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Endodontic Topics 2002, 2, 89102 Copyright C Blackwell Munksgaard

Printed in Denmark. All rights reserved ENDODONTIC TOPICS 2002

1601-1538

Technical aspects of treatment in

relation to treatment outcomeLISE-LOTTE KIRKEVANG & PREBEN HRSTED-BINDSLEV

Apical periodontitis

Apical periodontitis (AP) is an inflammatory processin the periapical tissues that may occur as a sequel tocaries, trauma or operative dental procedures whenbacteria have been introduced into the dental pulp.The relationship between AP and bacteria infectingthe root canal system is well established (13). Infec-tion of the coronal pulp may spread apically, usuallycausing necrosis of pulpal tissues and may reach theapical part of the root canal. The infection then in-

vades the periapical area resulting in local bone de-struction. The success of root canal treatment de-pends on several factors:O elimination of surviving microorganisms in the

root canal;O creation of a tight seal in order to prevent tissue

fluid from the periapical tissues feeding bacteria, whilst nonetheless remaining in the root canal,and;

O establishment of an effective blockade of any com-munication between the oral cavity and the peri-radicular tissue through a high quality of endodon-tic and coronal restorations (4).

When focusing on the relation between the technical

and the biological aspect of periapical repair, severalexplanations for slow or absent healing of AP havebeen pointed out. The low success rates when root-fillings are too short are probably due to infected pulpremnants or dentin chips in the apical part of a rootcanal. Overfilling may induce an inflammatory reac-tion caused by extrusion of the root-filling materialor infected debris into the periapical area, combined

with physical tissue damage caused by over-instru-mentation.

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The chronic nature of AP means that patients oftenhave no subjective symptoms. Given these circum-stances, oral radiography plays an important role inthe diagnosis and treatment of AP (5). The presenceof AP is important for tooth survival since caries, in-cluding pulpitis and AP, has been identified as beingone of the main reasons for tooth extractions in sev-eral populations (611). It is important to realize thatthe infection cannot resolve itself, as the working con-ditions of the immune defence system are impairedby the localization of the infection inside the root ca-nal. The goal of contemporary endodontic treatmentis both to prevent the spreading of the infection, andto create conditions under which healing can occur,meaning that the tooth can be preserved. To selectthe best treatment, it is important to gather infor-mation on different aspects of treatment and relatethis to the treatment outcome.

General methodologicalconsiderations

Cross-sectional studies are investigations in which in-formation is collected in a systematic way in a well-de-fined population at a given point in time. This type of

study can be used to describe disease prevalence, andrelate the disease to subjects exposure to etiologicagents and pathogenic factors (12). In the context of

AP, the cross-sectional study could be used to describethe association between the presence of AP (diseaseprevalence, outcome) and the quality of endodontic orcoronal restorations (in this instance, exposure infor-mation). Thecross-sectional study does notprovide in-formation on the time of event occurrences, but de-scribes exposure and disease status at the time of the


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Kirkevang & Hrsted-Bindslev

investigation. It is therefore not possible in this type ofstudy to decide whether the exposure preceded the dis-ease or the disease preceded the exposure. This doesnot, however, preclude the use of cross-sectional datain the development of a risk assessment model target-

ing, for example, the periapical status.Since the historic dimension of the exposure infor-mation retained in the cross-sectional study is notavailable, it is not possible to identify why or when arestoration has been made; only that it is present atthe time of the examination. This means that thetreatment/disease history is illustrated by proxy vari-ables in the mouth, e.g. the number and quality ofthe restorations. Another problem in the cross-sec-tional study design is that only information on thepresent status of the individual is available, and sincemany diseases, for example, AP, often take time todevelop or heal, the exposure information may havebeen too recent to have had any influence on the de-

velopment of AP. On the other hand, some of theexposure information accumulates in/around the in-dividual, thereby creating a picture of both presentand previous exposures.

In the cross-sectional study, it is possible to identifypotential risk indicators, but longitudinal studies areneeded to identify a causal direction. The concept ofcauses has been, and still is, the subject of extensivedebate among epidemiologists, and a variety of termshave been used. In order to understand the conceptof causes, it is first necessary to define what causemeans. Rothman and Greenland define it as:

...an event, condition, or characteristic that pre-ceded the disease event and without which the diseaseevent either would not have occurred at all or wouldnot have occurred until some later time (12) .

This definition describes a cause as a component ofa sufficient cause in which several causes act togetherat the same time as a completely causal mechanism.MacMahon and Trichopoulos (13) used the concept

of direct and indirect causal associations where thecause may be described as direct or indirect, situatedin a causal web, and the association with the outcomemight be of varying magnitude. These definitions ofcause seem to be relevant also to the etiology thatapplies to most diseases, as only very few diseases, ifany at all, can be said to be monocausal. Most longi-tudinal studies focus on one part of the treatment inan attempt to expound the relationship between thatparticular issue and the treatment outcome.

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When looking at the literature, it is essential to real-ize that the epidemiological and controlled longitudi-nal studies work together in a kind of symbiosis

where ideas are exchanged to be further elucidated.

History of/criteria for the outcomeof root canal treatment

The diagnosis of AP is predominantly based on devi-ations from the normal periapical anatomy as display-ed by radiography. Strindberg (14) presented a fre-quently quoted set of criteria for classification of en-dodontic treatment results based on radiographicsigns. He conducted a comprehensive longitudinalstudy on factors related to the results of pulp therapy,

where a total of 254 patients with 529 root filledteeth were followed for 210years, and defined theradiographic criteria for evaluating the result of rootcanal treatment as follows

a success when (a) the contours, width and struc-ture of the periodontal margin were normal, (b) theperiodontal contours were widened mainly aroundthe excess filling; a failure when there was (a) a de-crease in the periradicular rarefaction, (b) unchangedperi-radicular rarefaction, and (c) an appearance ofnew rarefaction or an increase in the initial; and asuncertain when (a) there were ambiguous or technic-ally unsatisfactory control radiographs which couldnot for some reason be repeated, or (b) the tooth

was extracted prior to the 3-year follow-up owing tounsuccessful treatment of another root of the tooth.

These criteria thus divided the cases into successes,failures, and uncertainties.

The width of the periodontal ligament, the integrityof the lamina dura and the presence of periapical ra-diolucency have, since Strindbergs description, beenused in both longitudinal (1521) and cross-sectional(2233) studies to evaluate the periapical status.

In 1967, Brynolf (34), in order to disclose to whatextent histologic changes are reflected in radiographs,compared histologic and radiographic appearances ofperiapical changes in human autopsy material from142 individuals. Sections of the apical region from292 upper incisors constituted the material for theinvestigation. She concluded that differentiation andclassification of the periapical status were possible inoral radiographs. The study very thoroughly de-scribed the changes characterising the different levels


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Technical aspects

Table1. Brynlofs histological and corresponding roentgenological main groups (34)

Histological Roentgenological Description

N Ng Normal

M Mg Marginal cases

I Ig Mild, chronic inflammation

Ix Irx Mild, chronic, more active inflammation

II IIg Moderate, chronic inflammation

III IIIg Severe, chronic inflammation

IV Iv g Severe, chronic inflammation with features of exacerbation

of inflammation and grouped them in seven maingroups (Table1).

The continuous inflammatory process could thusbe classified radiographically, and this constituted thebasis for development and application of an ordinalscoring scale in the radiographic evaluation of AP.

In 1986, rstavik et al. (35) used the results ofBrynolfs study (34) to develop an index for the regis-tration of AP, the Periapical Index (PAI). The indexconsists of five categories, each representing a step onan ordinal scale from sound periapical bone to severeapical periodontitis. One or two radiographs fromBrynolfs original material represented each of the

five groups, and these radiographs were used as visualreferences (Fig. 1).

Before using PAI, a calibration course for the PAIsystem should be followed. The course involves scor-

Fig.1. The visual references of the periapical index (PAI) (Fig 8.2, rstavik D, Pitt Ford TR eds. Essential EndontologyOxford: Blackwell Science, 1998; 181).

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ing of 100 radiographic images of teeth; the group ofteeth consist of various tooth types, with and withoutroot-fillings. For each tooth, a true periapical statushas been established by consensus between five endo-dontists, one dental radiologist, four general prac-titioners and one dental assistant (35); while theradiographs and histological correlates of Brynolf(34) may be viewed as a gold standard, the definedtruth of the 100 teeth may be viewed as a silverstandard atlas. After scoring 100 teeth in the calibrat-ing course, the observers results are compared to thesilver standard atlas.

When a tooth is to be scored, the observer finds the

reference radiograph by visual comparison of whichperiapical area is most similar to the periapical area ofthe tooth under evaluation. The corresponding scoreis then assigned to the tooth. If the tooth is multi-


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rooted, the highest score given to a root should beassigned to the tooth. The use of visual references inthe PAI de-emphasised the importance of the ob-server, since no clinical judgement is permitted in theassessment of AP. This has resulted in a better repro-

ducibility in the radiographic scoring, and differentstudies may be more easily compared (35, 36).It can be debated if the PAI system is valid for can-

ines, premolars and molars, as the histologic materialon which it was based only included maxillary in-cisors. The anatomic structures in the jaws vary andmay confound the diagnostic process, but this prob-lem is the same for all radiographic studies. It wouldseem reasonable to assume that the radiographic ap-pearance of AP should be comparable in all teeth.

The PAI has been used in several longitudinal (3741) and cross-sectional studies (40,4248).

Reliability and reproducibility ofperiapical radiography

In both longitudinal and cross-sectional investi-gations on endodontic treatment, the assessment oftreatment quality has been primarily based on radi-ography, and the cross-sectional studies especiallyoften rely on radiographic images alone.

Obviously, the two-dimensional nature of radio-graphic images imposes some limitations. Radio-graphs may not reveal minor occlusal, buccal or oraldefects, which could lead to the amount of inad-equate coronal restoration required being underesti-mated. In addition, in multirooted teeth, the lengthof the roots and root-fillings may not be reproducedcorrectly (49).

When studies have included the lateral seal as oneof the criteria, there is general agreement that, if a

void is present in the lateral aspect, the root-fillingshould be categorised as inadequate. However, the

limited reproducibility of the lateral seal as a descrip-tive parameter for the quality of the root-filling hasbeen demonstrated in several studies (47,5053).Therefore, Eckerbom & Magnusson (52) demon-strated that the reproducibility of one orthoradial, in-traoral radiograph was poor when evaluating the lat-eral seal; this was probably due to the common occur-rence of oval- and ribbon-shaped root canals. Theevaluation of the lateral seal of a root-filling shouldbe evaluated in images with a mesial and/or distal

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angulation to get a realistic estimate of the quality ofthe seal.

The length of the root-filling has proved to be amuch more reproducible quality parameter than thelateral seal (47, 52, 53), probably because it is easier

to measure the length of the root-filling than it is todetect voids.Reit and Hollender (54) noticed that, in radio-

graphic studies, it is difficult to define and maintaincriteria for the quality of the root-filling and for diag-nosing AP. The precision of the quality assessment ofthe root-filling has, therefore, not been convincing,and large inter-examiner variation has been reported(54, 55).

Concerning the radiographic diagnosis of AP, Gold-man et al. (56) found that the inter-observer agree-ment in radiographic assessments of endodontic suc-cess or failure was very poor. Several attempts havebeen made to minimize the observer variationthrough calibration (51, 54, 57, 58). Reit (59) evalu-ated the effect of two calibration programs accord-ing to different principles. In one of the two pro-grams, the examiners evaluated a separate radio-graphic sample in which they, through discussions,exemplified the scoring system that was going to beused to score the original material. In the other cali-bration program, the examiners were introduced tothe signal-detection theory. This theory assumesthat the observer, through a continuum of obser-

vations in his own mind, defines a cut-off point fordisease. The calibration programs, however, only re-sulted in significant improvement when diagnosingperiapical destruction of bone definitely not present.That the effect of observer calibration is not signifi-cant was also demonstrated in other studies (55, 57).It was concluded that the benefits of calibration pro-grams seemed to be limited and suggested that thiscould be due to the complex structure of the de-cision making process (57).

By statistical evaluation of the scoring performanceof different methods of evaluation, the PAI scoringsystem produced better receiver-operating-character-istic (ROC) curves than the probability assessmentindex (35).

Different methods of recording and maintainingcriteria for AP and treatment quality, as well as differ-ent thresholds for AP and treatment quality, indicatethat great caution must be exercised when resultsfrom different studies are being compared.


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Technical aspects

Quality of root-fillings and coronalrestorations

Quality of root-fillings

Longitudinal studies

Information on the quality and prognosis of root ca-nal treatment has mainly been based on clinicalstudies made in controlled environments at dentalschools or in specialist clinics. The results from thesecontrolled, longitudinal studies have shown successrates up to 96% in establishing periapically sound con-ditions after endodontic treatment (1417,1921,37,38, 6063).

The longitudinal studies have found that severalfactors may influence the outcome of the treatment.It has been demonstrated that the preoperative diag-nosis of the tooth is of importance for the outcomeof the treatment, but the quality of the endodonticand the coronal restoration have also been found toinfluence the treatment outcome (64).

The quality of the root-filling has been evaluated inseveral studies. The parameters defining the quality ofthe root-filling differ among investigators, and differ-ent thresholds have been used when categorisingroot-fillings as adequate or inadequate. In somestudies, the quality parameters were defined only bythe length of the root-filling (14, 15, 20, 6062, 65,66). In other studies, the quality was assessed both inthe lateral and in the apical aspect (16, 17, 19) (Table2).

The working length and the optimal apical limit ofroot canal obturation has been the subject of on-go-ing discussion for decades. As a consequence, studies

vary greatly in the categorisation of adequate length.Some define root-filled teeth, filled flush with apex,as adequate whilst others view it as inadequate. Somerequire the distance from the radiographic apex to be2mm, others 3mm. Some accept extrusion ofthe root-filling if1mm. The actual position of theapical foramen/foramina has been found to be from0.2 to 3.8mm short of the radiographic apex (67).Most studies have indicated that the apical limit ofthe root-filling should be at the apical constriction ofthe root canal, and that extrusion of root-filling ma-terial into the periapical tissue should therefore beavoided (6870).

When the technical quality of the root-filling was

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related to the treatment outcome, the studies demon-strated success rates of 70100% if the quality wasassessed to be optimal. If the root-fillings were shortof the apex, a lower success rate of 57%-95% wasfound (Table2). If extrusion of root-filling material

in the periapical tissue were found, the success ratewas even lower at 50%-90%. Some studies, however,found no significant difference between root-fillings

within 2mm from apex and root-fillings that were tooshort (65, 66). It should be noted that the thresholdbetween adequate and inadequate vary among thestudies and, therefore, the results should be com-pared with certain reservations.

In a study by Weiger et al. (71), another methodol-ogical and statistical problem was discussed. In longi-tudinal studies, success rates have been calculated asthe percentage of successfully treated teeth followed-up or included in the study. This approach does notdeal with the problem of the individual time requiredfor healing/development of AP; in other words, indi-

vidual observation times are not accounted for. Theeffect of clustering in a sample, e.g. when severalteeth/roots from the same individual have been in-cluded in the study, may result in under- or over-esti-mation of the outcome. It was suggested that theanalysis of event times according to Kaplan & Meier(72) should be used for estimating prognosis of rootcanal therapy.

Despite the methodological differences, the con-trolled longitudinal studies suggest that it is possibleto control and eliminate AP, at least if the treatmentis performed by highly-skilled personnel or supervisedstudents, probably by reduction of the more commonreasons for failure, such as poor aseptic technique, un-detected infected root canals, inadequate instrumen-tation, and inadequate temporary and permanent fill-ings.

Cross-sectional studiesCross-sectional studies from different populationshave, on the other hand, failed to demonstrate thatthe dental profession in general has succeeded in thecontrol and elimination of AP (Table 3). On the con-trary, such studies have revealed a high frequency ofinadequate root-fillings and of AP associated withroot-filled teeth (22, 24, 27, 28, 30, 4247, 73, 74).

In addition, in the cross-sectional studies, the qual-ity of root-fillings has been related to the periapical


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status, and again the parameters defining the qualityof the root-filling differ among investigators, with dif-ferent thresholds being used when categorising root-fillings as adequate or inadequate. Some have concen-trated merely on the length of the root-filling (28,

30), whilst others have used the length of the root-filling and the lateral seal without combining the two(4244), and some have used both length and lateralseal and a combination of the two recordings (22, 24,25, 27, 32, 33, 4547)(Table4).

Despite the differences in populations, diagnosticcriteria and evaluation methods, most studies findthat the quality of the endodontic treatment isstrongly related to the periapical status. In studies ofNorwegian adults, about 30% of the endodontic res-torations had an inadequate seal, and about 70% ofthese had AP (42,43). Regarding the length of theroot-filling, studies of European populations havefound that 15%57% of teeth with adequate lengthof the root-filling had AP. If the root-filling was tooshort, 15%85% of the teeth had AP, and if the root-filling was too long, about 52%75% of the teethshowed periapical lesions (Table4).

Due to the methodological variations among thedifferent studies, it is difficult to directly compare per-

Table 2. Technical quality of root fillings in longitudinal studies related to the outcome.

Study Cases Adequate Inadequate Adequate Short % Long %lateral seal lateral seal length % (success %) (succes %)(success %) (success %) (success %)

Strindberg (14) 774 (roots) 42.4 (90)* 29.1 (90) 28.8 (81)

Grahen & Hansson (15) 1277 (roots) 35.5 (83)* 27 (93) 37.5 (75)

Harty et al. (16) 1139 87.4 (93) 11.6 (65) 48.8 (93) 17.2 (88) 31.9 (87)

Heling & Tamshe (58) 344 (roots) 53 (71) 18 (57) 29 (68)

Heling & Shapira (59) 128 (roots) 36 (80) 52 (82) 12 (73)

Kerekes & Tronstad (17) 501 (roots) 96 (93) 4.9 (28) 62.1 (92) 34.4 (90) 3.5 (67)

Swartz et al. (63) 1770 (roots) 12 (90)** 80.9 (92) 7 (63)

Bystrm et al. (64) 79 14 (100) 48.1 (95) 37.9 (90)

Sjgren et al. (21) 849 (roots) (87) (67)*** (82) (31)*** (94) (67)*** (68) (65)*** (76) (50)***

Smith et al. (20) 821 613 (87) 116 (76) 92 (75)

Friedman et al. (60) 378 (teeth) 81 (79) 19 (74)****

*filled to apex or 1mm excess**filled flush to apex

***1. parentheses teeth with necrosis/AP, 2. parentheses previously treated teeth****short and long

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centages from them. However, the tendency is thesame: cross-sectional studies on endodontic treat-ment fail to demonstrate the same high success rateas controlled follow-up studies. It may be claimedthat, despite the obvious study differences, various

studies have consistently found that the poor qualityof the root-fillings is related to AP, makes this findingeven more evident.

Quality of coronal restorations

In recent years emphasis has also been placed on thequality of the coronal restoration and its relation tothe periapical status in root-filled teeth. It has beensuggested that the coronal restoration, as well as theroot-filling, serve as a barrier against fluid and bac-terial penetration into the periapical area. The relationbetween the quality of the coronal restoration and theperiapical status has been investigated in severalstudies (46, 47, 75, 76). Ray & Trope (75) foundthat the technical quality of the coronal restoration

was even more important for the periapical statusthan the quality of the endodontic treatment. Siderav-icius et al. (46) identified a correlation between thequality of the coronal restoration and the periapical


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Technical aspects

Table3. Studies on endondontic treatment and AP.

N Teeth Root-filledindi- Mean N with Root-filled teeth Patient population

Author Year vidual N teeth teeth AP (%) teeth with AP (%) (country)

Bergenholtz et al.(101) 1973 240 5472 22.8 6.1 12.7 31.0 Dental school patients (S)

Hansen & 35 year olds from urbanJohansen (102) 1976 2981 1.5 3.4 46.0 area (N)

General poppulation onlyPetersson et al. premolars were included(22) 1986 861 4985 5.8* 6.6 3.4 13.0 (S)

Allard & Elderly population fromPalmqvist (23) 1986 183 2567 14.0 9.8 17.6 27.0 rural area (S)

Eckerbom et al. Patients referred for(51) 1987 200 4889 24.4 5.2 13.0 26.4 radiographic survey (S)

Bergstrom et al. Patients visiting their

(25) 1987 250 6593 26.2 3.5 6.5 (root) 28.8 (root) dentist regularly (S)35 year olds from urban

Eriksen et al. (42) 1988 141 3197 22.7 1.4 3.4 34.0 area (N)

Petersson et al. Patients requiring(26) 1989 567 11497 20.3 8.7 22.2 26.5 substantial dental care (S)

Odesjo et al. (27) 1990 967 17430 18.0 2.9 8.6 24.6 General population (S)

Eriksen & 50 year-olds from an urbanBjertness (43) 1991 119 2940 24.7 3.5 6.0 36.6 area (N)

66 year-olds from an urbanImfeld (103) 1991 2004 8.0 26.0 31.0 area (CH)

Hlsmann et al.(104) 1991 4845 3.2 60.0 Dental school patients (D)

De Cleen et al. Patients from oral surgery (28) 1993 184 4196 22.8 6.0 2.3 39.2 (NL)

35 year olds from urbanEriksen et al. (44) 1995 118 3282 27.8 0.6 1.3 38.1 area (N)

Buckley & Patients fromdental schoolSpngberg (33) 1995 208 5272 25.3 4.1 5.5 31.3 (USA)

Dentate old peopleliving atSoikkonen (29) 1995 293 2355 8.0 6.6 21.5 16.0 home (FIN)

Saunders et al. Dental school 20 years-(30) 1997 340 8420 24.8 4.6 5.6 58.1 old (GB)

Patients from private

Weiger et al. (31) 1997 323 7897 24.4 2.7 61.0 surgery 12 years old (D)Marques et al. 3039 year-olds from an(45) 1998 179 4446 24.8 2.0 1.5 21.7 urban area (P)

Sidaravicius et al. 3544 year-oldsan urban(46) 1999 147 3892 26.5 7.2 15.0 39.4 area (Lith)

De Moor et al. Dental school 18 years(70) 2000 206 4617 22.4 6.6 6.8 40.4 old (B)

Kirkevang et al.(101) 2001 613 15984 28 3.4 4.8 52.2 General population (DK)

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status of root-filled teeth, but not one as pronouncedas Ray & Trope (75). Kirkevang et al. (47) also foundthat, when the root-filling and the coronal restoration

were both of high quality, less than one-third of theteeth had AP, but if both were inadequate, more than

three-quarters of the teeth had AP. If the root-fillingwas adequate and the coronal restoration was inad-equate, almost half of the teeth had AP. If, on theother hand, the coronal restoration was adequate andthe root-filling inadequate, more than two-thirds had

AP. Tronstad et al. (76) demonstrated that, if theroot-filling was inadequate, it did not matter whetherthe coronal restoration was adequate or inadequate;the tooth would still have a poor prognosis. This wassupported by a study by Ricucci et al. (77) whichconcluded that the problem of coronal leakage seemsnot to be of great clinical importance if the instru-mentation and filling of the root canal was optimised.

The studies indicate that both the quality of theendodontic and coronal restoration play importantroles in obtaining an efficient seal of the root canal,even though it is suggested that the quality of theroot-filling may be the most decisive parameter.

Table 4 Technical quality of root fillings in epidemiological studies related to the outcome.

Author Year N cases Adequate Inadequate Adequate Short % Long %roots/ lateral lateral length (success %) (success %)teeth seal % seal (success %)

(success %) (success %)

Bergenholtz et al. (94) 1973 984R 48.5 51.5 (69) 32 (79) 55.9 (72) 12.1 (63)

Petersson et al. (22) 1986 650T 37.9 (93)* 50.7 11.4 (41)

Eckerbom et al (24) 1987 899R 56.3 43.7 45.7 45.7 9.4

Eriksen et al (42) 1988 79T 68.3 (63) 31.7 (70) 41.0 (86) 43.0 (53) 16.0 (37)

Odesjo et al (27) 1990 1876R 30.2 (78) 69.8 (79) 41.4 (79) 48.5 (85) 10.1 (48)

Eriksen & 1991 141T 73 (73) 27 (29) 32 (77) 48.9 (51) 19.1 (26)

Bjertness (43)

De Cleen et al. (28) 1993 53T 52.8 (43) 43.4 (15) 3.8 (0)Saunders et al. (30) 1997 592T 41.5 (61) 41.5 (45) 17 (43)

Marques et al. (45) 1998 65T 46 (87)** 54 (69)**

Sidaravicius et al. (46) 1999 320T 30.9 (70) 68.8 (63) 33.8 (78) 41.3 (75) 24.7 (30)

De Moor et al. (70) 2000 312T 40.7 (61) 54.2 (25) 2.6 (0)

Kirkevang et al (47) 2000 773T 40.9 (56) 59.1 (42) 60.0 (58) 39.6 (32)***

* No lateral or apical lumen visible.** Adequate lateral and apical seal

*** Short and long

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Methods of instrumentation

Instrumentation of the root canal aims to remove allintracanal soft tissue and to prepare the canal so thatthe canal is aseptic and a bacteria-tight root-filling can

be made.Numerous instruments and methods have been developed to attain this objective. Examples includehand instruments of various metals and design, sonicand ultrasonic instruments, and engine-driven instru-ments of different design and materials, which oper-ate with different movements. Each instrument hasto be used in combination with an irrigation solutionin order to flush tissue remnants, dentine shavingsand microbiological elements out of the canal. Appar-ently, no instrument or method for cleaning andshaping available for the clinician can, in all situations,entirely remove tissue remnants from the canal lu-mina and debris smeared on the canal wall (7882).This is not surprising if the often very irregular canalconfiguration is taken into consideration (Fig.2). Asan example, the recently introduced Ni-Ti instru-ments may follow the curvature of the canal more


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Technical aspects

precisely than stainless steel instruments but thecleaning effect is comparable to stainless steel instru-ments (83, 84). Furthermore, if the cleaning efficacyis measured as reduction of bacteria in the canal afteruse of either Ni-Ti instruments or stainless steel in-

struments, no difference has been found (85). Apparently, only few clinical and radiographicalstudies have evaluated the effect of specific instru-ments on the outcome of endodontic treatment. Theproblem may be that among the numerous factorsinvolved, such as preoperative diagnosis, root canalmorphology, aseptic treatment regimen, irrigationsolution, quality of root-filling and skill of the oper-ator, it is rather difficult to single out the effect of aspecific instrument or a specific cleaning and shapingmethod. However, the results from a recent retro-spective study is in accordance with the findings from

various experimental laboratory studies, which gener-ally show only small differences among currentmethods of instrumentation. Therefore, Peters et al.(86) did not find differences in treatment outcomeafter use of two different Ni-Ti rotating systems in astudy where the same root-filling method was used inboth groups.

Overinstrumentation

Overinstrumentation may happen at any stage of in-strumentation. Provided aseptic conditions are main-tained, it induces a sterile trauma to the periapicaltissue and the healing potential is good. An experi-mental study showed that removal of the entire vitalpulp and a slight periapical overinstrumentation, fol-

Fig.2. Cleared teeth demonstrating the irregularity of theroot canal system (courtesy of Dr Chr. Stock).

97

lowed by termination of the root-filling some milli-metres from the radiographical apex, did not causepersistent inflammation of the tissue in the residualroot canal or in the periapical tissue (87). In the apicalpart of the canal, a loosely arranged granulation tissue

was formed and resorption of the canal walls was after36months followed by a cell-rich fibrous tissue andapposition of hard tissue on the walls (Fig.3). How-ever, gross overinstrumentation in vital and necroticcases, and packing or extrusion of infected dentindebris and pulp remnants, induces periapical inflam-mation and may, therefore, be of prognostic import-ance (8890). Thus, dentin chips have been found inperiapical granulomas from cases of failed root canaltreatments (91), and Bergenholtz et al. (18) found a

Fig. 3. Microphotograph of decalcified human root. Sixmonths previously, the entire pulp was removed, followedby root-filling about 3mm short of the radiographic apex.A slight accumulation of lymphocytes is seen adjacent to aplug of dentin particles and remnants of the root canalsealer (Rf.). The apical part of the pulp canal is occupiedby a cell rich fibrous connective tissue and a considerabledeposition of hard tissue is seen onto the canal walls.


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higher frequency of periapical lesions in roots withoverinstrumentation in comparison to cases with nooverinstrumentation.

Overinstrumentation, defined as an excessive re-moval of the canal wall, may lead to weakening of

the root and lateral perforations, especially in curvedcanals. Lateral perforations are a negative prognosticfactor, either because the main canal cannot be instru-mented or because of an overfilling of the perforation(17, 92).

Methods of root-filling

Like materials and methods for instrumentation, anabundant number of root-filling methods are avail-able for the clinician. Numerous laboratory studieshave been performed to demonstrate the sealabilityof the various obturation methods and to comparethe different methods(e.g. 93). In the 1990 volumesof two major endodontic journals, there was aboutone in every four of the scientific articles were leakagestudies (93).

Dye penetration tests are most commonly used.These tests are based on the philosophy that the dyemimics in size microorganisms metabolic products,and either penetrate along the root-filling materialand the root canal wall or along confluencing voidsin the filling, reflecting a risk that bacteria may multi-ply in these lacunae and a periapical inflammation willdevelop or be maintained.

However, the methodology used in many of thesedye penetration tests has been questioned (9395).Therefore, it has been claimed that air entrapped inroot-fillings must be removed by vacuum before test-ing apical dye penetration in order to get a reliableimpression of leakage (94). In addition, other meth-odological problems, such as the pH of the dye and

whether leakage is evaluated in cross-sections of obtu-rated root canals or in cleared roots or whether dye

penetration should be measured linearly or spectro-photometrically, have to be considered (93, 96). Ad-ditional factors are tooth anatomy and root canal con-figuration, instrumentation, type of sealer and fillingmaterial and the skill of the operator.

A fundamental question is how well the outcomeof the endodontic treatment correlates with leakagedemonstrated microscopically in the laboratory. Oliv-ier and Abbott (97) studied apical dye penetration in116 extracted teeth root filled more than 6months

98

prior to extraction. Any teeth with canals not filled within 2.0mm of the apical foramen were excludedfrom the study. They found a significant differencebetween the successful and the unsuccessful groups,

with a mean percentage linear dye penetration being

greater in the unsuccessful specimens. But apical dyepenetration was observed in all but one tooth. Thus,the clinical implications of leakage found in the lab-oratory should be viewed with some caution. Leakageis only one factor characterizing root-filling tech-niques.

Guttapercha is part of all contemporary root-fillingmaterials. Guttapercha is used with a solid core ora softened core technique and both methods implyadditional use of a sealer.

The cold lateral compaction guttapercha techniquemay be seen as the classical root-filling methodagainst which other methods are tested in the labora-tory. The technique or slight variations of the tech-

Fig.4. Excess of root-filling material following use of thewarm guttapercha core carrier technique.


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Technical aspects

nique has been used in many of the longitudinalstudies on outcome of endodontic treatments. In or-der to improve the sealability and to form a morehomogeneous root-filling, several techniques usingsoftened guttapercha have been developed. The warm

vertical technique was first introduced by Schilder(98) and has gained wide acceptance. Later manyvariations of this technique have been introduced. Aguttapercha-condensing instrument may be heatedoutside the canal, or the guttapercha may be intro-duced in the canal after being heated. In some ofthese systems the temperature of the guttapercha orcondenser rises to about 200c which decreases toabout 70c when introduced in the canal. In a labora-tory setting, this temperature increases the surfacetemperature of the root more than 10C which isconsidered harmful to the periodontal membrane andmay cause external resorptions (99). Thus, an animalstudy showed external root resorption after thermo-mechanical compaction of guttapercha (100).

The advocates of the various warm techniques claimto make root-fillings in three dimensions, but due tothe pressure applied to achieve this, surplus of ma-terial is a common finding (Fig.4), the effect of whichhas been addressed above. In the clinic, the relativeperformance of any of these plasticized techniques incomparison to the cold lateral condensation tech-nique has not been shown. Even root-fillings with asingle point technique and sealer, which in several invitro studies have shown substantial leakage and

which in general has been abandoned by endodonticspecialists, has not shown inferior results in the clinic(62).

It can thus be concluded that, even though there isno doubt that sealability is of great importance, asdemonstrated in longitudinal studies, the importanceof differences in microsealability as found in the lab-oratory should not be over-emphasized. It must berealised that the outcome of endodontic treatment

depends on a multitude of factors, and no method offilling can boast superior clinical documentation.

Concluding remarks

Despite the differences in defining the radiographicquality parameters of the root-filling, the rather lowreproducibility for some of them and the differencein thresholds used to categorise root-fillings as ade-quate or inadequate, the studies have demonstrated

99

that there is an association between the quality of theroot-filling and the periapical status. All studies haveagreed that AP is more frequent in teeth with inad-equate root-fillings than in teeth with adequate root-fillings. Furthermore, studies have indicated that the

quality of the coronal restoration may be related tothe outcome of root canal treatment.Longitudinal studies have demonstrated that it is

possible to control and cure AP. Ideally, this wouldbe reflected in cross-sectional studies of general popu-lations. This is not the case, however. On the con-trary, it seems that the present methods of performingroot canal therapy is not ideal when performed ingeneral practice. General dentists do not succeed inpreventing or curing AP as demonstrated by thecross-sectional studies on periapical and endodonticstatus that demonstrate high rates of AP in root-filledteeth. It is therefore essential that efforts should bemade to optimise the treatment of teeth with pulpalor periapical infection, and that endodontic treatmentstrategies should be brought into focus in the plan-ning of future under- and postgraduate education.Several technical aspects of treatment are not easilytraceable in radiographs and do not lend themselveseasily to cross-sectional or epidemiological investi-gations. While specific methods of instrumentationand filling have been ardently promoted, based onlaboratory studies of efficacy, few if any clinical dataare available in support of superiority. Well-designedand targeted clinical studies are needed for assessmentof clinical performance.

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