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28 Cards in this Set
- Front
- Back
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What are the tests for strength of materials?
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tensile strength
compressive strength shear strenth diametric strength flexural strength fatigue stress |
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Draw a typical stress vs strain graph
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has labels for elastic deformation and plastic deformation
label for Yield Point, UTS and Fracture Strength Label resilience and toughness Correct shape of the graph |
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what is the difference between BCC and FCC stress/strain graph?
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BCC shows slip
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which of BCC and FCC show clear distinctive Yield Point?
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BCC
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the yield point is the ____ at which ____ and ____ start to move
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stress
defects dislocations |
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Describe the properties of materials below YP
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stress is proportional to strain (Hooke's law)
always return to original shap when load is removed |
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the slope of the stress/strain is referred to as ____. It is a measure of ____
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Young's modulus
stiffness |
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what is resilience and how is it depicted in a stress/strain diagram?
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recoverable elastic work of deformation
the area under the elatic component |
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What is toughness and how is it depicted in a stress/strain diagram?
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the total energy required to break the material
total area under the graph until Fracture Strength |
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Define ductility
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strength of plastic range
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brittleness is the absence of ____ ____
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plastic flow
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what's the difference between engineering stress and true stress?
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engineering stress: force over x sectional area
true stress: during plastic flow, the x sectinoal area decreases thus increasing stress |
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draw typical stress/strain graphs for ceramic, aluminium, wax, brass
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all shapes are correct
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What is the significance of Young's modulus in dental materials?
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if it's less than that of tooth, chewing puts tensile forces on the adhesive interface.
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For what materials are compression testings done?
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brittle materials. eg plaster or cast-iron
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What strength test is used for GIC?
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diametrical testing
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Flexural strength is a combination of ____ and ____ strength
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tensile and compressible
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Is shear strength test reliable? Why or why not?
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No. because the orientation of the specimen with respect to its crystal structure will alter the results.
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What is fatigue strength and why is it important in dental materials?
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Ability to withstand cyclical loading (thousands of repetitions) which are within plastic deformation range. Affected by high stress concentration and impurities or bubbles during manufacture. Bridges must have good fatigue strength
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Explain the term Creep Resistance
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Ability to withstand plastic flow under its own weight or normal operational load at half of its melting point.
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What two dental materials exhibit creep?
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Wax and amalgam
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How does watersorption affect the materials? Give example
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water absorption usually cause breakdown of the parent material. eg composite
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How does erosion of materials occur?
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attrition due to fiction
collision of a 2nd abrasive medium with the parent material (eg food) |
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What are the 6 factors of biocompatibility?
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TTTMSL
Thermal expansion/contraction Coefficient thermal conductivity marginal integrity setting expansion/contraction toxicity leaching or corrosion |
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What are the factors involved in choosing materials for aesthetics?
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PTONRFM
ability to take polish translucence opacity natural colour ability to resist tarnish fluorescence metameric match |
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Explain the differences between direct and indirect restorations
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direct:directly into the mouth
indirect: involve impressions and the construction of a prosthesis followed by placement and gluing |
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What are the criteria for successful placement of direct restorative materials?
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-must be soft when first placed and then hardens
-setting/hardening cannot be exothermic and must take place at 37C -setting/hardening must take place in a reasonable time -sufficient strength must be attained during the clinic time -non toxic -aesthetic importance |
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What are the processes that comply with criteria for successful placement of direct restorative materials?
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amalgation
polymerisation cementation |
