For instance, under conditions of nitrogen starvation, the activation of the Ntr gene system enables bacteria that require ammonia as a nitrogen source to scavenge even small traces of ammonia. Under high concentration of ammonia, the Ntr gene system is uncoupled.Some facultative bacteria may activate the Arc system (aerobic respiration regulatory), composed of the arcA and arcB genes, under conditions of low concentrations of molecular oxygen. As a consequence, metabolic pathways are activated, which permit the utilization of alternate terminal electron acceptors for respiratory metabolism so that a shift can occur from aerobic to anaerobic metabolism.
Endodontic Failures and Mishaps
Dr. Abhishek John Samuel
III yr MDS
Dept of Conservative Dentisty & Endodontics
Schilder’s Objectives of RCT
1. The root canal preparation should develop a
continuously tapering cone
2. Decreasing cross sectional diameters at every point
apically and increasing at each point as the access
cavity is approached
3. In multiple planes which introduces the concept of
4. Do not transport the foramen
5. The apical opening should be kept as small as
practical in all cases.
Objectives of RCT
SUCCESS IS DEFINED BY THE GOALS ESTABLISHED
TO BE ACHIEVED
The ultimate goal of Endodontic treatment is to
maintain or restore 1. the health of periapical tissues
and 2. the tooth.
The treatment of teeth with irreversibly inflamed
pulps is essentially prophylactic.
But in cases or infected necrotic pulp – established
infection – apical periodontitis.
In such cases focus is on – 1) Prevention of
introduction of new microorganisms
2) Elimination of those colonizing the root canal.
The virtual and REAL goal!
Given the complex anatomy of the RCS,
Even with the multitude of instruments and materials
Fulfilling 100% of the goals is virtually impossible.
Therefor the Realistic Goal is to reduce bacterial
populations to a level below that necessary to induce or
sustain periapical disease.
Accomplish this by an Evidence- based antibacterial
protocol Clinician’s Aim!
Root canal treatment usually fails when treatment falls
short of acceptable standards (Seltzer et al.
1963, Engström et al. 1964, Sjögren 1996, Sundqvist et
Persistence of microbial infection in the root canal
system and/or the periradicular area (Nair et al.
1990a, Lin et al. 1992).
Desirable End point
The apical constriction is the narrowest point of the
apical root canal - the ideal apical end point for RC
Apex locators, in reality detect a point somewhere
between the apical constriction and the major apical
The radiographic apex is the most apical point of the
root as seen on a radiograph. This does not necessarily
form the apical foramen.
There are some cases in which the treatment has followed
the highest technical standards and yet failure results.
Scientific evidence indicates that some factors may be
associated with the unsatisfactory outcome of well-treated
They include 1. microbial factors,
(comprising extraradicular and/or intraradicular
And 2.intrinsic or extrinsic nonmicrobial factors.
(Nair et al. 1990a, Nair et al. 1990b, Lin et al. 1992, Nair et al.
1993, Sjögren 1996, Nair et al. 1999)
Sundqvist (1976) confirmed the important role of
bacteria in periradicular lesions in a study using
human teeth, in which bacteria were only found in
root canals of pulpless teeth with periradicular bone
destruction. [similar to Kakehashi et al. (1965)]
How high the risk of reinfection will be - dependent on
the quality of the root filling and the coronal seal
(Saunders & Saunders 1994)
Studies have demonstrated that part of the root canal
space often remains untouched during
chemomechanical preparation, regardless of the
technique and instruments employed (Lin et al.
1991, Siqueira et al. 1997).
A radiograph of a seemingly well-treated root canal
does not necessarily ensure the complete cleanliness
and/or filling of the root canal system (Kersten et al.
If the root canal filling fails to provide a complete seal,
seepage of tissue fluids can provide substrate for
bacterial growth. (Sundqvist & Figdor 1998, Lopes &
the occurrence of viable microbial cells - in treated
teeth with a persistent periradicular lesion indicates
that microorganisms derive nutrition, presumably
from tissue fluid which can seep into the root canal
space (Sjögren 1996, Sundqvist et al. 1998, Molander et al.
Anaerobic bacteria corresponded to 51% of the
isolates. Enterococcus faecalis was found in 29% of the
cases. - Möller (1966)
Sundqvist et al. (1998) observed a mean of 1.3 bacterial
species per canal and 42% of the recovered strains
were anaerobic bacteria. E. faecalis was detected in
38% of the infected root canals
In different studies success rate ranges from 54
percent to 95 percent.
The definition of success in RCT is ambiguous
- stringent : radiographic and clinical normalcy
- lenient : only clinical normalcy
Endodontic treatment outcome
both clinical and radiographic presentations are
it’s a dynamic process, reduced radiolucency
combined with normal clinical presentation
No change or increase in radiolucency, clinical
signs may or may not be present or vice versa
“How successful is endodontic therapy?” a study was
undertaken at the University of Washington School of
91 to 95% of all endodontic treatments have a
Retreatment gives a 50 % chance to a tooth deemed to
be a failure.
Sjogren’s study on Success vs.
Sjögren and his associates from Sweden - study of 356
endodontic patients, re-examined 8 to 10 years
later, reported a 96% success rate if
- the teeth had vital pulps prior to treatment.
The success rate dropped to 86% if the pulps were necrotic
with periradicular lesions.
They dropped still lower to 62% if the teeth had been re-
They concluded by stating that “teeth with pulp necrosis
and periradicular lesions and those with periradicular
lesions undergoing re-treatment constitute major
Failures are broadly categorised
15% of the failures
and canal grossly
Evaluation of success
Success or failures following endodontic therapy
could be evaluated from combination of
clinical, histopathological and radio graphical
Clinical evaluation for
No tenderness to percussion or palpation
Normal tooth mobility
No evidence of subjective discomfort
Tooth having normal form, function and aesthetics
No sign of infection or swelling
No sinus tract or integrated periodontal disease
Minimal to no scarring or discoloration
Radiographic evaluation for
Normal or slightly thickened periodontal ligament
Reduction or elimination of previous rarefaction
No evidence of resorption
Normal lamina dura
A dense three dimensional obturation of canal
Histological evaluation for
Absence of inflammation
Regeneration of periodontal ligament fibers
Presence of osseous repair
Repair of cementum
Absence of resorption
Repair of previously resorbed areas
Procedure has been successful clinically, yet
histologically pulp lesion may present (seltzer et al –
It should not assumed that following endodontic
treatment periapical lesion always resolves.
TREATMENT IS CONSIDERED FAILED IF.
1) Treated tooth is symptomatic or has an abnormal
2) Soft tissue response abnormally to manual
A Radiographic examination of the tooth is usually
suggested for the same.
The criteria for failure are
1) Development of radiographic rarefaction of
periapical area after completion endodontic treatment.
2) in cases, where none has been present before
treatment appearance of radiographic rarefaction of
periapical area after endodontic treatment.
3) The increase in size of area of rarefaction after
completion of root canal treatment. (Bender et al, 1964
,Luebike et al 1964 ,Seltzer et al 1963 )
Factors affecting success or failure of
endodontic therapy in every case
Diagnosis and the treatment planning
Anatomy of the tooth and root canal system
Debridement of the root canal space
1) Incorrect diagnosis
It can be result of misdiagnosis, poor case selection, &
Incorrect diagnosis usually results from a
misinterpretation or lack of information, either
clinical or radiographic.
Errors in case selection are not so easily overcome as
A careful medical history is essential.
3) Anatomical Variations.
According to Ostrander (1958) such factors as presence
of excessively curved canal, excessive root
mineralization , impenetrable accessory canal & canal
bifurcation near root open may result in endodontic
Problems in cleaning and shaping & incomplete filling of
4) Poor debridement.
Untreated or inadequate debridement of root canals
has a definite relationship to the failure of endodontic
treatment (Grossman 1972).
Debridement of root canal reduces the microbial flora,
but apparently does not eliminate it (Ingle 1965).
Incomplete debridement of the
root canal system
Main objective of root canal therapy→complete
elimination of the microorganisms and their
Poor debridement → residual
microorganisms, byproducts and
tissue debris → recolonize
When instrument has been confine to root canal & presumably
instrument root have damage the apical pulp stump , chances for
repair are enhanced (Strindberg 1956).
Strindberg (1956) found that, even teeth with non-vital pulp.
There was lower frequency of failure when canal could not be
reamed through apex as compared to these where
instrumentation was carried out to or beyond the apex.
Grahnen &Hansson (1961) & Frosteu (1963) even found that
failure frequency was greatest in single noted teeth when the
canal is apparently easiest to file & ream.
During endodontic treatment, various medications are used as
dressing in root canal. Their functions are presumably to
eliminate or reduce microbial flora, prevent or lessen pain,
reduce inflammation or stimulate repair.
Torreck (1961), Schilder and Amesterdam (1956) have
demonstrated irritating potential of many root canal
Intracanal medicaments and irrigating solution
→extruded in the periapical tissues→the
prognosis of endodontic treatment ↓
One should take care while Using medicaments to
avoid their periapical extrusion
Factors affecting success or failure
of endodontic therapy in every case
Quality and extent of apical seal
Quality of post endodontic restoration (coronal
seal, resistance and retention)
Systemic health of the patient
Skill of the operator
Factors affecting success or failure of a
Pulpal and Periodontal status
Size of periapical radiolucency
Crown and root fracture
Factors affecting success or failure of a
Extent and quality of the obturation
Quality of the post endodontic restoration
Time of post treatment evaluation
Local Factors causing endodontic failures
Incomplete debridement of the root canal system
infected and necrotic pulp tissue→main irritant to
the periapical tissues
The host parasite relationship、virulence of
microorganisms , ability of infected tissues to
heal→influence the repair of the periapical tissues
Endo success →debridement
Oral Microbiology and Immunology
Volume 19, Issue 2, pages 71–76, April 2004
Extirpation of pulp and instrumentation beyond
Local accumulation of the blood→mild
Extravasated blood cells and fluid：foreign body
nidus for bacterial growth
Instrumentation beyond apical foramen→PDL
and alveolar bone trauma→the prognosis of
endodontic treatment ↓
Shortcomings that promote loss of
Failure to irrigate frequently and copiously with a
tissue dissolving irrigant.
Failure to recapitulate
Failure to radiographically verify the working length.
Malpositioned instrument stops
Failure to record and use stable reference points.
Skipping instrument sizes
Caused by improper or overuse of
instruments and forcing them in curved
Prognosis ：no much affected in vital pulps
poor in necrotic tissue.
Canal blockage and ledge formation—
Accumulation of dentin chips or tissue debris
prevent the instruments to reach its
full working length
Ledge formation—straight instruments in
These lead to bacteria & debris remaining
Management of debris blockade
Stiff file (15 or above)
Curved in apical 1 to 3 mm at
a 30 to 45- degree bend
Rotated till catch obtained
Then in and out winding!
Lack of knowledge of anatomy of the tooth,
attention, misdirection of the instruments
Prognosis：location, time, perforation seal and
Poor prognosis remaining
Incompletely filled teeth—
Teeth filled more than 2mm short of apex
Several studies shown：
poor prognosis—underfillings with necrotic pulps
Overfilling of root canals—
Overfilling extending ≧2mm beyond
Continuous irritation of the periapical
tissues endo failure
According to Crump (1979), it is not necessary to treat
overfill unless clinical symptoms develop.
Causes of overfilling:
1. Failure in determine the exact location of the apical
2. An absence of apical stop or constriction in mature
2. Incorrect selecting of master cone.
3. Open apices.
Partial or complete fractures of roots
Prognosis of teeth：vertical root is poor than
Traumatic occlusion –
Cause endo failures because of its effect on
Strindberg L Z (1956): - endodontic failure is about six decade
old story started by Strindberg by his comprehensive study and
has made attempt to answer the basic questions about the
success and failure of endodontic treatment.
Jokinen et al (1978), Morse et al (1983) & Pekruhn (1986) -
conducted study to assess the success and failure rate of
endodontic treatment. Success rate ranged from 53% - 65%.
Grossman et al(1965): - conducted study of 1229 cases treated by
student & practitioner , success rate was 91.5% while failure was
8.5%.Divided the causes of endodontic failure in four category
i.e. poor diagnosis ,poor prognosis , technical difficulties &
Torpe, Transtad & Maltzdo: - Described the contribution of
overextended access preparation leads to excess reduction of
dentin leads to weaking of tooth.
Seltzer s,Sinai & Agust D(1970) : Irritating effect or the micro
leakage of materials used` for repair of perforations causes
endodontic lesion to develop and subsequent failure of
Grossman LI (1972) : Objective of endodontic treatment is
complete removal of potential irritant from root canal space
, control of infections , shaping of the canal and removal of
organic debris is considered as critical requirement of
endodontic therapy to do successfully.
Crumps (1979): Has listed several alternatives for differential
diagnosis of endodontic failures i.e.
perforation, obturation, overfilled, root canal
missed, periodontal disease , another tooth and trauma.Szajkiss
and Fagger M (1983) : - said that more rigid the criteria of
operator in case selection, greater the chances of success, where
as treatment of all cases without case selection criteria increases
the chances of failures.
Ingle (1985) : - Described causes of endodontic failures into three
main groups. Apical perforation, operative errors and errors in
Kaffe I and Saint Louis (1987) : - Describes that incorrect
diagnosis resulted from a misinterpretation or lack of
information either clinical or radiographic leads to endodontic
treatment in wrong tooth and causes subsequent failures of