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POST & CORE.ppt
1. POST & CORE
DR. HARSHA R H
MDS
Dept Of
Prosthodontics
Navodaya Dental
College
2. INTRODUCTION
Endodontic treatment good prognosis
Loss of considerable amount of tooth structure
Caries
Endodontic treatment &/or previous restoration
Retention of subsequent restoration problematic
Increases # function
Restoring teeth complex procedures
3. HISTORY
Methods of restoring pulp less teeth for more than 250yrs.
1728-Pierre Fouchard -roots of maxillary anteriors teeth
Pivot teeth –Mastic “Tenons”
Replacement crowns
1800-Dubois de chamante
-porcelain teeth-pivot teeth
1839-Chapin Harris - The Dental Art –
pivoting of the artificial crowns to natural roots
“The best that can be employed”
4. 1849-Sir John Tomes - Dental philosophy and surgery
principles of fabricating posts
1878-C.M.Richmond-porcelain faced dowel crowns
Pivot/post with porcelain facing
5. 1880-U.S. seasoned wood as pivots
19th century-Davis crown -gold casting
1960-carbon fiber post
1968-Mare Reymond-
DT Light transmitting post
1989- modification of carbon fiber post
1996-Meyeberg - Zirconium posts
6. TREATMENT PLANNING
Good apical seal
No apical sensitivity
No sensitivity to pressure
No active inflammation
No exudate
No sinus
7. Changes accompanying root canal therapy
Loss of tooth structure
Altered physical characteristics
Altered esthetics
Amount of remaining tooth structure
Anatomic position of the tooth
Functional load on the tooth
Esthetic requirements for the tooth
8. Why post and core?
Retain the core buildup material
&
Reinforce coronal tooth structure
Replace the missing portion and to
protect the remaining tooth structure
Basically consists of
•Post
•Core and
•Final restoration
post strengthen the root??
9. POST AND CORE
POST(DOWEL):
The dowel is a post or other relatively rigid restorative material
placed in the root of a non vital tooth”
CORE:
The core consists of restorative material placed in the
coronal area of a tooth
It replaces the carious, fractured or otherwise missing
coronal structure and retains the final restoration/crown.
CLASSIFICATION OF POST(DOWEL):
Categorized by number of different ways
Broadly categorized into:
Custom cast posts and
Preformed post systems
10. Preformed dowel system can be further categorized based
on their geometric shape
Tapered posts
Parallel posts
further classified by their surface configuration as
Smooth posts
Serrated posts
Threaded posts
Based on mode of retention of the post to the canal portion
Active posts Passive posts
v-lock post c-post snow post
flexi-post cosmopost aestheti post
para pos
11. Based on material
Non metallic posts
C-post
Aestheti Plus post
Cera post
Metallic posts
Dentatus post
Root post
Para post
12. Ideal properties of a post
.Maximum protection
.Adequate retention with in the root
.Maximum retention of the core and crown
.Maximum protection of the crown margin/cement seal
.Pleasing esthetics when indicated
.High radiographic visibility
.Retrievability
.Biocompatibility
13. Factors which effect the post selection
post length
post shape
post diameter
Surface configuration
post material/composition
Luting agent
14. POST LENGTH
Equal to the cervico incisal or cervico occlusal length of crown
Longer than the crown
One and one third the crown length
Half the root length
Two third the root length
Four fifth the root length
Half way between crestal bone and root apex
As long as possible without disturbing the apical seal
4.00mm safety zone is required for apical seal
• 2-3mm ---definite leakage
4 mm-- adequate—Nixon et al
5mm—Apical seal---Mattison et al
15. Three quarters the length of root in long rooted teeth
In average length teeth-retain apical 5.00mm
Should extend at least 4mm apical to bone crest
Molar posts not be extended more than 7mm
16. POST SHAPE
Parallel sided
parallel sided posts - removal of more tooth structure
less chance of root fracture
Parallel design improves post retention and force distribution.
More retentive than tapered forms
Tapered form
Produce wedging effect - significant lateral forces
vertical root fracture
Requires less removal of tooth structure
Limited to use in tapered root systems
17. POST DIAMETER
Large diameter post - higher retention
-Standlee, Kvist
Increase in diameter - no significant increase in retention
-Kurer,Harison
Length is most important factor in post retention
and diameter is only a secondary factor
- Krupp et al
Increase in post diameter causes higher stress in the tooth
— Mattison
Potential for root fracture increases by SIX times/mm of
diameter
18. Teeth with thicker diameter (1.8mm) post fractured more
easily than with a thinner (1.3mm)
--Trabert et al
Photoelastic studies - internal stresses are less with thinner posts
FEM studies have failed to demonstrate increase in stress
with increase in diameter of the posts
Recent FEM analysis and fractographic analysis
—Dent. Trauma—2004
Tensile loading—strains/deformations in inner dentin and
stress at the outer dentin surface
19. To avoid root perforation by excessive preparation,
safe instrument diameters are proposed
Tilk et al Shillingburg et al
Small teeth 0.6-0.7mm 0.7mm
Larger diameter 1.00mm 1.7mm
Remaining 0.8-0.9mm 1.3mm
small diameter root—0.6-0.7mm
large diameter root---1-1.2mm
in molars-should not exceed more than 7mm in length
even in thicker roots.
20. SURFACE CONFIGURATION
Smooth surface - least retentive
Serrated surface - more retentive
Threaded surface - most retentive
intended to engage canal walls
significant stress in the tooth
Modifications of surface
21. LUTING AGENTS
Resin cements
Higher retention
Lower microleakage
protection by strengthening of root
Superiority of one cement over another is not clear
Bonded resin cements - strengthening effects in roots
for some period of time
Technique sensitive
Contamination
Delivery of the etchent/ bonding agent
When using resin cements use dual cure resin cement
22. POST MATERIALS
functional stress, resist corrosion and biocompatible
– adequate stiffness
- high yield strength
- favorable fatigue properties to function adequately
Allergy and sensitivity with Ni-Cr alloy
Titanium preformed post-carbon fiber post
Ceramic posts
Poly ethylene woven posts
23. PRINCIPLES OF TOOTH PREPARATION
Many of the principles relating to the tooth preparation
apply equally to the endodotically treated teeth
Additional concepts to avoid failure
Conservation of tooth structure
Retention form
Resistance form
24. Conservation of tooth structure
ROOT CANAL
Remove only minimal tooth structure from the canal
Over enlargement lead to weakening or perforation
chances of splitting while cementation or functioning
Canal be enlarged to enable the post
to fit snugly for strength & retention
25. Crown
The amount of remaining tooth structure
is the single most important predictor of clinical success
Caries, previous restoration and
endodontic cavity preparation considerable loss of tooth structure
Further reduction to accommodate the crown and
to remove undercuts
little coronal dentin
As much coronal tooth structure should be conserved
to reduce the stress concentration at the gingival margin
Extension of the axial wall of the crown apical to
the missing tooth structure provides as a ferrule - hold the
remaining tooth structure preventing root fracture during function
26. RETENTION FORM
Dislodgement of post retained anterior crown
is due to inadequate retention form of the prepared post
Retention of the post is mainly affected by –
The preparation geometry
Post length
Post diameter
Surface texture
The luting agent
27. PREPARATION GEOMETRY
Anterior teeth
Some canals have nearly circular cross section - prepared to give
parallel walls or a minimum taper allowing the use of preformed
post of respective configuration
Retention is proportional to the surface area
28. Posterior teeth
Relatively long post with circular cross section should be
avoided
Relatively short posts in divergent canals better retention
3mm or more amount of tooth structure is present --
preparation of the root canal is not necessary
Widest canals are selected for post placement in posterior
teeth
29. RESISTANCE FORM
An excessive internal preparation of root
weakens the root and possibility of failure in restoration
Post design should distribute stresses as evenly as possible
FACTORS AFFECTING RESISTANCE
1. Crown bevel-
Part of the crown extends past post & core margin - extends
on natural tooth structure
Effective tooth 360 degrees and
at least 1.5mm on to tooth structure below margin
30. 2. Vertical remaining tooth structure-
3. Anti rotational features-
Oblong canal space provides resistance to rotational forces
When coronal dentin is lost, anti rotation element can be
placed in the bulkiest aspect of teeth
31. Crown& crown preparation
Minimum of 2mm dentin axial wall height
Parallel axial walls
Metal should encircle the tooth
Margins on solid tooth structure
Not invade attachment apparatus
32. Greatest stress concentration in the tooth is found at the shoulder,
inter proximally and at the apex
dentin should be preserved in these areas if possible
Stresses are reduced as the post length increases
Parallel sided posts distribute stresses more evenly
Sharp angles should be avoided high stress during loading
High stress will be generated when cementing parallel sided posts
which don’t have escape vent
33. THE FERRULE EFFECT
FERRULE is a metal ring or cap put around the end
of a tool, cane to provide added strength
OR
Is a vertical band of tooth structure at the gingival aspect of
a crown preparation
Primarily -- resistance form and enhances longevity
Circumferential contra bevel reinforces the coronal aspect
Positive occlusal seat - acts as a anti rotational device
In teeth with little or no clinical crown remaining
large contra bevel on root surface with finish of crown preparation
acts as ferrule
Ferrule must be on tooth structure and not invade the
attachment apparatus
34. Types of ferrule
&
Core ferrule and
Crown ferrule
Crown ferrule > effective - core ferrule
Ferrule length is more important than the post length
in increasing # of tooth.
--- Int J P 1999
2mm of dentin ferrule of crown more effectively
enhances # resistance of custom cast post and core.
-----JPD2003
Even presence of 1mm of ferrule provides twice the amount
of resistance to fracture
35. CORE AND CORE MATERIALS
The core is anchored to the tooth by a direct connection
of the core into canal or through a post
Tooth + post & core mechanical, chemical/adhesive
The remaining tooth structure can be altered to
enhance retention of the core or to provide resistance
to core rotation under function
The irregular nature -residual coronal tooth structure,
morphology of the pulp chamber & canal orifices
additional alterations
36. Desirable properties of core material include
•Dimensional stability
•Ease of manipulation
•Natural tooth color
•Rapid and hard setting > immediate crown preparation
•High compressive and tensile strength
•High modulus of elasticity and fracture toughness
•Low plastic deformation
•Bio compatibility
•Cariostatic and low cost
37. CAST CORE
A cast core forming a one piece post and core
traditional and proven method of restoring a tooth
Advantages
Core does not depend on mechanical means
Can be retrieved for endodontic retreatment
Non corrosive when cast with noble metal
Disadvantages
The number of appointments required are more
Laboratory expenses and time required for fabrication
Technique sensitive in the laboratory phase
38. COMPOSITE RESIN CORE
Advantages
Ease of manipulation
Less time consuming and
A additional retention and anti rotation features easily achieved
Disadvantages
Polymerization shrinkage & contraction- marginal discrepancy & micro cracks
Difference in co-efficient of thermal expansion micro leakage
At least 2mm coronal tooth structure - for build up
Technique sensitivity
Retention of core with zirconium posts
39. GLASS IONOMER/ METAL MODOFIED GIC CORE
In teeth with significant amount of dentin
remaining and additional retention is available
Main advantage is the anticariogenic potential
High solubility and moisture sensitivity
Limited for building up of small area
Low retention to preformed dowels
Low strength and fracture toughness
Technique sensitivity
Usually not recommended - low strength
--JPD-1982
40. RMGIC CORE:
Improved properties conventional GIC
Bond strength close to that of bonded composite restoration
Minimal microleakage
Disadvantage
Dimensional instability in the presence of moisture > expansion
Can fracture/ failure of the ceramic crowns
-IJP-1998
41. CORONAL RADICULAR CORE
Used as an alternative - traditional cast post and core
This consists of core that replaces the coronal tooth structure
extends 2-4mm into coronal portion of root canal
Utilizes conventional restorative materials-amalgam,
composite resins or modified GIC
Provides adequate strength and retention as a core
In combination with bonding - gingival discoloration, provides
protection against coronal leakage
42. TECHNIQUES FOR POST AND CORE FABRICATION
Tooth preparation for post and core can be accomplished in
3 steps-
1.removal of root canal filling material
2.enlargement of the canal
3.preparation of the coronal tooth structure
post and core fabrication is best done
after the coronal preparation of the tooth structure
Amount of tooth preparation to be done
depends on the final restoration it in turn
affects the extent of core fabrication
43. REMOVAL OF ENDODONTIC FILLING MATERIAL
The amount of gutta percha removal is dictated by
The desired post length, type, bone height and
the root morphology
Warmed endodontic plugger
rotary instrument
Rotary instrumentation > straying from the canal and cutting the
excess radicular dentin - weakening / result in lateral perforation
44. ENLAREMENT OF THE ROOT CANAL SPACE
The Peeso reamers & Gates Glidden drill
Available in sizes 0.7-1.7mm & 0.6-1.5mm dia
in graduated sizes from 1-6, non cutting tips
canal preparation - keyway or a groove with
bur no. 170 in the bulkiest portion of Canal to
a depth of diameter of the bur and length of bur
45. PHILOSOPHIES OF POST SPACE PREPARATION
Conservationist –
narrowest diameter for certain post length
Pilo & Tamse
Proportionists -
diameter should not be > 1/3 root diameter
Stern & Harshfield
Preservationists –
at least 1mm of sound dentin around entire post
46. PROCEDURE
Begin removal of gutta percha with heated condenser
Measure as large size Peeso reamer as will fit the
obturated space against a radiograph leaving apical 5mm of filling
with reference to a stable land mark
Once gutta percha is removed check the accuracy
Enlarge the canal to a desired size - preserve a minimum of 1mm
around the post at mid root and beyond and should not be one
third the diameter of the root at the CEJ
47. PREPARATION OF THE CORONAL TOOTH STRUCTURE
Prepare the remaining tooth structure adequately
for the extra coronal restoration
All internal and external under cuts are removed
Any unsupported tooth structure if present should be removed
The remaining portion is prepared perpendicular to
the post which will create a positive stop while cementing the
post
48.
49. PREFABRICATED POSTS
Enlarge the canal one to two sizes with a drill or reamer
smaller than the drill prescribed by the manufacturer
A wide range of prefabricated posts
shapes and sizes
parallel sided prefabricated are recommended for conservatively
prepared root canals with roots of circular cross section.
Excessively prepared canals managed with custom post.
however situation should be evaluated on individual basis
50. Maximum recommended dowel size with outline of
root at mid root portion with root outline
and post diameters.
Outline of
Root at mid
root area
and
post diameters
51. CUSTOM CAST POST AND CORE
FABRICATION TECHNIQUE
Direct or indirect technique
A direct technique using inlay wax, auto polymerizing or light
polymerizing resin usually for single teeth restoration
Indirect technique – multiple teeth or tooth with multiple canals
The post/pin should extend the full length of prepared canal
soft wax is added or a brush bead technique is used to add resin
52. Deficiency or excess is corrected and coronal part
is shaped
The finish line prepared should be on tooth and
not on the core
Remove the pattern and proceed with the
laboratory steps
53. Indirect technique
impression is made with a elastomeric impression material with
adequate reinforcement to prevent distortion
the impression material can either be placed in the canal with a
lentulo spiral or can be injected into the post Space
impression is removed , evaluated and working cast prepared
post pattern prepared and other procedures carried out
55. PROVISIONAL RESTRORATIONS IN
POST AND CORE FABRICATION
A provisional restoration plays an important role
in the successful restoration of a tooth
FUNCTIONS
•Esthetics
•Protection of the tooth from further damage
•Prevents migration of adjacent teeth
•provides occlusal function
56. crown formers and posts can be used in various combinations-
•Polycarbonate crowns relined with acrylic
•Plastic posts relined with acrylic resin
•Silicone post reinforced with a paper clip or orthodontic wire
•Braided SS wire with acrylic resin crown
•SS crowns with reinforcement
•Reamers or files reinforced with acrylic
57. RECENT ADVANCES
Prefabricated posts- increasingly popular
Ease of placement and
Crown preparation
FIBER POSTS
CARBON FIBER COMPOSITE POSTS-
More flexible than metal posts and
have same modulus of elasticity of dentin approximately
Even distribution of forces when bonded with resins
Biocompatible and non cytotoxic
Less root fracture
Have the highest strength among the fiber posts
58. Disadvantages
Dark in color
Radiolucent in appearance
Reduction of strength after placement
Cause stress concentration at the margins of the restorations
--JDR-1999
Fibers were unidirectional
Multidirectional arrangement has improved their longevity
Dark color is over come- coating the post with zirconium
- aestheti plus post
Recent versions are white and are relatively easier to remove by
boring the middle of the post with ultrasonic or rotary instrument
60. Bond between tooth, core and post - adhesive technique
parapost,glassix, fiberkor, lucent anchor, Mirafit white - glass
fiber posts
luminex, light post—light transmitting posts
Aestheti plus, DT light post –quartz fiber post
Para post white fiber Aestheti plus – A 2
61. FRC POSTEC
Glass fiber reinforced Composite post
Elasticity dentin and dentin like shade
size 1 and 3 with corresponding
reamer as white and Red color
Polymer matrix of urethane dimethacrylate & glycol dimethacrylate
yitterbium trifluoride & dispersed si. Dioxide
Impression post of Cr-Ni Size 1-15mm, 0.8mm size 2 -18mm, 1m
Size 1- 0.7mm
Size 3- 0.9mm
Direct or indirect tech.
62. CERAMIC AND ZIRCONIUM POSTS
ceramic and zirconium posts - translucent
Esthetically superior to metal posts and for all ceramic crowns
---JPD2000
Its impossible to grind away the posts
Zirconium posts are not etchable
---Int sym-1998
Retention of the core
ceramic and zirconium posts #retrievable and
they should be avoided
–AAE-2004
Weaker than the metal posts
Thicker posts - Require additional removal of root dentin
64. METAL POSTS
World post
supplied with primary reamer and secondary drill
secondary drill- tier-stabilizes & bottoming out
Length & head position
Peeso Gates Primary reamer
1 2 0
3 4 1
4 5 2
5 6 3
66. Para post xp- ss, Ti
Para post xh – Ti
Para post xt – Ti
Para post xp-casting kit
PRO POST
Y-2-0.94mm
R-3-1.20mm
B-4-1.45mm
G-5-1.70mm
Surface of post- acid etched
68. CUSTOM MADE VS PRE FABRICATED POST
The canal is prepared to fit the prefabricated post,
but custom made post is made to fit the tooth
Custom made cast post better adaptation
to canal configuration
Do not require auxiliary means of retention routinely
Gives the best results when change in the path
of insertion or crown angulation is required
