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64 Cards in this Set
- Front
- Back
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WHo oversees the Accredited Standards Committee (ASC) MD 156 of ANSI?
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The ADA Council of Scientific Affairs
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What is the ADA seal of acceptance?
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It is a voluntary accrediation process for consumer products only
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Where are the MSDS forms for dental material used at UNLV SDM located?
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On SDMnet, under emergency Info/MSDS
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What are the publications that evaluate dental materials?
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The Clinician's Report, the Dental Advisor, USAF DECS, ADA Professional Product Review, and Reality
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What kind of bonding do polymers exhibit?
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Covalent bonding of carbon atoms
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What is chelation in regards to bonding?
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It is a chemical compound that has bonds emanating from two places in the molecule towards a single atom. The bonds may be primary, secondary, or a combination
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Are most materials stronger under compression or tension?
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Most are stronger under compression because the energy-distance curve is steeper as atoms get closer
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Physical characteristic of harder materials
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THey usually have a higher melting temperature and have covalent or ionic bonds usually
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Physical characteristic of soft materials
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They have low melting temperatures and often considerable secondary bonding
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What is the glass transition temperature (Tg)?
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The point where a solidifying material first becomes a rigid mass.
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What is stress?
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A materials resistance to an applied force (=force/area)
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What is strain?
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It is a measure of the amount of deformation that takes place when force is applied (=change in length/original length)
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What is the proportional limit?
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It is the maximum stress at which the stress-strain graph deviates from linearity (this is the limit of elastic deformation)
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What is yield strength?
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It is the stress at which a small amount of permanent (plastic) strain occurs
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What is Young's modulus (modulus of elasticity)?
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It is the stiffness of a material within the elastic range (=stress/strain). A high modulus indicates a stiff material
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Young's modulus (elasticity) of dentin and enamel?
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Enamel is 84.1 and dentin is 18.3
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What is ductility?
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The ability of a material to withstand permanent deformation under tensile load without fracturing (ability to stretch it out)
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What is malleability?
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The ability of a material to withstand permanent deformation under pressure (can be pounded or pressed into a sheet)
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What is resilience?
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The energy absorbed by a material undergoing elastic deformation or the resistance of the material to permanent deformation.
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What is toughness?
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The energy required to break a material
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What is a viscoelastic material?
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They have mechanical properties dependent on loading rate and have characteristics of both elastic solids and viscous fluids
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What is viscosity?
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It is defined graphically as the shear stress/shear strain rate. High viscosity material have low shear strain rate for high shear stress.
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What are newtonian fluids?
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The viscosity remains constant with increasing shear stress (mixing). Its a linear relationship. Water is an example of a newtonian fluid
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What are pseudoplastic fluids?
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The viscosity decreases (thinning) with an increase in shear stress (mixing). Example is flouride gels, paint, and some impression materials
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What are dilatent fluids?
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The viscosity increases (thickening) with an increase in shear stress (mixing). Example is starch
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What are plastic fluids?
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No flow occurs until a minimum shear stress threshold is reached. Example is ketchup
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What is thixotropy?
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A decrease in viscosity under constant shear rate. Example is zinc polycarboxylate cement
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What is rheopexy?
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An increase in viscosity under constant shear rate. Example is inceram porcelain
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Which restorative material is most subject to creep?
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Amalgam, due to its components with melting temps just above body temp
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What is fatigue?
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Fracture of a material after repeated loads below the elastic limit
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What are the wavelength limits of visible light?
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400nm is blue light and 700nm is red light.
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What is metamerism?
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When objects appear to match under one light source but appear different under another light
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What is the spectral power distribution of cool white light (daylight fluorescent)?
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Green-yellowish
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What does hue refer to?
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The color of an object
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What does value refer to?
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The darkness to lightness of a color. High values are light and low values are dark
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What does chroma refer to?
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The intensity of a color (bright or dull)
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What chemicals are used as colorants in porcelain?
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Metal oxides
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Define contrast ratio
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It is a measure of light transmission (opacity) against a black and a white background
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What is the effect of surface finish on color?
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Rough surfaces reflect more white light that mixes with the reflection of the colored object-increasing value and decreasing chroma
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Effect of polishing composite
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More light will penetrate the surface and value will decrease and chroma will increase
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What is the CIE?
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The International Commission on Illumination (CIE). THey developed standards for defining colors.
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What is metamerism?
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When objects appear to match under one light source but appear different under another light
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What is the spectral power distribution of cool white light (daylight fluorescent)?
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Green-yellowish
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What does hue refer to?
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The color of an object
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What does value refer to?
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The darkness to lightness of a color. High values are light and low values are dark
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What does chroma refer to?
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The intensity of a color (bright or dull)
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What does the L in CIE L*a*b* represent?
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Lightness to darkness (value). L=100 is white, L=0 is black
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What does the a* in CIE L*a*b* represent?
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Green to red. -a=green and +a=red
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What does the b* in CIE L*a*b* represent?
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Blue to yellow. -b=blue and +b=yellow
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When would you use the Vitapan classical shade guide?
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For all-porcelain and PFM crowns and some resin based composite
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What are the A shades?
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Reddish-brownish
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What are the B shades?
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Reddish-yellowish
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What are the C shades?
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Grayish
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What are the D shades?
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Reddish-gray
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How do you proceed in obtaining a shade match?
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Get the value first, then chroma, then hue.
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What is the effect of curing on final shade?
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It makes most shades become more translucent
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What is the difference between surface energy and surface tension?
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Surface energy is applied to solids and surface tension applies to liquids
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Define surface tension
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The amount of work required to increase the surface area of the liquid
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Relationship between surface free energy and wetting
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The higher the surface energy, the more easily the surface will be wetted.
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Relationship of contact angle and wetting
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The greater the contact angle, the lower the degree of wetting (due to lower surface free energy)
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Relationship between liquid surface tension and wetting
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The lower the liquids surface tension, the more easily it will wet a surface
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What is adsorption?
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The concentration of atoms at the surface of a solid or liquid. Higher energy surfaces will attract more mobile atoms
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How do surfactants work?
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They decrease the work required to increase the interfacial area, resulting in a decrease in surface tension (which facilitates wetting)
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What are the conditions for good adhesion?
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Close contact between adhesive and adherend surface molecules, minimal stress concentrations at the interface (it needs to be clean), thin adhesive film thickness, rough bonding surfaces to increase area,
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