Determination of location of root perforations by electronic apex locators

Zvi Fuss, DMD, a Levi Shaul Assooline, DMD, b and Arieh Y. Kaufman, DMD, c Tel Aviv, Israel SECTION OF ENDODONTOLOGY, THE MAURICE AND GABRIELA GOLDSCHLEGER SCHOOL OF DENTAL MEDICINE, TEL AVIV UNIVERSITY

Objectives. This study was conducted to evaluate the accuracy of two electronic apex Iocators, the Sono Explorer Mark 2 Junior (Hakusui, Osaka, Japan) and Apit 2 (Osada, Tokyo, Japan) in detecting root perforations. The adequacy of radiographs for identifying root perforations was also assessed. Study design. Thirty-two extracted human teeth were perforated in the middle third of the root and embedded in alginate. Determination of all perforations were carried out with K-files no. 25 attached to the apex Iocators tested. Two radiographs were taken at two angulations after each electronic measurement. The actual location of the file tip in relation to the perforation was determined with a stereomicroscope. A total of 512 radiographs were evaluated to attempt to identify root perforations. Results: The mean distance of the file tip from the external outl ine of the root surface was short for both instruments. A statistical difference (p < 0.05) was found between the two apex Iocators in dry canals or if saline solution was present. There was no significant difference between the two instruments in the presence of sodium hypochlorite. Evaluators radiographically identified 45% of the root perforations when located in buccal-lingual directions. Conclusion. Under the in vitro conditions of this study, both devices determined the location of the perforations in an acceptable clinical range short of the root surface. Radiographs were found to be less reliable in identification of perforation locations. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1996;82:324-9)

Accurate determination of the presence and location root perforations is important. This can prevent over- instrumentation during the root canal treatment and may minimize the chances of extruding irritating ma- terials, such as irrigation solutions or sealers into the surrounding tissues,.t-6 In addition, accurate determi- nation of the perforation can assist in evaluating the prognosis and selecting the proper therapy. 7 Radio- graphic detection toward the buccal or lingual root surface is often impractical because the image of the perforation is superimposed on that of the root. 8 Other disadvantages of the radiographs include the follow- ing: (1) anatomic structures and radiopaque materials may be superimposed on the image of the root; (2) the procedure is time consuming; (3) patients with a gag reflex may inhibit taking radiographs; (4) the accu- racy of the radiographs is limited; and (5) the biologic risks of radiation.

It has been suggested that an electronic apex loca- tor (EAL) can accurately determine the location of

aIn charge, Graduate Endodontic Program. bGraduate student. CAssociate Professor. Received for publication Nov. 22, 1995; returned for revision Jam. 12, 1996; accepted for publication May 7, 1996. Copyright 9 1996 by Mosby-Year Book, Inc. 1079-2104/96/$5.00 + 0 7/15/74877

3 2 4

root perforations?' lo However, no study has evalu- ated the accuracy of the EAL for this purpose. The aim of this study was to determine the location of root Perforations by evaluating the accuracy of two elec- tronic apex locators with differing function and by assessing the adequacy of radiographic identification.

MATERIAL A N D M E T H O D S Two EALs were used. The Sono Explorer Mark 2

Junior (Hakusui, Osaka, Japan) (Fig. 1) also known as Sono Explorer Mark III (Union Broach, York, Pa.). This unit 's mechanism of function is based on the premise that the low frequency oscillation as pr o - duced by the resistance and capacitance between the oral mucous membrane and the gingival sulcus is the same as the frequency between the periodontal l iga- ment at the apical foramen and oral mucous mem- brane, u The device operates on a current of single low frequency. The second EAL was Apit 2 (Osada Tokyo, Japan) (Fig. 2), also known as Endex (Osada Electric Co., Los Angeles, Calif.). This unit uses two different frequencies, 1 KHz and 5 KHz. The differ- ence in the impedance measurements with the two frequencies at different points in the root canal are compared according to the operator 's manual. The operating principle is that impedance measurements between electrodes differ depending on frequencies used especially at the apical constriction.

ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Fuss, Assooline, and Kaufman 325 Volume 82, Number 3

Fig. 2 Apit 2 known in the United States as Endex.

Fig. 1. Sono Explorer Mark II Junior known in the United States as Sono Explorer Mark III.

Thirty-two extracted single and multirooted per- manent intact human teeth preserved in buffer for- malin were selected. Access cavities were prepared in a high-speed contra angle. Canals were instrumented with K-files (Zipperer, Munich, Germany) up to size 45, 1.0 m m short of the anatomical apex with 2.5% sodium hypochlorite (NaC10) as an irrigation solu- tion. Patency of the apical foramen was maintained with K-file size 15 to avoid blockage by dentinal de- bris, which could interfere with the electrical con- ductance. 12

The roots were artificially perforated at the middle third with a no. 25 engine plugger (Zipperer) in a counterclockwise motion until the tip of the instru- ment was shown approximately 1 m m beyond the external root surface. The size of the perforations was 0.27 mm, and the patency was maintained with a size 20 K-file. In the maxillary multirooted teeth, the pal- atal root was perforated, and in the mandibular teeth the distal root was perforated. Roots in the multi- rooted teeth were left in place in order to provide clinical conditions for radiographic identification of the perforations.

The perforated teeth were embedded in a plastic

rectangle box containing freshly mixed alginate powder with water (blue print normal set, Densply Limited Weybridge Surrey, England), according to an in vitro model by Kanfman and Katz. 13 The roots in- cluding the perforations were completely covered under the alginate with the crowns exposed. The boxes were covered throughout the experiment to maintain the humidity of the alginate. For radio- graphic purposes, the teeth were placed in alginate so that the perforations were facing the long axis of the rectangle box (Fig. 3). A periapical film (Ektaspeed, A.N.S.I. size-2 EP-21, Eastman Kodak Co, Roches- ter, N.Y.) was mounted on a posterior bite block of an XCP (Rinn, Elgin, Ill.), and the model was posi- tioned on the block so that the long axis was adjacent to the film. The long cone of the x-ray machine was placed 8 cm from the other long axis of the model facing the perforation. This angulation was recorded as 0 degrees. A second radiograph was taken with the x-ray cone at a 25 degree horizontal shift to the first one. Exposure time was 0.5 second, with 7.5 MA and 65 KVp (Philips Secondente, Monza, Italy).

The root canals were then irrigated with saline so- lution and dried with paper points. Perforations were detected by the EALs under dry conditions according to the manufacturers' instructions with a size 25 K- file. The lip clip of the EAL was attached to the al- ginate in one angle of the model. With the Sono

326 Fuss, Assooline, and Kaufrnan ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY September 1996

Table I. Mean distance of file tip at perforation from external root surface in different conditions of the root canal (n = 32)

Saline solutiOn* NaOCl Dry*

EAL Group Mean (SD) Mean (SD) Mean (SD)

Sono-Explorer A -0.18 (0.11) -0.29 (0.36) -0.17 (0.07) B -0.20 (0.07) -0.24 (0.39) -0.19 (0.15)

Apit (Endex) A -0.34 (0.17) -0.34 (0.29) -0.42 (0.42) B -0.40 (0.28) -0.38 (0.27) -0.37 (0.39)

No significant (p > 0.05) difference between Group A and Group B for each apex locator (paired t test). *Significant (19 < 0.05) difference between the two apex locators in the presence of saline solution or in dry canals (paired t test).

Explorer the reference tuner was preset on nine according to pilot measurements that found this value suitable to the experimental model. For the Apit the file was introduced 2 to 3 m m into the canal and the reset button pressed. Detection of the perforation by the EALs was obtained when the indicator reached the sign " A p e x " on the scale. The K-file was then fixed tightly to the crown with a glass ionomer cement, Ketac Bond (ESPE GMBH & Co., KG, Seefeld/Oberbey, Germany), to prevent any move- ment of the endodontic instrument.

The teeth were removed from the alginate. Actual location of each file tip in relation to the perforation was determined with a measuring microscope (Tool- makers Microscope Mitutoyo, Japan). Zero values were recorded when the tip was at the same level of the external root surface; positive or negative values were recorded when the tip was detected beyond or short. When the file tip was short of the surface, a standard voltmeter was used to determine the distance of the tip from the external root surface, as described by Berman and Fleischman. 14 The largest file that passed in the retrograde fashion through the perfora- tion was connected to one of the leads of the voltme- ter. A second lead was connected to a file introduced orthograde to electronically determine the location of the perforation. The retrograde file was inserted into the perforation until contact was made between the two files and the circuit was completed as indicated by a zero ohm reading. The retrograde file was marked flush with the root surface and was then re- moved; the distance from its tip to the line mark was measured.

Each tooth was reembedded in freshly mixed alg- inate in a position that placed the perforation in front of a short axis of the model ' s box (90 degrees to the position in the first set of measurements). The perfo- rations were electronically detected in dry canals for the second time. After fixation of the files to the tooth' s crown, two additional radiographs were taken. The x-ray cone was placed again in front of the long

axis of the model ' s box to achieve a different angu- lation between the perforation and the x-ray beam, 90 and 1 l 5 degrees, respectively (Fig. 4). This procedure was repeated for each experimental tooth in the pres- ence of NaC10 and saline solution in the canal and with freshly mixed alginate in the model 's box. In these groups, a small cotton pellet was used to dry the pulp chamber of each tooth and the coronal orifice of the root canals before the electronic measurement in order to avoid overloading of the units. 15

For radiographic evaluation, measurements were recorded in two groups according to the position of the tooth in the model: Group A (Fig. 1) included measurements taken when the perforations were fac- ing the long axis of the box (0 degrees; 25 degrees); Group B (Fig. 2) included measurements taken when the perforations were facing the short axis of the box (90 degrees; 115 degrees). Radiographs in Group A mimicked the clinical condition of perforations lo- cated at the buccal or lingual aspects of the root, whereas radiographs in Group B resembled clinical cases in which the perforations were located at the interproximal aspects.

Two endodontists evaluated 512 radiographs of perforated roots divided to four equal groups accord- ing to the angulations: 0, 25, 90, and 115 degrees. The evaluators identified suspected perforations that clin- ically would have required further tests. They were not aware of the methods used in the study and how many roots were perforated. The results of detecting root perforations by the two electronic apex locators were statistically analyzed with a paired t test. The results of radiographic identification of root perfora- tions were statistically analyzed with Pearson's chi- square test.

RESULTS The mean distances of the file tip from the external

root surface are presented in Table I. The range of both devices in the different groups was -0.17 to -0.42 mm. Applying the paired t test, no significant

ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Fuss. Assooline, and Kaufman 327 Volume 82. Number 3

2roup A

~ 1 periapical film i

ration fadng the lon2 ] ] axas of the model I

long cone of X-Ray ]

Fig. 3. Group A model with tooth embedded in alginate and the perforation facing the long axis (0 and 25 de- grees).

2rouo B

~ . ~ - " ~ - [ pefiapical film I

m facing the short I e model I

e of X-Ray ]

Fig. 4. Group B model with tooth embedded in alginate and the perforation facing the long axis (90 and 115 degrees).

Table I I . Root perforations as identified on 512 radiographs

Group Angulation (degrees) Number of radiographs

Number of perforations

Endodontist 1 Endodontist 2

A 0 128 46 (36%) 45 (35%) 25 128 57 (45%) 51 (40%)

B 90 128 109 (85%) 117 (91%) 115 128 113 (88%) 119 (93%)

No significant (p > 0.05) difference between the numbers of root perforations identified by the two endodontists (Pearson's chi square test). Significant (p < 0.05) difference between the numbers of root perforations identified in group A compared with group B (Pearson's chi square test).

(/7 > 0.05) difference was found between Group A (Fig. 3) and Group B (Fig. 4) for each apex locator, A significant (p < 0.05) difference was found be- tween the two apex locators in the presence of saline solution or in dry canals. However, there was no sig- nificant (p > 0.05) difference between the two devices in the presence of NaC10.

The results of identifying perforations in the radio- graphs are presented in Table II. With Pearson's chi square test, no significant (p > 0.05) difference was found between the numbers of root perforations identified. The first evaluator identified between 36% and 45% of the perforations in Group A and 85% and 88% in Group B. The second evaluator identified 35% to 40% of the perforations in Group A and 91% to 93% in Group B. A statistically significant ~p < 0.05) difference was found between the numbers of root perforations identified in Group A compared with Group B.

D I S C U S S I O N It has been suggested that EALs operate on the

principles of electricity rather than biologic properties

of tissues involved. ]6 Therefore in vitro models in which extracted teeth are immersed in media with similar electrical resistance to the periodontium can provide valuable information into the function of EALs. 17-2~ We selected an in vitro model with algi- nate as a media for the extracted teeth. In a prelim- inary study, the adequacy of the model was tested; the alginate appeared to be an appropriate material with high elasticity and viscosity and was easy to handle. Measurements to determine tooth length compared with actual tooth length and length calculated through radiographs proved the validity of the model. 21 The relatively firm consistency and viscosity of the algi- nate prevented material extrusion into the small diameters of the apical foramen and the perforations. Patency was confirmed with size 15 K-file at the api- cal foramen and size 20 at the perforation site to en- sure electrical conductivity. The fact that there was no difference between Group A and Group B for each EAL under different conditions also validated the ac- ceptability of the model. The only difference between the groups was the position of the tooth in the algi- nate for radiographing purposes. It should be empha-

328 Fuss, Assooline, and Kaufman ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY September 1996

sized that the results obtained in this in vitro study cannot be directly extrapolated to the clinical situa- t ion but can provide an objective examinat ion of a number of variables that are not practical to test clin- ically. It is our opinion, based on personal use, that the in vitro calibration corresponds well with clinical findings.

An accurate detection of root perforation along the root surface is an essential factor for successful treat- ment. The results of this study conf i rmed previous suggestions 9, 10 that EAL is an acceptable method for that purpose. Both devices detected the perforations within a cl inically accepted distance from the exter- nal root surface (0.17 to 0.42 short). As expected, the results obtained with the Sono Explorer were less consistent in the presence of NaC10; this EAL is not r ecommended with highly conductive solutions. How- ever, the inconsis tency of the results with the Apit in the presence of NaC10 was unexpected; this unit has been found accurate in detection of apical foramen under similar conditions. 22 A possible explanation could be that perforations in the presence of highly conduct ive solutions could interfere with the initial calibration of the device and therefore with the accu- racy and consistency of the readings.

Several studies have shown that the resistance-type EALs are inaccurate in teeth with large apical foram- ina.14, 16, 22, 23, 24 In our study the size of the perfora- tions was 0.27 mm; this is smaller than the size of the apical foramen in the studies ment ioned and therefore accuracy and consis tency of the results were ex- pected. Further studies should be conducted to eval- uate the impact of the perforat ion 's size and location on the accuracy of different types of EALs in vitro and in vivo.

There are confl ict ing results with respect to the ac- curacy of EAL in detecting the apical foramen com- pared with radiographs. Becker et a l Y and Hem- brough et al. 26 found radiographic determinat ion to be more accurate than that of EAL device. Conversely, Busch et al.27 and Plant and Newman ~8 found the Sono Explorer superior to radiographic length deter- minat ion. Radiographic detection of perforations in the present study was unreliable. When the perfora- tions were located at the buccal or l ingual surfaces of the root, the percentage of successful detection was at most 45%, It is conceivable that radiographs cannot replace the EALs in detecting the location of root perforations. However, it is essential to radiograph the teeth after locating the perforation with an EAL to determine the location relative to the crestal bone. The prognosis and treatment are directly related to the proximity of the root perforation to the epithelial at- tachment and crestal bone. l, 7, 29

CONCLUSIONS In this in Vitro study, the electronic devices were

accurate tools for locating root perforations within a cl inically acceptable range. Radiographs were unre- l iable in ident i fying root perforations. More in vivo studies should be conducted to conf i rm the in vitro results.

We thank Prof. Israel Kaffe for assistance in evaluation of the radiographs and to Ms. Rita Lazar for editorial as- sistance.

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21. Keila S, Linn H, Katz A, Kanfman AY. Morphometric anal- ysis of working length determined by impedance type apex locators [abstract]. J Endod 1994;20:196.

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Reprint requests: Dr. Zvi Fuss Section of Endodontology The Manrice and Gabriela Goldschleger School of Dental Medicine Tel Aviv University Tel Aviv, Israel

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