A question that should be asked of any discipline or tech-nique in dentistry is, “What degree of success should beexpected?” Success, in turn, should be measured longitu-dinally in time—long-range success as opposed toshort-term success. The beautiful resin restoration turn-ing an ugly yellow in 1 year is not an unqualified success.By the same token, the denture “worn” in the bureaudrawer is far from successful, nor is the well-fitting partialdenture successful if it leads to clasp caries in 6 months.Moreover, the endodontically treated tooth with a largeperiradicular lesion that does not show signs of healing 2years after treatment cannot be considered a success.

To answer the question, “How successful isendodontic therapy?” a study was undertaken at theUniversity of Washington School of Dentistry to evalu-ate endodontically treated teeth to determine their rateof success. More important to the study, the rate of fail-ure was also established, and the causes of failure werecarefully examined. Analysis of the failures led to mod-ifications in technique and treatment. Finally, the entirediscipline of endodontic therapy was re-examined, anddefinitive improvements were made as a result. Theimprovements in treatment are reflected in theimprovement in success, which increased to 94.45%from a former success rate of 91.10%, an improvementof 3.35 percentage points. In other words, nearly 95%of all endodontically treated teeth were successful.

There was also a hidden agenda to the Washingtonstudy—to prove ourselves to a profession that, at thattime, was skeptical of root canal therapy. In light oftoday’s knowledge, the project had some design flawsand misinterpretations and was not that well con-trolled, even though each phase was subjected to statis-tical analysis. The null hypothesis was ignored in aneffort to prove a point: root canal therapy could besuccessful if properly done. On the other hand, the fig-ures of the Washington study compared favorably withother reports of success.1–13

A group at Temple University, for example, reporteda 95.2% success rate at the end of 1 year with 458 canalsfilled by the gutta-percha-euchapercha method.5 Theyfound that teeth that started with vital inflamed pulpshad more success (98.2%) than teeth with nonvitalpulps (93.1%). Contrary to other reports, however, theywere far less successful with short-filled canals (71.1%)than with flush-filled or overfilled canals (100%).(Reports of 100% success must be questioned.)

South African researchers enjoyed a success ratesimilar to that of the Temple University group: 89%success at the end of 1 year.6 Also, as with the Templegroup, they were successful 92% of the time in teethfilled to the apex and 91% of the time if the canals wereoverfilled. Filling short of the apex reduced their suc-cess rate to 82%.6

The poorest reported rate of success dealt with 845Dutch military servicemen.7 After 17 years, 45% of theendodontically treated teeth had failed in nonaviators,whereas only 7% had failed in aviator patients. There isa simple explanation for this wide discrepancy in fail-ure rate. The aviators were usually treated withgutta-percha or silver point fillings, whereas the non-aviators were more frequently treated by “therapy withspecial chemical compounds.” Furthermore, the avia-tors’ teeth were more frequently crowned.7

Hession, a highly respected endodontist in Australia,reported the highest rate of success: 98.7% of 151teeth.8 Nelson reported lower rates in England: 81.9%of 299 teeth. With re-treatment, however, Nelson sal-vaged 11 of the treatment failures, raising the successrate to 85.6%.9 Kerekes and Tronstad, using the stan-dardized technique recommended in this text, had asuccess rate similar to the Washington study,10 as didSjögren and his associates from Sweden.11 Theirremarkable study of 356 endodontic patients, re-exam-ined 8 to 10 years later, reported a 96% success rate ifthe teeth had vital pulps prior to treatment. The success

Chapter 13

OUTCOME OF ENDODONTIC TREATMENT AND RE-TREATMENT

John I. Ingle, James H. Simon, Pierre Machtou, and Patrick Bogaerts

rate dropped to 86% if the pulps were necrotic and theteeth had periradicular lesions and dropped still lowerto 62% if the teeth had been re-treated. They conclud-ed by stating that “teeth with pulp necrosis and peri-radicular lesions and those with periradicular lesionsundergoing re-treatment constitute major therapeuticproblems…” They surmised that bacteria in “sites inac-cessible” might be the cause of increased failure.11

Worldwide, most controlled studies seem to agreethat a lower success rate is associated with overfilledcanals, teeth with preexisting periradicular lesions, andteeth not properly restored after root canal thera-py.11–15 A Swedish group reported a high failure rate ifcanals were not totally obturated.13 Sjögren et al., quot-ed above, also noted a direct correlation between suc-cess and the point of termination of the root filling.11

As Figure 13-1 shows, teeth filled within 0 to 2 mmfrom the apex enjoyed a 94% success rate, which fell to76% if the teeth were overfilled and fell further to 68%if they were filled more than 2 mm short.

In reported re-treatment of initial endodontic fail-ures, success figures have been unacceptably low. Only50% of the overfilled teeth were acceptable (Figure 13-2). Similarly, a Japanese group reported a much high-er failure rate if root fillings were overextended.14

Surprisingly, a Dutch group enjoyed as high a healingrate whether or not the canals were filled.16 The Dutchreport was only a 2-year study. Unfilled canals had notbeen followed over a long period of time (such as 10 to20 years). Most endodontically treated teeth shouldlast as long as other teeth. Vire examined 116root-filled teeth that were extracted because of failureand found that only 8.6% failed for endodontic rea-sons compared with 59.4% restorative failures and32% periodontal failures.17

748 Endodontics

The Washington Study

The figures above from the University of Washingtonare only a few from an exhaustive study encompassingmany aspects of endodontic therapy. The modifica-tions in treatment mentioned above were institutedfollowing a pilot study of endodontic success and fail-ure. Even with the limited number of patients in thepilot study, the causes of failure became apparent.Clinical techniques were then changed in an effort toovercome failure. Patients were recalled for follow-upat 6 months, 1 year, 2 years, and 5 years, and the recallradiographs were carefully evaluated for improvementor lack of improvement. Teeth included in the successgroup were those that demonstrated decided periradic-ular improvement (Figures 13-3 and 13-4) and thosewith continuing periradicular health (Figure 13-5).The failures were made up of those teeth that initiallydemonstrated periradicular damage and that had notimproved (Figure 13-6), as well as those that had dete-riorated since treatment (see Figure 13-6). As soon as astatistically significant group of cases built up in thefile, the material was ready to be analyzed.

The 2-year recall series was found to be ideal for thisstudy because a statistically significant sample devel-oped within this group. The 5-year recall sample wasalso analyzed but in understandably smaller, thoughsignificant, numbers. The study did not take into con-sideration any illnesses or systemic differences betweenpatients.

Two-Year Recall Analysis. Of a total population of3,678 patients who could have returned for 2 years,1,229 actually did return, a recall rate of 33.41%—astatistically significant cohort. Before improvements intechnique and case selection were instituted, there was

Figure 13-1 Outcome of treatment according to the level of theroot filling in relation to the root apex in cases with preoperativepulp necrosis and apical periodontitis. Number of healedlesions/number of preoperative lesions. Reproduced with permis-sion from Sjögren U.11

Figure 13-2 Results of re-treatment of previously filled roots withapical periodontitis with regard to the level of the final root fillingin relation to the root apex. Number of healed lesions/number ofpreoperative lesions. Reproduced with permission from SjögrenU.11

Outcome of Endodontic Treatment and Retreatment 749

a 91.10% success rate—104 failures of 1,067 cases.After these improvements were instituted, the successrate rose to 94.45%—9 failures of 162 cases.

Five-Year Recall Analysis. From the beginning ofthe study, enough 5-year recalls had returned to make astatistically valid analysis of these cases. Of the 302 5-

year recalls, 281 teeth were successful—a success rate of93.05%; 21 teeth were considered failures—a failurerate of 6.95%. These figures compare favorably with the2-year recall analysis.

Two-Year Recall Analysis by Age of Patient.Reference is frequently made to age as a criterion for

Figure 13-3 Special mount for radiographstaken of each case. Note that recall films areexposed at 6 months, 1 year, 2 years, and 5 yearsfollowing therapy. Figures at the top of the cardindicate that complete healing had occurred at 6months and was maintained for 5 years.

Figure 13-4 A, “Before” radiograph, with large periradicular lesion. B, “Treatment” radiograph immediately following periradicular sur-gery. Also note the fractured root tip of a central incisor (arrow) that tests vital. C, Two-year postoperative radiograph of successfully treat-ed case. Lack of total periradicular repair (moderate repair) is related to extensive surface of filling material over which cementum cannotgrow. Also note fracture repair (arrow) of vital central incisor.

A B C

750 Endodontics

endodontic treatment. The youngest patient treated inthe study was 21⁄2 years old; the oldest patient was 92years old. There was a fairly consistent rate of successand failure according to age as shown by statisticalanalysis (χ2 = 2.72; p > .09). Age, of course, has a greatdeal to do with the size and shape of the canal. It wasfound that older teeth, with more restricted canals,were more successfully obturated than very “young”teeth with large-diameter canals. It also became obvi-ous that the size and shape of the lumen of the canal, aswell as the direction of root curvature, play an impor-tant part in the successful completion of a root canalfilling. Analysis of success, by individual tooth, willdemonstrate these points.

Two-Year Recall Analysis by Individual Tooth. Nosignificant difference in failure existed between any ofthe teeth in either arch (χ 2 = 2.45; p > .10). Thus, noparticular tooth can be considered a higher endodonticrisk, although there was a wide discrepancy betweenthe mandibular second premolar with a failure rate of4.54% and the mandibular first premolar with a failurerate of 11.45%. Canal anatomy might account for thegreater increase in failure in the first premolar. Pucciand Reig, in their monumental work ConductosRadiculares, pointed out the great anatomic differences

Figure 13-5 A, Pulpless mandibular lateral incisor with no periradicular lesion. B, Constant periradicular health is revealed in a 2-year post-operative radiograph, a successful case.

Figure 13-6 Two failure cases demonstrated in a single radi-ograph. Curved arrow (right) points to a lesion that has failed toheal 2 years following endodontic treatment. Straight arrow (left)points to a lesion that has grown worse 2 years following therapy.Lack of total obturation of canals is revealed by the fuzzy appear-ance of root canal fillings. Defective amalgam restoration (openarrow) contributes to an interproximal periodontal lesion.

BA

Outcome of Endodontic Treatment and Retreatment 751

between the two mandibular premolars.18 Whereas themandibular second premolar has two canals and twoforamina 11.5% of the time, the mandibular first pre-molar has branching canals, apical bifurcation, andtrifurcation 26.5% of the time.18

Others have found similar discrepancies betweenmandibular premolars, most recently Trope et al. at theUniversity of Pennsylvania.19 These researchers con-firmed one of Pucci and Reig’s findings almost exactly:23.2% of the mandibular first premolars examinedhad two canals. They also found that 7.8% of secondpremolars had two canals, a figure differing from Pucciand Reig’s 11.5%. This discrepancy could well beexplained on an ethnic basis: the researchers atPennsylvania reporting on a US African American pop-ulation and Pucci reporting on a Uruguayan popula-tion containing some aborigines.

The Pennsylvania study also confirmed the notionthat African American patients more frequently havetwo canals in lower premolars than white patients. Inthe first premolars, 32.8% had two canals, comparedwith 13.7% of whites. In the second premolars, 7.8% ofAfrican Americans had two canals, compared with2.8% of whites. Nearly 40% of the African Americansin the study had at least one premolar with two canalsand 16% of the time presented two separate roots inmandibular first premolars.19

Failures in the maxillary lateral incisor may also beexplained by anatomic differences. Pucci and Reigshowed extensive distal curvature of the maxillary lat-eral incisor root 49.2% of the time.18 Here again, poorjudgment and preparation frequently prevent adequateinstrumentation and obturation, with root perforationat the curvature a common occurrence (Figure 13-7).Increased failure rate in the maxillary lateral incisor isalso related to continuing root resorption followingtreatment, a finding peculiar to these teeth.

The overall failure rate, mandible to maxilla, is strik-ing but not statistically significant. Failure in themandibular arch was encountered 6.65% of the timeand 9.03% of the time in the maxilla.

Two-Year Recall Analysis: Nonsurgical versusSurgical Intervention. The degree of success achievedby surgical intervention in treated endodontic cases haslong been a contentious point. The Washington studydemonstrated that although nonsurgical treatmentappears to be slightly more successful than surgicaltreatment, differences are not statistically significant (χ2 = 3.44; p > .05).

It is tempting to indict case selection as the basis forincreased failure of surgical treatment. One of the indi-cations for surgical intervention has been the grossly

involved periradicular lesion, where a lower rate ofrepair might be expected. Although the 10 to 12 mmperiradicular lesion appears to heal as readily, if notquite as rapidly, as the 2 mm lesion (Figure 13-8), thismay not always be true. Others have shown that largerlesions, or cases with lesions versus those without, areless successful. Nelson reported that the failure rate wasthree times higher if a periradicular lesion existedbefore treatment.9 In another study, the failure rate wasthe same.16 The Dutch study, interestingly enough,found that “teeth with periradicular granulomas tendto heal less successfully than teeth showing cysts.”12

Similarly, Japanese researchers reported a wide discrep-ancy in success between treated teeth that had no peri-radicular rarefaction (88%) and those with a 5.0 mm orgreater rarefaction (38.5%).14 For those teeth withoutperiradicular lesions, Sjögren et al. reported a 96% suc-cess rate, but this rate dropped to 86% if periradicularlesions were present.11

Two-Year Recall Analysis of Endodontic Failures.The final and most important portion of theWashington study dealt with 104 failure cases as agroup. Careful analysis of these particular cases is mostrevealing.

Arrangement of Failures by Frequency ofOccurrence. As Table 13-1 shows, the most strikingfinding is the 58.66% of the failures caused by incom-plete obturation of the canal (Figure 13-9). This is ahighly significant figure. This most common cause offailure is almost 50 percentage points ahead of the nextgreatest cause of failure, root perforation, which

Figure 13-7 Root tip biopsy from the curved apex of a maxillarylateral incisor. Severe inflammatory reaction surrounding the rootend is related to perforation as well as failure to débride and obtu-rate the curved portion of the canal. Reproduced with permissionfrom Luebke RG, Glick DH, Ingle JI. Oral Surg 1964;18:97.

752 Endodontics

accounts for 9.61% of the failures. Thus, the two great-est causes of failure stand revealed: inadequate clean-ing and shaping and incomplete obturation. In otherwords, over two-thirds of all of the endodontic failuresin the study were related to inadequate performance oftwo points of the endodontic triad, “canal instrumen-tation and canal obturation.” This alone would call forimproved technique and attention to detail.

Categorical Arrangement of Causes of Failure.The 13 causes of endodontic failure may be arranged inthree general categories of causes leading to failure: (1)apical percolation, (2) operative errors, and (3) errorsin case selection (Table 13-2). Actually, a clear-cutdelineation of the agents of failure is difficult; apicalpercolation into the canal accounts for almost all ofthese failures, as Table 13-2 shows.

Apical Percolation. Three of the causes of failureshown in Table 13-2 lead to apical percolation and sub-sequent diffusion stasis into the canal (Figures 13-10and 13-11). Factor in the bacteria lurking in the regionand these three causes together account for 63.47% ofall of the endodontic failures in the study and demon-strate how vital careful therapy is to success. One mustalso consider the potential of microleakage under andaround coronal restorations: bacteria penetrating fromthe crown to the periapex alongside poorly obturatedcanals.

Operative Errors. A category made up of errors incoronal cavity preparation and canal preparationaccounts for almost 15% of the failures (root perfora-tion, 9.61%; broken instrument, 0.96%; and canal gross-ly overfilled, 3.85%; total, 14.42% of all of the failures).

Figure 13-8 Large periradicular lesion (left) has healed completely (right) within 6 months in a patient 20 years of age.

Table 13-1 Distribution of Failures of TreatedEndodontic Cases: Two-Year Recall by Frequency ofOccurrence

Causes of Failure Number of Failures % Failures

Incomplete obturation 61 58.66

Root perforation 10 9.61

External root resorption 8 7.70

Coexistent periodontal- 6 5.78periradicular lesion

Canal grossly overfilled 4 3.85or overextended

Canal left unfilled 3 2.88

Developing apical cyst 3 2.88

Adjacent pulpless tooth 3 2.88

Silver point 2 1.92inadvertently removed

Broken instrument 1 0.96

Accessory canal unfilled 1 0.96

Constant trauma 1 0.96

Perforation, nasal floor 1 0.96

Total failures 104 100.00

Distribution of 104 endodontic failures 2 years following therapy.When arranged by frequency of occurrence, note that incompleteobturation accounts for almost 60% of all failures, followed by rootperforation, which accounts for nearly 10% of 104 failures. Causeof failure includes infrequently encountered conditions that occurless than 1% of the time.

Outcome of Endodontic Treatment and Retreatment 753

These operative errors are all related to inadequate coro-nal cavity preparation, improper use of endodonticinstruments and filling materials, and lack of standardi-zation of endodontic equipment and material as itarrives from the manufacturer. The latter problem hasnow been reduced through instrument standardization.

On the other hand, delicate root canal instrumentsmust not be mistreated by the inexperienced, and oneof the common complaints of the neophyte is “instru-ment breakage.” Also, improper use of the instrumentscausing root perforation and apex perforationaccounted for 14 of the 104 failures in the study.Penetrating through the side of a curved root ultimate-ly leads to incomplete instrumentation and incompleteobturation (Figure 13-12).

Opening wide the apical foramen during instru-mentation illustrates that this is also a form of perfora-tion and leads to gross overfilling or overextension.Healing is delayed and often incomplete around thegrossly overfilled areas that may be caused by foreign-body reaction. Moreover, the perforated apical foramenhas destroyed the apical “stop” and does not allow com-paction during canal filling. Although the canal mayappear overfilled, it is actually incompletely obturated,with resulting percolation and failure (Figure 13-13).

The paucity of failures in this study owing to brokeninstruments illustrates that this is not as desperate a sit-uation as it is often considered to be. In analyzing theUniversity of Washington caseload, Crump and Natkinfound that failure following instrument fragmentationwas the same as in other endodontic cases.20

Broken instruments, however, are not favored anymore than overfilling and underfilling are favored, but,occasionally, both accidents may occur. Surgical treat-ment is recommended in operable teeth if the instru-ment is broken off in the apical one-third of the canal

Figure 13-9 Left, Careful examination of aninitial radiograph reveals internal resorption andwidening of the canal apical to the curved arrow.Right, In a 2-year recall radiograph, periradicularlesion persists owing to failure to totally obliter-ate the root canal space (arrow).

Table 13-2 Distribution of Failures of TreatedEndodontic Cases: Two-Year Recall by Category ofCause of Failure

Causes of Failure Number of Failures % Failures

Apical percolation—total 66 63.46

Incomplete obturation 61 58.66

Unfilled canal 3 2.88

Ag point inadvertently 2 1.92removed

Operative error—total 15 14.42

Root perforation 10 9.61

Canal grossly overfilled 4 3.85or overextended

Broken instrument 1 0.96

Errors in case selection—total 23 22.12

External root resorption 8 7.70

Coexistent periodontal- 6 5.78periradicular lesion

Developing apical cyst 3 2.88

Adjacent pulpless tooth 3 2.88

Accessory canal unfilled 1 0.96

Constant trauma 1 0.96

Perforation, nasal floor 1 0.96

Total failures 104 100.00

Distribution of 104 endodontic failures 2 years following therapy.Causes of failure may be categorized into three general groupings:apical percolation, which accounts for 63.46% of failures; operativeerrors, which account for 14.42% of failures; and errors in caseselection, which account for 22.12% of the 104 failures.

754 Endodontics

Figure 13-10 A, Although the root canal filling appears to be overextended, the fuzzy appearance indicates a lack of density necessary fortotal obturation. Apical perforation destroyed the apical constriction necessary for compaction of the root canal filling. B, Root end biopsyof this failure case shows root canal cement and cellular debris rather than well-condensed gutta-percha filling. Constant percolation into theroot canal space provides media for bacterial growth.

Figure 13-11 A, Constantly draining sinus tract opposite the mesiobuccal root of a maxillary first molar (arrow) was thought to be relat-ed to an advanced periodontal lesion. Total amputation of the mesiobuccal root is indicated. B, Amputated root reveals an error in diagno-sis. The reamer is in an undetected second canal, whereas the arrow points to an obturated primary canal. Secondary canals in mesiobuccalroots of first permanent molars occur about 60% of the time.

A B

A B

Outcome of Endodontic Treatment and Retreatment 755

and is loose in the canal and cannot be removed orbypassed. Surgery may also be the approach if the canalis grossly overfilled with irretrievable gutta-percha and

cement. Broken instruments may often be retrieved by“floating” out the piece with an ultrasonically poweredinstrument. Broken instruments, loose in the canal,have also been seen to “rust out.” Failures associatedwith underfilled canals can usually be remedied by re-treatment rather than surgery (see Chapter 14).

All of these errors of operation may be prevented bycareful cavity preparation and canal obturation. Forexample, if the operator is unsure of the instrumentposition in the canal, a radiograph should be taken.Also, more accuracy in fitting the primary or initial fill-ing point will lead to less overfilling. In the final analy-sis, operative error is the simplest cause of failure tocontrol and requires more patience, care, and under-standing to overcome.

Errors in Case Selection. Errors in case selection arenot as easily overcome as operative errors and may oftenbe listed as the “bad breaks of the game” rather thanerrors in judgment. Who could predict, for example, thatexternal root resorption would continue, an apical cystwould develop following treatment, an adjacent toothwould become pulpless, or an associated periodontal

Figure 13-12 Failure owing to root perforation accompanied byincomplete débridement and imperfect obturation. Note the breakin the lamina dura opposite the perforation (arrow).

Figure 13-13 A, Although this incisor appears to be grossly overfilled, careful examination (arrow) reveals failure to totally obturate thecanal. B, Tissue reaction to overfilling and underfilling in a single biopsy specimen from this failure case. Curved arrows direct attention toa mass of cement forced into periradicular tissue. Heavy black arrow (right) indicates noninflammatory tissue capsule that has developed asforeign-body reaction. Open arrow (bottom) points to a violent inflammatory reaction and an abscess related to bacterial products perco-lating from the unfilled canal.

A B

lesion would lead to failure?21 These are all factors thatled to some of the failures in the Washington study, fac-tors that constitute 22.12% of the total failures. Somecould well have been predicted at the time of therapy,but others were entirely unpredictable.

As Table 13-2 shows, there were also minor causesof failure: constant occlusal trauma from bruxism,22

perforation of the nasal floor, and unfilled accessoryor lateral canals. The low incidence of failure associat-ed with unfilled accessory canals came as a surpriseconsidering the degree of emphasis placed by some onthe absolute necessity of totally obliterating these lat-eral canals.

Returning to some of the greater causes of failure,one should note that all eight cases of continuing rootresorption were in maxillary lateral incisors. So oneshould be wary in evaluating the future of these teeth ifthey exhibit extensive apical resorption prior to treat-ment. Most external apical root resorption stops inresponse to successful root canal treatment!

Endodontic failure associated with periodontalpockets is usually the fault of the dentist for not recog-nizing the pocket’s existence. One stumbles ahead withthe endodontics before careful probing reveals thepresence of an associated pocket and that concurrentperiodontal/endodontal therapy will be necessary.23

In some cases, concurrent treatment may not solvean unsolvable problem. Witness the destructive andirreparable nature of some dens invaginatus or radicu-

756 Endodontics

lar lingual grooves extending to the apex24 (Figure 13-14) or the resorptive invasion from one endodonticlesion causing the necrosis of an adjoining tooth25

(Figure 13-15).There are, of course, multiple causes of failure not

revealed in the Washington study: retrofilling failures,root tip and foreign bodies left in surgical sites, rootfenestration following surgery (Figure 13-16), crackedor split roots, or carious destruction unrelated to theroot canal treatment (Figure 13-17). Ultimately, in allof these situations, bacteria are the final cause of fail-ure. One must also recognize that one of the most fre-quent causes of failure of the treated pulpless tooth isfracture of the crown. The tooth must be carefully pro-tected by an adequate restoration.

The Washington study has been faulted by some forbeing only a radiographic study. As Brynolf pointedout in her classic punch biopsy study of root-filledteeth in cadavers, histologic evaluation is a much moreaccurate method of determining if inflammationremains at the apex than is radiologic evidence.26 Buther research was done on cadavers, proving the imprac-ticality of punch biopsy on live patients. Green andWalton followed up on Brynolf ’s approach, comparinghistologic and radiographic findings on cadavers, andalso found that 26% of the teeth with no radiolucen-cies showed chronic inflammation histologically.27 Butthat is not to say that these teeth were uncomfortable orcontributing to the patient’s poor health. How success-

Figure 13-14 Developmental defect,invagination, and radicular lingualgroove, resulting in an unattached peri-odontal ligament tract to the apex. Thedefect at the cingulum probably com-municated with the pulp. Endodonticand periodontic therapy were to noavail. Reproduced with permissionfrom Simon JHS, Glick DH, Frank AL.Oral Surg 1971;37:823.

Outcome of Endodontic Treatment and Retreatment 757

ful is success? Better yet, what are the criteria of suc-cess? Comfort and function? Radiographic? Histologic?Since histologic evaluation is impractical, if not illegal,one would have to go with comfort and function andthe radiographic findings.

There are well over 50 studies attempting to delin-eate how successful our treatment procedures are andwhat the prognosis is for a particular form of treat-ment.28 All in all, the studies that have been done sug-gest the following generalizations:

1. The more extensive and severe the endodonticpathosis, the poorer the prognosis. In other words,

the highest percentage of success is with teeth withvital pulps and the worst prognosis is for those withlarge, long-standing periradicular lesions.

2. The more dental treatment that is done, the poorerthe prognosis. In other words, good nonsurgicalendodontic treatment has the best prognosis. Theworst prognosis lies with teeth that have been re-treated nonsurgically and then re-treated surgicallyonce or twice more.

MICROBES

To further elaborate on the role bacteria play in pulpaland periradicular disease, one must turn to the classicresearch by Kakehashi and his associates at the NationalInstitute of Dental Research.29 They were able to show,in a gnotobiotic study, that microorganisms alonecause pulpal inflammation and necrosis as well as peri-radicular infection.29 It follows that inadequateremoval of microbes (ie, bacteria, fungi, and viruses)from the canal leads to continued infection and inflam-mation30 and that all of the defects listed in theWashington study are ultimately reduced to bacterialinvasion and/or colonization.

But what happens when everything is done right (ie,cleaning, shaping, and obturation), yet failure stilloccurs?31–34 Can bacteria still be present after adequateendodontic treatment?

There is strong evidence that bacteria may not becompletely eliminated after thorough cleaning, shap-ing, and disinfection.35–37 Moreover, when obturationis postponed, bacteria may be able to recolonize in thecanal.38 Furthermore, try as one might, no preparation

Figure 13-15 A, No radiolucency is apparent on a 4-year recall radiograph following root canal filling of a first premolar. Note the anatomic defecton the canine (arrow). B, Radiograph taken 6 years after the lesion was first noticed. Failed root canal filling in the premolar led to periradicularlesions, inflammatory external resorption of canine, and ultimately necrosis of the canine pulp. Reproduced with permission from Frank AL.25

A B

Figure 13-16 Severe bony and soft tissue dehiscence extending tothe periapex of a traumatized incisor. Postoperative defects of thistype may develop following surgery in an area of osseous fenestra-tion. Reproduced with permission from Luebke RG, Glick DH,Ingle JI. Oral Surg 1964;18:97.

technique can totally eliminate the intracanal irritants,and a “critical amount” can sustain periradicularinflammation (Figure 13-18).39,40

In addition, as stated previously, the obturatedcanal may be recontaminated from coronal leak-

758 Endodontics

age.41 Indeed, gutta-percha root canal fillings do notresist salivary contamination.42,43 As Ray and Tropehave been able to show, “long term prognosis oftreatment seems to correlate directly with the quali-ty of the coronal seal.”44

Figure 13-17 Postoperative failure owing toextension of dental caries rather thanendodontic therapy per se. Loss of these abut-ment teeth led to full denture in this case.

Figure 13-18 A, The radiograph shows a mandibular cuspid that appears well obturated with a well-fitting coronal restoration. B, A sinustract is traced with a gutta-percha point to the apical lesion that has not responded to treatment. C, Surgical resection of the root end. D,High-power photomicrographs show bacteria containing plaque on the external root surface.

A B

C D

Outcome of Endodontic Treatment and Retreatment 759

There are also times when an irritant, such as infecteddentin chips, is packed at the apex or pushed through theapex, there to serve as a continuing irritant45,46 that over-whelms the body’s defense system. As stated before, theperiapical tissue could become colonized by periodontalcontamination,47 the virulence of the bacteria, or extru-sion by overaggressive instrument action.48–50

In most cases, the host’s immune system can overcomethese antigens.51 On the other hand, some bacteria pos-sess mechanisms to resist phagocytosis such as encapsu-lation or the production of proteases aimed against theimmune system.52,53 Bacteria may also bury themselvesin a thick matrix that acts as a sort of apical plaque (seeFigure 13-18, D).54–56

Many organisms can survive in periradicular lesions:Actinomyces, Peptostreptococcus,57–60 Propionibac-terium,61,62 Prevotella and Porphyromonas, 63–65

Staphylococcus,66,67 and Pseudomonas aeruginosa.35

Barnett, in fact, has stated that Pseudomonas refractoryperiradicular infection could be “cured” only by heavydoses of metronidazole (Flagyl) following the failure ofre-treatment and apicoectomy.68

FOREIGN BODIES

In spite of what has been stated above, “foreign-bodygiant cell reaction” can occur without the presence ofbacteria, but no fulminating infection will developwithout the bacteria.

A number of foreign bodies have been reported:lentil beans,69 other vegetables,70 popcorn kernels71

(Figure 13-19), paper points, cellulose, and a variety ofunidentified materials.72 Human body defense cells areunable to digest cellulose or cotton pellets.72,73

In addition, various lipids, cholesterols, and crystalshave also been implicated as periradicular irritants. Bytheir very presence, these intrinsic factors are capable ofsustaining an apical lesion despite correct endodontictreatment.74

Root canal sealers can also act as a foreign body andthus sustain a lesion, although, over time, extrudedsealers (and gutta-percha) may be phagocytized bymacrophages.75

The cytotoxicity of freshly mixed and unset sealers iswell documented.76 In the long term, however, obtura-tion materials are far less irritating than microbes.75 Itcan be concluded that an overfill may cause a delay inhealing but will not prevent it.77

EPITHELIUM

The role of epithelium must also be taken into accountwhen reviewing failure to heal periapically. If the rest-ing cells of Malassez remain in the region, they may

respond to the irritants and inflammation and prolifer-ate into a cyst-like attempt to wall off the irritants.78

It has been suggested that these latent epithelial cellrests could be activated by the epidermal growth factorpresent in saliva that contaminates canals left open fordrainage.79,80 In the absence of treatment, or in the pres-ence of persistent bacteria, epithelium continues to pro-liferate to become a bay (pocket) cyst and eventually atrue cyst.81,82 The distinction between a bay (pocket)cyst (Figure 13-20) and a true cyst is important from aclinical standpoint. Since root canal therapy can directlyaffect the lumen of the bay (pocket) cyst, the environ-mental change may bring resolution of the lesion.

There is a controversy over whether cysts heal afternonsurgical endodontic treatment. The true cyst isindependent of the root canal system, so conventionaltherapy may have no effect on it. The prevalence of truecysts is less than 10%. 65,66 Most practitioners now real-ize that true cysts, as well as some bay (pocket) cysts,probably do not heal with nonsurgical therapy. In spiteof good cleaning, shaping, and filling, these lesionshave to be surgically removed to effect healing.

The dangers delineated above emphasize the pointinitially stressed: if the case is carefully selected beforetreatment, if the canal is correctly instrumented andobturated, and if the crown is properly restored, theultimate outcome should be successful.

Figure 13-19 Biopsy of what was thought to be a root tip revealscolumnar-like cells (arrow) of the outer husk of a popcorn kernel thatwas trapped in a fresh surgical area and served as a severe irritant.

Measures to be Employed to Improve Success.One may draw certain conclusions from this study andfinally list a number of procedures to improve the rateof success of treated endodontic cases. These are theTen Commandments of Endodontics:

1. Use great care in case selection. Be wary of the casethat will be an obvious failure, but, at the same time,be daring within the limits of capability.

2. Use greater care in treatment. Do not hurry; main-tain an organized approach. Be certain of instru-ment position and procedure before progressing.

3. Establish adequate cavity preparation of both theaccess cavity, which can be improved by modifica-tions of the coronal preparation, and the radicularpreparation, which can be improved by more thor-ough canal débridement—cleaning and shaping.

4. Determine the exact length of tooth to the foramenand be certain to operate only to the apical stop,about 0.5 to 1.0 mm from the external orifice of theforamen.

5. Always use curved, sharp instruments in curvedcanals, and especially remember to clean andreshape the curved instrument each time it is used.This applies to stainless steel instruments.

760 Endodontics

6. Use great care in fitting the primary filling point.One must be certain to obliterate the apical portionof the canal. Be more exacting in the total obtura-tion of the entire root canal. Always use a root canalsealer cement.

7. Use periradicular surgery only in those cases forwhich surgery is definitely indicated.

8. Always check the apical density of the completedroot canal filling of the patient undergoing peri-radicular surgical treatment, and this should bedone by using a sharp right-angled explorer. Iffound wanting, the apical foramen is prepared andretrofilled.

9. Properly restore each treated pulpless tooth to pre-vent coronal fracture and microleakage.

10. Practice endodontic techniques until the proce-dures are as routine as the placement of an amal-gam restoration or the extraction of a central inci-sor. Practice on extracted teeth mounted in acrylicblocks is especially recommended.

Careful attention to details in following the TenCommandments of Endodontics will ensure a degreeof success approaching 100%.

Figure 13-20 A, Periradicular lesion persisting 2 years following endodontic therapy appears to be either an apical cyst or chronic apicalperiodontitis. B, Biopsy of the periapex demonstrated the epithelial lining of an apical cyst (arrow). Persistence of development of apical cystsled to failure in three cases in study.

A B

Outcome of Endodontic Treatment and Retreatment 761

PROGNOSIS

All of this having been said, it should be possible topredict the outcome of endodontic treatment. With thebenefit of education and experience and some plainluck, one should be able to choose the proper cases forendodontic treatment and reject those that will obvi-ously fail. But it is not quite that simple.

The practicing dentist should not be cited for faultyjudgment when even the experts tend to disagree onprognosis. A North Carolina group, for example, foundconsiderable disparity in treatment choice betweengeneral practitioners and endodontists who wereshown seven controversial cases.83 In another instance,Holland and his collaborators reviewed 17 prognosisstudies dealing with success or failure of teeth with andwithout periradicular lesions.84 In the “with lesion” col-umn, successful outcome ranged from a low of 31.8%to a high of 85%. On the other hand, there was generalagreement among these 17 experts that a greater suc-cess rate may be enjoyed if there is no initial periradic-ular lesion present. This is not to say that teeth withperiradicular lesions should be shunned. On the con-trary, respectable success rates have been reported bymany who have treated teeth with radiolucent lesions.

All in all, one must ultimately develop confidence inone’s own abilities. Being able to practice using a vari-ety of techniques and not being “married” to a singleapproach in every case greatly enhances one’s capabili-ties. This is the basis of good prognosis, the result ofskill, knowledge, and self-confidence. On the otherhand, if a treated tooth does fail, it may be resurrectedby skillful re-treatment!

SUCCESSFUL RE-TREATMENT

One must recognize that the patients in theWashington study were all controlled university clinicor specialty practice patients, as were the patients inmany of the other success and failure reports, animportant consideration in evaluating these outcomes.

In marked contrast, worldwide reports of endodon-tic success and failure in a cohort of general practicepatients is an entirely different matter.44,85–103 To makematters worse, the periradicular lesions in thesereports were associated with previously treatedendodontic general practice cases and were much high-er (24.5 to 46%) than the periradicular lesions in non-treated teeth (1.4 to 10%) (Table 13-3).

There is also a very disappointing finding in a gen-eral survey by Buckley and Spångberg at the Universityof Connecticut; they noted that periradicular lesionsare found 5 to 10 times more often in endodonticallytreated teeth than for teeth without root fillings.101

Mactou pointed out that “the quality of treatmentplays a decisive role in the successful outcome ofendodontic therapy” (Figure 13-21) (personal com-munication, April 2000).

Fortunately, treated root canals with inadequateresults may be re-treated to improve the quality of thetreatment and heal any apical lesion. (Figure 13-22)Bergenholtz et al., for example, reported on 556 re-treatment cases in which 50% completely healed after2 years, and in an additional 30%, the lesions were sig-nificantly reduced in size.104 In a 2-year follow-upstudy, Bergenholtz et al. also reported a 94% successrate for re-treatments done for one reason only, toimprove root canal filling quality prior to prosthodon-tic therapy.105

Friedman et al. claimed a 100% success rate in re-treatment of endodontic cases presenting withoutperiradicular lesions, which suggests that if infection isnot present, and re-treatment is performed by skilledclinicians, the success rate can be expected to be veryhigh (Table 13-4). On the other hand, if periradicularlesions are present before re-treatment, the success ratecan be expected to fall to around 70% (Table 13-5).28

As many as 22 factors have been listed to affect theprognosis of endodontic re-treatment, the preoperative

Figure 13-21 Apical perforation through overinstrumentationleads to loss of the apical stop, gross overextension, and failure tocompact the canal filling. Notice that instrumentation has resultedin a canal that is short of the apex. (Courtesy of Dr. Pierre Mactou.)

state of the tooth (as above) obviously being a key fac-tor in outcome.106 Stabholz et al.107 and Friedman108

have noted that causes of endodontic failure fall intothree categories: preoperative, intraoperative, and post-operative causes. Of these three, intraoperative, that is,iatrogenic, causes are the most prevalent but the mosteasily controlled.109 For example, Nair has pointed outthat refractory periradicular infections are found in

762 Endodontics

acute symptomatic teeth.110 At the same time, othershave noted that these bacteria may have been “planted”there as contaminants during previous endodontictreatment.110–116 As previously stated, infected dentinchips, extruded from overinstrumentation, may also bethe “root” cause of refractory infections.103 Bergenholtzhas stated that“…root filling material [per se] was notthe immediate cause of the unsuccessful cases, but that

Figure 13-22 A, Failure case with apical and lateral periradicular lesions. B, Re-treatment eliminates bacterial infection through extensiverecleaning, reshaping, and canal medication. Obturation by vertical compaction fills the lateral canal as well. C, Complete healing 1 year later.(Courtesy of Dr. Pierre Mactou.)

A B C

Table 13-3 Cross-sectional Studies on the Presence of Periapical Periodontitis (PAP) in Nontreated andEndodontically Treated Teeth and Quality of Treatment

Endodontically Endodontically Treated Technically Inadequate

Lead Author Country Teeth with PAP (%) Treated Teeth (%) Teeth with PAP (%) Treatment (%)

Bergenholtz, 1973 Sweden 6 12.7 31 —

Hansen, 1976 Norway 1.5 3.4 46 —

Petersson, 1986 Sweden 6.9 12.4 31 > 60

Allard, 1986 Sweden 10 18 27 69

Eckerbom, 1987 Sweden 5.2 13 26.4 55

Eriksen, 1988 Norway 1.4 3.4 34 59

Odesjo, 1990 Sweden 2.9 8.6 24.5 70

Imfeld, 1991 Switzerland 8 20.3 31 64

De Cleen, 1993 Netherlands 6 2.3 38 50.6

Buckley, 1995 United States 4.1 5.5 31.3 58

Soikkonen, 1995 Finland 4 21 16 75

Outcome of Endodontic Treatment and Retreatment 763

unsuccessful cases were caused…by a reinfection in theapical areas favored by overinstrumentation”105

(Figure 13-23).Mactou has laid out the important factors that must

be adhered to if re-treatment is to be successful: first ofall, complete recleaning and reshaping of the canals.This should be carried out in a step-down fashion:early coronal enlargement and canal body shapingprior to apical preparation (personal communication,April 2000).

Table 13-4 Nonsurgical Endodontic Re-treatmentOutcome in Pulpless Teeth without PeriapicalPeriodontitis

Authors Cases Success (%)

Strindberg, 1956 64 95

Grahnon and Hansson, 1961 323 (roots) 94

Engstrom et al., 1964 68 93

Bergenhotz et al., 1979 322 (roots) 94

Molven and Halse, 1988 76 (roots) 89

Allen et al., 1989 48 96

Sjögren et al., 1990 173 (roots) 98

Friedman et al., 1995 42 100

From Friedman.28

Table 13-5 Nonsurgical Endodontic Re-treatmentOutcome in Teeth with Periapical Periodontitis

Success Failure

Authors Cases (%) Uncertain (%)

Strindberg, 123 84 — 161956

Grahnen and 118 (roots) 74 — 26Hansson, 1961

Engstrom et al., 85 74 — 261964

Bergenhotz et al., 234 (roots) 48 30 221979

Molven and 98 (roots) 71 — 29Halse, 1988

Sjögren et al., 94 (roots) 62 — 381990

Friedman et al., 86 56 34 101995

Sundqvist et al., 50 74 — 261998

From Friedman.28

A B CFigure 13-23 A, Failed endodontic treatment caused by overinstrumentation and failure to totally obturate the canal. Note the gross overex-tension of sealer and that the final 6 mm of the canal are sealer only. B, Re-treatment by complete recleaning, reshaping, and canal medica-tion before final obturation. C, Twelve-year recall shows total healing. Note recurrent decay at the distal margin of the crown (arrow) thatcan lead to microleakage and potential failure. (Courtesy of Dr. Pierre Mactou.)

The canal should be cleaned segment by segmentthrough a coronal reservoir of 2.5% of sodiumhypochlorite. Working length at the radiographic ter-minus is established late in treatment, when theremainder of the canal has already been cleaned andshaped. Maintenance of apical potency and constantrecapitulation with fine files avoids canal blockage withdentin debris. It also allows the sodium hypochlorite toreach this area. Great care must be exercised whenremoving the previous filling material, particularlywhen solvents such as chloroform are used.

It is very difficult to remove all of the sealer andgutta-percha from the canal walls. Wilcox et al. con-tended that the last remnants of sealer can be removedonly by vigorous reinstrumentation and reshaping ofthe canal117,118 but cautioned that overenlargementmay result.119 It would appear that sealer removal ismost important since bacteria can easily “hide” underprevious sealer.

CANAL MEDICATION

Re-treatment cases are notorious for continued failure!In all probability this is caused by the failure to removeor kill the refractory bacteria responsible for the lesions

764 Endodontics

in the first place. One is warned that these cases arechallenging, and this is probably not the occasion forone-appointment therapy. Continuing failure isundoubtedly owing to remaining bacteria, and theirelimination calls for extra effort. New data regardingfailed root canals indicate that these microflora120–122

differ from those of untreated necrotic teeth.Enterococci, for example, are quite prevalent in previ-

ously root-filled teeth and are quite difficult to elimi-nate. Enterococcus faecalis is the most frequent strain and,as a monoinfection, is found in 33% of the cases.123

Entercocci are quite resistant to calcium hydroxide, soSafaui et al. have recommended the addition of iodinepotassium iodide in these cases.124 Heling and Chandlerhave recommended a mixture of 3% hydrogen peroxideand 1.8% chlorhexidine as an alternative against E. fae-calis.125 Staphylococcus aureus and Pseudomonos are alsonotorious refractory contaminants and may require aprescription of metronidazole and amoxicillin to rid theperiapex of these bacteria.126–128

OBTURATION AND RESTORATION

It goes without saying that total obturation is the sinequa non of successful re-treatment.

Figure 13-24 A, Pretreatment radiograph reveals failed endodon-tic treatment and a periradicular lesion. B, Re-treament by totalrecleaning, reshaping, and canal medication. Final obturation byvertical compaction fills the lateral canal as well. C, Six-year follow-up. (Courtesy of Dr. Pierre Mactou.)

A

C

B

Outcome of Endodontic Treatment and Retreatment 765

For this, the reader is referred to chapter 11.Furthermore, since many failures are believed to berelated to microleakage from around coronal restora-tions, it is imperative that the re-treated tooth be prop-erly restored, at once, not weeks later (Figure 13-24).

Molven and Halse have said it best: “Success dependson the elimination of root canal infection present whentreatment starts, and the prevention of both contami-nation during treatment and re-infection later. So suc-cess rates reflect the standard of the cleaning, shapingand filling of root canals”129 (Figure 13-25).

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