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Fixed Prosth > Quiz 2 > Flashcards

Quiz 2 Flashcards

1
Q

Master Cast

A

Definitive Cast
Working Cast

Replica of prepared tooth/teeth, ridge areas, and other parts of dental arch
Also called Models

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2
Q

Die

A

Positive reproduction of prepared tooth

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3
Q 
Master Cast requirements
Must represent which teeth
Quality
Contacting surfaces
Soft tissues
Appearance and bubbles
A

Must accurately represent both prepared and unprepared tooth surfaces
Unprepared teeth immediately adjacent to the prepared teeth must be free of voids, defects or other irregularities
All contacting surfaces of opposing teeth in MI and any tooth surfaces involved in anterior guidance must be free of defects and allow for precise articulation
All relevant soft tissues must be accurately reproduced, especially edentulous ridges that will be involved in a fixed prosthesis
Overall cast shape and form must be an accurate representation of the relevant anatomical structures
Must be neatly trimmed and de-bubbleized

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4
Q 
Die requirements
Which teeth
Margins
Which portion of tooth structure must be visible
Type of material
A

Must accurately reproduce the prepared tooth or teeth
All marginal areas must be accessible
The unprepared tooth structure immediately cervical to the margins should be easily discernible (0.5 to 1.0 mm beyond prepared margin if possible). This enables the correct cervical contours to be determined.
Must be of a durable material that is not easily abraded

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5
Q

List of die materials

A 
Epoxy Resin
Polyurethane
Electroplated Sliver or Copper Over Gypsum
Flexible Silicone or Polyether
Gypsum
cyanoacrylate Reinforced Gypsum
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6
Q

Epoxy resin is more abrasion resistant than

A

Gypsum

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7
Q

Epoxy Resin and Gypsum cost difference

A

Epoxy resin more expensive than gypsum

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8
Q

Size change in epoxy resin

A

Some formulations undergo slight shrinkage upon polymerization

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9
Q

Which impression materials for Epoxy Resin

A

PVS or Polyether

Incompatible with hydrocolloid and polysulfide rubber base

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10
Q

Polyurethane is more abrasion resistant than what

A

Gypsum

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11
Q

Polyurethane vs gypsum in cost

A

Polyurethane more expensive than gypsum

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12
Q

Impression materials for Polyurethane

A

PVS or Polyether

not compatible with hydrocolloid and polysulfide rubber base

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13
Q

Which die material has toxicity and disposal challenges

A

Electroplated

silver plating requires a cyanide solution

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14
Q

Which die material is easily distorted, difficult process, but very accurate and durable when done properly

A

Electroplated

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15
Q

Impression material not for electroplated

A

Not Polyether and Polysulfide rubber base

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16
Q

Which die can be fabricated in a matter of minutes

A

Flexible Silicone or Polyether

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17
Q

Flexible silicone or Polyether use primarily for what

A

used primarily for chairside indirect composite resin inlays or onlays
Also used for interim restorations
Restoration easily separated from die

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18
Q

Is Gypsum accurate

A

Yes

also inexpensive and easy to use

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19
Q

Bad side of gypsum

A

easily abraided

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20
Q

What can make gypsum more resistant to abrasion

A

Cyanoacrylate (Cyanoacrylate Reinforced Gypsum)

low-viscosity cyanoacrylate is applied to die and further thinned with compressed air

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21
Q

Mined Gypsum

A

CaSO4 * 2H2O - Calcium sulfate dihydrate

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22
Q

Gypsum form supplied in dentistry

A

CaSO4 * 1/2H20 - Calcium Sulfate Hemihydrate

Reverts back to dihydrate when mixed with water

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23
Q

The form of gypsum used as starting form for casts and casting investments

A

Calcium sulfate hemihydrate (plaster of Paris) and calcium sulfate anhydrite (powder) (types 4 and 5 are anhydrite)

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24
Q

The set form of dental stone

A

Calcium sulfate dihydrate CaSO4*2H2O

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25
Q

Name of process by which gypsum loses water

A

Calcination

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26
Q

Gypsum Processing

A 
Calcium sulfate dihydrate (gypsum)
110-130 degrees C
Calcium sulfate hemihydrate (Plaster or Stone)
130-200
Calcium sulfate Hexagonal anhydrite
200-1000
Calcium sulfate Orthorhombic anhydrite
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27
Q

What is produced when gypsum is heated in an open kettle at 110-130

A

Dental plasters

beta-hemihydrate

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28
Q

beta-hemihydrate is used to produce which type of dental stone

A

type II stone

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29
Q

What is produced when gypsum is dehydrated under pressure in the presence of water vapor at 125 C

A

Hydrocal

alpha-hemihydrate form of calcium sulfate

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30
Q

Which type of dental stone is dyrocal

A

type III

type III dental stone is an alpha - hemihydrate

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31
Q

Type III stone is used for what

A

many lab procedures
fabricate diagnostic casts
partial and complete dentures

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32
Q

What is produced when gypsum mineral is boiled in 30% calcium chloride solution
Chloride is washed from the rock, mineral is ground to the desired level of fineness

A

Densite

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33
Q

Densite used to make which type of dental stone

A

types IV and V die stones

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34
Q

Types IV and V die stones are which type of calcium sulfate

A

alpha-hemihydrate

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35
Q

Type IV and V die stones are used for what

A

Many types of fixed indirect restorations

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36
Q

Qualities of type IV stone

type V stone

A

IV - high strength, low expansion

V - high strength, high expansion

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37
Q

When is calcination reaction is reversed

A

when alpha or beta hemihydrate is mixed with water

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38
Q

Reversed calcination reaction

A

CaSO4 *1/2 H2O + 3H2O goes to 2CaSO4 * 2H2O + Heat

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39
Q

Theoretical lowest required volume of water o hydrate 100g of hemihydrate in either the alpha or beta form

A

18.6 ml
not a practical mass to manipulate,
need a bit more stone to actually mix it

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40
Q

Reason for differences among the recommended volumes of mixing water for plaster, stone, and dies stone

A

shape and size of the different forms of calcium sulfate hemihydrate particles

41
Q

How do alpha and beta hemihydrates differ

A

crystal size, surface area, and lattice perfection

42
Q

which hemihydrate requires the most water, why

A

Beta hemihydrate - crystals are more irregular in shape and porous, more is needed to wet particles when mixing

43
Q

3 types of gypsum hemi-hydrites?

A

Plasters
Hydrocal
Densite

44
Q

Water values?

A

j

45
Q

Nature of powder particles of alpha-hemihydrate

A

used for dental stone
smaller, more prismatic/regular shape than plaster
Produces harder, stronger, denser structure than Beta-hemihydrate, mixed with less water

46
Q

Die stones to focus on

A

Die-Keen

Die-Stone

47
Q

Model Stones to focus on

A

Dentstone
Labstone
Mounting stone

48
Q

Important note for mounting stone

A

wait for mounting stone to set, inaccuracies occur if not

49
Q

Gypsum products: increasing speed of spatulation or length of spatulation time

A

shortens setting time

new nuclei centers for crystal formation are created

50
Q

Temperature and set time for gypsum products

A

Moderate increase in temp decreases set time

Also lowers solubility of hemihydrate relative to dihydrate
At 100C the solubilities are equal, no reaction occurs, plaster does not set

51
Q

Working time

A

time that elapses from start of mix until the mix loses its gloss and viscosity reaches a point where it will not flow into impression

52
Q

Set time for dental plaster largely under control of who

A

the manufacturer

53
Q

Factors that affect set time

A 
Temperature
Spatulation
2% K2SO4 instead of water - accelerate set time
Slurry water
Adding more water
54
Q

Water beyond 18.6 ml/100 grams of product

A

excess water

55
Q

What has greatest quantity of excess water = more voids, less compressive strength

What has least excess water

A

Plaster

High strength dental stone

56
Q

What has the greatest effect on compressive strength regardless of plaster/stone type

A

water/powder ratio

different stones have about the same compressive strength when mixed with same water/powder ratio

57
Q

Vacuum mixing has what effect

A

slightly improves compressive strength of dental stone

58
Q

Wet strength

Dry strength

A

strength measured when excess water remains in the hardened

Dry - all excess water driven out

59
Q

How much stronger is dry strength than wet

A

Twice as strong

60
Q

How long after mixing and pouring until hardened gypsum appears to have reached max strength
Real time

A

1-2 hours

Actual time is about 7 days for excess water to leave

61
Q

The effect of drying on compressive strength

At what values of weight loss from water does compressive strength change/not change

A

up to 7%, not a lot of change in compressive strength

When 7.5% + of excess water/weight loss, compressive strength increases sharply

62
Q

What happens when last trace of water is lost

A

fine crystals of gypsum precipitate, serve as anchors between larger crystals
These are first to go when water is added again

63
Q

Hardness

A

surface measurement of the resistance of one material to be deformed by indenting or scratching another material

64
Q

First hardness scale proposed by Fredrich Mohs

A

Scratch test

65
Q

Knoop and Vickers

A

Indentation test

66
Q

Depth of surface penetration is reported in units of

A

force/area

67
Q

Abrasion or wear

A

removal of material that occurs when surfaces slide across or against each other

Two body abrasion
Three body abrasion

68
Q

Hardness and wear resistance

A

Surface hardness is a poor predictor of material wear

69
Q

Abrasion resistance or wear resistance influenced by

A 
Strength
Surface hardness and roughness
third-body wear particle size
Mode of fracture (ductile vs. brittle material)
Applied force
70
Q

Attempt to increase hardness and scratch resistance by embedding epoxy resins or light cured dimethacrylate resins

A

but differences in abrasion resistance in these have not been established

71
Q

Surface of set gypsum is what

A

porous microscopically

electroplated or epoxy dies generally provide better surface detail than gypsum dies

72
Q

75% of expansion of gypsum ovserved when

A

in first hour of setting

73
Q

order of water and powder

A

water first, then powder

74
Q

Five types of gypsum products

A

I - plaster, impression, Plaster of Paris, beta hemihydrate
II - plaster, model
III - dental stone
IV - Dental stone, high strength
V - dental stone, high strength, high expansion

75
Q

Type II dental stone

A

Lab plaster, plaster of Paris - beta hemihydrate
Used in lab in removable denture construction
Commonly used to articulate casts - but should not be due to significant expansion
White color

76
Q

Type III dental stone
type of hemihydrate
used for what/benefits

A

alpha hemihydrate
wide range of uses, higher strength than I and II, but not IV and V
Diagnostic casts, working casts for removable dentures, altered casts for general utility purposes including: bleach trays, athletic mouthguards, night guards, duplicate casts

77
Q

Type IV dental stone
properties
uses

A 
High strength, low expansion
alpha hemihydrate
Cast inlays and onlays
implant prostheses
Removable partial denture frameworks
Milled restorations
78
Q

Type V dental stone
properties
uses
used with what

A

high strength, high expansion
alpha hemihydrate
Full coverage cast crowns, inlays and onlays, fixed partial dentures with full coverage cast retainers
Used with cast full-coverage restorations to compensate for casting shrinkage

79
Q

requirements of definitive casts and dies

A

must accurately maintain relationships of prepared tooth or teeth to surrounding structures
Must allow easy retrieval and replacement of dies

80
Q

What are the limitations of the partial arch articulation system

A

No contralateral guidance in excursions

No condylar reference

81
Q

Advantages of triple-tray technique

A

Can provide extremely accurate bite record
error is inherent of any copy
fewer interactive surfaces can increase accuracy
reasonable quality with minimal time investment

82
Q

Lost wax technique

A

Impression poured with stone
Wax pattern placed on die
Wax pattern attached with sprue to rubber crucible former and is invested
Casting
Luted restoration placed on prepared tooth

83
Q

Distance from margin to die spacer

A

1mm from margin

84
Q

Ideal dimension for luting agent space

A

20-40 microns for each wall
this implies that complete crown should have internal diameter between
40-80 microns

85
Q

Always heat what part of instrument

A

Shank

86
Q

Inlay wax composition

A 
Paraffin (40-60%)
Dammar Resin
Carnuba
Ceresin
Candelilla Wax
Beeswax
Dyes
87
Q 
Wax type 1
Consistency
What technique
Solid at what temp
Shrinkage
A

Medium to hard consistency
Used with direct technique for making patterns in oral cavity
Solid at 37C
Shrinks more than type II inlay wax

88
Q

Inlay wax type 2
Consistency
technique
Solid at what temp

A

Softer
More commonly used in indirect techniques
Solid at 25 degrees C

89
Q

First step in waxing procedure

A

lubricate die

90
Q

Remove wax by

A

bending fingers holding the die

91
Q

To ensure proper contacts while waxing

A

scrape stone of adjacent tooth prior to waxing

Broaden contact in all directions

92
Q

Flat receiving area for cusp tip

A

centrum

no contacts on inlines

93
Q

Reflowing margins

A

1mm area
heated instrument melts completely through wax all the way around margin
Add wax to fill the depression

94
Q

Most practical way to finish margins properly

A

Magnification

95
Q

Die sealer

A

After red pencil
Protects margins
Fills pores in stone
Strengthens die

96
Q

After die sealer

how much

A

Die Spacer
Two coats of 20 microns each
helps when seating crown
used to drill holes in tops of crowns

97
Q

After die sealer

A

Die lube
Coat die
coat adjacent teeth and contact areas
Coat opposing teeth

98
Q

Dipping wax

A

Correct angle
Put in slow, take out fast
Provides wax with a good anchor

Fixed Prosth (2 decks)

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