Introduction to Endodontics Forth Year

1. POST RETAINED ENDODONTIC
RESTORATIONS

2. POST RETAINED ENDODONTIC RESTORATIONS
 When a non vital anterior or posterior tooth has lost significant tooth structure, a
coronal restoration is required. A post /dowel is used to retain this restoration.
 The post must be fixed firmly in the root
→ Strong enough not to snap under load
→ Be able to achieve optimal stress distribution in the root
 The final configuration of the restoration includes four parts.
1. residual tooth structure and periodontal attachment apparatus
2. dowel/post material located within the root
3. core material located in the coronal area of the tooth
4. definite coronal restoration

5. 
The primary purpose of a post is to retain a core in a tooth with extensive
loss of coronal tooth structure

Earlier posts were regarded as a method of reinforcing a pulpless tooth

But several studies have suggested that the post weakens the tooth rather
than reinforcing it.
 The placement of posts also may increase the chances of root fracture and treatment
failure ,especially if an oversized post channel is prepared

6. The excessive post diameter in the maxillary second premolar created a
perforation in the mesial root concavity

7. Considerations for use of a post:
1. Anterior teeth:
 If an endodontically treated anterior tooth is to receive a crown, a post often is
indicated → the remaining coronal tooth structure is quite thin after it has
received root-canal treatment and been prepared for a crown.
 The amount of remaining coronal tooth structure and the functional requirements
of the tooth determine whether an anterior tooth requires a post

8.  If tooth has non broken circumferential wall of sound tooth structure of adequate
thickness after initial tooth preparation then a dowel and core may not be necessary.
Plastic restorative material such as composite or amalgam can be used as a build up.

9.  If an inadequate amount of tooth structure remains after initial tooth preparation
then a cast dowel post and core is indicated

11. Molars:

Endodontically treated posterior teeth are subject to greater loading
than anterior teeth because of their proximity to the transverse
horizontal axis

12.  Molar teeth should receive cuspal coverage, but in most cases, do not require
a post, unless the destruction of coronal tooth structure is extensive.
 If posts are indicated then they are placed in the widest and straightest canals:
→ palatal of maxillary molars
→ distal of mandibular molars

13. Premolars:

Premolars by virtue of their location may be subjected to both the vertical as
well as lateral forces.

The pulp chambers are too small to provide the required retention

14. In order to achieve clinical success a post should satisfy three criteria:
1.
It must be atleast as long as the crown it is going to carry
2.
It must have parallel sides or atleast 4º off parallel
3.
It must have a precision fit within the root canal

15. IMPORTANT PRINCIPLES FOR POSTS
1. Retention and Resistance
 Post retention refers to the ability of a post to resist vertical dislodging forces.
 Retention is influenced by the post’s
→ Length
→ Diameter and taper
→ luting cement
→ whether a post is active or passive

16.  Resistance refers to the ability of the post and tooth to withstand lateral and rotational
forces.
 It is influenced by the → remaining tooth structure
→ post’s length and rigidity
→ presence of antirotation features
→ presence of a ferrule.
 A restoration lacking resistance form is not likely to be a long-term success,
regardless of the retentiveness of the post

17. Anti-rotational features

18. 2. Length of the post:
When the length of the post = crown length → failure rate was 2.5%
When length of the posts
= one quarter the clinical crown→ failure rate was 25%
 Several studies of teeth with vertical root fractures showed that two thirds of posts were
extremely short, terminating in the cervical third.
 Invitro biomechanical studies have shown that better stress distribution occurred with
longer posts.

20. 
2/3 length of the root

1/2 distance of the
remaining root into the
bone

4 mm of apical seal

Equal to length of
clinical core

21. 3. Failure mode:
 An important factor related to resistance is failure mode.
 Teeth restored with less rigid posts, such as fiber posts, tend to have failures that are
more likely to be restorable
 Studies have reported that composite cores tended to fail more favorably than
amalgam or gold.

22. Fractured post and crown
Fractured root

23. 4. Preservation of the tooth structure:
 Whenever possible, coronal and radicular tooth structure should be conserved.
 Preparation of a post space should require minimal removal of additional radicular
dentin
 Custom made cast post are more conservative than the prefabricated posts especially
when the posts are required for mandibular anterior teeth

25. 5. The ferrule effect:
 If the artificial crown extends apical to the margin of the core and encircles sound
tooth structure for 360º, the crown serves as a reinforcing ring or ferrule to help
protect the root from vertical root fracture.
 A ferrule is defined as a vertical band of tooth structure at the gingival aspect of a
crown preparation. It adds some retention, but primarily provides resistance form
and enhances longevity
 Ferrule with 1.5 to 2 mm of vertical height has been shown to double the resistance
to fracture versus teeth restored without a ferrule

28. Ferrule criteria and dimensions

29. 6. Retrievability:
 Although nonsurgical endodontic treatment enjoys a reputation as a highly
successful treatment, some studies have reported lower rates of success. For this
reason, it is important that
 posts be retrieved if only endodontic retreatment becomes necessary

30.  In most cases, metal posts can be removed effectively and safely.
 Ceramic and zirconium posts are considered to be very difficult and sometimes
impossible to retrieve.
 Retrievability should be considered when treatment planning for a post.

31. 7. Apical seal:
 After the post preparation the only barrier against the re-infection is the remaining
gutta percha
 The apical barrier of Gutta percha should be atleast 4-6mm

32. TYPES OF POSTS
ACTIVE POSTS
Pre tapped posts
Self threading
Parallel
PASSIVE POSTS
Tapered
Combination

33.  Active posts derive their primary retention directly from the root dentine by the use of
threads.
 Passive posts on the other hand gain retention by passively seating in close proximity to
the post hole walls, and rely primarily on the luting cement for their retention.

34.  Active posts are more retentive than passive posts, but introduce more stress into the
root than passive posts
[They can be used safely, however, in substantial roots with maximum remaining
dentin]
 Their use should be limited to short roots in which maximum retention is needed

Active posts:
•
Self threading posts
•
Pre tapped posts

35. Self threading posts:
 Self-threading posts have a shank (shaft) that is fractionally narrower than the
post channel that is cut into the root and has a thread of wider diameter.
 As the post is screwed into place the threads cut their own counter-channel into
the dentine
 Can be of two types:
i.
parallel
ii.
tapered

36. 
Parallel posts are more retentive than tapered posts

The preparation of a parallel-sided post channel, and subsequent
cementation of a square-ended parallel post may produce increased stress in
the narrow and tapering root-end

The preparation of the post space for the parallel post system may involve
removal of more dentin

37. a) Stress concentration at the base of a parallel post preparation.
b) Reduced stress concentration with a chamfered tip

38.  Tapered posts, on the other hand, require less dentin removal because most roots are
tapered. They are primarily indicated in teeth with thin roots and delicate
morphology
 Concerns have often been raised over the generation of wedging stresses by tapered
posts, and the tendency to promote root fracture

41.  Flexi-posts have been developed to overcome the
disadvantages of both the parallel posts and the tapered
posts.
 The Flexi-Posts’ unique split-shank design

42. Prefabricated post designs.
A. Tapered, smooth.
B. Parallel, serrated.
C. Tapered, self-threading..
D. Parallel, threaded. [Note that the post fits
into pretapped threads cut into the dentin]
E. Parallel, serrated, tapered end

43. According to Manufacture and materials
Pre-fabricated
Metallic
Custom made
Non Metallic
Stainless steel
Ni-Cr
Fiber posts
Gold
Titanium
Carbon fiber
Quartz fiber
Silicon fibre
Composite posts
Ceramic posts
Zirconium

44. Prefabricated Post and Cores:
 Prefabricated posts are typically made of stainless steel, nickel chromium alloy,
or titanium alloy
 They are very rigid, and with the exception of the titanium alloys, very strong.
 Passive, tapered posts offer the least retention of the prefabricated posts, but
allow minimal removal of radicular dentin because
 Their tapered shape resembles the overall canal morphology.

45.  Many of the prefabricated posts are made of titanium alloys
Disadvantages of Titanium posts:
 Have a radiodensity similar to gutta-percha and sealer and are sometimes hard to
detect on radiographs.
 Titanium posts have low fracture strength, which means they are not strong
enough to be used in thin post channels.
 Removal of titanium posts can be a problem because they sometimes
break when force is applied with a post removal instrument

46. Custom Cast Post and Cores
 Cast post and cores were the standard for many years and are still used by some
clinicians.
 Generally, they do not perform as well as other types of posts
 They have fallen from favor because they require two appointments,
temporization, and a laboratory
 A cast post and core may be indicated when a tooth is misaligned and the core
must be angled in relation to the post to achieve proper alignment with the
adjacent teeth.
 Cast post and cores are generally easy to retrieve when endodontic retreatment is
necessary

47. NON-METALLIC POSTS
 Rigid, metal post systems are now known to transfer functional stresses to the tooth
and root structure and actually increase the risk for root fracture.
 Accumulation of metallic corrosion byproducts also weakens the dentin and the
interface between the post and the canal.

48.  The newer fiber-reinforced post systems preserve tooth structure, are noncorroding, and have a similar elastic modulus compared to dentin making them
more compatible that their metal counterparts.

49.  When two or more components are placed into contact with one another, Components
with higher e-modulus (cast post/core) will transfer functional stresses to the lower emodulus components (dentin) and ultimately result in endodontic or restorative
failure.
 When all components have similar e-moduli there is a uniform stress distribution and
lowered interfacial stress and failure.
 This phenomenon has been coined “monobloc.”
 “Monobloc” requires that all components of a tooth restoration have similar emoduli to dentin to allow the components to move, flex, and stress as one
assembly.

51. AESTHETIC POSTS

Introduction of tooth colored materials :



aesthetic demands
functional abilities
Most of the aesthetic posts used, generally employ resin based composite
materials for the cementation and also the core build up.

The use of light cured composites as luting agents encouraged the development
of posts that can transmit light into the depth of the canals.

Most of the composite posts, fibre reinforced composite posts (exception of
carbon fibre posts) transmit light [light transmitting posts]

52. CERAMIC AND ZIRCONIUM POSTS:
These posts are translucent or white in colour and hence categorized under
aesthetic posts.
DISADVANTAGES OF CERAMIC AND ZIRCONIUM POSTS
 They tend to be weaker than metal posts, so a thicker post is necessary, which
may require removal of additional radicular tooth structure.
 Zirconium posts can not be etched, therefore, it is not possible to bond a
composite core material to the post, making core retention a problem .
 Retrieval of zirconium and ceramic posts is very difficult if endodontic
retreatment is necessary or if the post fractures

53. FIBER POSTS
 Carbon fiber posts gained popularity in the 1990s.
 A carbon-epoxy composite post was reinforced with long carbon unidirectional,
high-performance fibers stretched parallel to the axis of the post.
 The fibers represented 64% of the structural volume and the matrix, which bound
the fibers together, was an epoxy resin.
 Their main proposed advantage was that they were more flexible than metal posts
and had approximately the same modulus of elasticity (stiffness) as dentin. When
bonded in place with resin cement, it was thought that forces would be
distributed more evenly in the root, resulting in fewer root fractures.

54.  The original carbon fiber posts were dark, which was a potential problem when
considering post-restorative esthetics.
 Other types of fiber posts also are available, including quartz fiber, glass fiber, and
silicon fiber posts

55. A. carbonfibre post
B&C . Two examples of
translucent quartz-fibre posts,
D. The opaque Fiber White
A
B
C
D
Post

58. If certain basic principles are followed in the restoration of endodontically treated
teeth, it is possible to achieve high levels of clinical success with most of the current
restorative systems. These principles include:
1. Avoid bacterial contamination of the root-canal system
2. Provide cuspal coverage for posterior teeth
3. Preserve radicular and coronal tooth structure
4. Use posts with adequate strength in thin diameters
5. Provide adequate post length for retention
6. Maximize resistance form including an adequate ferrule
7. Use posts that are retrievable.