Metal Ceramic Crowns

Question 1

What are the crown types in order of strongest to weakest?

Answer 1

Full veneer metal crown/all metal (FVMC), metal ceramic crown, all ceramic, and composite crowns

Question 2

What are the types of all ceramic crowns?

Answer 2

Zirconia crown, modern high strength ceramics, and porcelain jacket crowns (PJC)

Question 3

What are the methods for improving ceramic strength?

Answer 3

Metal substructure (MCC) and reinforced core systems

Question 4

What are the types of reinforced core systems?

Answer 4

Aluminous substructure (PJC), glass infused ceramics, hot pressed injection moulded, and machined ceramics

Question 5

Why is a metal ceramic crown substructure used?

Answer 5

Gives strength to overlying ceramic

Question 6

What does metal ceramic crown substructure need to strongly bond onto?

Answer 6

Overlying ceramic

Question 7

What does metal ceramic crown substructure use to strongly bond onto overlying ceramic?

Answer 7

Specific bonding alloys

Question 8

What is the melting point of alloy?

Answer 8

Higher than that of ceramic

Question 9

How is the melting point of alloy achieved?

Answer 9

By addition of Palladium and Platinum to Gold/by using base metal alloys (Co/Cr)

Question 10

What are the forces in ceramic-metal bonding?

Answer 10

Mechanical interlock and chemical bonding

Question 11

How is mechanical interlock achieved?

Answer 11

Sandblast metal surface

Question 12

How is chemical bonding achieved?

Answer 12

Formation of oxide layer on metal surface

Question 13

How is compression fit achieved?

Answer 13

Difference in co-efficient of thermal expansion

Question 14

What are the advantages of metal ceramic crowns?

Answer 14

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

Question 15

What are the disadvantages of metal ceramic crowns?

Answer 15

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

Question 16

What is parafunction?

Answer 16

Movements of the mandible that are outside normal function

Question 17

What are the generic principles of crown preparation?

Answer 17

Preservation of tooth structure, non-undercut preparation, retention and resistance, occlusal reduction appropriate, and margin type appropriate for crown type

Question 18

What are the metal ceramic crown principles of crown preparation?

Answer 18

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

Question 19

What is the ideal angle of the taper?

Answer 19

6 degrees

Question 20

What is the anterior preparation order?

Answer 20

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

Question 21

What is the margin of a metal-ceramic crown?

Answer 21

1.2mm shoulder minimum

Question 22

What is the occlusal reduction of a metal-ceramic crown?

Answer 22

1.5-2mm

Question 23

What is the functional cusp reduction?

Answer 23

0.5mm more

Question 24

What is the occlusal reduction of a metal only crown?

Answer 24

1-1.5mm

Question 25

What is the margin of a metal only crown?

Answer 25

0.5mm chamfer

Question 26

What is the diameter of Hi Di 554?

Answer 26

1.2-1.4mm

Question 27

What are the metal ceramic crown preparation burs?

Answer 27

Hi Di 554, Hi Di 501, Hi Di 557, and ‘rugby ball’ bur