Flashcards in Dental Materials Deck (293)
What is fatigue?
Failure of material at force well below static strength due to repeated force/strain cycles
Define fatigue life, strength and limit
Life: number of cycles to cause failure at specified stress
Strength: level of stress at which failure will occur after specified number of cycles
Limit: level of stress below which fatigue failure will not occur
What is static fatigue?
Failure of material at small load after period of constant loading
Load required to cause failure will dec. w/ inc. time loading
What 4 things is wear a combination of?
Define abrasive wear
Materials against each other:
2 body: tooth-tooth
3 body: tooth-tooth w/ food stuff between
What is adhesive wear?
Material sticks to tooth and when pulled away removes part of tooth
What is fatigue wear?
Propagation and combining of micro-cracks w/ successive loading cycles
Define corrosive/erosive wear
Corrosive: acid attack remove weakened enamel
Erosive: grinding, bruxism
What is fluid flow governed by?
Strength of intermolecular forces and molecular entanglement
Resistance to flow of a fluid
Measure of internal resistance of material
What is a Newtonian fluid?
Fluid in which applied shear stress produces flow w/ constant shear strain rate response
Water, solvents, mineral oils
What are non-Newtonian fluids?
Fluids in which there is no define viscosity
Viscosity changes with shear rate or shear rate history
What are the 5 types of non-Newtonian fluids?
Define pseudoplastic fluids
Dec. viscosity as shear rate inc.
Define dilatant fluids
Inc. viscosity as shear rate inc.
composites, porcelains in water
Define viscoplastic fluids
Will not flow until initial shear stress has been reached then can have Newtonian, pseudoplastic or dilatant properties
Define thrixotropic fluids
Viscosity dec. w/ time at constant shear rate
Ketchup, toothpaste, clays, quicksand
Define theopoxic fluids
Viscosity inc. w/ time at constant shear rate
Some lubricants, v rare
Define stress relaxation and creep
Relaxation: time dependent dec. in stress at constant strain
Creep: time dependent dec. in strain under constant load (stress)
What are the 7 types of adverse reactions?
2. Irritant contact dermatitis
3. Allergic contact dermatitis
4. Oral lichenoid
6. Contact urticaria
What are the 2 types of adverse effects?
Describe irritant dermatose reaction
May be of acute toxic nature causing direct and immediate cytotoxic effects to skin cells
Cumulative dermatitis is from repeated contact w/ chemical agent at sub-toxic conc
Localised and restricted to the area of exposure
Describe allergic dermatose reactions
Acquired by contact w/ haptens in materials
Tissue develops antigens by contact w/ dermal protein
Next contact produces allergic response
In/organic molecule that alone is not antigenic but is when linked to carrier protein
What are some of the materials that can cause dermatose reactions?
Rubber dam: latex or nitrile
What is sodium hypochlorite and its risk?
Disinfectant used for irrigation in RCT
Can cause pain if introduced into periapical tissue, periapical bleeding and extensive swelling
What effects can acute systemic toxicity have?
Primarily eyes and airway
Long term exposure lead to renal, neural, liver disorders
Associated with repeated dosage
How can mutagenic changes arise from materials?
Associated with chemicals in material
Result from breakdown of material
How do methacrylates affect the body?
Chronic toxicological effects
First respiratory problems then neurological disorders