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: andyendo@yuhs.ac0099-2399/$ - 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

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.

References1. Friedman S, Abitbol S, Lawrence HP. Treatment outcome in endodontics: the

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 rather low frequency of 8.7%. This is because an isthmuswith a missing or leaky canal would be included in the missing canalor leaky canal category. In addition, teeth diagnosed with definiteroot fractures or cracks were excluded from this study, so apical cracksalso showed a low frequency of 1.2%. Anatomical complexity, apicalcalculus, and apical cracks might not be the main cause of failure,but they are difficult to detect.

The root canal anatomy of each tooth type is considered a factorassociated with the outcomes of endodontic treatment (25). In thisstudy, the frequency of the possible failure causes differed accordingto the tooth position (P < .001). Although the anterior teeth failedmainly because of a leaky canal, the posterior teeth except the maxillarypremolar failed because of a missing canal. The results of the maxillaryanterior and premolar were attributed to the fact that the relativelynarrow root canals in multirooted teeth are managed more thoroughlythan the wider canals in single-rooted teeth (26). In contrast, molarshave a complex anatomy and difficulty in access and vision, so that itis likely to miss a canal such as second mesiobuccal canal in the maxil-lary molar and distolingual canal in the mandibular molar. The lingualcanals in mandibular incisor tend to be overlooked despite the easyaccess. Therefore, successful endodontic treatment might requiredifferent concerns according to the tooth type.

In this study, the possible causes of failure were examined byobserving apical root tip before root-end resection and resected rootsurface after the root-end resection. Unfortunately, we did not lookinto the resected root tip itself, and this might be the reason that theunknown etiology was as high as 18% and became the limitation ofthis study. There are few studies (15, 16) that inspected the root tipminutely, such as SEM observation or microscopic inspection afterdemineralization, and found anatomical complexities such asaccessory canals/apical ramifications in majority of them. Thus, if weused additional methods to identify the causes such as SEMobservation or demineralization of resected root tip, the anatomicalcomplexity category would have been much larger, and unknownetiology would have been much smaller.

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7. Gomes BPFA, Pinheiro ET, Jacinto RC, Zaia AA, Ferraz CCR, Souza-Filbo FJ. Micro-bial analysis of canals of root-filled teeth with periapical lesions using polymerasechain reaction. J Endod 2008;34:53740.

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18. Raina R, Loushine RJ, Weller RN, Tay FR, Pashley DH. Evaluation of the quality of theapical seal in Resilon/Epiphany and Gutta-Percha/AH plus-filled root canals by usinga fluid filtration approach. J Endod 2007;33:9447.

19. Tay FR, Pashley DH. Monoblocks in root canals: a hypothetical or a tangible goal.J Endod 2007;33:3918.

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26. Tronstad L, ed. Clinical endodontics: a textbook. 2nd ed. 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