Enamel & Amelogenesis Flashcards
Dentine is of ectomesenchymal origin. Enamel however, is from ectodermal origin. True or False?
True
Where would you find the thickest layer of enamel over teeth? Thinnist?
Thickest over cusps.
Thinnest over cervical region
What does Birefringent mean? What substance is birefringent?
Refracts light in different directions
Enamel
What would you expect to have lower translucency? Enamel from primary or permanent dentition?
primary
Enamel is resistant to abrasion, fractures, and cannot regenerate. It also has high tensile strength and is generally hard, but brittle.
True or false?
False, low tensile strength.
Rest is of the paragraph is true.
What are the benefits of a ground section vs demineralized section for observing enamel?
Ground section loses soft tissue, but you can actually see enamel.
Enamel is completly lost in demineralized sections.
What are the 3 prism patterns of enamel? Which one is predominant in humans?
Circular
Parallel
Keyhole
Keyhole for humans
What are hunter-schreger lines?
10-13 layers of prisms that follow the same direction with blocks below and above that follow different directions.
Prisms that are cut tranversely, known as diazones, show up are dark banding while the prisms that are cut longitudally, known as parazones, show up as white lines
Hunter Schreger Bands are useful because?
The complex pattern confers resistance to fracture
What part of enamel is most susceptible to fracturing?
The outer 1/3 layer. Hunter Schreger bands do not reach the outer 1/3 of enamel.
Where would you see gnarled enamel? What is it?
Enamel over cusps and incisal edges that appear to have some coiling of prisms
What is aprismatic enamel? Where do you usually see it?
90 degree angled crystallites from the surface that don’t have a prism structure. Usually see it in newly erupted teeth although it in on the outermost layer of enamel from both primary and perm dentition
What are incremental lines and how are they important?
During development changes in the enamel secretory rhythm, chemical composition and/or the position of the developing enamel front are recorded as incremental features.
Short period are cross striations 24 hour period
Long period are striae of retzius - weekly
SOR run obliquly down enamel
What is perikymata?
Ridges and drooves seen in perm teeth and cervical enamel of primary 2nd molars
What are these rings?
Striae of Retziuss (transverse section)
What are theses lines?
Striae of Retziuss (longitudinal section)
What is this?
Neonatal line
Surface enamel is prismatic. True or false?
False, aprismatic
What is the differences between Attrition, Abrasion, and Erosion?
Attrition caused by tooth to tooth
Abrasion caused by tooth to external object
Erosion caused by tooth to acid (not from caries)
What is the structure of the DEJ? How does it aid in the function of teeth?
Scallops and microscallops (convexity is towards enamel)
Fine dentine collagen fibrils overlay into enamel
Helps withstand shearing forces and limits crack propogation
What are enamel spindles?
Extensions of odontoblastic proccesses past the DEJ
What are enamel tufts?
Hypomineralized protein rich (tuftellin) areas of enamel. Same directions as prisms and only within inner third of enamel.
What are enamel lamellae?
Fault lines running through entire thickness of enamel.
Lamellae may arise developmentally due to incomplete maturation of groups of prisms (in which case they would contain enamel proteins) or after eruption as cracks produced during loading of enamel and containing saliva and oral debris.
Enamel’s modulus of elasticity is low which makes it brittle.
A) The statement is true but the reasoning is false
B) The statement is false but the reasoning is true
C) Both statement and reasoning is false
D) Both statement and reasoning is true
C
Modulus of elasticity is high (stiffness)
It’s brittle due to tensile strength being low
What are the five stages of amelogenesis?
Presecretory
Secretory
Transition
Maturation
Post Maturation
Ameloblasts can exist in different stages on a single tooth at one instant. True or false?
True
What happens in presecretory stage?
Redistribution of organelles (reversal of polarity)
Appearance of organelles
Columnar
Formation and resorption of basal lamina
What happens in secretory stage?
Secretion of enamel proteins – matrix deposition in the interpit prongs after dentine is formed
Tomes process is formed
Mutations in cell junction proteins during amelogensis are known to cause:
amelogenesis imperfecta
What happens in the transition stage?
Enamel secretion stops and matrix is removed
Cell organelles reduced
Ameloblast morphology and numbers change
What happens in the maturation stage?
Tome process disappears and organelles gather on distal end
Matrix and proteins are removed and calcium/phosphate/carbonate are moved in via ruffle ended section of ameloblast
What happens in enamel post maturation?
Flattening of ameloblast
Primary enamel cuticle seperates ameloblasts from enamel
Remnants of enaml organ merge with flat emeloblasts to form the reduced enamel epithelium (Nasmyth’s membrane) to protect the enamel during eruption
Which direction is enamal formed (mineralized)?
From cusp tips downwards along DEJ
First and last formed enamel is:
Aprismatic
What are some clinical importance of enamel formation?
Amelogenesis imperfecta
Fluorosis
Trauma
Medications
