Effect of endodontic treatment on the tooth/teeth:
The major changes in the endodontically treated teeth include:
• loss of tooth structure
• altered physical characteristics (functional loss)
• altered esthetic characteristics of the residual tooth
Thus it is the loss of structural integrity that plays a major role in
fracture of endodontically treated teeth.
Access preparations result in increased cuspal deflection during
function and increase the possibility of cusp fracture and microleakage at
the margins of restorations.
General considerations in the restoration of endodontically treated teeth:
Root-treated teeth are in a vulnerable state until they are permanently restored.
The risks they face fall into two major categories:
Fracture of remaining tooth tissue
Reinfection of the root canal from the mouth
Irrespective of type of restoration chosen for placement in a root
canal treated tooth, it is important to carry out a thorough preoperative clinical and radiographic assessment
Restoration of root-filled teeth - pre-treatment assessment:
The benefits of root canal treatment or re-treatment and the placement of an indirect
restoration, both of which are time-consuming and expensive procedures, must be
weighed against extraction of the tooth.
Teeth with hopeless prognosis→ extraction
Medically compromised individual→ endodontic intervention despite guarded
Clinical endodontic tests should determine the condition of the supporting structures
with regards to the presence of inflammation of the periodontal ligament and
surrounding peri-radicular tissues.
A positive test → persistent or new pathology→ further treatment prior to placement
of the definitive restoration
Following endodontic clinical tests should be carried out as part of the pre-operative
2. Palpation :
3. Presence of a sinus tract
The presence of tooth mobility may suggest the loss of connective tissue
attachment and inflammation of the periodontal ligament that can be of pulpal
or periodontal origin.
?? → root fracture / trauma [occlusal trauma]
Prognosis of a tooth → satisfactory root canal and restorative treatment→ existing
It is important that combined perio-endo lesions are correctly diagnosed to ensure that
the patient receives the correct treatment
Treatment planning for non-vital teeth
Quality of the endodontic
Anatomic position of the tooth
The amount of remaining
coronal tooth structure
The functional load on the tooth
Factors to be considered for treatment planning are:
amount of remaining tooth structure
anatomic position of the teeth
functional load on the tooth
aesthetic requirements for the tooth
Wherever possible posts should be avoided in posterior teeth as the roots
are often narrow and/or curved and post space preparation can lead to a
strip or lateral perforation
Sufficient tooth structure and / pulp chamber→ retention
Restoration of the endodontically treated teeth serve two most important functions.
Prevent recontamination of the root canal space and the peri-apex.
Replace the lost coronal structure and reinforce the strength of remaining tooth
RESTORATION OF TEETH WITH MINIMAL LOSS OF CORONAL TOOTH
Influence of temporary/provisional restorations on the final restorations
One of the most common materials used is zinc oxide –eugenol.
Studies have proved that residual eugenol → deleterious effect on the physical
properties of composite resin restorations→ surface roughness, micro hardness and
Neither IRM or CAVIT interfered with dentin or enamel bonding
Many of the temporary cements whether they contain eugenol or not, leave behind
an oily layer of debris that must be removed before bonding.
Acid etching demineralizes the dentin surface to a depth of 5 μm and removes the
eugenol rich layer.
An ‘etch and rinse’adhesive system should be used instead of self-etch systems,
which incorporate the eugenol rich smear layer into the hybrid layer.
Studies have shown that dentin that has been exposed to sodium hypochlorite
exhibits resin bond strengths that are significantly lower than untreated dentin
Sodium hypochlorite is an oxidizing agent and leaves behind an oxygen rich layer on
the dentin surface. Oxygen has been shown to inhibit polymerization.
It has been showed that application of 10% ascorbic acid or 10% sodium ascorbate
( reducing agents), reversed the effects of NaOCl.
MATERIALS COMMONLY USED:
Silver amalgam alloy:
One of the most common and popular choice in restoring the access cavities.
A ‘bonded amalgam’ restoration is often recommended in which a resin adhesive [(4META)-based systems]* is placed on a cavity walls before condensation of amalgam
*4-methyloxy ethyl trimellitic anhydride
Glass ionomer cements:
Only restorative materials, that depend primarily on a chemical bond to the tooth
They form an ionic bond to the hydroxyapatite at dentin surface and also obtain
mechanical retention from microporosities in the hydroxyapatite.
Other advantages are
→ low polymerization shrinkage,
co-efficient of thermal expansion = dentin,
[Type VI GIC - Core build up ]
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
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
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
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.
If an inadequate amount of tooth structure remains after initial tooth preparation
then a cast dowel post and core is indicated
Endodontically treated posterior teeth are subject to greater loading
than anterior teeth because of their proximity to the transverse
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
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
In order to achieve clinical success a post should satisfy three criteria:
It must be atleast as long as the crown it is going to carry
It must have parallel sides or atleast 4º off parallel
It must have a precision fit within the root canal
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
→ Diameter and taper
→ luting cement
→ whether a post is active or passive
Resistance refers to the ability of the post and tooth to withstand lateral and rotational
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
2/3 length of the root
1/2 distance of the
remaining root into the
4 mm of apical seal
Equal to length of
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.
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
Custom made cast post are more conservative than the prefabricated posts especially
when the posts are required for mandibular anterior teeth
5. The ferrule effect:
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
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
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.
7. Apical seal:
After the post preparation the only barrier against the re-infection is the remaining
The apical barrier of Gutta percha should be atleast 4-6mm
TYPES OF POSTS
Pre tapped posts
According to Manufacture and materials
Active posts derive their primary retention directly from the root dentine by the use of
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.
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
Their use should be limited to short roots in which maximum retention is needed
Self threading posts
Pre tapped posts
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
Can be of two types:
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
a) Stress concentration at the base of a parallel post preparation.
b) Reduced stress concentration with a chamfered tip
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
Concerns have often been raised over the generation of wedging stresses by tapered
posts, and the tendency to promote root fracture
Flexi-posts have been developed to overcome the
disadvantages of both the parallel posts and the tapered
The Flexi-Posts’ unique split-shank design
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.
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
Custom Cast Post and Cores
Cast post and cores were the standard for many years and are still used by some
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
Cast post and cores are generally easy to retrieve when endodontic retreatment is
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.
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.
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
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
Introduction of tooth colored materials :
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]
CERAMIC AND ZIRCONIUM POSTS:
These posts are translucent or white in colour and hence categorized under
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
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.
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