PRS02 - Lecture 5 - Anterior RCT

Question 1

Why is restoring root filled anterior teeth difficult?

Answer 1

Outcome of the RCT - if a pre-existing endodontic infection is present then the length of time the infection will take to heal should be made prior to restoring the tooth.

Unknown amount of tooth substance remaining - there needs to sufficient tooth Remaining supragingivally to provide retention for the restoration (i.e. crown)

Quality of tooth subtance

Type of restoration used - each preparation will require different features to retain the restoration.

Question 2

What are the different treatment options for restoring an RCT anterior? (6)

Answer 2

Composite

GIC + composite

Composite core + crown

Metal post : composite + crown

Non-metal post : composite + crown

Cast post : cast core + crown

Question 3

What are the disadvantages of using a GIC or composite to restore an RCT anterior tooth? (2)

Answer 3

↑ size of the restoration -> ↓ in success rate -> due to coronal seal or marginal leakage

This could lead to the re-infection of the root canal

Question 4

When should you use a crown to restore RCT teeth (posterior and anterior)? (2)

Answer 4

RCT posterior teeth - all should be crowned to provide cuspal coverage to protect teeth and avoid further root fracture

RCT anterior teeth - it’s more subjective and indicated for: (5)

Appearance

Unknown remaining strength

Risk of tooth fracture

Little tooth substance remaining

Restore function

Question 5

What is the function of a post? (5)

Answer 5

Provide adequate retention of a core which supports a crown

Resist rotation within root canal

Preserve the apical seal (preserve 4-5mm of GP)

Avoid undue weakening of root

Avoid stress concentration in root

Question 6

What are the indications for a post? (3)

Answer 6

Only used for non-vital teeth (after RCT)

When there is < 3mm (height) of sound tooth remaining

After all other alternatives have been considered first (i.e. simple bonded restorations)

Question 7

What is the function of the core? (4)

Answer 7

Be firmly attached to the post (bonded)

Obtain resistance from root face (dentine supragingivally)

Ideal shape for the crown

Be correctly aligned in the interdental space

Question 8

What are the 2 types of posts? (4:3)

Answer 8

Direct - ready made

Can either be -> metal or fibre based

Cemented into mouth straight after canal preparation

↓ treatment time + appointments

Allows you to achieve a good coronal seal immediately (↓ risk of re-infection)

Indirect - made in the laboratory

An impression of the tooth needs to be taken after canal preparation

Its sent to the labratory for the post to be made

Only when it comes back can it be cemented

Question 9

What are the different post shapes - which is more retentive? (2:3)

Answer 9

Shape

Parallel

Tapered

(Retention -> parallel > tapered)

Surface

Smooth

Serrated

Threaded

(Retention -> threaded > serrated > smooth)

Question 10

Threaded posts are the most retentive but why should they be avoided? (1)

Answer 10

Although they provide mechanical retention they ↑ stress in the root canal system

Question 11

What factors make posts retentive?

Answer 11

↑ length = ↑ retention

↑ serrations = ↑ retention

Adhesive cement = ↑ retention

Question 12

How does width affect posts retention? (1)

Answer 12

↑ Width = ↑ risk of perofration or root fracture

Question 13

What should be the ideal length and width of a post? (2)

Answer 13

length - same as the height of the clinical crown

Width - should be 1-2mm dentine (at the apical portion of the canal) surrounding tip of the post (this is where the stress concentration occurs and is an area prone to root fracture)

Question 14

Compare the properties of different types of posts (3)

Answer 14

Parallel - smooth or serrated

Good for canals that are relatively parallel sided

Direct = metal (wrought) or fibre / Indirect = plastic (impression post) + cast (lab)

↑ Retention (compared to tapered)

↑ Risk of perforation

Tapered - smooth or serrated

Indirect only (made in the lab) - cast only (weaker than wrought post)

↓ Retention

↓ Risk of perforation (follows canal - narrow tip and wider coronal section)

Parallel Threaded (not recommended)

Most retentive

↑ Stresses on dentine

↑ Risk of root fracture

Question 15

How would you treat a tooth that has a ferrule of <2mm? (5)

Answer 15

Unrestorable - however you can:

Proceed with treatment but warn patient that prognosis is uncertain

Improve the amount of coronal tooth structure via crown lengthening surgery

Extract tooth

Bridge

Implants

Question 16

Describe the clincal steps of placing a post (16)

Answer 16

1) The tooth needs >2mm of supragingival coronal tooth structure (ferrule) 360^o around tooth

2) Take a PA radiograph to assess shape and size of the root and canal

3) Choose a canal that is straight (parallel) and wide

4) The longer the post, the more retentive

5) Determine the working length

6) Use Gates Glidens to remove GP from the canal (leaving atleast 5mm of GP apically)

7) Prepare the canal using post drills accordingly to desired width

8) Leave 1-2mm of dentine surrounding the tip of the post (prevents root fracture)

9) Verify that the post X fits snuggly into the canal

10) Remove 2-3mm of the post coronally

11) Use self-etching adhesive cement (i.e. RelyX Unicem) - it needs to be activated for 2 seconds then mixed (vibrate) for 10-15 seconds.

12) Insert cement into canal using elongation tip (quickly)

13) Clean excess cement

14) Light cure for 20 seconds or wait for 5 minutes

15) Bond and build up the composite core around the post

16) Prepare the core for a crown (in the normal way)