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fixed 3- midterm 2 > ceramics review > Flashcards

ceramics review Flashcards

1
Q

what are the contraindications for all ceramic crowns?

A

• Parafunctional Activity
• Insufficient support from tooth
preparation
• Insufficient porcelain thickness in lingual aspect (0.8mm)
• Opposing teeth that occlude with cervical fifth of crown
• Short clinical crowns

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2
Q

what are the advantages of all ceramic crowns?

A

• Best esthetics
• Best color stability
• Some all-ceramic crown systems can be bonded to natural tooth structure

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3
Q

what causes catastrophic failure of all ceramic crowns?

A

weak strength and the brittle nature of ceramics

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4
Q

name the silica based ceramics

A
  • Feldspathic Porcelains
  • Hot-pressed Glass Ceramics
  • Leucite reinforced glass ceramics
  • Lithium disilicate reinforced glass ceramics
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5
Q

name the non-silica based ceramics

A

• Slip-cast, Glass Infiltrated Ceramics
- Alumina, alumina/zirconia and magnesium alumina

• Polycrystalline “Densely Sintered” Alumina and Zirconia

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6
Q

T/F: silica based ceramics are difficult to bond

A

false- silica ceramics can, and must, bond with resin cement to improve strength

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7
Q

which type of ceramics are more translucent? more opaque?

A

silica based- more translucent

non-silica based- more opaque

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8
Q

what type of ceramics have the highest strength?

A

non-silica based

strong, but opaque, and you cannot bond them

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9
Q

what is “Feldspar”?

A

potassium and sodium aluminosilicates

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10
Q

T/F: dental feldspar ceramics are mostly opaque, and have a small amount of leucite crystal (min 12%)

A

False:

they are GLOSSY, and have small amount of leucite crystal

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11
Q

_______ crystal has a much higher thermal expansion than glass

A

leucite

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12
Q

what factor determines the size of leucite crystals?

A

temperature

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13
Q

Leucite is needed to make bonding to _____ possible

A

metal

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14
Q

Leucite has a _______ coefficient of thermal expansion (CTE) than the surrounding glass.

A

higher

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15
Q

Ceramic materials are susceptible to _____ fracture

A

brittle

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16
Q

T/F: Ceramics are weaker when in tension and stronger when under compression

A

true

17
Q

how does feldspar reinforce the ceramic? (crystalline reinforcement)

A

crystalline reinforcement strengthens the ceramic by resisting crack propagation via deflection of the advancing crack.

18
Q

how does the coefficient of thermal expansion of Feldspar crystals enhance the strength of the glass around it?

A

it results in a layer of glass under compression immediately adjacent to the crystal.

This stronger layer within the glassy matrix deflects the advancing crack.

19
Q

what are the characteristics of “opaque” dental porcelain?

A

high concentration of ceramic and metal oxides

block out metal substructure

(0.1mm thick)

20
Q

what do porcelain laminate veneers require?

A

Requires silination and resin bonding for strength

21
Q

modern feldspathic glass contains at least ____% leucite

A

20%

22
Q

why is modern feldspathic ceramic weaker than other forms of ceramics?

A

Relatively low strength (60 – 80 MPa) due to lower crystalline phase (high glass content for esthetics)

23
Q

______________ has the Highest Translucency (Superior Esthetics) of any dental ceramic

A

dental feldspathic porcelain

24
Q

what are the disadvantages of feldspathic porcelain?

A
  • Low strength

- Translucency prevents masking of discolored teeth

25
Q

ceramic fractures usually start from the ______ surface

A

internal

26
Q

why do ceramics fail?

A 
•  Brittle fracture –  (Griffiths flaws)
•  Initiated from internal surface
•  Cyclic fatigue –  Low loads
–  Many cycles
•  Stress corrosion
27
Q

what are the 2 development strategies for dental ceramics?

A

– Develop stronger materials to substitute for metal and veneer with feldspathic porcelain

– Develop higher strength translucent materials that can be used in full thickness or minimal reduction

28
Q

do “dicor like” (monolithic) or “Metal-ceramic like” (layered substructure) porcelain crowns use more feldspathic porcelain?

A

metal-ceramic like

29
Q

what are Griffith’s slips?

A

dislocation slips in the ceramic

-cause brittle fractures

30
Q

in what situations would feldspathic porcelain be indicated for use?

A
  • Layering porcelain for metal and all ceramic crowns
  • Feldspathic porcelain veneers

(any time you need aesthetics, but not a lot of strength)

fixed 3- midterm 2 (4 decks)

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