Foramenal Location

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48 oralhealth August 2004

E N D O D O N T I C S

P

redictable endodontic success

demands accurate determina-tion of, and strict adherence tothe preparation length of the rootcanal space in order to create asmall wound site and good healingconditions.1 Each portal of exit(POE) on the root face has biolog-ic significance; this includesthe furcal canals of bifurca-tions and trifurcations, lat-eral and accessory arboriza-tions and the myriad of api-cal termini (Figs. 1A-D).

The ability to distinguishbetween the inner-most(physiologic/histologic fora-men) and outer-most (ana-tomic foramen) diameters of theapical terminus is essential to thecreation of the Apical ControlZone.2 The Apical Control Zone isa mechanical alteration of theapical terminus of the root canalspace that addresses the rheologyof thermolabile filling materials,

offering resistance and matrix

style retention form against thecondensation pressures of obtu-ration (Figs. 2A-C).

The determination of the in-strumentation finishing level isone of the primary factors associ-

ated with the resolution of anendodontic infection both clinical-ly and histologically.3,4 The major-ity of studies postulate that opti-mal success rates occur wheninstrumentation, debridement,disinfection and obturation arecontained within the region of api-

cal narrowing (bracketed by the

minor apical diameter and apicalforamen.5,6,7 In teeth/roots withapical periodontitis (AP) for exam-ple, a millimeter loss in workinglength can increase the chance oftreatment failure by 14 percent.8

The Toronto Study notedthat the highest healingrate differential (15 percent)was observed in teeth with

AP that were most likelyover-instrumented resulting

in transportation of contam-inated debris periapically.9

The evidence is indisputablethat electronic root canallength measuring devices

provide significantly more accu-rate results than radiographs10,11

and therefore offer greater controlof the creation of the ApicalControl Zone (Fig. 3).

In 1942, Suzuki discoveredthat the electrical resistance (sin-

The New Era of

Foramenal Location

Kenneth S. Serota, DDS, MMSc, Jorge Vera DDS,Frederick Barnett, DMD, Yosef Nahmias, DDS, MSc

New modes ofdebridement and disinfection

are constantly arrivingin the endodonticarmamentarium.


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August 2004 oralhealth 49

gle current source) between an

instrument inserted into a rootcanal and an electrode attachedto the oral mucosa registered aconsistent value. In 1962, Sunadausing a direct current device witha simple circuit, demonstratedthat the consistent electrical re-sistance between the periodon-tium and the mucous membranewas 6.5 kOhms [DC Resistance].Through the 1970s, frequencymeasurements were measuredthrough the feedback of an oscil-

lator loop by calibration at theperiodontal pocket of each tooth.This culminated with the effortsof Hasedgawa in 1979 with theuse of high frequency waves and aspecially coated file which couldrecord in conductive fluids.

In 1983, Ushiyama introducedthe voltage gradient methodwhere a concentric bipolar elec-trode measured the current den-sity evoked in a limited area of

the canal. Maximum potential

was reached when the electrodewas at the apical constriction.The mid 80s saw the develop-ment of a relative value of fre-quency response method wherethe apical constriction was pickedby filtering the difference be-tween two direct potentials aftera 1 kHz rectinlinear wave wasapplied to the canal space.

A Third Generation electronicforamenal locator (EFL) devel-

oped in the late 80s by Kobayashiused multi-channel impedance/ratio based technology to simul-taneously measure the imped-ance of two different frequencies,calculate the quotient of theimpedance and express it interms of the position of the elec-trode (file) in the canal. Thisformed the basis of the technolo-gy used in the ROOT ZX (J.Morita USA, Inc. Irvine, CA)where no calibration was re-

quired and a microprocessor cal-

culated the impedance quotient.

Fourth Generation EFLs (Ele-ments Diagnostic, SybronEndo,Orange, CA) measure resistanceand capacitance separately ratherthan the resultant impedance

value (impedance being a func-tion of resistance and capaci-tance) [Fig. 4A]. There can be dif-ferent combinations of values ofcapacitance and resistance thatprovide the same impedance (and

thus the same foramenal read-ing); this can then be brokendown into the primary compo-nents and measured separatelyensuring better accuracy and lesschance for error. In addition, theElements unit uses a lookupmatrix (Fig. 4B) rather than mak-ing any internal calculations.

While calculations take place very quickly, they are still rela-tively much slower than simply


FIGURE 1AArrows indicate mul-tiple POEs associated with the

mesial-buccal and distal-buccalapices of a maxillary first molar.

FIGURES 1B & CThe complexity of the root canal system has been graphically evidencedsince the work of Hess in the 1920s. Radical improvement in materials and techniques arenow enabling the clinician to replicate that complexity as evidenced in the cleared speci-men (1B) and the radiograph (1C). (Courtesy of Dr. William Watson.)

FIGURE 1D(right) The number, shape and diameter of thephysiologic foramena at the root apex mandate the continu-ing pursuit of excellence in endodontics through increasedsophistication in materials and methods and the alliance of sci-entific innovation and clinical acumen. From Gutierrez andAguayo, OS, OM, OP June 1995.


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looking up comparative values ina pre-calculated matrix (in therange of 10-20x slower). Thisallows the unit to crunchthrough much more data in agiven amount of time; a largersample size tends to make theresults more accurate. Figure 5demonstrates the technologic

protocol difference between 3rdand 4th generation foramenallocators.

In the course of preparation ofthis paper, the importance of regu-lation of battery power wasassessed.The Elements Diagnosticcircuitry runs at 3.3 volts (commonfor electronics), which is internallyregulated to remain extremelyconsistent. The battery pack israted at a nominal 6 volts, 7.5 volts

with a full charge and no load.

As the battery pack is depleted,the voltage decreases to a pointwhere the electronics cannot con-tinue to regulate the operating

voltage to such a precise valueand therefore the signals sentthrough the electrodes will not beas reliable either. The device is setto automatically shut off whenbattery voltage is a little abovethis threshold.

The ROOT ZX runs on AAalkaline or lithium batteries(mixing types is to be avoided)

and will shut itself off after twen-ty minutes. There is a bar graphon the face of the unit which indi-cates residual battery power. Thequestion of the accuracy of sig-nals sent through the electrode isin doubt if the battery powerlevel drops below the first threeor four bars (authors observa-tion) [Fig. 7].

A paper point measurement,foramenal detection technique has

been advocated by Rosenberg.12 Itis designed to determine the pointpositional location of the apical

foramen as well as three-dimen-sional information regarding theslope of the foramen. A trial paperpoint is placed 1mm short of theEFL determined length. If thepoint is retrieved dry, it isadvanced further until fluid isnoted. The length of the segmentof the point that is dry is noted.

This sequence is repeated asevidenced in Figs 6A, B & C andthe maximum length of the point



FIGURE 2AThe definitions of the morphologicentities comprising the regional terminus of the

apex are shown diagrammatically with super-imposition of the histologic anatomy.

FIGURE 2BRetreatment of tooth #4.6 with K3 nickel-titanium [NiTi] files(G Pack system). The goal is identification of the histologic terminus of theroot canal space and the use of variable tapered rotary NiTi instrumen-tation to create an apical control zone and optimize the seal producedby the new generation of resin thermoplastic root canal filling materialsand sealers. (Courtesy of Dr. Gary Glassman.)

FIGURE 2CRetreatment of tooth #3.6 with K3 nickel-titanium [NiTi] filesVarible Tip Varible Taper (VTVT) system. The K3 file sequence after thetwo Orifice Openers/Body Shapers is: #35/.06, #30/.04, #25/.06,#20/.04. In the majority of cases, the #25/.06 or the #20/.04 willreach the desired working length on the first pass. If not, the sequence isrepeated from the beginning. (Courtesy of Dr. Fred Barnett.)


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that can be placed into the canaland remain dry reflects the ori-entation of the cavosurface ofthe apical foramen (Fig. 6D).

There are several basic condi-tions that ensure accuracy ofusage for all generations of fora-menal locators;

1) preliminary debridementshould remove most tissue ordebris obstructions,

2) cervical leakage must beeliminated and excess fluidremoved from the chamber asthis may cause inaccuratereadings,

3) extremely dry canals may re-sult in low readings [longworking length],

4) long canals can produce highreadings [short workinglengths],

4) lateral canals may give afalse foramenal reading, and

5) the use with open apices is con-traindicated. The residual fluidin the canal should possess alow conductivity value. In de-scending order of conductivitythese are; sodium hypochlorite(NaOCl 5.25 percent), EDTA(17 percent), Smear Clear(SybronEndo, Orange, CA),

saline, FileEze (UltradentProducts, S. Jordan, UT), andisopropyl alcohol.

It is advisable to use a crowndown canal preparation tech-nique13 and take the preliminaryelectronic measurement using afile that is approximately bigenough to bind at the apical con-

striction.14 A second workinglength measurement is advisableafter flaring the coronal and mid-dle thirds as shortening of workinglength occurs when instrumentingcurved canals; this shortening can

vary from 0.22mm to 0.5mm. How-ever, once coronal flaring has beendone little change in lengthoccurs.15,16 From a medico-legal



FIGURE 3The subtraction approxima-tion technique; the average disparity of0.5 to 1mm between the radiographicapex or terminus (RT) and the cavosur-face point of exit of the root canal spaceused as the standard for length determi-nation is fraught with inaccuracy.(Courtesy of Dr. William Watson.)

FIGURE 4AFourth Generation forame-nal locator (Elements Diagnostic,SybronEndo, Orange CA).

FIGURE 4BLookup matrix generatedfrom in-vivo studies (x-axis capacitance,y-axis resistance, vertical z-axis is resul-tant displayed location in the canal).

FIGURE 5

The graphic shows the technologic difference between the operation ofthird and fourth generation foramenal locators.


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standpoint, a verification radi-ograph is recommended at this

juncture. It is also advisable to doa final confirmation EFL readingafter drying the canal and priorto obturation.

In the case of the third gener-ation ROOT ZX (Fig. 7), theworking length of the canalused to calculate the length ofthe filling material is actuallysomewhat shorter; the length ofthe canal up to the apical seat(i.e. the end point of the fillingmaterial) is found by subtract-ing 0.5 to 1.0mm from the work-ing length indicated by the 0.5reading on the meter.

The meters 0.5 reading indi-cates that the tip of the file is inthe vicinity of the apical fora-men (i.e. an average of 0.2 to0.3mm past the entrance to theapical constriction towards theapex). The disparity betweenthe EFL reading of such unitsas the Ultima EZ and the ROOTZX is demonstrated to be the+.0.5/-0.5 position indicated bythe 0.5 reading on the meter.

This finding has been consis-tently verified by numerousinvestigators.17,18

A recent investigation of thefourth generation EFL, the Ele-ments Diagnostic (Sybron Endo,Orange, CA) demonstrated anunprecedented level of accuracyin usage. Length calibrationswere performed on teeth to beextracted, the files cemented toposition and the teeth cleared for

microscopic examination.19 In 22out of 22 cases where the readingof the file was taken to 0.0 or intothe minus numbers and with-drawn to the 0.5 mark on thescale, the file terminus was con-sistent with the position of the api-cal constriction (Fig. 8A).

When the file was cementedafter going down to the 0.5 mark,in 20 out of 24 cases, the file waspositioned a distance of 0.5mm

from the external foramen (Fig.8B). Of note was the finding thatwhen the device displayed aminus number, the file wasalways beyond the apical con-striction and in most cases out ofthe root structure (Fig. 8C).

CONCLUSION

Evolutionary technologic soph-istication is the hallmark of allscientific and clinical endeavour.Endodontics is the bedrock of allcomprehensive care. As such, it isimperative that predictable endo-

August 2004 oralhealth 53


FIGURE 6BHydrostatics will cause peri-apical fluids to accumulate on theoverextended paper point. (Courtesy of Dr.David Rosenberg.)

FIGURE 6CThe angle of the paper pointdiscolouration reflects the three dimension-al orientation of the cavosurface of the api-cal foramen. (Courtesy of Dr. David Rosenberg.)

FIGURE 6DThe terminus of the canal isnot a point in space; it is a multidimen-sional, topographically diverse plane.(Courtesy of Dr. David Rosenberg.)

FIGURE 6AThe paper point is intro-duced coronal to the level of the EFLdetermination. As it is shy of the cavo-surface of the canal terminus, it shouldremain dry. (Courtesy of Dr. David Rosenberg.)

FIGURE 7The Root ZX is a fully auto-matic, self-calibrating root canal fora-menal locator.

FIGURE 8AWhen the file glide path isstopped at 0.5 on the digital display,the units accuracy in determining theapical foramen is less than 85 percent.


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dontic success is projected asclose to 100 percent as biological-ly possible. Outcome assessment

studies indicate that formenalposition is a pivotal factor if notthe pivotal factor in the mostfavourable end result. New modesof debridement and disinfectionare constantly arriving in theendodontic armamentarium. TheFourth Generation of foramenallocators will ensure that theirusage in evolutionary endodontic

protocols is optimized. OH

Drs. Serota, Vera, Barnett, Nahmias,

Watson and Glassman are membersof the cybercommunity ROOTS

www.rxroots.com.

Oral Health welcomes this original

article.

REFERENCES

1. Simon JHS. The apex: How critical is it? Gen Dent1994 42:330-4.

2. Serota KS, Nahmias Y, Barnett F, Brock M, Senia ES.Predictable endodontic success. The apical control

zone. Dent Today. 2003 May;22(5):90-7.3. Chugal NM, Clive JM, Spangberg LS. Endodontic

infection: Some biologic and treatment factors associ-ated with outcome. Oral Surg Oral Med Oral PatholOral Radiol Endod. 2003 Jul;96(1):81-90.

4. Ricucci D, Langeland K. Apical limit of root canalinstrumentation and obturation, Part II: A histologicalstudy. Int Endod J 1998;31:394-409.

5. Dammaschke T, Steven D, Kaup M, Ott KH. Long-term survival of root-canal-treated teeth: A retrospec-

tive study over 10 years. J Endod. 2003 Oct;29(10):638-43.

6. Kojima K, Inamoto K, et al. Success rate of endodon-tic treatment of teeth with vital and nonvital pulps. Ameta-analysis. Oral Surg Oral Med Oral Pathol OralRadiol Endod. 2004 Jan;97(1):95-9.

7. Basmadjian-Charles CL, Farge P, Bourgeois DM,Lebrun T. Factors influencing the long-term results ofendodontic treatment: a review of the literature. IntDent J. 2002 Apr;52(2):81-6.

8. Vachey E, Lemagnen G, Grislain L, Miquel JL. Alter-natives to radiography for determining root canallength. Odontostomatol Trop. Sep 2003;26(103):15-8.

9. Friedman S, Abitbol S, Lawrence HP. TreatmentOutcome in Endodontics: The Toronto Study. Phase I:Initial Treatment. J Endod December 2003;29(12):787-793.

10. Pratten D, McDonald NJ. Comparison of radiographic

and electronic working lengths. 1996 J Endo April1996;22(4):173-6.

11. Pommer O. In vitro comparison of an electronic rootcanal length measuring device and the radiographicdetermination of working length. Schweiz MonatsschrZahnmed. 2001;111(10):1165.

12. Rosenberg D. Paper Point Technique: Part II.Endodontic Practice May 2004 7;(2):7-11.

13. Ibarrola JL, Chapman BL, Howard JH, Knowles KI,Ludlow MO. Effect of preflaring on Root ZX apex loca-tors. J Endod September 1999;25(9):625-6.

14. Nguyen HQ, Kaufman AY, Komorowski RC, FriedmanS. Electronic length measurement using small andlarge files in enlarged canals. Int Endod J. 1996Nov;29(6):359-64.

15. Davis RD, Marshall JG, Baumgartner JC. Effect ofearly coronal flaring on working length change incurved canals using rotary Nickel-Titanium versus

stainless steel instrumentation. J Endod 2002;28:438-441.

16. Caldwell JL. Change in working length following instru-mentation of molar canals. Oral Surg Oral Med OralPath 1976; 41:114-8.

17. Welk A, Baumgarnter C, Marshall G. An in vivo com-parison of two frequency-based electronic apex loca-tors. J Endod August 2003; 29(8):497-500.

18. Shabahang S, Goon WW, Gluskin AH. An in vivo eva-lution of ROOT ZX electronic apex locator. J EndodNovember 1996; 22(11):616-8.

19. Vera J, Gutierrez M. Accurate working lengthdetermination using a fourth generation apex loca-tor (in press).

FIGURE 8BWhen the file reaches theperiodontal ligament, the digital displayshows 0.0. When the file is withdrawn0.5mm, an instrumentation terminuspoint consistent with the apical constric-tion resulted 100 percent of the time.

FIGURE 8CWhen the file glidepath is extended into a negativereading on the display, the filewas out of the canal in all cases.



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Foramenal Location