Oral Histology Theory Past Paper 2022

3PART 2 ❖ Regions of the dentin: properties and composition of dentine vary from the predentine to DEJ. mineral content decreases and the thickness of mineral crystals increase towards DEJ. Hardness and elastic modulus both decrease towards the junction. o Crown ✓ There are 4 different regions, whic...

3PART 2 ❖ Regions of the dentin: properties and composition of dentine vary from the predentine to DEJ. mineral content decreases and the thickness of mineral crystals increase towards DEJ. Hardness and elastic modulus both decrease towards the junction. o Crown ✓ There are 4 different regions, which are: Mantle Dentine. Interglobular dentine Circumpulpal dentine. Predentine. o Root ✓ In the root we will see: Hyaline layer. Granular layer of Tomes. Interglobular dentine Circumpulpal dentine. Predentine. o We can classify the regions of dentine in different way (will discussed later): Primary Secondary Tertiary Sclerotic Translucent -Let’s start with the regions of the crown: ❖ Mantle dentin: The most peripheral first to be formed layer (in the picture seen a red line). 20-150 micrometer in width. Differs from circumpulpal dentin: o 5% less mineralised. o Collagen fibrils perpendicular on DEJ ▪ To prevent small cracks developing in the enamel near DEJ from spreading into the dentine. ▪ give the mantle region an appearance distinct from that of the circumpulpal dentine when seen in polarizing light microscopy of ground, undermineralized sections. o Branching of tubules happens in this area. o Different mineralisation process (dentin ogenesis) Mantle dentin is different from bulk of dentin underneath it. ❖ Interglobular Dentine: Underneath the mantle dentine, there is a layer called interglobular dentine which is the area between globules. In dentin minerals deposited as globules (calcospheres) then fuse to form a uniform calcified tissue. in some areas, usually beneath the mantle layer in the crown and beneath the granular layer in the root, the fusion may be incomplete which means that if these globules fail to calcify or these areas in between them don’t calcify, we see these areas of interglobular dentin, which are the areas between globules. They are hypocalcified areas found under the mantle dentin. failure of fusion beneath mantle dentine produces undercalcified interglobular areas, appear dark in ground sections viewed under transmitted light. Tubules pass through these areas without deviation, peritubular dentine is also absent from the tubules as they pass through interglobular dentine. We can see this layer in the crown and root. -moving to the root: ❖ Hyaline layer: narrow clear area between the cementum and the dentin, 20 micrometer in width band. Outside the granular layer. Obscure origin dentin or cementum. Atubular and structureless. Helps in bonding dentine to cementum. ❖ Granular layer of Tome: Underneath the hyaline layer, a black area at the peripheral root dentine, that looks like From book interglobular dentine but it’s not. Caused by tubules branch and loop back on themselves creating air spaces (that’s why look black) in ground sections that result in internal reflection of transmitted light OR Incomplete fusion of calcospherites and because the loops are more profused in root, they are seen in root but not in crown. Hypomineralized compared to circumpulpal dentin. may be the result of the presence of more tubular branches. ❖ Circumpulpal dentine: Forms the bulk of the dentine, there is nothing special inside of it, tubules in mineralised matrix. Uniform in structure except at peripheries, interglobular and predentin. ❖ Predentine: the inner- most layer of dentine, Initially laid dentine matrix prior to mineralization, that is the collagen matrix before it calcify. In demineralized H&E sections has a distinct pale-staining appearance as it is not yet minerlised Mineralization front may show a globular or a linear appearance (dentinogenesis). 10-40um in width. Thicker in young teeth. ❖ Structural lines in Dentine: 1. Lines associated with the primary curvatures of dentinal tubules. 2. Lines associated with the secondary curvatures of dentinal tubules. 3. Incremental lines: von Ebner's lines & Andresen lines. o All of them are approximately perpendicular to dentinal tubules ❖ Schreger lines (primary curvatures lines) As a remember, we said that there is S-shaped of the tubules from the pulp to DEJ, the line that shows us this convexity and concavity of the S-shaped, all the convexities come together to make a line and all the concavities come together to make a line, these lines are called Schreger lines. They are seen in longitudinal sections. These are not apparent in many sections, and rarely can two be seen, we are only going to see one, maximum two of them (one convexity and one concavity). Difficult to see in cross sections. ❖ Contour lines of Owen )secondary curvatures lines) Caused by: 1. Small secondary curvatures inside the primary curvature. 2. Neonatal line (can be considered a Contour lines of Owen or an andersen line as there is a change in composition, minerlisation and curvature of tubules). 3. Line between primary and secondary Dentin (can be considered a Contour lines of Owen. Coincidence of secondary curvatures. rare in primary dentin. Interrupted, doesn’t follow the whole lane of dentine. ❖ Neonatal line Change in composition of matrix and minerlisation of dentin before and after birth. We will find it near the dentinoenamel junction. It is small It doesn’t go the whole thickness of the dentine and most probably you will find one near to it on the enamel or between primary and secondary. ❖ Incremental lines: Short term striations (von Ebner's lines) & Long term striations (Andresen lines). Seen in: ground sections, demenerlised sections under polarized light or in microradiographs Cause: Fluctuations in acid-base balance effects the mineral content, thus the refractive index. Change in collagen fibrils orientation in andersen lines make them more marked under polarised light. 1-Von Ebner's Lines: As you remember in the enamel, we see short term striations (cross striation), in the dentin we will see the Von ebner’s lines, which are short term striations, almost daily deposition of dentine. Needs high magnification. ▪ Cuspal dentine: 4um separate every 2 lines. ▪ Root dentine near the granular layer : 2um separate every 2 lines. 2-Andersen line The other are Andersen lines which are long term lines, weekly in dentine secretion 16-20μm apart. There are almost 6-10 vonEbner’s lines between every 2 andersen lines suggesting 6- 10 days rhythm, could be seen in lower magnification Also, in Andersen lines, sometimes we find Exaggerated Andersen lines (hypocalcified ones), because of differences in mineralization, if this happens, we see these lines that walk in the whole dentin. ▪ Are also considered a Contour lines of Owen caused this time by change in composition and Hypominerlisation of Andersen lines. ▪ Continuous with the path of incremental line of Andersen ✓ So let’s summarize, Contour lines of Owen are caused by: 1. change in composition and mineralization (hypominerlisation) of Andersen lines --> continuous whole thickness of dentine 2. coincidence of secondary curvatures of tubules together -->interupted &short 3. neonatal line and between 1ry &2ry dentine Mantle dentine Circumpupul dentine Andersen lines Primary dentine We can see in this section contour lines of owen caused by hypominerlization of andersen lines Secondary dentine And a contour line of owen caused by primary and secondary dentine -Again, the neonatal line could be considered one of the Andersen lines or contour line of owen, because there is change in mineralization. -How to define? Found in the deciduous teeth and in the first permanent molars, where dentine is formed partly before and partly after birth, so it is close to DEJ and usually seen with enamel neonatal line in close proximity. ❖ Regions of the Dentine primary secondary tertiary Sclerotic Translucent ❖ Age related and post eruptive changes ✓ Physiological age changes: ▪ Secondary dentine. ▪ Translucent dentine. ✓ Changes associated with dentinal responses to stimuli (pathological): ▪ Tertiary dentine. ▪ Sclerotic dentine. ▪ Dead tracts of Fish. o Secondary Dentine starts to form once the root is completed and the tooth comes into occlusion. still forms in unerupted, impacted teeth. Very similar to primary dentine. Sudden change in the tubule’s direction, line of owen. Slower deposition, Closer incremental lines. Faster secretion of it on pulp floor, cause narrowing of chamber and canals with age (with age the more secondary dentine deposited the smaller the pulp chamber and root become) In physiological ageing, especially in root dentine, the tubules can become completely occluded with peritubular dentine to form translucent dentine. particularly pronounced at the root apex This is again when the dentine occludes all the tubules so the peri and inter have the same reflected index and they reflect light the same way makes them translucent. Cross section shape: butterfly Translucent is physiological While sclerotic is pathological, soon we will talk about it Translucent dentin and sclerotic dentin have the same histology but different etiology o Tertiary dentine (pathological) It is the dentine that is secreted because of pathological stimulus like Caries, leakage, cavity preparation etc.. Pathological stimuli might induce the pulp to produce more calcified material. It has many names: Irregular secondary dentine, reparative, reactionary dentine, response dentine and osteodentin. Why?! Because each stimulus makes the odontoblast react in different way that’s why the tertiary may have many different appearances: ▪ Variable appearance and composition, May be tubular, may contain irregular tubule or be atubular Continuity of dentinal tubules between normal dentine and tertiary dentine will therefore be lost in many instances. ✓ B image : when the stimulus makes some odontoblast die ✓ C image : odontoblast enters the dentine so we see cells inside dentine *remember the dentine’s cell located in pulp* ✓ D image: Weird looking with different directions and cells inside Not uniform , we can’t see tubular structures High magnification Haphazard, collagen and mineralized matrix ✓ info about tertiary dentine: Stimuli induce cells in the pulp to differentiate into " odnontoblasts". Production of collagen type I and dentine sialoprotein by new odontoblasts still applies only the regularity of the tubes is affected Primary odontoblasts might be involved in the early stages. o Sclerotic Dentine (pathological) Slow going Stimuli like slow caries & attrition induce the deposition of material inside the tubules (gives chance to odontoblast to occlude all the tubules under caries). ▪ Remember what will happen (the peritubules and inter tubules will reflect light in the same way and become translucent) but in this case it is not physiological, so Sclerotic dentine is the result. areas of dentine that lack structure and appear transparent. Very similar in appearance to translucent dentine. But the difference is translucent is physiological Different composition from intratubular dentine. Easier to fracture o Dead tract of fish If the stimulus or carries were very strong, primary odontoblasts could be killed. They could retreat before the formation of intratubular dentine. This results in empty tubules. Might be sealed at their pulpal end by tertiary dentine. In ground section, tubules are air filled, thus Under the micro- scope transmitted light will be internally reflected and they will appear dark. Dead tracts are the term given to these air- filled tubules. THE END OF SHEET #3 PART 2 GOOK LUCK !