6/16 - Wax Patterns, Investing and Casting, 343-360, 363-376, S4a-S4c Flashcards
T/F: definitive restoration can be no better than wax pattern
TRUE
can a few extra minutes spent on the wax pattern save hours correcting the casting
YES
direct technique vs. indirect
direct: in patient mouth
indirect: outside patient mouth
which technique allows for better visualization and ready access to waxing the margin
indirect
which technique is the most popular technique: direct or indirect
indirect
Is type I wax direct or indirect
direct
is type II “inlay” wawax direct or indirect
indirect
what colors of wax should you use for wax up
red, green or blue
can you leave the pattern of the die on for long periods of time
NEVER
when should you invest the pattern
immediately after fabrication
what is a thin layer of wax resembling a thimble that is fabricated on the die to serve as a foundation for the final wax up
wax coping
how do you being wax up
lubricate the die and dip into molten wax (head start)
OR
begin without dipping
how to start building wax pattern
- begin with proximal contacts
- proximal surface should be mirror image of prox surface
- continue with axial contours
- lingual embrasures slightly larger than facial embrasures
what is the part of the axial contour that extends from the base of the gingival sulcus past the free margin of the gingiva
emergence profile
what extends to HOC, allows for effective oral hygiene, easier to evaluate with a periodontal probe
emergence profile
___ leads to inflammation, ___ leads to no significant changes
overcontour; undercontour
is is better to undercontour than overcontour
undercontour
when can you start waxing up occlusal surface
after building axial surfaces
what does max mesiopalatal cusp of first molar occlude
cusp-fossa: central fossa of first molar
cusp-marginal ridge: central fossa of the first molar
___ cusps placed as far lingually as possible and as far apart as possible
lingual
___ cusps are shorter than ___ cusps
lingual; facial
should you put excess wax on margins
YES
should you use a sharp instrument to remove excess wax from margin
NO! carving and burnishing
do you want highly polished wax up
not necessary, just need an extremely smooth surface
should you place a thin layer of cyanoacrylate over the whole prep? why?
YES! this harden the die and acts as a spacer
where should you place die lube on cast
EVERYWHERE you don’t want the wax to stick
what angle should the sprue be placed on wax up
45 degrees
when placing wax up inside the investing place
wax up should be slightly off center
should you use water to mix with CERAFINA?
NO! use special liquid Smoothex??
surrounding the wax pattern with a material that can accurately duplicate its shape
investing
removal of the wax pattern so that a mold is created into which molten alloy can be placed/forced
burnout
introducing the molten alloy into the previously prepared mold
casting
who is the person that introduced the lost wax technique
Taggart 1906
what alludes to the cost of the metal
precious
what refers to how the metal behaves chemically
noble
what pertains to the purity of the metal
Karat
what metals are resistant to corosion and oxidation in moist air
noble metal
examples of noble metals
- gold
- silver
- copper
- platinum
what are rare, naturally occurring and highly valuable metals
precious metal
examples of precious metals
- gold, palladium and platinum
- silver (less expensive but still rare so precious
what metals are both noble and precious
gold, silver, platinum, and palladium
how to calculate Karats
24x mass of gold/ total mass
e.g. 50% gold alloy = 12 karat
50/100 = K/24
K=12
dental alloys are identified by the ___ content
gold
noble metals impart what?
tarnish resistance and ductility
___ lightens color and gives some noble qualities without increasing cost too much
silver
___ adds hardness and strength
copper
what must have a composition that is over 60% noble metal of which over 40% must be gold
high noble alloys
what must have at least 25% noble metal
noble alloys
what has less than 25% noble metal (often called base metal)
non-noble metals
chromium-cobalt and nickel-chromium are examples of what type of metal
non-noble(non-precious)
what are dental casting alloys? which one is cancer causing
- nickel
- beryllium - cancer causing
- titanium (non-noble)
what are characteristics of investment materials
- must precisely reproduce detailed form of wax pattern
- must provide sufficient strength to withstand the heat of burnout and casting of metal
- must expand sufficiently to compensate for solidification shrinkage of alloy
gold alloys shrink ___% and nickel-chromium alloys shrink ___% upon solidification
1.5, 2.4
how can you compensate for solidification shrinkage
expanding the mold
types of expansions
- setting expansion
- hygroscopic expansion
- wax pattern expansion
- thermal expansion
what type of expansion:
- occurs by crystal growth of investment
- 0.4%
setting expansion
what type of expansion:
- letting investment set in a 100 degree water bath
- 1.2%-2.2%
- expansion occurs due to expansion of wax pattern caused by increased temperature of water
hygroscopic expansion
what type of expansion:
low-temp burnout allows for wax expansion
wax pattern expansion
what type of expansion:
- investment expands when heated in the open
- high temp burnout method compensates for entire alloy shrinkage
thermal expansion
what does sprue former attach to
one end to wax pattern, the other end to crucible former
the channel left after the burnout is called what
the sprue
what is the sprue made of
10 or 12 gauge and made of wax, plastic or metal
where is the sprue former atached to wax pattern
at area of greatest bulk
how is the sprue attached
at a angle to allow free flow of molten metal (minimal turbulence)
Cera-Fina phosphate-bonded investments = __ degrees F
<1975
how many mm from wax pattern to top of device
6 mm
what is the name of the ring liner in the crucible
Kaolin liner (wet)
how to invest
- wet liner after it is placed into the ring
- vacuum mix is a must
- connect the tubing
- hand mix initially to incorporate liquid into the powder
- follow instructions for machine mixing
why must you vacuum mix cera fina
hand mixing = 3X the amount of nodules
what does burnout do
prepare the mold for molten alloy and allows for thermal expansion
do you use the high temp technique or low temp technique for burnout
either
steps for burnout and casting
- use high temp or low temp technique
- use low temp technique if hygroscopic expansion(water bath) was used
- remove the crucible former and place into over
- gas-air torch
- wind the arm, place ingots, melt the metal, place the ring into cradle
- pull back on the arm and let go
how to clear the casting
- do not quench base metal castings (put in water)
- remove excess investment with hammer then a handpiece
- sandblaster will remove the last bit of investment air abrade the surface
- do not pickle base metal castings (soak in hot acid)
what are parts of the casting machine
- cradle
- crucible
- pin
- handle
- counterweight
what happened when one large nodule is present on metal
air trapped during investing
what happened when there are multiple random nodules on metal
inadequate vacuum during mixing
what happened when there are nodules on underside only on metal
prolonged vibration after pouring
what happened if there is a shrink spot porosity on metal
sprue attachment too bulky. sprue too long or thing. button too small
what happened if theres random porosity on metal
dirt in wax pattern. loose particles of investment from sharp edge
what happened if there are fins on metal
dropped ring, rapid heating of wet or unhardened mold, liner flush with end of ring, excessive casting forces
what happened if there are short rounded margins with rounded or lumpy button on metal
alloy not hot enough or insufficient casting forces
what happened if theree are short, rounded margins with sharp button on metal
pattern too far from end of ring or if casting is shiny, incomplete burnout of wax
what happened if the metal has black, rough casting
breakdown of investment from excessive heat
T/F: quenching (put in water) of the investment should not be done because it makes it harder to remove the investment
TRUE
it may be necessary to remove the wax ___ mm from the marginal periphery of the pattern to ensure that it will seat all the way on the working cast
1 mm
which teeth have a lingual prominence of 0.5 mm
maxillary teeth and mandibular first premolars
which teeth have a lingual prominence of 0.75 mm
mandibular second premolars
which teeth have a lingual prominence of 1.0 mm
mandibular molars
is rexillium III precious or non-precious
non-precious (nickel-chrominum base)
rexillium contains ___% of beryllium
1.8
what non-precious alloy has an outstanding bond strength and is equivalent to precious ceramic alloys
rexillium III
