A rational approach to assessing root filled teeth in order to select an appropriate long term restorative option

1. 1
Restoration of
Endodontically
Treated Teeth
Selecting the Best Option
Restorative Treatment
Planning – First ensure:
Successful obturation of canal(s)
No symptoms (sens. to biting pressure)
No clinical signs (sens. to percussion)
No sens. to palpation
No sinus tract
No perio. probing deeper than 3mm
No radiographic evidence of
inflammatory disease
Restorative Treatment Goals
Maintain coronal and apical seal
Protect/preserve remaining
tooth
Provide supportive/retentive
foundation for definitive
restoration
Restore function and aesthetics
How does endo. weaken
remaining tooth structure?
1
Fracture
In Endo
Treated
Teeth
Iatrogenic
Causes
Non-
Iatrogenic
Causes
Tooth
Structure
Loss
Intra-
canal
Medicaments
Restorative
Procedures
Primary
Causes
Secondary
Causes
History of
Recurrent
Pathology
Anatomical
Position of
tooth
Ageing of
Dental
Tissues
3

2. 2
Inorganic Fraction
Carbonated Apatite
•Stiffness
•Ultimate Compressive strength
Water (free & bound)
Viscoelasticity
Stress absorbtion
Plasticizing & toughening
Distribution of stress/strain
Organic Fraction
(Type 1 collagen)
Resistance to crack propagation
Toughness
Ultimate tensile strength
Dentine
The role of different constituents on the mechanical integrity of dentine
3
Please see reference 3.
For a thorough discussion of
factors in play in the
predisposition of endo. treated
teeth to fracture
Endodontic Factors
Tooth stiffness
Access cavity preparation
Removal of roof of pulp chamber
Canal preparation
Medicaments
Heavy obturation forces?
(Lateral condensation)
5% reduction in tooth stiffness3
How does previous
restorative ₮ weaken teeth?
Isolates cusps
Undermines cusps
Broken cusps –
too weak to
withstand occlusal
forces
Sub-gingival
margins2
Restorative Factors
Tooth Stiffness
Occlusal cavity prep. – 20%
reduction
Loss of marginal ridge
integrity
MOD cavity prep. – 63%
reduction
3
Planning Treatment

3. 3
Consider
1. Amount of remaining tooth
structure
2. Anatomic position
3. Occlusal/Para-function forces
4. Restorative purpose/
requirements
5. Aesthetic requirements
1. Remaining Tooth Structure
More tooth structure – better
prognosis
E.g Crown prep. with even 1 mm
dentine above gingival margin
Double the fracture resistance of
preps finishing flat & level with
gingival margin
Ideally a ferrule effect2
Assessment of Remaining
Tooth Structure
1
2. Anatomic Position
Canines – Canine Guidance – Sufficient
natural dentine to resist lateral forces
Group function –
Canine/Pre-molar
guidance
1
3. Occlusal / Para-functional
Forces
Evidence of heavy
bruxism
Thin weak mesio- &
disto-buccal cusps
Early silver-
reinforced GIC base
Cut back and tooth
prepared for full
gold inlay/onlay
(partial crown)
1
4. Restorative purpose?
Single stand alone
restoration?
Bridge abutment?
RPD
Overdenture abutment?

4. 4
Stand-alone
1
Bridge abutment
1
Crown lengthening to
obtain sufficient tooth
structure for ferrule
Crown/root ratio?
Over-denture Root Filled
Anterior teeth
Assessment of
Remaining Structure
De-vitalized
by Trauma
Otherwise
intact
Restore the
access
cavity only
Aesthetics?
Minimally restored-
The other proximal surface is intact
Restore with composite
Small proximal rest. Small proximal-incisal rest.

5. 5
Large mesial
and distal
cavities plus
access cavity
Restore with
post-core and
full coverage
crown
Heavily
restored
Structurally
compromised
tooth
Long crown –
insufficient
remaining stucture
Reduce tooth and
Crown lengthening
procedure for the
distal & facial –
ferrule
Post?
Root Filled
Posterior Teeth
Assessment of
Remaining Structure Marginal
ridges
intact
1.
1
Restore access
cavity only
1
Moderately sized
cavity
Remove all
restoration – any
cracks?????? 1
Marginal ridge
undermined?

6. 6
Restoration
only
Marginal
ridge intact
1
Thin, weak or
undermined
cusps
Restore with
overlay
restoration
Cusp
reduction
External bevel
Cast metal overlay
Ceramic and pre-processed resin also possible
1
Core Build-ups
Avoid posts wherever
possible
Preps. for
partial crowns
Grooves for added resistance and
retention
Core
paste
Core paste
Using the pulp chamber
to retain the core
•Shoulder for ceramic or pre-processed resin
•chamfer for cast metal
1

7. 7
Margins to finish on sound
tooth
Partial crown
preparation to finish
on sound tooth
1
Nayyar
core-
for full
crown
2mm
2mm
Undercut
Weak sections
trimmed down
Ferrule
Crown restoration
Core paste
4
Undercuts in
the pulp
chamber
provide
retention and
resistance for
the core
Use the pulp
chamber Core paste
1
Posts?
Insufficient tooth
to retain the core
Insufficient core length
to retain crown
Post
Core paste2
2
Varying
amounts of
loss of tooth
structure
***** ***
?
Prognosis

8. 8
2 mm of remaining
coronal tooth allows for
preparation creating
ferrule effect4
Types of Posts
Pre-fabricated and
Cast
Prefabricated(*)
and Cast/Custom Posts(#)
Uniformly distributed
through cement layer
Little or noneSimilar to parallel,
serrated
#Cast post – parallel,
serrated
Wedging effectLittle or noneLow#Cast post – smooth
tapered
Wedging effect at the
tapered end
Little or noneSimilar to parallel
serrated
*Parallel, serrated -
tapered end
Relatively low –
distributed by
individual threads
Low after counter
rotation
Highest*Parallel threaded
High stresses -
accentuating
installation stress
Very high – wedging
stress
Intermediate*Tapered self-tapping
Uniformly distributed
through cement layer
Little or noneHigher
*Parallel serrated
(cemented vented)
Wedging effectLittle or noneLow*Tapered smooth
Functional StressInstallation stressRetentionType
5
Post Materials
Pre-fabricated
Stainless steel *
Titanium *
Glass-fibre reinforced
resin (bondable) #
Carbon-fibre
reinforced resin
(bondable) #
Cast/custom
Metallic
Gold *
Semi/Non-precious
C+B alloys *
Zirconia *
Rigid * Non-rigid #
Stress of Self Threading Posts
1. Threaded post
after placement1.
2. Increased stress
after tightening by ¼
turn
2.
1
Cemented Posts
Stress
upon
cementation
Stress in
function
+-
- +
1

9. 9
Cast Posts
1
Post length
Post should be at least as long
as the desired clinical crown
Mitigating factors
Curved canals
Taper of the root
Maintaining apical seal (4-5mm of GP)
Post diameter
Choice of post diameter is
based on canal/root size
Avoid unnecessary removal of
internal dentine (weakens root)
Post should fit canal dentine
walls snugly
Other Features
Positive stop of the core on coronal
tooth structure to prevent the post/
core unit from being forced apically
1.5 – 2.0mm of tooth structure for 360°
to receive the crown ferrule
Maintain no less than 1mm wall
thickness of radicular dentine
(preferably 2-3mm)
Risk of root fracture
Core
•Material
Crown
•Loading angle
•Ferrule
Remaining
Structure
•Dentine
•Water content
Post
•Length
•Shape
•Adhesion
•Diameter
•Elastic modulus
3
Fracture predisposing factors in post-core restorations

10. 10
3
Post
length
What type of post is
best?
Studies have shown
Bonded posts, parallel-sided posts - less
dentine stress
Non-bonded and tapered posts – more
dentine stress
Increase mod. of elasticity (stiffer) and
increased diameter of bonded post – less
dentine stress
Decreased post length – more dentine
stress3
Anterior tooth with little
coronal structure
Cast post/core
Serrated,
parallel-
sided post
with tapered
or rounded
tip
Posterior tooth with some
coronal structure
One or two
pre-fabricated
posts and
core paste
build-up
Posterior tooth with little
coronal structure
Cast post/core
unit with
secondary
insertion of a
wrought
post/s
through the
core
The final crown restoration
The reinforcement effect of
cementation of a full crown
with ferrule effect will make
the difference between stiff
and elastic posts less
obvious
3

11. 11
Tooth anatomy
Considerations for post
placement
Maxillary first molars
Deep concavities on furcal
surfaces
94% mesio-buccal roots
31% disto-buccal roots
17% palatal roots
Mandibular first molars
Concavities on furcal
surfaces of
All mesial roots
99% of distal roots
Maxillary first premolars
Deep mesial concavities
Slender roots with thin dentine
Maxillary first premolar
In this situation
the palatal root
would be the
ideal candidate
for the post
The buccal root is
highly irregular in
form
Buccal
Palatal
CEJ 2mm
4mm 6mm
2
How to tell from x-ray?
Root form
Curvature and
post
placement
2

12. 12
Post Cementation
Zinc Phosphate
Mechanical retention
No chemical
adhesion
Resin-modified GIC
(auto- or dual cure)
Adhesion to dentine
Resin Cement
(dual cure)
Adhesion to dentine
In-soluble when set
Moisture sensitive
prior to set
Difficult to place the
bond apically
References
1: Endodontics – 3rd Ed. Stock, Walker, Gulabivala
2:Pathways of the Pulp 9th Ed. Cohen & Hargreaves
3. “Mechanisms an Risk Factors for Fracture Predilection in Endodontically Treated
Teeth” Anil Kishen Endodontic Topics 2006, 13, 57-83
4. Colour Atlas of Endodontics William T Johnson
5. Problem Solving in Endodontics 4th Ed. Gutman, Dumsha, Lovdahl
6. “Restoration of Endodontically Treated Teeth” Morgano, Rodrigues, Sabrosa
Dental Clinics of North America 48 (2004) 397-416