Week3 Flashcards
What is the objective of restorative dentistry
To replace diseased or lost tooth structure; restore tooth for function and appearance
Dental materials in oral environment must be? (6)
Biocompatible
Durable
Nonreactive in acid or alkaline conditions
Compatible with other materials
Esthetically acceptable
Tolerable to differing temp & forces
Dental materials are classified by their use which includes (3)
Preventive/ therapeutic materials
Restorative materials
Auxiliary materials
What are examples of preventive /therapeutic materials
Pit and fissure sealants
Mouth guards
Fluoride
What is a direct restoration
Placed immediately and directly into the prepared tooth in a pliable state then sets to harden
What is an indirect restoration
Customized tooth replacements, fabricated in the lab
What are examples of auxiliary materials
Impression materials
Gypsum
Dental waxes
Finishing and polishing materials
What is a nickel allergy
Adverse response from breakdown of the materials components (nickel) in oral environment
What is force
Push pull or twist or a combination of these
What is stress
The force (weight) applied at the surface will create stress within the object that tries to resist the weight
What is strain
The amount of change that the force has produced on the object
What is normal Masticatory forces on the occlusal surface of molar teeth
28,000 lbs/square inch on a cusp tip
What are the 3 basic types of forces
Compressive (pushing together)
Tensile (pulls and stretches)
Shearing (slice apart)
Compressive forces deal with which teeth
Posterior teeth
Torsion force is aka
Torque
Describe torsion force (torque)
Twisting force that has tensile and compressive forces
-descriptive of normal Masticatory events
What is flexural stress
Bending stress
Combo of tension and compression
What is more likely to fracture under compressive stresses
Porcelain
Desirable materials should have ___ solubility
Low solubility
What are examples of materials with low solubility
Gold and porcelain
What is galvanism
Phenomenon of electrical current being transmitted between two dissimilar metals
What is the current that may result in stimulation to the pulp
Galvanic shock
What are excellent thermal conductors
Metals
What are poor thermal conductors
Non metals (ceramics, composite resins)
Dental materials in the mouth are subjected to temperature changes which can result in
Thermal expansion
If the thermal expansion of the restoration does not match the expansion of the tooth what may occur
Microleakage
What is percolation
The space between the tooth and the restoration
What is interface
The space between the walls of the preparation and the restoration
Mechanical retention involves the use of
Undercuts or other projections into which the material is locked in place
The surface of composite resins may have
A rougher surface than enamel
What aids in the identification/detection of restorative materials
Illumination and air
For a restorative material to function properly it must be (3)
Hard (hardness)
Strong (yield strength)
Stiff (modulus)
What are the three basic forms that materials may take on
Solid
Liquid
Gas
What is a defining characteristic of a solid
Is has shape and volume
If the pattern are arranged in a random form with no pattern the solid is less
Stable (amorphous)
The denser the material is the less
Air or spacing there is between atoms
Which tooth structure is described as being the most dense
Enamel
Which restorative material is classified as being the most dense
Gold
Hardness is used to define a materials resistance to
Wear and abrasion
Tooth structure and biomaterial that are classified as the hardest materials and more resistant to being scratched
Enamel
Porcelain
What tests can be done to test hardness
Knoop test
Rockwell test
What is ultimate strength
Max amount of stress a material can withstand without breaking
If the deformation is not permanent and the material recovers from the force completely then
It has good elasticity
What is stiffness and what is it measured by
Resistance to deformation of a biomaterial and is measured by young’s elastic modulus
Suffer materials have a _____ modulus
Higher
High value (modulus elastic value) indicates that the material is
Very rigid (enamel)
Low value (modulus elastic value) indicates the material is
Flexible
What is proportional limit
The greatest stress a structure can withstand without permanent deformation
When stress exceeds this point called the proportional limit the object
Does not return to its original shape
What is resilience
Example?
The resistance of a biomaterial to permanently deform
(Ortho arch wire)
What is toughness
Ability of a biomaterial to resist fracture
What is malleability
Ability for a material to be compressed without breaking
Ductility is the
Amount of dimensional change a material can withstand without breaking
-materials with poor ductility are classified as brittle
What is fatigue in terms of dental materials
Occurs within a material when it is subjected to repeat stresses; can result in sudden failure or fracture of the material
Viscosity refers to
The resistance of a liquid to flow
Thin fluids have
Low viscosity
Thick fluid have
High viscosity
The viscosity of a liquid usually _____ as the temp increases
Decreases
What are thixotropic materials
Liquids that flow more easily under mechanical forces
(Ex. Fluoride gel)
What are examples of direct restorations
Amalgam
Composite
Sealants
What are examples of indirect restorations
Inlays
Onlays
Crowns
Bridges
Implants
What is the manipulation stage
Mixing and working time
What is reaction stage
Initial and final set
Mixing time refers to
Length of time from beginning of mixing time to the beginning of working time
Working time refers to
Time permitted to manipulate the material in the mouth
Initial set time refers to
Time begins when the dental material no longer can be manipulated in the mouth
Final set time refers to
Material has reached its ultimate state
High temperatures and humidity will accelerate the
Reaction of the material
