03008200290000899

Cited by 12 publications

(6 citation statements)

References 25 publications

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“…This is the basis for the hierarchical organization of enamel ribbons into rod and interrod structures (Figure 3). 34,56 In rodents, the Tomes' processes in one row of ameloblasts are inclined in the same direction, while those of adjacent rows are inclined in the opposite direction, 57 resulting in a decussating (X-shaped) pattern of enamel rods, each filled with enamel ribbons oriented along the long axis of the rod, but at an angle to the rod in the adjacent row. Near the end of the secretory stage of amelogenesis, ameloblasts retract their Tomes' processes and the final enamel, like the initial enamel deposited prior to formation of the Tomes' processes, lacks rod/interrod divisions and the ribbons run perpendicular to the enamel surface.…”

Section: The Mineralization Front Apparatusmentioning

confidence: 99%

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

Simmer

Richardson

et al. 2012

Int J Oral Sci

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Enamel crystals are unique in shape, orientation and organization. They are hundreds of thousands times longer than they are wide, run parallel to each other, are oriented with respect to the ameloblast membrane at the mineralization front and are organized into rod or interrod enamel. The classical theory of amelogenesis postulates that extracellular matrix proteins shape crystallites by specifically inhibiting ion deposition on the crystal sides, orient them by binding multiple crystallites and establish higher levels of crystal organization. Elements of the classical theory are supported in principle by in vitro studies; however, the classical theory does not explain how enamel forms in vivo. In this review, we describe how amelogenesis is highly integrated with ameloblast cell activities and how the shape, orientation and organization of enamel mineral ribbons are established by a mineralization front apparatus along the secretory surface of the ameloblast cell membrane.

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Section: The Mineralization Front Apparatusmentioning

confidence: 99%

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

Simmer

Richardson

et al. 2012

Int J Oral Sci

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“…Each enamel rod traces the path followed by a single ameloblast (Boyde, , ; Smith & Warshawsky, ; Risnes et al. ; Skobe, ). As noted above, a great deal of descriptive information currently exists about ameloblasts and how they form and help mineralize the enamel layer, and how the enamel rods they create form a variety of structural arrangements in two‐ and three‐dimensional space.…”

Section: Introductionmentioning

confidence: 99%

Quantitative analysis of the core 2D arrangement and distribution of enamel rods in cross‐sections of mandibular mouse incisors

Smith

et al. 2018

Journal of Anatomy

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Considerable descriptive information about the overall organization of mouse mandibular incisor enamel is available but almost nothing is known about the quantitative characteristics of enamel rod arrangement and distribution in these teeth. This has important implications concerning cell movement during the secretory stage because each ameloblast makes one enamel rod. Knowing how many enamel rods are cut open in a cross-section of the enamel layer could provide insights into understanding the dynamics of how groups of ameloblasts form the enamel layer. In this study, cross-sections of fully mineralized enamel were cut on 24 mandibular mouse incisors, polished and etched, and imaged by scanning electron microscopy in backscatter mode. Montaged maps of the entire enamel layer were made at high magnification and the enamel rod profiles in each map were color-coded based upon rod category. Quantitative analyses of each color layer in the maps were then performed using standard routines available in imagej. The data indicated that that there were on average 7233 ± 575 enamel rod profiles per cross-section in mandibular incisors of 7-week-old mice, with 70% located in the inner enamel layer, 27% located in the outer enamel layer, and 3% positioned near the mesial and lateral cementoenamel junctions. All enamel rod profiles showed progressive increases in tilt angles, some very large in magnitude, from the lateral to mesial sides of the enamel layer, whereas only minor variations in tilt angle were found relative to enamel thickness at given locations across the enamel layer. The decussation angle between alternating rows of rod profiles within the inner enamel layer was fairly constant from the lateral to central labial sides of the enamel layer, but it increased dramatically in the mesial region of the enamel layer. The packing density of all rod profiles decreased from lateral to central labial regions of the enamel layer and then in progressing mesially, decreased slightly (inner enamel, mesial tilt), increased slightly (outer enamel layer) or almost doubled in magnitude (inner enamel, lateral tilt). It was concluded that these variations in rod tilt angle and packing densities are adaptations that allow the tooth to maintain a sharp incisal edge and shovel-shape as renewing segments formed by around 7200 ameloblasts are brought onto the occluding surface of the tooth by continuous renewal.

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“…, ; Risnes et al. ; Skobe, ; Yuan & Nishikawa, ; Nishikawa, ). Irregular row arrangements such as paired, branching/merging with or without row pairing, and focal stacks to the knowledge of the authors have not been described to any extent in ameloblast row arrangements.…”

Section: Discussionmentioning

confidence: 99%

Characteristics of the transverse 2D uniserial arrangement of rows of decussating enamel rods in the inner enamel layer of mouse mandibular incisors

Smith

et al. 2019

Journal of Anatomy

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The 2D arrangement of rows of enamel rods with alternating (decussating) tilt angles across the thickness of the inner layer in rat and mouse incisor enamel is well known and assumed to occur in a uniform and repetitive pattern. Some irregularities in the arrangement of rows have been reported, but no detailed investigation of row structure across the entire inner enamel layer currently exists. This investigation was undertaken to determine if the global row pattern in mouse mandibular incisor enamel is predominately regular in nature with only occasional anomalies or if rows of enamel rods have more spatial complexity than previously suspected. The data from this investigation indicate that rows of enamel rods are highly variable in length and have complex transverse arrangements across the width and thickness of the inner enamel layer. The majority of rows are short or medium in length, with 87% having < 100 rods per row. The remaining 13% are long rows (with 100–233 rods per row) that contain 46% of all enamel rods seen in transverse sections. Variable numbers of rows were associated with the lateral, central and mesial regions of the enamel layer. Each region contained different ratios of short, medium and long rows. A variety of relationships was found along the transverse length of rows in each region, including uniform associations of alternating rod tilts between neighboring rows, and instances where two rows having the same rod tilt were paired for variable distances then moved apart to accommodate rows of opposite tilt. Sometimes a row appeared to branch into two rows with the same tilt, or conversely where two rows merged into one row depending upon the mesial‐to‐lateral direction in which the row was viewed. Some rows showed both pairing and branching/merging along their length. These tended to be among the longest rows identified, and they often crossed the central region with extensions into the lateral and mesial regions. The most frequent row arrangement was a row of petite length nestled at the side of another row having the same rod tilt (30% of all rows). These were termed ‘focal stacks’ and may relate to the evolution of uniserial rat and mouse incisor enamel from a multilayered ancestor. The mesial and lateral endpoints of rows also showed complex arrangements with the dentinoenamel junction (DEJ), the inner enamel layer itself, and the boundary area to the outer enamel layer. It was concluded that the diversity in row lengths and various spatial arrangements both within and between rows across the transverse plane provides a method to interlock the enamel layer across each region and keep the enamel layer compact relative to the curving DEJ surface. The uniserial pattern for rows in mouse mandibular incisors is not uniform, but diverse and very complex.

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TEM Observations on the Ameloblast/Enamel Interface in the Rat Incisor

Cited by 12 publications

References 25 publications

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

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

Quantitative analysis of the core 2D arrangement and distribution of enamel rods in cross‐sections of mandibular mouse incisors

Characteristics of the transverse 2D uniserial arrangement of rows of decussating enamel rods in the inner enamel layer of mouse mandibular incisors

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