EMAX Crowns Flashcards
What types of ceramic are there?
Glass (contains silica):
-feldspathic (contains high percentage of silica)
Reinforced glass (silica reinforced by filler):
- Leucite reinforced
- Lithium Disilicate (Emax)
- Glass infiltrated alumina
Glass free:
Zirconium oxide (Emax)
Aluminia
What Emax products are used in the adh?
IPS Emax CAD and Press
-Lithium disilicate (used to create monolithic/single unit restorations in adh)
(the rest of the cards refer to this type of crown)
Why do glass free ceramics not require a metal coping?
Higher flexural strength
What ceramic is used for PBM’s? What is their flexural strengtH?
Feldspathic: 60-70 MPa
Leucite reinforced: 120 MPa
What is the flexural strength of lithium disilicate?
400MPa
What is the flexural strength of glass filled ceramic?
250-650 MPa
What is the flexural strength of glass free ceramics?
Aluminia: 600-700MPa
Zirconia: 1120MPa
What is the size of the lithium disilicate crystals which compose lithium disilicate cermaics?
5 micrometres x 0.8 micrometres
How do lithium disilicate crowns retain good translucency?
Low refractive index
What is special about the crystal alignment in emax crowns?
Limit crack propogation
crack deflection
What are the indications for emax press lithium disilicate crowns?
All single unit restorations:
- Anterior, posterior crowns
- Veneers
- Thin veneers
- Inlays, onlays
- Implants
Short span bridges in low stress environment:
-Anterior bridges
What are the contraindications of emax press lithium disilicate crowns?
Posterior bridges Long span bridges Subgingival margins Severely reduced residual dentition Bruxism
What 3 factors should an operator be aware of in shade selection?
- Shade of tooth/restoration
- Shade of preparation (assists technician in producing final shade of restoration)
- Shade of cement
(Due to translucency shade of cement can affect shade of final crown)
What are the rules dictating Emax preps?
- Supragingival margins
- No sharp points/edges
- All margins should be chamfer
What are the reduction dimensions for anterior emax crowns?
- Incisal: 1.5mm
- Labial+ lingual incisal 2/3: 1.2mm
- 1mm chamfer around circumference of tooth
- Margins should not be in occlusal contact
What are the reduction depths for an emax veneer?
- Labial: 0.6mm for both incisal and gingival 1/3 / 2/3
- Incisal: 0.7mm
- Margins should not be in occlusal contact
What are the reduction dimensions for an emax posterior crown?
- 1mm chamfer around circumference of tooth
- Buccal + lingual occlusal 2/3: 1.5mm
- Occlusal: 1.5mm
- Margins should not be in occlusal contact
What are the minimum dimensions and rules for onlay/inlay preps with lithium disilicate emax crowns?
1mm deep x 1mm wide
Proximal boxes should be flared (divergent) and form 100-120 degree angle with outer surface
Cusp reduction 1mm
What is the stone used to pour study models for lithium disilicate crowns?
Diestone
What should be included in the lab form?
- Pour upper tooth preparation in diestone
- Section 11 die
- Construct emax crown as per shade description (illustrate a digaram)
- Match shape of 11 crown to 21
What should be checked at teh cementation appointment?
- Fit
- Margin
- Occlusion
- contact points
- Contour
- Aesthetics
What conventional cements can be used and when can they be used?
Resin, RMGIC, GIC
- High strength material (lithium disilicate, metal and metal ceramic, oxide/glass free ceramic)
- Adequate retention (less than 8 degree taper and 4mm+ height)
- Adequate thickness (1.0mm + anterior, 1.5mm+ posterior)
When can adhesive cements be used?
All types (including feldspathic and leucite reinforced)
How should the fitting surface of the crown be treated prior to cementation
Etch with 5% HF acid (ADH have 9%) for 20 seconds
What extra step should be taken in using adhesive cement vs. conventional cement?
-Silane coupling agent applied to surface, left for 60 seconds and lightly air dried+ follow manufacturer’s instruction (vs just following manufacturer’s instruction)
What is the means survival rate of emax crowns?
98.4% at 4 years
What are the reasons for failure of emax crowns?
Fracture: 0.4%
Endodontic: 0.2%
Secondary caries: 0.2%
What are the advantages of emax crowns over PBM crowns?
- Metal free thus better aesthetics
- Can be adhesively cemented
- Lithium disilicate structure can prevent crack propogation
What are the disadvantages of emax crowns vs PBM crowns?
- Not as strong
- Limited data as to longevity
- Can not be burnished at margins (PBM lingual metal surface can)
- Not suitable for long span and posterior bridges
