Oral Anatomy & Histology (Review: Outcome 7) Flashcards
Tooth Tissues
1) Enamel
2) Dentin
3) Pulp
4) Cementum
Where did enamel originated from?
Ectoderm
What type of cells was enamel formed by?
Ameloblasts
Why is enamel not a living tissue?
- Mature enamel does not contain cells that are capable of repair and regeneration
- No blood supply or nerves
Is enamel permeable or non-permeable?
Permeable
- allows for the exchange of ions
- demineralization and remineralization
Characteristics of enamel
1) Hardest tissue in the body
2) Composed of inorganic (mineral) and organic substance
3) Mature enamel
a) ~ 96% inorganic materials and 1% organic materials and 3% water
b) Main mineral component: Calcium hydroxyapatite
- found in lesser extents in dentin, cementum, and bone
- appears more radiopaque on radiograph
- other minerals present in smaller amounts: carbonate, magnesium, potassium, sodium, fluoride
How thick is enamel?
0.2 - 2.6 mm
- thick at the cusps of molar teeth (2.6mm)
- thinner at incisal edges
What is the colour of enamel?
- Translucent
- Colour varies: yellowish to grayish/bluish white
- Varies with age
What is the colour of enamel in primary teeth?
Whiter
- more opaque crystalline form
What is the colour of enamel in permanent teeth?
Yellowish-white to gray
- reflects underlying dentin
Lines of Retzius
Incremental lines
- represent the deposition of enamel during the formation of a tooth
- similar to growth rings of a tree
Hunter-Schreger bands
Alternating light and dark bands
- causes by enamel prisms changing direction
What is enamel composed of?
Enamel rods, also known as enamel prisms
What are enamel rods?
Also known as enamel prisms
- crystalline structural unit of enamel
- extend from the surface of the tooth to the DEJ
- grouped in rows and organized around the circumference of the long axis of the tooth
- rows are generally perpendicular to the surface of the tooth
Enamel rod structure
1) Rod sheath
- covering of the enamel rod
- acid resistant (hardest enamel structure)
2) Inter-rod substance (interprismatic substance)
- the material between the keyhole shaped enamel rods
- like a cement or glue
How do you think the arrangement of the enamel rods influences the penetration of decay? Do you think the rate of decay slows or increases once it reaches the dentin? Explain your answer.
- The enamel rods influences the penetration of decay (decay is going to follow the pattern of the rods)
- The rate of decay will increase because dentin is not as hard (not as mineralized)
What are enamel lamellae? Are enamel lamellae of
any clinical significance?
- Thin, leaflike structures that extend from the enamel surface toward the DEJ.
- Consist of organic material with little mineral content
- Little hypo-mineralization areas
- No clinical significance
What are enamel tufts? Is there any clinical
importance of enamel tufts?
- Appearance of tufts of grass.
- Enamel tufts are the hypocalcified or uncalcified
ends of groups of enamel prisms. - Start at the DEJ and may extend to the inner third of the enamel
- no clinical importance
What are enamel spindles? Is there any clinical
significance to enamel spindles?
The ends of odontoblasts (dentin-forming
cells) that extend across the DEJ a short distance into the enamel
- no clinical significance
What is the wear of enamel considered as when enamel is loss as a result from friction caused by excessive toothbrushing and use of abrasive toothpastes?
Abfraction
- V-shaped notched usually on the facial
Attrition
Hard tooth tissue loss caused by tooth-to-tooth contact during mastication or parafunctional habits
Abrasion
Enamel loss caused by friction from toothbrushing and/or toothpaste
Abfraction
Enamel loss from tensile and compressive forces during tooth flexure
- V-shaped notched
Erosion
Enamel loss through chemical means not involving bacteria
- Acid dissolves tooth away (food, beverage, acids from stomach that dissolves away tooth structure)
Where is Dentin located?
- Makes up bulk of a tooth
- Not clinically visible (usually covered by enamel or cementum; except attrition or abrasion of enamel or cementum)
Origin of Dentin
Ectoderm –> dental papilla –> mesenchyme cells
Is dentin a living tissue or non-living tissue?
Odontoblasts (dentin producing cells) are present throughout life of a tooth to continuously produce dentin
Is dentin harder or softer than enamel?
- Softer than enamel (less calcified)
- More flexible than enamel
- Less mineralized = more radiolucent on a radiograph
- Also harder than bone and cementum (resembles bone in physical and chemical properties)
What is dentin made up of?
70% - inorganic substance (hydroxyapatite crystals)
20% - organic substance (proteins)
10% - water
What is the colour of dentin?
Yellow
- Clinical colour of a tooth - can be seen through translucency of enamel
Dentinal Tubule
- Long tube running from DEJ/DCJ to pulp
- Least mineralized
- Contains odontoblastic process (provides nutrients to dentin)
- May play a role in pain sensation of tooth
What is the arrangement of dentinal tubule?
- Apex and cusp areas: straight and perpendicular to DEJ/DCJ
- Sides of tooth and top 1/2 of root: S-shaped
Dentinal Fluid
- Extravascular fluid which appears on the surface of freshly cut dentin
- Composed of mainly cytoplasm from odontoblastic process
Odontoblastic Process
- Long cellular extension of the cell inside the dentinal tubule
- Still attached to the cell body of the odontoblast in the pulp
Types of Dentin
1) Peritubular Dentin
- Walls of the dentinal tubules
2) Intertubular Dentin
- between the tubules
- bulk of dentin
Types of dentin by time of formation
1) Primary dentin: dentin formed BEFORE eruption, forms the bulk of tooth
- generally deposited evenly with regular pattern of tubules
2) Secondary dentin: formed AFTER eruption due to normal occlusal forces
- purpose: protects pulp
- formation: regular with mild deviation from original pathway
3) Tertiary (Reparative) dentin: formed IN RESPONSE TO TRAUMA
- purpose: protects pulp
- formation: irregular
Development of Dentin
Odontoblast (dentin producing cells)
- lay pre-dentin
- as it moves, it leaves part of its cell, causes cell wall to stretch and lengthen
- remains in pulp
- only odontoblastic process in mineralized tissue (tube)
If the outer layers of enamel are lost with aging,
such as with attrition. How is a clinician able to
differentiate between enamel and dentin?
Colour difference
- dentin is yellow, enamel is translucent
- dental stains (e.g. tobacco stain)
Do you think attrition in dentin would occur at the
same rate, faster or slower than that of enamel?
It would occur faster because dentin is not as hard as enamel (less calcified)
How can root dentin become exposed? What
surgical procedure may be performed to correct this
dentin root exposure?
Root dentin can become exposed by recession
- loss of gingiva, exposing tooth root
- cementum is very thin so it can be worn away easily
Where is the pulp located?
- Occupies pulp chamber in crown
- Occupies root canals in roots
- Enclosed by dentin
Development of pulp
- Comes from dental papilla
- It is the only non-mineralized tissue of a tooth
- Consists of blood vessels, lymph tissue and nerves
What types of cells are in the pulp?
1) Fibroblast cells
2) Odontoblasts
3) Histocyte cells
4) Lymphocytes
Fibroblast cells
- Predominant cell type in pulp
- Mesenchymal cells which become fibroblasts
- Responsible for the formation of intercellular substance in the pulp
Odontoblasts in the pulp
- Only the cell body is in the pulp (Odontoblastic process is in dentin)
- Originated from mesenchyme
—- produces dentin
—- dentin pulpal wall changes position over time (formation of secondary/reparative dentin and narrowing of the pulp)
Histocyte Cells
Start as undifferentiated mesenchymal cells
- localized around capillaries
- part of pulp’s defense mechanism (respond to injury)
Lymphocytes
- Localized around capillaries
- Specialized WBC
- Defense mechanism
(T-cells - defense)
(B-cells - antibodies)
Korff’s Fibers
- In intercellular substance
- Fibrous substance (appears as coiled rope)
- Mostly functional role: forms dentin matrix
Other components in the pulp
1) Blood vessels and lymphatic vessels
- supply oxygen and nutrients and take away CO2 waste
- plentiful in young pulp
- superior and inferior alveolar artery enter via apical foramen
2) Nerves
- 2nd division of Trigeminal nerve (sensation maxilla)
- 3rd division of Trigeminal nerve (sensation mandible)
Denticles (Pulp stones)
- Mineralized bodies of irregular rounded shape
- Location:
i. free in soft tissue of pulp
ii. attached to dentin surrounded by secondary dentin - Various shapes (size increases with age)
- Dental concerns: problems with endo treatment
- Never a source of infection
Diffuse mineralizations
- Known as false pulp stones
- Diffuse calcifications
- Small thin scatterings of calcified material
- Found in older teeth or those with root canals
- Usually of no clinical significance
What are the pulp zones?
1) Odontoblastic zone
- cell bodies of odontoblasts that line outer pulpal wall
- first line of defense (forms dentin - primary and secondary)
2) Cell Free Zone
- fewer cells than odontoblastic layer, but not 100% cell free
- buffer area
- movement area for other zones especially when secondary/reparative dentin is forming
3) Cell Rich Zone
- reservoir of undifferentiated cells (new odontoblasts, defense cells)
- extensive vascular system
- WBC for defense
Functions of the pulp
1) Formative - in development of tissues
- odontoblasts for forming dentin
- Korff’s fibers (fibrils in dentin) - forming ground substance/matrix for dentin
2) Sensory function
- nerve fibers in pulp (sensation of pain)
- nerves capable of pain only when stimulated
- sensation of pressure from nerves connected to the pulp from the PDL (nerves outside of tooth)
3) Nutritive function
- nutrients delivered from bloodstream
- supplies itself and odontoblast with nutrients
4) Defense function
- inflammatory response (if pulpal damage or irritants to the pulp)
- production of sclerotic dentin (calcium salts)
- production of reparative dentin (odontoblasts)
5) Vitality
- keeps the tooth alive
- keeps tooth enamel from becoming excessively brittle
(endodontic tooth - non vital - perfectly fine, but can become brittle over time)
