Post crowns Flashcards
When is a post-retained crown used?
Used when there is a lack of coronal tissue which prevents a conventional direct restoration
What does a post help aid?
Retention
Do posts strengthen teeth?
NO, they weaken them
What is the purpose of a post?
Provides retention for the core by utilising the root canal
What is the purpose of a core?
Replaced dentine and provide retention for the crown
What is the purpose of the crown?
To restore morphology and provide function
What are the indications for a post retained crown?
Insufficient coronal structure to support a conventional restoration (due to carries/fracture)
Root treated tooth (indicated or elective)
Commonly single rooted anterior teeth
What is ferrule?
A band of metal that totally encircles the tooth extending 2, onto sound tooth tissue.
What amount of coronal dentine is needed as a minimum?
1.5-2mm coronal dentine needed supragingivally needed as a minimum
Ideally continuously around the tooth
Increases resistance to lateral forces reducing a longitudinal fracture
What happens if there is a lack of ferrule?
Stress in post canal - root fracture
Presence of a ferrule means that the forces can be directed along the long axis of the tooth root tissue
What other advantages are there of a ferrule?
Increases post length which is important for retention
What is the difference between a passive and an active post?
Passive post sits in the tooth whereas an active post actively engages in the tooth
How is an indirect post/core made?
Impression of root canal needed
Preserve tooth structure - undercuts must be removed
Must fit the canal well
Less risk of iatrogenic complications during prep
Time consuming
Costly
Describe the active direct posts
Threaded screw posts - flutes engage with the tooth
Most retentive type of post
High risk of root fracture as they place stress on the root
Not routinely used
Describe passive direct posts
Retention through prep and luting cements
Parallel post retention > tapered post
Tapered post is more likely to cause a root fracture due to a wedging effect
Smooth or serrated
Serrated increases retention by 30-40%
Smooth sided posts create more stress compared to serrated - increased risk of root fracture
What are the advantages of a SS post?
easy to use
strong
inexpensive
What are the disadvantages of a SS post?
Rigidity can cause root fracture
Not aesthetic
Can corrode
Nickel allergy possible
What are the advantages of a titanium post?
Non allergenic
Does not corrode
What are the disadvantages of a titanium post?
Rigidity can cause a root fracture
Weaker than steel
Non aesthetic
What are the advantages of a carbon fibre post?
Bonds to tooth
Flexible
Removable
What are the disadvantages of a carbon fibre tooth?
Weak - prone to fracture
Non aesthetic - black
What are the advantages of a glass fibre post? (quartz>silica)
Bonds to tooth
Flexible
High tensile strength
Removable
Aesthetic
Similar elasticity to dentine
What are the disadvantages to glass fibre/quartz silica posts?
Weaker than metal posts
What are the benefits of fibre posts?
Glass content allows bonding
Bonding reduces root stress
Allows use of shorter, thinner posts conserving tooth tissue
Shape less important for retention
Depth of cure is same as for metal posts - cement considerations important
What are the 4 considerations during post prep?
Ferrule
Type of post
Length of post
Width of post
How much GP should be left apically?
3-5mm
5mm for more curved roots
Is retention better for a longer or shorter post
Longer post
Shorter post introduce greater stress than longer posts
At what length is retention adequate?
2/3rds root length
Post:crown
1.5:1
What are the properties of the post width?
Wider post prep (greater removal) increases the risk of root fracture
Thicker/wider posts introduce more stress. effect is pronounced in shorter posts
Post length is more important in generating stresses
Post diameter no greater than 1/3rd root width at length
Why is composite the best core to use?
Fractures are not catastrophic - composite fracture before tooth
Avoid amalgam in MOD cavity in root filled teeth
Which cements are used in cast posts
GIC
ZnP
Which cements are used in metal posts
GIC
ZNP
Which resins are used in fibre posts
Self or dual cured panacea/rely X unices
Tooth related reasons: post crowns fail?
Insufficient tooth
Caries
Root fracture
Endo fails
Perio fails
Restoration related post-crown fails?
Inadequate post design
Crown/post fracture
Occlusal factors
Cement failure
Iatrogenic reasons for failure
Perforation during prep
