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Analysis of the Cause of Failure in Nonsurgical
EndodonticTreatment by Microscopic Inspection during
EndodonticMicrosurgeryMinju Song, DDS, MSD,* Hyeon-Cheol Kim, DDS,
MS, PhD, Woocheol Lee, DDS, PhD,
and Euiseong Kim, DDS, MSD, PhD*
anatomyfractures and those with a history of endodontic surgery
were excluded. All patients
Clinical ResearchCopyright 2011 American Association of
Endodontists.From the *Microscope Center, Department of
Conservative Dentistry, College of Dentistry, Yonsei University,
Seoul; Department of Conservative Dentistry, School ofDentistry,
Pusan National University, Busan City; and Department of
Conservative Dentistry, School of Dentistry and Dental Research
Institute, Seoul National University,Seoul, Korea.
Supported by Basic Science Research Program through the National
Research Foundation of Korea (NRF) funded by the Ministry of
Education, Science and Tech-nology (2010-0021281).
Address requests for reprints to Dr Euiseong Kim, Microscope
Center, Department of Conservative Dentistry, College of Dentistry,
Yonsei University, 250 Seongsanno,Seodaemun-Gu, Seoul, 120-752,
South Korea. E-mail address: [email protected]/$ - see
front matterCause of failure, endodontic microsurgery,
non-surgicalendodontic treatment, resected root surface, root
canalretreatment had been performed. Teeth with signs of cracks or
horizontal and verticalAbstractIntroduction: This study examined
the clinical causesof failure and the limitation of a previous
endodontictreatment by an inspection of the root apex and
resectedroot surface at 26 magnification during
endodonticmicrosurgery. Methods: The data were collected
frompatients in the Department of Conservative Dentistry atthe
Dental College, Yonsei University in Seoul, Koreabetween March 2001
and January 2011. All root-filledcaseswith symptomatic or
asymptomatic apical periodon-titis were enrolled in this study. All
surgical procedureswere performed by using an operating microscope.
Thesurface of the apical root to be resected or the resectedroot
surface after methylene blue staining was examinedduring the
surgical procedure and recorded carefully with26magnification to
determine the state of the previousendodontic treatment by using an
operating microscope.Results: Among the 557 cases with periapical
surgery,493 teeth were included in this study. With the exclusionof
unknown cases, the most common possible cause offailure was
perceived leakage around the canal fillingmaterial (30.4%),
followed by a missing canal (19.7%),underfilling (14.2%),
anatomical complexity (8.7%), over-filling (3.0%), iatrogenic
problems (2.8%), apical calculus(1.8%), and cracks (1.2%). The
frequency of possiblefailure causes differed according to the tooth
position(P < .001). Conclusions: An appreciation of the
rootcanal anatomy by using an operating microscope innonsurgical
endodontic treatment canmake theprognosismore predictable and
favorable. (J Endod 2011;37:15161519)
Key Wordsdoi:10.1016/j.joen.2011.06.032
1516 Song et al.Nonsurgical endodontic treatment is a
predictable and reliable treatment with highsuccess rates ranging
from 86%98% (1, 2). Nevertheless, for a variety of
reasons,endodontic failure still occurs, and presence of clinical
signs and symptoms along withradiographic evidence of periapical
bone destruction indicates the need for retreatment(3, 4).
The first and most important step for retreatment is to
determine the cause ofendodontic failure. Normally, the etiologic
factors of endodontic failure can be placedinto 4 groups: (1)
persistent or reintroduced intraradicular microorganism, (2)
extra-radicular infection, (3) foreign body reaction, and (4) true
cysts (5). Among those,many studies reported that microorganisms in
the root canals or periradicular lesionsplay a major role in the
persistence of apical periodontitis lesions after a root
canaltreatment (68).
Endodontic failure related to microorganisms can be caused by
procedural errorssuch as root perforation, ledge formation,
separated instruments, missed canals, as wellas anatomical
difficulties such as apical ramification, isthmuses, and other
morphologicirregularities (8, 9). Nevertheless, a precise diagnosis
can be made only after surgery orextraction, and there are few
reports dealing with the clinical implications andmicrobiologic
persistence (10). A precise inspection of the root apex or
resectedroot surface is one of the best advantages of endodontic
microsurgery (11, 12). Ithelps identify the cause of endodontic
failure, so that causative factors can beremoved completely during
the surgical procedure.
Therefore, this study examined the clinical causes of failure
and the limitation ofa previous endodontic treatment by examining
the root apex and resected root surfaceat 26magnification during
the endodonticmicrosurgery of failed teeth with a
previousendodontic treatment.
Materials and MethodsCase Selection
The data were collected from patients in the Department of
Conservative Dentistryat the Dental College, Yonsei University in
Seoul, Korea between March 2001 andJanuary 2011. All root-filled
cases with symptomatic or asymptomatic apical periodon-titis were
included, regardless of whether initial root canal treatment or
nonsurgicalJOE Volume 37, Number 11, November 2011
-
were placed on a preoperative regimen of antibiotics and
anti-inflammatory drugs. Oral amoxicillin (250 mg) 3 times daily
wasprescribed starting 1 day before surgery and was continued for a
totalof 7 days. Ibuprofen (400 mg) was administered 1 hour before
andafter surgery in all patients.
Surgical ProcedureWith the exception of incisions, flap
elevation, and suturing, all
surgical procedures were performed by using an operating
microscope(OPMIRPICO; Carl Zeiss, Gottingen, Germany). All clinical
procedureswere the same as those reported in a previous study (11,
13) and werecarried out by the same operator.
Briefly, the flap was reflected after deep anesthesia, and the
osteot-omy was performed. After removing the soft tissue debris, an
additional2- to 3-mm root tip with a 010 bevel angle was sectioned
with a 170tapered fissure bur under copious water irrigation. The
resected rootsurfaces were then dried by using a Stropko
(SybronEndo, Orange,CA) irrigator/drier, stained with methylene
blue, and examined with mi-cromirrors (ObturaSpartan, Fenton, MO)
under 26 magnification todetermine the possible cause of failure.
The root-end preparation androot-end filling were performed. The
wound site was closed and suturedwith 5 0 monofilament sutures, and
a postoperative radiograph wastaken.
Assessment of Possible Cause of Failurein the Endodontic
Treatment
During the surgical procedure, the surface of the apical root to
be
the presence of an isthmus; (2) leaky canal: a gap between the
previousroot filling and dentin or obvious leakage after methylene
blue staining;(3) apical calculus; (4) anatomical complexity:
isthmus between the 2canals filled, apical ramification that has
not been treated; (5) under-filling: fillings more than 2 mm short
of the apex in the preoperativeradiographs; (6) apical cracks; (7)
iatrogenic problem: perforation(transportation), file separation;
(8) overfilling: excess root filling;and (9) etc: unknown.
Figure 1 gives an example of each category.To analyze the
frequency of each cause of failure according to the
tooth position, a Pearson c2 test was used with a significance
levelof .05.
ResultsAmong the 557 cases with periapical surgery, a total of
493 roots
were analyzed. Figure 2 shows the possible causes of failure in
theprevious root canal treatment. The most common possible cause
offailure was a leaky canal (30.4%), followed by a missing
canal(19.7%), underfilling (14.2%), anatomical complexity (8.7%),
over-filling (3.0%), iatrogenic problems (2.8%), apical calculus
(1.8%),and apical cracks (1.2%). Teeth on which nothing was found
afterthe surgical procedure were observed in 18% of all cases.
The frequency of possible failure causes differed according to
thetooth position (P < .001). Table 1 lists the overview of
cause of failureper tooth position. In the maxillary anteriors and
premolars, a leakycanal was the most common cause of failure. On
the other hand, inthe maxillary molar, mandibular premolar and
molar, a missing canal
e arr), Athatlar.
Clinical Researchresected was assessed after hemostasis. The
surface was examined andrecorded carefully at 26 magnification to
determine the state of theprevious endodontic treatment by using an
operating microscope.When the cause of the previous endodontic
failure was obscure, the re-sected root surface after the root-end
resection was stained with meth-ylene blue and inspected in the
samemanner. The causes of failure werecategorized as follows: (1)
missing canal: untreated canal regardless of
Figure 1. Example of each category of the causes of endodontic
failure. Note thmolar. (B) Leaky canal: gap between gutta-percha
and dentin. (C-1) and (C-2image of apical calculus (30K). (D)
Anatomical complexity: accessory canalsof root. (G) Iatrogenic
problem: broken file in mesial root in mandibular moJOE Volume 37,
Number 11, November 2011was the most common cause. A missing canal
and leaky canal showeda similar frequency in the mandibular
anterior teeth.
DiscussionThe underlying reason for the failure of endodontic
treatment is
almost invariably due to a bacterial infection (5). The bacteria
mightbe located within a previously missed or uninstrumented
portion of
ows. (A) Missing canal: second mesiobuccal canal with an isthmus
in maxillarypical calculus: calculus deposition caused by chronic
sinus tract. (C-3), SEMhave not been touched. (E) Underfilling. (F)
Crack: apical crack at lingual side(H) Overfilling: overextended
gutta-percha.Cause of Failure in Nonsurgical Endodontic Treatment
1517
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20%(97)18%(89)Missing canal
Leaky canal
3%(14)
3%(15) Apical calculus
Anatomical complexity
1%(6) Underfilling
Crack
30%(150)14%(70) Iatrogenic problem
anal
Clinical Researchthe root canal, infiltrate via a leaky coronal
restoration and root filling,or cause contamination from an
extraradicular infection (14).However, there are few reports
dealing withmicrobiological persistenceand clinical
implications.
Scanning electron microscopy (SEM) was used to examine the
re-sected root canal ends after the apicoectomy. Furusawa et al
(15) re-ported that 80% of teeth examined displayed an apical
foramen witha wide opening, >350 mm, as a result of
overinstrumentation or path-ologic resorption, and accessory
canals/apical ramifications wereobserved in 64% of the teeth. Wada
et al (16) examined themorphologyof the root apex by observing the
anatomy of the specimens obtained byan apicoectomy. Apical
ramifications were present in 19 (70%) of theroots, suggesting a
close relationship between the anatomicalcomplexity of the root
canal and the occurrence of refractory apicalperiodontitis.
2%(9)
9%(43)
Figure 2. Percentage (N) of the possible causes of failure in
previous root cIn this study during the surgical procedure, the
possible causes offailure were recorded under an operating
microscope (Fig. 1). Amongthem, the most common was a leaky canal
(30.4%). For endodonticsuccess, it is important to minimize and
keep the amount of bacteriaunder the critical level by sealing the
canal tightly. However, no materialor technique prevents leakage.
Indeed, obtaining an impervious sealmight not be feasible because
of the porous tubular structure of dentinand canal irregularities
(17). Nevertheless, resin-based obturationsystems have been
introduced as alternatives to the traditional tech-
TABLE 1. Overview of Cause of Failure per Tooth Position
Cause of fa
1 2 3 4
MaxillaryAnterior 8.25, (16) 40.21, (78) 2.58, (5) 5.67, (11)
13Premolar 11.70, (11) 30.85, (29) 0.00, (0) 13.83, (13) 23Molar
45.90, (28) 16.39, (10) 0.00, (0) 4.92, (3) 6
MandibularAnterior 25.00, (11) 29.55, (13) 6.82, (3) 4.55, (2)
6Premolar 31.25, (10) 18.75, (6) 3.13, (1) 6.25, (2) 9Molar 30.88,
(21) 20.59, (14) 0.00, (0) 17.65, (12) 16
1, Missing canal; 2, leaky canal; 3, apical calculus; 4,
anatomical complexity; 5, underfilling; 6, crack; 7,
1518 Song et al.nique of gutta-percha and sealer. The resin
sealer bonds to a poly-mer-based root canal filling material and
attaches to the etched rootsurface, which makes a monoblock
achievable despite the controversy(18, 19).
The second most common reason was a missing canal (19.7%).Second
canals, such as second mesiobuccal canal in maxillary molarsor with
calcified orifice, are easy to miss. These missed or
untreatedcanals contain necrotic tissue and bacteria that
contribute to thechronic symptoms and nonhealing periapical lesions
(20). There-fore, the use of a dental operating microscope is
another importantaid in nonsurgical endodontics as well as surgical
endodonticsbecause it has helped tremendously in locating
additional canals(21, 22). In particular, the use of a dental
operating microscopeand ultrasonic device is strongly recommended
in a single rootwith a second canal.
Overfilling
Unknown
treatment.Endodontic procedural errors such as underfilling,
overfilling, fileseparations, and root perforations are believed to
be the direct cause oftreatment failure. However, procedure errors
themselves do not jeop-ardize the outcome of treatment; rather,
they increase the risk of failurebecause of the clinicians
inability to eliminate intraradicular microor-ganisms from the
infected root canals (9). In this study, iatrogenicproblems and
overfilling were responsible for small portion of failures,within
3%. In contrast, underfilling showed a 14.2% failure rate, whichis
the third most common cause. A failure to achieve patency to the
apex
ilure, % (N)
P value5 6 7 8 9
-
of the root canal, whether it is caused by ledge formation,
inaccuratemeasurement of the working length, or incomplete
instrumentation,can make it difficult to remove infected necrotic
tissue remaining inthe apical portion of the root canal. Chugal et
al (23) reported thata 1-mm loss in working length increased the
likelihood of treatmentfailure by 14% in teeth with apical
periodontitis.
AcknowledgmentsThe authors deny any conflicts of interest
related to this study.
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Clinical ResearchMany studies have revealed anatomical
complexity such as isthmusand apical ramification with high
frequency (15, 16, 24). Von Arx (24)reported that none of the
isthmuses were filled, emphasizing the diffi-culty of orthograde
instrumentation and root filling of canal isthmuses.On the other
hand, in the present study, the anatomical complexityshowed a
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missing or leaky canal would be included in the missing canalor
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Stuttgart: Thieme; 2003.Cause of Failure in Nonsurgical Endodontic
Treatment 1519
Analysis of the Cause of Failure in Nonsurgical Endodontic
Treatment by Microscopic Inspection during Endodontic
MicrosurgeryMaterials and MethodsCase SelectionSurgical
ProcedureAssessment of Possible Cause of Failure in the Endodontic
Treatment
ResultsDiscussionAcknowledgmentsReferences