Anatomy - Outcome 7 Flashcards
Origin of Enamel
Ectoderm
Degree of Calcification (Hardness)
- the hardest tissue in the body
- only calcified tissue from the epithelium
Permeability of the Enamel
- allows for the exchange of ions
- demineralized versus remineralization
Nonvital - Enamel
- not a living tissue
- contains no living cells, blood or nerves
- no more enamel after eruption
thickenss of enamel
0.2 - 2.5 mm
colour of enamel
yellowish-white to grey
translucent
colour affected by dentin
Chemical Composition
96% inorganic material
-Mainly calcium hydroxyapatite Ca10(PO4)6(OH)2
-Smaller amounts of carbonate, magnesium, potassium, sodium, and fluoride
3% Water
1% organic collagen-like substances (keratin, mucopolysaccharides)
Macroscopic Structure of Enamel - Appearance
hard, shiny, translucent
Macroscopic Structure of Enamel - Location
- Primary dentition: clinical crown in enamel only
- Permanent dentition: clinical crown including cementum and dentin due to recession and tooth wear
Macroscopic Structure of Enamel - Lines of Retzius
- wear down over time
- Imbrication lines: horizontal raised lines
- Perikymata: grooves
Macroscopic Structure of Enamel - Colour
- varies with age
- intrinsic vs extrinsic
- “natural colour”
Macroscopic Structure of Enamel - Attrition
- wearing off enamel under the friction of use
- incisal edge and posterior cusps
- dentin changes appearance
Macroscopic Structure of Enamel - Mamelons
- incisal edges of erupted incisors
- wear away
- of no clinical importance
Macroscopic Structure of Enamel - Grooves on posterior teeth
- occlusal
- buccal
- lingual
- may be shallow and smooth or deep
Macroscopic Structure of Enamel - Fissures
- deep, the bottom of the groove
- end in enamel
Macroscopic Structure of Enamel - Pits
- depressions
- at either end of a groove
Macroscopic Structure of Enamel - Nasmyth’s Membrane (enamel cuticle)
- Residue on newly erupted teeth: last ameloblast product (mineralized)
- secondary enamel cuticle: product of reduced enamel epithelium (junctional epithelium) non-mineralized, wears away with tooth use
Histologic Structure of Enamel - Enamel Rod (enamel prism)
-extend from DEJ to the outer surface of the enamel
-perpendicular to DEJ
-maxillary central incisor has approximately 8,586,000 rods
-fit together - a keyhole shape
-most highly mineralized part of the histological structures of the enamel
Histologic Structure of Enamel - Rod (prism) sheath
encases rods
Histologic Structure of Enamel - Inter-rod substance (interprismatic subsance)
-cement all together
Development of Enamel
- is a product of the enamel organ
-the ameloblasts produce an organic enamel matrix
Apposition Stage of Enamel
-Amelogenesis
*ameloblasts lay down gel matrix beginning at cusp tip and move outward
*from DEJ and OEE
*ameloblasts are producing enamel matrix from their Tomes processes
*They actively pump calcium hydroxyapatite into the forming enamel matrix as it is secreted by the Tomes processes
Matruation Stage of Calcification of Enamel Rods
-Enamel matrix completes its mineralization process after the apposition of enamel matrix when it is only 30% mineralized
-Ameloblasts actively pump even more calcium hydroxyapatite into the already partially mineralized enamel matrix
-minerals increase in size
-tightly packed
-hypoplasia or hypocalcification
Clinical Importance of Structure of Enamel - incremental lines of Retzius (stripe of Retzius)
-microscopic brownish lines, extending diagonally from DEJ
-the result from layer upon layer of the matrix form
-terminate on the occlusal surface creating perikymata
-areas of less mineralization may aid the lateral spread of caries along each stripe
Clinical Importance of Structure of Enamel - arrangement of enamel rods
-influences penetration of decay
*follows enamel rods to dentin/pulp
Clinical Importance of Structure of Enamel - dentino-enamel junction
-scalloped around tooth
-more scalloping at incisal and cusp tips
-spread out occlusal forces
-stronger tooth
Clinical Importance of Structure of Enamel - Enamel Lamellae (little layers)
-microscopic separations in enamel
-filled with organic material
-susceptible to caries
-extend from the enamel surface to DEJ
-may be faults in enamel matrix formation of cracks in enamel caused by injury
Clinical Importance of Structure of Enamel - Enamel Tufts
-shorter than enamel lamallae
-small brush appearance
-hypomineralized ends of some of the enamel rods/sheaths/inter-rod substance
-attached to the DEJ and extends outward in the enamel
-reduce resistance to caries, spreads horizontally at the DEJ
Clinical Importance of Structure of Enamel - Enamel Spindles
-odontoblast of dentin extending over the DEJ
-odontoblastic process caught in enamel
-now vital tissue in enamel
-very thin corkscrew shape
-reduce resistance to caries, spread horizontally at DEJ
Clinical Importance of Structure of Enamel - bands of Hunter-Schreger
-alternating light and dark bands caused by curvatures in the enamel rods
-reduce splitting of enamel along rod sheath
Variations of Dentin
- forms throughout the life of the tooth
Interglobular Dentin
-hypomineralized areas in crowns of some teeth
-metabolic disturbances
-disturbances in calcification
Tome’s Granular Layer - Dentin
-also hypomineralized areas in dentin
-granular appearance
-immediately below cementum at end of dentinal tubules
-contributing factor to sensitive teeth
Sclerotic Dentin
-found in older teeth
-the odontoblastic process is withdrawn
-filled with Ca salts
-tubule decrease in size and blocks off access to the pulp
-continual formation of peritubular dentin
-makes it difficult for toxic substances and microorganisms to move from the oral cavity to the pulp
Clinical correlation of dental caries and sensitivity to the histological study of dentin: Caries Progression
-reaches DEJ
-bacteria → enter tubule → destroy the odontoblastic process
-directly to pulp
-spreads rapidly in dentin under the enamel
Clinical correlation of dental caries and sensitivity to the histological study of dentin: Defence Reactions
-sclerotic dentin – block bacterial penetration
-reparative dentin – increase dentin thickness and temporarily protects the pulp
Clinical correlation of dental caries and sensitivity to the histological study of dentin: Dentinal Hypersensitivity
-When dentin is exposed as a result of caries, cavity preparation, gingival recession, or attrition, the open dentinal tubules may be painful for the patient
-protective layers of both cementum and dentin inadvertently removed as a result of scaling with hand instruments can cause sensitivity
-One explanation for dentinal hypersensitivity is the hydrodynamic theory.
*Stimulation of the exposed dentinal tubules (such as the application of cold water) causes changes in the dentinal fluid, which is transmitted to the nerves associated with the cell bodies of the odontoblasts in the pulp tissue.
Location of Pulp
-enclosed in dentin
-occupies pulp cavity
-it fills the pulp chamber in the crown and root canal in the root
Development of Pulp
As the pulp develops, it will consist of blood vessels, lymph vessels, and nerves (sensory nerves that will transmit pain and motor nerves that will innervate smooth muscle cells in walls of blood vessels → constriction).
Histologic Structure of Pulp
only non-mineralized tissue of a tooth
Pulp is made up of..
Cells
Intercellular Substance
Tissue Fluid
Fibroblast Cells - of pulp
-the largest group of cells
-responsible for forming the intercellular substance of the pulp tissue
Odontoblasts - of pulp
-nucleus of pulp
-the bulk of cytoplasm in dentin
-the gradual narrowing of pulp
-the specialized connective tissue cells
Histocyte cells - of pulp
-undifferentiated
-defence mechanisms
-anti-inflammatory
Lymphocytes - of pulp
-specialized white blood cells
-defence - t cells, b cells - antibodies
Korff’s fibers - of pulp
-in intracellular substance
-fibrous-coiled rope
-formation of dentin matrix
Blood vessels, Lymphatic vessels - of pulp
-superior and inferior alveolar artery enters through the apical foramen
-contain red blood cells, white blood cells, and lymphocytes
Nerves - of pulp
-Trigeminal Nerve
-Nerve endings in the odontoblastic process
Denticles (pulp stones)
-mineralized bodies found in the pulp
-vary in shape and size
-size usually increases with age
Diffuse mineralizations
-a small, thin scattering of calcified materials
-usually found in the pulps of older teeth
-usually in root canals
Zones of Pulp
- odontoblastic zone
- cell-free zone
- cell-rich zone
Cells of Pulp
- Fibroblastic cells
- Odontoblasts
- Histocyte cells
- lymphocytes
- Korff’s fibers
- Blood vessels, lymphatic vessles
- Nerves
- Denticles (pulp stones)
- Diffuse Mineralizations
Odontoblastic Zone - of pulp
- cell bodies of odontoblasts
- lines the outer pulpal wall
- capable of forming secondary or tertiary dentin along the outer pulpal wall.
Cell-Free Zone of Pulp not entirely cell free
- consists of fewer cells in contrast to the odontoblastic layer, but it is not entirely cell-free.
- buffer area
- movement for other zones
- especially secondary/reparative dentin
- A nerve and capillary plexus is also located in this zone.
Cell-Rich Zone of Pulp
- a reservoir of undifferentiated cells
- more extensive vascular system than cell-free zone
- new odontoblasts
- white blood cells
Pulp Function - Formative
-produce collagen fibrils
-produce dentin
-ceases if odontoblast die or root canal therapy is performed
Pulp Function - Sensory
-senses external stimuli
-perceived as pain only
-pressure from periodontal ligament produces a sensation of pressure or touch
Pulp Function - Nutritive
-living tissue
-nutrients enter the dentinal tubules to DEJ
-recieves nutrients from the bloodstream
Pulp Function - Defensive
-inflammatory reaction
-sclerosis of dentin tubules
-reparative dentin (production of dentin)
-all 3 defenses work together
Pulp Function - Vitality
-keeps tooth alive
-keeps the enamel from becoming brittle
-endodontic - non-vital
-living tissue in the socket
Pulp Functions
- Formative
- Sensory
- Nutritive
- Defensive
- Vitality
Age changes in pulp
do not alter the function of the tooth
Increasing age → changes in different parts of the human body including dental pulp. (Therefore normal, not pathological)
Examples of changes in pulp with age include:
- secondary Dentin → smaller pulp chamber and pulp canal(s)
- number of cells decreases
- fibrous intercellular substance increases
- nerve and blood supply decreases
- denticles are larger and more numerous
- diffuse calcifications increase
Clinical Importance of Pulp - Endodontic Treatment
-function for years without pulp
-enamel becomes brittle
-no reparative or sclerotic dentin
-for tooth to remain in formation endodontic therapy must be complete
Clinical Importance of Pulp - Tooth Vitality
-pulpitis
-infection from decay, fracture, periodontitis
-abscess – exudate (pus) exiting through apical foramen
-blood leaking into dentin – colour change
