Enamel Tissue Flashcards
T/F - Enamel is the hardest of the 4 mineralized tissues of the body
True
T/F - All 4 mineralized tissues of the body are connective tissue
False - Enamel is NOT a connective tissue
T/F - All mineralized tissues have a partially mineralized (immature) stage, and a fully mineralized (mature) stage
False - Enamel is the only mineralized tissue that goes through an immature stage….the other 3 go from unmineralized to mineralized (never partially mineralized)
T/F - Enamel formation is finite
True - Ameloblasts complete its enamel formative cycle once the thickness of enamel is reached at a site
What is the first appearing mineralized tissue in a developing tooth? What is second?
Dentin is first
Enamel is second
What is lacking in enamel?
Enclosed cells (acellular) Nerves (aneural) Blood vessels (avascular) Lymph vessels (alymphatic)
What tissue in a tooth contains enclosed cells, nerves, blood vessels, and lymph vessels?
Pulp
Enamel definition
A composite biological mineral with apatite crystals oriented in a complex, three-dimensional pattern
Hardness of enamel
5 on Moh’s scale - comparable to mild steel
Can withstand both shearing and impact forces well
Brittle without dentin support
Enamel translucency
Hue depends on location, surface condition of enamel, attraction to stain substances, and age changes
What is required for enamel to maintain its integrity?
A wet environement
Attrition
Normal, slow wearing of tooth substances under the stress of mastication
Abrasion
Abnormal wearing of tooth substance from extraoral substances (toothpick)
Erosion
Abnormal wearing of tooth substances from acid
Microporosity of enamel
The pathway for diffusion of small molecules such as water
Electrochemical effects on pore walls lead to carious lesions
Remineralization of enamel
Mineral is returned to the molecular structure of enamel by the way of saliva
When demineralization exceeds remineralization, cavitation occurs
Inorganic substances of enamel
96% of enamel by weight
Hydroxyapatite crystals - principle component is calcium hydroxyapatite
How do enamel crystals compare to other mineralized tissues?
Enamel crystals are larger and consist of more impurities (fluoride, carbide)
Organic substances of enamel
1% by weight
What are the types of proteins unique to enamel?
Amelogenin and non-amelogenin
What are some non-amelogenin proteins
Enamelin
Amelin
Tuftelin
What is the most prominent organic substance of enamel?
Amelogenin - a seed protein for normal mineralization
Enamel protein arrangement
Arranged in a lace-like patern throughout the volume of enamel and clsoesly associated with the surface of the crystals
Enamel is the only mineralized tissue that does not contain what?
Collagen fibers
Water in enamel
3% of weight
Distributed throughout the volume of enamel by the way of micropores between crystals and proteins
Most of the water forms a hydration shell around the crystals
What is the clinical importance of water to the enamel?
- Provides a route for fluoride ions, calcum, and phosphorous ions for remineralization
- Provides distribution for whitening substances, artificial, and natural substances
- Provides distribution for acidophilic microorganisms, age changes, etc
Age changes to enamel
Enamel wears slowly (attrition) Color darkens Composition of surface changes Fluoride increases at the surface Porosity is reduced Less susceptible to caries Subject to changes due to systemic age changes
What are the different CEJ relationships?
Cementum overlaps enamel (most common)
Cementum meets enamel
Cementum does not meet enamel (least common)
What is the clinical significance of CEJ relationship?
The CEJ relationships vary around the tooth and form tooth to tooth
DEJ configuration at the coronal area
Scalloped to help adapt to withstand occlusal forces
DEJ configuration at cervical areas
Smooth - these are non-load bearing areas
Formation of enamel
Inner epithelial cells of enamel organ differentiate into ameloblasts (columnar epithelial cells)
Line of Retzius
Growth lines that go from the DEJ coronally
They end on the enamel surface as grooves/ridges called Perikymata
Perikymata
Numerous small transverse ridges on the exposed surfaces of enamel
Surface manifestations of lines of Retzius
Anthrpologists uses these to determine the age and origin of specimins
Hunter-Schrager bands
Alternating dark and light bands of varying width
Originate at the DEJ border and pass outward ending at some distance from the outer enamel surface
What causes Hunter-Schrager bands
Different direction of enamel rods in adjacent layers
-the change in rod direction is a functional adaptation that minimizes the risk of cleavage in the axial direction under the influence of masticatory forces
What is the clinical significance of Hunter-Schrager bands
Whe performin operative dentistry, need to be mindful of the direction the rods are going so we don’t leave anything unsupported
What is the main structural unit of enamel
Enamel rods
Enamel rods size
Diameter = 5-6um Length = up to 2.5mm
What is the structure of enamel rods
Hydroxyapatite crystals densely packed a core of the rod and run parallel to the long axis of the rod
Built of segments separated by dark lines that give it a striated apperance
What forms one rod?
One ameloblast
What causes the enamel rods to be segmented?
Rods are secreted in a rhythmic manner
-there is a rest period of an ameloblast marked by an interrod striation
Striations
The dark lines that segment the enamel rods
Enamel sheath
Outer surface of the enamel rod
Crystals are less dense than the core and run in a different direction
Here, the highest percentage of organic material is amelin
Interrod substance
Between the sheaths of the rods
Crystals are more dense and run at different directions than those of the sheath (still less dense than core)
Two or more ameloblasts contribute to the secretion of interrod substance
What are the different types of hypomineralized enamel structures?
Enamel lamella
Enamel tuft
Enamel spindle
Enamel lamella
Originate from the coronal surface of the enamel and extend for varying depths
Consist of longitudinally oriented defects with enamel protein or organic debris form the oral cavity
Enamel lamella clinical significance
Can create access of acidophilic organisms (caries) and stain substances (esthetic considerations)
Enamel tuft
Tufts project from the dentinoenamel junction for a short distance into the enamel and contain a greater concentraiton of enamel protein (tuftelin)
Enamel tuft clinical significance
Contributes to the spread of caries at the DEJ
Enamel spindle
Extend from the dentin, across the DEJ, into the enamel for a short distance
Dentin forms first with processes that go past the DEJ, and some of these processes get stuck between forming enamel rods
Enamel spindle clinical significance
Contributes to the spread of caries along the DEJ
