Ceramics 2

Question 1

what are the uses of felspar/leucite ceramics used for?

Answer 1

• ceramic metal restos (mostly feldspar-based ceramics), all ceramic restos, partial dentures, and denture teeth

Question 2

describe the PFM bonding mechanisms

Answer 2

mechanical bonding– produced by sandblasting the casting alloy before bonding to porcelain

-chemical: mostly occurs because of the mixing of the OXIDE layer on the alloy surface and the oxide of the porcelain–> initial oxide is partially eliminated by sandblaster, but when temp rises the oxide reforms; it encourages GOOD WETTING of the porcelain; at the high temp, the two oxides diffuse into one another and create a mixed oxide zone

• in gold alloys, Fe promotes iron oxide film
  in other alloys, In, Sn, or Zn is added

however, if the alloy is overheated, the elements that create the oxide film are depleted –> no oxide

if an overly thick layer is created, it weakens the mixed oxide layer –> should be sandpblasted to minimize oxide film

Question 3

too great a mismatch of CTE between P and M creates DEBONDING and CRAZING

• when cooling, they must SRHINK at the SAME RATE so the stressed that may compromise the bond do not form; however, the metal canhave a slightly larger thermal coeff–>porcelain will be placed under compression (griffith cracks?)

Answer 3

ye

Question 4

ceramo-metal alloys are used for crowns and bridges

Answer 4

ye

Question 5

what are the majoy advantages of metal ceramics?

Answer 5

• more conservative tooth prep (metal is only a 0.5 margin, porcelain is 1.25mm)
• stronger, tougher
• margins
• long-span bridge
• more successful in posterior restos

Question 6

what are the major disadvantages of metal ceramics?

Answer 6

inferior esthetics–opaque

Question 7

properties of lithium disilicate? (glass ceramic)

Answer 7

• zero porosity
• high strength
• high toughness
• translucency
• pigmentation
• opalescence
• low or negative thermal expansion
• high temp stability
• machinability
• high chemical durability
• biocompatibility

Question 8

describe how glass ceramics are formed?

Answer 8

heat pressed

- ceramic is injected UNDER PRESSURE into the mold space then sintered

Question 9

what advantages does /lithium disilicate glass ceramic have over feldspathic?

Answer 9

stronger than feldspathic, plus an excellent fit

Question 10

what are the advantages and disadv of heat pressing lithium disilicate?

Answer 10

avoid large voids
produce high density ceramics with small crystals

disadv: equipment costs

Question 11

describe the process and logic behind creating glass-infiltrated alumina?

Answer 11

• ceramic powder is built up on POROUS
• produces porous low density core or coping
• glass poweder is placed in core, thn fired–>melts and flows into pores to create HIGH DENSITY GLASS CERAMIC CORE

Question 12

what is inceram spinell use for?

Answer 12

anterior crown, veneers, inlays and onlays; is the most TRANSLUCENT

Question 13

what is inceram alumina use for?

Answer 13

anterior crowns, bridges, and single cfowns in the post region, high translucency

Question 14

what is inceram xirconia used for?

Answer 14

post crowns and bridges

• moderate translucency

Question 15

spinell, alumina,and zirocnia is order of increase translucency

Answer 15

spinell > alumina > zirconia

Question 16

spinell, alumina, zirconia in order of increasing flexural strength

Answer 16

zirconia > alumina > spinell

Question 17

what are the methods used to improve porcelain low tensile and transverse strength

Answer 17

1. substrate reinforced
2. crack arresting
3. surface compression/crack closing
4. griffith crack elimination

Question 18

how does substrate reinforocing improve low tensile and transverse strength in porcelain?

Answer 18

core is VENEERED with CONVENTIONAL porcelain

Question 19

how does crack arresting inmprove the low tensile and transverse strength in porcelain?

Answer 19

increase crystalline phase –> improves resistance to crack propagation

Question 20

what is ceramming?

Answer 20

process of ppting crysalline phase in glassy matrix increase strength

Question 21

what does toughening of ceramic depend on?

Answer 21

• crystal type
• size
• volume
• interparticle spacing
• CTE

Question 22

why are small and uniformly dispersed particles favourable in porcelains?

Answer 22

if they are large and non-uniformly dispersed, they leave large large regions of unreinforced glass;

as well, the particles may not have the same CTE as the glass, so if they are large and clumped together, they may create tensile stress and could fracture the glass

Question 23

how does surface compression/crack closing work?

Answer 23

place SURFACE of glass resto under compression-closes griffith’s cracks; for crack propagation the external force must first overcome the compressive stress;

Question 24

what is griffith crack elimination?

Answer 24

ceramic fused and bonds to metal, eliminates cracks

Question 25

what are the best types of porcelain to use in stress-bearing situations?

Answer 25

glass-infiltrated core porcelain

Question 26

what are the best porcelains for esthetics?

Answer 26

feldspathic porcelain

Question 27

bond strength always decreases with time

Answer 27

ye

Question 28

what metals are added to promote oxides forming for PFMs?

Answer 28

• in gold alloys, Fe promotes iron oxide film

in other alloys, In, Sn, or Zn is added