6. ACC I Flashcards
When treatment planning ACC crowns the tooth most likely to have an ACC fracture is
molar
Define refractive index
the amount of light that passes through a material
_ is a function of refractive index
translucency
Excellent optical properties of teeth include
- Translucency
- Fluorescence
- Opalescence
Translucency is defined as
the ability to transmit light
Fluoresence of teeth is derived from
dentin (in absorbs fluorescent light and reflects back a bluish color)
What is opalescence
optic proper to teeth that has the ability to scatter blue light
Advantages and disadvantages of ACC
Advantages
- Superior esthetocs
- Good tissue response
- Conservative facial reduction (compared to PFM)
Disadvantages
- Reduced strength (lack of reinforced metal coping)
- Less conservative proximal and lingual reduction
How is the strength of ceramic materials tested
flexural strength measurement
How is flexural strength tested for
3-point bend test
3 point bend test places the ceramic material under (compressive/tensile) forces
tensile
What are the two phase of all ceramic restorations
glass (or silica) phase
crystalline phase
Tensile strength of feldspathic porcelain is (high/low)… glass phase is (high/low)… translucency is (high/low)… crystalline phase is (high/low)(high/low)
Strength= low
Glass phase= high
Translucency= high
Crystalline phase= low
Traditional feldspathic porcelain is used for what restorations
All ceramic veneers only
What are the two techniques used to make veneers from feldspathic porcelain
- Platinum foil
- Refractory die
Describe the difference in fabrication techniques
- Platinum foil
- Refractory die
Platinum foil
- Adapt foil to working cast
- layer porcelain
- Remove from die and bake (die is not strong enough to go in the oven
Refractory die
- Die is strong enough to go into the oven
- Layer porcelain on refractory die
Another name for leucite reinforces restoration is
IPS empress
Compare the amount of glass and crystalline phase in leucite compared to fedspathic porcelain
Leucite= less glass and more crystalline
Compare the composition of the leucite crystals and the feldspathic porcelain crystals
Leucite
-K2O, Al2O3, SiO2
Feldspathic porcelain
-Na2O, Al2O3, SiO2
Advantages of increased crystal conc. in leucite compared to feldspathic
- Increases CTE (coefficient thermal expansion)
- Crack deflection
- Enhanced etching pattern
- Increased bonding to resin cements
Indications for leucite reinforced restorations
- Anterior veneers
- Anterior crowns
- Posterior crowns
- Inlays and onlays
What are the two methods of fabrication for leucite reinforced restorations
- Pressed
- CAD CAM
Advantages of pressed technique for leucite
Better marginal adaptation
What are the two fabrication methods for lithium disilicate
- Lost wax technique (pressed)
- CAD CAM
T/F Lithium disilicate indicated for 3 unit bridges
t0 unless extending into molar region
LD is about _% crystalline phase
70%
Another name for LD is
e.max
Which has better marginal adaptation for LD restoration (pressed/CADCAM)
pressed
why is the marginal adaptation of pressed LD better than CAD CAM
when the ceramic is molten it has a low viscosity at high temps and pressures resulting in great marginal adaptation
Is Emax fulling sintered when milled? Why or why not?
no partially sintered in blue block because the partially milled form is softer and will not undergo dimensional change
Final sintering of an Emax restoration is achieved how
oven at 840 degrees C for ~16 mins
Final sintering of E.max results in
final strength and final shade
T/F There is a glass and crystalline phase with zirconia
f only crystalline
Uses for zirconia include
- Substructure (veneering)
- Full contour restorations
- Ortho brackets
- Post and cores
- IMplants and implant abutments
Characteristics of zirconia include
- High flexural strength
- High fracture toughness
- High radiopacity
- Biocompatible
- Low thermal conductivity
- Good esthetics (compared to PFM)
What are the three allotropes of zirconia
- Monoclinic
- Tetragonal
- Cubic
What are the temperatures at which each allotrope of zirconia is stable at
- Monoclinic- room temp
- Tetragonal - 1170 degrees C
- Cubic - 2370 degrees C
How can we attain different allotropes of zirconia at lower temps
addition of yytrium oxides (Y2O3), CeO2, MgO, or CaO
Pros and cons of cubic zirconia
Pros= translucent Cons= less strength and ability to inhibit crack propagation is less than tetragonal
Describe transformation toughening
- Addition of mineral oxides to the tetragonal phase –> stable at room temps –> transformation toughness
- Under external stress (crack) –> tetragonal converts to monoclinic (more stable at room temp) –> transformation is associated with volumetric expansion –> compression forces on the crack which prevents its propagation
What are the metals in each of the ACC materials
Zirconia= ZrO2 –> Zr
Leucite= K2AlSi2O2 –> Al
Lithium Disilicate= LiO2 –> Li
Alumina= Al2O3 –> Al
Initial use for zirconia was
Substructure (zirconia core with veneering ceramic over the top)
Full contour zirconia was introduced as a way to overcome
the chipping and fracture rates of veneering veramic
Full contour zirconia is indicated for
- Alternative to CCC and PFM
- Not meant to replace glass ceramic in esthetic zone
- Indicated in posterior region
- Parafunctional habits
- Short crowns
- Posterior bridges
Concerns of zirconia are
- Lack of long term clinical trials
- Abrassive to opposing dentition
- Compromised esthetics (high opacity)
- Adhesion not as reliable as ceramics
- Removal is difficult
Advantages of zirconia
- Esthetics superior to CCC and PFM
- Conservative prep
- High durability and biocompatible
- Inexpensive (relatively)
- Durable alternative to people with metal allergy
Is zirconia fully sintered when it is milled
no
Sintering time for a single unit zirconia crown is how long? Milling time?
90 min… 20 min
Options for shading zirconia
- Preshaded zirconia (zenostar shade concept)
- White zirconia shaded using infiltration liquid
- White zirconia with external staining
Pre-shaded zirconia can be used for what shades
A-D
What are the different pre-shades
- Pure (white)
- Light
- Medium
- Intense
- Sun
- Sun chroma
Feldspathic porcelains were (flexible/brittle)
brittle
Give the % of crystals in each restoration material
- Feldspathic
- Empress
- Emax
- Zirconia
20, 40, 70, 100%
What is the difference between monolithic and layered restoration
Monolithic= Restoration is made entirely from the same material like Lithium disilicate reinforced or zirconia
Layered= Lithium disilicate reinforced or zirconia with overlayed with porcelain
How can you increase esthetics while also maintaining strength
layering- can even do partial layering
List the amount of force than can be tolerated by these restorative materials
Veneering ceramic= 90 MPa
LiSiO2= 360-400 MPa
Zirconia= 1000 MPa
List the following materials in order of longest to shortest survival rates after 5 years. LD reinforced glass ceramic, Feldspathic porcelain, PFM
LD= PFM> Fedspathic/silica based crowns
Compare the survival rates in the posterior. Feldspathc/silica based ceramic, Layered zirconia, PFM
Feldspathc/silica based ceramic, Layered zirconia
Conclusions of the Sailer study which discussed the longevity of ACC and PFM restorations
- Survival of most types of ACC SC restorations= same as PFM in anterior and posterior regions
- Weaker feldspathic porcelain should be limited to anterior
- Zirconia based SC should not be considered as primary option due to high incidence of technical complications (refers to veneering Zr not monolithic Zr)
Why are sharp angles undesirable in crown preps
- stress fracture zone
Prep guidelines for ACC
- 1 mm finishline (modified shoulder or deep chamfer)
- 1.5mm incisal reduction
- (milled preps) incisal edge must be at least 1 mm thick
Why is a 1mm shoulder finishline desirable for ACC
places the ceramic under compressive forces (ceramic is stronger under compressive forces)
Deep chamfer places ceramic under (compressive/tensile) forces
tensile
For milled restorations why must the min. thickness of the prep be 1 mm
due to milling tool geometry
Minimal and maximal thickness of the finish line for empress in anterior and posterior
Anterior
-No less than 0.6 mm
Posterior
-No less than 1 mm
Minimal thickness for Pressed E.max at finishline for anterior and posterior restorations
Anterior
-0.3mm
Posterior
-1 mm
Minimal thickness for CAD E.max at finishline for anterior and posterior restorations
Anterior
-Min= 0.6mm
Posterior
-Min= 1 mm
Minimal thickness for zirconia for occlusal/incisal reduction and facial reduction
Occlusal/incisal
-1 mm
Facial
-0.7 mm
