Restorative - Bridges/crowns

Question 1

What is Ante’s law?

Answer 1

The root surface area of abutment tooth should be equal to or greater than that of the tooth being replaced with Pontic.

Question 2

What bridge is better for cases of mal-alignment?

Answer 2

Fixed moveable - reduces risk of excessive tooth tissue removal and pulpal damage
Indicated for use when abutment teeth are not parallel.

Question 3

What is the most mechanically unsound bridge design?

Answer 3

Cantilevers - all load is transmitted onto sole abutment tooth

Question 4

What type of cantilever bridge carries the lowest risk of failure?

Answer 4

Posterior bridge with large single abutment design mesial Pontic (mesial cantilever with distal abutment)
However, for 3 and 4 distal cantilever may be more advantageous due to antes law.

Question 5

When would you use a spring cantilever bridge?

Answer 5

When there is spacing anteriorly e.g. central missing - the 6 would be abutment and a bar would come over to the space meaning no metal is seen anteriorly.

Question 6

In RBB’s, what is the thickness or retainer and what material is used?

Answer 6

Nickel chromium/CoCr should be at least 0.7mm to achieve adequate rigidity.

Question 7

How is the fitting surface for a RBB prepared?

Answer 7

Prepare fitting surface by sandblasting with 50micron aluminium oxide (Al203)

Question 8

What is the 5 and 10yr surgical rates of RBB compared to conventional bridges?

Answer 8

RBB:
5yr 88%; 10yr 44%
Conventional:
94%

Question 9

What cements should be used for metal conventional bridges?

Answer 9

RMGI:

- Relyx, adhesive resin or GI, zinc phosphate

Question 10

What cements should be used for metal ceramic substructure bridges?

Answer 10

RMGI:

- relyx, adhesive resin or GI, zinc phosphate

Question 11

What cements should be used for adhesive bridges?

Answer 11

Panavia 21

- adhesive resin cement that cures when oxygen is excluded

Question 12

What cements should be used for ceramic adhesive resin bridges?

Answer 12

Relyx Unicem or nexus (adhesive universal resin cement)

Question 13

What prep is required for a MCC?

Answer 13

Non functional cusps: 2mm 
Functional cusps: 2.5mm 
Incisal: 1.5-2mm
Axial: 1-1.5mm 
Shoulder 1.2-1.3mm 
Between 10-20degree taper

Question 14

What prep is required for a metal crown?

Answer 14

Non functional cusps: >1mm
Functional cusps: >1.5mm
Thickness at least 0.5mm
Chamfer 0.3-0.5mm 10degree taper

Question 15

What prep is required for ceramic crowns?

Answer 15

Non functional cusps: 2mm
Functional cusps: 2.5mm
Occlusal: 1.5-2mm
Shoulder/heavy chamfer 1mm

Question 16

What type of resin bonded bridge design would give the best prognosis?

Answer 16

Distal cantilever anterior bridge

Question 17

How is porcelain used when creating all ceramic crowns and veneers?

Answer 17

Porcelain is fired into refractory die

Question 18

What type of crown has metal that acts as a heat sink reducing tendency for porcelain to crack on cooling?

Answer 18

Metal ceramic crowns

Question 19

What crown is constructed over a platinum foil matrix?

Answer 19

Porcelain jacket crown

Question 20

What crown involves sintering which increases the coping strength prior to veneering with feldspathic porcelain?

Answer 20

Zirconia supported crown

Question 21

What type of crown has colour and characterisation provided by surface tinting with a tendency to chip off?

Answer 21

Cast glass crown (dicor)

Question 22

What component helps to minimise creep in amalgam?

Answer 22

Copper (Cu)

Question 23

What component acts as oxygen scavenger in amalgam?

Answer 23

Zinc

Question 24

What is the role of a dentine conditioner (phosphoric acid)?

Answer 24

To dissolve the smear layer and demineralise the surface mineral exposing a collagenous matrix and the dentine tubules

Question 25

What is the purpose of the Denar self centring Facebow?

Answer 25

To locate the maxillary cast to the articular hinge axis in a similar way to the relative location of the maxilla to the mandible hinge axis.

Question 26

Protection of a polyaklenoate restoration immediately after placement is best achieved by?

Answer 26

Use of a barrier such as unfilled resin or varnish is best for protecting GIC restorations from imbibition/

Question 27

Why should a conventional GIC be covered and finished delayed for at least 24 hours?

Answer 27

Silaceous hydrogel is sensitive for moisture imbibition and desication