• Users Online: 112
  • Home
  • Print this page
  • Email this page
Home About us Editorial board Ahead of print Current issue Search Archives Submit article Instructions Subscribe Contacts Login 

 Table of Contents  
Year : 2017  |  Volume : 29  |  Issue : 2  |  Page : 125-129

Accuracy of two different apex locators for working length determination during root canal retreatment of mandibular molars using two different retreatment files: An in vitro study

Department of Conservative Dentistry and Endodontics, Bhojia Dental College and Hospital, Baddi, Solan, Himachal Pradesh, India

Date of Web Publication6-Nov-2017

Correspondence Address:
Ajay Chhabra
Department of Conservative Dentistry and Endodontics, Bhojia Dental College and Hospital, Baddi, Solan - 173 205, Himachal Pradesh
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/endo.endo_29_17

Rights and Permissions

Aim: The aim of this study was to determine the accuracy of two different apex locators for measurement of working length during root canal retreatment of mandibular molars with two different file systems in an ex vivo study.
Materials and Methods: Sample consisting of sixty extracted mandibular first molars was selected. Tooth length was measured with a file. Biomechanical preparation of the roots was done with Protaper files 1mm short of the tooth length. Canals were coated using AH Plus sealer and were obturated with gutta percha. Obturating material was removed after one week with two files i.e Protaper and Mtwo retreatment files. Tooth length was remeasured and recorded as the retreatment tooth length (RTL). Then electronic measurements were taken with Root ZX and Apex ID apex locator as suggested by the instrument display. These lengths were compared with RTL at 0.5 and 1 mm short of this distance.
Results: For both canals, no significant difference was found between RTL and EAL measurements with Root ZX apex locator and protaper retreatment files. There was a significant difference between Apex ID apex locator with M2 retreatment files readings.
Conclusion: Root ZX apex locator was more accurate as compared to Apex ID apex locator in determining the working length in teeth after removing the root canal obturating material using two different files.

Keywords: Apex ID apex locator, Mtwo retreatment files, ProTaper retreatment files, retreatment, Root Zx apex locator, working length

How to cite this article:
Chhabra A, Bhatia R, Garg N, Sharma S, Dogra A, Jhamb A. Accuracy of two different apex locators for working length determination during root canal retreatment of mandibular molars using two different retreatment files: An in vitro study. Endodontology 2017;29:125-9

How to cite this URL:
Chhabra A, Bhatia R, Garg N, Sharma S, Dogra A, Jhamb A. Accuracy of two different apex locators for working length determination during root canal retreatment of mandibular molars using two different retreatment files: An in vitro study. Endodontology [serial online] 2017 [cited 2021 Apr 11];29:125-9. Available from: https://www.endodontologyonweb.org/text.asp?2017/29/2/125/217712

  Introduction Top

Working length plays an important role during endodontic treatment. It helps in complete removal of the debris from the canal and is considered to be the most critical juncture of successful therapy.[1] Canal preparation is ideally done and filled to the minor foramen which is considered to be the narrowest point of the canal. At this point, there is a minimum diameter and has innate repair potential.[2] There are various methods for determination of working length, of which radiographic is generally accepted. This method has a disadvantage that it cannot determine the apical constriction; however, with the introduction of the electronic apex locators, this problem can be solved as it works on the electronic principle and can determine the treatment and retreatment working length up to the minor foramen.[3] Although many studies have been conducted on apex locators, there are no evidences of studies comparing efficacy of two retreatment files along with two apex locators. This study aims to evaluate the accuracy of Root ZX and Apex ID apex locators for retreatment working length determination in the molar root canals.

  Materials and Methods Top

The present study was conducted in the Department of Conservative Dentistry and Endodontics at Bhojia Dental College and Hospital. Our sample constituted of 60 extracted mandibular first molars. Teeth with three canals (canals were tentatively checked with radiographs and were confirmed after access opening), morphologically normal, and no evidence of fracture or resorption were included in the study while teeth with carious roots, external or internal root resorption, and open apex roots were excluded from the study. With the use of ultrasonic scaler, external debris was removed. Expedious bur (Mani, Tochigi, Japan) was used for access preparation and Endo Z bur (Dentsply Tulsa Dental Specialties; Tulsa, Oklahoma, USA) for refinement was used. Decoronation was done at the cementoenamel junction following access preparation as it provides a stable horizontal reference point for measurement of working length. Size #15 K-file (Mani, Tochigi, Japan) was used for pulp debridement. Irrigation protocol was followed using 3% sodium hypochlorite (Dentpro, India). ×2.5 loupes were used for calculating length of mesiobuccal and distal root with #15 K-file which was advanced until it appeared at the apical foramen. Silicon stop was accustomed at the reference point and the length between stop and tip was calculated using Vernier caliper to the nearest 0.5 mm. After repeating measurements for three times by two individuals, their mean value was calculated. This length achieved is called as tooth length (TL) and after deducting 1 mm, the length established is the working length. ProTaper files were used for biomechanical preparation. For working in the middle-third of the root, shaping files S1 and S2 were used followed by finishing file F1 keeping in mind the manufacturers guidelines. Ethylenediaminetetraacetic acid paste was used to smear the files before introducing them into canal. 2 ml of 3% NaOCl was flushed into canal during preparation. Paper points were used for drying the canals and were then obturated with F1 gutta percha points which were coated with AH Plus sealer using single-cone technique. Cavity was closed with cavit and teeth were stored in 100% moisture for 7 days. Two different rotary files were used for retreatment after 7 days and accordingly samples were divided into two groups.

Group I: With the help of ProTaper retreatment files, obturating material was removed from the canal. Removal from coronal third was done with D1 file while D2 file was used for the removal from the middle and D3 to the working length.

Group II: Mtwo retreatment files were used for the removal of obturating material. Two files 15/0.5 and Mtwo retreatment files 25/0.5 were used up to the working length. 3% NaOCl was used for irrigation after the removal of material from the canals. With #15 K-file, mesiobuccal and distal root was remeasured with silicon stop adjusted to the reference point and distance from stop till the file tip was measured with Vernier caliper to the closest to 0.5 mm. Two individuals repeatedly measured each tooth thrice and calculated its mean. Working length after removing the material was obtained by deducting 1 mm from the TL. With the help of radiographs, amount of gutta percha remained in the canal was calculated. Next, to the setting alginate, roots were embedded with their apical third submerged into the alginate and the lip clip of the apex locator was placed into the setting alginate so that the circuit of apex locator can be completed. These groups were further divided into subgroups:

  • Subgroup I: Root ZX apex locator was used for the measurement of working length
  • Subgroup II: Apex ID apex locator was used for measuring the working length.

Working length determination using Root ZX and Apex ID apex locator

For Root ZX apex locator, #15 K-file was used for the measurement of working length till the lowermost part of the green bar on the apex locator screen. For Apex ID apex locator, measurements were taken when the display on the screen showed “0.” The length between the stopper and file tip was measured and these readings for each tooth were repeated three times by two operators and the values were recorded. Complete procedure was performed within 2 h. These values were compared with the retreatment TL.

  Results Top

Data were calculated in the tabulated form and were subjected to statistical analysis [Table 1]. One-way ANOVA test was used to evaluate the values which revealed the mean difference values of SBIA, SBIIA, SBIB, and SBIIB to be 0.93, 0.33, 0.03, and 0.10 and the standard deviation for SBIA, SBIIA, SBIB, and SBIIB to be ±0.21, ±0.40, ±0.12, and ±0.02, respectively. These results were then evaluated with post hoc test which showed no significant difference in Apex ID with Mtwo retreatment files, but a significant difference was seen in the Root ZX apex locator and ProTaper retreatment files. Difference of Apex ID with Mtwo retreatment files was −0.3000 with P = 0.015 and that for Root ZX with ProTaper retreatment files was −0.0100 with P = 0.015 [Table 2].
Table 1: Mean difference and standard deviation of working length determination between subgroups

Click here to view
Table 2: Mean difference between retreatment working length in subgroups

Click here to view

[Graph 1] shows mean difference between working length calculated with Vernier caliper and apex locator.

[Graph 2] shows mean difference between working length calculated with Vernier caliper and apex locator after retreatment of the tooth.

  Discussion Top

Apex locator is based on the principle that certain features of human tissue can be designed using electrical components, These features can be determined by completing the electric circuit.[4] In number of studies performed on apex locator, teeth with single straight canals were used. We selected canals from mandibular molars so that more exacting model can be generated. Another reason was that mesiobuccal root of mandibular molar is more constricted, irregularly formed, and is a complicated structure as compared to the teeth with single canal. Reason for selecting the distal canal was to create standardization. 3% sodium hypochlorite was used to immerse teeth so as to remove soft or hard tissue tags present on the root surface. Crowns were removed to generate a horizontal reference point.[5],[6],[7]

Access opening was done after preparing reference surface and working length was measured with the help of Vernier caliper. The preparation of the root canal was done to the F1 ProTaper universal file size.

Peters et al. have shown that ProTaper file does not have U-shaped design and because of the presence of variable taper on its working end, it minimizes the number of instrument per se t, also claims that there is a reduction in the torsional load that decreases the frictional surface resulting in the decrease in the effectiveness of cutting of the instrument.[8] Using single-cone technique root canals were filled with F1 gutta percha. AH plus sealer was used to smear the canal and gutta percha cone before sealing it into the canal. The advantage of using single-cone technique is that the master cone best matches the geometry of nickel titanium rotary files. Sealing canal with single cone and sealer helps in formation of a single mass that does not result in failure as seen in multiple cone technique.[9],[10],[11],[12] Because of the presence of less shrinkage during setting and long-term stability, resin-based sealer (AH Plus) was preferred. To generate conditions similar to the oral cavity and to establish total setting of the sealer, teeth were immersed in 100% moisture postobturation for 1 week.[13],[14],[15],[16],[17]

Wilcox and Juhlin in their study showed that the detection and removal of obturating material which gets deposited on the walls of root canal is difficult if solvent is used.[18] It may also hamper the antimicrobial properties of irrigants, and increase operating time, therefore using two file systems, i.e., ProTaper and Mtwo retreatment files were used for removing obturating material from the canals.[18],[19] ProTaper retreatment files constitute three files that have an active tip which aid in initial entrance into the obturating material during its removal. According to the manufacturer's recommendations, D1 and D2 should be used for preparation of coronal and middle-third while D3 was used up to the working length. Mtwo retreatment file system constituting two instruments of size 15 and 25 with 0.5% taper and two blades of S-shaped cross section with an active tip claims easy entrance into the obturating material. The findings of this study are in accordance with the study done by Marfisi et al. showed that because of the presence of S-shaped cross section and a shorter pitch length, it becomes easy to penetrate into the root canal material. Mtwo retreatment files have inferior properties as compared to ProTaper retreatment files because of the presence of two cutting edges which aggressively cuts the dentin.[20],[21]

In the present study, Root ZX showed better results as compared to Apex ID, possibly because the residual root filling material occluding the dentinal tubules predisposes to a reduction in electrical conductivity and an increase in impedance, a factor potentially enhancing the electrical detection of the apical file. Working length determined by the Root ZX before obturating the root canals and after removing the root fillings was not significantly different.[22]

When the result of ProTaper and Mtwo retreatment system was combined with that of the Root ZX and Apex ID apex locator, Root ZX with ProTaper retreatment files proved to have better results as compared to Apex ID with Mtwo retreatment files with significant values as it does not aggressively cut the dentin during retreatment thus does not alter the apical constriction as compared to the Mtwo retreatment files which cuts the dentin aggressively during the removal of the gutta percha during retreatment of the tooth thus alters the position of the apical constriction. Chirila et al. in their study also showed that Root ZX (third generation) apex locator is more accurate than Apex ID (fourth generation) apex locator. The accuracy of Root ZX was found to be 98.28% while that of Apex ID apex locator was 86.66% ±0.5 mm from the actual length.[23],[24]

  Conclusion Top

The apex locators can be successfully used to determine the working length in endodontic retreatment. Under the conditions of ourin vitro study, ProTaper retreatment files left significantly lesser gutta percha and root canal sealer as compared to Mtwo retreatment files and hence, proved to be more efficient than Mtwo retreatment files. Under the parameters of our study, Root ZX apex locator was more accurate as compared to Apex ID apex locator in determining the working length in teeth after removing the root canal obturating material.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Nasil S, Asifulla M, Chandra V, Idris M, Razvi FS, Geeta IB.In vitro evaluation of the accuracy of five different electronic apex locators. Saudi Endod J 2015;5:177-81.  Back to cited text no. 1
Cimilli H, Aydemir S, Ancan B, Mumcu G, Chandler N, Kartal N. Accuracy of the Dentaport ZX apex locator for the working length determination when retreating molar root canals. Aust Dent J 2014;40:2-5.  Back to cited text no. 2
Gordon MP, Chandler NP. Electronic apex locators. Int Endod J 2004;37:425-37.  Back to cited text no. 3
Shanmugaraj M, Nivedha R, Mathan R, Balagopal S. Evaluation of working length determination methods: An in vivo/ex vivo study. Indian J Dent Res 2007;18:60-2.  Back to cited text no. 4
[PUBMED]  [Full text]  
Masiero AV, Barletta FB. Effectiveness of different techniques for removing gutta-percha during retreatment. Int Dent J 2005;38:2-7.  Back to cited text no. 5
Tilakchand M, Malu KN, Kidiyoorc KH. Evaluation of accuracy of two electronic apex locators Viz Propex-II and elements apex locator: An in-vitro study. IJDA 2010;2:327-31.  Back to cited text no. 6
Santhosh L, Raiththa P, Aswathanarayana S, Panchajanya S, Reddy JT, Susheela SR. Influence of root canal curvature on the accuracy of an electronic apex locator: Anin vitro study. J Conserv Dent 2014;17:583-6.  Back to cited text no. 7
  [Full text]  
Peters OA, Peters CI, Schönenberger K, Barbakow F. ProTaper rotary root canal preparation: Effects of canal anatomy on final shape analysed by micro CT. Int Endod J 2003;36:86-92.  Back to cited text no. 8
Pereira AC, Nishiyama CK, Pinto LC. Single cone obturation technique: A literature review. RSBO 2012;9:442-7.  Back to cited text no. 9
Sadr S, Golmoradizadeh A, Raoof M, Tabanfar MJ. Microleakage of single-cone gutta-percha obturation technique in combination with different types of sealers. Iran Endod J 2015;10:199-203.  Back to cited text no. 10
Katalinic I, Baraba A, Glavicic S, Segovic S, Anic I, Miletic I. Comparison of vertical forces during root canal filling with three different obturation techniques. Coll Antropol 2013;37:895-9.  Back to cited text no. 11
Pitout E, Oberholzer TG. Leakage of teeth root-filled with GuttaFlow and a single GP cone compared to lateral condensation and warm vertical condensation. SADJ 2009;64:104, 106-8.  Back to cited text no. 12
Nunes VH, Silva RG, Alfredo E, Sousa-Neto MD, Silva-Sousa YT. Adhesion of Epiphany and AH Plus sealers to human root dentin treated with different solutions. Braz Dent J 2008;19:46-50.  Back to cited text no. 13
Ozok AR, van der Sluis LW, Wu MK, Wesselink PR. Sealing ability of a new polydimethylsiloxane-based root canal filling material. J Endod 2008;34:204-7.  Back to cited text no. 14
Fisher MA, Berzins DW, Bahcall JK. Anin vitro comparison of bond strength of various obturation materials to root canal dentin using a push-out test design. J Endod 2007;33:856-8.  Back to cited text no. 15
Ungor M, Onay EO, Orucoglu H. Push-out bond strengths: The Epiphany-Resilon endodontic obturation system compared with different pairings of Epiphany, Resilon, AH Plus and gutta-percha. Int Endod J 2006;39:643-7.  Back to cited text no. 16
Gesi A, Raffaelli O, Goracci C, Pashley DH, Tay FR, Ferrari M. Interfacial strength of Resilon and gutta-percha to intraradicular dentin. J Endod 2005;31:809-13.  Back to cited text no. 17
Wilcox LR, Juhlin JJ. Endodontic retreatment of Thermafil versus laterally condensed gutta-percha. J Endod 1994;20:115-7.  Back to cited text no. 18
Erdemir A, Eldeniz AU, Belli S, Pashley DH. Effect of solvents on bonding to root canal dentin. J Endod 2004;30:589-92.  Back to cited text no. 19
Marfisi K, Mercade M, Plotino G, Duran-Sindreu F, Bueno R, Roig M. Efficacy of three different rotary files to remove gutta-percha and Resilon from root canals. Int Endod J 2010;43:1022-8.  Back to cited text no. 20
Alothmani OS. The accuracy of Root ZX electronic apex locator. Saudi Endod J 2012;2:115-28.  Back to cited text no. 21
  [Full text]  
Plotino G, Grande NM, Brigante L, Lesti B, Somma F. Ex vivo accuracy of three electronic apex locators: Root ZX, elements diagnostic unit and apex locator and ProPex. Int Endod J 2006;39:408-14.  Back to cited text no. 22
Welk AR, Baumgartner JC, Marshall JG. Anin vivo comparison of two frequency-based electronic apex locators. J Endod 2003;29:497-500.  Back to cited text no. 23
Chirila M, Scarlatescu SA, Nistor CC, Moldoveanu GF. The accuracy of working length determination during endodontic retreatment. J Oral Rehabil 2011;3:63-7.  Back to cited text no. 24


  [Table 1], [Table 2]


Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

  In this article
Materials and Me...
Article Tables

 Article Access Statistics
    PDF Downloaded241    
    Comments [Add]    

Recommend this journal