Endodontics

The Accuracy of the Neosono Ultima EZ Apex Locator Using Files of Different Alloys: An In Vitro Study

M.H. Nekoofar; K. Sadeghi; E. Sadighi Akha; M. Sadegh Namazikhah, DMD

Copyright 2002 Journal of the California Dental Association.

About the Authors: M.H. Nekoofar, K. Sadeghi, and E. Sadighi Akha are with the Dental Faculty, University of Medical Science in Tehran, Iran.

M. Sadegh Namazikhah, DMD, is in private practice in Woodland Hills, Calif.

The purpose of this study was to compare the precision of the new generation of root canal measuring devices, Neosono Ultima EZ, while using files manufactured of different alloys. Fifty-four root canals of extracted teeth were chosen. They were placed in special tubes with roots immersed in 2 percent agar with phosphate buffered saline. The device was used to locate the apex of each canal in wet conditions at the zero digital reading, first using a stainless steel file and then using a nickel-titanium file. These values were compared to the actual lengths obtained by measuring the distance of the coronal reference point to the apical opening with a size 10 file minus 0.5 mm. The accuracy of the device was 94 percent with nickel-titanium files and 91 percent with stainless steel. No significant difference was noted between the results for either file. The accuracy of the Neosono Ultima EZ in wet conditions exceeded 90 percent regardless of the alloy used.

Successful root canal therapy depends upon complete and accurate biomechanical preparation followed by a three-dimensional obturation of the root canal system without injuring the periapical tissue.¹ To attain these objectives, the endpoint of the root canal system should be detected carefully prior to preparation of the canal. The ideal apical endpoint of a root canal is considered to be the apical constriction or cementodentinal junction of a tooth with completed root formation.²

Although radiography is an indispensable part of endodontic therapy and is used in a variety of ways to determine working length, techniques formulated to calculate it have not been shown to be accurate due to technical limitations. Moreover, the operation takes a considerable amount of time. In addition, patients, particularly those who are pregnant, increasingly express concern about the possible hazards of radiation exposure.

Because of the technical problems, time consumed, and hazards of radiation, the technique of electronic working length determination has recently gained considerable popularity among both general dentists and endodontists.

The scientific rationale for the function of electronic root canal length measuring instruments is based on pioneer studies by Suzuki (1942) and Sunada (1962). The latter found that the electrical resistance between periodontium and oral mucosa is constant at approximately 6.5 kΩ regardless of the age of the patient or the type or shape of the tooth.³ On the basis of this concept, resistance-type apex locators were manufactured and introduced into the market.

Further development of apex locators has resulted in units that operate by measuring changes in impedance across the wall of the root canal by applying two different frequencies to a file and measuring the difference between them. As a file is advanced apically, the difference in the impedance values begins to become greater and is maximally different at the apical constriction.⁴

Manufacturers claim that third-generation apex locators locate the apical foramen in the presence of moisture, pulp tissue, blood, exudates, or solutions such as sodium hypochlorite or EDTA. They also claim that no special instruments are necessary to operate the device; a standard endodontic file is used as the intracanal probe.⁵

Dental literature is replete with studies evaluating the influence of pulp status,^6,7 tooth type,⁸ apical foramen diameter,⁹ type of irrigation solution,¹⁰ size of the master apical file,¹¹ and recapitulation¹² on the accuracy of apex locators.

For this study, a third-generation electronic apex locator, Neosono Ultima EZ (Amadent, U.S.) was chosen. The purpose of this study was to evaluate the reliability of the apex locator in a moist environment in an experimental model while using files manufactured of different alloys.

Materials and Method

Experimental Device

Ultima EZ, a dual-circuitry third-generation apex locator, was chosen (Figure 1). This particular apex locator uses multiple frequency technology for measurements in wet conditions and a second resistance-based circuitry for measurements in dry canals. The locator has a digital distance readout and an audible indicator for determining when the desired point in the canal has been reached.

Experimental Model

The in vitro model used in this experiment was introduced by Aurelio and Nahmias.¹³ It consisted of a polystyrene tube containing 2 percent agar in phosphate-buffered saline with the roots of extracted teeth immersed in the medium, and the crowns fitted at the cervical area in a opening in the cap of the tube. A 3/4-inch nail extended from the medium through the sides of the tube, acting as an electrode.

Experimental Group

Fifty-four root canals of extracted human teeth were selected. They were constantly hydrated during storage. The teeth were soaked in 5.25 percent sodium hypochlorite for three hours to remove periodontal ligament. Stains and calculi were removed with scalers and curettes. The teeth were inspected for root fractures and evidence of incomplete root formation, and any suspect teeth were discarded.

Method

The incisal edges of each tooth were ground lightly with a grinding wheel to create a flat surface to simplify length measurements. A coronal access opening for each tooth was created in the standard manner. Each tooth was placed into its own experimental model using the method described earlier. Based on the authors’ pilot study, a 2 percent concentration of agar was used; and after 55 seconds, complete moisturizing of the root canals was recorded as a result of seepage of fluid into the canals through the apical foramen. By means of an alligator clip, the lip clip of the unit was connected to the nail at the base of the experiment model.

The apex of each canal was located, first using a stainless steel file (Thomas, France) and then a nickel-titanium file (Nitiflex, Dentsply Maillefer, Switzerland). Each file was slowly inserted into the canal until the digital reading on the apex locator was 0.0. The rubber stop was adjusted to the flattened coronal or incisal tooth surface. The file was then removed from the tooth, and the length was measured to the nearest 0.5 mm. This length was termed the electronic working length. All measurements were verified three times before being recorded. The teeth were then removed from the model, and the file was reinserted into the canal until the tip was just visible at the apical foramen with a magnifier (2x). The rubber stop was placed to the flattened coronal or incisal surface, the file was removed, and the length was recorded to the nearest 0.5 mm. This length minus 0.5 mm was termed the actual root canal length. These values were compared with each other, and the differences were recorded.

Results

Under the conditions of this experiment, using Ni-Ti files, the electronic working length of 66.6 percent of the root canals (36 root canals) was found to equal the actual root canal length. In 14.8 percent (eight root canals), the electronic working length was 0.5 mm shorter than the actual root canal length. In 13 percent (seven root canals) the electronic working length was 0.5 mm longer than the actual root canal length. The endodontic file tip protruded beyond the foramen in 5.6 percent (three root canals). The overextended cases were 1 to 2 mm longer than the actual root canal length. These results show that in 94.4 percent (51 root canals) the Ultima EZ apex locator measurements, using Ni-Ti files, were within ± 0.5 mm of the actual root canal length.

Under the conditions of this experiment, using stainless steel files, the electronic working length of 57.4 percent of the root canals (31) was found to equal the actual root canal length. In 9.25 percent (five root canals), the electronic working length was 0.5 mm longer than the actual root canal length. The endodontic file tip protruded beyond the foramen in one root canal and did not reach the foramen in three root canals. The overextended case was 1 mm longer than the actual root canal length and the underextended cases were 1 mm shorter than the actual root canal length. These results show that in 91.6 percent (50 root canals) the Ultima EZ apex locator measurements, using stainless steel files, were within ± 0.5 mm of the actual root canal length.

The results obtained were compared using the Wilcoxon signed-ranks test. No significant difference was noted between the results for either file.

Discussion

It is general opinion among the dental profession that the preparation of the root canal should ideally be carried out to the CDJ or the apical constriction.² Therefore, accurate determination of the root canal length is a key factor in successful root canal therapy. Modalities employed for this purpose include tactile sensation, radiographic interpretation, and electronic methods.¹

The performances of electronic apex locators have traditionally been afforded some latitude of acceptable error in locating the apex. Thus, radiographic positions within the ± 0.5 mm range to the apex are considered by some investigators as the narrowest acceptable range.¹⁴ Measurements attained within this tolerance are considered highly accurate. Some other studies rely on a more lax clinical range of ± 1.0 mm to the foramen. One reason cited for accepting a ± 1.0 mm margin of error is the wide range seen in the shape of the apical zone. Root canals do not always end with an apical constriction, a well-delineated minor or major apical diameter, or an apical foramen within the base of the cemental canal. Lacking such demarcations, an error tolerance of ± 1.0 mm is deemed clinically acceptable.¹⁵

In this study, when the strictest clinical tolerance was applied, the Ultima EZ device located the apical foramen within ± 0.5 mm in 50 root canals with a clinical accuracy rate of 91.6 percent and in 51 root canals with a clinical accuracy rate of 94.4 percent using stainless steel and Ni-Ti files respectively. The results of this study confirm those obtained by the authors’ previous study⁹ and other investigators’ studies for similar types of electronic apex locators regardless of the alloy used.^5,14,15 In Steffen and colleagues, study measurements obtained with hand files and a Canal Leader handpiece attached to an electronic apex locator are compared. Although in this study the type of file alloy is not taken into account, the results obtained are consistent with the authors’ result.¹⁷ It should be noted that moisture in the canal under the conditions of this study did not affect the results obtained with the Ultima EZ. But the variability observed could be exaggerated in less-controlled clinical conditions. This indicates that radiographic confirmation of master cone placement is still desirable, although the performance of the device is not influenced by the contents of the canals.

This study indicates that the agar/phosphate buffered saline model appears to be an effective model for evaluating the Ultima EZ apex locator and in familiarizing the operators with usage, although the apex locator is operated easily.

Since the Ultima EZ apex locator provides accurate information, it is possible to reduce a patient’s radiation exposure. Additionally, electronic apex locators have advantages over radiographs in several specific applications. These applications include instances in which anatomical structures such as the zygomatic arch, the external oblique ridge, the maxillary sinuses, or adjacent roots impede clear visual interpretation of the apices. The device can also be useful for the pregnant, handicapped, sedated, or gagger patient, and for the patient with malformed or ankylosed jaws in whom it is impossible to obtain radiographs.

Conclusion

The accuracy of the Neosono-Ultima EZ apex locator in wet conditions exceeded 90 percent regardless of the alloy used. The results suggest that the Ultima EZ apex locator has a place in the endodontic armamentarium.

References

1. Walton R, Torabinejad M, Principle and Practice of Endodontics, 2nd ed. WB Saunders Co, 1996.

2. Kuttler Y, Microscopic investigation of root apexes. J Am Dent Assoc 50:544-52, 1975.

3. Sunada I, New method for measuring the length of the root canal. J Dent Res 41:375-87, 1962.

4. McDonald NJ, The electronic determination of working length. Dent Clinic N Am 36(2):293-307, 1992

5. Ounsi HF, Haddad G, In vitro evaluation of the reliability of the Endex electronic apex locator. J Endodont 22(11):616-8, 1996.

6. Mayeda DL, Simon JH et al, Electronic in vivo measurement accuracy in vital and necrotic canals with the Endex apex locator. J Endodont 19:545, 1993.

7. Dunlap CA, Remeikis NA, et al, An in vivo evaluation of an electronic apex locator that uses the ratio method in vital and necrotic canals. J Endodont 24(1):48-50, 1998.

8. Hembrough J, Weine F, et al, Accuracy of an electronic apex locator: A clinical evaluation in maxillary molars. J Endodont 19(5):242-6, 1993.

9. Stein TJ, Corcoran JF, Zillich RM, Influence of the major and minor foramen diameters on apical electronic probe measurements. J Endodont 16(11):520-2, 1990.

10. Jenkins JA, Walker WA, et al, an in vitro evaluation of the accuracy of the root ZX in the presence of various irrigants. J Endodont 27(3):209-11, 2001.

11. Nguyen HQ, Kaufman AY, et al, Electronic length measurement using small and large files in enlarged canals. Int Endodont J 29(6):359-64, 1996.

12. Rivera EM, Seraji MK, Effect of recapitulation on accuracy of electronically determined canal length. Oral Surg Oral Med Oral Pathol 76(2):225-30, 1993.

13. Aurelio J, Nahmias Y, A model for demonstrating an electronic canal length-measuring device. J Endodont 9(12):568-9, 1983.

14. Frank AL, Torabinejad M, An in vivo evaluation of Endex electronic apex locator. J Endodont 19(4):177-9, 1993.

15. Shabahang S, Good WW, Gluskin AH, An in vivo evaluation of Root ZX electronic apex locator. J Endodont 22(11):616-8, 1996.

16. Nekoofar MH, Sadeghi K, Sadighi Akha E, In vitro evaluation of the reliability of Neosono-Ultima EZ apex locator. Int Dent J 50(6):335 [Abstract], 2000.

17. Steffen H, Splieth CH, Behr K, Comparison of measurements obtained with hand files or the Canal Leader attached to electronic apex locators: an in vitro study. Int Endodont J 32(2):103-7, 1999.

To request a printed copy of this article, please contact: M. Sadegh Namazikhah, DMD, MSEd, 6325 Topanga Canyon Blvd., #515, Woodland Hills, CA 91367.

Legends

Figure 1. Ultima EZ dual-circuitry third-generation apex locator.