Oral Histology Introduction 1_merged.pdf

1 Introduction to Oral Histology  In the last semester we have studied the macroscopic appearance of the oral tissues (we use the nacked eye to discribe), while in Oral Histology, we will study the tissues microscopic appearance using microscope to look at the tissue under a high magnification at c...

1 Introduction to Oral Histology  In the last semester we have studied the macroscopic appearance of the oral tissues (we use the nacked eye to discribe), while in Oral Histology, we will study the tissues microscopic appearance using microscope to look at the tissue under a high magnification at cellular level or organelle level (by EM).  So, we see the tissue under microscope, we describe all the structures and we give names to these structures. As usall, the names are mostly related to function, and sometimes the structures are named after person who discovered it. o Why do we study oral histology & biology? To understand the structure and function of oral tissues: because there is a strong connection between them, the histological tissues structures are related to there function & related to how you are going to treat these tissues. To understand the development of oral tissues: when you understand how tissues develped you will understand a lot of pathologies are related to these tissues. To understand the general oral physiology. To understand oral diseases. o How can we study oral histology and biology? By Studying : Gross Anatomy: macroscopic with nacked eye Physical properties: which means how do they react with forces coming from different sources Chemical composition: which means what compounds and components are actually responsible for the formation of this tissue. Histological sections: can be divided into: 1. Hard tissues: can be studied by Ground sections & Decalcified Sections. 2. Soft tissues: the normal way by H&E stain. o What’s the difference between Ground and decalcified sections?  Decalcified Section : it is where the inorganic substance is dissolved and the organic substance remains. Look at the pic, the enamel is dissolved it (leaves a space called enamel space), but the dentin has higher organic percentage than enamel we can still see, same applies to the cementum.  Ground section : it is where the organic substance is burnt and the inorganic substance remains. Look at the pic, all tissues of the tooth are appearent because all of them are hard tissues (inogranic materials), but the pulp is burned out (we cant see it) -the enamel, cementum and the dentin are hard tissues (are mostly made from inorganic materials) -enamel has the highest percentage of inorganic materials which is 96% Oral Structures Hard tissues Soft tissues 1- Enamel 2- Dentine 3- Cementum 4- Alveolar bone 5- Jaw bones 6- temporomandibular joint. 1- Pulp 2- Periodontal ligament. 3- oral mucosa. 4- sub-mucosa (blood vessels, nerves). 5- salivary glands. Oral Structure What are the oral structures that we are going to study in this course?  Teeth: which are composed of enamel (outer layer of crown), dentine (the bulk under the enamel), cementum (outer layer of root) and pulp.  Periodontium: which are the structures that attach the teeth to bone which are composed of gingiva, alveolar bone,periodontal ligament and root cementum.  Jaw bones: the bones that teeth set in and and attach with peridotium.  Temporomandibular joint (TMJ)  Oral mucosa: which covers the bones with underlaying submucosa  Sub-mucosa: which has blood vessels and nerves  Salivary glands Tooth Structure  crown and root(s) with a pulp chamber and root canal(s).  Enamel, dentine, pulp tissue and cementum make up a tooth. o Enamel : Is the most highly mineralized tissue (hardest tissue) in the body it has 96% inorganic material It is non-vital (doesn't have blood vessels & nerves), insensitive, cannot be regenerated. Ameloblasts produce enamel and move outward, leaving it behind until it's fully formed. Once they're done, they settle on the enamel surface and die, which is why enamel can't regenerate. o Dentine : It forms the bulk of the tooth. Rigid but elastic (ideal to support enamel) Protects enamel form breaking , because it is: -Rigid: Unbreakable (unlike enamel) -Elastic Covered by enamel in the crown area, and by cementum in the root area. It is a vital (have only nerve supply), sensitive Capable of repair. During the embryonic stage, odontoblasts are responsible for dentine formation. They migrate in the opposite direction of ameloblasts, moving inward until they reach the pulp, where they settle at the surface. Unlike ameloblasts, odontoblasts remain alive, enabling dentine to regenerate. o Pulp : The pulp forms, nourishes ,innervates and repairs dentine (bcz the odnotoblastas are setting on the surface of the pulp) It is a soft connective tissue contained within the pulp chamber (in the crown=coronal part) and the root canal (in the root=radicular part). Tooth Supporting Structures It is the supporting system that attaches the tooth to the alveolar bone which is called periodontium which consists of:  The gingiva: is part of oral mucosa and forms collar around a tooth  Root cementum: the hard tissue that covers dentine in the root  Periodontal ligaments: a group of ligaments that pentrates the cementum and bones connecting them together  Alveolar bone o The gingiva ▪ It has two regions : The attached gingiva (attached to the bone). The free gingiva (it is not attached to anything). o Root cementum Thin layer of calcified tissue covering the dentine of the root. It's hard tissue but less hard than enamel & dentin It can be repaired and regenerated. o Periodontal ligament Dense fibrous connective tissue that attaches the tooth to the alveolar bone (the white lines between cementum and bone) o Alveolar bone It’s a part of maxilla or the mandible that supports the teeth It is composed from the outer and inner cortical plates, while in the middle there is a spongy bone Individual tooth socket are separated by the interdental septa. Socket means the groove that a tooth sets in. The histology of the bone: compact and spongy bone o Maxilla & Mandible They are much similar to other bones in the body, but they have different embriological way in calcification, we will disscus it more in the bone lecture. o Temporomandibular joint The TMJ is synovial articulation between the mandible & the cranium covered by a capsule. The most important and the only articulation found in the oral cavity. o Oral mucosa The oral mucosa represents the lining of the oral cavity It consists of oral epithelium and an underlying connective tissue (lamina propria), and the basement membrane in between. o Oral sub-mucosa Oral sub-mucosa is a layer of loose fatty or glandular connective tissue. This layer contains major blood vessels and nerves supplying the mucosa and separating it from underlying bones and muscles. o Salivary glands Three pairs of major salivary glands and minor salivary glands. The major salivary glands are: ▪ Parotid ▪ Submandibular ▪ Sublingual THE END OF SHEET #1 2part-1 Enamel ✓ As always, we will study the physical properties, then the chemical properties, then the histology of our subject. 1) Physical properties Enamel is the hardest tissue in the body, it covers the tooth and can be seen in the oral cavity. It withstands shearing forces and impact forces and has a high resistance to being abraded. In permanent teeth thickness varies from up to 2.5mm over the cusps to feather edge at cervical margin (very thin) In primary teeth the thickness of enamel is almost uniform at all areas 1.3mm (thinner than permanent) *Shearing forces: two forces that work in opposite directions *Impact forces: the pressure that heppens during occlusion. *Abrasion: the loss of tooth structure resulting form friction with a hard object (other than teeth) Enamel can’t be repaired or replaced because the cells which secrete enamel (ameloblasts) perform apoptosis after they finish secreting. It has low tensile strength (brittle, don't handle tension), in easy words you can easily break enamel despite it is very hard but it doesn't withstand the forces in different directions, and that's why enamel requires the support of the resilient dentine (dentin not as much hard as enamel but it can withstand forces in different directions). In other hand enamel has a high modulus of elasticity resist elastic deformation. Surface enamel is harder, denser and less porous than sub-surface enamel, so hardness and density decrease from the cusp tip to the cervical margins and from exterior to interior (inorganic material percentage increases from DEJ to surface). Young enamel appears white (because the crystals reflect almost all the light) turning to a more yellow appearance because translucency increases with age (with age we start to lose the enamel and the yellow dentine starts to appear) 2) Chemical properties ✓ Enamel is composed of 96% inorganic mater, 2% organic material, 2% water (which makes it the hardest tissue in the body). A. Inorganic Composition: ✓ Calcium hydroxyapatite crystals are the principle mineral component of enamel. The enamel hydroxyapatite crystals (Ca10(PO4)6(OH)2): ▪ They are about 70nm in width, 25nm thick, and have a great length (almost the full thickness of enamel). ▪ Most crystallites are hexagonal in cross sections. ▪ The cores of the crystals are richer in magnesium and carbonate in comparison to the peripheries which means more soluble. ▪ Each crystal unit has a hydroxyl group surrounded by 3 calcium ions which are surrounded by 3 phosphate ions, then there are 6 calcium ions in the hexagon enclosed with the phosphate ions. ▪ The crystals are made of a repetition of these planes of ions side by side in stacked layers. o Substitution in the hydroxyapatite crystals: ✓ The main substitutions of human appetite are: 1- Carbon substitute phosphate or hydroxyl site 2- Magnesium substitute calcium ion 3- Fluoride substitute hydroxyl ions, fluoride is a big molecule so when it comes and fit instead of hydroxyl ion in the middle of the crystal it is makes it stable and resistant to acidic dissolution. Fluoride levels (unlike magnesium and carbonate) decline from the outer surface towards the dentine, perhaps because fluoride is acquired enamel maturation. Chloride, lead, zinc, sodium, strontium, and aluminium ion may also substitute into the apatite lattice. The ions presenting in the enamel may influence dental carries by affecting the dissolution of the apatite crystals and/or affecting remineralization, for example: 1) Fluoride’s incorporation in the crystal inhibits carries. 2) Carbonate’s incorporation in the crystal promotes the carious attack, because it makes enamel more soluble. o Water: It makes up 2% of enamel by weight and 5-10% by volume. Water presence is related to the porosity of the tissue, because it can be found between the crystals surrounding the organic components. It might be trapped within crystalline defects forming a hydration layer, and Ions such as fluoride travel through the water components. B. Organic Composition: It consists of free amino acids, small molecules, peptides and large proteins complexes (mainly amelogenins and some non-amelogenins). Mature enamel has 1-2% organic matrix (it varies from 0.05% to 3% depending on the regularity of the crystals). Organic matrix consists of proteins that are exclusively found in enamel, these proteins are either amelogenins 90% or non-amelogenins 10% and they don’t contribute to the enamel structure. Highest concentration of this proteins is in tufts at the dentino-enamel junction. Lipid content is 1% by weight of enamel, it may exist as it represents the remnants of cell membrane. Amelogenins : Are hydrophobic, low molecular weight and tend to aggregate into clumps. They are produced by ameloblasts. They spread throughout the whole developing enamel resulting in a gel matrix through which molecules and ions spread readily, this helps in the formation of large crystals in the mineralization stage. Non-amelogenins (such as tuftelin, ameloblastin, enamelin) : They have low molecular weight May be derived from plasma albumin Contain distinct components secreted by ameloblasts Have a role in mineralization along with amelogenins 3)Histology of enamel ✓ Due to high mineral content (96%) enamel is totally lost in demineralization sections, so enamel structure is mainly studied in ground sections. ✓ Immature enamel can be studied in demineralization section due to its high protein content (25-30%). ✓ Immature enamel has a high protein content because its formation starts as organic matrix which will be mineralized in the 2nd stage and becomes inorganic, so before mineralized you can see the enamel in decalcified section. -(we will discuss the further in amelogenins lectures) o Enamel prisms: The basic structure unit of the enamel is called the rod or the prism. Each prism consists of several million hydroxyapatite crystals packed into a long thin rod (5-6 micrometers in diameter and up to 2.5 mm in length). Prism runs from the DEJ to the surface. In the longitudinal section they look like passages. Prisms are separated by inter-rod substance where crystals change direction and deviation by 40-60 degrees leaving some space for organic material to accommodate. Prisms have a slightly undulating course that reflects ameloblasts path during secretion. The enamel between the prisms has been termed ‘inter-prismatic’. Its composition is similar to that inside the prisms, but it has a different optical effect because of the crystal deviation. -Enamel prism in cross section: ✓ Enamel prisms take different shapes (different patterns) but the keyhole pattern (pattern III) predominates. ✓ An abrupt change of crystal orientation at the prism boundary is responsible for the optical appearance of the boundary, which means the the boundary looks a little bit darker than the inside. ‫(يعني اطراف الشكل بتالقيهم اغمق من المنتصف ليش؟ النه بصير فيه تغير التجاه الكريستال على‬ )‫األطراف ف بالمايكروسكوب بنشوفه كانه كريستاالت متراكمة فوق بعض لهيك ببين معنا انه غامق‬ -Look at these two sections to understand: Prisms have head and tail regions, the tail of one prism lies between the head of two adjacent prisms. The crystals in the head and in the middle of the prism run parallel to the long axis of the prism but in the tail, they diverge gradually to become angled at 65-70 degree to the long axis (they also diverge at the boundaries like we discussed before). This change is gradual in each prism, however the tail of one prism shows a sudden divergence from the head of an adjacent prism. Remember: these divergences make the boundaries of the keyhole pattern -This is a cross deminerlised section, notice the prisms in c.s look like keyhole. -In deminerlised section we can see the keyhole pattern, but we will see the prisms empty from inside, why is that? -> As we said the interrod crystals deviate leaving some area for some organic material and water which are still visible in deminerlised section. -These prisms don’t move in one line, look at the pic and see how the black prism comes from one place (orange dot) and ends in another (blue dot), this is a mechanism to make the enamel more resistance to fracture. (Same thing for the grey and white prisms) -They don’t go in a straight line because of ameloblasts that takes this undulating course during secretion of enamel. -The angle at which the sections is cut determines the shape of the prism, so when we cut the section in 90 degree angle we get a perfect keyhole pattern. -As we go from 90 to 0 the shape becomes more and more circular until we don’t have a pattern anymore. -We have 4 patterns 1- almost circular 2- stacked 3-keyhole 4-no pattern. -Hunter-Schreger bands: As we said because the prisms don’t go in straight line. Every 10-13 layers of prisms go in the same direction but blocks above and below follow paths in different directions, and this gives a rise to a banding pattern called the Hunter-Schreger bands. They are approximately 50um in width and are visible due to light reflection in different directions. It’s an optical phenomenon (not real), it only appears under the microscope. In the outer ¼ of enamel, all prisms run in the same direction and so there’s no banding. longitudinally cut prism bands are light (parazones), while transverse cut bands are dark (diazones). The angle between these cuts is 40 degrees. This pattern strengthens enamel against fracture. - Gnarled Enamel: The space for the prisms in the cusps is a little bit tighter than another area, so prisms over the cusps appear twisted around each other in a complex arrangement known as gnarled enamel. Kinds of Physical stress: https://youtu.be/1cftaE5fX8o?si=C5VW11HK8VFtFxwz How enamel prisms are made: https://youtu.be/Lw3VEVt_tpU?si=bXBhQYevsLtSk-vS Summary video: https://youtu.be/Gxy6f0BKgk0?si=WcftUiajyqtUt2QS The End of the sheet #2 part 1 KEEP GOING! 2 PART 2 Aprismatic Enamel (no prisms) The outer surface layer of enamel (20-100 micrometer in primary teeth and 20-70 micrometer in permanent) is aprismatic. The crystallites are aligned at right angles (90o) to the surface and parallel to each other. The surface layer is more highly mineralized than the rest of the enamel. This is due to the absence of prism boundaries where organic material is located, and this is very important, to make the surface respond to acidic attacks and caries. ▪ As previously discussed, the crystals at the peripheries of enamel rods deviate to create space for organic molecules. Consequently, the absence of rods at the surface results in a reduction of organic material and an increase in mineralized material. HISTOLOGY OF THE ENAMEL Now we will talk about histology of enamel starting from dentino-enamel Junction (DEJ) to surface and taking section ENAMEL to see and explain. Firstly, we will take the DEJ and all features on it like tufts, DENTIN spindles and lamella. Then, we will go to the bulk of the enamel and see what are called incremental lines (lines are caused by the deposition Note: Dentin appears more yellowish in of the enamel), cross and stria. compared with enamel Then, we will go the surface of enamel and see its features Finally, we will see also on the surface how cementum and enamel meet at Cemento-enamel junction (CEJ), let’s start! 1-Dentino-enamel junction (DEJ) This junction must have unique features to retard crack propagation between the two interfaces, which means when we wanna glue two surfaces, the glue should be very good to prevent separation of these two surfaces. It has a scalloped pattern whether shearing forces would be high beneath cusps and incisal edges. while it’s smooth in lateral surfaces. The DEJ is less mineralized than enamel and dentin. We have three different structures that are on DEJ, the scientists described them and gave them names: A-Enamel spindles ▪ They are narrow and round tubules (8 µm in diameter), extending very short distance (up to 25 µm) into the enamel. ▪ They don’t have the same color or structure or direction of enamel but actually they have the same color of dentine. ▪ So, they’re actually odontoblastic processes that are extending from dentine to enamel. Note: in next lectures, we will be able ▪ We’ll learn in next lectures that dentine is to differentiate between these tissues well, we can name every tissue we composed of something called dentinal tubules very see, don’t worry right now which are long thin structures, and these tubules sometimes don’t stop at DEJ, a little of it extends into the enamel, making these spindles (small thread-like) ▪ Most commonly seen beneath cusps as crowding of odontoblast processes ▪ We can say that they are odontoblastic processes among ameloblasts remnants of dead odontoblasts, dentinal collagen. B-Enamel Tufts (tuft means grass) ▪ Located near DEJ in the inner third of enamel. ▪ They have the same direction as prisms and don’t look like the dentine, so It’s actually a part of the enamel. ▪ recur at 100 µm intervals.(taller than spindles) ▪ They’re hypominerlized areas that shows residuals matrix protein at the prism boundaries (high percentage of organic matrix) ▪ Tuft protein is a minor non-amelogenin protein Remember: most of the organic proteins are found in the tufts called tuftelin. C-Enamel lamellae: ▪ Structural faults run the entire enamel thickness from the surface to the DEJ. ▪ It’s caused by an incomplete maturation of groups of prisms. ▪ Hypomineralized areas ▪ Don’t confuse them with the cracks produced during ground secretion preparation, cracks disappear with demineralization. A represents lamella ---------------------------------------------------------------------------------------------------------- 2-The Core of The Tooth A- incremental lines ▪ They are lines seen in teeth sections showing the periodic deposition of dentin, enamel, and cementum occurring during tooth growth. ▪ Enamel (just like any other hard tissue of the tooth) is formed in increments, as its development includes periods of activity alternating with periods of inactivity and this results in incremental lines. ▪ So, each time the cells take a rest, they sit down before they become active again, they form lines! ▪ There are three types of incremental lines: 1- Enamel striae (long periods of activity) (weekly activity) 2- Cross striations (short periods of activity) (daily activity) 3- Neonatal line I)Cross striations ▪ Cross striations appear as lines crossing the enamel prisms at right angles to their long axis. ▪ They reflect a diurnal rhythm (daily increment of growth). ▪ They appear as lines 2.5-6 µm apart (closer to each other near the DEJ) ▪ May represent variations in the organic matrix, crystals orientation and composition or prism width. ▪ We can’t see them under light microscope, so we need electron microscope to see them (high magnification). NOTE: prisms are longitudinal, the lines that perpendicular to prisms are cross striations II)Enamel striae (striae of retzius) NOTE: demarginalized section So, We can see striae of retzius under the light microscope ▪ Enamel striae run obliquely across the prisms. ▪ They represent incremental lines and are known as the striae of retzius ▪ The cells rest here, then work and secrete for a week between two lines, then they rest again, so this is the weekend of the cells. ▪ In this section we can see ameloblasts which tell us that we are in the early stages of formation and the enamel has a high organic matrix percentage, which is called immature enamel. ▪ In cross sections, the striae run circumferentially like the rings of a tree. ▪ There are 7-10 cross striations between two adjacent enamel striae. ▪ Enamel striae are 25-30 µm apart in the middle portion (cross striations are 4 µm apart) while they are 15-20 µm apart cervically (cross striations are 2 µm apart) B C D A:Dentine B:DEJ C:Enamel bulk D:Enamel surface (different in color due to its aprismitc, more mineralized) ▪ In longitudinal sections, we can see the stria going obliquely on the rods, but on the cusp tips the stria don’t reach the surface, they actually make circles, go up and back. ▪ Stria apparent in ground sections differential light- scattering effects at this fault line, possibly due to a slight change in prism direction/thickness, or slight differences in crystallite composition/ orientation, and/or differences in organic content. ▪ in demineralized sections, the site of striae having a higher carbonate content, which causes greater solubility of the crystals and greater porosity. They are hypomenerlised areas. III)Neonatal line: ▪ It’s one of the incremental lines, it shows the difference between the enamel formation before and after birth. ▪ A particularly marked stria is formed at birth and reflects the metabolic changes at birth. Prisms appear to change both direction and thickness at the time of this event. ---------------------------------------------------------------------------------------------------------o These enamel striae are there on the whole enamel, and it actually reaches the enamel surface, if you take a closer look at the surface of this tooth, you can see there are lines on the surface and these striae are given another name which is perikymata, o The lines are called perikymata grooves, with perikymata ridges in between, these grooves running circumferentially around the crown, and they are removed after eruption by attrition (loss of tooth structure which is caused by friction with other teeth) and abrasion. o If we put EM on the surface of enamel we will see this pic, high areas are perikymata ridges and low areas are perikymata grooves. ---------------------------------------------------------------------------------------------------------o Surface enamel: ▪ surface enamel differs from sub-surface enamel physically and chemically. ▪ Surface enamel is harder, less porous and less soluble more radio-opaque (more whiter on x-ray) ▪ It’s richer in trace elements especially Fluoride, less carbonate. ▪ It’s aprismatic, therefore highly mineralized, more resistant to carries. Some phenomena that can be seen on the surface:  Small pits: these pits can be seen within the perikymata, and they mark the end of the ameloblast (as ameloblasts were sitting on the surface before the committed apoptosis), and they are 1-1.5 micrometers in depth.  Enamel caps: they are small elevations 10-15 micrometers across, they result from enamel deposition on top pf debris late during tooth development, and they are frequent on lateral surfaces  Focal holes: they are depressions on the surface caused by the loss of enamel caps with the underlying material, this through abrasion and attrition, frequent on the lateral surfaces  Enamel brochs: they’re elevations on the surface, 30-50 micrometers in diameter, larger than caps, radiating groups of crystals, and they are more common in premolars. --------------------------------------------------------------------------------------------------------- 3-Cemento enamel junction (CEJ): ✓ It is how cementum and enamel correlate to each other. ▪ There are three arrangements between cementum and enamel: ▪ Pattern 1: the cementum overlaps the enamel (60% of the cases) ▪ Pattern 2: the cementum and enamel meet at butt joint A (30%) ▪ Pattern 3: the cementum and enamel fail to meet and the dentine, in between them is exposed (10%) ▪ Pattern 4: enamel overlaps the cementum (very rare 1.6%) ➔ All these patterns may be present in a single tooth. D B C A:Dentine B:CEJ C:Cementum D:enamel ---------------------------------------------------------------------------------------------------------- o Enamel pearls: ▪ Small droplets of enamel on the root near the furcation, because sometimes in the stage of teeth formation, some cells that form enamel (differentiation of ameloblasts), slip down into the root and continues to form enamel there. (This phenomenon is called Hertwig’s root sheath), (and we call this enamel, enamel bird) The End of Sheet #2 part 2 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. 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 pre-dentine 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 a morpheus 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 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 ! Amr Raed Mays abu-sara Heba alzer Dental pulp The dental pulp is a specialized connective tissue, it is contained within the pulp chamber and root canals of the tooth. At the apical constriction of the root canal, it becomes continuous with the periodontal ligament, and as we know previously, it forms dentin on the walls of pulp by odontoblasts. If we look at the periphery of the dental pulp, we will find a line of columnar, polarized cells which are odontoblasts covering the line between the pulp and dentine. Also in the periphery are two elements capable of detecting external stimuli and initiating a response to them. These are the nerve terminals of trigeminal afferents and specialized dendritic antigen-presenting cells. The rest of dental pulp which is loose connective tissue act as a support system for these components. -------------------------------------------------------------------------------------------------------------------------✓ We know that at the end of the roots we have a foramen called apical foramen (at least one, many have two), it’s where the nerves and vessels enter the tooth, they both enter together in what is called neurovascular bundle and branch inside the tooth and the crown. ▪ In addition to the apical foramen, there are accessory canals Main canal found on the sides of the roots, they branch from the main canal and they have their own foramina, most commonly seen in the apical third of the root. ▪ In multirooted teeth some small vascular canals enter the pulp chamber from the bone between the roots by furcation foramina. -------------------------------------------------------------------------------------------------------------------------- ❖ Composition of the dental pulp: o 75% water by weight o 25% organic materials: Cells and ECM ▪ Loose CT, and it is made up of a combination of cells embedded in an extracellular matrix of fibers in a semifluid gel. NOW, we will discuss the organic materials which are ECM and Cells of the dental pulp, starting with ECM: Extra cellular matrix (ECM): The ECM is a versatile group of polysaccharides and proteins secreted by the cells of the tissue, assembled into a complex framework or scaffold closely associated for the cells to function and make the tissue. The scaffold stabilizes the structure of the tissue. The matrix plays a very active role in controlling the activity of the cells within it, it affects their development, migration, division, shape and function. Collagen is the predominant extracellular matrix component, comprising 25–32% of the dry weight. Note: This ECM COMPONENTS TOPIC is self-reading from book, and it is included in the exam, so instead of )‫(نغلبكم‬i’ll go back The ECM has two components: to the book and put the important things that are required o ECM-Fibers component: ▪ mainly collagen type I (60%), and collagen type III (40%) present as fibrils 50 nm in diameter grouped into fibers thinly and irregularly scattered throughout the tissue, and collagen almost forms 3-5% of wet weight of pulp. ▪ The arrangement becomes more organised in the periphery, with the fibers aligned parallel to the forming predentine surface. ▪ Small amounts of type V and type VI collagen are also present as a meshwork of fine microfibrils. Type IV is nonfibrous and present in the basement membrane of blood vessels. ▪ Fibronectin is a glycoprotein found in several forms, one of which is fibrous and is distributed throughout the pulp. It anchors cells and may be important in determining their shape. ▪ Noncollagenous beaded microfibrils 10–14 nm in diameter are also present. These are formed from fibrillin, a large glycoprotein which, in other tissues, is associated with elastic fibers. o ECM-Non-fibers component: ▪ The macromolecules that make up the bulk of the nonfibrous component of the extracellular matrix are proteoglycans, glycoproteins and unbound glycosaminoglycans. 1. Glycosaminoglycans (GAGs): unbranched polysaccharide chains composed of repeating disaccharide units, there are four GAGs; chondroitin sulphate, dermatan sulphate, heparan sulphate and hyaluronic acid (60% the major in mature pulp). Most of the GAGs are covalently bound to a protein core to form proteoglycans forming gels that Note: Hyaluronic acid is the only GAG found unbound to protein in any quantity. As well as having a mechanical function it is thought to fill most of the extracellular space. In the developing facilitate cell migration, particularly during development. pulp chondroitin sulphate is the major GAG. 2. Proteoglycans: are functionally diverse molecules. Some, such as versican, contribute to the bulk of the matrix, others may bind to fibers, to other nonfibrous components of the tissue, or contribute (e.g., syndecan) to the basement membranes of epithelially derived cells such as Schwann cells and endothelial cells. 3. Glycoprotein: Two other glycoproteins than collagen, fibronectin (which also occurs in fibrous form – see above) and tenascin, have been described in the pulp and are at their highest concentration near the odontoblast layer. Four groups of cell adhesion molecules are generally recognised: the immunoglobulin superfamily, the selectins, the cadherins and the integrins. remember: odontoblasts send their processes into dentine. Cells: The second component of the organic matrix is the cells, there are 4 main components, odontoblasts, fibroblasts (most abundant), immune cells and some stem cells. Remember: immune cells include T-cell, macrophages, dendritic cells, etc.. LET’S discuss each type of cells :) : 1. Odontoblasts: columnar, polarized, fully differentiated cells, with a long process inside the tubule. ▪ Differentiated cells: means if they are insulted or injured will result in the death of odontoblasts. ▪ Polarization (asymmetrical): means that the plasma membrane has different invaginations which divide the cell into different compartments with different functions. ▪ There are small processes link adjacent odontoblasts and other pulp cells such gap junctions, desmosomes and tight junctions. Cell body: 50μm long, 5-10μm in width, the nucleus sits in the basal (pulpal) half of the cell with the other organelles involved in dentine synthesis, the rough endoplasmic reticulum, Golgi complex and mitochondria, above it. When we look at the odontoblasts in the histological section, they look like multilayered columnar cells which are pseudostratified columnar cells, why? Because it is impossible to cut the section (oblique section) in the thickness of one cell, so they appear multiple cells layers of cells above each to oher. Note: when we take a section from cervical root, they appear cuboidal, from apical root, they appear spindle shape. Note: these boxes are extra info from book for better understanding We talked about the histological section, but in reality, Odontoblasts form a layer of single cells attached to the predentine by a single process. What are the functions of odnotblasts?! ▪ Dentine secretion ▪ barrier reducing toxins to reach the pulp (integrity of the odontoblast layer and its limited permeability are maintained by numerous cell-to-cell junctions) ▪ allowing tissue fluid from the pulp to enter dentinal tubules (outward washing pressure), and controlling composition of this fluid. ▪ producing proinflammatory mediators in response to bacterial toxins. ▪ produce cytokines such as interleukin (IL)-8, which participates in the recruitment of neutrophils in case of injury. this topic is also self The integrity of the odontoblast layer and its limited permeability are Note: reading, but I’m here for you dear. I’ll put the info that maintained by numerous cell-to-cell junctions, what are these my are important from the book. junctions? ▪ Desmosomes (The macula adherens junctions): have a clear intercellular component as well as an intracellular system of anchoring fibrils and are largely responsible for mechanical union. ▪ gap junction: allows the movement of small molecules directly between adjacent cells. It is important in cell-to-cell communication and would presumably have a role in synchronising the activity of all the odontoblasts in the layer. ▪ Tight junctions: appear as a near fusion of apposing cell membranes and limit the permeability of the cell layer. The more tight junctions there are and the closer they are together, the lower the permeability. Age changes: ▪ The odontoblast continues to lay down secondary dentine at a slow rate throughout life. As it does so the pulp chamber becomes smaller and root canals narrower. ▪ The odontoblast layer becomes a flatter layer of cells columnar in the beginning then they become cuboidal and finally spindle shaped and the number of cells declines by apoptosis with age. ▪ It has been estimated that in a premolar half the odontoblasts will die in the 4 years following the completion of root formation. 2. Fibroblasts: Most ubiquitous cells, and they form a loose network throughout the tissue linked by adherens type junctions and gap junctions. Their morphology is highly variable but is most aptly described as stellate, with the arms of the stars linking fibroblast to fibroblast or fibroblast to odontoblast. Their functions: ▪ They slowly produce fibers and ground substances. ▪ degrade extracellular matrix, matrix turnover. ▪ Production of growth factors and cytokines. 3. Immune cells: They are T-cells, macrophages, dendritic cell,etc… (we will take them briefly, bcz we have already learned about them in General Histology, I hope :P ) ▪ T-lymphocytes: -Small numbers in normal pulp -Numbers increase when the pulp is injured. ▪ Macrophages: -Different morphologies in resting form. -Widely distributed in the pulp in big numbers. - Denser around blood vessels and odontoblasts. ▪ Dendritic Antigen Presenting Cells: -Three or more branching processes, some extend in tubules. -They are in close relationship with odontoblasts. -More numerous around blood vessels, nerves and odontoblasts. -what are these cells do? They actually look for antigens, catch them and then give them to T cells which actually do the rest of immunological reactions to defend the cell. 4. Stem cells: Different populations in different locations The subodontoblastic layer contains odontoblasts progenitors, these progenitors means a cell has the capability to differentiate to only one kind of cell. Could be isolated and directed to differentiate into different cell types for regenerative purposes. -------------------------------------------------------------------------------------------------------------------------- ❖ Blood vessels: As we mentioned in the beginning of sheet, the blood supply (arterioles and venules) has a close relation with the nerve and becoming neuro vascular bundle, that enters the tooth from the apical foramen and lateral canals, to branch in the peripheries and in the crown until they reach the coronal part where they branch profusely making up plexus. Larger vessels are 150 um in diameter. Arterio-venous and venous-venous anastomoses to allow rapid changes in blood perfusion. Terminals of sympathetic nerves are in association with arteriole’s smooth muscles to control the arteriole Vasoconstriction. High Pulpal blood flow 20-60ml/minute per 100g of tissue creates High fluid pressure that is pushed through the dentinal tubules as a defensive mechanism to push all the pathogens away. Profuse branching once within the coronal pulp chamber ending with Subodontoblastic capillary plexus that is: ▪ Capillaries are 6-8μm in diameter. ▪ Within and beneath odontoblastic layer and between the odontoblasts and the predentine ▪ 4-5% are fenestrated with only a basement membrane at their wall allowing rapid movement of materials out of the capillary. Note: these sections show how the trunk entered as a big trunk and then branches become smaller and smaller, reaching capillary plexus that actually becoming so profuse under the odontoblastic layer. You can see the blood vessels under microscope (cross sections) as circles with a lumen (maybe empty), if it is arteriole, you’re gonna see a thick wall because of the muscles around it, if it is venule, you’re gonna see a thin wall. Note: vessels in longitudinal sections Note: thick wall indicates to arteriole ❖ Lymphatics: Like any another tissue there are some lymphatics, but hard to observe. We can sometimes know from the lumen, the arterioles and venules maybe have RBCs, lymphatics don’t (the dr said that she won’t ask us identify lymphatic cuz it’s hard to differentiate them from the A,V). ❖ Nerves: Nerves enter the pulp as part of the neuro-vascular bundle, pulp is heavily innervated. They branch in the coronal part of the pulp profusely making a plexus of nerves beneath the odontoblasts called Plexus of Raschkow. Branches end in and around the odontoblastic layer. The plexus is evident after tooth eruption. Branches from the plexus enter the dentinal tubules. Many axons in the tubules, at the peripheries of dentine and among odontoblastic bodies are devoid of Schwann cells (unmyelinated), This facilitates their response to stimuli from the immediate environment. Note: these sections under EM, of dentinal tubules with the odontoblastic process inside, and some terminal axons Now, let’s discuss the inner nerve fibers, they are two types: ▪ 25% myelinated afferents whose cell bodies lie in the trigeminal ganglion, 90% of which are Aδ fibers (1-6μm in diameter), the remainder of myelinated nerves are Aβ fibers (6-12μm) in diameter. They sense Sharp pain. ▪ 75% Unmyelinated C fibers: the majority of nerve fibres in the pulp. mostly trigemenal afferents for Dull pain and scarce sympathetic efferents to control arterioles smooth muscles contraction. ❖ Regions in the dental pulp: There are 5 different regions: ▪ Supraodontoblastic region. ▪ Odontoblastic layer. ▪ Subodontoblastic region: Cell free zone of Weil. Cell rich zone. ▪ Bulk of the pulp Note: b: predintine, A: odontoblast cell bodies, the black arrows: supraodontobalstic layer and the layer underneath it is cell free zone. 1. Supraodontoblastic Region: Between the odontoblastic cell bodies and the predentine. They appear due to tissue shrinkag when you prepare a section. unsheathed axons are present (predentinal plexus of Bradlaw), Only in crown, they are not a true plexus (network) but an area where a number of axons congregate and enter the tubules. Dendritic antigen presenting cells, or their processes are present also. 2. Cell free zone of weil: It is cell processes of fibroblasts and antigen-presenting cells, axons and capillaries cross this region. Anuclear zone is a better description as Electron microscopy reveals that many cell processes of fibroblasts, odontoblasts, axons and capillaries cross this region that usual stains like H&E don't expose. So, it’s not empty and most probably the cause of it is the shrinkage that happens because of the processing of the tissue. absent from the radicular pulp and usually appears in the coronal pulp of erupted teeth, is it an artefact? NO! 3. Cell rich zone: This area, as the name implies, is full of cells. It’s either because the shrinkage that happens pulling the cells from the free zone to rich zone, or because Subodontoblastic capillary plexus, Subodontoblasticneural plexus, and a lot of other cells in this area, making them rich in cells (Schwan cells and endothelial cells) Is it artefact? NO! 4. Bulk of the pulp: The pulp is formed by the ECM with fibroblasts, and there is where we find the capillaries, lymphatics and nerve supply. It is the central area of the pulp, from loose CT. ❖ Ageing of the pulp: The pulpal size decreases (in crown and root) with age as secondary dentin forms. Decreased vascularity. More fibrous. Reduced innervation. Calcification happens: Pulp stones or small specs snow storm calcification. Note: the old pulp is more fibrous, less cellularity, less innervation and blood supply. Note: also calcification happens showing snow storm, because it looks like a snow freak. Pulp stones: Single or in groups, And can be detected on radiographs They can be: ▪ True denticles resemble dentine (tubular). ▪ False denticles resemble bone (trapped cells) or lamellated (layers) stones. Large stones may attach to dentine or free. Some could be embeded in dentine. The problem of these is when the tooth needs root canal therapy, they make the root therapy complicated. Note: as you can see, the right one pic, there are stones embedded in the dentine, and there are attached and there are free Note: another section, the left is free pulp stone while the right is attached pulp stone Note: A PIC: free false pulp stones, because it looks like bones B PIC: also false pulp stones. This is the other kind of calcification that can happen in the pulp, called snowflake which means random calcification throughout the pulp. THE END OF SHEET #4 ‫عرس ال دارت الدنيا يلي‬ ‫كل‬ ٍ ‫وكل ضيق ى‬ ‫يلق بامر هللا ِسعة‬ ٍ Mays abu sara & Amr Raed Mays abu sara & Amr Raed Aseel sharaireh Cementum ✓ In the previous sheets we discussed the enamel, dentine, and pulp. In this sheet we will discuss the periodontium (which is the structure that covers the root of the tooth, we will focus on cementum). ( Enamel, Dentine, Pulp, Periodontium ) ✓ The periodontium is the specialized tissues that both surround and support the teeth, maintaining them in the maxillary and mandibular bones. The word comes from the Greek terms (peri-, meaning "around" and -odont, meaning "tooth"). ✓ The periodontium is a complex structure composed of: 1. Cementum, which covers all the root portion. 2. Alveolar bone. 3. Periodontal ligaments (PDL), in between cementum and the bone (gluing them together). 4. Gingiva. ❖ Functions of periodontium: The periodontium serves many functions, and each anatomical part serves a specific role that will be discussed thoroughly. - Generally the primary functions of the periodontium are: ▪ Attachment and support of teeth to the surrounding bone in the jaws during their function and in the relaxed state. ▪ Providing a barrier for the underlying structures from the oral microflora (it’s the function of gingiva with help from the periodontal ligament). ❖ Physiology of periodontium: The periodontium depends on the stimulation it receives from teeth function and mastication for preservation of its structure. The periodontium is under a constant state of homeostasis, the tooth always trying to achieve stability by continuous remodeling and accommodation with the external forces on it to withstand them, so that periodontal structures can adapt with the external forces. Both cementoblasts and osteoblasts are known to have receptors for parathormone (PRT) and parathormone receptor protein (PTHrP), so it’s under control of thyroid, parathyroid glands Look at the pic, you can obviously see that if u applied a vertical force on the surface of ur tooth this force will distribute in different directions to reduce the amount of mechanical force on it, so the tool will be in a full function state for a very long period as long as u take care of them (): ‫)فرشوا اسنانكم‬. This pic shows you that there is a physiological normal limit of movement that the tooth allows to be able to accommodate to their external forces. In premolar we have a horizontal plane of about 0.1 mm movement, and a vertical plane of about 0.03 mm movement. There is a constant state of remodeling in order for the jaws to accommodate normal types of occlusal forces and any changes of occlusal forces the tissue is designed so that it can be constantly adapting. This requires the tissue to be flexible and proliferative, contain types of cells that can build and destruct and contain proprioception. By looking to the pic you will notice that wither we applied a vertical or lateral external force on the tooth, the forces will be distributed to the whole surrounding tissue to bearing this weight that supposed to carry. Cementum : CEMENT-UM, a “cement” is a binder, a substance used for construction that sets, hardens, and adheres to other materials to bind them together, “Um” in medical language means: structure, tissue, thing Definition: Cementum is a specialized calcified substance covering the root of a tooth. The cementum is the part of the periodontium that attaches the teeth to the alveolar bone by anchoring the periodontal ligaments. It’s a hard, avascular connective tissue that covers the root. No vessels, nerves, lymph. No physiologic resorption or remodeling should be seen in cementum (if it happens it’s pathological). Dentin Continuing deposition throughout life. e Cementum Thin layer of calcified tissue covering radicular dentine adheres firmly to its deep surface and is contiguous with the periodontal ligaments Cervically, it is 10-15μm in thickness, and increase in thickness, Apically it is 50-200μm thick, and could exceed 600μm at root apex The layer of calcified cementum have different components depend on where you are in the tooth, on the CEJ we have different type of cementum than that covers the root ( due to embryogenic reasons, will discuss later) The highly responsive mineralised tissue maintains the integrity of the root through the re-attachment of the periodontal ligaments, this preserve the tooth in its functional position in the mouth through its role in tooth repair and regeneration. There is always a layer of unclassified pre-cementum at the outermost area, this layer is similar to bone in composition, but not innervated and avascular and does not have a lamellar appearance or marrow space. ❖ Physical properties of cementum : ✓ Pale yellow and Dull surface. ✓ Softer than dentine Provides cushioning effect. ✓ Variable permeability differs by age and type, (cellular type is more permeable and it decreases with age). ✓ More permeable than dentine. ✓ Easily abraded (taken away) cervically (due to its relative softness and thinness), that causes dentine exposure ❖ Notice how it become thicker when we go apicaly Chemical properties of cementum : Inorganic component: Mainly hydroxyapatite, with other calcium forms, thin plate like apatite crystals Organic component: Collagen type I, and non-collagenous elements similar to bone; sialoprotein and osteopontin ❖ Classification : We classify cementum either by: 1. Presence of cells : -Cellular -Acellular 2. Origin of fibers : -Intrinsic -Extrinsic We have types that are combination of both: AEFC (acellular extrinsic fibre cementum) CIFC (cellular intrinsic fibre cementum) MFC (mixed fibre cementum) CMSC (cellular mixed stratified cementum) Afibrillar cementum (this is the type that firstly disposed around the root, and the type that stays around the CEJ) Cellular cementum contains cementocytes, Acellular cementum covers the dentine. Cellular cementum is mainly in the apical area and interradicular areas overlying acellular cementum. Acellular cementum appears structureless(no cells). There is dark line between hyaline layer and acellular cementum marking afibrillar cementum. Differences between cellular and acellular cementum are due to the differences in the formation rate of both tissues. Lacunae (spaces contain the cementocyte), more widely spaced in incremental lines and a layer of pre-cementum compared to cellular cementum. Dentine Acellular layer Cellular layer Periodontal ligament Pre-cementum Cementocyte Cementoblast Canaliculi ❖ Cementocytes: Different relations between cellular and acellular cementum, which is determined by based on the existence of cementocyes. Cementocytes are trapped in lacunae with canaliculi which are spaces that contain the cylindrical processes of these cells. Canaliculi oriented towards periodontal ligament, as if the cells are trying to stay in contact with their origin. Cementocytes are usually inactive, they don’t do a lot, with low cytoplasmic/nuclear ratio. Minute amounts of energy and protein synthesizing organelles Cementum is deposited with an irregular rhythm resulting in incremental lines of Salter which are weekly intervals of rests. Incremental lines of salter mark differences both in mineralization and in organic matrix composition, and these lines are more calcified compared to the rest of cementum. ❖ NOTE: cells in their lacune enable more calcification, and that when cementoblasts pause their activity, they create a space that allows for the deposition of more inorganic material, leading to the formation of incremental lines of salter Origin of fibers: Cementum derives its organic matrix from two sources: ▪ Derived from cementoblasts as intrinsic fibers which run parallel to the root surface ✓ that make cellular intrinsic fiber cementum. ▪ Derived from fibroblasts of the periodontal ligament, by the inserting Sharpey fibers as extrinsic fibers, which are continuation of periodontal ligaments that enter the cementum perpendicular or slightly oblique to the root surface, then these fibroblasts Note: sharpey fibers get calcified into the deep layers of cementum, all become cementoblasts and they also help in making and of the layers of cementum enable the calcification of the sharpey fibers the attachment of the Sharpey fibers ✓ that make acellular extrinsic cementum. https://youtu.be/5Mi4AX50LO0?si=hiq2w3Pqlkx3qw o Mixed fiber cementum contains both types Note: the cells are from different origin, the right one is cementoblast (like fibroblasts) , their origin from cells of hertwigs epithelial root sheet and looks like spindle/fusiform shaped and they secrete the acellular extrinsic fiber cementum, however the left one is the actual cemenoblast (like osteoblasts), their origin from cells of dental sea and they look like cuboidal and they secrete cellular intrinsic cementum. …4 Note: the purple cells are fibroblasts and they are making extrinsic fibers as shown in the yellow, the green cells are the actual cementoblasts and they are making intrinsic fibers Now let’s talk about each region of cementum: Remember: the first layer is always an afibrillar cementum covered by with an acellular extrinsic fiber cementum Acellular extrinsic fiber cementum (AFFC) For this type of cementum all the collagen is derived as Sharpey fibers from the periodontal ligament (the ground substance itself may be produced by the cementoblasts). Mainly over cervical two thirds of the root. Bulk of cementum in premolars The first formed cementum and it’s well mineralized Could reach 15µm in thickness Cellular Intrinsic fibillar cementum (CIFC) Intrinsic fibers parallel to the root surface of intrinsic type only No role in tooth attachment to the periodontal ligament Apical third of the root and in the inter-radicular area, however as the person ages, you’ll fine more and more CIFC covering up to the mid portion of the root. If formed slowly, acellular intrinsic fiber cementum could result. Mixed fiber cementum (MFC) Both extrinsic and intrinsic fibers Different orientation almost at right angles, since one is parallel to NOTE: you have to distinguish between them root surface and the another is perpendicular. Different bundle sizes: ▪ Extrinsic fibers are ovoid or round, about 5-6µm in diameter ▪ Intrinsic fibers are 1-2µm in diameter (very small and thin) Based on formation rate it can be: ▪ Cellular mixed fibre cementum (fast formation, less mineraliazation) ▪ Acellular mixed fibre cementum (slow formation, well mineralized) Afibrillar cementum The First layer of cementum, it does not have collagen fibers It is sparsely distributed and well mineralised ground substance They think its origin from Epithelial cells, and the hyaline layer appears as a part of uncalcified afibillar cementum It is thin, acellular could overlap with enamel Between fibrillar cementum and dentine ❖ Cementum relation with surrounding tissues: ▪ Cemento-enamel junction ▪ Cemento-dentinal junction ▪ Attachment of cementum to the periodontal ligament Cemento-enamel junction (CEJ): It has three patterns as mentioned before. One may predominate in any individual tooth All three patterns can be found in the same tooth In pattern III, the dentine is exposed and this is where the problems happen like cold sensation. NOTE: Pattern I, II and III NOTE: sometimes there is a fourth type which is quite small in proportion, enamel is overlying the cementum at the meeting point. Cemento-Dentine junction (CDJ): Particular importance as it forms a fit or an interface between two differently mineralized tissues that are contemporarily developing. Clinically important because of the processes involved in maintaining tooth function while repairing a diseased root surface The junction has lower mineral content (hyaline layer and afibrillar cementum) and is composed of organic and inorganic components. Anchors Periodontal fibers into dentine Intermediate layer between the 2 tissues Often referred to as: Innermost cementum layer, superficial layer of root dentine, intermediate cementum, hyaline layer Wide irregular spaces that may interconnect with tubules NOTE: from the book to better understanding it is named intermediate cementum or hyaline layer of Hopewell-smith, which is the first layer formed by the inner cells of the HERS and is deposited on the root’s surface. Deposition occurs before the HERS disintegrates, and we can consider it a kind of sealing the dentinal tubules and it is between the granular dentin layer of the tomes and secondary cementum that is formed by the cementoblasts (which arise from the dental follicle) Approximately 10 um thick and mineralizes greater than the adjacent dentin or the secondary cementum. The spaces might be related to entrapped cells or maybe enlarged tubular terminals. There are differences between species, In humans, this layer is the product of Hertwig’s root sheath Sometimes, there is no region between dentine and cementum, instead there is direct contact between the tubules and the cementum fibers. Cementum periodontal ligaments junction Fibers in the periodontal ligament run into the organic matrix of the pre-cementum which is secreted by cementoblasts Mineralisation of the pre-cementum leads to the incorporation of these extrinsic fibers such as Sharpey’s fibers 30’000 principal fibre of periodontal ligaments attached onto cementum/ square millimeter ❖ Resorption and Repair As we said, we don’t have normal physiological resorption, so it is less susceptible to resorption than bone. However, roots show small localised areas of resorption These may be associated with trauma and pressure applied onto these roots This happens due to existing multinucleated odontoclasts (or cementoclasts), which have a kind of eating the tissue, the resorption may reach dentine and could be serious. Deficiencies resulting from resorption can be filled by deposition of cementum, a line known as a reversal line may be seen separating the repair tissue from the normal underlying dental tissues which apparent when the repair starts. The repair tissue resembles cellular cementum. However, differences can be noted between the repair tissue and cementum: ▪ the width of the precementum of reparative cementum (15 µm) is greater than that for precementum (5–10 µm), this is due to the fact that it’s fastly being disposed and it does not have as much minerals as the normal cementum. ▪ its degree of mineralisation is less ▪ its crystals are smaller ❖ Clinical Considerations: 1. Exposed root dentine: ▪ Relative softness with cementum, combined with its thinness cervically, means that it can be easily removed by abrasion when there is recession. ▪ If the dentine is exposed, it will be dissolved rapidly cervical caries can develop and may give rise to the painful symptoms of hypersensitivity. 2. Root fracture repaired by cementum callus: ▪ Root fractures may, on some occasions, repair by the formation of a cemental callus, callus is similar to the fibroid that forms when you are wounded and then excessive skin covers up and tries to NOTE: callus is not same as repair. calculus, calculus is a pathological disease where ▪ In other instances, the pulp may become necrotic the food that accumulates in the gum gets calcified and ▪ Look at the pic, the repair looks like a bandage. stuck on the teeth 3. Cementicles: ▪ Cementicles are abnormal secretions of cementum in the periodontal ligaments, found in approximately 35% of human roots. ▪ They are not always attached to the cementum surface but may be located free (in the pic, it is free) ▪ They are more common in the apical and middle third of the root and in root furcation areas. ▪ They don’t have much significance, but if you see them on a radiograph, you don’t freak out. 4. Hypercementosis: ▪ Hypercementosis is the increased cementum thickness throughout life, sometimes that can be due to chronic periapical inflammation or paget’s disease of bone (when seen in all teeth) ▪ The problem in hypercementosis is replacing the periodontal ligaments attachment NOTE: as you can see in these radiographs, you can’t see the periodontal space because it has been replaced by cementum THE END OF SHEET #5 Mays Abu sara & Amr Raed Mays Abu sara & Amr Raed Aseel sharaireh Periodontal ligament (PDL) ❖ We started talking about the periodontium in the previous sheet, so we discussed the cementum and in this sheet our topic will be the PDL. ❖ Periodontal ligament is dense fibrous connective tissue that occupies the periodontal space between the root cementum and the alveolar bone and attache them together. ❖ The PDL is derived from the dental follicle. ❖ It’s continuous with the gingival connective tissue (above alveolar crest) and the pulp (at the apical foramen), The continuity with the pulp explains why inflammation from this dental tissue (often related to dental caries) spreads to involve the periodontal ligament and the other apical supporting tissues. ❖ Width is around 0.25mm, and there is variation in width according to: location, function and age between teeth and within an individual tooth exist. ❖ The space is narrower in non-functional and un-erupted teeth, and is wider in teeth with high occlusal loads. ❖ There is a test that dentist do, the test is inserting a probe in the attached gingiva that connect the tooth to the soft tissue (PDL), the probe should stop at 1-2mm inside the tooth gingival socket and not going deep anymore, if that happen and probe go beyond 2mm this indicate a periodontium disease. ❖ Periodontal ligament in research, Research is focusing on this tissue roles as its associated with mechanisms of tooth eruption and tooth support; involved in inflammatory periodontal disease and how can this tissue be reattached if lost due to pathology or aging. Also, why do PDL remains a soft connective tissue and does not calcify? And there is a proposed “signalling system” that measures and maintains the periodontal space, and Failure in this system results in ankylosis (meaning that the tooth is directly connected to the bone -not normal condition-). ❖ Function of PDL: 1. Provide tissue attachment between the tooth and alveolar bone.Thus is responsible of tooth support and protection and resisting displacing forces and protecting dental tissues form damage due to excessive occlusal forces. 2. Responsibility for the mechanism by which the tooth attains and maintains its functional position (tooth eruption and support). 3. Maintenance (through cellular content) and repair of cementum and alveolar bone. 4. Neurological control of mastication by its mechanoreceptors (this receptors only found on the PDL, so if the PDL is lost the receptors will lost too). ❖ Component of PDL : As we said that PDL is a dense regular connective tissue, and like all types of dense CT, PDL consist of: 1. stroma of fibres (collagen and oxytalan). 2. ground substance (The GAGs, proteoglycan and glycoproteins). 3. cells (fibroblasts, cementoblasts, osteoblasts, osteoclasts -in normal bone remodeling-, cementoclasts -when there is pathological conditions-, immune cells and epithelial cells). 4. blood vessels and nerves. 1. Fibers : 90% of PDL are mainly collagenous, with small amounts of oxytalan and reticulin fibres. A.COLLAGEN: 80% type I, 15% type III -Epithelial cell rests of Malassez,are quiescent Small amounts of types V and VI epithelial remnants of the Hertwig's epithelial root Fibrils show the classical banding of collagen. sheath (a bilayer sheath surrounding the root) that are involved in the formation of tooth roots. 50nm in diameter (small and uniform) Small amounts of IV and VII (basement membrane) with the epithelial cell rests of malassez and blood vessels. Type XII collagen which is non fibrous, and linked to other collagens and may be involved in the periodontal ligament’s architecture regulation. Much of the collagen is gathered into bundles (the principal fiber) and it is 5μm in diameter. Collagen fibrils are subunits within each principal fiber (look at the pic of collagen structure). Fibroblasts are closely associated with the PDLs as they are responsible for the synthesis and degradation of collagen an their processes surround or envelope the fibre bundles. Collagen origination in different regions of PDL : 1. Alveolar crest fibers (at the top) 2. Horizontal fibers 3. Oblique fibers 4. Apical fibers (around the apex) 5. Inter-radicular fibers (in multi-root teeth only) 6. Transseptal (between two teeth to attach them) 7. Gingival group (will discussed later). The extent of individual fibres across the width of the periodontal ligament: 1. Tooth related and bone related fibres that intercalate in an intermediate plexus 2. Each fibre crosses the entire width of the ligament branching in the way to join neighbouring fibres to form a 3D network The role of PDL in tooth eruption : During eruption, fibroblasts of dental follicle become active when the crown approaches the mucosa and start producing fibrils 1. Fibrils initially lack orientation but soon become oblique. 2. As tooth eruption progresses, the detaching and reattaching of PDL are within the zone of shear which is the site of remodelling during eruption 3. Additional oblique fibres appear and attaches to the newly formed cementum and bone 4. Trans-septal and alveolar crest fibres develop when the tooth merges in the oral cavity 5. Alveolar bone is disposed simultaneously with PDL organization Appearance of the fibers : The principal fibres have a wavy course to better accommodation of occlusal forces. Sharpey’s fibres as we said are the collagen fibres inserted into cementum and bone, from the cementum side the fibers are more numerous but smaller and vice versa. Cemental Sharpey’s fibres appear first then followed by Sharpey’s fibres emerging from bone. -Fibers that attach the PDL to the cementum is called cemental sharpey’s fiber (‫)نفس االشي من جهة العظم‬. There is fast turnover (remodelling) of collagen in periodontal ligament, and it is fastest towards the root apex due to the large amount of stress. B. OXYTALAN : Is immature elastin fibres (pre-elastin). Attaches to cementum and leave to the ligament in different directions. Rarely incorporated in bone (do not attach to the bone). Follow different courses according to region and terminate around blood vessels and nerves. Fibres are 0.5μm-2.5μm in diameter. What the Role of oxytalan? Evidence of thickness indicates a role in tooth support with high occlusal loading or a role in aiding fibroblast migration within the ligament and giving elasticity. 2. Ground substance : Mainly secreted by fibroblasts, and they are: (‫ األهم هو الوظيفة‬، ‫)أسمائهم مش حفظ‬ Hyaluronate glycosaminoglycans Proteoglycans: ▪ Proteodermatan sulphate ▪ PG1 (contains hybrids of chondroitin sulphate and dermatan sulphate) Glycoproteins: ▪ Fibronectin ▪ Tenascin Functions of ground substance: 1. Ion and water binding and exchange 2. Control of collagen synthesis 3. Fibre orientation 4. Tooth support and eruption mechanisms (providing pressure) 5. Fibronectin may be involved in cell migration and orientation 6. Scientist discovered that they have a role in preventing calcification of the PDL tissue, and they know that from experiment in vitro: (imp) -the experiment was to add hyaluronidase and chondroitinase which are enzymes that dissolve GAGs and proteoglycan, they noticed that the tissue start to produce mineral crystals (being hard tissue), so the result that this ground substance was prevent the mineralization. -another experiment was to add Calcium binding proteins (S100A4) and all what you have to know about this one that it has a role in inhibit the mineralization through its effect on ground substance. Ankylosis : Bisphosphonate is drug uses to treat osteoporosis, but it has a bad side effect on the ground substance that it makes destruction in them and increases the osteogenic factors, so it make the ankylosis which is lost of PDL and the tooth being in direct contact with the bone. Normal condition where you can see the PD space that contain the PDL Ankylosis where we lost the PDL and you can't see anything between the bone and the tooth (direct attach) ❖ Cells: We will discuss only the cells in bold Fi