Week 4-7: Body Cavities & Anatomy (PDF)

WEEK 4 Body cavities: 1. Dorsal cavities a. Cranial cavity i. Contains the brain b. Vertebral canal i. Contains the spinal cord 2. Ventral cavities a. Thoracic cavity i. Contains the heart and lungs b....

WEEK 4 Body cavities: 1. Dorsal cavities a. Cranial cavity i. Contains the brain b. Vertebral canal i. Contains the spinal cord 2. Ventral cavities a. Thoracic cavity i. Contains the heart and lungs b. Abdominopelvic cavity i. A continuous structure as there is no structure that divides the abdominal and pelvic cavity *Diaphragm separates the thoracic cavity and abdominopelvic cavity Coronal section of trunk 1. Thoracic cavity a. Pulmonary cavity i. Lungs and pleural membranes b. Mediastinum i. Subdivided by a transverse thoracic plane into superior and inferior mediastinum at T4 – bisects the sternomanubrial joint anteriorly between the two bones 1. Superior: thymus, trachea, oesophagus, aortic arch, SVC 2. Inferior: heart, IVC, pericardial cavity, descending aorta 2. Abdominopelvic cavity a. No physical separation between the abdominal and pelvic cavity b. Abdominal cavity i. Spleen, kidneys, stomach, duodenum, jejunum, ileum liver, gallbladder, pancreas and transverse colon c. Pelvic cavity i. Bladder, ureter, rectum, terminal end of descending colon, uterus, ovaries, fallopian tubes, prostate Boundaries of thorax 1. Anterior: Sternum (sternomanubrial joint), ribs, intercostal muscles and costal cartilages a. Manubrium b. Body of sternum c. Xiphoid process 2. Posterior: Thoracic vertebrae T1-T12, ribs and intercostal muscles 3. Lateral: Ribs and intercostal muscles a. Each rib articulates with the sternum anteriorly via costal cartilage and body of thoracic vertebrae posteriorly b. Ribs 1-7 attach directly to sternum, 8-10 attach to the 7th costal cartilage, 11 and 12 do not attach to the sternum i. Costal cartilages from ribs 9-10 form a costal margin c. Ribs 1-7 are true ribs, 8-10 are false ribs and 11-12 are floating ribs 4. Roof: Suprapleural membranes a. Lies on top of parietal pleura 5. Floor: Thoracic diaphragm a. Dome shaped muscle Only T11 and T12 are visible in anterior view Rib anatomy 1. Head – articulates with body of thoracic vertebrae 2. Body/shaft – comes around anteriorly 3. Tubercle – articulates with the transverse process Ribs traverse obliquely downwards. In transverse platinated sections, they look vertical but each ‘bone segment’ are different ribs at different regions. Costal cartilage made of hyaline cartilage Boundaries of abdominopelvic cavity Abdominal cavity is superior to the pelvic cavity with no structure separating the two cavities, thus considered one large anatomical space. 1. Roof/Upper limit: Inferior thoracic opening and thoracic diaphragm a. Anterior: Bounded by xiphoid process b. Anterolateral: Costal margin c. Posterolateral: 11th and 12 ribs d. Posterior: 12th vertebrae or vertebral column 2. Anterior: Anterior abdominal wall a. Abdominal muscles and aponeurosis 3. Posterior: Lumbar vertebrae L1-L5, sacrum and coccyx 4. Floor: Pelvic outlet and pelvic diaphragm Anterior thoracic wall Contributed by (superficial to deep): o Pectoral and intercostal muscles o Rib cage ▪ Sternum, ribs and costal cartilages o Parietal pleura  o Visceral pleura o Pericardium o Heart and lungs Tissue type: o Bone o Hyaline cartilage o Skeletal muscle Function: o Bone provides structural support and protection to vital organs o Hyaline cartilage allows for attachments o When contracted, muscles helps stabilise thorax and provide stability Anterior abdominal wall Contributed by (superficial to deep): o Abdominal muscles and aponeuroses o Peritoneum o Abdominal organs Tissue type: o Skeletal muscle and dense connective tissue Function: o When contracted, muscles increase intrabdominal pressure No hard tissue in anterior abdominal wall to allow abdominopelvic cavity to expand during respiration or pregnancy Visceral cavities of head and neck 1. Nostrils are entrances to the nasal cavity 2. Oral orifice is an entrance to the oral cavity Both lead to the pharynx (nasopharynx, oropharynx and laryngopharynx) Air will pass through the larynx > trachea > lungs Food will pass through the oesophagus > stomach > GI tract Pharynx transitions into oesophagus at C6 Pharynx is a dual purpose tube Pharyngeal isthmus – junction between nasopharynx and oropharynx Oral cavity 1. Boundaries: a. Roof: Hard and soft palate b. Floor: Mylohyoid muscle c. Lateral: Cheeks, alveolar ridges and teeth 2. Opening to other cavities: a. Anterior: External environment via lips b. Posterior: Oropharynx via fauces and vestibule (area behind last molar) c. Other: ducts of salivary glands 3. Contents: a. Teeth and tongue 4. Functions: a. Initial digestion of food and water b. Accessory airway c. Phonation Pharynx and oral cavity belongs to both the digestive and respiratory system Nasal cavity 1. Boundaries: a. Medial: bony septum b. Lateral: nasal conchae (bony projections) c. Floor: Hard and soft palate d. Roof: Ethmoid bone 2. Openings to other cavities: a. Posterior: Nasopharynx via choanae b. Superior: Cranial cavity via foramina in cribriform plate c. Anterior: Atmosphere via nostrils d. Other: paranasal sinuses and nasolacrimal duct 3. Contents: a. Mucous membrane (lines cavity) b. Air 4. Function: a. Airway via nares and choanae b. Warm and humidify air i. Secretions of mucous membrane and large surface are of chonae c. Smell via olfactory nerve endings in cribriform foramina Epithelial linings 1. Airways a. Pseudostratified columnar ciliated epithelium i. Mucous secretion b. Nasal, nasopharynx, larynx and trachea 2. Digestive system a. Stratified squamous non-keratinised epithelium  i. Mucous secretion ii. Also salivary glands b. Oral, oropharynx, laryngopharynx and oesophagus Innervation of nasal cavity 1. Tactile sensation – ophthalmic and maxillary divisions of trigeminal nerve a. Cell bodies located in trigeminal ganglion 2. Sensation of smell – olfactory nerve Ethmoid, sphenoid, frontal and maxilla bone contain the cranial pneumatic bones Paranasal sinuses – air sinuses seen within pneumatic bone Sinuses are cavities within pneumatic bones that are lined by mucous membranes o Cavities make bones lightweight o Mucous membranes humidifies air o Large space also helps add resonance to sound Pneumatic bones 1. Maxillary bone – maxillary sinus 2. Frontal bone – frontal sinus 3. Ethmoid bone – ethmoidal sinus a. Anterior, middle and posterior group 4. Body of sphenoid bone – sphenoidal sinus a. The most posterior of all sinuses All paranasal sinus drain into the nasal cavity Compartmentalised by right and left lateral walls and nasal septum Lateral walls contain nasal conchae Superior and middle nasal concha are mucous projections but inferior nasal concha is an independent bone E= ethmoidal, M= maxillary and S= sphenoidal air sinuses Sphenoethmoidal recess: 1. Sphenoidal sinus (due to its posterior position) Superior nasal meatus: 1. Posterior ethmoidal sinus Middle nasal meatus (largest): 1. Anterior and middle ethmoidal sinus 2. Frontal sinus 3. Maxillary sinus Inferior nasal meatus: 1. Nasolacrimal/tear duct Bone Compact bone is dense and strong Trabecular bone is spongy and lightweight but weak Contain a network like appearance with marrow spaces which contain bone marrow and blood vessels Diploic bones found in flat bones of the skull Long bones have trabecular bone at epiphysis covered by a layer of compact bone. Diaphysis is mainly compact bone to handle stress. Medullary cavity – the central canal in shaft of long bones where bone marrow is located Periosteum – outer lining of bone  Made of dense irregular connective tissue Endosteum – inner lining of medullary cavity Reticular connective tissue Bone is a modified type of connective tissue because it has cells, fibres, matrix and is hard in structure Made of calcium and phosphates Chemical composition of bone 1. Organic a. Cells i. Osteoprogenitor cells – stem cells ii. Osteoblasts – bone forming cells and secretes bone matrix iii. Osteocytes – predominant cells, mature iv. Osteoclasts – remove bone cells 2. Inorganic a. Minerals – seen in the form of hydroxyapatite crystals i. Makes bone hard due to mainly calcium phosphate 3. Collagen fibres, glycoproteins and proteoglycans Bone remodelling involves osteoblasts and osteoclasts Microscopic structures 1. Compact bone a. Lacunae – small openings containing osteocytes b. Lamellae – concentric rings contains , fibres, matrix, crystals c. Osteons – key identifying features of bone structure, groups of lamellae i. Made of a central haversian canal surrounded by concentric rings of lamellae 1. Central canal contains blood vessels and nerves  d. Canaliculi – small canals that communicate lacunae and the central haversian canal e. Volkmann’s canal – connect blood vessels of periosteum with that of the central haversian canal and the medullary cavity Central haversian canal = large central circle, concentric lamellae = rows of rings, lacunae = black dots containing osteocytes, canaliculi are the radiating fibres/bands, osteon is one whole circular structure and Volkmann’s canal = long hollow projections  2. Cancellous bone a. Many marrow spaces i. Filled by adipocytes (yellow bone marrow) b. Lamellae in the form of a network i. Stained pink due to density of cells c. Often surrounded by a plate of compact bone for strength Bone marrow found in marrow spaces. Red is involved in haematopoiesis e.g. pelvis, ribs, sternum vertebrae and ends of long bones Yellow is involved is energy storage e.g. medullary cavities of long bones WEEK 5 Embryology The study of the developmental stages of the human from fertilisation to birth. Brachial/pharyngeal arches – bilateral bulges beneath the developing brain mass of growing embryo Structures of the face derive from the first 2 pharyngeal arches o 1st arch: Trigeminal nerve, muscles of mastication and their blood supply o 2nd arch: Facial nerve, muscles of facial expression and their blood supply 6 arches initially emerge but only 5 survive Contains components of muscle, nervous, vascular tissues and cartilage bar Each arch has an artery and a nerve Prenatal development stages: 1. Pre-implantation period – 1st week a. Fertilisation of eggs in fallopian tube, usually 24hrs after ovulation b. Zygote undergoes cell division, 2, 4, 8, 16-cell stage c. At day 3 to 4, the cell mass becomes a morula (16-cell stage) d. Morula enters uterine cavity and develops into a blastocyst e. At day 5-6, implantation occurs at the uterine wall/endometrium 2. Embryonic period – 2nd to 8th week a. Commencement of development of all major structures of the body b. Cells proliferate, differentiate and integrate (form systems) c. Tadpole appearance until baby becomes a foetus on the 8th week d. Formation of germ layers 3. Foetal period – 9th week until birth a. Body systems continue to develop and mature b. Distinguishable characteristics e.g. ears, arms, hands, legs and feet i. Even fingerprints and footprints Germ layers Amniotic cavity and yolk sac develop on either side of cell mass o Embryonic disk/notochord situated in between the two cavities o Amniotic cavity lined with ectodermal cells and yolk sac lined with endodermal cells  Ectoderm: o Nervous system, sensory epithelium of eye/ear/nose, epidermis, hair, nails, epithelium of sinuses, oral and nasal cavities, intraoral glands and tooth enamel Mesoderm: o Muscles, bone, cartilage, blood, dentin, pulp, cementum, periodontal ligament Endoderm: o GI tract epithelium and associated glands Pharyngeal/Branchial arches Begins at day 22 Has an outer covering of ectoderm, inner lining of endoderm and a mesenchyme core (embryonic connective tissue derived from mesoderm) o Ectoderm – pharyngeal clefts/grooves, endoderm – pharyngeal pouches Transient structure – they disappear as soon as features arise from them The 5th pouch is rudimentary (if present) Endodermal epithelial lining forms organs in the head and neck 1st pharyngeal pouch becomes the auditory tube and the middle ear (endodermal) 1st pharyngeal cleft becomes the external auditory meatus (ectodermal) 2nd pharyngeal pouch becomes the tonsillar fossa between the palatoglossal and palatopharyngeal folds Further develops into palatine tonsil A typical pharyngeal arch contains: 1. Arteries 2. Cartilage that ossify to bone 3. Muscular components in head and neck 4. Nerves supplying the mucosa and muscles Formation of face, palate, tongue and jaws Development occurs between 4th and 10th week of gestation Derived from the joining of the five prominences (1st pharyngeal arch) that surround the stomodeum: 1. The frontonasal prominence 2. Two maxillary prominences a. Palate 3. Two mandibular prominences The tongue develops between the 4th and 8th weeks from independent swellings on the floor of the primitive pharynx formed by the first four pharyngeal arches Hence, nerve supply are derived from first four arches Face Primitive oral cavity = stomodeum At 5th week, the paired maxillary prominences enlarge and grow ventrally and medially Nasal or olfactory placodes also begin to form on the frontonasal prominence o Becomes nasal cavity At 6th week, ectoderm at nasal placode invaginates to form a nasal pit, forming the lateral and medial nasal processes At 7th week, medial and lateral nasal processes fuse at midline to form intermaxillary process Maxillary prominences grow and fuse with intermaxillary process o Arises the philtrum and primary palate with four incisor teeth o Maxillary prominence forms the cheek and mandibular prominence the lower jaw Palate Forms between 5th and 10th week, separate the oral and nasal cavity Derived from: 1. Unpaired medial palatine process of maxilla a. Forms primary palate/premaxilla where the four upper incisors arise from i. Premaxillary segment of maxilla in postnatal life 2. Paired lateral palatine process of maxilla a. Forms the secondary palate between 7th and 8th week i. First appear as outgrowths of the maxillary process during the 6th week ii. Palatal shelves fuse at 7th week to from secondary palate separated by palatine raphe Tongue Mesenchymal swelling of mandibular process of first pharyngeal arch Median lingual swelling first followed by lateral lingual swelling o Together forms the anterior 2/3rd of tongue Hypobranchial eminence from 3rd branchial arch swells o Forms the posterior 1/3rd of tongue Jaws Maxilla arises from mesenchyme of maxillary prominences  No precursor cartilage but entirely by intramembranous ossification Mandible arises from the mesenchyme of mandibular prominences 1. Meckel’s cartilage from 1st pharyngeal arch extends as a solid hyaline cartilaginous rod surrounded by a fibro cellular capsule o No major contribution to the mandible 2. Mandibular prominence fuse at midline to form the mandibular arch 3. Ossification of mesenchymal tissue lateral to the cartilage o Cartilage later disappears Trough formed called mandibular canal that contains the inferior alveolar nerve The bone above the trough becomes alveolar processes housing teeth Odontogenesis Humans present with 2 types of dentition (diphyodont) – 20 primary and 32 permanent teeth Involves the interaction between the oral ectodermal cells (derives enamel organ) and ectomesenchyme cells/neural crest cells (derives dental papilla) At 6th week, presentation of u-shaped dental lamina in upper and lower jaw 1. Stomodeum lined by ectoderm 2. Outer part give rise to oral epithelium 3. Deeper part are ectomesenchyme derived from neural crest cells At 7th week, 10 invaginations of each dental lamina, each representing 1 tooth bud Oral epithelium grows deeper to produce dental lamina o Dental lamina are two band-like structures representing upper and lower jaws Neural crest cells derive from dorsal surface of embryo that migrate to mesenchyme of stomodeum Becomes ectomesenchyme or neuroectoderm in the process The name reflects its origin These cells are essential for developing craniofacial skeleton and teeth Stages of tooth development: 1. Bud stage (formation of bud) a. Begins at 8th week, inner and outer enamel epithelium b. 3D oval masses penetrating the surrounding ectomesenchyme c. Each bud surrounded by ectomesenchyme condensation i. Eventually develops into a tooth germ 2. Cap stage (proliferation of cells to form tooth germ layers) a. Begins between 9th and 10th week b. Proliferation continues at this stage c. Unequal growth in different parts of tooth bud, resulting in cap shape overlying the ectomesenchyme d. Various levels of differentiation occurs: i. Inner enamel epithelium – inner surface of enamel organ lined by columnar cells ii. Outer enamel epithelium – outer surface of enamel organ line be cuboidal cells iii. Enamel knot and enamel cord (transient) – rounded cells connecting inner and outer enamel epithelium. Gives rise to stratum intermedium. iv. Dental papilla v. Dental sac 3. Bell stage a. Early stage (differentiation of enamel organ layers) i. Occurs between 11th and 12th week ii. Continuation of proliferation, differentiation and morphogenesis iii. Four different types of cells found within enamel organ (outer to inner): 1. Outer enamel epithelium 2. Stellate reticulum 3. Stratum intermedium 4. Inner enamel epithelium  b. Late stage (deposition of dentin and enamel matrix) i. Dental papilla differentiate into odontoblasts, producing predentine (dentinogenesis) ii. Predentine becomes mineralised to become dentine 1. Predentine – non-mineralised matrix of dentine 2. Begins at 3rd molar iii. Inner enamel epithelium differentiates into preameloblast and then ameloblast 1. Preameloblasts differentiate into ameloblasts when in contact with predentine 2. Ameloblasts produces enamel matrix (amelogenesis) iv. Enamel organ detaches from dental lamina leaving remnants called Epithelial Rests of Serres (ERS) Amelogenesis begins first but dentine formed first Root formation Proceeds once crown of teeth is formed at cervical loop (the point where outer and inner enamel epithelium meet). The most cervical part of the enamel organ. o A bilayer rim consisting of internal and outer enamel epithelium. Only completed once tooth erupts in the oral cavity. 2-3 years post eruption As the cervical loop begins to grow into surrounding ectomesenchyme of dental sac it forms Hertwig Epithelial Root Sheath (HERS) Functions to shape the root, inducing dentin formation in root continuous with coronal dentin o Determines curvature, length and bifurcation of root Induction of outer cells of dental papilla in root > odontoblasts > root dentin formed Once root dentin formed, HERS disintegrates to Epithelial Rests of Malassez (ERM) o Also triggers cementogensis o Contact of dental sac cells with root dentin surfaces induces cells to become immature cementoblasts Fibroblasts – produce periodontal ligament fibres Osteoblasts – produces alveolar bone Clinical considerations: 1. Dilaceration – pushing of deciduous teeth against tooth germ, bending HERS o Severe root curvature ▪ Difficulty with eruption (and extraction) 2. Enamel pearl – late degeneration of HERS after complete formation of root dentin  a. Enamel formation in root 3. Cysts – proliferation of ERS giving rise to odontogenic keratocyst and ERM producing radicular cyst (most common cyst) WEEK 6 Enamel Derived from ectoderm and forms a protective covering on tooth’s crown. o Cannot regenerate unlike other ectodermal derived tissues Develops from the inner enamel epithelium of tooth germ via reciprocal epithelial/mesenchymal interactions The hardest tissue in the body. It lacks cells within it Amelogenesis = preameloblast > becomes ameloblast with exposure to predentine > produces enamel matrix > remineralisation of matrix becomes enamel Physical properties of Enamel 1. Yellowish-white to greyish-white in colour a. Dependent on the degree of calcification and orientation of enamel crystals b. Darker = stronger i. More complex enamel crystal orientation 2. Thicker in masticatory surfaces and thinner and cervical region a. Diversity in thickness depending on tooth i. 0 to 2 mm for incisors to 2.6 mm for molars 3. Hardness decrease from the surface towards the interior and from the cusp/incisal tip towards the cervical margin a. Highly mineralised and complex crystal orientation b. Permanent > deciduous 4. Very brittle due to high mineralisation a. An isolated enamel rod breaks away easily b. Dentin supports enamel – less mineralised and thus less brittle c. Clinical significance: must remove unsupported enamel as it will break away easily exposing the dentine beneath it 5. Semi-permeable to fluoride ions, calcium ions and saliva Chemical composition of Enamel: Composed of inorganic materials/minerals (96% by weight and 90% by volume), organic substances (1%) and water (3%) – highly mineralised tissue o Mineral is mostly calcium hydroxyapatite in crystalline form – hydroxyapatite crystals o Organic content is mostly proteins e.g. amelogenin, ameloblastin, enamelin Enamel Rod The functional units of enamel No fixed geometric outline 5 million in permanent lower central incisors, 12 million in permanent upper first molar Generally wavy direction but adopts a complex intertwined course (gnarled enamel) at the incisal edge and cusp tips o Withstand great forces Life History of an Ameloblasts No life cycle because they do not regenerate Enamel formation: 1. Differentiating stage – inner enamel epithelium become preameloblasts, outer cells of dental papilla induced to become odontoblasts a. Induction promotes odontoblast differentiation by preameloblasts b. Cells undergo repolarisation 2. Secretory stage – preameloblast becomes ameloblast via reciprocal induction from odontoblasts  a. Amelogenesis follows ameloblast formation – the appositional growth of enamel matrix i. Secreted by Tomes Process 1. A conical process responsible for the different orientation of crystals in the enamel rod and interrod substance 3. Transitional stage – ameloblast transitions from secretory to maturation form, halting enamel matrix secretion a. Reduced height of ameloblast signals onset of transition and withdrawal of Tomes process b. 50% of ameloblast undergo apoptosis c. Remaining ameloblast undergo autophagocytosis – organelles responsible for protein synthesis are reduced 4. Maturation stage – presence of ruffled-ended ameloblasts (80%) and smooth-ended ameloblasts (20%) 5. Protective stage – layers of enamel organ reduced into Reduced Enamel Epithelium (REE) a. Protects enamel from resorption by dental sac cells 6. Desmolytic stage – REE secrete desmolytic enzymes to eliminate dental sac and allow fusion of REE and oral epithelium a. Enables eruption of tooth without bleeding Histological preparation of hard tissue Decalcified section Ground section Pass tissues through many Microtome grinds tissues at high colouring agents heat Shows shades of pink and blue Best way to observe mature enamel Enamel appears white because its is Dentine can be seen in both 90-96% inorganic materials/minerals Pulp cannot be seen as it is soft and a. Enamel matrix can be seen cannot withstand heat better because it is less a. Appears as dark black mineralised Dentine can be seen in both Best way to observe pulp Hypocalcified Structures of Enamel 1. Incremental lines of enamel – formed in increments with period of activity and rests a. Cross striations (short period) – daily rest of ameloblasts i. 4 microns thick ii. Forms throughout enamel b. Incremental lines of retzius/Brown Striae of Retzius (long period) – weekly rests of ameloblasts i. 16 microns thick ii. Concentric rings in microscope iii. A series of dark bands longitudinally iv. Forms throughout enamel c. Neonatal line – separates enamel formed before and after birth i. 20-40 microns thick – a single dark line ii. It forms because body is at shock at birth, cells stop working iii. Appears a few days after birth iv. Reflects the metabolic changes at birth – prism changes direction v. Prenatal enamel quality is better than postnatal due to constant nutrition from mother vi. Found in deciduous teeth and permanent first molars 2. Enamel tufts a. Junctional structures in the inner third of enamel b. Begins at DEJ and extends 1/3rd or 1/5th into enamel c. Hypomineralised d. Grass-like appearance – many lines e. Highest protein content in enamel f. Likened to geologic faults – no known clinical significance 3. Enamel lamellae a. Extend from outer surface of enamel to DEJ or dentin b. Best seen on transverse sections of enamel c. Narrower and longer than enamel tufts d. Likened to geologic faults – no known clinical significance e. Types: i. Developmental (type A) – occurs during enamel formation  ii. Non-developmental (type B and C) – unmineralized - occurs before and after enamel formation 4. Dentino-Enamel Junction – scalloped profile in cross section a. Sometimes smooth in deciduous teeth b. Hypocalcified/high organic content c. Shape and nature prevent shearing of the enamel i. Looping of dentinal tubules Look at slides for images of histology Uncalcified Structures of Enamel Enamel spindle – short dentinal tubules near the DEJ Results from odontoblasts that crossed the basement membrane before it mineralised into the DEJ Found under incisal edge or cusp tips Single short lines Ageing Changes in Enamel 1. Attrition a. Wearing of incisal or occlusal surfaces of teeth caused by functional or parafunctional habits i. Bruxism b. Loss of enamel and exposure of dentin 2. Abrasion a. Due to mechanical forces i. Improper brushing habits 3. Erosion a. Due to chemical agents or acids i. Carbonated drinks Look at slides for images Clinical implications 1. Fluoridation – becomes more resistant to acid dissolution and hydroxyapatite crystals become fluorapatite crystals when fluoride ions incorporated 2. Acid etching – removal of enamel rods Dentine Dentinogenesis = outer cells dental papilla > becomes odontoblasts > produce predentine > mineralised to become mature dentine Forms bulk of tooth tissue Covered by enamel in crown and cementum in root Distinctive characteristics:  o Dentine is sensitive o Continuously produced throughout life unlike amelogenesis o Increasing thickness at the expense of dental pulp Dentinal tubules (in a mineralised collagen matrix) are functional units of dentine o Odontoblast cytoplasmic processes extend only 25-50% of the full length of dentinal tubule ▪ Coordinates formation of peritubular dentine Physical properties of dentine: 1. Fresh dentine is pale yellow in colour 2. Softer than enamel but harder than cementum and bone 3. Higher fracture toughness (less brittle) than enamel 4. Permeable – dependent on size and patency of tubules 5. More radiolucent than enamel and radiopaque than cementum in radiograph Chemical composition of dentine: 1. 70% inorganic a. Impure calcium hydroxyapatite crystallites 2. 20% organic a. Collagen fibrils (type 1 collagen) embedded in an amorphous ground substance 3. 10% water Life cycle of dentine: 1. Preodontoblasts a. Small, ovoid cells b. High nucleus/cytoplasmic ratio 2. Secretory odontoblast a. Formed of a cell body and odontoblastic process b. Large plump cell, open-face nucleus c. Produce predentine 3. Resting odontoblast a. Quiescent state post dentine formation and mineralisation b. When dentinogenesis cease, cell shrinks but can be reactivated for tertiary dentine Dentinogenisis: 1. Matrix formation (predentine) a. Composed of small collagen fibrils (mostly type 1) and ground substance b. Blue in decalcified section 2. Maturation (mineralisation) a. Occurs soon after appositional growth of dentin (maturation) or predentine (mineralisation) b. Formation of calcium hydroxyapatite crystals i. Globular or linear pattern of mineralisation 1. Linear is better quality because more compact, less gaps that are hypomineralised dentine (unlike interglobular dentine)  2. Linear pattern found in mantle dentine and globular found in circumpulpal dentine Types of Dentin: Dentine is not uniform across the whole tissue  Dentinal Canaliculi that traverse the dentin tubules layer Extend through the entire thickness of dentine layer S-shaped path in crown and straight course in root or cusp tip Odp = odontoblast Arrowheads = dentinal tubules Inter-tub Located between the dentinal ular tubules dentin Primary formative product of odontoblasts Tightly interwoven network of type 1 collagen fibrils o Apatite crystals deposited here o 50-200 nm Main bulk of dentin Peri-tub Also considered intra-tubular dentin ular Hypermineralised collar dentin Formation leads to obliteration of tubule Translucent rings in ground section Coating of the dentinal tubules Hypocalcified structures of dentin: Inter-globul Areas of hypomineralised dentin ar dentin Gaps within globular patterns of mineralisation Appear dark in ground sections viewed in transmitted light due to internal reflection  Tome’s Seen just below surface of granular dentin, where root covered by layer cementum Progressive increase in granularity between CEJ to apex of tooth Spotty appearance due to hypomineralisation or branching of the terminal parts of dentinal tubules Found in root dentine only Incrementa Incremental lines of Von Ebner l lines of o 5-day increment dentin o 16-20 microns apart o Dark lines Counter lines of Owen o Lines at contact in S-shaped dentinal tubules Neonatal line o Wide, dark contour line o Disturbance in mineralisation at birth due to physiological trauma Age-related and post-eruptive changes in dentin 1. Secondary Dentin a. Formed after of root formation i. Primary dentine is formed before root formation b. Formation of secondary dentin is the most conspicuous age-associated change in dentine c. Very similar in structure to primary dentine i. There is a change in direction of dentinal tubules from primary to secondary dentine  ii. A – primary and B - dentine 2. Irregular Secondary Dentine/Tertiary Dentine a. Formed quickly and locally in response to injury to exposed dentine i. E.g. caries or trauma b. Forms underneath the exposed dentinal tubules along the outer pulpal wall i. To seal off injury – protect the pulp from stimulus c. A.k.a reparative dentine (more severe), reactionary dentine (less severe), response dentine and osteodentine d. Lower quality than secondary and primary 3. Sclerotic Dentin a. Loss of tubular structure, appearing transparent as dentinal tubules are completely occluded by minerals i. Associated with chronic injury of caries, attrition, abrasion and ageing b. Most likely caused by tubular occlusion by peritubular dentin c. Can be formed simultaneously with tertiary dentine  4. Dead Tracts d. Empty tubules – primary odontoblasts killed by external stimulus or retract before peritubular dentine occludes tubules e. Appear dark under microscope i. Partly due to pulpal response and preparatory procedure Innervations of Dentin Rich nerve supply 25% myelinated afferents whose cell bodies lie in trigeminal ganglion Nerve bundles run centrally in radicular pulp close to blood vessels Branches terminate at odontoblastic or subodonotoblastic regions in dentine o Plexus of Raschkow Dentinal Hypersensitivity Sensation of sharp and short pain Due to exposure to cold, air or touch o Dentine is exposed to stimulus Theories: o Direct nerve stimulation – nerve fibres extend to dentinal tubules and stimulation causes pain o Odontoblastic process associated with sensation – odontoblast act as receptors and transmit pain signals to nerve fibres o Hydrodynamic theory – fluid movement in dental tubule causes mechanical distortion of odontoblastic process ▪ The most acceptable theory Pulp A soft connective tissue at the innermost region of teeth, responsible for nourishing and maintaining dentine. 1. Coronal pulp a. Pulp occupying the pulp chamber of the crown b. Resembles shape of outer dentine in young teeth c. Pulp horns are projections into the cusp d. Constricts at the cervical region where it continues as radicular pulp 2. Radicular pulp a. Pulp occupying the pulp canals of the root b. Upper anterior teeth is usually single rooted; in all other teeth, it may be multiple c. Radicular portion of pulp is continuous with the periapical tissues through the apical foramen Coronal pulp mass > radicular pulp mass Pulp Histology A connective tissue, thus contains: o Intracellular substance, tissue fluid, cells, lymphatics, vascular system, nerves, and fibres ▪ Fibroblasts are the most common cells followed by cell bodies of odontoblasts Zones of pulp: Cells of Pulp 1. Odontoblasts and odontoblast process 2. Pulp fibroblast 3. Macrophage 4. Dendritic cell 5. Lymphocyte 6. Mast cell Matrix and Ground Substance of Pulp Extracellular compartment of pulp made of collagen fibres and ground substance o Type I and III collagen fibres Collagen content of pulp increases with age Dark brown substance in slide Age-related changes of pulp Pulp shrinks with age as secondary dentine deposition continues throughout life Becomes less vascular and more fibrous More hyaluronan and less chondroitin sulphate in pulp Reduced innervation Mineralisation of pulp into pulp stones/denticles o Radiopaque masses in radiograph o Unattached to outer pulpal wall or attached to dentin at dentin-pulp interface o Formed due to microtrauma May cause issues during root canal therapy, but otherwise non-pathologic  Dystrophic calcification o Located in the central pulp o Originate in relation to blood vessels or as diffuse mineral deposits along collagen bundles o Radiopacity in radiograph WEEK 7 Cementum Hard tissue covering the root formed by cells called cementoblasts. Continuously produced. Avascular, calcified tissue of mesenchymal origin. Part of both tooth and periodontium. Periodontium 1. Hard tissues a. Cementum b. Alveolar bone 2. Soft tissues a. Periodontal ligament b. Gingiva Physical Properties of Cementum: 1. Hard, calcified tissue a. Thickest at apex and inter radicular areas of multirooted teeth (50-200 microns) b. Thinnest at CEJ (10-50 microns)  2. Low mineralisation a. More radiolucent (darker) than either enamel or dentin b. More radiopaque (lighter) than pulp 3. Permeable a. Absorptive from both dentin and PDL sides b. Cellular cementum more permeable than acellular cementum i. Absorptive capability is good and bad 1. Can absorb nutrients but also microbes and toxins Chemical Composition of Cementum: 45-50% inorganic material (calcium hydroxyapatite) 50-55% organic matter (type I collagen, glycoprotein and proteoglycans) and water Greatest amount of fluoride in all mineralised tissues Functions of Cementum: 1. Anchorage a. Sharpey fibres allow anchorage of the tooth within the osseus socket i. Terminal fibres of the periodontal ligament 2. Adaptation a. Mainly achieved by cellular cementum b. Continuous deposition in apical and furcation areas to compensate for wear and tear during eruption 3. Repair a. Mainly achieved by cellular cementum 4. Seal tubules of root dentine Cementogensis 1. Production of predentine by odontoblast in developing root causes breakdown of HERS 2. Mesenchymal cells of dental sac differentiate into cementoblasts, depositing collagen fibrils – pre-cementum formation a. Also differentiates into osteoblast to form alveolar bone and fibroblasts to form PDL fibres 3. As one layer of pre-cementum forms, the older layer calcifies into mature cementum a. Incremental growth Types of Cementum: 1. Acellular cementum a. First to be formed at DCJ i. Primary cementum b. Covers the cervical third or half of root c. Does not contain cells d. Consists of mostly Sharpey’s fibres e. To support tooth f. Less permeable than cellular cementum g. Formed at slower rate 2. Cellular cementum a. Secondary cementum  b. Consists of the last layers of cementum closest to PDL and Alveolar bone c. Covers apical 1/3rd of each root d. 150-200 microns thick e. More permeable than acellular cementum f. Formed at faster rate g. Made of cementocytes i. Enclosed within lacunae with processes in canaliculi directed toward the tooth surface (bush towards PDL side due to direction of nutrition absorption) Refer to slides for more histology images Intermediate Cementum First to be deposited on root surface Formed by inner epithelial root sheath cells derived from dentinogensis o Occurs before root sheath layer disintegrates Situated between the granular dentin layer of Tomes and secondary cementum Incremental Lines of Salter Deposited rhythmically thus uneven spacing between incremental lines o Closer together and more even in acellular cementum o Further apart and more irregular in cellular cementum due to faster rate of formation They are hypermineralised areas with less collagen and more ground substance Types of CEJ interfaces: Occurs in acellular afbrillar cementum. 1. Overlap (60%) – cementum over enamel because of rupture of reduced enamel epithelium, cells of dental sac lays down cementoblasts on the exposed enamel. 2. Meet (30%) – conventional 3. Gap (10%) – dentin exposed Age Changes of Cementum 1. Smooth surface becomes more irregular 2. Cementum resorption a. Caused by local or systemic factors or no apparent aetiology b. Not always continuous, may alternate between periods of repair and deposition of new cementum i. Demarcated by reversal line Cementicles Mineralised spherical bodies of cementum o Attached to cemental root surface or lying free in the PDL Origin may be nidus or epithelial cells Form from appositional growth of cementum around cellular debris in PDL More prevalent along root in ageing person or site of trauma Hypercementosis Excessive production of cellular cementum Mostly occurs at apex or apices of roots and inter radicular region of molars Radiopaque mass at each root apex Implicates complicated tooth extraction but not pathologic if localised Alveolar Bone Hard and mineralised tissues much like other bones. 60% inorganic material (calcium hydroxyapatite) 25% organic (potassium, manganese, magnesium, silica, iron, zinc etc.) 15% water by weight More easily remodelled than cementum, allowing orthodontic tooth movement. Alveolar process - bones of the jaws containing the sockets, supporting the teeth (top half) No teeth then no alveolar process Basal bone – bony part of mandible or maxilla (bottom half) Layers: 1. Compact bone 2. Cancellous/spongy bone 3. Labial and lingual cortical plates a. Thickness: i. Anterior teeth – lingual plate > labial plate ii. Lower posterior teeth – Buccal plate > lingual plate iii. Upper posterior teeth – Lingual plate > buccal plate Interdental septum – alveolar bone between two teeth Inter-radicular septum – alveolar bone between root of multi-rooted tooth Septums contain nutrient canals/Canals of Zuckerkandl and Hirschfeld carrying blood vessels and nerves Bundle bone – also known as alveolar bone, where principle fibres of PDL are bundled together and embedded Radiopaque (lamina dura) Clinical considerations During tooth extraction, thickness of cortical plate determines direction of initial movement o All teeth are extracted with labial or buccal movement except lower molars ▪ Movement towards thinner cortical plate ▪ Lower molars bones thickened by oblique ridge Periodontal Ligament Heavy fibrous connective tissue located between the alveolar bone proper and cementum. The ligament envelops the root and connects with gingival tissue Occupies periodontal space Made of fibres, cells (fibroblasts), collagen fibres and ground substances. Originate from mesenchymal cells of dental sac/follicle. Structure of PDL 1. Complex vascular and highly cellular connective tissue surrounding the tooth 2. Made of collagen fibres that insert into cementum and alveolar bone Function of PDL 1. Maintains tooth in a functional position 2. Resists occlusal loading 3. Protects dental tissues from excessive loading 4. Maintains and repairs alveolar bone and cementum a. Contains stem cells Histological structure: Cells o Synthetic – fibroblasts, osteoblasts and cementoblasts o Resorptive – cementoclasts, osteoclasts o Progenitor – undifferentiated mesenchymal cells o Defensive – macrophage, lymphocyte and mast cells o Epithelial – ERM Intercellular substance o Fibres o Ground substance o Blood vessels, nerves and lymphatics Types of fibres: 1. Principle fibres a. Most important fibre b. Terminal ends are called Sharpey’s fibres c. Groups of fibres: i. Gingival – form rigid cuff around the tooth for additional stability ii. Interdental/transseptal – connect two adjacent teeth, runs between cementum of the two teeth iii. Alveodental – most important 1. Alveolar crest group – radiates from crest of alveolar process to cervical part of cementum 2. Horizontal crest group – run perpendicular to cementum to attach to bone 3. Oblique fibres – run obliquely and most predominant 4. Apical fibres – radiate from apical root cementum to bone 5. Interradicular fibres – radiate in furcation areas from cementum to bone 2. Accessory fibres a. Collagenous in nature and run in different planes b. Found in the region of horizontal group 3. Oxytalan fibres a. Immature elastic fibres b. One end in bone or cementum, the other end in wall of blood vessels c. They support blood vessels during mastication Blood and nerve supply of PDL Arterial supply derived from o Branches of gingival vessels o Branches of intra-alveolar vessels o Branches of apical vessels Inferior and superior dental nerves Age changes of PDL Decrease in vascularity, cellularity and thickness Cementicles appear near surface of cementum o Nidus favour deposition of calcospherites Clinical considerations 1. Timing is important when re-implanting a fallen tooth. 90% chance of success if reimplanted within 30 mins. Submerge tooth in milk to keep PDL cells alive, allowing PDL to regenerate and revascularize when reimplanted. 2. Dental implants fail mainly due to lack of PDL. Cannot withstand excessive load from mastication Gingiva Covers alveolar bone and tooth root to a level just coronal to cementoenamel junction. 1. Marginal/unattached gingiva a. Terminal edge or border of gingiva surrounding teeth b. Collar-like fashion c. Separated from attached gingiva by marginal groove d. Forms soft tissue wall of gingival sulcus 2. Attached gingiva a. Firm, resilient and tightly bounded to underlying periosteum of alveolar bone b. Continuous with marginal gingiva c. Mucogingival junction (health line) separates attached gingiva from alveolar mucosa  d. Stippled appearance e. Width is an important diagnostic parameter to determine pathology 3. Interdental gingiva a. Occupies interproximal space/embrasure cervical to contact point 4. Gingival sulcus a. Shallow crevice or space around tooth b. Bounded by tooth surface on one side and epithelium lining on the other c. V-shaped d. Normal = 0mm e. Depth is an important diagnostic parameter to determine pathology Clinical considerations Gingiva should be pale pink and alveolar mucosa red. Inflammation of gingiva – pink -> red in colour, mucogingival junction cannot be seen. Histology Comprised of stratified squamous epithelium and central core connective tissue components. Keratinocyte is the primary cell type Contains rete pegs – extensions of epithelium into connective tissue Taller and numeral Keratinisation – thicker than non-keratinised mucosa 1. Orthokeratinisiation 2. Parakeratinisation 3. Non-keratinised mucosa Connective tissue is made of cells and collagen fibres. Functions of Gingiva Gingival epithelium Gingival connective tissue Physical barrier against pathogens High proliferation of cells producing Host defence coordination collagen matrix ensures good repair Rapid clearance of invading bacteria and regenerative capacity and their metabolic products from gingival sulcus  o Particularly JE cells Abundance blood and nerve supply allowing quick healing and little scarring Oral mucosa Mucous membrane keeps surfaces moist. Lines many internal hollow organs/cavities. Mucosa/mucous membrane consists of: 1. Epithelial lining (may have glands opening into its surface) a. Simple columnar in stomach – allowing secretions b. Stratified squamous epithelium in oral cavity – to withstand abrasion 2. Underlying connective tissue called lamina propria a. Connects epithelium to submucosa i. Dense irregular connective tissue in hard palate – tight connection with epithelial lining ii. Loose areolar connective tissue in GI tract – loose connection with epithelial lining 3. Muscularis mucosa found only in the GI tract a. Smooth muscle layer i. Contraction causes surface movement of the mucous membrane to increase surface area and absorption 4. Submucosa a. Supporting connective tissue ranges form loose areolar to dense irregular connective tissue b. Where glands reside that open into surface epithelium i. Minor/accessory salivary glands 1. Mucous acini or serous acini or both  2. Mucous acini is lighter in colour (predominant) than serous acini Types of oral mucosa: 1. Lining mucosa a. Internal surface of lips and cheek, soft palate, floor of mouth 2. Masticatory mucosa a. Gingivae and hard palate b. Subject to friction 3. Specialised mucosa a. Anterior 2/3rd of dorsum of tongue i. Contains taste buds Histology of Lips A continuous surface. From outside inside: 1. Surrounded by thin skin of face a. Vermillion border and face b. Presence of hair follicles and sebaceous glands, as well as sweat glands c. Keratinised epidermis (true skin)  2. External surface lined by thin skin a. Vermillion zone/transition zone b. No hair follicles and sebaceous glands c. Still true skin 3. Inner surface line by lining mucosa a. Now mucosa not skin b. Presence of minor salivary glands c. Superficial layer is epithelium i. Stratified squamous non-keratinised epithelium 1. Cell nucleus present in outermost layer of epithelium d. Deeper layer is lamina propria i. Loose areolar connective tissue 1. Moisture, flexibility and mobility for speaking and eating e. Deeper layer is submucosa i. Loose areolar connective tissue ii. Minor salivary glands Bulk of section is made of skeletal muscle: Orbicularis Oris Histology of Hard Palate Diploic in nature. Deepest to outermost: 1. Spongy bone a. Trabecular network b. Marrow spaces 2. Submucosa a. Dense irregular connective tissue 3. Lamina propria a. Dense irregular connective tissue 4. Lining of masticatory mucosa a. Minor salivary glands b. Stratified squamous para-keratinised epithelium i. Some nucleus present in outmost layer of epithelium Mid-palatine raphe does not show submucosa  Has similar appearance to gingivae Gingiva – keritinised stratitified squamous epithelium – tall, numerous, slender rete-pegs, no submucosa Palate – keratinised epithelium – tall numerous rete-pegs, has submucosa, glandular zone, fatty zone