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 »  Home  »  Endodontic Articles 2  »  Accuracy of a new apex locator: an in vitro study
Accuracy of a new apex locator: an in vitro study
Introduction - Materials and methods.



Introduction.
Recently, electronic methods for tooth length determination have gained popularity. Many studies report on the accuracy achieved by the new generation of electronic apex locators (EALs) as well as their extended measurement capabilities, which include accurate measurements in the presence of electrolytes (Fouad et al. 1993, Frank & Torabinejad 1993, Mayeda et al. 1993, Kobayashi 1995). Moreover, it has been reported that radiographic methods for tooth length determination might be less accurate than the electronic method (Stein & Corcoran 1992).
Most studies on EALs using two frequencies (the third generation) report accuracy rates of 85–95% (Fouad et al. 1993, Frank & Torabinejad 1993, Mayeda et al. 1993, Weiger et al. 1999). Recently, a new apex locator, Bingo 1020 (Forum Engineering Technologies, Rishon Lezion, Israel) has been introduced (Fig. 1). The manufacturer claims that this apex locator may be regarded as the fourth generation of EALs. Similar to the third generation of EALs, the device uses two separate frequencies, 400 Hz and 8 KHz, produced by a variable frequency generator. Unlike the latter devices, the Bingo 1020 uses only one frequency at a time. The use of a single frequency signal eliminates the need for filters that separate the different frequencies of the complex signal. This prevents the noise inherent in such filters and increases measurement accuracy. In addition, the calculations of the position of the file tip in Bingo 1020 are based on measurements of root mean square (RMS) values of the signals. RMS expresses the energy of the measured signal and is more immune to various noises or signal distortions than other parameters of the signal, such as amplitude or phase, that are used in other devices. The manufacturers claim that the combination of these two techniques increases the measurement accuracy and the reliability of the device (Apex Locator Bingo-1020 1999). However, these claims have not been substantiated.

Bingo 1020 EAL
Figure 1. The Bingo 1020 EAL.

Alginate model with embedded teeth
Figure 2. Alginate model with embedded teeth.

The objectives of the present study were to test the Bingo 1020 in an in vitro model and to compare its accuracy to the actual tooth length, to another apex locator (Root ZX, Morita, Tokyo, Japan), and to results obtained radiographically.

Materials and methods.
A total of 120 extracted multi- and single-rooted teeth, preserved in Thymol solution and kept refrigerated, was used for the study. Access cavities were prepared (Tungsten carbide 1157, SS White Burs, NJ, USA) and in each multirooted tooth, one canal was randomly chosen for study. The actual length (AL) was measured with the aid of a binocular microscope ( 5) (Wild M-8, Leitz LTD, Heerbrugg, Switzerland) by introducing a no. 10 or no. 15 K-file until it emerged in the apical foramen. Each measurement was repeated three times and the mean value computed.
Teeth were divided randomly into 12 groups of 10 teeth each, which were then embedded in an alginate model specially developed to test apex locators (Kaufman & Katz 1993). The model consisted of a plastic box (lid of a photograph slide box, 10 3 3 cm). When not in use, the model was wrapped with a wet paper and refrigerated to keep it in a moist environment throughout the experiment (45 days). Previous studies have shown that keeping the model in such an environment was satisfactory (Kaufman & Katz 1993). Each tooth was glued (Superglue-3, Loctite Corp, Ireland) to a plastic frame taken from a box of dental carpules (Tevacaine, Teva, Jerusalem, Israel) to form a group of 10 teeth. Alginate (Blue Print normal set, Dentsply, Weybridge, UK) was poured into the box and the frame with the teeth was embedded into the alginate. At the inner rear side of the box, a periapical radiograph was inserted to create a space that could accommodate radiographs taken at a later stage (Fig. 2).

Flowchart of the experiment
Figures 3. Flowchart of the experiment.

Figure 3 is a flowchart depicting the study design. Prior to root canal preparation, electronic tooth length (EL) measurements were carried out as follows: EL measurements of 60 teeth with the Root ZX were recorded followed by Bingo 1020, whilst on the other 60 teeth, the order was reversed. The ‘apex’ as indicated by both devices was chosen as the apical reference. Measurements were repeated three times and the average was calculated and computed. After the third measurement, the file was left in the root canal and a periapical radiograph taken under standardized conditions: Oralix 65 S, 220, 240 V, 5 A (momentary load) 5-/60 Hz, exposure time 0.4 s, exposure distance 12.5 Cm (Kodak Ektaspeed, Safety EO-41 Film, Rochester, NY, USA), developing time was 4 min and fixing time was 8 min (Adefo, Nuremberg, Germany). The radiographic length (RL) was determined by measuring the file on the radiograph from the coronal reference point to the tip of the file. The RL was compared to the third EL measurement only.
Each root canal was prepared using a standardized technique to a no. 40 K-file diameter (Zipperer, Munich, Germany). RC-Prep (Premier, Norristown, PA, USA) was used for lubrication and saline for irrigation. After root canal preparation, EL measurements were taken with various irrigants in the root canals:

  • dry root canals;
  • 3% NaOCl;
  • saline;
  • 0.2% chlorhexidine (Tarodent, Taro Pharmaceutical Industries Ltd, Haifa Bay, Israel);
  • 17% EDTA;
  • Xylol.

Each group contained 20 roots divided into two subgroups. In the first subgroup, EL measurements were taken using the Bingo 1020 followed by the Root ZX; in the second, the order was reversed. Each measurement was repeated three times and the average was calculated and computed. This average was used to compare the accuracy of each EAL and between the two devices. The third measurement was recorded radiographically, as mentioned previously.
Results were subjected to statistical analysis as follows:

  1. Effect of the order of use of the EALs on the results ( anova ) with repeated measurements.
  2. Comparison between the AL and the initial electronic measurements before preparation of the root canal (paired t -test).
  3. Comparison between the AL and the EL obtained by each EAL after completion of canal preparation in the presence of the various irrigants (post hoc test Tukey’s methods).
  4. Comparison between the AL, the RL and the EL before and after preparation of the root canal ( anova with repeated measurements).
Article Series
This article is part 1 of a 3 part series. Other articles in this series are shown below:
  1. Accuracy of a new apex locator: an in vitro study
  2. The capability of two hand instrumentation techniques to remove the inner layer of dentine in oval canals
  3. Evaluation of smear layer removal by EDTAC and sodium hypochlorite with ultrasonic agitation