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Enamel & Co.Lts, 1998 † 2.Physiology for Dental Students 1St Ed

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Enamel & Co.Lts, 1998 † 2.Physiology for Dental Students 1St Ed 口腔生理學（含顎咬合） Oral physiology (occlusion included) 學習目標 1. let the student to understand the PDL and alveolar Bone base knolwedge of oral physisology. 2.The student can firsther studying the advance courses of dental 臺北醫學大學牙醫學系 science. 張維仁 E-mail [email protected] 參考資料 1.Applied Oral Physiology, 2nd ed. Christopher L.B.Lavelle Butterworths Enamel & Co.Lts, 1998 2.Physiology for dental students 1st ed. D.B.Ferguson. Butterworths & Co.Lts, 1998. ENAMEL Physical characteristics Enamel's primary mineral is hydroxyapatite, which is a the hardest and most highly mineralized crystalline calcium phosphate . The large amount of substance of the body, and with dentin, minerals in enamel accounts not only for its strength but cementum, and dental pulp is one of the four also for its brittleness. Dentin, which is less mineralized major tissues which make up the tooth. It is the and less brittle, compensates for enamel and is normally visible dental tissue of a tooth and necessary as a support. must be supported by underlying dentin. 96% of Unlike dentin and bone, enamel does not contain enamel consists of mineral, with water and collagen. Instead, it has two unique classes of proteins organic material composing the rest called amelogenins and enamelins. While the role of these proteins is not fully understood, it is believed that Enamel varies in thickness over the surface of they aid in the development of enamel by serving as a the tooth and is often thickest at the cusp, up to framework 2.5 mm, and thinnest at its border, which is seen clinically as the cementoenamel junction (CEJ) Structure of enamel Scanning electron The basic unit of enamel is called an enamel rod . microscope views of (A) Measuring 4 μm-8 μm in diameter an enamel rod, the enamel layer covering formerly called an enamel prism, is a tightly packed mass coronal dentin, (B) the of hydroxyapatite crystals in an organized pattern . In complex distribution of cross section, it is best compared to a keyhole, with the enamel rods across the top, or head, oriented toward the crown of the tooth, and layer, (C and D) and the bottom, or tail, oriented toward the root of the tooth. perspectives of the rod- The area around the enamel rod is known as interrod interrod relationship when enamel. Interrod enamel has the same composition as rods are exposed (C) enamel rod, however a histologic distinction is made longitudinally or (D) in between the two because crystal orientation is different in cross section. Interrod each . The border where the crystals of enamel rods and enamel surrounds each crystals of interrod enamel meet is called the rod sheath . rod. R, Rod; IR, interrod; DEJ, dentinoenamel junction. Hydroxyapatite P6 /m A and B, High- 3 resolution scanning electron microscope images showing that crystals in rod and interrod enamel are similar in structure but a diverge in = 9. 42 orientation. A P Ca Ca5(PO4)3OH OH,F D.R.Simpson, 1972) Structure of enamel The arrangement of the crystals within each enamel rod is highly complex. Both ameloblasts (the cells which initiate enamel formation) and Tomes' processes affect the crystals' pattern. Enamel crystals in the head of the enamel rod are oriented parallel to the long axis of the rod . When found in the tail of the enamel rod, the crystals' orientation diverges slightly from the long axis. The arrangement of enamel rods is understood more clearly than their internal structure. Enamel rods are found in rows along the tooth, and within each row, the long axis of the enamel rod is generally perpendicular to the underlying dentin . In permanent teeth, the enamel rods near the cementoenamel junction (CEJ) tilt slightly toward the root of the tooth. Understanding enamel orientation is very important in restorative dentistry, because enamel unsupported by underlying dentin is prone to fracture. Amelogenesis Amelogenesis 1. Produces a partially mineralized 1. Presecretory stage: differentiating ameloblasts (approximately 30%) enamel. Once the acquire their phenotype, change polarity, full width of this enamel has been develop an extensive protein synthetic apparatus, and prepare to secrete the organic deposited…….. matrix of enamel. 2. Significant influx of additional mineral 2. Secretory stage: ameloblsts elaborate and coincident with the removal of organic organize the entire enamel thickness, resulting material and water to attain greater in the formation of a highly ordered tissue. than 96% mineral content. This mineral 3. Maturation stage: ameloblasts modulate and influx makes the crystal formed during transport specific ions required for the the first step grow wider and thicker concurrent accretion of mineral. Scanning electron micrograph of the surface of a developing human tooth from which ameloblasts have been removed. The surface consists of a series of pits previously filled by Tomes’ processes the walls of which are formed by interrod enamel. The (A) first (initial) and (B) last (final) enamel layers are aprismatic, that is, they do not contain rods. A and B, Scanning electron microscope illustrations showing the complex trajectory of rods in the inner two thirds of the enamel layer. B, The rods are organized in groups exhibiting different orientations; this illustration shows four adjacent groups. Enamel protein Four phases of enamel mineralization. Amelogenins: 90% regulate growth in thickness and width, nucleate cystals Nonamelogenin 1. Ameloblastin: promote mineral formation and crstal elongaation 2. Enamelin: the molecule binds HA, crystal nucleation and growth 3. Sulfated glycoprotein 4. Tuftlin: cell signaling?? For DEJ 5. Enzymes Metalloproteinase: enamelysin MMP20 Serines proteinase: bulk degradation Phosphatase 6. Dentin phosphoprotein/ dentin sialoprotein Striae of Retzius Cross striations In scanning electron microscopy, periodic Longitudinal ground varicosities and depressions are seen along section showing enamel rods (R) in (A) rodent and (B) human disposition of the teeth, producing the impression of cross- striae of Retzius striations along their length. IR, Interrod (arrows).the outermost enamel. layer is the enamel, the two sections adjacent to the enamel represent the dentin, and the pulp chamber is in the center. 參與細胞增加而產生？ Human enamel is known to form a rate of approximately 4um/day Enamel tufts & lamellae Enamel tufts & lamellae Enamel tufts: abrupt changes in the direction of groups of rods that arise from different regions of the scalloped DEJ Lamellae: longitudinal oriented defects filled with organic material (enamel organ or connective tissue) Transverse ground section of enamel. Enamel tufts are the branched structures extending from the dentinoenamel junction (DEJ) into the enamel (arrowheads). The junction is seen as a scalloped profile. Geologic faults Enamel spindles perikymata Scanning electron micrograph of the labial surface of a tooth, showing the perikymata. (Courtesy D. Weber.) Enamel spindles (arrows) in a ground section extend from the dentinoenamel junction into the enamel and most frequently are found at cusp tips. Odontoblast processes extend into the ameloblast layer Ground section of enamel showing the relationship between the striae of Retzius and surface perikymata. The relationship between the striae of Retzius and surface perikymata (arrows). Aging Defects of amelogenesis Discoloration Febrile diseases Reduced permeability Tetracycline-induced disturbaneces Modifications in the surface layer Fluoride ion >5ppm Acid etching Dentition of a patient who had two illnesses at separate times. Scanning electron micrographs of etching patterns in enamel. A, Type I The enamel defects, separated by normal enamel, are clearly pattern: rod preferentially eroded. B, Type II pattern: rod boundary (interrod) visible. preferentially eroded; C, Type III pattern: indiscriminate erosion. D, Junction between type I and type II etching zones. Summary 介紹口腔中正常的組織，解剖、生理和 END 口腔組織的演化及生長過程，使同學們 對人體口腔有基本概念。.
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