TOOTH COMPOSITION & DEVELOPMENT REVIEW

 

TOOTH COMPOSITION & DEVELOPMENT REVIEW

v  Basically everything is from Ectomesenchyme except for Enamel, which is from Ectoderm

v  A quick review of Odontogenesis

Ø  Initiation

§  Induction – interaction between ectomesenchyme and epithelium

§  6^th week

§  Formation of dental lamina

Ø  Bud Stage

§  Proliferation – both dental lamina and underlying ectomesenchyme

§  8^th week

§  Dental lamina into 10 buds per arch

§  Shape of tooth is evident

§  Enamel organ starts to form

§  Tooth buds of the Maxilla appear 1^st!

Ø  Cap Stage

§  Proliferation and Differentiation

·         Morphodifferntiation – change into other shapes

·         Histodifferentiation – branch into different tissues

§  9-10^th week

Ø  ***NOW tooth germ is complete – You get your Cap when you graduate - Even though your not fully differentiated.

Ø  Bell Stage

§  Differentiation of Odontoblasts

§  For the whom the BELL TOMES

§  Differentiation to its furthest extent resulting in 4 different cell types in the bell-shaped enamel organ (makes enamel and Hertwig’s root sheath)

·         OEE – cuboidal

·         IEE – columnar (Think I looks like a column)

·         Stellate reticulum – network of star-shaped cells

·         Stratum intermedium – flat to cuboidal

§  Dental papilla (makes dentin and dental pulp) differentiate into 2 layers

·         Outer cells

·         Central cells

§  Dental sac (makes Cementum, PDL, and alveolar bone proper) increases in collagen fibers

§  11-12 weeks

·         Remember enamel organ makes Enamel

Ø  Appositional Stage

§  Cells that were differentiated into specific tissue-forming cells begin to deposit the specific dental tissues (i.e. enamel, dentin, cementum and pulp)

Ø  Maturation Stage

§  Mineralization begins at the DEJ and continues until total development accomplished, taking approximately 2 yrs to complete 

v  Enamel

Ø  Ectodermal Origin

Ø  4 Layers of Enamel Organ

§  1)  Outer enamel epithelium

·         Outer cellular layer

§  2)  Inner enamel epithelium (IEE)

·         Innermost layer

·         Cells will become ameloblasts

·         Essential for the initiation of dentin formation

·         *NOTE: In a developing tooth, the junction of the dental papilla and the IEE becomes the DEJ

§  3)  Stratum Intermedium Think I is next to I

·         Lateral to inner enamel epithelium

·         Essential to enamel formation (nutrients for the ameloblasts of inner enamel epithelium) – during calcification

§  4)  Stellate Reticulum

·         Central core and fills bulk of organ

·         Contains lots of intercellular fluid (mucous type rich in albumin) which is lost prior to enamel deposition

Ø  After enamel formation, all 4 layers become 1 and form the Reduced Enamel Epithelium

·         What is the reduced enamel epithelium made from???   Attached epithelial cuff???

§  Very important in forming the dentogingival jxn, where the enamel and epithelium meet as tooth erupts

§  This forms initial junctional epithelium

Ø  96% inorganic, 1% organic, 3% water

§  Inorganic

·         Hydroxyapatite

¨       Calcium and Phosphate

¨       Fluoride and Zinc (Minor)

¨       Optically clear

§  Organic

·         Protein rich in Proline

Ø  Brittle, but can endure 100,000 PSI of pressure

Ø  Yellow to grayish

Ø  Selectively permeable membrane (water and ions via osmosis)

Ø  Enamel Rods or Prism

§  Fundamental morphologic primary unit

§  Aligned perpendiculary to the DEJ (except in cervical regions of primaryteeth)

·         A chamfer or long bevel is commonly used as a gingival finish line in permanent tooth preparations because the direction of the enamel rods in the region of the CEJ is such that the rods deviate from the horizontal in an apical direction

·         The direction of enamel rods in primary teeth is inclined in an occlusal direction in the cervical 1/3 of the crown

§  5–12 million per crown

§  Rods increase in diameter as they flare outward “Tails” (from 4–8 microns).  As you move towards pulp from outer surface, # of rods increases.

§  Begin at the future cusp and spread down the cusp slope

§  Oldest enamel is at DEJ under cusp or Cingulum

§  Good thermal insulator

§  Hunter Schreger bands??

·         Alternating light and dark bands seen in enamel that begin at DEJ and end before they hit the surface

·         Represent areas of enamel rods cut in x-section dispersed between areas of rods cut longitudinally

§  Lines of Retzius

·         As ameloblasts retreat in incremental steps, they create artifact lines

·         Where these lines terminate, they form tiny valleys on tooth surface called perikymata

¨       The small ridges, perikymata, seen on facial surfaces of canines, are the result of normal development

¨       Perikymata are the result of normal enamel apposition

·         A Neonatal line exists where enamel was formed before and after birth

¨       Found in both perm and prim

Ø  Enamel tufts

§  Fan-shaped, hypocalcified structures of enamel rods that project from the DEJ into the enamel proper

§  Unknown fxn

Ø  Enamel Spindles

§  Elongated Odontoblastic processes (hair-like) that transverse the DEJ from the underlying odontoblast

§  Tomes fibers

§  May serve as pain receptors

¨       Tomes processes are from Enamel at the DEJ

¨       Tomes Granular Layer is found in radicular dentin and lies just beneath the cementum, and distinguishes root dentin from crown dentin

Ø  Enamel lamellae

§  Defects in the enamel resembling cracks or fractures which transverse the entire length of the crown from the surface to the DEJ

§  Contain mostly organic material and may be carious

§  Perikymata and lamellae are seen on the surface of enamel, where Tufts are not

v  DEJ

Ø  Remnant of the onset of enamel formation – from the junction of the dental papilla & IEE

Ø  Ameloblasts secrete enamel matrix as they retreat away from the DEJ, then matrix mineralizes

Ø  Odontoblasts begin dentin formation immediately before enamel formation, by laying down collagen matrix and then moving from the DEJ inwards towards the pulp (newest dentin always closest to the pulp)

Ø  Area at which calcification begins

Ø  Morphology determined at Bell Stage

v  Dentin

Ø  Composition

§  70% inorganic, 20% organic, and 10% water

·         Test Q says 20-30% organic

§  Organic

·         Mostly of collagen fibers, Type I

§  Inorganic

·         More mineralized than cementum or bone, but less than enamel

¨       Hard→soft: enamel→dentin→cementum

·         Calcium Hydroxyapatite

·         Main cell is odontoblast – derived from ectomesenchyme

§  Avascular

Ø  More flexible than enamel

Ø  Forms the greatest amount of tooth structure

Ø  Fxn

§  Nutritive

§  Sensory

§  Protective

Ø  Along with pulp tissue, is formed by the dental papilla

Ø  Dentinogenesis

§  Steps

·         The ectomesenchyme influences the oral epi to grow down into the ectomesenchyme

·         Elongation of inner enamel epithelium and differentiation into ameloblasts

Ø   (making it columnar, but outer is still cuboidal)

¨       This triggers the mesenchymal cells to differentiate into odontoblasts

·         Differentiation of Odontoblasts

·         Deposition of first layer of dentin

·         Deposition of first layer of enamel

·         *Deposition of root dentin and cementum

§  Mantle Dentin

·         Peripheral or first layer of dentin adjacent to enamel or cementum

·         Consists of more coarse fibers (Korff’s) – Think Dorff on Golf

§  Peritubular Dentin (Intratubular Dentin)

·         Lines each dentinal tubule

·         More mineralized than intertubular dentin

§  Intertubular Dentin

·         This is the main bulk of dentin

·         Surrounds peritubular dentin

·         Less mineralized

§  Interglobular Dentin

·         Imperfectly calcified matrix of dentin situated between the calcified globules near the periphery of the dentin

§  **Each tubule contains a cytoplasmic process (Tomes’ fiber) of an odontoblast

·         Dead tracts are tubules with dead cytoplasmic fibers in them

Ø  Primary dentin

§  Layed down before apical foramen closure

§  Dentin laid down before birth???            

Ø  Secondary dentin

§  Formed after foramen closure

§  Slower forming than primary, as functional stresses are placed on tooth

§  Following the initial period of functional activity, an appreciable alteration in the size of the pulp chamber is a direct result of deposition of secondary dentin

§  Regular and uniform layer

·         **There is a sharp change in the direction of tubules at junction of primary and secondary

§  The tubules of secondary dentin are wavy

Ø  Reparative dentin

§  What indicates Trauma during Dentin Formation????

§  Forms in response to stimuli produced by carious penetration of a tooth

§  Formed very rapidly in response to irritants like attrition, abrasion, erosion, caries, etc.

§  The tubules of reparative dentin are twisted

Ø  Sclerotic dentin

§  From aging and slowly advancing dental caries

§  Tubules become obliterated, which blocks access of irritants

Ø  All the following are seen dentin except

§  Tomes granular layer, Odontoblastic processes, Stria of retzius, and contour lines of Owen

v  Cementum

Ø  Formed by cementoblasts from PDL, not from odontoblasts from pulp

Ø  Slightly softer and yellower (lighter yellow)

Ø  Most closely resembles bone, except no Haversian systems or blood vessels

Ø  Avascular, No innervation

Ø  Fxn

§  Compensates for tooth loss

§  Protects from resorption

§  Reparative fxn

Ø  50% Inorganic, 40% Organic, and 10% Water

Ø  Has the Highest Organic Content

§  Organic

·         Collagen and protein

Ø  More resistant to resorption than alveolar bone (permits ortho movement of teeth w/o resorption)

§  2 Types

·         Acellular

¨       No cells

¨       Coronal 2/3^rds

·         Cellular

¨       Contains cementoblasts, cememtocytes, fibroblasts from PDL and cementoclasts

¨       Apical 1/3^rd

¨       Thickest to compensate for attritional wear of the occlusal/incisal surface and passive eruption

§  Cementoid

·         Peripheral layer of developing cementum that is not calicified

v  Pulp

Ø  From Dental Papilla

Ø  Vascular and noncalcified

Ø  Composition

§  Cells

·         Fibroblasts (Majority)

·         Odontoblasts – no cementoblasts or ameloblasts

·         Histiocytes – fixed macrophages

·         Lymphocytes

·         Undifferentiated Mesenchymal cells (reparative fxn)

¨       NOT Adipocytes

§  Loose CT (collagen and reticular fibers – there are no elastic fibers in the pulp)

§  Blood vessels & nerves & lymph vessels

·         Blood flow is most like it is in the cranium

§  Ground Substance (water and long carbohydrate chains attached to protein backbones)

Ø  Large when tooth first erupts, then gets smaller (usually from progressive trauma)

§  The size of the pulp chambers of the maxillary first premolars usually decreases with age due to thermal shock; normal physiological & masticatory functions; excessive attrition and abrasion

§  The size of the pulp cavity within a tooth is influenced by the age of the tooth, parafunctional activity of the tooth, & history of the tooth (abrasion, erosion, caries, etc.) –

·         NOT related to sex

·         NOT related to ability of Ameloblasts to form dentin (duh, they don’t, odontoblasts do)

Ø  Function

§  The primary function of the dental pulp is to form dentin

§  Transmission of pain stimuli

§  Production of a defensive reaction when tooth is exposed to irritation

§  Does not cause formation of the mesenchyme of the dental papilla

§  Does not innervate the enamel

Ø  Anatomy of the pulp

§  Central zone Pulp proper or Pulp Chamber)

·         Pulp chamber

¨       The space occupied by the dental pulp w/in the tooth crown

¨       The pulp chamber of a mature tooth contains

Ø  Blood vessels and nerves

§  NOT Odontoblasts or enamel lining

§  Lined peripherally by a specialized odontogenic area which has the following zones (inner to outer):

·         Pulpal Core – similar to cell rich zone

·         Cell-rich zone – contains fibroblasts

·         Cell-free zone of Weil – capillary and nerve plexus (Plexus of Raschkow)

¨       Think Cell Free of Weil has to be next to odontoblasts for Sensory (Hydrodynamic)

·         Odontoblastic layer – contains odontoblasts and lies next to predentin and mature dentin

Ø  Pulp canals

§  Radicular pulp is continuous with tissues of the periapical area via the apical foramen

Ø  Accessory Pulp canals

§  May be found in the cervical third of the root

§  Contain nervous and vascular tissues

§  May be found in furcation areas of molars

§  Allow the pulp tissue to communicate with the PDL space

Ø  Pain

§  All stimuli to the pulp result in pain sensation (heat, cold, chemicals, touch)

§  Free nerve ending is only type of nerve in pulp, so regardless of source, you get pain

§  Contains both myelinated and unmyelinated nerve fibers

·         Myelinated – sensory

·         Unmyelinated – Motor (regulate size of vessel lumen)

¨       NOT to concerned with speed here

§  Afferent and sympathetic

§  Proprioception is NOT found in pulp

Ø  Pulp capping

§  More successful in young teeth because:

·         Apical foramen is large

·         More cells

·         Very vascular

·         Less fibrous elements

·         More tissue fluid

¨       BUT young pulp does lack a collateral circulation

§  Old pulp is more likely to have denticle or pulp stone

·         True denticle – complete with tubule and processes

·         False denticle – amorphous in structure – no dentin structure

·         Free denticle – unattached to outer pulpal wall

·         Attached denticle – attached at dentin-pulp interface