Tooth Histology Practicals PDF

ENAMEL STRUCTURE Slide 9 This is a longitudinal ground section of a permanent tooth. Firstly, examine the section with the naked eye: look at a light through the section and note that the enamel has an overall brown colour. Now hold the section over a dark background (so that the room lighting is in...

ENAMEL STRUCTURE Slide 9 This is a longitudinal ground section of a permanent tooth. Firstly, examine the section with the naked eye: look at a light through the section and note that the enamel has an overall brown colour. Now hold the section over a dark background (so that the room lighting is incident on it) and note that the enamel has a blue-white colour. Examine the section under low power: note the distribution and variation in thickness of the enamel and also the scalloped amelodentinal (enamel-dentine) junction. Using polarised light, look for HunterSchreger bands. Account for their appearance. Concentrically arranged curved lines in the enamel are striae of Retzius. Choose any particular line and determine which portion of the enamel relative to this line was formed earlier and which formed later. Sketch the enamel at low power to show the arrangement of striae of Retzius. Look for the external surface manifestations of striae of Retzius and what is their distance apart? Examine the enamel with the high power objective. Note the general direction and any curves in the enamel prisms (=rods). Are there any areas where there are no prisms? Look for cross-striations in the rods: these occur at intervals of about 4-5 m, about the same distance as the width of an enamel rod. How is the rate of enamel formation related to the cross-striations of the rods? Look, in the enamel near the amelodentinal junction, for enamel spindles: narrow, cigarshaped structures which project a little way into the enamel from the dentine. Spindles represent extensions of dentinal tubules into the enamel and are caused by the entrapping of odontoblast processes between ameloblasts during early tooth formation. Can you see continuity between enamel spindles and dentinal tubules? Draw a spindle in high power to show its size in relation to the scalloped EDJ. Slide 13 This is a transverse ground section of the crown of a tooth. Examine the prism direction and note their large curves in the deeper enamel. By progressively focussing through the thickness of the specimen, confirm that the direction of enamel prisms varies as you move from plane to plane. This regular change in direction of prisms through a vertical stack is called the decussation of prisms. Note the configuration of the striae of Retzius in this type of section (concentric rings). Make a sketch to show the arrangement of striae in TS. In this section, identify enamel tufts and enamel lamellae. Draw a tuft at high power to show its relation to the prism directions. Why are tufts and lamellae less prominent in longitudinal than in transverse sections? How would you distinguish a crack from a lamella? Slide 11 This is a longitudinal ground section of a deciduous tooth. Features in the enamel are similar to those of permanent teeth but in enamel forming at birth, a growth line known as the neonatal line is usually conspicuous. This line separates enamel formed before birth from that formed after birth: birth itself seems to halt secretion by ameloblasts for several days. The neonatal line, which is concentric with striae of Retzius, is sometimes used to establish the age at death, then the number of cross-striations between the neonatal line and the surface will indicate the age in days. The presence of a neonatal line in teeth from the remains of an infant would also indicate that the infant had died after birth (rather than being stillborn). Which teeth will possess a neonatal line? In which cusp of which permanent tooth might you find a neonatal line? CHECKLIST Basic Structure: Physical properties; Chemical composition (organic - hydroxyapatite crystals); Prisms, rods; Prism sheath, interprismatic substance; Crystallite orientation; Pores in enamel; Hunter-Schreger bands; Gnarled enamel; Prismless enamel Structural lines in enamel: Cross striations; Striae; Perikymata; Neonatal line Amelodentinal junction: Scalloping; Tufts; Spindles; Lamellae Surface enamel: Physical & chemical differences; Perikymata & striae; Prism end markings; Pits and brochs NOTES NOTES NOTES ENAMEL FORMATION (AMELOGENESIS) Revise the appearance of the enamel organ at the early bell stage (slide 38). What are the histochemical features and functions of each layer during amelogenesis? Slide 6 or 7 These sections of fetal heads show tooth germs in which enamel formation has begun. Note the enamel organ, ameloblasts, enamel matrix, pre-ameloblasts, inner enamel epithelium, dentine and odontoblasts. Note also that the ameloblasts are tall columnar cells and adjacent to them (at the non-secreting end) are cells of the stratum intermedium. The secreting end of the ameloblast shows, at high power, a Tomes’ process. Where the ameloblasts have pulled away from the forming surface of enamel, the enamel surface may show a serrated appearance due to the pits in which Tomes’ processes were situated. How can early enamel and dentine matrix be distinguished? Why can you see enamel in these decalcified sections of embryos but not in decalcified sections of mature teeth? Does the ameloblast retain a constant morphology during enamel formation? Does the odontoblast retain a constant morphology during dentine formation? Does the enamel matrix present a prismatic appearance with incremental markings? Slide 33 This is a longitudinal section through the lower jaw of a young monkey. Find an unerupted tooth with a large space where mature enamel has been dissolved during decalcification. Around the enamel ‘space’ there is a thin layer of epithelium (here stained red). This is the reduced enamel epithelium, the remains of the enamel organ. It is said to be protective to the crown of the unerupted tooth and just prior to eruption it unites with the oral epithelium thereby forming an epithelium-lined channel. CHECKLIST The role of the enamel organ; Inductive influences; Differentiation of ameloblasts; Matrix secretions Mineralisation: Role of Tomes processes; primary; maturation Development of enamel structures: Prisms; Cross striations; Striae Primary enamel cuticle Reduced enamel epithelium Nasmyth's membrane Summary of life cycle of ameloblasts: morphogenic stage; organising stage; formative stage; maturative stage; protective stage; desmolytic stage. QUESTIONS 1. Enamel - Rock or Tissue? 2. How is the structure of enamel related to its function? 3. How are the structures seen as a ground longitudinal section of enamel related to the development of the tissue? 4. Write an essay on enamel matrix. 5. How does the changing structure of the ameloblast reflect the changing functions of the cell during its lifecycle? 6. Write short notes on: a. Enamel prisms b. Incremental lines c. Surface enamel NOTES NOTES NOTES DENTINE STRUCTURE Slide 9 This is a longitudinal ground section of a permanent tooth. Examine the dentinal tubules, noting any primary and secondary curvatures. Dark areas of dentine may be caused by the trapping of air in the tubules when the section was prepared. Some of these dark regions indicate the presence of dead tracts in which the tubules have been sealed off at the pulpal ends as a response to caries, attrition or other damage to the dentine. Note, about 0.2 mm from the amelodentinal junction, a region where the globules or calcospherites (accumulations of crystals) may fail to fuse together, leaving interglobular dentine resembling holly leaves. In the root, particularly in the apical half, there is a region of interglobular dentine a few micrometres from the cement. This is the granular layer of Tomes. [It may also be visible in the TS of root, slide 12]. The dentine peripheral to this granular layer is equivalent in position to the mantle layer of the crown. In the root, the outer layer has few tubules and is called the hyaline layer of Hopewell-Smith. Look, under high power, for areas of dentine where the tubules are cut transversely. This will give you some idea of the size of the tubules and you may see bright rings around the dark space of the tubule: this bright, translucent region is peritubular (sometimes called intratubular) dentine. What is the composition of peritubular (=intratubular dentine)? Using the polarised light set-up, what features can be identified which cannot otherwise be seen? Slide 30 This is a decalcified longitudinal section of a tooth impregnated with picrothionin to show tubules. Examine the crown and then the root under medium and high power. Note the numerous lateral and terminal branching of the dentinal tubules. In the crown, the tubules extend to the enamel-dentine junction but in the root they do not usually approach the cementum - note that the hyaline layer is relatively devoid of tubules. Sketch the outer dentine of crown and of root. How does the mantle layer differ from the rest of the circumpulpal dentine? Slide 14 This is a decalcified longitudinal section of a permanent tooth stained with H&E. The bulk of the dentine is bluish/purple but the unmineralised inner layer consisting of predentine is paler in colour. Note that the predentine/dentine junction is not flat but scalloped. The odontoblasts (or their darkly stained nuclei) are numerous near to the predentine. Slide 20 This is a longitudinal decalcified section of a tooth showing a region of tertiary dentine (=irregular secondary dentine or reactionary dentine) in the crown. This tissue seals off the pulp from the outside world, protecting it from injury and distancing the vital tissues from advancing decay. Note the transition between the primary and reactionary dentine: very few if any tubules continue across the boundary. Note that the reactionary dentine has fewer tubules and these are more irregularly arranged than in primary dentine. Cells and even blood vessels can sometimes be trapped in this rapidly forming tissue. The tertiary dentine in this section may be reactionary dentine or it may be reparative dentine. What is the difference between these two types of tertiary dentine? Slide 43 A variety of incremental lines have been described in dentine and some can be seen in this section of a tooth stained with Masson. Note the general arrangement of these lines which of course indicate the incremental nature of dentine deposition. True incremental lines in dentine are of two types: (I) daily, 5-8 m apart and often called von Ebner lines; (ii) 16-30 m apart and sometimes called Andresen lines. They can also be called respectively short or long periodicity lines. A third type of incremental line in dentine, although not a true growth line, is the contour line of Owen. How is this line produced? A special type of Owen line is called the neonatal line, associated with a general disturbance of growth in the days following birth. A neonatal line in dentine may be apparent in slide 11 which is a longitudinal ground section of a deciduous tooth. CHECK LIST Physical properties; Chemical composition (organic, inorganic) Tubules: course - contents; peritubular dentine; odontoblast processes; nerves Zones: mantle dentine; granular and hyaline layers; circumpulpal dentine; intermediate dentine; predentine Structural lines in dentine: Schreger lines; Owen's lines; von Ebner lines; mineralising lines Interglobular dentine Post-eruptive features of dentine: Occlusion of tubules; Secondary dentine irregular; Dead tracts; Sclerotic - translucent - dentine - regular, PATTERN OF DENTINE GROWTH Draw the outline of a partially developed deciduous canine tooth in longitudinal section. Enamel and dentine are still being deposited in the least mature regions of the crown. At the appropriate location on this outline add the components listed below. Use variously coloured lines to indicate the positions of the structures (no cellular detail is required). 1. Odontoblast layer 9. Enamel dentine junction (amelodentinal junction) 2. Predentine 10. Enamel 3. Sub-odontoblast layer 11. In a selected region, mark the direction of dentinal tubules between the EDJ and the formative surface 4. Mineralising front 5. Mantle dentine 6. Circumpulpal dentine 7. Neonatal 8. Further incremental lines in dentine 12. Mark with an X the oldest or first formed part of the dentine NOTES NOTES NOTES DENTINE FORMATION (DENTINOGENESIS) Look at the appearance of the dental papilla prior to hard tissue genesis (slides 4, 38). Compare this with the appearance of the dental papilla during dentinogenesis (slides 6, 7). Revise the basic principles of epithelial/mesenchymal interactions during tooth development. s Is enamel or dentine formed first? Does enamel or dentine appear to be formed at the fastest rate? Why do the matrices of developing enamel and dentine have different staining properties? Look at mature teeth in which the primary dentine is fully formed (slide 14). Some dentine is formed throughout the life of the tooth and so the dentine/pulp border is typical for most stages of dentinogenesis. Why is the dentine/predentine junction globular in appearance? Why does the matrix of calcified dentine stain differently from that of predentine? In what way does the development of mantle dentine differ from the development of circumpulpar dentine? What differences are there between the formation of crown dentine and root dentine? What can examination of a ground section of a tooth in polarised light tell you about dentine formation? CHECKLIST Dental papilla; Inductive influences; Differentiation of odontoblasts; Initial matrix secretion by sub-odontoblastic cells of papilla (mantle dentine); Von Korff fibres; Role and structure of odontoblasts in later stages of dentinogenesis; Odontoblast processes and tubule formation; Predentine; Mineralisation: matrix vesicles containing crystallites; linear mineralisation; calcospheritic mineralisation Rhythmic pattern of development of dentine incremental lines in dentine Migratory pattern of odontoblasts during formation of primary dentine in relation to formation of curvatures of tubules QUESTIONS 1. How is the structure of dentine related to its functions? 2. Compare and contrast enamel and dentine. 3. How does the structure of dentine as seen in a ground longitudinal section relate to the development of the tissue? 4. Compare and contrast enamel and dentine formation. 5. Write notes on: 6. 1. Dentine collagen 2. Pentibular dentine 3. The odontoblast process Give an account of the age changes in dentine. NOTES NOTES NOTES DENTAL PULP Slide 14 This is a longitudinal section of a decalcified lower molar and is stained with haematoxylin and eosin. It shows a healthy, young pulp. Note that the apex of one root is curved and therefore cut transversely. At low power observe the general arrangement of tissues within and relative sizes of type pulp chamber and the root canals. With medium power observe the odontoblasts with prominent nuclei adjacent to the predentine. Fibroblasts, the predominant cell type within the body of the pulp, have long interconnecting processes and are scattered among fine collagen fibres. Immediately beneath the odontoblast layer, a zone with few cells will be seen (more easily in some areas than others). This is the cell free zone of Weil and just deep to it a concentration of nuclei is evidence of a cell rich zone. Observe these regions with high power and note the large number of blood capillaries. The capillaries arise from arterioles which can be seen within the body of the pulp and also traced along the root canals. Solid, pale pink structures within the pulp are likely to be nerves but these will be examined on a subsequent section. Note the differences in number, size and distribution of odontoblasts lining the pulp chamber compared with those in the root canal and explain your observations. What is the unique cell type in the pulp and what is the embryological origin of these cells? Slide 18 This is a longitudinal section showing an erupted and a developing tooth: pulp is present on some of these sections which are stained by a triple method in which red blood cells are coloured red. If pulp is present on your section, note the distribution of blood vessels: capillaries near to the odontoblasts and larger vessels more deeply within the pulp. Where the pulp has shrunken away from the dentine during fixation, very fine odontoblastic processes can be seen passing into the dentinal tubules. Slide 34 This is a longitudinal section of a decalcified lower molar stained by a silver method to show nerves and nerve fibres (axons) which appear black against a golden background. Odontoblasts and their nuclei are readily visible. Observe the arrangement of nerves and nerve fibres within the pulp at medium power. Fairly large nerves are visible within the body of the pulp, some running alongside blood vessels. The latter may be autonomic (sympathetic) postganglionic fibres. Just beneath the odontoblasts, a dense arrangement of fine nerves is visible - the plexus of Raschkow. Examine this region with high power. Note that some fibres, now likely to be all unmyelinated, cross the cell free zone and mingle with the odontoblasts. We know that a few axons enter dentinal tubules, especially those beneath cusps, where up to 1 in 10 tubules may contain an axon, penetrating no more than 0.4 mm into the dentine. But in this young tooth, axons within dentinal tubules are very difficult to find. What is the function of the different types of nerve fibres in the pulp? Where are the cell bodies of these nerve fibres? How would you tell from the appearance of the pulp whether you are looking at a young tooth or an old tooth? CHECKLIST Disposition of the tissue; Functions; Composition Arrangement of outer and inner regions of pulp: odontoblast layer; cell free zone; Raschkow's nerve plexus; subodontoblastic capillary plexus - cell rich zone - homogeneous bulk of pulp - centre containing large nerves - blood vascular system. Cells of dental pulp: odontoblasts; fibroblasts; defence cells. Fibres and ground substances of the dental pulp; Blood vascular system; Nervous elements in the dental pulp; Age changes; Reactions to stimuli; Pulp/dentine sensitivity; Clinical aspects QUESTIONS 1. Discuss the concept that dental pulp and dentine form a pulp-dentine complex rather than two separate tissues. 2. Write notes on: a) the pulp vasculature b) the nerves of the pulp c) age changes in the pulp d) odontoblasts NOTES NOTES NOTES