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Fixed Midterm Spring > 6. ACC I > Flashcards

6. ACC I Flashcards

1
Q

When treatment planning ACC crowns the tooth most likely to have an ACC fracture is

A

molar

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2
Q

Define refractive index

A

the amount of light that passes through a material

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3
Q

_ is a function of refractive index

A

translucency

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4
Q

Excellent optical properties of teeth include

A
  • Translucency
  • Fluorescence
  • Opalescence
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5
Q

Translucency is defined as

A

the ability to transmit light

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6
Q

Fluoresence of teeth is derived from

A

dentin (in absorbs fluorescent light and reflects back a bluish color)

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7
Q

What is opalescence

A

optic proper to teeth that has the ability to scatter blue light

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8
Q

Advantages and disadvantages of ACC

A

Advantages

  • Superior esthetocs
  • Good tissue response
  • Conservative facial reduction (compared to PFM)

Disadvantages

  • Reduced strength (lack of reinforced metal coping)
  • Less conservative proximal and lingual reduction
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9
Q

How is the strength of ceramic materials tested

A

flexural strength measurement

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10
Q

How is flexural strength tested for

A

3-point bend test

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11
Q

3 point bend test places the ceramic material under (compressive/tensile) forces

A

tensile

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12
Q

What are the two phase of all ceramic restorations

A

glass (or silica) phase

crystalline phase

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13
Q

Tensile strength of feldspathic porcelain is (high/low)… glass phase is (high/low)… translucency is (high/low)… crystalline phase is (high/low)(high/low)

A

Strength= low
Glass phase= high
Translucency= high
Crystalline phase= low

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14
Q

Traditional feldspathic porcelain is used for what restorations

A

All ceramic veneers only

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15
Q

What are the two techniques used to make veneers from feldspathic porcelain

A
  • Platinum foil

- Refractory die

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16
Q

Describe the difference in fabrication techniques

  • Platinum foil
  • Refractory die
A

Platinum foil

  • Adapt foil to working cast
  • layer porcelain
  • Remove from die and bake (die is not strong enough to go in the oven

Refractory die

  • Die is strong enough to go into the oven
  • Layer porcelain on refractory die
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17
Q

Another name for leucite reinforces restoration is

A

IPS empress

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18
Q

Compare the amount of glass and crystalline phase in leucite compared to fedspathic porcelain

A

Leucite= less glass and more crystalline

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19
Q

Compare the composition of the leucite crystals and the feldspathic porcelain crystals

A

Leucite
-K2O, Al2O3, SiO2

Feldspathic porcelain
-Na2O, Al2O3, SiO2

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20
Q

Advantages of increased crystal conc. in leucite compared to feldspathic

A
  • Increases CTE (coefficient thermal expansion)
  • Crack deflection
  • Enhanced etching pattern
  • Increased bonding to resin cements
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21
Q

Indications for leucite reinforced restorations

A
  • Anterior veneers
  • Anterior crowns
  • Posterior crowns
  • Inlays and onlays
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22
Q

What are the two methods of fabrication for leucite reinforced restorations

A
  • Pressed

- CAD CAM

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23
Q

Advantages of pressed technique for leucite

A

Better marginal adaptation

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24
Q

What are the two fabrication methods for lithium disilicate

A
  • Lost wax technique (pressed)

- CAD CAM

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25
Q

T/F Lithium disilicate indicated for 3 unit bridges

A

t0 unless extending into molar region

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26
Q

LD is about _% crystalline phase

A

70%

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27
Q

Another name for LD is

A

e.max

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28
Q

Which has better marginal adaptation for LD restoration (pressed/CADCAM)

A

pressed

29
Q

why is the marginal adaptation of pressed LD better than CAD CAM

A

when the ceramic is molten it has a low viscosity at high temps and pressures resulting in great marginal adaptation

30
Q

Is Emax fulling sintered when milled? Why or why not?

A

no partially sintered in blue block because the partially milled form is softer and will not undergo dimensional change

31
Q

Final sintering of an Emax restoration is achieved how

A

oven at 840 degrees C for ~16 mins

32
Q

Final sintering of E.max results in

A

final strength and final shade

33
Q

T/F There is a glass and crystalline phase with zirconia

A

f only crystalline

34
Q

Uses for zirconia include

A
  • Substructure (veneering)
  • Full contour restorations
  • Ortho brackets
  • Post and cores
  • IMplants and implant abutments
35
Q

Characteristics of zirconia include

A
  • High flexural strength
  • High fracture toughness
  • High radiopacity
  • Biocompatible
  • Low thermal conductivity
  • Good esthetics (compared to PFM)
36
Q

What are the three allotropes of zirconia

A
  • Monoclinic
  • Tetragonal
  • Cubic
37
Q

What are the temperatures at which each allotrope of zirconia is stable at

A
  • Monoclinic- room temp
  • Tetragonal - 1170 degrees C
  • Cubic - 2370 degrees C
38
Q

How can we attain different allotropes of zirconia at lower temps

A

addition of yytrium oxides (Y2O3), CeO2, MgO, or CaO

39
Q

Pros and cons of cubic zirconia

A 
Pros= translucent
Cons= less strength and ability to inhibit crack propagation is less than tetragonal
40
Q

Describe transformation toughening

A
  • Addition of mineral oxides to the tetragonal phase –> stable at room temps –> transformation toughness
  • Under external stress (crack) –> tetragonal converts to monoclinic (more stable at room temp) –> transformation is associated with volumetric expansion –> compression forces on the crack which prevents its propagation
41
Q

What are the metals in each of the ACC materials

A

Zirconia= ZrO2 –> Zr
Leucite= K2AlSi2O2 –> Al
Lithium Disilicate= LiO2 –> Li
Alumina= Al2O3 –> Al

42
Q

Initial use for zirconia was

A

Substructure (zirconia core with veneering ceramic over the top)

43
Q

Full contour zirconia was introduced as a way to overcome

A

the chipping and fracture rates of veneering veramic

44
Q

Full contour zirconia is indicated for

A
  • Alternative to CCC and PFM
  • Not meant to replace glass ceramic in esthetic zone
  • Indicated in posterior region
  • Parafunctional habits
  • Short crowns
  • Posterior bridges
45
Q

Concerns of zirconia are

A
  • Lack of long term clinical trials
  • Abrassive to opposing dentition
  • Compromised esthetics (high opacity)
  • Adhesion not as reliable as ceramics
  • Removal is difficult
46
Q

Advantages of zirconia

A
  • Esthetics superior to CCC and PFM
  • Conservative prep
  • High durability and biocompatible
  • Inexpensive (relatively)
  • Durable alternative to people with metal allergy
47
Q

Is zirconia fully sintered when it is milled

A

no

48
Q

Sintering time for a single unit zirconia crown is how long? Milling time?

A

90 min… 20 min

49
Q

Options for shading zirconia

A
  • Preshaded zirconia (zenostar shade concept)
  • White zirconia shaded using infiltration liquid
  • White zirconia with external staining
50
Q

Pre-shaded zirconia can be used for what shades

A

A-D

51
Q

What are the different pre-shades

A
  • Pure (white)
  • Light
  • Medium
  • Intense
  • Sun
  • Sun chroma
52
Q

Feldspathic porcelains were (flexible/brittle)

A

brittle

53
Q

Give the % of crystals in each restoration material

  • Feldspathic
  • Empress
  • Emax
  • Zirconia
A

20, 40, 70, 100%

54
Q

What is the difference between monolithic and layered restoration

A

Monolithic= Restoration is made entirely from the same material like Lithium disilicate reinforced or zirconia

Layered= Lithium disilicate reinforced or zirconia with overlayed with porcelain

55
Q

How can you increase esthetics while also maintaining strength

A

layering- can even do partial layering

56
Q

List the amount of force than can be tolerated by these restorative materials

A

Veneering ceramic= 90 MPa
LiSiO2= 360-400 MPa
Zirconia= 1000 MPa

57
Q

List the following materials in order of longest to shortest survival rates after 5 years. LD reinforced glass ceramic, Feldspathic porcelain, PFM

A

LD= PFM> Fedspathic/silica based crowns

58
Q

Compare the survival rates in the posterior. Feldspathc/silica based ceramic, Layered zirconia, PFM

A

Feldspathc/silica based ceramic, Layered zirconia

59
Q

Conclusions of the Sailer study which discussed the longevity of ACC and PFM restorations

A
  • Survival of most types of ACC SC restorations= same as PFM in anterior and posterior regions
  • Weaker feldspathic porcelain should be limited to anterior
  • Zirconia based SC should not be considered as primary option due to high incidence of technical complications (refers to veneering Zr not monolithic Zr)
60
Q

Why are sharp angles undesirable in crown preps

A
  • stress fracture zone
61
Q

Prep guidelines for ACC

A
  • 1 mm finishline (modified shoulder or deep chamfer)
  • 1.5mm incisal reduction
  • (milled preps) incisal edge must be at least 1 mm thick
62
Q

Why is a 1mm shoulder finishline desirable for ACC

A

places the ceramic under compressive forces (ceramic is stronger under compressive forces)

63
Q

Deep chamfer places ceramic under (compressive/tensile) forces

A

tensile

64
Q

For milled restorations why must the min. thickness of the prep be 1 mm

A

due to milling tool geometry

65
Q

Minimal and maximal thickness of the finish line for empress in anterior and posterior

A

Anterior
-No less than 0.6 mm

Posterior
-No less than 1 mm

66
Q

Minimal thickness for Pressed E.max at finishline for anterior and posterior restorations

A

Anterior
-0.3mm

Posterior
-1 mm

67
Q

Minimal thickness for CAD E.max at finishline for anterior and posterior restorations

A

Anterior
-Min= 0.6mm

Posterior
-Min= 1 mm

68
Q

Minimal thickness for zirconia for occlusal/incisal reduction and facial reduction

A

Occlusal/incisal
-1 mm

Facial
-0.7 mm

Fixed Midterm Spring (9 decks)

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