L8 Post retained crowns: restoring endodontically treated teeth Flashcards
What is different about root filled teeth compared to non-root filled teeth?
- Extensive coronal damage and lack of tooth tissue
- Loss of radicular dentine
- General long-term prognosis is less favourable
What factors need to be considered before crowning a root treated tooth?
- Restorability assessment
- Resistance to tooth/root fracture, excessive loads will be placed on this tooth- is it able to withstand this?
- Retention of the core and final restoration with the remianing dental tissue
What are the restorative options for endo treated teeth?
- Direct restoration
- Onlay/inlay
- Post retained crown
What is a post-retained crown?
- A crown which mostly relies on a post inserted into the root canal for retention
- Used when the remaining coronal tooth structure is not sufficient for direct retention
- The post can be separate to the core, or a single intergral unit (bottom right image)
Describe the stucture of a post-retained crown.
- Tooth with ferrule
- Core matrix: fibre post and composite
- Metal substructure
- Ceramic outer crown
Are endodontically treated teeth more brittle?
No this is not a proven fact.
Brittleness is not a result of pulp necrosis. It tends to be a result of heavily restored and decayed teeth.
What risks are there when placing a post?
- Iatrogenic perforation
- Root fracture
- Cement failure
The majority of root filled teeth (61.4%) that fail, do so due to restorative reasons such as non-restorable caries and root fracture rather than endodontic failure.
What factors may influence your decision when deciding how to restore a tooth?
- Extensive coronal damage: a post will improve the retention of the core material
- Posterior root filled teeth: a cast restoration with occlusal coverage/full coronal coverage is preferred due to the high loads/forces applied on this tooth type
- Anterior root filled teeth: usually better suited to a large composite restoration rather than a conventional post and crown
Why is a radiograph required prior to treatment? What type of radiograph is needed?
- IOPA is the gold standard, an OPT can be used dependent on clarity
Need to have a good periapical radiograph to:
- Aid diagnosis
- Check status of periapical tissues
- Check status of root filling
- Check status of perio tissues
- Check root length and morphology
If endo re-treatment is needed, how should this be carried out?
- Consider the reasons why the current RCT is inadequate e.g. complex morphology
- Ensure the tooth is restorable
- Assess for signs and symptoms of disease
- Undertake re-treatment if tooth is favourable and you have the skill set
- Re assess and begin the restorative phase quickly to avoid risk of coronal microbial leakage
- Proceed with crown/post reatined crown ASAP to secure a coronal seal
How can posts be classified?
- Shape, fit, surface characteristics, material, fabrication method (prefabricated, customised/cast or lab made)
Which posts are active fit and which are passive fit?
Active:
- Tapered/threaded
- Flexi post
Passive:
- Fibre post
- Parallel/threaded
- Parallel/serated
- Cast post and core
What is the difference between active fit and passive fit posts?
Active: cut into dentine to aid retention
Passive: rely on adhesive to give the post retention
How does post length influence the success of post retained crowns?
- Longer post = more retention
- Post must be at least the length of the crown height
- Post cannot be too long: risk of apical root fracture
- Keep at least 4-5mm of root filling at the apex
How does post shape influence the success of post retained crowns?
- Post can be parallel or tapered
- Choice depends on canal configuration and root shape
- Tapered is generally less retentive but is also less destructive so is the preferred choice
- Hybrid = good compromise
How do post surface characteristics influence the success of post retained crowns?
- Smooth, serated or threaded
- Smooth is very passive, no where for cement to spread around the post
- Serrated preferred, increase surface area so more surface to bond to, and acts as micro mechanical retention
- Threading into canal may cause damage, especially tapered self-tapping
What feature must be added when using a post with a circular cross section?
An anti-rotation lock:
- Required to stop parallel or round posts from rotating around the canal
- Add a slot/groove to the canal
- Quite destructive, better idea to incorporate anti-rotation into the post design
What 2 materials can a post be made of?
- Metal
- Fibre reinforced resin
What fibre post material is easier to remove?
- Metal can be removed using a vibration technique
- Fibre posts tend to be much more challenging to remove and results in removing more natural tooth structure
Compare these 2 teeth and their crown:root and post ratio.
A:
- Short post
- When oblique force is applied to the tooth it will make the post want to rotate at the point of the dot
- Will either get crack propagation at this point, small microfracture and displacement higher up the post, or post will debond completely
B:
- Post is longer than crown height
- Point of rotation more apical
- Tooth will be more resistive to this force and rotation
- Will cause microflecture of the post, stress points at margin of crown, cement and post will be well maintained
- Tooth is supporting the crown and the post.
Why do we need to conserve coronal dentine?
- To create a ferrule of at least 2mm
- Bigger interface between tooth and post/core structure
- Protection against root fracture
How does a ferrule aid against rotative forces?
- Without a ferrule (middle image): rotational forcesare transferred laterally to the tooth, tooth is effectively screwed and will fracture
- With a ferrule (top image): whole structure will want to rotate, tooth will provide natural resistance against this
NB: bottom image (internal ring ferrule) not used in UDH, crown sat above ferrule and ferrule locks down into tooth, extra retention, circular so no anti-rotation support
What are the indirect and indirect post and core systems?
Cast gold alloys require impression of internal structure of the tooth which can be challenging.
Hybrid is no longer used.
What post systems are used in the UDH?
- ParaPost XP is titanium, grooves on surface to allow cement to flow out and for retention
What are the features of direct post and core systems?
- No lab required
- Reduced appointment time
- Can be metal or fibre posts
- Anterior or posterior
- Can be fiddly and tricky
What are the features of indirect post and core systems?
- Traditional
- Cast gold or hybrid
- Usually used for anterior teeth
- Requires straight canals because materials don’t bend
- More time consuming, more clinical stages so greater risk of errors
What are the features of metal posts?
- Traditional
- Generally considered to be stronger (not conclusive)
- Potentially more likely to cause root fracture dependent on tooth choice and other tooth related factors
- Metal shines through translucent crowns (unaesthetic)
- Can corrode
- Can be removed with US and burs (fibre posts tend to deflect the bur)
What are the features of fibre posts?
- Direct adhesive technique
- Less strong (contentious)
- Less likely to cause root fracture
- More aesthetic under some ceramic crowns
- Doesn’t corrode but resin degradation does occur (oestrogen release)
- Removal usually damages the tooth to beyond restoration
What are the key recommendations regarding post retained crowns?
- Only if apical condition is stable
- Only if canal length is greater than crown height
- Need approx. 1mm of remaining dentine around the post
- Consider multiple smaller posts for better prognosis
- Consider root anatomy and post shape
Describe the ParaPost Indirect System used in the phantom head lab.
- Impression post
- Burn out post
- Temporisation post
- Use drill of same diameter of all 3 posts
- Impression post placed in, impression taken, sent to lab and model made
- Burnt out post put into model, all cast, burnt out post turns into metal in the casting process
How do you prepare a tooth for a ParaPost?
- Remove coronal root filling with ultrasonic
- Gates-Glidden burs size 1-6 to prepare canal and remove GP
- ParaPost drills, start small and work up
Describe the process of creating a fibre post retained crown.
- Direct technique
- Once canal is correct depth and width for desired post, clean and prepare it using a TePe brush
- Paper points to dry canal
- Try in the post and check occlusion
- Cement post, ensure cement reaches very apex
- Build up core
- Crown prep
What is a Nayyar core, and what is a Nayyar style core?
- Nayyar core: coronal-radicular amalgam core
- Nayyar style core: different materials but same concept (e.g. reinforced glass ionomer or paracore instead of amalgam)
What are the critical points for success when restoring endo treated teeth?
- Adequate apical seal
- Minimal canal enlargement
- Adequate post length:crown ratio
- Anti-rotational stop (vertical stop)
- Presence of ferrule (2mm minimum)
- Good impression/cementation technique
- Interappointment seal and rapid provision
