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Flashcards in Dental Materials Deck (293)
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91

What is fatigue?

Failure of material at force well below static strength due to repeated force/strain cycles

92

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

93

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

94

What 4 things is wear a combination of?

1. Abrasive
2. Adhesive
3. Fatigue
4. Corrosive/erosive

95

Define abrasive wear

Materials against each other:
2 body: tooth-tooth
3 body: tooth-tooth w/ food stuff between

96

What is adhesive wear?

Material sticks to tooth and when pulled away removes part of tooth

97

What is fatigue wear?

Propagation and combining of micro-cracks w/ successive loading cycles

98

Define corrosive/erosive wear

Corrosive: acid attack remove weakened enamel
Erosive: grinding, bruxism

99

What is fluid flow governed by?

Strength of intermolecular forces and molecular entanglement

100

Define viscosity

Resistance to flow of a fluid
Measure of internal resistance of material

101

What is a Newtonian fluid?

Fluid in which applied shear stress produces flow w/ constant shear strain rate response

Water, solvents, mineral oils

102

What are non-Newtonian fluids?

Fluids in which there is no define viscosity
Viscosity changes with shear rate or shear rate history

103

What are the 5 types of non-Newtonian fluids?

1. Pseudoplastic
2. Dilatant
3. Viscoplastic
4. Thixotropy
5. Rheopexy

104

Define pseudoplastic fluids

Dec. viscosity as shear rate inc.
plaster, stone

105

Define dilatant fluids

Inc. viscosity as shear rate inc.
composites, porcelains in water

106

Define viscoplastic fluids

Will not flow until initial shear stress has been reached then can have Newtonian, pseudoplastic or dilatant properties

107

Define thrixotropic fluids

Viscosity dec. w/ time at constant shear rate
Ketchup, toothpaste, clays, quicksand

108

Define theopoxic fluids

Viscosity inc. w/ time at constant shear rate
Some lubricants, v rare

109

Define stress relaxation and creep

Relaxation: time dependent dec. in stress at constant strain
Creep: time dependent dec. in strain under constant load (stress)

110

What are the 7 types of adverse reactions?

1. Toxic
2. Irritant contact dermatitis
3. Allergic contact dermatitis
4. Oral lichenoid
5. Anaphylactoid
6. Contact urticaria
7. Intolerance

111

What are the 2 types of adverse effects?

1. Dermatoses
2. Non-dermatological

112

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

113

Describe allergic dermatose reactions

Acquired by contact w/ haptens in materials
Tissue develops antigens by contact w/ dermal protein
Next contact produces allergic response

114

Define haptens

In/organic molecule that alone is not antigenic but is when linked to carrier protein

115

What are some of the materials that can cause dermatose reactions?

Metals
Polymers/monomers
Hydroxyethyl methacrylate
Latex gloves
Formaldehyde
Eugenol
Disinfectants
Rubber dam: latex or nitrile

116

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

117

What effects can acute systemic toxicity have?

Primarily eyes and airway
Long term exposure lead to renal, neural, liver disorders

Associated with repeated dosage

118

How can mutagenic changes arise from materials?

Associated with chemicals in material
Result from breakdown of material

119

How do methacrylates affect the body?

Chronic toxicological effects
First respiratory problems then neurological disorders

120

How can mercury and nickel affect the body?

Mercury: short term memory loss, irritability
Nickel: carcinogenic