Quiz 1 Review Flashcards
what is the result of overdrying a preparation?
it can dessicate the dentinal tubules
in other words, it’s bad
pain can stimulate/increase ___
salivation
is esthetics an acceptable reason to do a full coverage zirconia crown?
yes
what is the appropriate method for caries removal?
slow speed with a large round bur and/or a hand instrument (spoon excavator)
what are the reduction measurements for a full zirconia crown preparation?
- occlusal reduction/clearance
- functional cusp: 1.5-2.0mm
- non-functional cusp: 1.5-2.0mm
- functional cusp bevel: 1.5-2.0mm
- axial reduction: 1.0mm at margin
what are the two typical margin types for a full zirconia crown preparation?
rounded shoulder or chamfer design
what is the target measurement of the margin above the gingiva?
0.5mm
what should the width of the non-functional cusp bevel be for a full coverage zirconia crown preparation?
about 1.0mm
for a full coverage zirconia crown preparation, all line and point angles should be ___
rounded
what is an undercut?
under-tapered preparation
what are the implications of an undercut?
- wasted chair time
- impression distortion
- difficulty with provisional
what are the 3 mechanical considerations for full coverage zirconia crown preparations?
- retention form
- resistance form
- anti-deformation form
*these are what keep the crown “fixed”
___ form prevents dislodgement of the restoration parallel to the path of insertion
retention form
what are the 4 factors that influence retention?
- magnitude of the dislodging forces (ex. caramel, taffy, gum, etc.)
- geometry of the tooth preparation
- roughness of intaglio (underside of fixed restoration) surface of fixed restoration
- material being cemented or bonded
geometrically speaking, what 3 things can increase retention?
- increased axial surface area
- increased preparation height
- decreased taper of axial walls (aka make walls more parallel)
the ideal axial wall taper is ___ degrees
6-10
what can increase intaglio surface roughness?
airborne particle abrasion (micro-etch) and acid etch with hydrofluoric acid
___ form prevents dislodgement of the restoration along a path other than the path of insertion
resistance form
this is resistance to tipping
which 3 factors influence resistance?
- magnitude and direction of dislodging forces
- geometry of the tooth preparation
- physical properties of the luting agent
what are 4 examples of factors that affect the magnitude and direction of dislodging forces?
- design occlusion to load tooth/implant axially
- parafunction
- habits (pipe smoking, nail biting, etc.)
- misuse of prosthesis
geometrically speaking, what are 5 things that can increase resistance?
- decreased preparation diameter
- decreased axial wall taper
- increased crown height
- proximal grooves and boxes
- definite line and point angles (not rounded) - remember that you want these rounded though…
what are 5 luting agent considerations that increase resistance?
- complete seating of restoration (decreased cement thickness)
- luting agents with increased compressive strength
- luting agents with increased modulus of elasticity
- chemically bonded restoration
- micro-mechanically bonded restoration
___ form prevents dislodgement of the restoration due to permanent deformation (bending) of the restoration during function
anti-deformation
what are 4 factors that influence deformation?
- material selection
- adequate tooth reduction
- proper occlusal or lingual concavity reduction form
- margin design
occlusal reduction creates ___ for strength, should conserve ___, should be uniform and follow ___ planes, and includes which 3 cusps?
- corrugated effect
- tooth structure
- cuspal planes
- functional cusp, non-functional cusp, and functional cusp bevel
alginate is a ___ impression material
irreversible hydrocolloid
is alginate expensive?
no, it is inexpensive
is alginate easy to use and manipulate?
yes
does alginate have a fast or slow set time?
fast
why is alginate not an appropriate impression material to create die models?
it is lacking in fine detail that is necessary to create die models
alginate impression material includes ___ which react with calcium to form ___
- sodium and potassium and other salts of alginic acid
- calcium alginate
what component of alginate is added to provide a source of calcium ions to cross-link the alginic acid?
calcium sulfate dihydrate
what component of alginate is added as a retarder and its concentration is adjusted to control set time?
sodium phosphate
___ is a naturally occurring hydrophilic colloidal polysaccharide obtained from brown seaweed
alginic acid
describe the sol-to-gel reaction of alginate impression material
- forms a sol when the powder is first added to water
- as the alginic acid becomes cross-linked via the calcium ions, the gel is formed (this is the set material)
the function of the ___ in alginate impression material is to dissolve in H2O and react with calcium
potassium alginate
the function of the ___ in alginate impression material is to react with potassium alginate to form an insoluble calcium alginate gel
calcium sulfate
the function of the ___ in alginate impression material is to counteract the inhibiting effect of the hydrocolloid on the fluoride, silicates, or borates setting of gypsum, giving a high quality surface to the die
potassium sulfate and potassium zinc
the function of the ___ in alginate impression material is to react preferentially with calcium ions to provide working time before gelation
sodium phosphate
the function of the ___ in alginate impression material is to control the consistency of the mixed alginate and the powder flexibility of the set impression
diatomaceous earth or silicate
the function of the ___ in alginate impression material is to make the powder dustless
organic glycols
the function of the ___ in alginate impression material is to produce a pleasant taste
wintergreen, peppermint, or anise
the function of the ___ in alginate impression material is to provide color
pigments
the function of the ___ in alginate impression material is to help in disinfection
disinfectants (quaternary ammonium salts and chlorhexidine)
how can you minimize permanent deformation of alginate impressions?
- use a quick snap motion when removing impressions - preferably in 5 seconds or less
- wait about 10 minutes before pouring to allow for elastic recovery
the space between the impression tray and the teeth allows for ___mm of alginate material
4-5
what happens to alginate impressions when they are exposed to air?
they lose water by evaporation and shrink
aka desiccation
what is the best method to prevent the desiccation of alginate?
either wrap them in a moist towel or disinfect in a plastic bag for 8-10 minutes, then pour immediately
what is imbibition?
the uptake of water by hydrocolloid when immersed in water, causing distortion
T or F:
you should never make an alginate impression if you cannot pour it immediately after (up to 10 minutes) the disinfection period
true
