Restoration of the root filled tooth Flashcards
Objectives of a restoration (4)
To create a mechanical system which mimics an un-restored tooth
- withstands impact loads
- resists wear
- distributes and dissipates stresses throughout the radicular dentine and supporting periodontal structures
Considerations for restoring and endodontically treated tooth? (8)
Adequacy of root filling
Preserving apical seal
Potential for coronal disassembly if necessary to re-navigate canal system
How long after RCT should I leave before restoring tooth?
Why was endo performed?
Was endo uneventful?
Is resultant root-filling technically excellent?
Is tooth asymptomatic?
Can I disassemble coronal resconstruction?
Why restore a RFT? (3)
Avoid bacterial leakage
Restore coronal structure
Restore aesthetics
Coronal leakage can be due to (6)
Breakdown of the temp
Delay in placing definitive coronal restoration
Fracture or crack of existing coronal restoration
Exposed dentine tubules
Presence of pre-existing or 2. caries
Contamination of pulpal space during post-hole prep and temp
How many teeth contaminated along whole length after 19 or 42 days? (2)
50%, length after dependent on type of micro-organism
100% of RFT exposed to saliva became contaminated within 30 days
What is the weak link in RCTs when it comes to coronal leakage? (4)
GP-Dentine interface
Sealer offers limited protection
Avoid packing excess GP across floor of pulp chamber in molars
Ensure effective seal of pulp chamber with GIC or RMGIC and restore with definitive restoration
Challenges in restoring RFT (7)
Severe or total coronal damage
Compromised mechanical integrity of remaining tooth
Reduced capability for stress distribution
Greater potential for bacterial leakage
Possible damage to perio supporting structures
Possible change in physical properties of dentine
Loss of proprioception from pulp
Loss of proprioception in RFT (2)
May be placed under greater oclcusal loads but are less able to withstand these forces
When to restore an RFT (2)
ASAP
When infection is resolved
Considerations when restoring an RFT (5)
Previous pulpal/ apical history? -elective -non-symptomatic -periapical abscess -periradicular cyst Rad history Symptoms history Effectiveness of RCT Age
Biomechanical principles of restoring RFT (5)
To restore structural integrity of radicular mass
To aid retention of coronal component
To restore crown with material adhesively united to radicular mass
Retain as much tooth structure as possible
Consider need for cuspal protection of posterior teeth
Considering need for cuspal protection of posterior teeth (2)
Required if more than 2 surfaces lost or under large occlusal forces
Does not always mean a crown!
Objectives when replacing dentine (8)
- Adeqaute compressive, tensile and flexural strengths to perform under load
- Matched elastic moduli
- Matched coefficient of thermal expansion
- Cariostatic chemistry
- Potential for bonding
- Radiopacity greater than dentine/ enamel
- Ease of mixing, manipulation and placement
- Cariostatic chemistry
Materials for replacing dentine (3)
Microfilled/ hybrid composites in combination with dentine bonding system
Amalgam
GIC to be used in limited circumstances
Materials used for intracoronal restorations (4)
Amalgam
Composite
Gold
Ceramics
Elastic modulus, fracture strength and compressive strength of enamel (3)
85GPa
10MPa
400MPa
Elastic modulus, fracture strength and compressive strength of dentine (3)
15GPa
50MPa
300MPa
Elastic modulus, fracture strength and compressive strength of composite (3)
20GPa
60MPa
100MPa
Elastic modulus, fracture strength and compressive strength of amalgam (3)
35GPa
100MPa
400MPa
Amalgam for intracoronal restorations (4)
Requires cuspal coverage
Substantial removal of tooth needed
Unaesthetic
May be bonded in posterior restorations
Composite for intracoronal restorations (7)
Adhesive
Unpredictable bond strength to dentine
Subject to chemical degridation
Highly effective for simple access closure of anterior teeth, in otherwise unrestored tooth
Adequate for small access cavities
Requires effective placement techniques
Large posterior restorations may benefit from cuspal protection
Gold intracoronal restorations (4)
Requires cuspal coverage
Provides cuspal bracing
Technically and clinically challenging
Can be cemented adhesively
Ceramic intracoronal restorations (5)
Adhesive cementation Same adhesive limitations as composite High elastic modulus - brittle Higher incidence of tooth fracture Small intracoronal OK
Extra-coronal restorations: there is a need for (5)
Intra-radicular retention Dentine core replacement Enamel replacement Requirements of each component Assembly of components
Challenges of total crown replacement (4)
Restoration needs to be retained by root
Must allow stress distribution
Must not cause root fracture
Must be durable
Principles in crown retention (3)
Retain as much dentine mass as possible
Restore dentine mass with suitable material if necessary
Use intra-radicular post in combination with the above only if retention is compromised
Core materials (4)
Amalgam
Core composite
Glass ionomers
Compomers
Core build-up with amalgam: factors (4)
Strong
Reliable
Successful
Adhesion?
Core build-up with composite: factors (4)
Strong
Adhesive
Predictable?
Mismatch in thermal expansion
Core build-up with glass ionomers: factors (6)
Low tensile strength - brittle Unreliable Poor adhesion Excellent thermal match to tooth Dimensionally stable Reserve for patches only
Intra-radicular posts function (2)
Retain and support core and coronal restoration
Aid in transferring functional loads to as wide an area as possible
Do intra-radicular posts increase tooth fracture strength? (1)
No
Ideal material for intra-radicular posts (4)
Ideally a rigid material or elastic with a Ferrule
Appropriate dimensions (width and length)
Prefabricated or cast
Integrated with an appropriate core material
Intra-radicular posts - considerations (8)
Parallel sided or tapered Surface configuration Active or passive fit Length, width Ferrule Anti-rotation Cast or prefabricated Choice of material
Why should intra-radicular posts be parallel sided? (1)
Force down axial direction of tooth (resistance to axial forces)
Intra-radicular posts: how is surface consideration achieved? (5)
Casting roughness Sandblasted Etched Grooved Fluted
Post retention: active vs passive system (4)
Active
-thread cuts into post-hole wall to aid post retention
-introduces great stresses into system
Passive
-post retained in hole by means of adhesive lute
-surface of post may be configures to aid adhesion
Depth of intra-radicular posts (4)
Deeper post holes distribute stress better
Deeper post holes increase retention
BUT
Deeper post holes disturb apical seals
Deeper post holes destroy tooth substance
Post design length (3)
3-4mm short of apex
2/3 of total root length
1/2 greater than crown height
Crown / root ratio in post design (2)
The greater the ratio the poorer the prognosis
Large building on small foundation is not safe place to live
Post design: width (2)
Strength more dependent upon outer perimeter of root
Post should be as narrow as possible but within strength limits of material
Post design: diameter (3)
Narrow posts are conservative of tooth substance
BUT
Narrow posts are weak
Narrow posts are easily rotated
Dentine Ferrule (3)
Retention of >1.5mm of vertical sound tooth structure between crown margin and dentine-core interface that wraps 360 degrees around tooth
Anti-rotation (1)
In most clinical cases, the irregular shape of access cavity will provide the required anti-rotation
Prefabricated post designs (3)
Circular post holes
Divergent roots
Narrow post holes (SS)
Cast post design (4)
Non-circular root-canals
Direct or indirect
Choice of alloy
Path of withdrawal and insertion
Choice of post material: two choices for elasticity (2)
Iso-elastic - same elasticity as dentine
Gradient of elasticity - increasing gradient from low dentine outside to a stiff (post) core inside
Metal alloys for intra-radicular posts (3)
Strong, corrosion resistant
Prefabricated: SS, TiVal
CastL gold alloys, nickel-chrome
Other precrabricated materials for intra-radicular posts (3)
Resin-reinforced carbon-fibre
Ceramics
Composite fibre
Rigid post systems (4)
SS
Gold alloys
Ni-Cr alloys
Zirconium ceramics
Zirconia post system properties (2)
High modulus of elasticity –> extreme stiffness
Acceptable strength
The Parapost system (6)
Complete integrated system Parallel posts Matching instruments and posts Anti-rotational pins Multiple clinical techniques Multiple materials and combinations
Extra-coronal restoration materials (3)
Gold
Ceramic
Porcelain fused to metal
Full-veneer gold crown (3)
Provides strong protective veneer over underlying structure
Margin of safety is greater than for ceramic or composite materials
Durable but unaesthetic
Aesthetic crowns types (2)
All ceramic
Ceramic bonded to metal
Biological fracture types (3)
Periapical abscess
Periodontal disease
Recurrent caries
Mechanical failure types (4)
Inappropriate coronal retention
Unfavourable displacing forces
Loss of structural integrity of tooth
Inappropriate use of materials and techniques
