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8/18/2019 Endodontic Topics Volume 31 Issue 1 2014 [Doi 10.1111%2Fetp.12066] Baba, Nadim Z.; Goodacre, Charles J. -- R…
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Restoration of endodontically
treated teeth: contemporary concepts and future perspectivesNADIM Z. BABA & CHARLES J. GOODACRE
The concept of using a root for the restoration of a missing crown is not new. Through continuous research, our
understanding of the causes of failure has improved. Recent research on endodontically treated teeth has changed
contemporary views concerning some principles while consolidating others. Clinical success in restoring
endodontically treated teeth depends on our ability to use the latest materials available in conjunction with soundclinical methods. A number of articles have discussed the major factors that play a key role in the long-term
survival of endodontically treated teeth and associated restorations. The purpose of this article is to identify key
principles that affect tooth and restoration survival and to present expectations regarding optimal future solutions
for the long-term retention of endodontically treated teeth.
Received 23 September 2014; accepted 2 October 2014.
Various methods and materials have been proposed
over the years for restoring pulpless teeth (1–3). Root
fractures and other difficulties encountered with theseearly treatments led to the development of cast post
and cores that continue to be used today. Recently,
in response to an increased demand for esthetic all-
ceramic restorations, a variety of non-metallic
prefabricated tooth-colored post systems have been
introduced as an alternative to metal posts. Today, the
prosthodontic and endodontic aspects of restoring
endodontically treated teeth (ETT) have appreciably
advanced and a significant body of scientific
knowledge on which to base our clinical treatment
decisions is available. However, retainingendodontically treated teeth throughout life requires
careful restoration and adherence to available
evidence.
Although the collaboration between different
specialties coupled with modern therapies allows
patients to retain severely compromised teeth for
longer periods of time, the restoration of such teeth
remains a challenge. Despite a number of innovations
and decades of research on posts, failures can still
occur when endodontically treated teeth are restored
(Fig. 1) (4). Fortunately the failure rate is relatively
low, but it could be even lower. As professionals,it is our obligation to do everything possible to
minimize complications. Some of the post
complications encountered clinically are pos
loosening, root fracture (Fig. 2), endodontic failure
(Fig. 3), root perforation (Fig. 4), post fracture
(Fig. 5), caries, and periodontal failure. The most
common post complications have been identified as
post loosening and root fracture (4). Several authors
(5–10) discussed the multifactorial origins of the
causes of cracks and fractures in ETT. Loss of tooth
structure, the use of endodontic irrigants andinstrumentation, a reduced level of proprioception,
changes in dentin, and the restorative procedures are
the main factors proposed as causes of fracture (i.e.
post placement). In addition, different variables, such
as the arch position, the presence of opposing occlusal
contacts, periodontal tissue support, endodontic
status, and the amount of remaining dentin, play an
important role in the prognosis of ETT. A number of
articles have discussed the major factors that play a key
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Endodontic Topics 2014, 31, 68–83
All rights reserved
© 2014 John Wiley & Sons A/S.
Published by John Wiley & Sons Ltd
ENDODONTIC TOPICS
1601-1538
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role in the long-term survival of endodontically
treated teeth and associated restorations (11,12). The
purpose of this article is to identify key principles that
affect tooth and restoration survival and to present
expectations regarding optimal future solutions for the
long-term retention of endodontically treated teeth.
Effect of endodontic treatment onthe tooth
When performing root canal therapy, the access cavity opening causes loss of coronal tooth substance (Fig. 6)
(13,14). In addition, root canal treatment as well as
retreatment can cause damage to the root dentin. A
study looked at the influence of retreatment
procedures on the appearance of defects on the root
canal walls (15). It was concluded that retreatment
caused more defects in dentin than initial treatment.
During initial treatment, craze lines and cracks can be
formed in the dentin. The latter can develop into
a c
b
Fig. 1. (a) A separated instrument within the mesial root canal of a mandibular right second molar. (b) Perforationof the roots of a mandibular second molar, the result of post space preparation with instruments not held parallel tothe root canals. (c) A radiograph of a fractured maxillary lateral with a prefabricated non-metallic post.
Fig. 2. Radiograph displaying a very short post in theroot of a maxillary first bicuspid that caused rootfracture.
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fractures during retreatment and under the functionalstresses applied to the tooth during chewing and
parafunction. Several studies (16,17) compared the
effect of hand files and rotary files on dentin after canal
preparation. They concluded that rotary instruments
caused more dentinal defects, such as craze lines and
cracks, which possibly could develop into fractures
after restorative treatment.
Several methods have been proposed for detecting
cracks and fractures when they are not visible clinically.
The most commonly used techniques are trans-
illumination (Fig. 7), occlusal tests, endodontic
microscopes, dyes, and quantitative percussion
diagnostics (18–22). Recently, cone beam computed
tomography (CBCT) has been suggested as a tool to
diagnose fractures, perforations, or suspected cracks
(23,24).
Another factor that could affect the mechanical
properties of dentin is the use of endodontic irrigants
Fig. 3. Radiograph displaying an inadequate root canaltherapy that caused a radiolucent apical lesion.
Fig. 4. Inappropriate placement of a screw post createda perforation in the pulpal floor of the maxillary firstmolar.
Fig. 5. Radiograph of a fractured maxillary lateralincisor with a prefabricated screw post.
Fig. 6. Excessive enlargement of the access cavity following root canal therapy.
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and medications (25–27). Following contact with
these products, chemical degradation of dentin is
evident and the dentin becomes weaker because of areduction in microhardness. However, the degree of
dentin change is related to the amount and duration of
contact between products and dentin. Other irrigation
agents such as mineral trioxide aggregate and bioactive
glass do not seem to affect the flexural strength of root
dentin (28–29).
In addition to the use of irrigants and medications,
Ferrari et al. showed that 10 to 12 years after
endodontic treatment, there is progressive degradation
of the demineralized collagen matrices (30). The aging
dentin becomes sclerotic and exhibits very limited
yielding before failure. The fracture toughness is lower,and the stress–strain response is characteristic of brittle
behavior (31). Most importantly, there is a reduction in
the stiffness and elasticity of dentin and a reduced
resistance to crack propagation (6,13,32,33).
These factors can affect the prognosis of the
endodontically treated tooth. As a consequence,
practitioners should strive to use restorative materials
with properties similar to that of dentin, along with
sound clinical principles to counteract the changes in
a
c
b
d
Fig. 7. (a) Clinical photo shows a crack line on the occlusal surface of a maxillary first molar. (b) The amalgamrestorations were replaced with new ones and the tooth was prepared to receive a partial coverage restoration. (c) A trans-illumination picture shows the crack running between the amalgams across the transverse ridge. (d) Occlusal
view of the 3/4 crown showing that it encompassed the buccal cusps.
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mechanical properties of dentin as well as the loss of
tooth structure following root canal treatment (RCT).
A systematic review investigated tooth survival after
RCT (34); 14 studies met the inclusion criteria. Four
key factors were identified as enhancing the survival
of teeth after RCT: the presence of interproximal
contacts, no plans for using the treated teeth asabutments for fixed or removable partial dentures,
tooth type, and crown restoration.
The restorative dentist plays an important role in the
success and failure of endodontic treatment. Before
endodontic treatment is contemplated, the restorative
dentist should: (i) have an overall treatment plan
for the patient based on their chief complaint
and desires; (ii) assess the restorability of the tooth,
which may involve the removal of all existing
restorations and/or caries to determine the tooth’s
restorability, and examine the tooth for the presence of cracks; and (iii) evaluate the need for any periodontal
treatment and appraise the periodontal prognosis of
the tooth to be restored. After endodontic treatment
has been performed, the dentist should minimize
recontaminating the root canal system.
A study by Balto et al. (35) found that all of the
provisional materials they tested in post-prepared root
canals failed to prevent coronal leakage when used for
an average of 30 days. Similarly, delayed placement of
the definitive restoration had an impact on the
prognosis of ETT. These teeth had a higher successrate when they were restored with a definitive
restoration than with a provisional coronal access
restoration (36). An in vitro study looking at bacterial
penetration of coronally unsealed endodontically
treated teeth found that defective restorations could
cause reinfection of the root canal system within 19
days (37). A combination of poor endodontic
treatment and poor restoration caused a high failure
rate for ETT (38). In comparing endodontic
treatment quality with restoration quality, Tronstad
et al. (39) found that the quality of root canaltreatment is more crucial than that of the coronal
restoration for the survival of ETT.
A well-fitting provisional restoration followed by a
post and core and a definitive coronal restoration
should be planned and cemented in as short a time as
possible. Avoiding reinfection of the root canal and
preventing mechanical failures such as fractures
enhances the survival of ETT (40,41). In a
retrospective study, Willershausen et al. (42) evaluated
775 ETT in 508 patients and found a higher survival
rate for teeth restored within 2 weeks.
If immediate restoration of the tooth is not possible,
it is recommended to protect the root canal system by
sealing the orifice of the canals and the floor of the
pulp chamber with intracoronal barriers (43–45).
Among the suggested materials to be used are flowablecomposite resin, mineral trioxide aggregate (MTA),
glass ionomer, fissure sealant, and conventional
restorative composite resin. This type of treatment has
mostly been suggested to protect the root canal system
from contamination during the provisionalization
period.
The use of digital impressions and CAD/CAM
fabrication can help the restorative dentist to seal the
filled root canal system and protect the tooth as soon
as possible, either with a provisional or definitive
restoration.
Principles that enhance success when restoring endodontically treated teeth
The prognosis of ETT does not depend solely on the
quality of the RCT or the quality and time required
for definitive restoration (38,46). Survival of the
restoration also depends on several basic principles
that affect tooth and restoration survival.
Cuspal coverage
ETT can benefit from the placement of crowns. An
epidemiological study in a large patient population
found that while 97% of teeth were retained in the oral
cavity 8 years after initial non-surgical endodontic
treatment, an analysis of the teeth that were extracted
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higher long-term survival rate compared to those not
restored with crowns (Figs. 8 and 9). A retrospective
cohort study found that the 5-year survival rate of
teeth without cuspal coverage was 36% (52). However,
while crowns significantly improved the success of
endodontically treated posterior teeth, they did not do
so for anterior teeth (53). Intact endodontically treated anterior teeth only require a crown when they
are weakened by large or multiple existing restorations
or when they require significant changes to their form
or color that are not manageable by conservative
restorations.
Several studies (54–56) indicated that ETT with
intact coronal surfaces (except for the access opening)
can be successfully restored using composite resin
restorations. However, the survival rate of ETT will
likely be lower when ETT have lost excessive amounts
of tooth structure. Sedgley & Messer (57) concluded
that the loss of axial dentin walls weakens the teeth.Composite resin is a popular core buildup material
because of its ease of use, and the possibility of
preparing and finishing it immediately (46). Some
clinicians consider composite resin as an esthetic
replacement for cuspal coverage crowns. Composite
resin appears to be an acceptable core material when
substantial coronal tooth structure remains but a poor
choice when a significant amount of tooth structure is
missing (56,58,59). The authors believe that if less
than 50% of the coronal tooth structure of an
endodontically treated tooth remains, a post should beused to retain the core material. The choice of buildup
material depends on the remaining adjacent teeth,
occlusion, and the planned definitive restoration. One
disadvantage of composite resin is that it is
dimensionally unstable (60). The setting shrinkage
during polymerization causes stress on the adhesive
bond resulting in cuspal strain with a disruption of the
bond, and gap formation that might contribute to
long-term bond failure followed by microleakage and
recurrent caries (54,55). The amount of shrinkage is
related to the amount of filler content in thecomposite resin. A reduced amount of filler will cause
greater shrinkage. For this reason it is necessary to
avoid using flowable composite resins as buildup
materials because of their low filler content and their
reduced mechanical properties (61).
A recent systematic review looking at the effects of
the restoration of ETT by crowns versus conventional
filing materials concluded that there is no evidence to
support or refute the effectiveness of crowns over
filling materials for the restoration of ETT (46).
After considering the available contrasting data, theauthors acknowledge the potential benefits of using
composite resin to restore posterior teeth that are
intact except for a conservative access opening.
However, when occlusal wear, heavy forces, or para-
functional habits are present in the mouth, more
clinical data are required to determine the long-term
survival of these teeth when large composite resin
restorations are present. For this reason, we
recommend that endodontically treated teeth which
Fig. 8. Occlusal view showing the fractured buccal cuspof an endodontically treated mandibular left first molar
without cuspal coverage.
Fig. 9. Fracture of the palatal cusp of a maxillary rightfirst molar with significant amount of tooth structuremissing restored with a composite resin and withoutcuspal coverage.
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have been previously restored and weakened by prior
tooth structure removal be restored with a crown that
encompasses the cusps. Conversely, it may be possible
to avoid crowns on some previously restored posterior
teeth with only a conservative access opening and
little-to-no wear present that would indicate the
presence of detrimental occlusal forces.It is highly recommended that a rubber dam be
placed when a composite resin is used as the core
buildup material. Composite resin is a technically
demanding material that requires careful adherence to
material-handling protocols. To ensure success, the
use of low-shrinkage composite resin (62), the buildup
of the core in small increments (63), and the use of
liners (64) has been advocated.
The high demand for esthetic restorations, the need
for an occlusal material stiffer than dentin, and the
benefit of covering the cusps has caused someclinicians to use all-ceramic onlays and crowns as a
conservative and effective treatment modality to
restore ETT (65–67). A suggested conservative
technique to restore ETT is the use of an endocrown
(68–70). This restoration consists of an onlay or
crown with the core material in a single unit (Fig. 10).
The core material engages in a cavity prepared into the
pulp chamber. A study by Magne et al. (68) found that
an endocrown fabricated from a resin nanoceramic has
a favorable mode of failure when ETT with no buildup
material are used. These crowns were found to be
more resistant to failure than teeth that had been
restored with a post, composite resin core, and a
ceramic crown (69,70). It is unknown whether this
type of conservative restoration will produce the same
problems as the one-piece crown–post combinationsmade using metal. Also, the impact of their subsequent
removal upon structure integrity is unknown.
Tooth preservation
Maximum preservation of coronal and radicular tooth
structure is a guiding principle for the restoration of
ETT. As clinicians we should preserve intact tooth
structure whenever possible in order to maintain an
adequate retention and resistance form of the final
restoration. The position of the tooth in the arch,the presence of opposing occlusal contacts, the
periodontal tissue support, the endodontic status, and
the amount of remaining dentin aids in selecting
the appropriate material for the definitive restoration.
The authors believe that gold onlays or crowns are
excellent restorations where esthetics is not of major
concern, on teeth with limited interocclusal space, and
when restoring heavy bruxers.
Cervical ferrule A ferrule can be established by the crown
encompassing sound tooth structure (Fig. 11) (71–
76). The data indicates that cervical ferrules increase
the tooth’s resistance to fracture (71,72,77). In spite
of the data supporting the benefit of cervical ferrules,
not all practitioners recognize their value. A survey
published by Morgano et al. (78) evaluated the
percent of respondents who felt that a ferrule increased
a tooth’s resistance to fracture: 56% of general dentists,
67% of prosthodontists, and 73% of board-certified
prosthodontists felt that core ferrules increased atooth’s fracture resistance.
Different lengths and forms of the ferrule have been
studied (71,73,74,79) and are essential factors for
the success of the “ferrule effect.” When possible,
encompassing 2.0 mm of intact tooth structure
around the entire circumference of a core creates an
optimally effective crown ferrule. Grasping larger
amounts of tooth structure further enhances ferrule
effectiveness. The amount of tooth structure engagedFig. 10. All-ceramic restoration consisting of a crown
with a core material in a single unit.
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by the overlying crown appears to be more important
than the length of the post in increasing a tooth’s
resistance to fracture.
If insufficient cervical tooth structure remains to
develop a ferrule, surgical crown lengthening or
orthodontic extrusion should be considered to expose
more tooth structure.
In some situations where teeth have been extensively
restored, have been subject to trauma, or have
substantial caries, it will be difficult to obtain a ferrule.In such cases it may be prudent to extract the tooth
and replace it with an implant and crown. Extraction
of ETT may also be required when crown lengthening
would create an unacceptable esthetic environment or
produce a furcation defect, or when a short root is
present that would not permit an appropriate post
length to be developed (80).
Studies have shown that a uniform ferrule produces
significantly greater fracture resistance than a non-
uniform ferrule (74,76,81), with the greatest variation
in failure load associated with the absence of portionsof the crown ferrule. The presence of a 2-mm ferrule
on the facial, lingual, distal, and mesial surfaces of the
tooth produces the most favorable resistance to tooth
fracture and decreases the weakening effect of a post
(Fig. 12) (76).
Need for a post
Studies have compared the fracture resistance of
endodontically treated extracted teeth without posts
or crowns with the fracture resistance of teeth restored
with posts and cores and crowns. Maxillary incisors
without posts resisted higher failure loads than the
other groups with posts and crowns (82) and
mandibular incisors with intact natural crowns
exhibited greater resistance to transverse loads than
teeth with posts and cores (83). These studies have
shown no evidence of a strengthening reinforcement
effect of posts. However, several studies showed arelatively high failure rate of endodontically treated
teeth that were restored with a composite resin filling
without a post (84–86). The failures occurred when
the teeth had small and curved roots. A study by Salvi
et al. (87) evaluated ETT restored with and without
post and cores in a specialist practice. They concluded
that there was no significant difference between teeth
restored with or without posts provided that at least
two-thirds of the dentin remained. They also found
Fig. 11. A ferrule will be created by the overlying crownengaging tooth structure. The final restoration is at least
2 mm apical to the junction core/tooth.
a
b
Fig. 12. Post and crown loosened from maxillary caninea few months after placement. (a) Both the post/prefabricated post and the crown came off. (b) Clinicalphoto shows the absence of cervical tooth structure(ferrule) for retention of the crown.
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that 11 out of 13 failures in mandibular molars were
due to fractures (Fig. 13).
Clinical studies have failed to provide definitive
support for the concept that posts strengthen
endodontically treated teeth (53,85,87). An analysis of
data from multiple clinical studies noted that 3% of
teeth with posts fractured with no evidence that posts
enhanced the survival of teeth (88). Posts have had
little enhancing effect on the clinical survival of fixed
partial denture abutments, but they did improve
the clinical survival of removable partial dentureabutments compared to endodontically treated
abutments where no posts were used (53).
Because clinical and laboratory data indicate teeth
are not strengthened by posts, their purpose is for the
retention of a core that will provide adequate retention
and support for the definitive crown or prosthesis.
When enough tooth structure is present in an
endodontically treated molar, there is absolutely no
need for a post (Fig. 14). The presence of adequate
dentin coupled with no preparation of a post space
helps avoid weakening the tooth, eliminates the risk of perforation during post preparation, and aids in
preventing the development of cracks that could be
detrimental to the ETT. In endodontically treated
molars, buildup materials usually have sufficient
retention from the pulp chamber, divergent coronal
portions of the root canals, and undercuts created in
the pulp chamber during removal of caries and RCT.
For endodontically treated anterior teeth and
premolars, if sufficient tooth structure remains to
a b
Fig. 13. (a) Radiograph of a broken mesial root of an endodontically treated mandibular right molar restored witha crown and no post. (b) Extracted tooth showing the fractured mesial root.
a
b
Fig. 14. (a) Occlusal view of a maondibular secondmolar showing the presence of enough tooth structureto retain the core. (b) Radiograph of the root canaltreatment.
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retain the core, the use of a post is not required;
bonding a core buildup material to dentin is sufficient.
However, if a substantive amount of tooth structure is
missing in these teeth, a post is needed in order to
retain the core and optimize the resistance form. The
best prognosis is obtained when a 2-mm ferrule
encompasses intact tooth structure around the entirecircumference of the core no matter what type of post
is used. Because posts do not reinforce a tooth, they
should only be used when the core cannot be retained
by some other means.
Types and properties of posts
In recent years, prefabricated posts have become quite
popular and a wide variety of systems are now
available. In response to a need for tooth-colored
posts, several non-metallic posts such as zirconia, glassfiber-reinforced epoxy resin (GFR), and ultra-high
polyethylene fiber-reinforced posts are available; early
data indicates that they can be acceptable alternatives
to metallic posts. However, gold alloys, titanium, and
chrome–cobalt are still clinically viable and are widely
used.
Among the non-metallic posts, GFR posts are the
most popular. They are available in different shapes:
cylindrical, cylindroconical, or conical. An in vitro
assessment of several GF post systems indicated that
parallel-sided GF posts are more retentive than taperedGFR posts (89). These posts could be made from glass
or silica fibers (white or translucent) but the most
commonly used fibers are silica based. The matrix
for this post is an epoxy resin. The fibers are in the
vicinity of 14 μm in diameter and uniformly
embedded in the epoxy resin matrix. The fibers are
stretched before injection of the resin matrix to
maximize the physical properties of the post. When
compared to metallic posts, GFR posts have a low
modulus of elasticity and are more flexible (90). This
flexibility induces more stress cervically, which, in thecase of minimal or no ferrule, causes a higher risk of
post fracture, debonding of the core, and loss of
retention of the post followed by microleakage and
secondary caries (Fig. 15). Several studies (91,92)
have determined that there is a 40% decrease in the
strength of GFR posts after thermocycling and cyclic
loading. In addition, contact of the post with oral
fluids (short- and long-term) reduced their flexural
strength. While failure with fiber posts might be less
likely to produce root fracture, post removal may
damage the root, and the cost to the patient versus
time of service before failure is a concern.
In contrast, metallic posts are stiffer than dentin and
can take more load than GFR posts. Their stiffness can
induce more stress apically, causing catastrophic root
fractures (Fig. 16). Similarly to GFR posts, metal postsalso undergo a process of cement failure during cyclic
loading (93). Metal posts have a longer lifespan than
GFR posts and they fracture less; but when they fail,
the failure is non-restorable (94).
A comprehensive review of the English literature was
conducted on evaluating the clinical performance of
GFP in order to seek evidence for the treatment of
teeth with non-metallic posts (95). Clinical research
articles showed that non-metallic posts have favorable
a
b
Fig. 15. (a) A radiograph of a fractured mandibularsecond premolar with a prefabricated non-metallic post.(b) Crown with broken post.
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mechanical and physical properties and the studies
presented with a wide range of reported failurepercentages, from 0% after a mean of 2.3 years to
11.4% after 2 years. Post debonding, post fracture,
crown debonding, and root fracture were the most
commonly reported complications. Post debonding
was reported in 16 of the 23 studies. A 10-year
prospective study on GFR posts found that the overall
failure rate of these posts was 37%, of which 11% were
due to post debonding (96). From these results, it can
be concluded that the failure might be due to
weaknesses in the bonding of composite resin to
the post and/or to the dentin. Studies (97–99)demonstrated that radicular dentin is different from
coronal dentin. It contains fewer tubules and forms a
thinner hybrid layer than coronal dentin. The efficacy
of bonding to radicular dentin could be compromised.
It is strongly recommended that chemical or dual-cure
composite resin cement be used to ensure complete
polymerization of the cement in the canal.
Another reason for post debonding could be the lack
of retention between the composite resin cement and
the surface of the GFR post. Studies have shown that
there is a low bond strength (5 to 6 MPa) between theGFR posts and composite resin (100,101). Differences
exist among brands of GFR posts in term of structural
characteristics and fatigue resistance (102,103). GFR
posts could present with voids and irregularities within
the resin and discontinuity at the interface between the
fibers and the matrix. It is recommended to condition
the surface of GFR posts prior to cementation with
soft air abrasion (2 bars) and the application of silane
(104,105).
Post debonding could be due to the polymerization
shrinkage of the composite resin cement, the
technique-sensitive cementation process, the difficult
access and visibility during cementation, the lack of a
clear and universal cementation protocol, the lack of
ferrule effect, or an inadequate choice in the type of
post for the given clinical situation and tooth. The wide range of failure percentages reported with GFR
posts may also be indicative of variations amongst
clinicians and differences in their experiences/
restorative techniques. It appears that more long-term
clinical data is needed in order to determine the
efficacy of fiber-reinforced posts.
A 10-year retrospective study of the survival rate of
teeth restored with metal prefabricated posts and cast
metal posts and cores found that their overall failure
rate was 15.4% and 17.4%, respectively (106). When
we compare these results to the high overall failure rateof non-metallic post, the authors believe that the GFR
posts are not superior to metallic or cast posts.
There are challenges related to the use of cylindrical
prefabricated posts when restoring teeth with ovoid,
wide, or particularly tapered canals. The lack of
intimate adaptability of these posts to the tooth
structure compromises their retention in the canal.
In addition, the low success rate of GFR posts
encouraged researchers to look for alternative
materials to restore ETT. Polyethylene fiber-reinforced
(PFR) posts made out of ultrahigh-molecular weightpolyethylene woven fiber ribbon (Ribbond, Seattle,
WA) have been proposed. It is not a post and core in
the traditional sense. It is a polyethylene woven fiber
ribbon that is coated with a dentin bonding agent and
packed in the canal, where it is then light polymerized
into position (107). Another proposed material is a
customized glass-fiber post (108,109). Costa et al.
(108) compared the root fracture strength of single-
rooted premolars restored with GFR posts to the ones
restored with customized GFR posts. They concluded
that the customized GFR posts did not show improved fracture resistance or differences in failure
patterns when compared to GFR posts. Some authors
suggested combining PFR with a customized GFR
post to restore ETT (110). Custom-milled zirconia
posts have also been suggested as an alternative
material to GFR posts in anterior teeth where the use
of a custom post is indicated. An in vitro study
comparing a one-piece milled zirconia post and core
to different core systems concluded that the mean
Fig. 16. A radiograph of a fractured maxillary secondpremolar with a metallic prefabricated post.
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load-bearing capacity of the one-piece milled zirconia
post and core was comparable to that of a cast gold
post and core (111). One explanation as to why
these post behaved similarly to cast post and core is the
absence of an interface between the post and the core,
which eliminates the debonding of the core evidenced
with GFR posts and cores.The authors believe that until more long-term
clinical data becomes available, fiber-reinforced resin
posts should be used with caution because of the wide
range of reported failure rates in available clinical
studies.
Future directions
In the future, we foresee that the advancement of
CAD/CAM technology, milling, and laser printing
along with an improvement in digital impressiontechnology will make it possible to more easily and
accurately fabricate customized post and cores from
several different materials. In addition, more
conservative endodontic treatment procedures are
likely to emerge and reduce the need for posts and
crowns. Pulpal regeneration procedures may even
eliminate or substantially reduce the need for the use
of crowns and posts and cores.
In future studies of ETT and new technologies, we
believe in vitro studies should be performed using
fatigue loading and chewing simulation conditions.
Summary
Based on this review of available evidence, the
following clinical recommendations are proposed:
1. When performing root canal therapy, the tooth
needs to be evaluated for the presence of cracks and
craze lines using several of the diagnostic tools
available. The restorability of the tooth needs to be
assessed along with the periodontal prognosis.
2. Following root canal therapy, the tooth needs to berestored with a definitive restoration in as short a
time as possible. If immediate restoration is not
possible, it is recommended to seal the orifice of the
canals and the floor of the pulp chamber with
intracoronal barriers.
3. Crowns are not needed on many endodontically
treated posterior teeth to enhance their long-term
survival because their structural integrity is often
compromised. There is some data indicating
posterior teeth that are intact except for the access
opening can be satisfactorily restored with
composite resin rather than a crown. However, the
long-term success of this more conservative
treatment is not known in the presence of heavy
occlusal forces.
4. Posts weaken teeth and they should only be used when the core cannot be adequately retained by
some other means.
5. When crowns are placed on endodontically treated
teeth, they should encompass 2.0 mm of tooth
structure apical to the core whenever possible since
crown ferrules increase the resistance of teeth to
fracture.
6. Until more long-term clinical data becomes
available, fiber-reinforced resin posts should be
used with caution due to the wide range of
reported failure rates in available clinical studies.7. Procedures will become available that preserve or
regenerate pulp vitality and may reduce or even
eliminate the need for restorations. For those teeth
that need RCT, even more conservative endodontic
procedures will be developed; and when combined
with new materials it may not be necessary to place
crowns on these teeth. When posts are needed due
to tooth condition, digital technologies will make it
possible to fabricate customized posts and cores
from a variety of materials.
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