Lecture 3 - Ceramic Restorations Flashcards
what are the applications for ceramics
- all ceramic crowns
- metal ceramic crowns
- implant abutments and implants
- denture teeth
- ceramic orthodontic brackets
what are the benefits of ceramics
- enhanced esthetics due to no metal and improved light transmission
- looks like a tooth
- most beneficial for teeth with normally colored dentin
can dentin color be shown through ceramic
yes
which materials do gingiva like
gold and ceramic
how does ceramic look like a real tooth
- great color replication to produce nearly any tooth shade
- reflect and absorb light rays stimulating enamel -refraction
- translucency with the different types of porcelain- incisal, dentin, opaque
describe the flexural strength of ceramics and what is flexural strength
- ceramics are brittle
- defined as strength of a material in bending
- stress on the outermost fibers of a bent test specimen at failure
what is fracture toughness
the resistance to fracture when crack present
describe the fracture toughness of metals
high fracture toughness due to plasticity at tip of crack, absorbs energy making crack propagation more difficult
describe the fracture toughness of ceramics
low fracture toughness
- little plasticity
ceramics _____ as they are fired
shrink
describe ceramics as a thermal insulator
- poor conductor of heat
- coefficient of thermal expansion is low. does not expand and contract much with heat and cold leading to fractures
the low fracture strength of glass ceramics is due to:
presence of microscopic flaws in the bulk material
what makes ceramics brittle
- porosities in the porcelain propagate cracks
- damage from grinding, heat propagates cracks
- these porosities can be extended or within the material
why do ceramics fail at lower than expected stress
crack propagation
what will stop the crack propagation in ceramics
until a particle is met
strength of ceramics is reduced in _____ environment
moist
what is stress corrosion
stress- dependent chemical reaction between water vapor and crack tip causing growth and fracture with comparatively little occlusal loading
what are the limitations of ceramics
- they are brittle
- crack propagation
- stress corrosion
what particle in ceramics make them more brittle
they dont have filler
what is the process of sintering
the reduction of porosities between particles as the ceramic becomes more rubbery
what is sintering in ceramics
- ceramic powder/liquid is built up and molded (feldspathic porcelain)
- process of heating ceramic powder once molded
- called firing the ceramic
what is glass transition temperature
- a range of temperature where porcelain starts to become molten
- a transition from solid to rubbery
what is the numbers of glass transition temperature
between 540 and 610 degrees celcius
glass transition temperature is _____ the ceramic melting point
below
what is heat pressing and what is another name for it
- relies on external pressure to sinter and shape the ceramic at high temperature
- restoration is made from a wax pattern - lost wax technique
- AKA high temperature injection molding
what does CAD/CAM stand for
computer aided design/ computer aided milling
what is hard milling
- already densely sintered material
- silicate, glass ceramics, resin based ceramics
- burs wear out quicker and takes longer to mill
what is soft milling
- partially sintered material
- zirconia and lithium disilicate (emax)
- sintering is completed in oven after manufacture
- more common
what are the types of blocks available for CAD/CAM and what are the kinds of each block
- glass ceramics: vita mark 2, IPS emax CAD, celtra duo ultra
- zirconia: IPS emac ZirCAD, 3M chairside zirconia, CEREC zirconia
- resin- ceramics: cerasmart, Vita enamic
- Resin: telio blocks
what are the CAD/CAM systems available
- Itero
- Trios
- Planmeca
-Carestream
what can be done to imrprove esthetics of blocks in CAD/CAM
stain and glaze
what are the classifications of ceramics
- predominately glass (veneers)
- particle filled glass ceramic (eMax)
- polycrystalline ceramic (zirconia)
describe predominately glass ceramics
-most translucent optical properties
- weakest material
- feldspathic porcelain
- can etch
describe particle filled glass ceramics (eMax)
- less translucency
- increased strength
- lithium disilicate
- can etch
describe polycrystalline ceramic (zirconia)
- low translucency
- highest strength
- alumina, zirconia
- cannot etch
how can we make ceramics stronger
- resin bonding with resin cements
- reinforcement of the crystalline structure of the ceramic
- transformation toughening
describe resin bonding
- can bond tooth to ceramic with the etchable ceramics
- use of a silane coupling agent enhances bond strength
- resin cement used- either light cure or dual cure
describe the reinforcement of the crystalline structure of the ceramic
- dispersed crystalline phase- higher strength and fracture resistance
- lithium disilicate
describe transformation toughening
- stress induced transformation
- unique to zirconia
- compressive forces at crack tip retard crack progagation
how does porcelain break
flexure and improper loading
how does resin bonding add strength to ceramics
resin bonding is a high strength cementation procedure so bonding ceramics will decrease the ability of the ceramic to flex, therefore adding strength
resin bonding causes a _______ in glass ceramic crown strength
50% increase
what specific components in resin bonding cause the increased strength in ceramics
- HF etched ceramic surface (retention)
- silane coupling agent (bifunctional monomers form a chemical bond)
- resin composite cement
- etched enamel/ dentin - adhesive layer
what is the mechanism of resin bonding
the movement of cement into the dentin tubules microtags and into the porcelain spaces
- this forms a matrix that has good retention
what is the minimal thickness of porcelain in veneers
0.3-0.5mm
how are tooth preps done for veneers
aimed at providing esthetics and physical support for the veneer
describe veeners
- not under heavy occlusal load
- resin bonded to enamel
- can be the most esthetic dental restoration possible
- can be so thin, underlying tooth color can affect optical properties
- most technically difficult to fabricate
what does adding crystalline aspects to the ceramic do
crack propagation is more difficult- small cracks begin but then have a harder time causing catastrophic failure
what is the flexural strength of feldspathic porcelain
60-70 MPa
what is the flexural strength of enamel
300 MPa
what is another method to strengthen porcelain
add a metal substructure - PFM
what is the only material used for veneers
feldspathic porcelain
what is leucite reinforced ceramic (empress) a hybrid of
feldspathic and eMax
what is the flexural strength of leucite reinforced ceramic
120-160MPa
would you use leucite reinforced ceramic on a posterior tooth
- crown: no
- onlay/inlay: maybe but only if occlusal forces are low
would resin bonding strengthen leucite reinforced ceramic
yes because it can be etched and therefore strength and retention is increased with resin bonding
what are the indications for leucite reinforced ceramic
anterior crowns and veneers
what is the flexural strength of lithium disilicate (eMax)
360-500 MPa
due to its increased strength lithium disilicate is used for:
- veneers
- anterior and posterior crowns
- anterior bridges
- inlays/onlays with low occlusal forces
what cements can lithium disilicate use
resin bonding and RMGI
should you use lithium disilicate ceramic for a posterior three unit bridge? why or why not
no because of increased fracture of material
what is survival rate
remaining in place either with or without complications
what is success rate
remaining unchanged and free of complications
what are the best to worst methods of strengthening ceramics
zirconia > infiltration and sintering > glass ceramic > veneering porcelain
what are the benefits of zirconia having a polycrystalline structure
- increased strength
- provides a surface that is not abrasive like porcelain but instead is gentle on opposing dentition
does resin bonding increase the strength of zirconia
no
what does resin bonding do for zirconia
increases retention
what do you have to do with zirconia since it cannot be etched
needs the internal restoration surface to be roughened
why cant zirconia be etched
contains no glass to etch
how can you roughen the internal surface of a zirconia restoration
- air abrasion
- diamond bur
what is needed for increased bonding of zirconia with resin cement
a bonding primer
what is the flexural strength of zirconia 3Y
1200 MPa
what cements can be used on 3Y zirconia
anything
describe the process of making a 3Y zirconia crown
has to be fired and will shrink to fit- shrinks about 25% during firing
how are zirconia crowns so strong
transformational toughening
what is transforamtional toughening
- stress induced transformation
- unique to zirconia
- compressive forces at crack tip retard crack progatation
what happens in zirconia when a crack is initiated
- tensile stress at crack tip causes tetragonal -> monoclinic shape change
- volume increase with compressive stresses in vicinity of crack tip leading to crack closure
what is added to make zirconia more translucent
yttria
what does the addition of yttria cause
decreased strength
describe 3Y zirconia
-100 percent tetragonal phase
- 0 percent cubic phase
- highest mechanical properties ~1200 MPa
- lowest translucency
describe 4Y zirconia
- 75% tetragonal phase
- 25% cubic phase
- high mechanical properties
- higher translucency
describe 5Y zirconia
- 50% tetragonal phase
- 50% cubic phase
- lowest mechanical properties
- highest translucency
where did PFZ crowns initially have failure
in the posterior
when a PFZ would fail, would the zirconia or porcelain fracture? and why
porcelain because of lack of porcelain support in zirconia substructure and the bond between the zirconia and the porcelain would not be able to overcome the difference in coefficient of thermal expansion between the zirconia core and the veneering porcelain
what is the most important factor to be right if placing a PFZ in the posterior
occlusion!
what is an additional benefit of PFZ crowns
the zirconia can help mask dark dentin- for example on an endo treated tooth
what cement can be used with zirconia
any cement
zirconia copings can be as thin as:
0.4mm
a monolithic zirconia crown prep can be very conservative similar to:
gold or PFM crown preps
is zirconia gentle on opposing teeth
yes it is considered wear friendly
what finish lines do you use for zirconia preps
chamfer or should finish line
what are the limitations of zirconia
- still finding sweet spot for strength and esthetics
- still working on bond of porcelain to zirconia
- dont have long term data
- still needs appropriate thickness and occlusion to survive the oral cavity
if you want the most esthetic anterior restoration what material would you use
- veneer: feldspathic porcleain
- crown: e.max or empress
if you want the most esthetic posterior restoration what material would you choose
- crown: emax or 5Y zirconia
if you have a bruxing patient what posterior restoration material would you use
- crown: 3Y zirconia or gold
what should you do for a bruxer/clencher who needs a bridge
monolithic zirconia or PFM
- possibly monolithic material with buccal porcleain
what materials have the most to least amount of wear on opposing dentition
ceramics > zirconia > gold and metal
how do you adjust glass ceramic veneers
- adjust after seated and bonded with resin cement
- use fine diamonds with a little water
- polish with diamond impregnated polishing paste
- internal surface should not be adjusted
how should you adjust e.max (lithium disilicate)
-adjustment outside the mouth is acceptable
- fine diamond with a little water
- polish with diamond impregnated polishing paste
- internal surface should not be adjusted
how should you adjust zirconia
- adjustment outside the mouth is acceptable
- fine diamond with a little water
- polish with diamond impregnanted polishing paste
- internal surface needs either air abrasion or diamond bur roughening prior to cementing
what do you do after adjustment with bur is done
- course polisher
- fine polisher
- felt wheel or brush with fine diamond polishing paste
what is the surface treatment for cementing lithium disilicate
apply 5% HF acid for 20 seconds, rinse and dry, apply silane for 1 minute and dry
what is the surface treatment before cementing for zirconium oxide
air abrasion with 50 micrometer aluminum oxiee at 7 PSI; apply an adhesion promoting agent containing MDP and dry
resin cements require a ____ environment
moisture free
resin cementes require a ____ for etched ceramics
silane coupling agent
what does the primer containing MDP with resin cements do
placed on zirconia to enhance the chemical bond to cements containing resin
when using RMGI cement what type of margin do you need and why
thick because it swells slightly
what type of margin can you use resin cements with
thin margins
when are RMGI cements contraindicated and why
in low strength ceramics because water absorption with setting of cement leading to slight expansion and possible fracture of ceramic at thin margin area
are RMGI cements acceptable with zirconia
yes
