Introduction of oral tissue Flashcards
what is percentage of teeth constitute to surface of the mouth?
Teeth constitute ~20% of the surface area of the mouth (upper more than lower)
what are functions of teeth?
Mastication
Speech
Weapons of attack and defense
what are components of tooth?
Consists of enamel of crown, cementum of root, form of dentin, inner core of pulp
which type of embryonic tissue does enamel derive from?
Epithelially derived protective covering for the crown of the tooth
what are characteristics of enamel?
-Most highty mineralized tissue in the body (96%)
-Formed by “ameloblasts”
Non-vital material, insensitive matrix
-Cannot be replaced or regenerated
-Can withstand large masticatory forces and continual assault by acids from food and bacterial sources
-Hard but brittle
-Translucent
what is functions of dentin?
Provides support for enamel so it will not fracture under masticatory forces
what are characteristics of dentin?
-Resilient
-Forms bulk of tooth for both crown and root
~65% mineralized, elastic, yellowish-white
-Same mineral as in other mineralized tissues
-Contains closely packed tubules traversing the entire thickness and containing the cytoplasmic extension of the cells that formed and later maintain it
-“Sensitive” tissue
-Capable of repair
what are functions of pulp?
formative, nutritive, protective, reparative
what are characteristics of pulp?
- Fills central cavity or pulp chamber of the tooth
- Soft connective tissue
- Related to dentin embryologically and functionally
what are supporting tissue of the tooth?
periodontal ligament and cementum
what are characteristics of periodontal ligament?
- Highly specialized CT between the tooth and bone
- Principal function is to connect tooth to jaw and withstand forces of mastication
- Sensory function
what are characteristics of cementum?
- Covers roots, attached to dentin
- Similar to bone, avascular
- Cellular/acellular
what is oral mucosa?
- Mucous membrane/soft tissue
- Epithelium + supporting tissue
- Lining and protection; mobility; taste
- Masticatory, lining, specialized
- Gingiva (surrounding erupted tooth)
- “Sealing” junction
what are characteristics of salivary gland?
- Saliva
- Majors (parotid, submandibular, sublingual)
- Functions of Saliva:Lubrication, speech, taste, digestion, antimicrobial, buffer
what are bones of the jaw?
Alveolar process and supporting (basal) bone
what are hard tissues of the body?
- Connective Tissues: bone, cementum, dentin
- Ectodermal Derivation: enamel
what are processes of hard tissue formation/ degradation?
- Organic matrix of hard tissues
- Mineral
- Mineralization
- Crystal growth
- Alkaline phosphase
- Transport of mineral ions
- Degradation
what is formation of hard tissue?
production of an organic matrix capable of accepting mineral, with activity of enzyme alkaline phosphate and a good blood supply prerequisites
what is organic matrix?
- Proteins that attract and organize calcium and phosphate ions into a structural mineral phase based on carbonated apatite
- Often characterized by “blast” cells which exhibit a polarized organization for vectoral secretions and appositional deposition of matrix proteins
- Cementum, dentin, and bone have collagen (type 1) in the organic matrix;
- enamel has NO collagen or similar fibrillar protein in the organic matrix (also special case of cementum: acellular afibrillar)
Mineral
-The base mineral is hydroxyapatite Ca10(PO4)6(OH)2 (Unit Cell)
-Hexagonal in shape
-Unit cells form a crystal when stacked together
-Crystals vary in size based on the number of stacks
-May exists as needle-like, plate-like, or ribbon-like
-Crystals possess a layer of water around them (hydration layer)
-Dynamic molecule, substitutions possible:Na -> Ca
FL, CL -> OH, PO4
-FL decreases solubility
-Carbonate increases solubility
-Mg in matrix inhibits crystal growth
-Other ions may be adsorbed to the crystal surface by electrostatic attraction or bound in the hydration layer
-Crystal retains its structural configuration
Mineralization
- Mineralization is not a physiologic process
- More dependent on rate-limiting activities
- When deposition is initiated,
- There is control of the spontaneous precipitation from a tissue fluid super-saturated in calcium and phosphate ions
- Precipitation is limited to well defined sites
regulation of mineral
- In the genes …
- In the genome there is a secretory Ca binding phosphoprotein gene cluster that regulates:Salivary proteins, Enamel matrix proteins,CT HT matrix proteins
- Spontaneous precipitation does NOT occur
- Tissue fluid contains macromolecules which inhibit crystal formation
- Seeding (initiation of precipitation) requires the expenditure of energy
- Matrix vesicles Heterogeneous nucleation
what is matrix vesicle?
- membrane bound structure
- found only in initial mineralization
- contains alkaline phosphatase, pyrophosphate, Ca-ATP-ase, metalloproteins, proteoglycans, and anionic phospholipids
what is heterogeneous nucleation?
- Occurs in collagen based HT
- apatite crystals are deposited in the “gaps” between the tropocollagen molecules of collagen fibrils
- some fibrils may act as nucleators, others control crystal growth
- gaps normally contain proteoglycans which may bind calcium
- In bone, 70-80% of the mineral is located within the collagen fibrils and precipitation is controlled by non-collagenous proteins
what is mineralization?
- Dephosphorylation of phosphoproteins (by alkaline phosphatase) provides additional phosphate for nucleation and crystal growth
- Anionic phospholipids bind Calcium
what is mineralization in enamel?
- None of these mechanisms are involved in the mineralization of enamel
- Matrix vesicles are absent
- Probably achieved by association with the already mineralized dentin
- Enamel proteins determine size and shape of crystals
what are characteristics of crystal growth?
- Initial growth is rapid
- growth influenced by substances in the organic matrix
- non-collagenous proteins bind selectively to different surfaces of the crystal
- pyrophosphate accumulates on the surface of the crystal and inhibits further growth
what is secondary nucleation of mineralization?
occurs from mineral-phase particles arising from collisions and fracture of crystals previously formed
what is alkaline phosphatase?
- Key marker for the production of any mineralized tissue
- distributed near blood vessels and cell membranes of hard tissue-forming cells
- found in matrix vesicles
- hydrolyzes phosphate ions from organic radicals at an alkaline pH
- a “class” of enzymes
- May play a role in calcium transport when associated with membranes
- Provides phosphate ions
- In matrix, cleaves pyrophosphate
Two possible mechanisms of mineral reaching the mineralization site
through cells
between cells
Location of mineral
- packed in the ground substance between collagen fibers
- incorporated within the collagen fibers (70-80% of mineral in bone)
hard tissue degradation
- Degradation and removal is a cellular event: osteoclasts in bone and odontoclasts in dental tissues
- Generally large cells, multinucleate, reside in Howship’s lacunae with unique ultrastructure
- Enzyme marker is acid phosphatase
- Proton pump in ruffled border membrane which pumps hydrogen ions into the sealed environment
- Carbonic anhydrase and isocitric dehydrogenase have been identified in the membranes (elaboration of carbonic and citric acids)
what is sequence of resorptive events?
- attachment of “resorptive cell” (osteoclast, cementoclast, odontoclast) to mineralized surface
- creation of a sealed acidic environment which demineralizes bone and exposes the organic matrix
- degradation of exposed organic matrix by acid phosphatase, cathepsin B, and collagenase
- uptake of mineral and amino acids by cell
