POSTERIOR FULL COVERAGE CROWNS I

Question 1

indications for posterior full coverage crowns

Answer 1

aesthetics
broken down posterior teeth 
TSL
trauma
atypical shape and hypoplastic conditions
aid support/retention for RPDs
retainers for cantilever bridges
alter occlusion

Question 2

reasons for provision of posterior crowns

Answer 2

1) Restoration or function
2) restoration of aesthetics (co primary with Mx premolars)
3) restore structural integrity and resist fracture
- esp with structurally compromised teeth and root filled teeth
4) integrate with other prosthesis

Question 3

root treated teeth are and why

Answer 3

weakened due to access cavity preparation
- loss of structural integreity associated with loss of roof of pulp chamber
loss of dentine elasticity
loss of roof of enamel over tooth

Question 4

why might posterior teeth require cuspal protection

Answer 4

structurally compromised by
- loss of marginal ridges
loss of substantial tooth structure inc cusps
large restorations

Question 5

how can you achieve cuspal protection

Answer 5

adhesive direct placement of composite restorations
adhesive indirect resin bonded restorations
cusp coverage cast restorations
full coverage restorations

Question 6

design considerations for posterior full coverage crowns

Answer 6

1) design considerations
- pulp status
- periodontal status
- caries status
2) restorative status
- eg crowns, restorations
3) ability to achieve retention and resistance form
4) occlusal considerations – is the tooth in function
5) position in the arch
6) aesthetic considerations
7) adjacent teeth: presence statis and position
8) materials for optimal function and aesthetics

Question 7

crowns disadvnatages

Answer 7

• aggressive insult to the tooth, dentine and odontoblasts (can infect pulp, may lead to irreversible or reversible pulpitis)
• thermal damage
• local anaesthesia (pulp less able to defend itself due to decreased vascularity)
• desiccation
• bacterial contamination

Question 8

dentine tubules are exposed to the following challenges

Answer 8

1) desiccation
2) thermal
3) chemical
4) osmotic

can lead them to bacterial toxins exposed to them

Question 9

materials that can be used

Answer 9

metal
metal ceramic (PFM)
ceramic (high strength, ie  zirconia)
acrylic
dentine bonded porcelain (feldespathic)
resin based composite

Question 10

preparation principles

Answer 10

preservation of tooth structure
retention
resistance
structural durability 
marginal integrity

Question 11

how is the crown retained ie what forms

Answer 11

1) retention form
- prevents dislodgement of crown in an axial direction
2) resistance form
- prevents dislodgement of the crown due to rotation from a lateral load

Question 12

tooth preparation desgin

Answer 12

1) preparations should be well defined and well finished
2) clear finish line should be visible
3) ceramic margins should be butt joint rounded shoulder
4) metal margin should have chamfer margins
5) all preparation line angels and point angles are best rounded

Question 13

what metal is used for full gold crown

Answer 13

type 3

hard due to the alloy w/copper

Question 14

PFM crown prep

Answer 14

buccal reduction 1.5mm shoulder
palatal 0.7mm cervical chamfer
functional cusp 1.5mm

Question 15

all ceramic crown

Answer 15

high strength ceramic core
most aesthetic but low edge strength
excensive reduction
generally milled CADCAM