Dental Materials I Flashcards
What are chemically intimate mixtures of metallic and non-metallic elements which allow covalent or ionic bonding?
(includes dental porcelains, refractories)
Ceramics
What are long molecules composed of non-metallic elements and bonded covalently?
Polymers
*acrylics, waxes, cements
Physical mixtures of metals, ceramics, or polymers (including resins, ionomers, compomers, bonding agents, cements) are?
Composites
What is the structure of enamel?
96% Hydroxyapatite
Ca10(PO4)6(OH)2
What 2 structural units make up enamel?
Cylindrical Enamel rods
Interrod enamel
What is found around the Enamel Rod?
Rod sheath
- narrow space delineating rod and interrod enamel
- *keyhole shaped
What makes up the bulk of the Dentin?
Intertubular dentin
What is Intertubular Dentin made out of?
Collagen matrix embedded with hydroxyapatite
What lines the tubular walls in Dentin?
What is it made of?
Peritubular Dentin
Mostly hydroxyapatite crystals
T/F
Peritubular Dentin increases with age
True
What makes up 60% of Dentin?
Other 40%?
Intertubular dentin
Peritubular dentin
What are the 3 types of Primary bonds that serve as building blocks in dental materials?
Covalent
Ionic
Metallic
What are the strongest and simplest atomic building blocks?
Covalent bonds
shared electrons
What are the concerns of Biological properties of materials?
Toxicity and Sensitivity rxns
*occur locally or systemically
What type of liquid will readily spread over a high surface energy substrate?
Low Surface Energy
What is the measure of the affinity of a liquid for a solid as indicated by the spreading of a drop?
Wettability
The ability of a dissimilar substance to adhere to the surface of a solid is know as…
Adsorption
____ energy surfaces will adsorb molecules more readily than ____ energy surfaces.
High
Low
The diffusion of liquid into the solid material is known as…
Absorption
What is the best and most expensive biocompatability test?
Usage tests
Where is material placed in a Usage Test?
Identical to clinical use
in humans, etc
What may happen if a material doesn’t bond with sufficient strength to resist contraction upon polymerization, wear, or thermal cycling?
Microleakage
What causes microleakage?
Gap between tooth and restoration
*influx irritates pulp
What is the RDT - Remaining Dental Thickness minimum requirement for pulp protection?
0.5mm
How is Stress calculated?
Ratio of force per area
Name 5 types of stress.
Tension Compression Shear Torsion Bending
What is the definition of Strain?
Deformation caused by stress
What does the highest linear portion of a Stress Strain curve delineate?
Proportional Limit
What is the greatest stress sustained without permanent deformation?
Elastic Limit
What is the difference between Elastic and Plastic deformation?
Elastic is Non-permanent
Plastic rearranges molecules and is Permanent
The point on a stress strain curve at which material is no longer elastic and is being displaced in a plastic manner is called?
Yield Strength
What amount of permanent strain defines Yield Strength?
- 2%
- totally arbitrary
How can permanent deformation of dental material be bad?
Be good?
Filling moves - bad occlusion
Orthodontic wires bent - better movement
Where does Ultimate Strength occur on the Stress Strain graph?
At the top
*this is max stress
What defines the stress at which material fractures?
Fracture strength
T/F
Fracture strength and Ultimate strength are the same thing.
False
What is the deformation that results from the application of tensile stress?
Elongation
*expressed in %
A steep slope in the Stress Strain graph suggests:
High rigidity
High Elastic Modulus (E)
Elastic Modulus =
Stress / Strain
A flat slope, or a low Elastic Modulus indicates…
Flexibility
The higher the value of E, the ______ the material.
More rigid
How is Resilience measured?
Area under Elastic portion of Stress-Strain graph
How is Toughness measured?
Area under Elastic and Plastic portions of graph
What does Fracture Toughness refer to?
Toughness of materials with defects, cracks, or flaws
What materials are generally weakened by fractures?
Brittle
How is tensile stress measured in brittle materials?
Diametral Compression Test
Why will brittle materials have a short non-linear portion in a Stress-Strain graph?
The plastic response is small
*fractures
T/F
Material can’t be tough and brittle
True
Stress Strain graph for the following: Stiff Ductile Strong Tough
Lecture 2 Slide 30
Stress Strain graph
Stipp
Brittle
Strong
2;30
Stress Strain graph
Stiff
Ductile
Weak
2;30
Stress Strain graph
Stiff
Brittle
Weak
2;30
Stress Strain graph Flexible Ductile Strong Resilient
2;30
Stress Strain graph Flexible Brittle Strong Resilient
2;30
Stress Strain graph
Flexible
Ductile
Weak
2;30
Stress Strain graph
Flexible
Brittle
Weak
2;30
Something breaks after repeated loading is known as…
Fatigue Strength
If a material can be loaded an infinite number of times without failing, this is known as…
Endurance Limit
How fast something is loaded is known as…
Rate of Loading
*important for dentures
A material that is independent of loading rate is…
Elastic
Materials dependent on Loading Rate are know as…
Viscoelastic
What is the resistance of a fluid to flow?
Viscosity
What is the increase in strain of a material under constant stress?
Creep
What is important for polymers in thin sections and is dependent on the loading rate?
Tear Strength
