Histology of Teeth and Supporting Structures PDF

**[Week 9]** **[Dr Amar L1- Histology of teeth and supporting structures]** **Structure** - Teeth are composed of three mineralised tissues: Enamel, Dentine and Cementum - A loose connective tissue- the pulp is surrounded by these hard tissues - Enamel and Dentine meet at the Dent...

**[Week 9]** **[Dr Amar L1- Histology of teeth and supporting structures]** **Structure** - Teeth are composed of three mineralised tissues: Enamel, Dentine and Cementum - A loose connective tissue- the pulp is surrounded by these hard tissues - Enamel and Dentine meet at the Dentino-enamel junction - Cementum and Dentine meet at Cemento-Dentinal junction **Amelogenesis** - Enamel is derived from ectoderm - Secreted by ameloblasts - Produced once in lifetime and has no regenerative capacity **Physical properties** - Thickest over cusps and incisal edges - 2.5mm thick cusps in permanent teeth - 1.3mm in deciduous teeth - High abrasion resistance - Extremely brittle **Chemical properties** - Calcium hydroxyapatite 1. Principle component 2. 95-96% by weight 3. Present as crystallites - Water 1. 2% by weight - Organic matrix 1. 1-2% by weight (enamel proteins) **Enamel: Histology** - Highly mineralised and difficult to study - Need ground sections for light microscopy - In demineralised sections no enamel remains **Enamel rod (prism)** - Basic structural unit is enamel rod (prism) - Rod consists of millions of HAP crystals packed together - Each rod is 2.5mm long and 5-6 micrometres thin - Rods run from dentino-enamel junction to surface - Diameter of the rod correspond with the diameter of the cell which produce it - In cross section an enamel prism appear to have the following patterns: 1. Pattern 1 (seen near the DEJ and surface) 2. Pattern 2 3. Pattern 3 (predominant pattern, also called key hole pattern) **Pattern 3** - The commonest pattern - Has head and tail regions **Interprismatic enamel** - Enamel between prisms - Composition similar to prismatic enamel - Has a different optical effect due to the angulation of crystals (40-60 degrees) - The border where the crystals of enamel rods and crystals of interprismatic enamel meet is called the rod sheath **Hunter-schreger bands** - An optical phenomenon-best seen in reflected light - Appearance is based on the way in which sectioned enamel rods reflect light - Dark bands correspond to cross sectional rods (diazones) - Lighter bnads correspond to longitudinally sectioned rods (parazones) **Gnarled enamel** - Prisms under cusp tips appear more marked and irregular - This is optical appearance of enamel - The strange appearance results from the enamel rods directed vertically under a cusp - The gnarled enamel can cause the drill problems and in some cases the dentist must replace the burr **Aprismatic/prismless enamel** - It is the outer 20-100 micrometres of enamel of newly erupted deciduous teeth - Prisms arranged parallel to the surface - Highly mineralised - No prism boundaries - Can also seen in relation to DEJ - Occurs due to the absence of Tomes processes **Incremental lines of enamel** - Appear due to the changes in the secretory rhythm of enamel - Two types: 1. Cross striations 2. Enamel striae **Cross striations (periodic bands)** - Lines run at right angles to the long axes of the enamel prisms - Seen at intervals of 4-6 micrometres across the rods in longitudinal sections - Cross-striations reflect a circadian rhythm in enamel matrix secretion **Enamel striae (Striae of Retzius)** - Longitudinal sections show enamel striae running obliquely across prisms (Stria of Retzius)- see brown lines - Appear as concentric rings in cross sections - Represent the successive positions of the enamel forming front - The occur as the follow a circaseptan (7-day) rhythm of enamel formation - And due to demarcation between activity and quiescence of enamel formation - Exaggeration of striae reflect systemic influence **Perikymata** - They are incremental growth lines that appear on the surface of tooth enamel as a series of linear grooves - They run circumferentially around the crown 1. Perikymata grooves 2. Perikymata ridges **Neonatal line** - They are type of striae of retzius - Seen in both enamel and dentine of primary teeth - Rarely seen in permanent dentition - This line represents the time of birth - The neonatal line is darker and larger than the rest of the striae of Retzius - In forensic dentistry, the line can be used to distinguish matters such as if the child died before or after birth and approximately how long a child lived after birth **Dentino-Enamel junction** - Boundary between enamel and dentine - Scalloping pattern is prominent under cusps and incisal edges - Concavities towards enamel - Usually less mineralised - This scalloped architecture provides stress relief during mastication - A number of features can be seen at DEJ extending from dentine to enamel **Enamel tufts** - Resembles tufts of grass - Arise at the DEJ and runs in the inner third of the enamel - Recur at approximately 100 micrometre intervals - Appear to travel in the same direction as the prisms - Each tuft is several prisms wide - Considered a hypo-mineralised areas **Enamel Spindles** - Appear as short, linear, dark, club shaped structures - Extend up to 25 micrometres into the enamel - Formed by entrapment of odontoblast processes between ameloblasts - Most commonly seen beneath cusps - Best seen in longitudinal sections **Enamel Lamellae** - Linear enamel defects that run in the entire thickness of enamel - Narrower, longer and less common than enamel tufts - Best visualise in transverse sections - May arise developmentally due to: 1. Incomplete maturation of group of prisms 2. Cracks after eruption due to occlusal loading **Clinical consideration** - Age changes 1. Wears away slowly with age- attrition 2. Tend to be darken - Caries 1. Vulnerable to acid attack (demineralisation) 2. Mineral loss occurs at the periphery of the prism - Restoration 1. Acid etching 2. Secondary caries - Defects in enamel formation are common - 8-80% of the population has at least one affected permanent tooth - Amelogenesis (formation of enamel) is sensitive to changes in the environment 1. Infection- turner tooth, Hutchinson's teeth 2. Radiation- Enamel defects or complete absence of teeth 3. Trauma- Hypoplasia 4. Fluoride- Fluorosis 5. Hereditary- Amelogenesis imperfecta **Histology of Dentine** **Dentine** - Forms the bulk of the tooth - Ectomesenchymal in origin - Produced by odontoblasts (dentinogenesis) - Covered in the crown by enamel and the root by cementum - Protective covering for dental pulp - Support for overlying enamel - Vital tissue- contains odontoblast processes and nerves - Tubular structure **Physical properties** - Pale yellow in colour - Harder than bone and cementum but softer than enamel - Organic matrix and tubular structure provides greater compressive, tensile and flexural strength - Permeable **Chemical properties** - 70% inorganic, 20% organic and 10% water by weight - Inorganic component 1. Calcium hydroxyapatite - Organic matrix 1. Collagen (90%)- Type 1 and traces of 111 and V **Dentine: structural components** - Odontoblast processes - Dentinal tubules - Peritubular dentine - Intertubular dentine **Odontoblastic processes** - Extensions of odontoblast cell bodies into dentinal tubules **Dentinal tubules** - Functional unit of dentine - Extend radially from pulp to DEJ and CDJ - Contains odontoblastic process, occasional nerve fibres and extracellular fluid - They taper from pulpal (2.5 micrometres) to periphery (1 micrometre) - Tubular density 1. Near pulp- 50,000/mm\^2 2. In the middle 40,000/mm\^2 3. Near DEJ- 20,000/mm\^2 - Such an appearance of dentinal tubules is called as primary curvatures **Intertubular dentine** - Forms the bulk of the dentine - Located between tubules (B) - Represent primary secretion of odontoblasts - Consists of type 1 collagen - Fibres arranged roughly at right angles to tubules **Intratubular dentine** - Dentine immediately surrounding (A) the odontoblastic process - It is 5-12% more mineralised than intertubular dentine **Dentine: Regional variations** - Primary dentine 1. Mantle dentine 2. Circumpulpal dentine - Tome's Ganular layer - Hyaline layer - Pre- dentine (Globular and interglobular dentine) - Age related and post-eruptive changes 1. Secondary dentine 2. Tertiary/reparative dentine 3. Sclerotic dentine 4. Dead tracts **Primary dentine** - Bulk of the dentine formed before eruption - Two types: 1. Mantle dentine 2. Circumpulpal dentine **Mantle dentine** - First formed dentine - 5% less mineralised - Collagen fibres are oriented perpendicular to DEJ - The dentinal tubules in this area branch profusely **Circumpulpal dentin** - It forms most of the dentin **Tome's granular Layer** - Hypo-mineralised areas - Seen in radicular dentine near the CDJ - Appear as dark (black) granular zone in ground sections - Spaces are filled with air and hence appear dark in ground sections - Caused due to profuse looping of dentinal tubules **Hyaline layer** - Present between tome's granular layer and cementum - 20 micrometres in thickness - Bonds dentine to cementum **Pre-dentine** - Newly formed dentine without mineralisation - It is the innermost layer (demineralised sections) - Width varies from 10 micrometres-40 micrometres (thicker in young teeth) **Pre-dentine (Globular and interglobular dentine)** - The dark staining spherules of mineralisation (A) are calcospherites. Because the spherules are globular in appearance they are referred to as globular dentin - The lighter-staining dentin between the globular dentin is called interglobular dentine (B) - Section of pre-dentine stained with H/E **Age related/prost eruptive changes of Dentine** **Secondary dentine** - Seen as age advances - It is formed after the tooth eruption and root formation is over - Its growth is much slowly than primary dentin and its deposition occurs mostly on roof and floor of the coronal pulp chamber - This is to protect the pulp chamber from exposure during cavity prep or if the caries is advancing towards the pulp - Due to the progressive deposition of secondary dentine, the pulp chambers may decrease in size, meaning the pulp chambers get obliterated - Sometimes clinician may find it difficult to do a root canal when the pulp chambers are blocked **Histologically** - Characterised by sharp bending of dentinal tubules **Tertiary/reactionary/regenerated/reparative/osteo dentine** - Dentine formed in response to various stimuli such as attrition/caries/restorative procedure - It is seen only in the region where the stimuli has occurred - Rate of deposition is proportional to the degree of injury - Its intention is to protect the pulp **Reactionary/regenerative dentine** - This dentine is formed by the odontoblasts that are survived after the stimulus (caries, attrition or restorative procedure) - Irregular and fewer tubules **Reparative dentine** - This dentine is formed by newly differentiated odontoblast-like cells that replace the original odontoblasts that are destroyed by the stimulus (caries, attrition or restorative procedure) - Irregular and fewer tubules plus more twisted tubules - Normally the odontoblast like cells move away from the dentine they form **Osteo dentine** - This is same as reparative but here the odontoblasts get entrapped into the dentine they form **Sclerotic/transparent dentine** - It refers to filling up of calcified material in the dentinal tubules in response to external stimuli such as caries, attrition or restorative procedure - This reduces the permeability of the dentine and hence protects the dentine - Highly mineralised in several tubules - Appear light in transmitted light and dark in reflected light **Dead tracts** - Odontoblasts are killed or retract due to injury - Empty tubules are filled with air in ground sections and hence appear black - Appear black in transmitted light and light in reflected light **Incremental lines of dentine** - Short periodic markings 1. May be seen as alternating light and dark bands (bon Ebner lines) and run at right angles to the tubules 2. 4 micrometres apart in crown and 2 micrometres in root - Long period lines 1. Andresen lines 2. 10-20 micrometres apart **Clinical considerations of Dentine** - Highly sensitive tissue- when exposed, lead to dentine sensitivity - Permeable and hence pulpal irritation - Tertiary dentine deposition in response to severe injury - Sclerotic dentine- deposited in response to an external stimulus such as slowly advancing caries **[Dr Amar L2-Histology of teeth and supporting structures wrap up]** **Histology of Pulp** **Development of Dental Pulp** - Derived from ectomesenchyme (dental papilla) - During dentinogenesis, dental papilla becomes dental pulp **Dental Pulp** - Contained in the pulp chamber of crown and in the root canal - At apical foramen it continues with the periodontium - Remains active throughout life - Responds to external stimuli **Regions of the Pulp** - **Odontoblast layer** 1. Peripheral layer adjacent to dentine - **Subodontoblast layer** 1. **Cell free zone (of Weil)** i. Directly beneath odontoblasts ii. Contains processes of fibroblasts, Traversing blood vessels and Network of nerves (plexus of Raschkow) 2. **Cell rich zone** i. Beneath the cell free zone ii. Numerous undifferentiated cells; fibroblasts, macrophages, lymphocytes - **Pulp core** 1. Periphery: smaller vessels and nerves 2. Centre: major vessels (arterioles) and nerve fibres **Cells of pulp** - Odontoblasts - Fibroblasts - Undifferentiated mesenchymal cells - Defense cells- Macrophages, lymphocytes and dendritic cells **Innervation of pulp** - Myelinated and unmyelinated fibres - Runs in association with blood vessels centrally - Branch profusely in the coronal pulp - Forms a subodontoblastic nerve plexus (plexus of Raschkow) in the crown - Branches pass into the odontoblastic layer and dentinal tubules **Blood vessels of the pulp** - Arterioles and venules enter via apical foramen and lateral canals - Branch profuse in the peripheral pulp and form subodontoblastic plexus - Pulpal blood flow is 20-60mL/min **Dental Pulp: Clinical considerations** - It is highly sensitive tissue in a closed chamber - Become non-vital on infection and trauma - Young teeth have better reparative capability - Pulp calcification may obliterate the canal making root canal therapy difficult or impossible - Internal resorption of dentine **Age changes** - Decrease in volume of the pulp chamber - Decrease vascular supply - Decrease in number of cells - Become more fibrous - Develop pulp stones **Periodontium** **Composed of:** - Cementum (C) - Periodontal ligament (narrow) - Alveolar bone (A) - Gingiva (B) and dento-gingival junction **Development of periodontium** - Derived from ectomesenchyme (dental follicle) - During dentinogenesis, dental papilla cells become dental pulp **Cementum: Histological types** - Based on development- Primary and secondary - Presence or absence of cells- cellular and Acellular - Origins of fibres 1. Intrinsic fibre cementum 2. Extrinsic fibre cementum 3. Mixed fibre cementum 4. Afibrillar cementum - Combination of above - The acellular cementum (A) is present in the upper 2/3^rd^ of the root - The cellular cementum (B) is present in the lower 1/3^rd^ of the root **Acellular cementum** - No cementoblasts/cementocytes - First formed cementum (Primary cementum) - Deposition is relatively slow - Appear relatively structureless - Present extending at full length of the root - Acellular cementum has extrinsic fibres (Sharpey's fibres) perpendicular to the root surface - Important for attachment and support-as they run form alveolar bone to the cementum - These extrinsic fibres are produced by fibroblasts and few cementoblasts **Cellular cementum** - Contains cementoblasts/cementocytes - Deposition is relatively fast - Present in apical third of the root - Less mineralised - Fibres are laid down by cementoblasts (intrinsic) - No role in tooth attachment **CEJ** - Where the cementum meets enamel - Three configurations 1. Cementum overlaps enamel for a short distance (60%) 2. Butt joins enamel and dentine (30%) 3. Dentine between enamel and cementum is exposed (10%) **Clinical considerations** - Cementum is less susceptible for resorption-orthodontic tooth movement - Root fractures are repaired by cementum callus - Cementum deposits as a compensation for attrition - May fuse with roots of adjacent teeth (concrescence) - Generalized hypercementosis seen in Paget's disease - Hypophosphatasia leads to significant reduction in the cementum formation-premature tooth loss **PDL** - A dense fibrous connective tissue - Occupies the periodontal space - 0.25mm and hourglass in shape (narrowest at the mid-root region) - Composed of: 1. Fibres 2. Cells 3. Ground substance **Functions of PDL** - Physical 1. Attach the tooth to bone 2. Transmit occlusal forces to bone 3. Shock absorption - Formative function 1. Form, maintain and repair of alveolar bone and cementum - Nutritional 1. Supply nutrition to bone, cementum and gingiva - Sensory 1. The PDL nerve fibres transmit sensation of touch, pressure and pain to higher centres **PDL Fibres** Fibre connect tooth to alveolar bone - Collagen 1. Main fibres (90%) 2. Main types are type 1-111 (98%) 3. Type 1- the most abundant (80%) 4. Type V and VI in small amounts - Oxytalan fibres 1. Extend to the PDL from cementum 2. Do not attach to bone **Principal fibres** - Arranged in distinct groups - Named according to the direction they run: 1. Alveolar crest fibres 2. Horizontal fibres 3. Oblique fibres 4. Apical fibres 5. Inter-radicular fibres **Cells of the PDL** - Fibroblasts (accounts for 60%) - Cementoblasts (making) - Cementoclasts (resorption) - Osteoblasts - Osteoclasts - Epithelial cells (rests of Malassez) - Defense cells **Blood supply of the PDL** - Superior and inferior alveolar arteries - From those entering the pulp at the Apex (A) - From gingival arteries (B) - From a series of perforation arteries passing through the alveolar bone (C) - Functionally of two types 1. Sensory 2. Autonomic- supply to blood vessels (vasomotor) - Derived from two sources: 1. From apex to the PDL 2. From openings of the alveolar bone to middle and cervical portion of PDL - Myelinated and unmyelinated - Mechanoreceptors (activate with loads as low as 0.01N) **Alveolar process/bone Histology** - Alveolar process is defined as the parts of the maxilla and mandible that form and support the tooth sockets - Forms with eruption of tooth to provide osseous attachment to the PDL - Disappears with loss of tooth **Gross histology of bone** - It consists of dense outer sheet of compact bone and central medullary bone - Medullary bone is usually filled with red or yellow bone marrow **Periosteum** - The tissue that covers the outer surface of bone - 2 layers 1. Outer (fibrous) layer- rich in blood vessels and nerves and composed of collagen fibres and fibroblasts 2. Inner layer- composed of osteoblasts surrounded by osteoprogenitor cells **Endosteum (lining membrane of the Bone marrow cavity)** - Tissue that lines the internal bone marrow cavities - The endosteum is composed of a single layer of osteoblasts and sometimes a small amount of connective tissue **Functions of alveolar bone** - Houses the roots of teeth - Anchors the roots of teeth to the alveoli, which is achieved by the insertion of sharpey's fibres into the alveolar bone proper - Absorbs and distribute occlusal forces - Supplies vessels to PDL - Helps in eruption of primary and permanent teeth **The alveolar process consists of:** 1. An external plate of thick cortical bone 2. Alveolar bone proper- the inner socket wall of thine, compact bone **Alveolar bone proper** - It is seen as the lamina dura in radiographs - Characterized by thin lamellae arranged in layers parallel to root - Histologically, it consists of sharpey's fibres and therefore also called as bundle bone - Cancellous bone- supporting alveolar bone present between the two compact layers (cortical bone and Alveolar bone proper) **Shape of alveolar crest** - Alveolar bone proper and cortical plate meet each other at 1.5 to 2 mm below the CEJ - If neighbouring teeth are inclined, then it may appear to be oblique **Clinical considerations** - Plaque associated inflammation-gingivitis - Enlargement of the gingiva- gingival hyperplasia - Extension of inflammation to periodontal- periodontitis - Trauma to occlusion- destruction of periodontal tissues - Orthodontic tooth movement - Proximal migration of teeth **[Dr Pierce L2- Renal system and disorders ]** **Excretion of urine** - Collecting ducts fuse to form large ducts (papillary ducts) as they approach the renal pelvis - Deliver urine to the minor calyces - Stretch of calyces initiates peristaltic contraction- begins in calyces, spreads to pelvis, and continues along ureter, forcing urine form renal pelvis to bladder - As bladder fills and pressure increases, it compresses, closing the distal ends of ureters **Urethra** - Thin-walled muscular tube that drains urine from the bladder to outside - At bladder- urethra junction, internal urethral sphincter- prevents leakage between voiding- not under voluntary control - External urethral sphincter surrounds the urethra as it passes through the urogenital diaphragm-formed by skeletal muscle-voluntarily controlled - In males, early part of the urethra runs within the prostate gland (urethra has double function in males- carries semen as well as urine) **UTI's** - Refers to presence of microorganisms in the urinary tract- bladder, prostate, collecting systems and kidneys - Mainly bacterial, but can be fungal and viral infections - Most common infections in clinical practice are hospital-acquired infections-urinary catheterisation - Medial treatment rests on antibiotics- must be bactericidal with appropriate spectrum for enterobacteria and good urinary excretion profile **Pyelonephritis** - One of the most common renal disorders and serious complications of common UTI's- affects one or both kidneys - Clinical features include flank pain, chills, dysuria, frequent urination or an urgent need to urinate, haematuria - Acute pyelonephritis caused by bacterial infection - Chronic pyelonephritis more complex-bacterial infection plays a dominant role-other factors such as vesicoureteral reflux or obstruction are involved - Can cause lasting kidney damage or bacteria can spread to bloodstream and cause a dangerous infection **Glomerulonephritis** - Inflammation of the glomeruli leading to damage-acute and chronic - Often asymptomatic- only diagnosed as a result of finding of protein and blood in the urine in the absence of infection - Little known about triggering agents but can be caused by strep throat or abscessed teeth-immune system overreaction to infection - Chronic glomerulonephritis one of the most common causes of chronic renal failure-slow cumulative damage and scarring to glomeruli usually due to inflammation - Management of hypertension (ACE inhibitors) critical to slow progression **Renal disease and hypertension** - Key factor associated with blood pressure is blood volume, which is greatly dependent on body sodium levels-sodium homeostasis central to blood pressure regulation - Many antihypertensive medications target the kidneys role in hypertension-diuretics, ACE inhibitors, angiotensin receptor agonists etc. - Associated with a sudden reduction in renal function accompanied by accumulation of waste products in the blood - marked decrease in urine output, or rarely, urine flow ceases - classified as be: 1. **Pre-renal failure**- associated with conditions that impair renal blood flow, such as hypotension, or renal artery blockage- normally easily reversed once the cause is identified and reversed 2. **Intra-renal failure**- nephron itself is damaged i. Variety of factors can cause injury, including infection, autoimmune reactions, severe hypertension etc. ii. Recovery usually slow or in the case of severe injury, may not occur at all-progression to chronic renal failure 3. **Post renal failure**- due to an obstruction within the urinary collecting system distal to the kidney i. Leads to a "back-pressure" that impedes glomerular filtration-may be reversed by removal of the obstruction (e.g. kidney stone) **Chronic renal failure** - Progressive loss of renal function over months to years-ultimately irreversible, leading to end-stage renal disease - Three stages of chronic renal failure which correspond to the degree of nephron loss: 1. Decreased renal reserve- corresponds to a loss of up to 50% of the kidney's nephrons-not associated with signs or symptoms of renal failure because of the hyperfunction in the remaining nephrons 2. Renal insufficiency- occurs when 75-80% of the nephrons are damaged-ability of kidneys to concentrate urine is impaired, leading to increased urinary output 3. End-stage renal disease- \>90% of nephrons destroyed and symptoms typical of renal failure. Common cause include hypertension, glomerulonephritis, diabetes mellitus, renovascular disease, pyelonephritis **End-stage renal disease** - Fatal without dialysis or a kidney transplant - Dialysis replaces kidney functions-removal of metabolic waste products and excess fluids as well as maintenance of electrolyte balance - Kidney transplantation- alternative to dialysis in patients with end-stage renal disease- primary limiting factor is availability of organs **[Dr Sfera L1- Primary Anterior Teeth]** **Development**  - Emergence of primary incisors and canines is in between 6 months and 2 years of age **Primary incisors development** **Centrals** - Calcification- 4 months in utero - Generally 1^st^ tooth to emerge at 8-10 months - Mandibular often precedes maxillary - Exofoliate-6-7 years **Laterals** - Calcification- 4.5 months in utero - Emergence-9-13 months - Exfoliation-7-8 years **Primary central** - FDI: 51, 61, 71, 81 - Crown appears wide and short - Prominent cervical construction - Usually no mamelons visible on incisal **Primary lateral incisors** - FDI: 52, 62, 72, 82 - In Mx smaller and less square than primary central - Narrower at the cervix giving triangular outline to the labial surface - This distal angle is more rounded - The root is more compressed mesio-distally and is often curved distally - In Md laterals, wider MD than centrals **Primary canines- development** - First evidence of calcification-5 months in utero - Emergence- 18 months - Exfoliation- Mandible 9 years and Maxilla 12 years **Canines** - FDI: 53, 63, 73, 83 - The maxillary canines have a proportionally shorter and more bulbous crown - Mesial cusp slope is longer than the distal slope on the Mx crown - Md canine crowns are longer than Mx primary canines - The roots are long and tapering **Primary vs permanent canines** - Similar shape - Primary are smaller and whiter - The crowns are wider mesiodistally in comparison with crown height - There are prominent cervical ridges due to cervical constriction - The roots are longer and more slender in comparison to the crowns **[Dr Sfera L2- Anatomy of maxillary posterior primary teeth]** **Development- Mx first molar** - First signs of calcification- 5 months in utero - Emergence- 16 months - Exfoliation- 10-11 years **Mx first molar** - FDI- 54, 64 - 4 cusps usually - 2 major cusps: mesiobuccal and mesiolingual - Mesiolingual cusp is the longest and sharpest of the cusps - Distobuccal cusp more developed that the distolingual cusp (can be missing) - Occlusal displays central and mesial fossae and pits linked by a developmental groove **Proximal aspects** - The dimension in the cervical 1/3 greater than the occlusal - Pronounced buccal convexity in the cervical 1/3 **Root structure** - Roots are long, slender and flared/splayed - Palatal root is the longest, then the mesiobuccal, then the disobuccal root - Short root trunk - Pronounced cervical constriction **Mx 2^nd^ molar development** - Calcification- 7 months in utero - Emergence- 2.5 years - Exfoliation 10-12 years - Last tooth in Mx primary arch to emerge **Mx Second Molar** - FDI: 55, 65 - Larger than the primary 1^st^ Mx molar - Resembles very much a Mx 1^st^ permanent molar - It is smaller and the cusps are sharper than in 6 - Marked cervical bulge/constriction where the enamel terminated - This is most pronounced on the buccal aspect but not as much as in the primary first molar - Tubercle may be present on mesiopalatal cusp **Mx 2^nd^ molar roots** - Larger than in 1^st^ Mx molar - Root structure is similar to the 16 and 26 however, the mesiobuccal root is broad and flat;may be as long as the palatal root - Root trunk is short - The roots have only one root canal **[Dr Sfera- L3 Anatomy of primary posterior teeth]** **Mandibular 1^st^ primary molar** - Mesiobuccal bulge is a distinctive feature of the 74 and 84 - Relatively large buccal curvature in the cervical 1/3 - Causes the cervical line to dip gingivally - Does not resemble any other tooth- primitive appearance - 4 cusps, 2 roots - 2 distinct buccal cusps, mesiobuccal cusp is larger - Crown height is greater on the mesial aspect - CEJ dips apically at the mesial root - Root trunk bifurcates close to cervical line/CEJ - Calcification- 5 months in utero - Eruption- 16 months - Exfoliation- 10-12 years **Md 1^st^ molar** - Mesiobuccal cusp is larger than the distobuccal cusp - Mesiolingual cusp is tall and sharp - Distobuccal and distolingual cusps not a developed as the mesial cusps - Zigzag central developmental groove - Mesial root is larger than distal root which is rounded and shorter - Root structure flared to accommodate the developing premolar **Md 2^nd^ molar** - Calcification- 6 months in utero - Emergence- 2-2.5 years - Exfoliation- 10-12 years **Md 2^nd^ molars** - FDI: 75, 85 - Much larger than the mandibular primary first molar - Resembles the mandibular fist permanent molar in most respects - The buccal surface shows a distinct bulge near the cervical margin - The crown is a little more rounded than the permanent molar - The roots furcate immediately below the CEJ **Md 2^nd^ molar roots** - Roots resemble those of the 1^st^ permanent molar - Roots often twice as long as the crown - Often flare mesiodistally at the apical and mid 1/3 - Short root trunk, point of bifurcation just below cervical line **Primary vs permanent molars** - Predecessors of premolars but morphologically more similar to permanent molars - Constricted in the cervical region - Prominent cervical ridges on the buccal (1^st^ ones particularly) - Roots longer in relation to their crowns, more slender and flare more and closer to the furcations to accommodate the developing premolars to accommodate the developing premolars - Pulpal horns are higher in primary molars and pulpal chambers proportionally larger - Enamel thinner and more consistent in thickness **[Dr Sfera L4- anatomy of primary teeth wrap up]** **Teething** - Emergence of teeth should not present with fever or general malaise - Local discomfort, hypersalivation is common **Caries in primary teeth** - Early childhood baby bottle caries 1. Leads to upper tooth decay (incisors) **Overview of primary occlusion** - Establishment of primary occlusion shortly after age of 2 - By the age of 3 to 3.5, all of the roots are fully formed - Soon after, because of the continuous growth of the jaws, diastemas commence to appear between the teeth - Primate spaces - Relationship of the primary molars in occlusion has effect on the development of the relationship of the permanent molars **Leeway space of Nancy**