Restoration of a root filled tooth II Flashcards
Challenges of total crown replacement?
Restoration needs to be retained by the root
It must allow stress distribution
Must not cause root fracture
Must be durable
Principles in crown retention?
Retain as much dentine mass as possible
Restore dentine mass with a suitable material
Use an intra-radicular post in combination with the above if retention is compromised
Core build up materials materials?
Amalgam
Core composite
Glass ionomers
Compomers
Core build up: features of amalgam?
Strong
Reliable
Successful
Adhesion?
Core build up: features of composite?
Strong
Adhesive
Predictable?
Mismatch in thermal expansion
Core build up: features of glass ionomers?
Low tensile strength - brittle Unreliable Poor adhesion Excellent thermal match to tooth Dimensionally stable Reserve for patches only
Intra-radicular posts
Retain and support the core and coronal restoration
Aid in transferring functional loads to as wide an area as possible
Posts do not increase tooth fracture strength
Ideally a rigid material or elastic with a ferrule
Appropriate dimensions
What to consider with an intra-radicular post?
Parallel sided or tapered Surface configuration Active or passive fit Length, width Ferrule Anti-rotation Choice of material
Why are some intra-radicular posts parallel sided?
Resistance to axial forces
Tapered intra-radicular posts - what can they create?
A wedge effect
What to consider with surface configuration?
Casting roughness Sandblasted Etched Grooved Fluted
= Want to increase the surface area e.g. by increasing the casting roughness or sandblasting it = mechanical retention
How to aid retention of a post with an active system?
A thread cuts into the post-hole wall to aid post retention
= Greater stresses into the system
How to aid retention of a post with a passive system?
Post is retained in the hole by means of an adhesive lute
Surface of the post may be configured to aid adhesion
Pros and cons of the post being deeper in the tooth?
Deeper poles distribute stress better and increase retention
BUT
Disturb apical seals and destroy tooth substance
What should the post design be?
3-4mm short of apex OR
2/3 of total root length
1/2 greater than crown height
Why should posts be as narrow as possible but within the strength limits of the material?
What is wrong with this?
Strength is more dependent upon the outer perimeter of the root and are conservative
BUT narrow posts are weak and easily rotated
Ferrule (most important) - what is it?
Distance between the crown margin and interface between core and dentine
Greater ferrule = greater resistance to breakage of the crown
Improves retention and prevents post from bending and fracturing
Ferrule - what should it be?
At least 1.5mm of vertical sound tooth structure between the crown margin and the dentine-core interface that wraps around the whole tooth
Wha can provide the anti-rotation requirement of the post?
The irregular shape of the access cavity
Or can insert an anti-rotational pin
Prefabricated posts - what are they good for?
Circular post holes
Divergent roots
Narrow post holes - use SS
Cast posts - when to use?
Non-circular root canals
Direct/indirect technique
Choice of alloy - cobalt chrome, gold, nickel chrome
Path of withdrawal and insertion
What materials are used for posts? Characteristics?
Metal alloys
- Strong, corrosion resistant
- Prefabricated: SS, TiVAL
- Cast - gold alloys, nickel-chrome
Other prefabricated materials:
- Resin reinforced carbon fibre
- Ceramics
- Composite fibre
Which post system - rigid and elastic materials?
Rigid:
- SS
- Gold alloys
- Ni-Cr alloys
- Zirconium ceramics
Elastic
- Titanium
- Ti alloys
- Carbon fibre
- Composite fibre
Zirconia features?
High modulus of elasticity = extreme stiffness
Acceptable strength
Carbon fibre?
Low modulus of elasticity
V difficult to remove
What is the parapost system?
Complete integrated system Parallel posts Matching instruments and posts Anti-rotational pins Multiple clinical techniques Multiple materials and combinations
Parapost XP?
1 visit technique
Traditional parapost head design with X pattern
Indicated for amalgam cores and multi-rooted teeth where space is limited
Titanium or SS
19mm long
Parallel sided
- Evenly distributes functional forces, eliminating wedging effect of a tapered post
Passive fit
- Eliminates stress in the dentine compared to a screw post
Aesthetic crown materials?
All ceramic
Ceramic bonded to metal
What to do when a root filled tooth fails?
Cause analysis - biological or mechanical
Elimination of cause
Prevention of recurrence
Restoration of function and aesthetics using the most appropriate materials and techniques
Failure mechanisms of RF teeth?
Fatigue disintegration of labial margins
Opening of palatal margins
Bending of post, rotation, dislodgement, fracture of post
Fracture of root
Biological failure?
Periapical abscess
Periodontal disease
Recurrent caries
Mechanical failure?
Inappropriate coronal retention
Unfavourable displacing forces
Loss of structural integrity of tooth
Inappropriate use of materials and techniques
Success with post core crowns?
Lateral/vertical condensation with GP and bland root sealer
Leave 3-5mm GP at apical root terminus
Use a passive, adhesively retained custom post
Ferrule design for crown prep
