Dental Materials Flashcards
Name the different sections of Dentin.
- Intertubular dentin: bulk of dentin-structureal comp. of hydroxyapatite w/ collagen
- Peritubular Dentin: lining of tubular walls, some organic matrix w/ much more apatite crystals
How is the outer layer of dentin different from the inner layer?
Outer Dentin: Near the DEJ, 20k tubules/mm2, .8 micro meters diameter
Inner Dentin: Near the PDJ, 58k tubules/mm2, 2.5-3.0 micro meters diameter
What is surface energy?
A measure of a molecule or atoms attraction inward toward its bulk
A Low surface energy will readily spread over a high surface energy substrate
What is the best factor for pulp protection?
Remaining Dentinal Thickness (RDT) - 0.5 mm minimum
What are 5 different types of stresses?
- Shearing: Forces directed parallel to e/o, not along the same straight line
- Tension/Elongation: forces directed away from e/o
- Compression/Shrinkage: Forces directed toward e/o
- Torsion: Twisting or rotational
- Bending: Two ends bending toward e/o
What is the difference between stress and strain?
Stress is when a force is applied to a constrained body, a resistance is developed which is equal in intensity and opposite direction. RATIO OF FORCE/AREA.
Strain is a DEFORMATION caused by stress measured as a %, deformation/length
What is the difference in bonds between metals, ceramics and polymers?
Metals: elements share valence electrons,”metallic bonds” among all the atoms in the solid
Ceramics: Chemically intimate mixtures of metallic and non-metallic elements which allow “covalent or ionic” bonding.
Polymers: Long molecules composed primarily of non-metallic elements (C,O,H,N) that are “covalently bonded”
What is the difference between plastic and elastic deformation?
Plastic deformation is permanent, where elastic is not permanent.
What are elastic materials?
They will return to their original form after a stress has been removed from them
What is creep?
It is the increase in strain in material under constant stress
What is the difference between Fatigue Strength and Endurance Limit?
FS: Is the stress at which a material fails under repeated loading. Depends on Magnitude and number of loadings.
EL: Is the stress at which the material can be loaded and infinite number of times w/o failing.
Explain the 6 stress curves.
Slide 28 “Properties of Materials”
What is toughness?
It is the resistance of a material to fracture.
**Combination of Yield Strength, Ultimate Strength, and strain. Increasing any of those will increase the toughness.
What is resilience?
It is the resistance of material to permanent deformation. The area under the elastic portion
Define the Elastic Modulus (E)
The measure of elasticity. Represents the stiffness of the material within the elastic region.
**The higher the value of E, the more stiff or rigid the material
What makes up tooth enamel?
- 96% inorganic hydroxyapatite
- Small organic matrix of glycoproteins (amelogenins & enamelins)
Why do materials fracture at less than their theoretical strength?
Defects within them weaken a material
Which properties characterize materials that have flaws or cracks in them?
Fracture toughness.
Defects generally weaken a material and may result in fractures at a stress well below yield stress,
What is the difference between yield strength, elastic limit and torsional?
Yield Strength: The stress at which the material begins to function in a “plastic” manner. Permanent strain has occurred.
Elastic limit: The greatest stress that can be sustained w/o permanent deformation
Torsional: Is the results in shear stress and a rotation of the specimen.
How can you increase the toughness of a material?
Increase yield strength, ultimate strength, and or strain
What is the Dimetral Compression Test?
It measures the tensile properties of brittle materials. Tensile stresses are produced as a cylinder is compressed by a load until fracture occurs
What is viscosity?
It is the resistance of a fluid to flow.
What type of reactions may have toxicity or sensitivity issues, and occur locally or systemically within associated tissues?
Biological
What is Adsorption?
Dissimilar substances in intimate contact with the surface of a solid = adhere
What is Absorption?
The uptake of a liquid by a bulk solid. The substance diffuses into the solid material.
What is a “Usage Test?”
Material is placed in a situation identical to its intended clinical use. In animals or humans. (Clinical trials)
What is Microleakage?
Materials may not bond with sufficient strength to resist contraction on polymerization, wear, or thermal cycling.
exp. Gap between tooth and restoration allows influx of materials that may irritate the pulp.
The greatest stress sustained without deviation from a linear proportionality of the stress and strain is _____________.
Proportional Limit
The greatest stress sustained without a permanent deformation is called _________.
Elastic Limit
True or False. Permanent deformation can be good, or bad in the oral cavity.
True. Destructive: fillings, crowns and bridges can be deformed causing improper occlusions.
Constructive: Orthodontic wires must be bent to retain shape. Partial clasps must be readjusted.
Name the two types of “Ultimate Strength.
Ultimate Tensile Strength (UTS) - max. stress that a material can withstand in tension
Ultimate Compression Strength (UCS)- max stress a material can withstand in compression
What is Fracture Strength?
The stress at which a brittle material fractures
What are Compressive Properties?
It compares materials that are brittle (amalgam, resin, cements, plaster, etc.)
**These materials have both elastic and plastic properties, but the plastic response is small. **
What is Viscoelasticity?
Is the RATE of loading. Materials with mechanical properties dependent on loading rate.
They have the properties of both elastic solids and viscous fluids.
What is Tear Strength?
A property of a material to resist tearing forces.
