principles of tooth preparations, all ceramic

Question 1

pjc, porcelain jacket crown

Answer 1

first ceramic crown, was most esthetic full veneer restoration dentistry offered, limited to single anterior teeth, tendency to fracture

Question 2

characteristics of pjc

Answer 2

made from high fusing porcelain.( platinum foils is used as support during firing process)

Question 3

first PJC with aluminum core was developed when?

Answer 3

1965 by mclean and hughes

Question 4

whats the benefit of the aluminum?

Answer 4

aluminum crystals prevent cracks from continuing. Usually about 40-50% alumina crystals

Question 5

advantages and disadvantages of the twin foil technique

Answer 5

A: the platinum matrix is left in the completed PJC. The platinum improves fracture resistance.
D: platinum foil ruins the esthetics of PJC

Question 6

how does the platinum bind to the porcelain?

Answer 6

chemical bond with oxides in porcelain.

Question 7

all ceramic systems are divided into what cementation types?

Answer 7

bonded-ceramic restorations

high-strength core restorations

Question 8

what are the bonded-ceramic restorations?

Answer 8

feldspathic porcelain restorations, highly filled glass ceramic restorations

Question 9

what are the high-stregth core restorations?

Answer 9

alumina reinforced substructures, zirconia reinforced substructures.

Question 10

advantages of bonded- ceramic restorations

Answer 10

prep is conservative, etched with hydrofluoric acid and bonded with resin cements

Question 11

feldspathic porcelain( bonded-ceramic restoration)

Answer 11

powder/liquid built, it condenses, requires sintering/firing, densification- shrinkage, requires 25% over-contoured

Question 12

highly filed glass ceramics

Answer 12

utilizes hot-pressed technique, These are IPS empress, IPS e.max

Question 13

what does CADCAM stand for?

Answer 13

computer aided design, computer aided manufacturing.

Question 14

additive CADCAM method

Answer 14

3D printing, has rapid prototyping

Question 15

subtractive CADCAM methos

Answer 15

mills from a solid block of material

Question 16

high-strength core restorations structure

Answer 16

substructure of ceramic + suprastructure of feldspathic porcelain( esthetics)

Question 17

possibilities of cores in high-stregth core restorations

Answer 17

alumina, zirconia, combination

Question 18

T/F, can you use hydrogluoric acid to etch high strength core restorations?

Answer 18

F, but it can be cemented with resin cement

Question 19

advantages of all ceramic crowns

Answer 19

excellent translucency, good tissue response, colors of luting agent affect appearance, No need for metal substructure which allows for less facial reduction but more lingual to resist the stronger forces.

Question 20

disadvantages of all ceramic crowns

Answer 20

reduced strength due to absence of reinforced metal, Its brittle so it requires a shoulder margin with 90 deg. cavosurface. Shoulder margins require more reduction.

Question 21

why are all ceramic crown not effective as retainers for FPD’s

Answer 21

brittleness requires large dimenstion of connectors (min. of 4X4mm cross sectionol dimension) this leads to impingement on interdental papilla and periodontal failure

Question 22

indicatios for all ceramic crowns

Answer 22

high esthetic areas, tooth needs to be relativley intact. a maximum porcelain thickness of 2mm is required for coronal areas.

Question 23

contraindications of all ceramic crowns

Answer 23

not good for molars, bad for teeth with unfavorable occlusal distribution. When its not possible to provide adequate support or even shoulder width of at least 1mm.

Question 24

incisal reduction of anteriors should be…..

Answer 24

1.5-2.0 mm

Question 25

how far apart should incical depth groups be?

Answer 25

1.3 mm

Question 26

facial and buccal surface reduction should be….

Answer 26

1mm. ( the depth initially should be .8mm to allow for finishing)

Question 27

lingual reduction

Answer 27

use football diamond bur after placing depth grooves of .8mm.

Question 28

margin preparation for all ceramic crown prep.

Answer 28

90 deg. cavosurface is optimal but at LECOM we do rounded shoulder margin. Margin should be 1mm wide smooth, continuous and free of any irregularities

Question 29

should you round off line angles?

Answer 29

yes, round off sharp line angles to prevent a wedging action which can cause fracture.