In vitro evaluation of the ability of three apex locators to determine the working length during retreatment.

Abstract

The purpose of this in vitro study was to evaluate the accuracy of three apex locators in determining the working length during the retreatment process. Twenty extracted single-rooted human teeth with mature apices were used in this study. The root canal length of each tooth was measured placing a #15 file until the tip was visible at the apical foramen. The direct visual measurement was reduced by 0.5 mm and recorded. The root canals were instrumented and filled to the direct visual measurement using lateral compaction technique. After 7 days the teeth were retreated using three apex locators: ProPex, NovApex, and Root ZX, for determining the retreatment working length. Afterward, comparison between the visual working length and the retreatment working length were made. ProPex, NovApex, and Root ZX were accurate within 0.5 mm 80, 85, and 95% of the time, and within 1 mm 95, 95, and 100%, respectively. No significant differences were detected between the three apex locators (p > 0.05).

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In Vitro Evaluation of the Ability of Three Apex Locators
to Determine the Working Length During Retreatment
Fernando Goldberg, DDS, PhD, Benjamı ´n Brisen ˜o Marroquı ´n, DMD,†Santiago Frajlich, DDS,
and Cristian Dreyer, DDS
Abstract
The purpose of this in vitro study was to evaluate the
accuracy of three apex locators in determining the
working length during the retreatment process. Twenty
extracted single-rooted human teeth with mature api-
ces were used in this study. The root canal length of
each tooth was measured placing a #15 file until the tip
was visible at the apical foramen. The direct visual
measurement was reduced by 0.5 mm and recorded.
The root canals were instrumented and filled to the
direct visual measurement using lateral compaction
technique. After 7 days the teeth were retreated using
three apex locators: ProPex, NovApex, and Root ZX, for
determining the retreatment working length. After-
ward, comparison between the visual working length
and the retreatment working length were made.
ProPex, NovApex, and Root ZX were accurate within
0.5 mm 80, 85, and 95% of the time, and within 1 mm
95, 95, and 100%, respectively. No significant differ-
ences were detected between the three apex locators
(p ? 0.05).
Key Words
Apex locators, retreatment, working length
From the Department of Endodontics, School of Dentistry,
USAL-AOA, Buenos Aires, Argentina; and†Department of Op-
erative Dentistry, Johannes Gutenberg University, Mainz, Ger-
many.
Address requests for reprint to Dr. Fernando Goldberg,
Viamonte 1620 (1055) Buenos Aires, Argentina. E-mail ad-
dress: fgoldberg@fibertel.com.ar.
Copyright © 2005 by the American Association of
Endodontists
T
and latent infection appear to be one of the major factors associated with endodontic
failures (1, 2).
Sjo ¨grenetal.(3)observed62%successinrootswithperiapicallesionsthatwere
previously filled and were retreated.
Bergenholtzetal.(4)reporteda94%successwhenthecauseforretreatmentwas
attributed to technical inadequacy. Retreatment is considered to be least complicated
when the failure of the primary endodontic treatment is because of the underfilling of
the root canal.
Sundqvistetal.(5)providedevidencethatmicroorganismsharborthemselvesin
anatomic branches of the root canal system and may even reside in areas that were
thought to be obliterated by the primary root canal filling material. As such, the com-
plete removal of the previous root canal filling material is necessary to enhance the
effect of irrigating solutions and intracanal medicaments.
An accurate working length determination during the retreatment process will
make it easier for an operator to completely remove the primary root canal filling
materialandbysodoingofferonetheopportunitytopreciselyprepareandreobturate
the canal.
The importance of establishing an adequate determination of the working length
during retreatment is supported by the findings of Bergenholtz et al. (6). In a clinical
radiographic follow-up investigation, they showed the overinstrumentation and over-
fillingofretreatedrootcanalssignificantlydecreasedthefrequencyofcompleteregen-
eration of apical lesion repair.
The conventional technique for the determination of canal length is the radio-
graphicmethod.However,inmanycasesitisdifficulttoestablishtheactuallengthofthe
canal with a two-dimensional image (7, 8).
Custer(9)wasthefirsttointroduceanelectricalmethodtoestimatetherootcanal
length. In 1962, Sunada (10) constructed the first electronic apex locator. Since then,
different generations of electronic apex locators have been developed to measure root
canal length (11).
Several studies have demonstrated the accuracy of apex locators in determining
theworkinglength(8,12–15).However,onlyafewstudieshaveconsideredthecanal
obstacles that influence retreatment (16).
With concerns over radiation exposure, the adjunctive use of electronic apex
locators during endodontic treatment decrease the radiation exposure to patients by
reducing the number of radiographs required for endodontic therapy (17).
The purpose of this in vitro study was to evaluate the accuracy of three apex
locators in determining working length during the retreatment process.
heretreatmentofendodonticfailureshasbecomearoutineprocedureinaclinical
endodontic practice. Procedural errors that lend themselves to intracanal leakage
Materials and Methods
Twentyextractedsingle-rootedhumanteethwithmatureapiceswereselectedfor
this study. Digital radiographs were taken in buccolingual and mesiodistal directions
and used to evaluate the existing root canal anatomy.
Conventional endodontic access cavities were prepared using diamond round
burs. The coronal and middle thirds of the canals were shaped using #1, #2, and #3
Gates-Glidden burs (Dentsply-Maillefer, Ballaigues, Switzerland). Intermittent irriga-
tion was performed with 2.5% sodium hypochlorite solution.
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Therootcanallengthofeachtoothwasmeasuredbyplacinga#15
fileintotherootcanaluntilthetipbecamevisibleattheapicalforamen.
The silicone stop on the inserted file was set to a flat anatomical refer-
encepointonthecrown.Thefilewascarefullyremovedandmeasured
from the file tip to the stop with an endodontic ruler. This direct visual
measurement (DVM) was reduced by 0.5 mm and recorded.
TherootcanalsweretheninstrumentedtotheDVMtoa#45Kfile
(Dentsply-Maillefer). Two milliliters of 2.5% sodium hypochlorite so-
lutionwasusedforirrigationbetweeneachinstrumentandagainupon
the completion of instrumentation. The canals were then dried with
paper points. A standardized #45 gutta-percha master cone (Dentsply-
Maillefer) coated with AH26 sealer (Dentsply DeTrey, Konstanz, Ger-
many)mixedaccordingtothemanufacturer’sinstructions,wasfittedto
the working length. Lateral compaction was performed using a #30
finger spreader (Dentsply-Maillefer). Fine accessory gutta-percha
cones (Dentsply, Petropolis, Brasil) were inserted and compacted as
needed.Digitalradiographsweretakentoconfirmobturation.Theteeth
were then stored for 7 days at 37°C and 100% humidity to ensure the
setting of the sealer.
After incubation the root canal filling material within the coronal
andmiddlethirdsofthecanalswasremoved4to5mmshyoftheDVM
with a #2 Peeso reamer (Dentsply-Maillefer). The roots of the teeth
were then seated to the CEJ in a plastic tube filled with normal saline
solution.Thelipclipwasalsoinsertedintheplastictube.Agutta-percha
solvent(Xylene,Farmadental,BuenosAires,Argentina)wasinjectedinto
the root canal and the softened apical gutta-percha was penetrated with a
#20 K file attached to the apex locator file holder. The file was advance
apically,removinggutta-perchaasitprogressed,untiltheapexlocatorsig-
nalindicatedtheapex.Thefilewasretractedslowlyuntilthedigitaldisplay
read 0.5. This is a position that most agree represents the location of the
apical constriction. The silicone stop was then set to the same anatomical
reference point as used during the DVM trials. The file was removed and
measured with the same endodontic ruler. This measurement was desig-
nated as retreatment working length (RWL). The measurement of each
toothwasrecorded.
For consistency, the individual tests of the three different elec-
tronicdevices:ProPex(Dentsply-Maillefer).NovApex(ForumTechnol-
ogies, Rishon Le-Zion, Israel) and Root ZX (J. Morita Corp., Kyoto,
Japan) were conducted, measured and recorded by one operator.
Comparisons between the DVM and the RWL were made, and the
accuracy of the electronic apex locators was evaluated within ? 0.5
and ? 1 mm, respectively.
The data were analyzed using analysis of variance and the ?2test
(Software:SPSS10.0).
Results
According to the results, as shown in Tables 1 and 2, measure-
ments determined by the three different apex locators (ProPex, No-
vApex, and Root ZX), were accurate within 0.5 mm 80, 85, and 95% of
the time, and within 1 mm 95, 95, and 100%, respectively.
Statistical analysis showed no significant differences between the
three apex locators tested (p ? 0.05).
Discussion
Severalstudieshavedemonstratedtheaccuracyofapexlocatorsin
determiningtheworkinglengthofrootcanalsduringroutineendodon-
tictreatment(8,12–15).Theexactdeterminationandthecriticalmain-
tenanceofworkinglengthduringretreatment,shouldbeconsideredas
just as vital an aspect of therapy (18).
Sjo ¨gren et al. (3) reported 50% success in retreated root canals
with overfilling compared to 67% success in teeth adequately sealed.
Bergenholtzetal.(6)foundcompleteapicalboneregenerationin
36% of retreated root canals with overfillings compared with 62% in
caseswithoutoverfillings.Theyreportedthefrequencyofapicalregen-
eration in retreated cases significantly decreased when overfilling ex-
isted.
In the present study the primary root canal treatment was per-
formeduptotheDVMleveltomimicclinicalfailureswhenradiograph-
ically acceptable fillings were observed. Allen et al. (19) investigated
factors that contributed to the failure of 1300 treated teeth. They found
22.6% of the teeth, with radiographically acceptable fillings but no
apparent cause for failure was detected. On the other hand, in some
clinical cases with radiographically acceptable fillings retreatment is
indicated because of coronal leakage (20–22).
In this study, electronic readings obtained with ProPex, NovApex,
and Root ZX showed an accuracy of 95, 95, and 100% within 1 mm of
the DVM. Based on the study of Shabahang et al. (14) where they
considered an error tolerance of 1 mm to be clinically acceptable, the
results of this study were quite meaningful.
The findings obtained in this in vitro study were similar to that
observed in vital and necrotic pulps by other authors (13, 15).
During root canal retreatment a number of radiographs are re-
quiredtocompletelyremovetheprimaryfillingmaterialandtoobtaina
controlled working length during reinstrumentation and reobturation.
According to Brunton et al. (17) the use of an electronic apex locator
reducesthenumberofradiographsrequiredforworkinglengthdeter-
mination, desirably decreasing the radiation exposure to patients.
The authors found the electronic devices employed in this study
generated no acoustic or visual signal when the file passed the gutta-
TABLE 1. Accuracy of the different apex locators within 0.5 mm of the direct visual measurement
Device/MeasurementProPexNovApex RootZXTotal
Acceptable
No acceptable
Total
16 (80%)
4 (20%)
20
17 (85%)
3 (15%)
20
19 (95%)
1 (5%)
20
52 (86.6%)
8 (13.3%)
60
?2? 2.02; p ? 0.36.
TABLE 2. Accuracy of the different apex locators within 1 mm of the direct visual measurement
Device/MeasurementProPexNovApexRootZXTotal
Acceptable
No acceptable
Total
19 (95%)
1 (5%)
20
19 (95%)
1 (5%)
20
20 (100%)
0 (0%)
20
58 (96.6%)
2 (3.3%)
60
?2? 1.03; p ? 0.60.
Basic Research—Technology
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percha filling and went through the apical foramen. Once the file was
retractedbackintotherootcanal,thevisualandacousticsignalsofthe
differentunitscouldconfirminstrumentpositionattheappropriate0.5
mm working length.
Theresultsofthisstudyindicateelectronicapexlocatorsareuse-
ful in determining the working length of root canals when retreating
endodontic failures.
Acknowledgments
TheauthorsthankDr.DonaldArensforhishelpwiththemanu-
script and Dr. Ricardo L. Macchi for his statistical assistance.
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