Basic Research—Technology

Influence of Preflaring on the Accuracy of LengthDetermination With Four Electronic Apex LocatorsEricson Janolio de Camargo,* Ronald Ordinola Zapata,* Paulo Leal Medeiros,*

Clovis Monteiro Bramante,* Norberti Bernardineli,* Roberto Brandao Garcia,* Ivaldo Gomes deMoraes,* and Marco Antonio Hungaro Duarte†

Abstract

Introduction: The aim of this study was to compare theinfluence of preflaring on the accuracy of 4 electronicapex locators (EALs): Root ZX, Elements DiagnosticUnit and Apex Locator, Mini Apex Locator, and ApexDSP. Methods: Forty extracted teeth were preflaredby using S1 and SX ProTaper instruments. The workinglength was established by reducing 1mm from the totallength (TL). The ability of the EALs to detect precise(–1mm from TL) and acceptable (–1�0.5mm from TL)measurements in unflared and preflared canals wasdetermined. Results: The precise and acceptable (P/A)readings in unflared canals for Root ZX, Elements Diag-nostic Unit and Apex Locator, Mini Apex ,and Apex DSPwere 50%/97.5%, 47.5%/95%, 50%/97.5%, and 45%/67.5%, respectively. For preflared canals, the readingswere 75%/97.5%, 55%/95%, 75%/97.5%, and 60%/87.5%, respectively. For precise criteria, the preflaredprocedure increased the percentage of accurate elec-tronic readings for the Root ZX and the Mini ApexLocator (P < .05). For acceptable criteria, no differenceswere found among Root ZX, Elements Diagnostic Unitand Apex Locator, and Mini Apex Locator (P > .05).Fisher test indicated the lower accuracy for Apex DSP(P < .05). Conclusions: The Root ZX and the MiniApex Locator devices increased significantly the preci-sion to determine the real working length after the pre-flaring procedure. All the EALs showed an acceptabledetermination of the working length between theranges of�0.5mm except for the Apex DSP device,which had the lowest accuracy. (J Endod2009;35:1300–1302)

KeywordsElectronic apex locator, Root ZX, working length

From the *Department of Endodontics, Bauru DentalSchool, University of Sao Paulo, Sao Paulo; and †Departamentof Endodontics, University of Sagrado Coracao, Bauru, Brazil.

Address requests for reprints to Clovis Monteiro Bramante,Al. Octavio Pinheiro Brisola n�. 9-75, 17012-901, Bauru, SP,Brazil. E-mail address: bramante@fob.usp.br.0099-2399/$0 - see front matter

Copyright ª 2009 American Association of Endodontists.doi:10.1016/j.joen.2009.05.030

1300 Camargo et al.

The establishment and maintenance of working length are a critical step duringendodontic therapy (1). An appropriate microbial disinfection, correct cleaning

and shaping, and hermetic sealing of the root canal depend on the correct determina-tion of working length. The apical constriction is also referred to as the minor constric-tion diameter and marks the transition between the pulpal and periodontal tissue (2).This anatomic landmark might be located at 0.5–1mm from the major foramen (2, 3),and it has been stated that it is an ideal point to end the instrumentation and obturationof the root canal system (3).

Traditionally, the working length has been determined by radiographs and elec-tronic apex locators (EALs) (1). The evolution of EALs made the assessment of theworking length more accurate and predictable (4–6). First, Sunada (4) introducedthe principle of EAL applied for clinical purposes. Then many other appliances weredeveloped, passing through the first generation of electrical resistance–based EALs(4) to the second generation impedance-based EALs and the third generationfrequency-based EALs such as the Root ZX (7, 8). In recent years multi-frequency–based apex locator has also been entered into the market (6). A few of these appliancesbecome more compact devices, which could be easier to operate in many clinical situ-ations, such as the Mini Apex locator (9, 10). The Root ZX measures the impedance of 2frequencies simultaneously (0.4 and 8kHz) (6) and expresses this quotient in terms ofthe position of the file inside the canal. On the other hand, other appliances such as theElements Diagnostic Unit and Apex Locator (11) and Apex NRG (Medical NRG, Afikim,Israel and Septodont, France) are multi-frequency–based devices (12). Gordon andChandler (1) classified multi-frequency devices as the fourth generation of EALs.

The coronal flaring of the root canals gives many advantages during the contem-porary cleaning and shaping procedures, such as to facilitate the insertion of manualand rotary instruments into the apical portion of the root canals (13, 14). To date,only 1 study suggested better accuracy with an EAL when the root canals were preflaredbefore the instrumentation (14). It is unknown whether new apex locators mightimprove their performance after preflaring the root canals before the working lengthdetermination.

The purpose of this in vitro investigation was to evaluate the influence of preflaringon performance of 4 EALs: Root ZX (J. Morita Corp, Tokyo, Japan), Elements DiagnosticUnit and Apex Locator (Sybron Endo, Sybron Dental, Anaheim, CA), Mini Apex Locator(Sybron Endo, Sybron Dental), and Apex DSP (Septodont, Saint-Maur des Fosses,Cedex, France).

Material and MethodsSelection of Sample

Forty mandibular incisor single-rooted teeth were used in this study. Teeth wereradiographed in both mesiodistal and buccolingual views to verify the absence of rootresorption or canal curvatures. Only root canals with Vertucci’s type I canal configura-tion were used (15). After coronal access, debris and remnants of pulp tissue wereremoved with a size 15K-file (Dentsply-Maillefer, Ballaigues, Switzerland). The rootcanals were irrigated by using 1% sodium hypochlorite (NaOCl) solution witha 23-gauge needle. For measurement of the tooth length, the incisal edges were planed(flattened) by using a polishing machine under refrigeration (APL-4; Arotec, Cotia, SP,

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Figure 1. Percentage of precise, acceptable, and mistaken readings found inunflared and preflared canals. Precise measurement, exact electronic readingsat 1mm short from apical foramen; acceptable measurement, value rangerestricted to 1mm short of the apical foramen or within�0.5mm of error vari-ation; mistaken measurement, values were higher or lower than acceptablemeasurements.

Basic Research—Technology

Brazil). A size 15K-file with a silicone stop was introduced into the rootcanal until its tip was seen at the level of the apical foramen (9, 16, 17).This procedure was performed with the aid of a surgical microscope(DF Vasconcelos, Sao Paulo, Brazil) at 8.0� magnification. Once thefile tip was observed at the apical foramen, the silicone stop was stabi-lized at the incisal edge of the tooth. The file was removed, and thedistance between the rubber stop and the file tip was measured witha 0.5-mm precision ruler (ARCH, Tokyo, Japan). This measure wasdefined as the total length of the root canal. The working length wasestablished by reducing 1mm from the total length.

For electronic measurements of the working length, the teeth wereimmersed in a plastic box containing fresh alginate (Jeltrate II; Dents-ply, Petropolis, Brazil) (18). Two orifices were made, one in the centerfor placing the tooth and the other laterally for placing the lip electrodeof the EALs. Before electronic location, the root canals were irrigatedwith 1% NaOCl solution. Cotton pellets were used to remove excessfrom the pulp chamber. The lip electrode was immersed in the respec-tive orifice in contact with the conductive medium, and a K-15 file wasthen connected to the other electrode for electronic measurement. Foreach one of the appliances, a file was gently inserted into the root canaluntil the ‘‘APEX’’ signal was seen on the LED or display screens. TheK-file was gently retracted until the LED or display showed the 1-mmmark. A rubber stop was then carefully adjusted to the reference level,and the distance between the rubber stop and the file was measured witha ruler.

All the canals were measured before and after the preflaringprocedure. For this purpose, the root canals were prepared up to themiddle third with an engine-driven instrument (X-Smart; Dentsply Mail-lefer) by using the S1 and SX ProTaper instruments (Maillefer). The S1instrument was introduced into the canal 3mm short of the workinglength. Then the SX instrument was used with a brushing motion upto the middle third. The irrigation was performed with 3mL 1% NaOClafter the use of each rotary instrument.

Accuracy of the apex locators was classified as the following:precise, if the measurement was restricted to 1mm short of apicalforamen (correct working length); acceptable, if the measurementrange was restricted to 1mm short of the apical foramen or within�0.5mm of error variation; and mistaken, if the measurement valueswere higher or lower than acceptable measurements.

Measurements were recorded on a chart and repeated 3 times, andan average was calculated. A mean value of these measurements wasrecorded for each tooth and analyzed by the c2 test to compare thenumber of teeth with precise and acceptable measurements for eachapex locator. A Fisher test was also applied to compare the measure-ments among the apex locators for each group. The level of significancewas established at P <.05. The analyses were performed with theGraphPad Prism 4 for Windows (Microsoft Corp, Redmond, WA).

ResultsThe electronic measurements were done before and after preflar-

ing the root canals, giving a total of 80 averages for each apex locator.The corresponding percentages and values of precise, acceptable, andmistaken electronic canal measurements are shown in Fig. 1. Consid-ering �0.5mm of error variation, 2 mistaken electronic readingswere found in the Root ZX and Mini Apex Locator. In both cases, theerrors were found in 1 unflared and 1 preflared canals. Four mistakenelectronic readings were found in the Elements Diagnostic Unit andApex Locator device, 2 unflared and 2 preflared canals. For ApexDSP, 13 and 5 mistaken readings were found in unflared and preflaredcanals, respectively. The mean of the distance of mistaken measure-ments was 1mm short to the working length for the Root ZX, Mini

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Apex Locator, and Elements Diagnostic Unit and Apex Locator in un-flared and preflared canals. For Apex DSP, the range was the samefor unflared and preflared canals, 0.7–2.3mm short to the workinglength. All mistaken measurements were positioned behind the apicalforamen. Chi-square test showed that there was no significant differencein acceptable measurements for unflared and preflared canals,irrespective of the device used (P > .05). The preflared procedureincreased the number of precise measurements for all the EALs evalu-ated (Fig. 1), but this difference was significantly higher for the Root ZXand the Mini Apex Locator devices (P < .05). Fisher test indicated differ-ences in accuracy between Apex DSP and the other devices (P < .05).

DiscussionThe working length should preferably end at the apical constric-

tion, which is the landmark for instrumentation (3, 19). Preflaring ofthe root canal during endodontic treatment is important to removecervical dentin interferences. Consequently, it allows the file to easilyreach the apical constriction (13, 14) and avoid changes in the workinglength. The coronal preflaring procedure is commonly advocated toteach different instrumentation techniques (20), which includenickel-titanium rotary systems (21). In addition, Ibarrola et al (14)stated that this procedure increases the accuracy of the Root ZX device.Despite several studies that indicate a high accuracy of different devicesfor electronic measurements of the working length (10, 22–24), it isunclear whether preflared root canals might affect the precision ofthe EALs used in this study.

Different ranges have been used in the evaluation of accuracy ofEALs. Diverse studies have usually considered the electronic measure-ments for the minor constriction between 0.5mm (9) or 1mm marks(16, 17). This variation is acceptable because microscopic studies re-vealed that this landmark might be positioned on this range (2). In vivostudies have shown that the Root ZX device can precisely locate theminor diameter within 1mm (22, 23). The�0.5mm of error variationwas established to let the working length be close to the apical constric-tion and to avoid being beyond the apical foramen, which will notcontribute to success in endodontic treatment (3).

Diverse studies have considered different precision ranges to eval-uate the EAL within �0.5mm (19, 22, 23, 25), whereas others use�1mm (26, 27). The precise measurements could not be achievedin more than 40%–47% of the unflared cases (28), which is consistent

Influence of Preflaring on Accuracy of EALs 1301

Basic Research—Technology

with the results of the present study. The tolerance chosen in this study isconsidered clinically acceptable and highly accurate (6, 28). This isimportant because those specific ranges of �0.5mm or �1mm mightlead to an accuracy variation between 82.3% (19) to 100% (23). Thus,the precision of some EALs can be overestimated.

In this study different criteria were established to attempt morereliable interpretations of the electronic readings. The number ofprecise readings was superior in the preflared canals for all devicestested, increasing for acceptable readings by using a�0.5-mm toler-ance range (Fig. 1). Our data are in agreement with those of Ibarrolaet al (14), which observed a better performance on the Root ZX apexlocator in the preflared mandibular molar canals.

The accuracy among the apex locators used is similar to the resultsof other studies: Root ZX (17), Elements Diagnostic Unit and ApexLocator (17, 29), and Mini Apex Locator (9, 10). The Apex DSP wasimpossible to compare with other studies because of the lack of similarstudies. However, lower accuracy for the Apex NRG, a similar devicebased also in the digital signal processing technology, had been foundin other in vitro studies that included retreatment (30), foramen vari-ation (16), and simulated root fractures (31).

ConclusionThe Root ZX and the Mini Apex Locator devices increased signif-

icantly the precision to determine the real working length after the pre-flaring procedure. All the EALs showed an acceptable determination ofthe working length between the ranges of�0.5mm except for the ApexDSP device, which had the lowest accuracy.

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