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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 12  »  A simple model to demonstrate the electronic apex locator
A simple model to demonstrate the electronic apex locator
Introduction - Materials and methods.

A.C. Tinaz, T. Alacam & O. Topuz
Department of Operative Dentistry and Endodontics, Faculty of Dentistry, Gazi University, Ankara, Turkey.

Electronic root canal length measuring devices should be validated for accuracy and reliability in vitro before clinical use. Reliable in vitro models are also needed for teaching. Such a model was described by Aurelio et al. (1983) who tested three electronic devices.  This model employed agar (Bacto-Agar; Difco Laboratory, Detroit, MI, USA; 2 g in 100 mL of phosphate buffered saline containing NaCl, 9 g; NaHPO4_H2O, 1.43 g; KH2PO4, 0.18 g; and H2O, 1 L) poured molten into a polystyrene culture tube unit, the test tooth being secured with a snap cap assembly. After setting the agar in a refrigerator, a 0.5-in. nail was placed through the base of the tube for attachment of the lip clip, whilst the other electrode was attached to an endodontic instrument in the usual way.
Donnelly (1993) suggested a simplified and less expensive model using sugar-free Jell-O (Kraft General Foods Inc., White Plains, NY, USA) mixed with 0.9% sodium chloride USP (Travenol Laboratory Inc., Deerfield, IL, USA) in 100-mL plastic specimen cups. After refrigeration to jell the liquid, a metal lip clip was placed into the gel and secured with wax. The test tooth was held in place by the dentist.
Katz et al. (1992) described a simpler model where teeth were embedded in alginate in a small plastic box. The teeth were embedded to CEJ level and the lip clip inserted before setting. This study was designed to construct and validate a further simple model for demonstrating, teaching and possibly testing electronic apex locators.

Materials and methods.

Three single-rooted human premolar and canine teeth with single root canals were chosen for study. Before the tests, teeth were stored in formalin solution (10%) and placed into 5.25% sodium hypochlorite solution for 2 h to remove the periodontal ligament. After rinsing in tap water they were transferred again to formalin solution. Standard access cavities were established and actual lengths determined with a size 10 K- file (Zipperer UDM, West Palm Beach, FL, USA) fitted with a rubber stop and inserted until the tip was just visible at the apical foramen. The distance from file tip to the base of the rubber stop was measured with a caliper to the nearest 0.02 mm. The model was tested with these three teeth in six different ways: Groups 1 and 4 comprised of a second premolar prepared with a size 15 reamer until the tip was visible 1 mm through the apical foramen to obtain an apical opening of 0.20 mm diameter. Groups 2 and 5 comprised of a first premolar prepared similarly with a size 25 reamer to produce a 0.30-mm opening. Groups 3 and 6 comprised of a canine prepared with a size 40 reamer to obtain an apical diameter of 0.45 mm. Groups 1–3 were irrigated with 2.65% NaOCl; groups 4–6 were irrigated with 5.25% NaOCl whilst making electronic measurements.

The mandibular premolars and canine were removed from their sockets in a plastic master model (Frasaco, Tettnang, Germany). The sockets were enlarged with a bur until the human teeth could be adapted and fitted easily (Fig. 1). Alginate (Blue-print, De Trey, Surrey, UK) was prepared according to the manufacturer’s instructions and packed into the sockets for immediate tooth insertion. More material was then placed under the master model and the lip clip electrode inserted (Figs 2 and 3). Excess alginate around the teeth and master model was removed with a knife before mounting the model in a phantom head. The apex locator (Root ZX, Morita, Tokyo, Japan) was then connected to the lip electrode. All root canals were irrigated with 2.65% NaOCl and canal lengths determined electronically with size 20 K-files (group 1), size 30 K-files (group 2), and size 45 K-files (group 3). Files were inserted slowly until the signal on the LCD screen display’s bar reached the ‘0.5’ mark, indicating the apical foramen (Kobayashi & Suda 1994). Measurements were repeated thrice and the whole procedure repeated every 3 h up to 45 h. After each series of measurements, canals were dried with paper points sizes 25–40 (Roeko, Langenau, Germany). After testing with 2.65% NaOCl, the same canals were irrigated with 5.25% NaOCl and lengths established in a similar manner. Records were made as previously for groups 4–6 for teeth with foramen diameters of 0.20, 0.30 and 0.45 mm. Measurements within 1–13 h were designated Period A. Period B included measurements during 16–28 h and Period C measurements during 31–45 h (Table 1). All electronic measurements were made at 19–248C and the model kept in 100% humidity throughout the investigation. Statistical evaluation was completed using the Analysis of Variance and Turkey multiple range test (P = 0.05).

Figure 1. Human teeth fitted to their sockets on the master model.

Human teeth fitted to their sockets on the master model

Figure 2. Lip clip inserted into unset alginate.

Lip clip inserted into unset alginate

Figure 3. The model ready for use.

The model ready for use

Table 1. Results of the electronic measurements in different concentrations of NaOCl and different time periods.

Results of the electronic measurements in different concentrations of NaOCl and different time periods