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Dental Materials > Midterm > Flashcards

Midterm Flashcards

1
Q

In ceramics, what are they two key phases that occur after firing

A

crystalline: most common today
glassy phase: surrounds the crystalline phase

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2
Q

in ceramics, the crystalline phase affects what

A

Depending on the nature and amount of crystalline phase present, the mechanical and optical properties vary greatly
o Increase in glassy phase = lowers resistance to crack propagation BUT increase translucency

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3
Q

All-ceramic restorations have inc/dec amounts of crystalline phase

A

INCREASE.
allows for better mechanical properties

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4
Q

after an impression is made,itispouredinagypsumproductsuchasdental stone. The section reproduced which represents a form of the prepared tooth is referred to as a:

A

DIE

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5
Q

what type if reproduction is a die/cast -/+

A

+

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6
Q

What is a die

A

reproduction of the form of a prepared tooth in a hard substance
o Impression of prepared tooth, trimmed down: die

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7
Q

what is a cast

A

reproduction of the surface form of oral/facial tissues obtained from
impressions
o Impression = (-) form of teeth
full arch poured up= cast

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8
Q

Whatistheprimarydifferencebetweendigitalimpressionsandtraditional impressions (i.e. alginate)?

A

Digital impressions are a positive reproduction of the oral structures and
traditional impressions are a negative reproduction.

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9
Q

are digital impressions pos or neg

A

POS

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10
Q

are aliginate impressoins pos or neg

A

NEG

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11
Q

Howdoesthechemicalformulaofcalciumsulfateα–hemihydratedifferfromthe chemical formula of calcium sulfate β-hemihydrate?

A

There is no difference in chemical formulas. Just physical shape, size,
crystal form

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12
Q

what is the chemical formula for naturally occuring gyspum

A

(CaSO4)2 * H2O
Calcium sulfate hemihydrate

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13
Q

what is plaster

A

plaster: BETA-hemi, open air kettle P,B,O

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14
Q

what is stone

A

stone: ALPHA- hemi, autoclave

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15
Q

Impressionmaterialshavemanycharacteristicsthateitherenhancetheir qualities as such or reduce their values for certain techniques. The characteristic that makes hydrocolloids useful impression materials is their tendency to be:

A

hydrophilic

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16
Q

Are Reversible Hydrocolloid impressions a chemical set impression?

A

NO- thermal

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17
Q

what is a reverisble hydrocolloid

A

agar agar which is THERMAL SET

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18
Q

what is an ireeversible hydrocolloid impression

A

alginate

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19
Q

what impression materials are chemcial set

A

alignate, polyether and elastomeric

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20
Q

what impression materails are thermal set

A

agar agar - reversible hydrocolloid

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21
Q

Digital scan is useful for

A

Crown, night guard, splints, edentulous impressions (do not do much of yet)
○ Indirect restorations (i.e., crowns, bridges, inlays/onlays, veneers) fabricated chairside in lab
○ Orthodontic tray fabrication (invisalign)
○ Virtual study models (implant treatment plan)
○ Any case sent to a lab

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22
Q

Autoclavingcalciumsulfatedihydrateinthepresenceofcalciumchlorideand magnesium chloride will produce what?

A

) High strength dental stone. chemicals

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23
Q

Intheconversionofcalciumsulfatedihydratetocalciumsulfatehemihydrate, which process would yield the beta version of hemihydrate?

A

Heatinginopenairkettles.Dentalplaster

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24
Q

stone characterics

A

stone is alpha- autoclave
■ Low Porosity/regular, less linear expansion

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25
Q

model plaster characterics

A

Model plaster is beta- open kettle
■ Porous/irregular, more linear expansion

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26
Q

what is used to form high strength stone

A

chemicals

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27
Q

The attribute of impression materials which allows them to be removed by stretching over a bulge and returning to its original shape without distortion is called:

A

memoruy

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28
Q

11.The tendency for wax to return to its original shape is referred to as:

A

elastic memory

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29
Q

Elastomeric impressions / alginate impressions are able to rebound to original shape / rebound in memory
○ What is in it that allows it to rebound to the original shape?

A

elastic memory

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30
Q

advantages of digital impressions

A

No impression materials needed
■ No models to pour
■ Download impressions directly to milling unit
■ Can store/send impression scans much easier
■ No distortion or warping
■ More accurate
■ Stable
■ Faster turnaround; more convenient to you and to your patients.

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31
Q

disadvantages of digital impressions

A

■ High initial cost
■ Data loss
■ Technique sensitive
■ Time consuming
■ Need to work in a digitally equipped lab

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32
Q

What causes the linear expansion of calcium sulfate dihydrate during the setting reaction?

A

a) The growth and pushing of the dihydrate crystals.

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33
Q

2 things happen when dental stone & plaster is setting:

A

Volumetric contraction: volume of calcium sulfate dihydrate formed is ~7%
less than the sum of volumes of calcium sulfate hemihydrate & water
○ Linear expansion: caused by growth and pushing action of the calcium
sulfate dihydrate crystals, results in porous material

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34
Q

Volumetric contraction:

A

volume of calcium sulfate dihydrate formed is ~7%
less than the sum of volumes of calcium sulfate hemihydrate & water

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35
Q

Linear expansion:

A

caused by growth and pushing action of the calcium
sulfate dihydrate crystals, results in porous material

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36
Q

Key concept in setting rxn of calcium sulfate 3

A

○ EXOTHERMIC
○ Water temp & solubilities
○ There is a definition

Temperature generated is equal to that used to heat during calcination
● Rxn takes place regardless of how the gypsum is being used

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37
Q

.Both irreversible and reversible hydrocolloids exude a liquid on their surface after setting which is partially water but has a different pH. This phenomenon is called:

A

Syneresis

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38
Q

where do you see hygroscopic expansion and syneresis

A

hydrocolloid impressions

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39
Q

Syneresis

A

excludes water on surface
Not pure water b/c pH is different
○ Gel shrinks

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40
Q

where can you find syneresis

A

agar and hydrocolloid impressions

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41
Q

If dental plaster/stone is left to set under water, what will happen?

A

Hygroscopic expansion. More water = more crystal growth, less surface tension

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42
Q

Hygroscopic expansion

A

the expansion that occurs if rxn is allowed to occur under water
○ Used w/ investment material for greater expansion

greater than the amount of expansion in air bc of constant supply of H2O
allowing additional crystal growth

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43
Q

What do you isolate to get a digital impression?

A

An ISOLITE, you would NOT use a rubber dam!

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44
Q

Which phase directly affects the mechanical and optical properties of all
ceramics??

A

The amount of crystalline phase

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45
Q

In the setting reaction of irreversible alginates, trisodium phosphate, sodium pyrophosphate, and tetrasodium pyrophosphate are able to expand the “working time” to allow for thorough mixing, loading the tray, and seating of the tray. As a group they are referred to as:

A

retarders

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46
Q

what is a retarder

A

Retarder: keeps “reactor” busy so it does NOT immediately combine w/ the
alginate sol’n

once retarder is used -> CaSO4 combines with soln to form gel

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47
Q

Isolation is necessary when taking a frame scan (YES/NO)

A

YES. need surfaces of teeth dry and free of shit

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48
Q

All of the following will decrease the set time of dental plaster/stone EXCEPT: a) Decrease the water powder ratio.
Hygroscopic expansion. More water = more crystal growth, less surface
tension
b) Increase the mixing time and mixing speed.
c) Use slurry water.
d) Use very hot water (near boiling). Boiling solubilities of hemi and di are
equal

A

d) Use very hot water (near boiling). Boiling solubilities of hemi and di are
equal

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49
Q

Best way to decrease setting time of plaster stone

A

decrease setting time -> increase speed of set BEST WAY!!!

increase the speed and temp of mix

50
Q

When dispensing elastomeric impressions materials, it is essential to dispense equal volumes of the materials.

A

FALSE
Base and accelerator: mix out equal LENGTHS, not volume

51
Q

take an impression & their blood from the gingiva gets on it & you do NOT rinse
it out… What will this do to the setting time of the stone?

A

● Leave debris (from body or whatever) increases set time, so clean it (takes longer)
o Sets slower/increase setting time

52
Q

How do you influence the set time of alginate?

A

Hot water = decreases set time so it sets faster
○ Cold water = increases set time so it sets slower

53
Q

Good hemorrhage control, but cannot be used near metal (i.e. implants).

A

Electrosurgery improved hemorrhage control, unable to use near metals

54
Q

Maximum hemorrhage control and visibility, safe to use near metal, but has safety issues in the military.

A

Soft tissue laser Max hemorrhage control and visibility, no tissue charring,
used near metals (implants) not in military

55
Q

Cheap, but has poor hemorrhage control and visibility.

A

Scalpel cost efficient, poor hemorrhage control and visibility, 2nd appointment

56
Q

Standard method for soft tissue management and hemorrhage control. Prefered method used at Creighton.

A

Retraction Cord

57
Q

Acceptable forms of tissue management when taking an impression (implant) w/ excess tissue– Use:

A

Laser
○ Scalpel
○ Cold steel (scalpel)- cheap but great hemorrhage
○ Electrosurgery- can NOT use with metal, little hemorrhage
○ Packing cord
○ Laser- can use with metal, no hemorrhage

58
Q

You prepared a tooth for a gold inlay. You would like to make a wax pattern using the indirect waxing technique. Which classification of dental inlay casting wax would you use?

A

Type1.Soft,greatflow,formwaxpatternsondentaldie,outsidetooth

59
Q

type 1 wax is used for

A

Soft,greatflow,formwaxpatternsondentaldie,outsidetooth

60
Q

type 2 wax is used for

A

direct,harder,lowerflow,directintooth

61
Q

Where will Type 1 and Type 2 inlay wax be used?

A

Type I- indirect restoration (softer)
○ Type II- direct (in mouth) restoration (harder)

62
Q

The major reason for removing the impression from the cast shortly after it is completely set is:

A

To prevent the imbibing of moisture from the cast by the drying, shrinking
alginate.

63
Q

The preferred way to control the dimensional stability of both Reversible and
Irreversible Hydrocolloids, prior to pouring up the impression, is to:

A

put in wet paper towel
If an impression cannot be poured up immediately: best thing to do is wrap impression in wet paper towel soaked in cold water

64
Q

Which of the following was not listed as a common error when taking digital impressions?

A

Image file taking up too much memory.

65
Q

Common errors when taking digital impressions:

A

○ Moving camera too fast
○ Poor isolation
○ Capturing things you don’t want (ex.finger)

66
Q

Common errors when taking digital impressions:

A

○ Moving camera too fast
○ Poor isolation
○ Capturing things you don’t want (ex.finger)

67
Q

slurry water does what

A

Use of Slurry water decreases set time/increases the rate of set.

68
Q

What can generate polymerization of acrylic

A

o Heat (warm water) o Microwaves
o Light cured
● Chemical activation at room temp

69
Q

2.True or False. Waxes are chosen based on their specific melting point.

A

FALSE. waxes have a melting RANGE

70
Q

waxeshave large/small coefficients of thermal expansion

A

LARGE!!

71
Q

waxes have low/high thermal conductivity

A

LOW

72
Q

What happens to wax when you heat it?

A

hermal expansion
○ Thermal contraction

73
Q

Many waxes are not good thermal conductors t/f

A

TRUE
Hard wax is not a good thermal conductor
○ Dental Waxes have the highest coefficient of thermal expansion

74
Q

Slip cast ceramic materials – know what that is
○ Low or High strength?

A

HIGH
advantages: it’s high in strength
○ Disadvantages: long time to process, high opacity
○ Two Types: Zirconia/Spinel Based, and Alumina Based
■ Zirconia is the STRONGEST ceramic material

75
Q

zirconia is what type of ceramic material

A

slip cast

76
Q

in light activated resin, the photoinitiator is:

A

CAMPHORQUINONE-AMINE

77
Q

Chemicals present in monomer in polymethyl methacrylate: will keep it from
setting automatically or auto polymerizing - what is it

A

Hydroquinone

78
Q

base material for triad light cured material =

A

Urethane Dimethacrylate

79
Q

Repairing denture, we used a self-repairing acrylic– it is GOOD if it is HARD
○ TRUE/FALSE

A

TRUE! its good if its hard

80
Q

unit of polymer

A

mers

81
Q

Both are good
○ Condensation Silicone has more shrinkage / shorter die
○ Use PVS (best mechanical stability)
● Condensation silicone impression material has more significant shorter dye so
we like to use polyvinyl siloxane instead

A
82
Q

Take impression materials, we talk about the wetting characteristics - low or high angle

A

A LOWER angle b/c the material will spread out on the tooth we are impressing. means it is hydrophilic

83
Q

Denture teeth – 2 little buttons on the back of porcelain teeth – for mechanical
retention
○ Buttons are called

A

diatorics

84
Q

what is stronger denture tooth- arycrlic or porecelain

A

porcelain is stronger but that will wear nature teeth down

85
Q

on denture, what type of teeth are used

A

acrylic bc is easier to adjust b/c it is softer
○ Less likely to wear opposing surfaces
■ Better bond with acrylic & denture than with porcelain ○ **Porcelain = a strong wearing tooth

86
Q

Elastomeric impressions
○ Which one forms hydrogen gas? – you do not want to pour this impression too soon b/c hydrogen gas will be coming off of it

A

Poly Vinyl Siloxane (PVS) impression material

87
Q

what can you add to PVS so it wont form hydrogen gas

A

palladium

88
Q

Is the least flexible of the impression materials

A

Polyether Impression Material

89
Q

impression:
Forms ethyl alcohol as a byproduct

A

Condensation Silicone Impression Material

90
Q

impression:
Uses lead dioxide as a catalyst

A

C: Polysulfide Impression Material

91
Q

impression:
Polymerization reaction is exothermic

A

ALL

92
Q

impression:
Uses a platinum salt as a catalyst

A

PolyVinyl-Siloxane Impression Material

93
Q

impression:
contracts during curing

A

ALL impression materials

94
Q

impressoins:
Has greatest dimensional stability (least linear contraction)

A

PolyVinyl-Siloxane Impression Material

95
Q

impressoins:
May form hydrogen gas

A

PolyVinyl-Siloxane Impression Material

96
Q
  1. All of the following were listed as dental uses of gypsum EXCEPT: a. Dentalcasts.
    b.Impressionsonpatientswithfulldentitions
    c. Dental dies.
    d. Dentureflaskingprocedures.
    e. Attachingcaststoanarticulator.
A

Impressionsonpatientswithfulldentitions.–can’tputinpatientmouth

97
Q

What is the key concept to understand in the setting reaction of calcium sulfate dihydrate?

A

Calciumsulfatehemihydrateismoresolublethandihydrate.

98
Q

The linear polymer of galactose extracted from seaweed and used as an impression material is:

A

Agar-Agar. Galactan

99
Q

The impression materials discussed in class that were referred to as Non- Elastics were waxes, impression compound, impression plasters, and :

A

Zinc oxide and eugenol.

100
Q

the characteristic of Reversible Hydrocolloids that make it compatible for use on humans is the big difference between their “Liquifaction Temperature” and their “Gelation Temperature.” That characteristic is called:

A

. Hysteresis.

101
Q

The large variation in temperatures between liquefaction and gelation in a Reversible Hydrocolloid permits us to use it in a range that is reasonably comfortable to use on a human being. That property is called:

A

c. Hysteresis.

102
Q

Which of the following is NOT true about reversible hydrocolloids:
a. Agarisapproximately10-15%water.
b. Containsboraxtoincreaseviscosityandstrength.True
c. Agglomerates to form micelles upon cooling.
d.Utilizessulfatesasahardenerwhichoffsetsthetendencyofboraxto retard the setting of gypsums.

A

A. 10-15% hydrocolloid

103
Q

Sodium, potassium, and triethanolamine alginates require another chemical to drive the reaction toward its gel stage. That chemical is:

A

CalciumSulfate.Onceallretarderisused,drivestobecomegel

104
Q

If one desired to increase the “setting time” or slow the “rate of set” of an irreversible hydrocolloid (alginate), one could do the following:

A

use water that is 10 degrees cooler

105
Q

Which wax was described in lecture as being the base or primary wax in many of the waxes we use in dentistry?

A

paraffin

106
Q

Used to enclose impressions; forms a wax box.

A

Boxingwax

107
Q

waxes:
Joins or stabilizes components temporarily.

A

Stickywax

108
Q

waxes:
Can be used as a temporary crown form.

A

baseplate wax

109
Q

waxes:
forms borders on impression trays.

A

utility wax

110
Q

waxes:
Used in the fabrication of indirect restorations (i.e. cast crowns).

A

inlay wax

111
Q

Volumetric contraction- occurs due

A

due to the precipitation of dihydrate out of solution

112
Q

Linear expansion-occurs due

A

to pushing action of the calcium sulfate dihydrate crystals

113
Q

What is the key reaction with calcium dihydrate?

A

Workable Hemihydrate suspension forms upon mixing, and hemihydrate
dissolves until solution is saturated. The saturated hemihydrate solution
becomes supersaturated with dihydrate.
● Hemihydrate is 4.5x as soluble as dihydrate, dihydrate will precipitate out.
● Hemihydrate continues to dissolve as dihydrate precipitates out

114
Q

Where do you see syneresis?

A

Will see in hydrocolloids but NOT in elastomeric impression materials.

115
Q

Accelerator- type of one

A

speeds up set (Potassium Sulfate)

PSA

116
Q

type of retarder

A

slows down set (Borax)

117
Q

What chemical is present in the monomer in acrylic keeps it from setting automatically?

A

Hydroquinone

118
Q

mixing time

A

time from addition of powder to water until mixing is complete

119
Q

working time

A

time available to use a workable mix

120
Q

loss of gloss

A

loses gloss when dihydrate takes up excess water. not strong

121
Q

setting time

A

beginning of mix until haed and compeletey set

122
Q

ready for use

A

time elasped when product can safetly be handled

Dental Materials (5 decks)

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