L7: Enamel Structure & Biomechanical Properties Flashcards
What is the thickness of enamel?
Incisors: 0-2mm
Molars: 2.6mm
What is the microscopic structure of enamel?
Clusters of prisms containing around 1000 crystallites;
The prisms are then arranged in larger groups, with interprismatic enamel in-between
What is the difference between the crystal alignment in enamel and Dentine?
Enamel: anisotropic
Dentine: insotropic
Cross-sectional enamel has a _________ elastic modulus than surface enamel
Lower
The higher the load applied, the _______ the elastic modulus measured
Lower
What is the elastic modulus?
Stress over strain
Measures a substances resistance to being elastically deformed when a stress is applied to it
what is the visual representation of enamel?
grayish/bluish white
- appears yellowish white as it semi-translucent and reflects colour of underlying dentine
what is the thikness of the enamel of molars and incisors?
incisor: 2mm
molar: 2.6mm
enamel is selectively permeabe
T/F
T
water can travel through enamel at 4mm3 /cm2 /24hrs
microscopic properties of enamel
Clusters of needle-like crystals into prisms containing around 1000 crystallites
what type of enamel is found between enamel prisms?
Interprismatic enamel
What is used to identify the nanostructure of enamel?
Synchrotron x-ray diffraction
what does an anisotropic structure mean?
organised, oriented, direction of prisms
what does an isotropic structure mean?
having a property which has the same value in different directions
dentine has a isotropic/anisotropic structure?
isotropic
enamel has a isotropic/anisotropic structure?
anisotropic
what is fracture toughness
Fracture toughness is a quantitative way of expressing a material’s resistance to brittle fracture when a crack is present.
what does a high fracture toughness mean?
a high fracture toughness shows improved clinical performance and reliability
what happens to a tooth during a fracture?
Crack propagation and subsequent fracture leads to ultimate structural failure
what does a high crystallite thickness of enamel mean?
high stress resistance
how is the wear resistance of enamel increased?
Rods are oriented in a way to reduce wear by increasing hardness
what increases the fracture toughness of enamel?
Inter-rod structure to holt cracks
What is present around the enamel prisms?
A protein sheath
What is the function of a protein sheath?
1) protein macromolecule chains may deform (polymer-like behaviour)
2) Thermodynamically unstable therefore will return to initial form and position on release of load (elastic behaviour)
