principles of tooth preparations, all ceramic Flashcards
pjc, porcelain jacket crown
first ceramic crown, was most esthetic full veneer restoration dentistry offered, limited to single anterior teeth, tendency to fracture
characteristics of pjc
made from high fusing porcelain.( platinum foils is used as support during firing process)
first PJC with aluminum core was developed when?
1965 by mclean and hughes
whats the benefit of the aluminum?
aluminum crystals prevent cracks from continuing. Usually about 40-50% alumina crystals
advantages and disadvantages of the twin foil technique
A: the platinum matrix is left in the completed PJC. The platinum improves fracture resistance.
D: platinum foil ruins the esthetics of PJC
how does the platinum bind to the porcelain?
chemical bond with oxides in porcelain.
all ceramic systems are divided into what cementation types?
bonded-ceramic restorations
high-strength core restorations
what are the bonded-ceramic restorations?
feldspathic porcelain restorations, highly filled glass ceramic restorations
what are the high-stregth core restorations?
alumina reinforced substructures, zirconia reinforced substructures.
advantages of bonded- ceramic restorations
prep is conservative, etched with hydrofluoric acid and bonded with resin cements
feldspathic porcelain( bonded-ceramic restoration)
powder/liquid built, it condenses, requires sintering/firing, densification- shrinkage, requires 25% over-contoured
highly filed glass ceramics
utilizes hot-pressed technique, These are IPS empress, IPS e.max
what does CADCAM stand for?
computer aided design, computer aided manufacturing.
additive CADCAM method
3D printing, has rapid prototyping
subtractive CADCAM methos
mills from a solid block of material
high-strength core restorations structure
substructure of ceramic + suprastructure of feldspathic porcelain( esthetics)
possibilities of cores in high-stregth core restorations
alumina, zirconia, combination
T/F, can you use hydrogluoric acid to etch high strength core restorations?
F, but it can be cemented with resin cement
advantages of all ceramic crowns
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.
disadvantages of all ceramic crowns
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.
why are all ceramic crown not effective as retainers for FPD’s
brittleness requires large dimenstion of connectors (min. of 4X4mm cross sectionol dimension) this leads to impingement on interdental papilla and periodontal failure
indicatios for all ceramic crowns
high esthetic areas, tooth needs to be relativley intact. a maximum porcelain thickness of 2mm is required for coronal areas.
contraindications of all ceramic crowns
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.
incisal reduction of anteriors should be…..
1.5-2.0 mm
how far apart should incical depth groups be?
1.3 mm
facial and buccal surface reduction should be….
1mm. ( the depth initially should be .8mm to allow for finishing)
lingual reduction
use football diamond bur after placing depth grooves of .8mm.
margin preparation for all ceramic crown prep.
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
should you round off line angles?
yes, round off sharp line angles to prevent a wedging action which can cause fracture.
