Quiz 2 Flashcards
1
Q
what is the consistency of type 1 inlay wax?
A
medium to hard
2
Q
what is type 1 inlay wax used for?
A
generally used with the direct technique for making patterns in the oral cavity
3
Q
what temperature is type 1 inlay wax solid at?
A
37 degrees celcius
4
Q
between type 1 and type 2 inlay wax, which shrinks more?
A
type 1 shrinks more than type 2
5
Q
what is the consistency of type 2 inlay wax?
A
softer than type 1
6
Q
what is type 2 inlay wax used for?
A
more commonly used in the indirect technique
7
Q
what temperature is type 2 inlay wax solid at?
A
25 degrees celcius
8
Q
what is “suck-back”? how can a reservoir help avoid suck-back?
A
- can happen during casting of gold crowns
- cools last at the greatest bulk of molten area (at the sprue) and sucks away from the thinner areas (metal that has filled the mold)
- reservoir - molten alloy stays molten longer so that suck-back occurs at the bottom instead of the crown
- compensation for shrinkage that occurs during the solidification of the casting alloy
9
Q
why are refractory materials added to investments?
A
it is a material that doesn’t burn, so when the investments are put in the oven, the refractory materials will prevent the investment from burning up
10
Q
what is the refractory material that is used in investments?
A
- SiO2
- also silica, quartz, and cristobalite
11
Q
what is the absolute minimum chamfer width?
A
0.5mm (used with gold)
12
Q
why do we want to avoid a smaller chamfer width than 0.5mm?
A
- any smaller can cause problems with:
- difficult casting
- reading the margin
- too thin
- labs are forced to overcontour to compensate
13
Q
what are the problems with under-reducing occlusally on a gold crown preparation?
A
it can cause thin spots in the crown and make it more difficult for the lab
14
Q
what are the problems with over-reducing occlusally on a gold crown preparation?
A
it will interfere with retention and resistance
15
Q
during casting, which of the following expands, and which contracts?
wax pattern, stone, investment, cooling alloy
A
- contracts - wax pattern and cooling alloy
- expands - stone and investment
16
Q
do you want your casting to be slight oversized or undersized?
A
oversized - it is advantageous for accurate seating
17
Q
what are factors that influence resistance?
A
- magnitude and direction of dislodging forces
- geometry of the tooth preparation
- physical properties of the luting agent
18
Q
what components of tooth preparation geometry can increase resistance?
A
- decreased preparation diameter
- decreased axial wall taper
- increased crown height
- proximarl grooves and boxes
- definite line and point angles (not rounded)
19
Q
what are 4 factors that influence retention?
A
- magnitude of dislodging forces
- geometry of the tooth preparation
- roughness of the intaglio surface of the fixed restoration
- material being cemented or bonded
20
Q
what components of tooth preparation geometry can increase retention?
A
- increased axial surface area
- increased preparation height
- decreased taper of axial walls
21
Q
T or F:
retentive features must be anchored in enamel
A
false
they must be anchored in dentin
22
Q
what are some geometrical features that increase resistance and retention?
A
grooves, box forms, isthmus
23
Q
2nd molars tend to have short clinical crowns. how can you increase resistance and retention?
A
- build the resistance and retention form into the preparation
- if the prep is less than 4mm in height, consider other features to augment the retention
24
Q
what two techniques can you utilize when using a die to make a crown?
A
scanning and lost wax technique
25
know the process of how to set up a die, and the order of application of materials when doing a wax-up
prep tooth → PVS impression → pour up stone model in articulator (don't forget silicone separator) → cut die → mark the margin with a red pencil → you can either scan at this point, or if you are doing a wax up, place 2 coats of die sealer → 2 coats of die spacer/relief (1st coat farther from the margin than 2nd coat) → die lube → dip in hot wax → add inlay wax and prepare wax-up → remove wax-up from die → add sprue → investment → put investment in oven for 45 minutes → cast
26
what is the most effective place on an instrument to apply heat?
shank
27
at what point is the flame the hottest?
top of the meniscus
28
what is a sufficient amount of Au alloy for casting a posterior gold crown?
2 pennyweights and a button
29
is dipping wax softer or harder than inlay wax?
softer
this can be problematic because the wax can more easily be pulled or stretched away from the margins while carving
30
why is it important to insert the die into the dipping wax at a 45 degree angle and then to rotate it vertically and remove?
you will avoid entrapment of air within the central fossa of the preparation
31
wax flows \_\_(to/away from)\_\_ heat, and \_\_(shrinks/expands)\_\_ as it cools
* away from
* shrinks
32
overheated or burnt wax leaves a ___ residue
carbon
33
why should you broaden, smooth, and shape the proximal contact of the tooth adjacent to your die before doing your waxup?
helps ensure that you will have sufficient material for an appropriate proximal contact
34
when working on your waxup, why should you not carve away all of the dipping wax that extends apical to the margins?
it helps keep the wax on the die
when you are ready to remove the wax pattern from the die, it is helpful to remove the wax that extends beyond the margin
35
T or F:
proximal contacts should be broad in all directions
true
36
what are appropriate places to have occlusal contacts on posterior teeth?
* marginal ridges
* cusp TIP to flat receiving area (like a marginal ridge or flat fossa)
* no contacts on inclines
37
if you cannot finish your wax-up in one sitting, you will need to remelt your margins prior to investing. why?
because wax shrinks
38
what material can be helpful in removing the wax pattern from the die? what is the proper technique for removing the wax pattern from the die?
* rubber dam material
* as you gently squeeze your finger pads, thumb toward forefinger, your hands will push in opposite directions, pulling the wax pattern off the die
39
how many occlusal contacts per posterior tooth should you have?
2-4
40
the sprue allows ___ to *escape* from the mold, and allows ___ to flow *into* the mold
* molten and volatile wax
* molten metal
41
what type of sprue material allows for better escape of the wax during burnout?
hollow plastic
42
what is the sprue size for molars? what about for premolars and partial coverage castings?
* molars - 10 gauge (2.5mm diameter)
* premolars and partial coverage castings - 12 gauge (2.0mm diameter)
* in general, larger is better (better reservoir)
43
where should sprues be attached to the wax pattern and what are two important concepts related to sprue placement?
* at the bulkiest, non-critical part of the pattern (usually the largest cusp tip)
* visualize "flow of molten metal" into the pattern
* creates the path of least resistance and turbulence
44
the ___ is usually made of rubber for easy separation from the investment and casting ring, attaches to the other end of the sprue, and creates the funnel shape through which the molten metal flows
crucible former
45
the ___ surrounds the wax pattern and confines the investment material to create the mold
casting ring
* fits into the rubber crucible former
* ring liner allows for investment expansion
46
when investing, how far should the top of the wax pattner be from the top of the plastic clear ring? how much of the top of the investment will you trim off after it is set?
* 6mm from the top of the clear plastic ring
* top 2-4mm of the investment will be trimmed
47
what are 3 types of investment?
* gypsum bonded
* phosphate bonded
* ethyl-silica bonded
48
which type of investment material is softer, making it easier to retrieve castings, and is also more porous, which facilitates mroe complete mold filling?
gypsum bonded
49
which type of investment material produces the best surface reproduction, resulting in smoother castings, and is also (probably) the easiest to work with?
gypsum bonded
50
what are 6 factors that increase expansion in gypsum bonded investments?
* decreased water/powder ratio
* prolonged spatulation
* water bath set - 100\*F for 1 hour immediately after setting
* "hygroscopic expansion"
* dry ring liner
* two ring liners
* ringless investment technique
51
what are two factors that reduce expansion with gypsum bonded investments?
* add water to the mix
* eliminate the casting ring liner
52
which type of investment material is suitable for metal-ceramic alloys which typically fuse around 2550\*F?
phosphate bonded
53
which investment material has more silical refractory material which creates more expansion in the burnout oven (this compensate for additional shrinkage of metal as it cools from a higher casting temperature)?
phosphoate bonded
54
what investment material is used for high-melting base metal alloys and partial denture frameworks?
ethyl-silica bonded
55
\_\_\_ is when the casting is placed in water when the button no longer has a red glow?
quenching
56
quenching interferes with the crystalline lattice of the alloy, which results in \_\_\_
a softer, more malleable alloy
57
which type of casting alloy is soft and used for simple inlays?
type I
58
which type of casting alloy is medium in hardness and is used for complex inlays, onlays, and single unit crowns?
type II
59
which type of casting alloy is hard and is used for crowns and fixed dental prostheses?
type III
60
which type of casting alloy is extra hard and is used for partial denture frameworks?
type IV
61
\_\_\_ is the melting point of the alloy
fusing temperature
62
is 9 or 20 karat gold more yellow?
* 9 karat (37.5% Au) is more yellow (jewelry gold)
* 20 karat (85% Au) is not very yellow (dental gold)
* in general: more gold, less tarnish and more biocompatible
* avoid Ni (allergies)
63
what are the best locations for sprue placement for a maxillary premolar? maxillary molar? mandibular premolar? mandibular molar?
usually on the functional cusps
* maxillary premolar - L cusp
* maxillary molar - ML cusp
* mandibular premolar - B cusp
* mandibular molar - MB cusp
64
when placing a sprue, you should try not to involve the ___ area
proximal contact area
65
T or F:
you can use the sprue as a handle when pulling the wax pattern off the die
false
the sprue only becomes the handle once the pattern is safely off the die
66
what is the main reasoning for making all wax connections fluid when adding the sprue to the wax pattern as well as the curcible former?
to reduce turbulence
67
what is the purpose of trimming the top of the investment?
it allows the escape of hot gasses from the mold, ahead of the incoming molten metal
68
do gypsum bonded or phosphate bonded investments produce a rougher surface on the casting?
phosphate bonded investments
69
what is the order of surfaces you should finish your casting?
zones 1-7
1. internal margin
2. intaglio surface
3. sprue area
4. proximal contacts
5. occlusal surface
6. axial walls
7. external margin
70
what is the most critical area of the entire casting?
zone 1 - internal margin
71
you should not try your casting onto the die until the entire ___ area is free of irregular areas
intaglio surface (zone 2)
72
what is the width that the uniform space between the casting and the die should be?
25-35um
73
the marginal area of the casting should create a tight seal at the die margin, with a gap of what width?
10um or less
74
when finishing a gold cast, what is the issue with progressing too rapidly to a finer grade abrasive?
wastes time
75
why is it important to create a highly polished axial wall surface of a gold casting?
it enables the patient to carry out optimum plaque control (under-finishing/polishing results in rough surfaces that harbor plaque)
76
what are two benefits of crown-master pliers being non-metallic?
* will not scratch polished surface of the crown
* will not conduct frictionally induced heat
77
when polishing a gold cast, which direction should the poliching brush be rotating?
in an apical direction
