PFM post and core

Question 1

What is a post retained crown?

Answer 1

Where insufficient coronal dentine remains to support a conventional preparation for a crown. The post in the root canal provides retention while the core replaces the lost dentine to provide sufficient height and parallelism for crown retention.

Question 2

What are the indications for post retained crown?

Answer 2

• mostly anterior teeth
• post root treatment
• insufficient tooth structure to enable crown prep
• to aid retention

Question 3

What are the dif posts available?

Answer 3

• tapered (less retentive)
• parallel (more retentive but can result in perforation)
• threaded (greatest retention but threads lead to stress fractures)
• serrated (best compromise between threaded and smooth, act by forming a cement lock between the metal of the post and the wall of the canal)

Question 4

Why have a separate post and crown?

Answer 4

• More retrievable

- enables the ferrule effect which provides extra strength

Question 5

What is the ferrule effect?

Answer 5

The ferrule effect be defined as ‘‘a 360 metal collar of the crown surrounding the parallel walls of the dentine extending coronal to the shoulder of the preparation”. Provides extra strength.
• A ferrule, in respect to teeth, is a band of coronal tooth structure that encircles the external dimension of residual tooth structure. At least 2mm high, 1mm thick.

Question 6

How do you do a post and core?

Answer 6

1. Remove coronal GP
2. Prepare the tooth
3. Take silicone impression of prep using impression post
4. Fit indirect cast metal post and core
5. Take new impression of crown prep with cost and core in situ
6. Fit crown

Question 7

Direct post and core method?

Answer 7

Bond fibre post and build up direct composite core

Question 8

How did you cement post and core?

Answer 8

Using zinc phosphate. Cleaned and dried post space, covered with thin layer of cement and seated with a pulsing motion whilst applying firm pressure until set.

Question 9

What are the advantages and disadvantages of a cast metal post and core?

Answer 9

+ Tried and tested, good results when used appropriately
+ Crown to root angle can be adjusted
+ Strength even in thin section
+ Removal possible but challenging
- post and root can fracture
- difficult to remove
- appearance if metal shines through crown
- possible corrosion and staining of dentine
- rigidity is more than dentine therefore places stress on it
- leakage of temp crown
- can get impression error

Question 10

What are the advantages and disadvantages of a fibre composite bonded core?

Answer 10

\+ reduced visits
\+ no demo post-crown
\+ metal free
\+ can be removed 
\+ good light transmission
\+ root fracture unusual
- Technique sensitive adhesive technology
- Bond is a weak link

Question 11

How did I remove original remaining post?

Answer 11

Used an ultrasonic scaler initially to loosen the cement around the tooth. And then used the trephine from the Masseran kit which I rotated anticlockwise to cut a 2mm channel around the post and then removed the post using a smaller trephine.