Metal Ceramic Crowns Flashcards
What are the crown types in order of strongest to weakest?
Full veneer metal crown/all metal (FVMC), metal ceramic crown, all ceramic, and composite crowns
What are the types of all ceramic crowns?
Zirconia crown, modern high strength ceramics, and porcelain jacket crowns (PJC)
What are the methods for improving ceramic strength?
Metal substructure (MCC) and reinforced core systems
What are the types of reinforced core systems?
Aluminous substructure (PJC), glass infused ceramics, hot pressed injection moulded, and machined ceramics
Why is a metal ceramic crown substructure used?
Gives strength to overlying ceramic
What does metal ceramic crown substructure need to strongly bond onto?
Overlying ceramic
What does metal ceramic crown substructure use to strongly bond onto overlying ceramic?
Specific bonding alloys
What is the melting point of alloy?
Higher than that of ceramic
How is the melting point of alloy achieved?
By addition of Palladium and Platinum to Gold/by using base metal alloys (Co/Cr)
What are the forces in ceramic-metal bonding?
Mechanical interlock and chemical bonding
How is mechanical interlock achieved?
Sandblast metal surface
How is chemical bonding achieved?
Formation of oxide layer on metal surface
How is compression fit achieved?
Difference in co-efficient of thermal expansion
What are the advantages of metal ceramic crowns?
Metal strong in thin sections…less tooth removed, metal margin may allow a shallower preparation if aesthetics less critical, metal better in parafunction, metal margins easier to adjust, cheaper to make currently
What are the disadvantages of metal ceramic crowns?
Metal ceramic thickness more…more tooth removed, opacity requires good ceramic work..higher technical challenge, failure exposes metal…aesthetically catastrophic to patient, and potential metal allergy issues
What is parafunction?
Movements of the mandible that are outside normal function
What are the generic principles of crown preparation?
Preservation of tooth structure, non-undercut preparation, retention and resistance, occlusal reduction appropriate, and margin type appropriate for crown type
What are the metal ceramic crown principles of crown preparation?
Increased reduction for metal and ceramic, non-undercut preparation, taper and prep height, depends on whether metal or ceramic/metal, shoulder if metal/ceramic, and chamfer if metal alone
What is the ideal angle of the taper?
6 degrees
What is the anterior preparation order?
Incisal edge reduction (with/without depth grooves), inter-proximal reduction, margin preparation (all round chamfer first, then refine buccal margin with shoulder bur, then, change plane of reduction on labial aspect, reduce palatal concavity, refine sharp edges
What is the margin of a metal-ceramic crown?
1.2mm shoulder minimum
What is the occlusal reduction of a metal-ceramic crown?
1.5-2mm
What is the functional cusp reduction?
0.5mm more
What is the occlusal reduction of a metal only crown?
1-1.5mm
What is the margin of a metal only crown?
0.5mm chamfer
What is the diameter of Hi Di 554?
1.2-1.4mm
What are the metal ceramic crown preparation burs?
Hi Di 554, Hi Di 501, Hi Di 557, and ‘rugby ball’ bur
