posts Flashcards
What are the tx objectives when restoring an endodontically treated tooth?
Retain tooth as functional unit in arch
Maintain coronal seal
Protect and preserve the remaining tooth structure
What should be considered when planning a final restoration?
Amount of supra-gingival remaining tooth structure
Position of tooth in the arch
Opposing dentition
Length, width and curvatures of root
What are the consequences of endo treating a tooth?
Proprioception reduced by 30%
Not more likely to fracture
Not more brittle
What is the aim of a post?
To retain a core
When is a post required?
If loss of 3 walls or no walls remaining
What is ferrule and how large should it be for a post?
The remaining circumference of dentine extending coronal of the preparation
2-3mm ideally but no less than 1.5mm
Why is a ferrule important?
Resists stresses which otherwise cause root fracture:
- functional lever forces
- lateral forces during post insertion
- wedging effect of tapered posts
What is the optimal post dimensions?
As long as possible while still leaving 3-5mm of GP apically
No more than 1/3 the root diameter
Placed in the straightest part of the canal
What are the different fabrication post types?
Prefabricated
Custom made - direct or indirect
What are the different post materials?
Metallic - SS, Ti and cast metal
Non metallic - glass fibre, ceramic fibre
What are the different post shapes?
Parallel
Tapered
What are the different post surface?
Serrated
Smooth
Threaded
What are the advantages of cast metal posts?
Used in flared canals
Follows canal shape as custom made
Conserves tooth tissue which reduces risk of perforation compared to parallel fibre posts
What are the disadvantages of cast metal posts?
Direct/indirect techniques:
- impression required
- lab and extra clinical stages
- more room for error
What are the advantages of fibre posts?
Tooth coloured - enhanced aesthetics
Compatible with current adhesive systems
Low elastic modulus - similar to dentine - posts absorb and dissipate stress rather than transfer to tooth
Can be placed immediately
What are the disadvantages of fibre posts?
Difficult to remove upon retreatment
Less conservative of tooth tissue than cast metal posts
When should fibre posts be avoided?
If there is less than 2-3mm of supragingival tooth structure present
If there is parafunction
If there is a deep overbite
What is the method of failure of cast metal posts?
Will fracture the root
What is the method of failure of fibre posts?
Will deboned at post-cement interface leading to recurrent caries
What are the advantages of tapered posts?
Follows root form ensuring maximal retaining root dentine apically
Stress concentration coronally
What are the disadvantages of tapered posts?
Wedging effect
Retained by cement
What are the advantages of parallel posts?
Uniform stress distributing along length
Increased pull-out strength
What are the disadvantages of parallel posts?
More tooth structure removed
Stress concentration apically
What is the advantage and disadvantage of self-threading posts?
Increased retention from self-threading into the dentine
This sets up fracture lines