Endodontics

Clinical evaluation of audiometric control root canaltreatment: A retrospective case study

Masaki Murakami, DDSVShintaro Inoue, DDS, PhDVNoboru Inoue, DDS, PhD, FICD^

Objective: The purpose of this study was to retrospectively assess the success of endodontic treatmentthat tiad been guided by audiometric (electronic) measurement. Method and materials: The lengths of66 infected root canals tbat demonstrated periapical patbosis were accurately measured by the Sono-Explorer before root canal obturation. Tbe results over time intervals ot 1 month to 20 years were evalu-ated on tbe basis of radiographie examinations. Results: Tbe rate of successful treatment was 90,4% forshort-filled root canals, 94.5% for flush-filled root canals, and a low 50.0% for long-filled root canals, Tberate of suocessful endodontic tberapy was 87,8% for restorations that did not exceed the apical foramenbut reached the apioal oonstriotion and 95,3% if cases in wbtcb tbe apical radiolucencies were disappear-ing were included as suocesses. If oases of uninlenlional long-filling (overextension) were excluded, thesucoess rate was as high as 98,4%, Conclusion: Tbe poor performance of overfilled root canals indicatestbat practitioners should not overextend these restorations. Use of the Sono-Explorer aided successfultreatment of infected root canals, (Quintessence Inl2002:33:465-^75)

Key words: apical limit, audiometric cotitrol, endodontic therapy, root canal, Sono-Explorer

CUNICAL RELEVANCE: Tbe electric (audiometric) rootcanal measurement metbod is more accurate than theradiograpbio measurement metbod, and an accuratemeasurement of root canal length is considered key tosuccessful endodontio treatment.

The success of endodontic treatment depends on anumber of factors, the most important of which is

the accurate measurement of root canal length. Manystudies have shown that a root canal has to be mea-sured carefully to determine an accurate workinglength for its treatment,'-** To proceed with treatmentwithout first obtaining an accurate measurement is notto apply due diligence in treatment. Guesswork insuch circumstances often resuh in underinstrumenta-tion or overinstrumentation, and underextension oroverextension. Care should fae taken not to waste timeand effort in this manner and to strive for the mostfavorable outcome.

'Staff, I roje Dental Clinic, Toltyo, Japan,

'Director, Inoue Dental Clinic, Tokyo, Japan; torme^iy. Visiting Protessor,Division ot Endodontics, Faculty of Dentistry, University of WesternOnrario, Lenden, Ontario, Canada,

Reprint requests ; Dr Noboru Incue, Inoue Dentai Clinic, Nisseki-Mitsjbishi Building B l , 1-3-12 Nishi-simbastii, Minato-kj, Tci<yo 1O5-0CC3,Japan, Fax; 813-3595-3599, E - mail ;se-i noue© siren, oon, ne.jp

Ideally, a practitioner should measure the rootcanal length up to the biologic apex. This measure-ment is then used as a basis for determining workinglength, the ideal length of instrumentation and filling.Studies have also shown the biologic apical foramen,or dentinocementum juncfion, is generally located 0,5to 1,0 mm or more short of the anatomic apex,'-^

Despite this knowledge, many practitioners haverepeatedly used the radiographie apex as a basis forclassification in conducting outcome research onendodontic therapy. In so doing, they classify a fillingthat reaches the radiographie apex as flush and anyfilling beyond or short of the apex as overfilled orunderfilled, respectively. Given the results of manyanatomic studies and knowledge of the function ofelectronic apex locators, the authors question theaccuracy of such a basis for classification,

Schilder' distinguished between the terms over-extension (exceeding the root apex on the radiograph)and underextension and the terms overfilling andunderfilling. Overfilling is achieved when root obtura-fion leads to a homogenous, dense filling of the rootcanal. Overextension and underextension thereforerefer solely to the vertical position of the root canalfilling, regardless of its volume. In overextension andunderextension, the filling may be grossly underfilled.This may give rise to the formation of large deadspaces or voids and hollows in the dental pulp cavity,resulting in exudation of tissue fluid and ultimately to

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• Murakami étal

Fig 1a Radiograpii for determining Itie working length witti ttieSo no-Explorer.

Fig 1b Radiograph after root canal obturation. The gutta-percinafills the entire root canal spaoe. Because this tooth is in torsiver-sion. the image shows a mesioeocentric projection.

Fig 2a Radiograph revealing a bent H file in the canai. The fiiewas removed with ultrasonic vibration

Fig 2b Radiograph attef root canal obturation The root canalhas been tilled by the laterovertical oondensation method, ensur-ing signitioant dispersal of restorative material to the accessorychannels and lateral oanals.

failure of the surgical procedure. Schilder' thereforeargued that overfilling may be permitted.

In contrast to this view, the authors are of the opin-ion that overfilling is best avoided, because it is ourexperience that, when gutta-percha leaks outside ofthe apical foramen, lesions wii! arise in the apical peri-odontium. In addition, obturation of the apical fora-men witb cementum as tbe ideal stop is difficult toachieve; it may take considerable time to absorb, andbiologic healing may be difficult.

Tbe authors have tried a spatial obturation tecb-nique in wbicb the root canal space is filled so tbatgutta-percha does not leak outside tbe root apex. Inthis metbod, tbe precise position of the apical foramenis measured witb a Sono-Explorer {DentalElectronics), and an apical stop is formed approxi-mately 0.5 mm short of tbe foramen. The main gutta-percha is coated witb sealer, an extremely small

amount of eucapercba is applied to tbe gutta-percha,and it is first fixed by lateral condensation to preventthe gutta-percha tip from protruding outside tbe apicalforamen. A plug is tbus formed in the root apex. Tberoot canal space is automatically softened by tberino-mecbanical condensation witb a McSpaddetiCompactor (Ranson & Randolpb) and N.T. Condenser(Analytic Endodontics), and vertical compaction isapplied to provide spatial obturation of tbe root canalThe name used by tbe autbors to describe this proce-dure is tbe laterovertical condensation method, wbichis currently under investigation (Figs 1 to 4).

It is evident tbat this method does not lend itself tothe phenomena described by Schilder' as overexten-sion and underextension, not to mention overfilling.Because this metbod can also manage tbe lateralcanal, it can certainly be regarded as a biologic obtu-ration tecbnique.

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• Murakami et al

Fig 3a Radiograph tor determining the working lenglh wilh theSono-Explorer. The tooth is in torsiversion. Fig 3b Radiograph after root canal obturalion. Lateroverlical

condensation has completely filled Ihe canal and ensured disper-sion of the restorative material to accessory channels and lateralcanals.

Furthermore, tbe location of tbe anatomic apicalforamen and apical constriction do not always coin-cide clinically^-'" (Figs 5 to 7). This fact was tbe basisfor developing an electronic device to apply to thetneasurement of root canal length, instead of having torely solely on the radiographie method."-^'

Measurement of the root canal length with an elec-tronic device ensures accuracy, despite the differencesin the locations of the anatomic apex and the apicalforamen. The method is also an effective way toreduce a patient's exposure to x-ray radiation. Theelectronic apex locator meets Ingle and Bakiand's cri-teria'* for measuring working length with an effectiveendodontic device. These criteria are (1) accuracy ofmeasurement, (2) ease of operation, and (3) repro-ducibility of results.

To test the long-term efficacy of endodontic treat-ment, outcomes were analyzed in a sample of patientswho received endodontic treatment that was guidedby the clinical results of electrical root canal lengthtneasurement.

METHOD AND MATERIALS

A clinical outcome study was done on patients aged20 to 65 years who had received root canal treatmentat the Inoue Dental Clinic between 1970 and 1990,Sixty-six endodontically treated teeth were selected fora follow-up examination. In the sample there were 25incisors, 13 premolars, and 13 molars, all exhihitingapical pathoses before clinical examination. The Sono-Explorer had been used to measure the root canallength in all 66 cases. Based on these measurements,the infected root canals were treated, prepared andfilled. The patients were divided into two groups,based on the filling material used. There was no differ-

Fig 4 Radiograph after roo[ canai ooturation. ihie sealer wasplaced and canals were obturated by the lateroverlicat condensa-tion of gutta-percha The material is dispersed to the accessorychannels and lateral canals.

ence in the ages or health of the patients in the twosample groups.

In a number of the 66 treatments, a combination offilling techniques using siiver point and gutta-percbawere used. Neodain (Neo Dental Cbemical Products}was used as the root canal sealer. The laterovertical con-densation method was used as the obturation procedure.

Teetb treated witb silver point-type root fillingmaterial were classified as group 1, because tbis typeof filling is electroconductive, and the lengtb of thefilling can he measured and reexamined accuratelywith the Sono-Explorer at the time the point is seated.

The remaining treatments used only gutta-perchafilling material with the endodontic sealer cementDentalis (KEZ, Neo Dental Chemical Products) as theroot canal sealer. Again, obturation was completed witbthe laterovertical condensation method. Teeth treatedwith this type of root filling were classified as group 2.

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Fig 5a (ieft) Radiograph tor determiningfhe working lengtfi with the Sono-Expfore;,Efectronic measuring shows an apioai fora-men mat is shorter than the radiographieroot ape«.

Fig 5b (right) Radiograph after rooi canaiobturation. The canai was filied wifh gutta-peroha, buf restoration resuited in overex-tension because the apicai stop wasincompiefe.

Fig 5c (left) Postsurgicai radiograph.Alter thG exoess gutta-percha was surgi-caiiy scraped out of the canai apex, it wasconfirmed that the apical foramen was afIhe same position as it was at the time otthe eiectronio measurement.

Fig 5d (rigiit) Extracted tooth from a dif-ferent patient, reveafing that the anatomicapex (A) and the position of the apicaf fora-men (B) may be remari<abiy different.

For group 2, the Sono-Explorer was used to obtainthe exact root canal length down to the apical fora-men, and this measurement was confirmed with radio-graphs. An apical stop was then formed 0.5 mmshorter than the measurement of the root canal length,and the canal was filled carefully so that the materialdid not go beyond the apical constriction,''

In subsequent follow-up examinations, the degreeof apical healing was assessed with radiographs.Radiographs taken at the follow-up examination werecompared with the radiographs taken at the titne ofobturation. The radiographs were specifically exam-

ined for changes in the apical radiolucency and thecondition of the trabecular bone. Close attention waspaid to identify the lamina dura and the periodontalmembrane space. The results of these radiographieexaminations were classified according to the changein radiolucency: (1) no change, (2) smaller or healing,and (3) disappeared or healed. In no instance was thelesion larger.

To allow comparison with other endodontic follow-up examinations reported by other practitioners, thelengths of root canal fillings were classified accordingto a system previously described by Bender et aV^

• Murakami et al

Fig 6a Badiograoti for determining the working length with theSono-Explorer. The position of the reamer stiows that Ihe workingiergth is shorter than the radiographie root apex.

Fig6b Raacgrr-r.- .-.••••••.-:•-;•-. ciuration. Tiie sealer, whichwas placea in the ¿a.-i.e locaüún ¿s (he lip ot the reamer, hasexpressed out, confirming the presenoe oí an apical foramen.

Fig 6e Raoiograpn at the 10-year recall. The radioluoenoy hascompletely aisappeared and healed well.

Heling," and Seltzer'^: According to their classifica-tion, a flush filling is a root canal ending 0.0 to 1-5 mmshort of the radiographie apex, a short filling is a fill-ing ending 1.6 mm to 3.0 mm short of the radio-graphic apex, and a long filling is any filling ending 0.1mra or more beyond the radiographie apex.

Because of variations in patient compliance, thefollow-up examinations were not always performedover the same time period. For this reason, the timesof follow-up examinations after root canal treatmentwere rounded off to 1, 2, and 3 months and 1, 3, 7, 10,15. and 20 years.

RESULTS

None of the patients experienced spontaneous pain orpercussion pain during the follow-up period. From aclitiical standpoint, the treatment had restored theteeth to normal function.

According to the aforementioned classification'^'^using radiography, there were 21 cases of underfilling(31.8%), 37 cases of fiush filling (56.0%), and eightcases of overfilling (overextension) (12.1%) in thesample. This distribution was almost identical to sam-ples in previous endodontic clinical studies conducted

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Fig 7a Preoperative radiograph. This lésion was diagnosed as a"mandibular cyst," but treatment was performed without surgery

Fig 7b Radiograph lor determining the wofi<ing length with theSono-Explorer, Because there is résorption at the distal root ape:*,electronic measuring indicates that the position may be too short.

Fig 7c Raaiograph atter root canal obturation. The sealer ieaksbeyond, but gutta-percha slops at the apicai oonstnction

Fig 7d Radiograph at the 5-year recall. There is bone regrowth,indicating that the lesion is on its way to healing

TABLE 1 Radiographie location of the canal filling

Condition otcanal fillings

ShortFlushLong

Distance I romradiographie apex (mm]

-1,6 - 3,00 , 0 - -1,50.1 ~ 1,5

Root canals

No, %

31.856,012,1

TABLE 2

Condition otcanal fillings

ShortFlushLong

Effect of length of the canal fiMinc

Change

No change

003

n radioiucency

Healing

221

Healed

19354

Total

21378

Success(%)

90.494,550,0

by Inoue,'^ Based on this distribution, it is our impres-sion that current root canal measurements using theSono-Explorer are accurate (Table 1).

Of the 21 cases of short filling, the radiolucencyhealed in 19 cases, representing a 90,4% success ratefor this group. Of the 37 flush fillings, the radiolucencydisappeared in 35 cases, giving this group the highestsuccess rate, 94,5%, Of the eight cases of long filling,the radiolucency disappeared completely in only fourcases, represenfing a success rate of only 50,0%, There

were no substanfial differences between the successrates of fiush-fiUed and short-filled endodontic treat-ments. There was, however, a clear difference betweenthe results of those treatments and the results of thelong-filled root canal treatments (Table 2),

During the entire period of the follow-up examina-tions, the radiolucency disappeared in 58 cases(87,8%), The flush-filled and short-filled root canaltreatments obtained the best results, and the long-filled treatments obtained the poorest results. No real

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TABLE 3 Radiographie condition ot the canal fillings and finalresults versus rate of disappearance of radiolucency

Change inradiolucency

No change

Healing

Healed

Total

Condition ofcanal filiing

ShortFlushLongShortFlushLongShortFlushLong

Silver point

No, %

0

0 581

1

0 5.80

5

10 88.20

17

Gutta-percha

No. %

0

0 4,02

1

2 8.01

14

25 87,74

49

No

0

0

3

2

2

1

19

35

4

66

Totai

%

4.5

7.5

87 8

100 0

differences could be observed between tbe resultsobtained witb silver point (group 1) and gutta-percba(group 2) üllings (Table 3). Despite tbe long 20-yearperiod of some teetb in tbe follow-up examination,there was no incidence of relapse, and a 95.3''/o suc-cess rate was recorded overall. Tbis includes theoccurrence of cases with radiolucency still in theprocess of healing. When two cases of unintentionaloverfilling (overextension) were excluded, the successrate reacbed 98.4%.

DISCUSSION

In 1972, Inoue^" first described the concept of tbeSono-Expiorer, a sound-activated root canal-measur-ing device. Since its debut in 1972, tbe Sono-Explorerhas evolved from tbe original to the Mark II, Mark III,and Mark IV models, undergoing many developmentalimprovements. In the 29 years since the product wasfirst introduced, many researchers and cliniciansworldwide''-^* have used tbe Sono-Explorer, andmany clinical studies have demonstrated its acctu'acyand reliability.

In addition to tbe Sono-Explorer, tbe Endex"-'^and the Root-ZX*'̂ -'-' are new methods that use twodifferent frequencies, but tbere are few long-term clini-cal studies to demonstrate tbeir accuracy.

Many reports bave been made on the accuracy ofthe Sono-Explorer (Table 4), In 1977, Inoue'^ measuredroot canal lengtb in vivo electronically, and tben veri-fied tbe measurements by direct observation after tbetootb was extracted. Of tbose cases wbere tbe apicalforamen and tbe tip of the measuring device coincided,a comparison was made of the preoperative appearanceof the radio^pbic apex, and a discrepancy was noted.

In the present retrospective study, tbe radiolucentlesion disappeared in 19 of tbe 21 teeth with under-filled root canals, 35 of 37 teeth with flush-filled rootcanals, and only 4 of 8 teeth with overfilled rootcanals (see Table 2). Wben tbese results are comparedwitb tbose obtained by Bender et al,'^ Heling," andSeltzer,'' tbe present success rates for short- and flusb-filled canals are higher, while the results for long-filledcanals are less successful (Table 5).

This high success rate may be possibly due to theinclusion of numerous root canals tbat were filled totbe biologic apical foramen or apical constriction andtbat were actually tbought to be underfilled accordingto tbe radiographie images (see Figs 6 and 7). It isimportant to note tbat tbe designation of underfillingor overfilling was based on tbe appearance of tbe radi-ograpbic image and tbus was not necessarily an accu-rate representation of wbether tbe obturating materialwas actually long of or short of the apical foramen orapical constriction. To make an accurate decision ofwhether it is a long or shortfilling. it is suggested tbattbe lengtb of tbe root canal be measured electronically.

In tbe present study, there were no major differ-ences in tbe success rates of the flush-filled and theshort-filled root canals. This may be because all under-fillings were defined by the apical foramen or apicaiconstriction. Tbe overfilled root canals experiencedpoorer bealing (Table 5 and Figs 8a to 8c).

Tbe final results of the root canal filling length, asjudged by the radiographie images were as follows:Three of 66 lesions (4.5%) were unchanged, primarilyall in tbe overfilled group. Five of 66 lesions (7,5%)were smaller or sbowing signs of bealing. Tbeseincluded two underfilled, two flusb-filled, and oneoverfilled tootb. Tbe remaining 58 of 66 apical radio-lucencies (95,3%) were healed, and they included

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• Murakami et al

TABLE 4 Accuracy of the Sono-Explorer root canal-measuring device

Study

Incue's

O'Neill^'Blank et al=*Seidberg et aPInoue"

Busch et aP"

Plant andNewman '̂'

Kautman^^Inoue and

Skinner"

Trope et aP

Fouad and KrelP^Fouad et al^'Hembrough et al=

A A ̂ anatomic apex

No, ofcanals

100

53

91

50

35

135

5S

32

106

310

127

20

20

26

Criterion

AA

AF

AF

AA

AF

AF

AA

AA

AF

AA

AAAA

AA

AA

AA

AA

AF

AF

AF = apical foram

-0.4-0±0

±0.2-0.2-0±0

-0,1-0±0,5±0.5±0

-0.5-0±0-1.0-0-3.0-0±0

-0.5-0-2.0-0+0.5±0.5±0.5

en.

Accuracy(%)

92.183.Q89.078.092.995.595,6B7.993.a

82.757.784.599.764.690.697.680.075.073,1

Comments

RadiographExtraotBdExtractedRadiographExtractedExtractedRadiograph (vital)Radiograph (nonvital)Extracted

RadiographRadiographRadicgraphRadiographRadicgraphRadiographRadiographIn vitroExtractedExtracted

TABLE 5 Success rates reported in other studiesot the Sono-Explorer

Condition otcanal filling

ShortFlushLcng

Benderet al'«

80.6%87.4%69.0%

Hei ing"

68.4%71.0%57.1%

Study

Seltzer'ä

72.5%83.6%69.8%

Vlurakami et al(current)

90.4%94.5%50.0%

restorations in all groups. Overall, the success rateincreased to 98.4% if unintentionally overfilled rootcanals were excluded.

Previous studies have suggested that superiorresults can be obtained if a root canal is prepared andfilled after accurate measurement.̂ -^ Tbis even led tosuccessful results for group one silver points (Table 3),which were previously considered unfavorable exam-ples in tbe present study. This indicates that it isextremely important to be fiexible wben the materialsare placed to tbe apical foramen of the root canal,rather than sticking to one method for length mea-surement. The key to successful endodontic treatmentis dependent on whether a root canal can be filled inthree dimensions.

CONCLUSION

The following conclusions are based on examinationof radiographs 1 montb to 20 years after root canalobturation.

1. According to the previously described classifica-tion, there were 21 cases of underfilling (31%), 37cases of fiush filling (56%), and eight cases of over-filling (12.P/0). This distribution is almost identicalto that in samples from previous endodontic stud-ies conducted by Inoue.'̂ '** Based on this distribu-tion, the measurements of root canal lengths inthis most recent sample are likely to have beenaccurate,

2. The rate of successful treatment was 90.4% forunderfilled teeth, 94.5̂ /0 for fiush-filled teeth, and50.0% for overfilled teeth.

3. Generally speaking, the success rate when theSono-Explorer was used to measure working lengthwas 87.8% for fillings that did not exceed the apicalforamen but reached the apical constriction and95.3% when fillings in which the apical radiolucen-cics were disappearing or in the process of healingwere included. Furthermore, if cases of uninten-tional overfilling (overextension) were excluded,the success rate was as high as 98.4%.

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• Murakami et al

Fig 8a Radiograph 1 month after roof canaf obturafion. The dis-tai canaf is overiiiied with gutta-peroha. The mesiai canals arefiiied with siiver point as indicated by ftie Sono-Expforer

Fig 8b Radiograph at the B-month recaif. The repair process isadvancing.

Electronic (audiometric) measurement of root canallength appears to be more accurate than the meth-ods using radiographie measurement. Accuratemeasurement of root canal lengths, to preventextension of filling material beyond the apical fora-men, was considered a key to successful endodontictreatment in these patients.

ACKNOWLEDGMENTS

The autho:5 thank Dr W. H, Christie, Associate Professor. SectionHead of Endodontology, Department of Restorative Dentistry,faculty of Dentistry, University' of Manitoba, Winnipeg, Manitoba.Canada, and Dr Jonathan Suzufii. Vancouver, British Columbia,Canada, for assistance with the translation of tfie manuscript. Wewonld also like to thank Dr F, S. Weine. Professor Emeritus, Loyofa[Jiiiversity. Chicago, who has made many vafuahie suggestions toimprove the Sono-Expforer.

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