Oral Histology Theory Past Paper 2022

3 part 1 Dentine What is the dentine? ▪ The dentine is the tissue that forms the bulk of the tooth covered by enamel in the crown or cementum in the root. ▪ It is composed of large number of parallel tubules in a mineralized collagen matrix, and the tubules contain the processes of odontoblasts (whi...

3 part 1 Dentine What is the dentine? ▪ The dentine is the tissue that forms the bulk of the tooth covered by enamel in the crown or cementum in the root. ▪ It is composed of large number of parallel tubules in a mineralized collagen matrix, and the tubules contain the processes of odontoblasts (which is the cell that make the dentine). ▪ It is a sensitive tissue, means that it has a nervous enervation. ▪ It is formed throughout life at expense of pulp (it is a regenerative tissue). Physical Properties : ▪ Fresh dentine is pale yellow (Getting darker with age). ▪ Harder than bone and cementum and softer than enamel. o Enamel > Dentine > bone& cementum. (Enamel is the hardest) ▪ Its tubular nature and organic matrix renders (makes) it strong so it can withstand : o High compressive strength (the force that happens when teeth occlude with each other) o High tensile strength (two forces working against each other( o High flexural strength (the resistance of a material against deformation) - All these strengths are higher in dentine than enamel. ▪ Dentin is permeable due to its tubular nature, this permeability depends on: o patency (openness of these tubules) o size of the tubules -As the person ages these tubules are occluded (blocked) with dentine , so permeability decreases with age. Chemical Composition : ❖ Dentine is composed of (by weight) : 1. 70% inorganic components (calcium hydroxyapatite). 2. 20% organic components (mainly collagen type 1). 3. 10% water. -Notice that the percentage of the inorganic material in dentine (70%) is less than in enamel (96%), and that's what makes enamel harder than dentine. 1.Inorganic composition (70%) ▪ Composed of calcium hydroxyapatite crystals Ca10 (PO4 )6 (OH)2. ▪ They are much smaller than enamel hydroxyapatite because here they don’t stack with each other and they don’t form rods. ▪ Crystals are calcium poor and carbonate rich , the carbonate make the dentine more soluble then it is more susceptible to caries. ▪ These inorganic material found on and between the collagen fibrils. Difference between crystals in enamel and dentine 2.Organic composition (20%) → This topic was a homework to read about it, we put here basic information about them and you have to read more from the book(included in the exam). a) Collagen: Over 90% of the organic material are collagen fibrils, mainly collagen type 1 (it’s the main component of almost all tissues). b) Non collagenous proteins: e.g Phosphophoryn(PP-H): The main phosphoprotein in dentine and the most acidic protein known, it is implicated in mineralization. c) Proteoglycans: mainly biglycan and decorin, proteoglycans have an important role in collagen assembly, cell adhesion, migration, differentiation and proliferation and may have a role in mineralization. The main glycosaminoglycans are chondroitin 4- sulphate and chondroitin 6-sulphate (imp). d) Gla proteins (Gamma Carboxyglutamate containing protein): Small proteins present in low amounts in dentine. They bind strongly but reversibly to hydroxyapatite crystals and may have a role in mineralization e) Acidic proteins: such as osteonectin, osteopontin. Used in histology or histopathology to identify odontoblasts and their products. f) Growth factors: (insulin growth factor 2) IGF-2, (bone morphogenetic protien 2 ) BMP 2, (tissue growth factor beta )TGF-ß, They are absorbed from circulating tissue fluid. Important for differentiation and regeneration of dentine tissue. g) Lipids: comprise 2% of the organic content in dentine. Phospholipids may be involved in the formation and growth of apatite crystals. Regions of the Dentin : ▪ predentine: first layer of dentine. ▪ primary dentine: dentine formed before birth and occlusion. (Its not explained in the pic but it represent majority of dentine). ▪ Secondary dentine: dentine formed after tooth eruption and occlusion and its closer to the pulp. ▪ Tertiary dentine: dentine formed due to pathological problems. ▪ Mantle dentine: dentine near the enamel ▪ Dentinal Tubules : ▪ Dentine is composed of large number of tubules sitting on a mineralized collagen matrix called intertubular dentine. ▪ These dentinal tubules extend from the pulp surface to the DEJ & the CDJ and in between tubules (brown color in pic) which is the collagen (look at the pic). ▪ Odontoblasts secrete dentine from enamel down to pulp. ▪ If you took a longitudinal section you will see the tubules follow a curved sigmoid course in the crown , this curve called (Primary curvatures). ▪ But they are Horizontal in the root , and under cusps they are vertical. The primary curve (S shape) in the crown ▪ If you took a cross section from dentine you will see the tubules as circles. ▪ The tubules are 2.5 um in diameter at the pulpal end, 1um or less at DEJ, as the odontoblasts retreat inwards they occupy a smaller area, thus the tubules become closer. ▪ As you can see near the pulp 22% of the cross sectional area is occupied by dentinal tubules (a lot of tubules), while 2.5% at the DEJ (much less tubules than near the pulp). ▪ Why the number is differ from the pulp to DEJ? o At the pulpal end the surface area become smaller than the surface area at the surface, so the tubules are gathered together in small spaces and it appears to be more numerous. ▪ Look at section B at the picture above, this shape of tubules appears when the S curves goes up , look like slots. ▪ This is a ground, partially demineralized section. ▪ We can identify 3 structure from the picture: 1) (B) dentine between the tubules, is called inter-tubular dentine (Hypo mineralized). 2) (C) dentine in the tubules is called peritubular dentine (Hyper mineralized). 3) inside these tubules you can see the odontoblastic process (dark circle within the tubule). ▪ It’s a demineralized section, notice that all the dentine inside the tubules (pertubular dentine) disappear because it is highly mineralized (inorganic) ▪ But the collagen matrix between tubules (inter-tubules dentine) still there because it is hypo mineralized (organic). Secondary curvatures : ▪ As we said before, the tubules are not straight , they form a curved S shape called primary curvature. ▪ And if you get closer you can notice a smaller curvatures (secondary curvatures) ▪ In some regions the secondary curvatures may coincide in adjacent tubules. At low magnification, this gives appearance of a line crossing the dentine called a contour line of Owen. ‫ هاد االنحناء لو تعمل زوم فيه‬، ‫ عنا نوعين من االنحناءات األول هو البرايمري الي وضحناه بالبداية‬:‫توضيح‬ ‫ هاي‬،‫ما بتالقيه عبارة عن مستقيم انما فيه كمان انحناءات صغيرة وهاد هو النوع الثاني الي بنحكي عنه هون‬ ‫االنحناءات الصغيرة في بعض المناطق بتكون كلها رايحة في نفس االتجاه ف بتبين كأنها خط واحد والي بنسميه‬.Contour line of Owen ▪ These are not commonly seen in most of the dentine, but one such line is usually evident at the junction of primary and secondary dentine where during deposition, all the odontoblasts seem to take a simultaneous and similar change in direction ▪ Contour line of Owen , you can see this line in tow places : 1-many tubules form the same secondary curvature inside the primary curvature. 2-between the primary and secondary dentine. ▪ Dentinal tubules branches : ▪ They have lateral branches that connect tubules like picture 1. ▪ The most profuse branching is in the peripheries: 1. near the enamel and mantle dentin like picture 2. 2. near the cementum In the root, the terminal branches loop to form the (granular layer of Tomes) in ground sections like picture 3 Pic 2 Pic 1 ▪ Contents of dentinal tubules : 1. Odontoblastic processes 2. Afferent & Sensory Nerve Terminals 3. Antigen Presenting Cells Processes 4. Extracellular Dentinal Fluid 5. Peritubular or intratubular dentine (That covers the tubule from inside) Pic 3 1. Odontoblastic processes : As you see in the picture below the odontoblast send there processes inside the tubules, they are responsible for forming the peritubular dentine, and here some info about these processes : periodontoblastic space ▪ They make variable structure at varies tissue levels. ▪ There are more organelles in the predentine area. ▪ There are microtubules & intermediate filaments along the process. ▪ These processes vary in length, sometimes it reaches the terminals of the tubules (to the DEJ) , and sometimes it is only in the predentine. ▪ In predentine which is the innermost layer near the pulp the process occupy almost the full width, and thins as it go toward DEJ creating a periodontoblastic space. ❖ There are three hypotheses that explain why we can find different components at the end or the periphery of the dentinal tubules near the enamel: A. When the odontoblasts retreat toward the pulp, the process stays in its place, and we can still see it at the terminal of the tubule. B. Sometimes there is a predetermined length of the process so the cell retreats and the process retreats with it. C. Sometimes the process was there, but it has degenerated for some reason (degradation at the peripheral end). -This topic was self reading from the book, if you still didn't understand it read the whole explanation from the book. This a cross section of the tubules. -As you see here there is some empty tubules because the processes didn't reach it, and others are full. 2. Afferent & Sensory Nerve Terminals : o Afferent Nerve Terminals ✓ Mainly present in the inner layers of the dentine ✓ Intimate relation )‫ (جنب بعض‬with the odontoblastic process intering the dentine. o Sensory terminals ✓ Their extent in the tubules is not certain. ✓ Found mostly in coronal dentine beneath cusps (80% of tubules), sparse in cervical and root dentine. This other cross section of the tubules: You can see the Odontoblastic processes with nerve terminal (that will be discussed again in the pulp lecture) 3. Antigen Presenting Cells Processes : ▪ They appear as small processes in the tubules near the pulp. ▪ Immunocpmpetent antigen presenting cells. ▪ Within and beneath odontoblasts (in really close relationship with odontoblasts). ▪ Processes limited to the predentine (most probably they stay here). ▪ If there is a carious region they extend to circumpulpal dentin in the tubules under carious dentine. 4. Extracellular Dentinal Fluid : ▪ Is a fluid coming from dental pulp into the tubules. ▪ Unknown composition (the odontoblasts is responsible for the composition of this fluid). ▪ Higher potassium and lower sodium ions level in comparison to other fluids (which means it has a higher osmolality that causes an outward pressure or positive pressure outside dentinal tubules to help getting the toxins & pathogens outside the dentinal tubules if any carious region happen). ▪ This balance affects the membrane properties of cells. ▪ Positive force from pulpal tissue pressure (defense criteria). 5. Peritubular or intratubular dentine : Found at the walls of newly formed dentinal tubules at the pulp surface. made of highly mineralized type I collagen (5-12 % more mineralized than inter-tubular dentine). Maturation of the tubules substitute it with another type of dentine narrowing the lumen and sometimes reach complete obliteration. ‫ وما بينهم‬،peri‫ الدائرة باللون الفاتح بينهم هي ال‬،processes‫النقط الي باالسود هي ال‬.inter ‫هو ال‬ As you can see in the picture: inside the tubule, there is distinctive circle of dentine which is different from the dentine between tubules that is called intratubular dentine. Under microradiographs & electron microscope you can see that peritubular dentine looks like white circle. The main protein inside the tubules different than the proteins in the intertubular dentine, in the intertubular dentine It looks like fibers, but inside the tubules it's amorphous which makes it easier to mineralize then making it highly mineralized. ▪ The main protein in intratubular dentine is different from phosphophoryn (the main protein in intertubular dentin). ▪ In demineralized sections at the electron microscope level the matrix appears as an amorphous material rather than fibers (collagen appearance) ▪ The inorganic component is mainly carbonated apatite with a different crystalline form than intertubular dentin. ▪ In outer dentine, peritubular dentine occupies two-thirds of the crosssectional area of the tissue;but near to the predentine it occupies only approximately 3%. Summry: At DEJ , there is more peritubular dentine, smaller odontoblastic processes. At the pulpal end , there is less peritubular dentine, wider odontoblastic processes. ▪ ▪ And that’s because as we said, when the processes goes up it leaves more and more spaces that will be filled with peritubular dentine. ➔ Look at this pic how the process become smaller as it goes up. Translucent Dentine : ▪ Physiologic aging in dentine leads to complete obliteration of the tubules with peritubular dentine. ▪ Most often in Root dentine. ▪ refractive index of intratubular and intertubular dentine become similar. ▪ When a ground section of a root is placed in water (which has a refractive index different from that of dentine), regions that blocked by peritubular dentine will appear translucent(‫)شفاف‬ (translucent dentine) while regions with patent tubules will fill with water and appear opaque (‫)غير شفاف‬. ▪ has a butterfly shape in cross section. ▪ This is due to the convergence of the tubules (smaller surface area near the pulp). ▪ Increases with age. ▪ Forensic dentistry use it for age estimation. ‫ ببلش يسكر التيوبات كاملة (ببطل في وجود‬peritubular dentine‫▪ مع العمر ال‬ ‫ وبالصور الجزء الي صار فيه‬، ‫ بتصير بالكراون والروت بس اكثر بالروت‬، )process ‫لل‬ )‫ (هاي الحالة بتصير مع التقدم بالعمر مش حالة مرضية‬..‫هيك ببين شفاف‬ Intertubular dentin : ▪ Between the tubules. ▪ Has collagenous fibrous matrix, look like a woven wool. ▪ Decreased radiographic and electron density. ▪ Less mineralized than peritubules. #End of sheet 3 part 1 3part1 CON’T Lajneh teejan Lajneh teejan Heba alzer In this brief sheet, we will talk about the info that are required for exam from book as mentioned in sheet #3 PART1, which is the organic matrix of dentin topic. -------------------------------------------------------------------------------------------------------------------------- ORGANIC MATRIX The organic matrix of dentine is composed of: Collagenous proteins: ▪ over 90% of organic materials. Maily collagen type 1 (which is the main component of almost all tissues), however, dentine collagen has more hydroxylysine than the equivalent in soft tissues collagen. ▪ Most of the collagens in dentine run parallel to the pupal surface. ▪ In mineralized dentine the collagen fibrils are larger diameter (100nm) and more closely packed than in predentine. ▪ Collagen fibrils in dentine are not assembled into bundles as they are in many nonmineralized CT such as tendons or the periodontal ligament. Noncollagenous proteins: ▪ Small percentage of organic matrix which is 8%. ▪ many are involved in mineralisation, they may have other functions. Some act as both inhibitors and promotors of mineralization. ▪ They include: 1. Phosphoproteins: These represent the main noncollagenous protein, Owing to their very high phosphate content it represents the most acidic protein known. indeed, about 80% of the amino acid residues carry negatively charged phosphate or carboxyl groups. Its high calcium ion binding properties have implicated PP-H in the process of mineralisation. One of them is Dentine Matrix Protein 1 (DMP-1) that presents in dentine and bone, play a rule in mineralisation as it can initiate apatite nucleation. It has an Arg–Gly–Asp (RGD) cell attachment sequence and may act as a morphogen for odontoblast differentiation and intertubular dentine formation for both primary and tertiary dentine. It is present in only small amounts in predentine and intertubular dentine but is strongly represented in peritubular dentine. 2. Proteoglycans: they are represented by the smaller molecular weight types known as biglycan and decorin, its glycosaminoglycans are primarily chondroitin-4-sulphate and chondroitin-6-sulphate. play a role in collagen fibril assembly and their cell-mediated effects such as cell adhesion, migration, proliferation, differentiation and maybe mineralization. They may be inhibitors of calcifications that need to undergo some degree of degradation before mineralisation will occur. 3. Glycoproteins/sialoproteins: Dentine also contains other acidic proteins such as osteonectin, osteopontin and dentine sialoprotein. ✓ Osteonectin, a protein containing high levels of glutamic and aspartic acid, is found in dentine at levels of about 5% of total protein. ✓ Osteopontin, a phosphorylated glycoprotein, has been identified in predentine and contains the receptor binding sequence RGD. ✓ These acidic proteins are used in histology and histopathology to identify odontoblasts and their products. 4. Gamma-carboxyglutamte-containing protines (GLA-proteins): Small proteins present in low amounts in dentine. They bind strongly, but reversibly, to hydroxyapatite crystallites and may play some role in mineralisation. 5. Growth factors: They are absorbed from circulating tissue fluid, these include insulin growth factor (IGF)-II, bone morphogenetic protein (BMP)-2 and transforming growth factor (TGF)-beta, play an everyday role in the tissue’s metabolism, but they could be released during the progress of dental caries and induce the production of reactionary or reparative dentine. 6. Metalloproteinases: the organic matrix of dentine contains small amounts of the enzymes collagenase (MMP-1) and enamelysin (MMP-20). Trace amounts of tissue inhibitors of matrix metalloproteinaes (TIMPs) can also be found. 7. Serum-derived proteins: such as albumin. o Several noncollagenous proteins have been grouped together as the SIBLING (small integrin-binding ligand N-linked glycoproteins) family, including osteopontin, bone sialoprotein, DMP-1, matrix extracellular phosphoglycoprotein and dentine sialophosphoprotein. The group members contain a large fraction of aspartic and glutamic acids and numerous serines that are 90% phosphorylated. They are therefore extremely acidic. Lipids: about 2% of the organic content of dentine and, as they are conspicuous at the mineralising front, are thought to play a role in mineralisation. They are in the form of phospholipids and cholesterol. Phospholipids have been detected in both predentine and mineralised dentine. They occupy the spaces between collagen fibrils along with the proteoglycans. In the predentine, they are most heavily concentrated near the mineralising front. In dentine, phospholipids are needlelike ‘crystal ghosts’ and may be involved in the formation and growth of crystals. They seem to be absent from the centres of calcospherites but present in interglobular dentine.