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An in vivo evaluation of the ENDEX and RCM Mark II electronic apex locators in root canals with different contents
An in vivo evaluation of the ENDEX* and RCM Mark l i t electronic apex iocators in root canals with different contents Rahul K. Arora, BDS, MSc, LDS, DGDP, a and Kishor Gulabivala, BDS, MSc, FDS, b London, U.K. The accuracy of many apex Iocators is affected by electrolytes including sodium hypochlorite. According to the manufacturer a new device, the ENDEX, overcomes this problem. The purpose of this study was to assess the accuracy of the ENDEX in comparison with a traditional device, the RCM Mark II. The lengths of 61 canals with various contents (vital pulp, necrotic pulp, pus/exudate, sodium hypochlorite, and water) were determined in vivo. Files were cemented within the canals at lengths determined by the ENDEX. The teeth were then radiographed and extracted, and the distance between the file tip and apical foramen was recorded. Derived readings for the RCM Mark II were compared with the actual ENDEX reading and corresponding radiograph. The results indicated that most of the file tips that were at the radiographic apex actually extended through the apical foramen, and canal content had a varying effect on each device. The overall accuracy of the ENDEX (71.7%) was higher than that of the RCM Mark II (43.5%) within 0.5 mm of the apical foramen. The ENDEX, unlike the RCM Mark 11, proved accurate in the presence of sodium hypochlorite. (ORALSURGORALMID ORALPATHOLORALRADIOLENDOO1995;79:497-503)
Establishment of correct working length is accepted as an important stage in root canal treatment, because sufficient evidence suggests that instrumentation either beyond or well short of the radiographic apex can adversely affect success. 1 Although the main root canal exits at the major foramen, the narrowest part of the canal is usually found at the minor apical foramen or apical constriction. 2 Accepted techniques for working length determination include tactile, radiographic, or electronic methods, and each may be used by itself or in combination. The major problem in working to or just short of the apical constriction lies in its detection. Neither tactile nor radiographic methods appear adequate for consistent location of this point, and many electronic apex locators are influenced by factors such as the diameter of the major foramen and apical constriction. 3 Sole use of the tactile method is generally deprecated 4, 5 because of its reliance on size of file and the variability of the apical constriction. 2 The use of radiographic techniques is well established. All radiographic techniques, however, have inherent limitations such as image distortion from magnification, 6 production of only a two-dimensional image, 7 the inaEndodontist, Endodontic Practice, Harley Street, London W1, and Department of Conservative Dentistry, Eastman Dental Institute and Hospital, London. bConsultant, Department of Conservative Dentistry, Eastman Dental Institute and Hospital, London. *Osada Electric Co., Tokyo, Japan. ?Evident Dental Co. Ltd., London, U.K. Copyright 9 1995 by Mosby-Year Book, Inc. 1079-2104/95/$3.00 + 0 7/15/58394
Table I. Comparison between electronic ( E N D E X
and R C M Mark II) and radiographic file positions. Data represent numbers and percentages of canals. No. of canals (n) Total Short
Long
Flush
(n)
ENDEX file position Radiographic file
9 14.7% 15
49 80.3% 11
3 4.9% 35
61
position (ENDEX) RCM derived file position
24.6%
18.0%
57.4%
30 49.2%
31 50.8%
0 0
61
61
ability to consistently visualize the major apical foramen or constriction, 8 and observer bias during interpretation. 9 The position of the major apical foramen is infrequently coincident with the true root apex and may be located up to 2 mm away. 1~ Furthermore the distance between the apical foramen and constriction varies between 0 to 1 mm. z, 14 Many available electronic apex locators claim to be reliable and accurate in determining working length. The typical device has two electrodes: one connected to the oral mucosa via a lip clip and a second attached to a file in the root canal. Between these electrodes is a modified ohmmeter that measures the change in impedance as the file is advanced down the canal. Impedance is a complex function of inductance and capacitance found in any alternating current (AC) circuit and is considered generalized resistance. A relatively constant value of impedance is at the junc497
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Vital Short Endex RCM
3 10
I
[
Necrotic
Pus/exudate
Flush
Long
Short
Flush
Long
Short
Flush
Long
2 0
13 8
0 0
0 0
11 11
0 2
0 0
6 4
NaOCI, Sodium hypochlorite. *Data represent number of canals. Overall total is 61 for each ENDEX and RCM Mark II group.
tion of the pulp tissue and periodontal ligament at the apical foramen. Sunada 15 suggested that it was a biologic characteristic; others, however, have reproduced it in vitro and consider it a physical property of biologic tissues.16, 17Most modern apex locators function on these basic principles. Some apex locators require calibration, whereas others have a built-in fixed-value reference resistor that takes into account the mean values of the capacitance/resistance ratio of the tissues, is In general both groups of apex locators are not reliable in the presence of electrolytes such as sodium hypochlorite and exudate. This problem was demonstrated by the lower resistance and capacitance readings obtained in wet as opposed to dry canals. 19 Ricard et al. 2~ evaluated the RCM Mark II apex locator in vivo. They found it to be accurate in locating to within 0.5 mm of the apical foramen in 86.5% of cases. However, it was noted that the device produced inaccurate readings in the presence of sodium hypochlorite or excessive hemorrhage. The presence of vital or necrotic tissue had little adverse influence on the readings obtained. According to the manufacturer the ENDEX apex locator functions in canals containing electrolytes. It works by comparing the difference in impedances with the use of relative value of two ACs at frequencies of 1 and 5 K Hz. 21 When a file is at the coronal canal orifice, the difference in impedances is large at these two AC frequencies. As the file then approaches the apical foramen, the frequency-dependent impedances reach a constant value. 21 An in vivo radiographic study conducted on the ENDEX by Mezawa et al. 22showed that 13.7% of file tips were at the radiographic apex, whereas 84.7% were between 0.0 to 3.0 mm short. The authors stated that the device was capable of determining canal length in the presence of blood, exudate, or sodium hypochlorite. With the exception of two other studies, 23,24 apparently no other detailed clinical evaluation of this apex locator or a comparison of it with other commonly used devices has been done. Mayeda et al. 24 found no statistical difference in measurements between necrotic and vital cases. The
readings ranged from 0.86 mm coronal to the major foramen to 0.5 mm apical to the major foramen. Several factors are known to affect the accuracy of electronic apex locators or the assessment of their accuracy. The diameter of the apical foramen, file size, and canal contents may each influence the reading obtained.17, 25 However, it is suggested that these influences can be negated when two AC frequencies are used instead of the single frequency commonly used. 21 The purpose of this study was to assess the accuracy of the ENDEX in the presence of vital and necrotic tissue and commonly encountered canal electrolytes and to compare its accuracy with that of the RCM Mark II.
MATERIAL AND METHOD The main clinical study was conducted in the Dental Department of the Batra Hospital, New Dehli. Seventy-one patients scheduled for dental extractions consented to the treatment protocol. Patients with endodontically treated teeth, extensive destruction of the clinical crowns, or periodontal support were excluded from the study. The response of each tooth to electric pulp testing (Analytic Technology Vitality Scanner 2006, Analytic Technology Corporation, Redmond, Wash.) was recorded, and a standardized periapical radiograph was taken with E-speed film (Ektaspeed EP21, Kodak U.K. Ltd., Hemel Hempstead, U.K.) held in a paralleling device (Rinn XCP, Rinn Corporation, Ill.). The ENDEX and RCM Mark II apex locators were assessed in canals containing one of the following (number of canals tested for each group are indicated in parentheses: (1) vital tissue that appeared healthy and bled when disturbed or was spontaneously hemorrhagic (18 canals in 18 teeth); (2) nonvital tissue that was necrotic and odorous (11 canals in 11 teeth); or (3) pus or exudate (six canals in six teeth). In addition the devices were assessed in canals containing the following solutions: (4) sodium hypochlorite (Sainsbury's Bleach: J.S. Sainsbury, London, U.K.) (15 canals in 13 teeth); or (5) sterile distilled water (11 canals in 11 teeth), After administration of local anesthesia (2%)
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NaOCI Short 2 12
Water
Total
Flush
Long
Short
Flush
Long
1 0
12 3
4 6
0 0
7
9
5
30
lidocaine hydrochloride [Xylocaine] with adrenaline 1:80,000, Astra Pharmaceuticals Ltd., Kings Langley, U.K.) was done, each tooth was isolated under a rubber dam. A uniform and stable occlusal reference plane was created by removing 2 mm of the incisal edge of anterior teeth and the occlusal surface of posterior teeth. After access into the pulp chamber was gained, the contents were noted and removed. Adequate access was provided to the root canals by removing the entire roof of the pulp chamber with a diamond bur (767/9C - two striper, Abrasive technology, Premier Dental Products, Philadelphia, Pa.). Undercuts were placed in opposing pulp chamber walls for retention of the composite material to be inserted later. The pulp chamber was then dried with sterile cotton pellets (Johnson & Johnson Ltd., Maidenhead, U.K.). The ENDEX was calibrated for each canal according to the manufacturer's instructions. Canal length was then determined with size 06, 08, or 10 K-flex files (Kerr U.K. Ltd., Peterborough, England). After the file was advanced apically until the ENDEX indicated the apical limit was reached, a silicone rubber stop (Maillefer S.A., Baillaigues, Switzerland) was carefully pushed down the file shank until it contacted the occlusal reference point. The ENDEX was then switched off, and the RCM Mark II was connected to the patient via a circuit switching box designed to allow interchange between the two apex locators without disturbing the file or electrical connections. The value of the figure on the digital display of the R C M Mark II corresponding to the zero value on the ENDEX was recorded. The file was then removed from the canal and was measured to the nearest 0.25 mm with a graduated metal ruler (No. 64R ruler: Rabone Chesterman, U.K.). The length was noted as L1. The file was replaced into the canal with the R C M Mark II switched on and advanced until the device indicated zero. With the use of the switching box, the ENDEX was brought into the circuit, and the file position corresponding to a zero reading on the R C M was recorded as long, flush, or short. The file was removed from the canal, and its length (L2) was measured as determined by the R C M Mark II. The file was then replaced in the canal to length L 1,
Short
Flush
Long
3 0
49 31
and its position was reconfirmed by the ENDEX. A diluted, light-cured, composite resin (Adaptic LC, Johnson & Johnson Ltd., Maidenhead, U.K.) was introduced around the file in the pulp chamber with a syringe (Centrix Mark II, Hawe-Neos Dental, Gentilino, Switzerland) and was light-cured for 1 minute (Visilux 2 light curing unit, 3M Ltd., Loughborough, U.K.). Further incremental layers of resin were placed and cured. The absence of file movement was checked by leaving the apex locators switched on. Sufficient composite was placed to cover the occlusal surface of the tooth by about 1 mm, and the file was sectioned through this superficial layer with a diamond bur. To confirm that the file had not moved, the original reading of the apex locator was verified by touching the file electrode to the embedded cut surface of the file. The rubber dam was then removed, and a postoperative radiograph was exposed with the file in situ. The tooth was then carefully extracted and stored in 70% 2-propanol isopropyl alcohol for transportation to the Eastman Dental Hospital. In the teeth in which sodium hypochlorite and sterile water were tested, the canals were enlarged apically with H-type files to International Standards Organization (ISO) size 25 (Kerr U.K. Ltd., Peterborough, U.K.) and were filled with the appropriate irrigant. Care was taken to ensure that the irrigant remained below the canal orifice. The evaluation of the position of the file tip in relation to the apical foramen was conducted at the Eastman Dental Hospital. A radiograph was taken of each tooth in the proximal and bucco-lingual planes, and these radiographs together with those from the clinical study were viewed under X2.5 magnification on a masked backlit viewer (Velopex, Medivance Instruments Ltd., London, U.K.). The distance between the file tip and radiographic apex was measured with a pair of electronic vernier callipers (Sylvac S.A., Switzerland) on both sets of radiographs. Adherent soft tissue was removed from the apical two thirds of each root by immersing the teeth in a 1% sodium hypochlorite solution for 30 minutes, rinsing under running water for 5 minutes, and gently air drying. A radiograph was taken to confirm that no
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Table IlL File measurements under different canal conditions for the ENDEX and R C M Mark II* Vital Distancefrom apical (mm) foramen >1 (%)
0.5-1 (%) <0.5 (%)
0.o (%) <-0.5 (%) -0.5--1 (%) >--1 (%) Total (%)
Endex
Necrotic
RCM Mark H
Endex
Pus/exudate
RCM Mark H
Endex
NaOCI
RCM Mark H
1
0
2
2
0
1
(5.6) 1 (5.6) 11 (61.1)
(0) 5 (27.8) 3 (16.7)
(18.2) 4 (36.4) 5 (45.4)
(18.2) 4 (36.4) 5 (45.4)
(0) 1 (16.7) 5 (83.3)
(16.7) 1 (16.7) 2 (33.3)
2 (11.1) 3 (16.6) 0 (0) 0 (0) 18 (100)
0 (0) 6 (33.3) 3 (16.7) 1 (5.5) 18 (100)
o
0
o
(0) 0 (0) 0 (0) 0 (0) 11 (100)
(0) 0 (0) 0 (0) 0 (0) 11 (100)
(0) 0 (0) 0 (0) 0 (0) 6 (100)
0 (0) 1 (16.7) 1 (16.7) 0 (0) 6 (100)
Endex 0
(0) 9 (60) 3 (20)
1 (6.7) 2 (13.3) 0 (0) 0 (0) 15 (100)
Water
RCM Mark H
Endex
RCM Mark H
0
1
1
(0) 2 (13.3) 1 (6.7)
(19.1) 2 (18.1) 4 (36.4)
(9.1) 4 (36.3) 0 (0)
o (0) 0 (0) 0 (0) 12 (80) 15 (100)
o (0) 3 (27.3) 1 (9.1) 0 (0) 11 (100)
0 (0) 3 (27.3) 1 (9.1) 2 (18.2) 11 (100)
NaOCI, Sodiumhypochlorite. *Positive and negativevaluesrepresent long and short files, respectively.Data represent numbersand percentages of canals.
apparent change in file position occurred. The relation between the file tip and apical foramen was then examined at X25 magnification with a stereomicroscope (M400 Makroscope, Wild, Heerbrug, Switzerland). Each root tip was rotated along its long axis so that the foramen was uppermost, and a record was made of whether the file tip was long, flush, or short of the apical foramen. Where the file tip was visible the greatest distance between it and the coronal-most margin of the foramen was measured with the vernier scale on the stereomicroscope. This measurement was the greatest amount that the file tip was extended out of the apical foramen. In those cases where the file tip was short of the apical foramen, the root apexes were demineralized in a 4.75% solution of formic acid (BDH Chemicalsl Leicestershire, U.K.) followed by serial dehydration in ethyl alcohol (BDH Chemicals). They were then cleared in methyl salicylate (BDH Chemicals). The apical anatomy in relation to the file was visualized, and the distance between the file tip and coronal-most margin was recorded under the stereomicroscope as described previously. Results for the R C M Mark II were derived by subtracting the difference in canal length measurements of the two apex locators, L1 and L2, from the actual distance between the file tip and apical foramen as recorded in the laboratory. The following equation shows the relationship: Derived file position = (actual distance between file tip and foramen) - ( L 1 - L2). Data relating the distance of the file tip from the apical foramen with canal contents was analyzed with
and without the presence of sodium hypochlorite. This procedure allowed for the manufacturer's recommendation that the R C M Mark I1 does not function well in the presence of this electrolyte. A chi-squared test was used to compare the difference between the file positions determined electronically and those estimated radiographically. A valid statistical analysis of differences in file positions between teeth with different canal contents was not considered possible because of inadequate numbers in some groups. RESULTS
Twelve teeth were excluded from the study; six teeth fractured during extraction, and six had poor quality radiographs. Consequently 59 teeth with a total of 61 root canals were examined in the laboratory. An overall comparison between actual file position, as determined electronically by the ENDEX and the apparent radiographic position, with the derived file position for the R C M Mark II is presented in Table I. Although the files were judged in many cases (57.4%) to be flush with the radiographic apex, the file tip in fact extended past the coronal-most margin of the apical foramen. More long readings occurred with the ENDEX (80.3%) than with the RCM Mark II (50.8%), and more short readings occurred with the RCM Mark II (49.2%) than with the ENDEX (14.7%). Chi-squared testing indicated a highly significant difference between each technique of canal length determination (p < 0.001). The overall results of the influence of the five different canal contents on the
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Total
Endex
Total minus NaOCI
R C M Mark H
Endex
R C M Mark H
4
4
4
4
17
16
8
14
28
11
25
10
3
0
2
0
8
10
6
10
1
5
1
5
0
15
0
3
61
61
46
46
ability of each apex locator to detect the apical foramen are presented in Table II. A more detailed assessment of the specific measurements from file tip to apical foramen for each apex locator under the different canal conditions is presented in Table III and summarized in Table IV. DISCUSSION The accepted technique for determining working length frequently involves radiographic estimation of a position 1 mm short of the radiographic apex where the main root canal is thought to exit onto the root surface at the apical foramen. 13,26 Radiographs, however, infrequently show the position of the apical foramen or constriction. The findings of the present study agree with others such as that of Olson et al. 27 These findings show that limitations exist in relying on radiographs for accurate length determination. The overall results indicated a large discrepancy between the observed radiographic and actual file positions; radiographs suggest a position shorter than the one that really exists. 8, 28 In general it is agreed that root canals obturated up to 2 mm short of the radiographic apex have improved success rates over those that are either flush, 29 overextended, 3~ 31 or more than 2 mm short 1 of it. Despite the difficulties that occur with the use of radiographs for consistent location of the apical foramen, success rates based on radiographic estimation of working length are relatively high. 32, 33 Nevertheless precise location of the apical foramen would be an advantage and may further improve success rates.
In vivo radiographic assessment of file position alone has been shown to be arbitrary, 34 and results from such studies can therefore be questioned. Studies involving tooth extraction to directly examine the relation between the file tip and root apex require that each file is securely fixed in situ with an appropriate material. Repositioning a file to its measured length after extraction of the tooth may be inaccurate because of differences in path of the file and effect of parallax on relative position of stop and reference point. In this study all precautions were taken to prevent movement of the file tip relative to the root tip. Careful file cementation with dilute resin, sectioning, tooth extraction, and subsequent in vitro processing were conducted to prevent loss or distortion of mineralized tissues apically. In addition, as reported by LeQuire et al., 35 placing the root apexes in a dilute solution of sodium hypochlorite adequately removed adherent soft tissue without altering the hard tissues. The results of the study showed that in the presence of vital tissue, even when hemorrhagic, both the ENDEX and RCM Mark II showed an accuracy of 94.4% within 1 mm of the apical foramen. The ENDEX, however, performed better when accuracy within 0.5 mm was considered (Table IV). The accuracy obtained for each device in the presence of necrotic tissue was identical, although in both cases it was lower than that for vital tissue (Table II). It was unlikely that these results were due to experimental error, because the samples occurred randomly throughout the study. The results obtained in the presence of pus or exudate should be interpreted with caution because of the low sample numbers. It was apparent, however, that the E N D E X provided only long readings, whereas the R C M Mark II gave a greater distribution of resuits (Table III). The presence of sterile water affected the accuracy of both apex locators, particularly when it was measured to within 0.5 mm of the apical foramen (RCM Mark II 27.3%, E N D E X 63.7%). Overall, however, the E N D E X performed better than the R C M Mark II in canals containing this electrolyte. The presence of sodium hypochlorite had the greatest effect on the accuracy of the instruments. Although the manufacturer of the R C M Mark II states that the device will not function accurately in the presence of sodium hypochlorite, it did so in a few cases. On the other hand the E N D E X gave long readings. If, however, readings within 1 mm of the apical foramen were considered, the device was accurate (RCM Mark II 20%, E N D E X 100%). The overall accuracies of the E N D E X and R C M Mark II (91.3% and 84.8%, respectively) within 1 mm
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April 1995 Table IV. File measurements for the E N D E X and R C M Mark II within 0.5 mm and 1.0 mm of the apical foramen under different canal conditions*
Distancefrom apical foramen (ram) Within + 0.5 ENDEX Within 1 R C M Mark II
Within + 0.5 Within + 1
Vital (%) 16 (88.9) 17 (94.4) 9 (50) 17 (94.4)
Necrotic (%)
Pus/exudate (%)
NaOCI (%)
Water (%)
Total (%)
Total minus NaOCl(%)
5 (45.4) 9 (81.8) 5 (45.4) 9 (81.8)
5 (83.3) 6 (100) 3 (50) 5
6 (40) 15 (100) 1 (6.7) 3
7 (63.6) 10 (90.0) 3 (27.3) 8
39 (63.9) 57 (93.4) 21 (34.4) 42
33 (71.7) 42 (91.3) 20 (43.5) 39
(72.7)
(68.9)
(84.8)
(83.3)
(20)
NaOCI, Sodium hypochlorite. *Data represent numbers and percentages of canals.
of the apical foramen (Table IV) compare well with those from other in vivo studies in which accuracies range from 1 5 % 34 t o 1 0 0 % . 36 When the results of this study are compared with the only other similar study involving the RCM Mark 1I, 20 a marked difference is seen in overall accuracies obtained within 0.5 mm of the apical foramen. One explanation for this difference may be attributed to the file movement noted in 18.9% of their samples. Furthermore their methodology differed in that the root apex was ground to make measurements of short file positions. This procedure may have led to a loss of orientation and therefore to less accuracy in measurement. The reference point used for the measurement of short files was also different from the present study, whereas that for long files was identical. A recent in vivo radiographic study of the ENDEX 23 found that the device was accurate within 0.5 mm of the apical foramen in 8 9.64% of cases. Another in vivo study 24 using extracted teeth achieved broadly similar results. All their files (100%) 24) were within 1 mm of the apical foramen in both vital and necrotic canals. In the present study the values were 94.4% for vital canals and 81.8% for necrotic canals (Table IV). The results for readings within 0.5 mm were similar for vital canals, 82.4% 24 and 88.9% (this study). The readings within 0.5 ram, however, were substantially different for necrotic canals, 87.5% (value was calculated by authors from figures of Mayeda et al.) and 45.4% (this study). The differences in results may be explained by the different methodology. Mayeda et al. 24 irrigated canals with 5.25% sodium hypochlorite and did not dry the canals before measurement. Additionally their method of measurement relied on grinding to expose the canal and apical foramen. Another explanation may be differences between the apex locators and the manner in which they were used, although the manufacturer's instructions were followed closely.
The greater number of long readings with the ENDEX compared with that of the RCM Mark II in this study suggests that the manufacturer's calibration resulted in an overestimation of canal length. In addition the R C M Mark II gave more short readings, although in a large number of cases (11), sodium hypochlorite was present, and many of these readings were more than 1.5 mm away from the apical foramen. If the short readings are adjusted to exclude the effect of sodium hypochlorite, most of the readings for both devices (ENDEX, 71.7%, R C M Mark II, 43.5%) fall within 0.5 mm of the apical foramen (Table IV). This study confirmed that the sole use of radiographs to establish canal length can be misleading and inaccurate.2O, 34, 37 It appears that a combination of electronic and radiographic methods are more accurate than a single method, which is in agreement with the findings of Keller et al. 38 CONCLUSIONS
The overall accuracies for both the E N D E X and RCM Mark II were well within a clinically acceptable range, 1 mm of the apical foramen, as defined in other in vivo studies. Each device, however, has its limitations, and it appears that neither apex locator nor radiographs are consistently accurate for canal length determination. This study concluded that the E N D E X was accurate to within 0.5 mm of the apical foramen in 71.7% of cases and to within 1 mm in 91.3% of canals tested. The presence of different canal contents and electrolytes had varying effects on the accuracy of each device. The ENDEX, unlike the RCM Mark II, appeared to function consistently in the presence of sodium hypochlorite. In necrotic tissue, however, both devices behaved identically. The accuracy of the ENDEX within 0.5 mm of the apical foramen in the presence of vital pulp tissue or pus was higher than that of the R C M Mark II.
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It was concluded that the ENDEX appeared more accurate than the RCM Mark II in locating the position of the apical foramen. W e gratefully acknowledge the assistance of Evident Dental Co. Ltd. (London, U.K.) and O s a d a Electric Co. (Tokyo, J a p a n ) t h r o u g h their agents Cottrell and Co. (London, England). T h e authors are also grateful to M i s s Louise T h o m p s o n for expert typing of the manuscript.
REFERENCES 1. Sj6gren U, Hfigglund B, Sundqvist G, Wing K. Factors affecting the long-term results of endodontic treatment. J Endod 1990;16:498-504. 2. Dummer PMH, McGinn JH, Rees DG. The position and topography of the apical canal constriction and apical foramen. Int Endod J 1984;17:192-8. 3. Stein JT, Corcoran JF, Zillich RM. The influence of the major and minor foramen diameters on apical electronic probe measurements. J Endod 1990;16:520-2. 4. Ingle JI, Mullaney TA, Grandich RA, Taintor JF, Fahid A. Endodontics. Philadelphia: Lea & Fabiger, 1985:102-255. 5. McDonald N J, Hovland EJ. An evaluation of the apex locator endocater. J Endod 1990;16:5-8. 6. Duinkerke ASH, van de Poel ACM. An analysis of apparently identical dental radiographs. ORAL SURG ORAL M D ORAL PATHOL 1974;38:962-7. 7. Tidmarsh BG, Sherson W, Stalker NL. Establishing endodontic working length: a comparison of radiographic and electronic methods. N Z Dent J 1985;81:93-6. 8. Lambjerg-Hansen H. Vital and mortal pulpectomy on permanent human teeth: an experimental comparative histologic investigation. Scand J Dent Res 1974;82:243-332. 9. Lambriandis T. Observer variations in radiographic evaluation of endodontic therapy. Endod Dent Traumato11985;1:235-41. 10. Kuttler Y. Microscopic investigation of root apexes. J Am Dent Assoc 1955;50:544-52. 11. Green D. A stereomicroscopic study of the root apices of 400 maxillary and mandibular anterior teeth. ORAL StJRG ORAL MED ORAL PATHOL 1956;9:1224-32. 12. Green D. Stereomicroscopic study of 700 root apices of maxillary and mandibular posterior teeth. ORAL SURG ORAL MED ORAL PATHOL 1960;13:728-33. 13. Burch JG, Hulen S. The relationship of the apical foramen to the anatomic apex of the tooth root. ORAL SURG ORAL MED ORAL PATHOL 1972;34:262-8. 14. Chapman CE. A microscopic study of the apical region of human anterior teeth. J Br Endod Soc 1969;3:52-8. 15. Sunada I. New method for measuring the length of the root canal. J Dent Res 1962;41:375-87. 16. Huang L. The principle of electronic root canal measurement. Bull Fourth Mil Med CoU 1959;8:32-4. 17. Huang L. An experimental study of the principle of electronic root canal measurement. J Endod 1987;13:60-4. 18. Dahlin J. Electrometric measuring of the apical foramen. Quintessence Int 1979;1:13-22. 19. Meredith N, Gulabivala K. An in-vivo investigation of the electrical characteristics of root canals in relation to length. Int Endod J 1992;25:30. 20. Ricard O, Roux D, Bourdeau L, Woda A. Clinical evaluation of the accuracy of the Evident RCM Mark II apex locator. J Endod 1991;17:567-9.
21. Saito T, Yamashita Y. Electronic determination of root canal length by newly developed measuring device. Dent Jpn 1990; 27:65-72. 22. Mezawa S, Komori N, Saito T. Clinical evaluation in electronic measuring of root canal length using several devices. J Endod 1992;18:184 (poster clinic #4). 23. Frank AL, Torabinejad M. An in-vivo evaluation of Endex electronic apex locator. J Endod 1993;19:177-9. 24. Mayeda DL, Simon JHS, Aimar DF, Finley K. In-vivo measurement accuracy in vital and necrotic canals with the ENDEX apex locator. J Endod 1993;19:545-8. 25. Yamashita Y. A study of a new electronic root canal measuring device using relative values of frequency response: influence of the diameter of apical foramen, the size of electrode and the concentration of sodium hypochlorite. Jpn J Conserv Dent 1990;33:547-59. 26. Weine FS. End0dontic therapy. 4th ed. St. Louis: CV Mosby, 1989: 295-7. 27. Olson AK, Goerig AC, Cavataio RE, Luciano J. The ability of the radiograph to determine the location of the apical foramen. Int Endod J 1991;24:28-35. 28. von der Lehr WN, Marsh RA. A radiographic study of the point of endodontic egress. ORAL SURG ORAL MED ORAL PATHOL 1973;35:105-9. 29. Strindberg LZ. Dependence of the results of pulp therapy on certain factors: an analytic study based on radiographic and clinical follow-up examinations. Dent Abstr 1957;2: 176-7. 30. Nair PNR, Sj6gren U, Krey G, Kahnberg K-E, Sundqvist G. Intraradicular bacteria and fungi in root-filled, asymptomatic human teeth with therapy-resistant periapical lesions: a longterm light and electron microscope follow-up. J Endod 1990; 16:580-95. 31. Harty F J, Parkins BJ, Wengraf AM. Success rate in root canal therapy: a retrospective study of conventional cases. Br Dent J 1970;128:65-70. 32. Odesjo B, Hellden L, Salonen L, Langeland K. Prevalance of previous endodontic treatment, technical standard and occurance of periapical lesions in a randomly selected adult, general population. Endod Dent Traumatol 1990;6:265-72. 33. Matsumoto T, Nagai T, Ida K, Ito M, Kawai Y, Horiba N, et al. Factors affecting successful prognosis of root canal treatment. J Endod 1987;i3:239-42. 34. Chunn CB, Zardiackas LD, Menke RA. In vivo root canal length determination using the Forameter. J Endod 1981 ;7:51520. 35. LeQuire AK, Cunningham C J, Pelleu GB. Radiographic interpretation of experimentally produced osseous lesions of the human mandible. J Endod 1977;3;274-6. 36. Plant J J, Newman RF. Clinical evaluation of the SonoExplorer. J Endod 1976;2:215-6. 37. Palmer M J, Weine FS, Healey HJ. Position of the apical foramen in relation to endodontic therapy. Can Dent J Assoc 1971;37:305-8. 38. Keller ME, Brown CE, Newton CW. A clinical evaluation of the Endocater: an electronic apex locator. J Endod 1991;17: 271-4.
Reprint requests: K. Gulabivala, BDS, MSc, FDS Department of Conservative Dentistry Eastman Dental Institute and Hospital 256 Grays Inn Road London WCIX 8LD U.K.
Establishment of correct working length is accepted as an important stage in root canal treatment, because sufficient evidence suggests that instrumentation either beyond or well short of the radiographic apex can adversely affect success. 1 Although the main root canal exits at the major foramen, the narrowest part of the canal is usually found at the minor apical foramen or apical constriction. 2 Accepted techniques for working length determination include tactile, radiographic, or electronic methods, and each may be used by itself or in combination. The major problem in working to or just short of the apical constriction lies in its detection. Neither tactile nor radiographic methods appear adequate for consistent location of this point, and many electronic apex locators are influenced by factors such as the diameter of the major foramen and apical constriction. 3 Sole use of the tactile method is generally deprecated 4, 5 because of its reliance on size of file and the variability of the apical constriction. 2 The use of radiographic techniques is well established. All radiographic techniques, however, have inherent limitations such as image distortion from magnification, 6 production of only a two-dimensional image, 7 the inaEndodontist, Endodontic Practice, Harley Street, London W1, and Department of Conservative Dentistry, Eastman Dental Institute and Hospital, London. bConsultant, Department of Conservative Dentistry, Eastman Dental Institute and Hospital, London. *Osada Electric Co., Tokyo, Japan. ?Evident Dental Co. Ltd., London, U.K. Copyright 9 1995 by Mosby-Year Book, Inc. 1079-2104/95/$3.00 + 0 7/15/58394
Table I. Comparison between electronic ( E N D E X
and R C M Mark II) and radiographic file positions. Data represent numbers and percentages of canals. No. of canals (n) Total Short
Long
Flush
(n)
ENDEX file position Radiographic file
9 14.7% 15
49 80.3% 11
3 4.9% 35
61
position (ENDEX) RCM derived file position
24.6%
18.0%
57.4%
30 49.2%
31 50.8%
0 0
61
61
ability to consistently visualize the major apical foramen or constriction, 8 and observer bias during interpretation. 9 The position of the major apical foramen is infrequently coincident with the true root apex and may be located up to 2 mm away. 1~ Furthermore the distance between the apical foramen and constriction varies between 0 to 1 mm. z, 14 Many available electronic apex locators claim to be reliable and accurate in determining working length. The typical device has two electrodes: one connected to the oral mucosa via a lip clip and a second attached to a file in the root canal. Between these electrodes is a modified ohmmeter that measures the change in impedance as the file is advanced down the canal. Impedance is a complex function of inductance and capacitance found in any alternating current (AC) circuit and is considered generalized resistance. A relatively constant value of impedance is at the junc497
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Vital Short Endex RCM
3 10
I
[
Necrotic
Pus/exudate
Flush
Long
Short
Flush
Long
Short
Flush
Long
2 0
13 8
0 0
0 0
11 11
0 2
0 0
6 4
NaOCI, Sodium hypochlorite. *Data represent number of canals. Overall total is 61 for each ENDEX and RCM Mark II group.
tion of the pulp tissue and periodontal ligament at the apical foramen. Sunada 15 suggested that it was a biologic characteristic; others, however, have reproduced it in vitro and consider it a physical property of biologic tissues.16, 17Most modern apex locators function on these basic principles. Some apex locators require calibration, whereas others have a built-in fixed-value reference resistor that takes into account the mean values of the capacitance/resistance ratio of the tissues, is In general both groups of apex locators are not reliable in the presence of electrolytes such as sodium hypochlorite and exudate. This problem was demonstrated by the lower resistance and capacitance readings obtained in wet as opposed to dry canals. 19 Ricard et al. 2~ evaluated the RCM Mark II apex locator in vivo. They found it to be accurate in locating to within 0.5 mm of the apical foramen in 86.5% of cases. However, it was noted that the device produced inaccurate readings in the presence of sodium hypochlorite or excessive hemorrhage. The presence of vital or necrotic tissue had little adverse influence on the readings obtained. According to the manufacturer the ENDEX apex locator functions in canals containing electrolytes. It works by comparing the difference in impedances with the use of relative value of two ACs at frequencies of 1 and 5 K Hz. 21 When a file is at the coronal canal orifice, the difference in impedances is large at these two AC frequencies. As the file then approaches the apical foramen, the frequency-dependent impedances reach a constant value. 21 An in vivo radiographic study conducted on the ENDEX by Mezawa et al. 22showed that 13.7% of file tips were at the radiographic apex, whereas 84.7% were between 0.0 to 3.0 mm short. The authors stated that the device was capable of determining canal length in the presence of blood, exudate, or sodium hypochlorite. With the exception of two other studies, 23,24 apparently no other detailed clinical evaluation of this apex locator or a comparison of it with other commonly used devices has been done. Mayeda et al. 24 found no statistical difference in measurements between necrotic and vital cases. The
readings ranged from 0.86 mm coronal to the major foramen to 0.5 mm apical to the major foramen. Several factors are known to affect the accuracy of electronic apex locators or the assessment of their accuracy. The diameter of the apical foramen, file size, and canal contents may each influence the reading obtained.17, 25 However, it is suggested that these influences can be negated when two AC frequencies are used instead of the single frequency commonly used. 21 The purpose of this study was to assess the accuracy of the ENDEX in the presence of vital and necrotic tissue and commonly encountered canal electrolytes and to compare its accuracy with that of the RCM Mark II.
MATERIAL AND METHOD The main clinical study was conducted in the Dental Department of the Batra Hospital, New Dehli. Seventy-one patients scheduled for dental extractions consented to the treatment protocol. Patients with endodontically treated teeth, extensive destruction of the clinical crowns, or periodontal support were excluded from the study. The response of each tooth to electric pulp testing (Analytic Technology Vitality Scanner 2006, Analytic Technology Corporation, Redmond, Wash.) was recorded, and a standardized periapical radiograph was taken with E-speed film (Ektaspeed EP21, Kodak U.K. Ltd., Hemel Hempstead, U.K.) held in a paralleling device (Rinn XCP, Rinn Corporation, Ill.). The ENDEX and RCM Mark II apex locators were assessed in canals containing one of the following (number of canals tested for each group are indicated in parentheses: (1) vital tissue that appeared healthy and bled when disturbed or was spontaneously hemorrhagic (18 canals in 18 teeth); (2) nonvital tissue that was necrotic and odorous (11 canals in 11 teeth); or (3) pus or exudate (six canals in six teeth). In addition the devices were assessed in canals containing the following solutions: (4) sodium hypochlorite (Sainsbury's Bleach: J.S. Sainsbury, London, U.K.) (15 canals in 13 teeth); or (5) sterile distilled water (11 canals in 11 teeth), After administration of local anesthesia (2%)
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Volume 79, Number 4
NaOCI Short 2 12
Water
Total
Flush
Long
Short
Flush
Long
1 0
12 3
4 6
0 0
7
9
5
30
lidocaine hydrochloride [Xylocaine] with adrenaline 1:80,000, Astra Pharmaceuticals Ltd., Kings Langley, U.K.) was done, each tooth was isolated under a rubber dam. A uniform and stable occlusal reference plane was created by removing 2 mm of the incisal edge of anterior teeth and the occlusal surface of posterior teeth. After access into the pulp chamber was gained, the contents were noted and removed. Adequate access was provided to the root canals by removing the entire roof of the pulp chamber with a diamond bur (767/9C - two striper, Abrasive technology, Premier Dental Products, Philadelphia, Pa.). Undercuts were placed in opposing pulp chamber walls for retention of the composite material to be inserted later. The pulp chamber was then dried with sterile cotton pellets (Johnson & Johnson Ltd., Maidenhead, U.K.). The ENDEX was calibrated for each canal according to the manufacturer's instructions. Canal length was then determined with size 06, 08, or 10 K-flex files (Kerr U.K. Ltd., Peterborough, England). After the file was advanced apically until the ENDEX indicated the apical limit was reached, a silicone rubber stop (Maillefer S.A., Baillaigues, Switzerland) was carefully pushed down the file shank until it contacted the occlusal reference point. The ENDEX was then switched off, and the RCM Mark II was connected to the patient via a circuit switching box designed to allow interchange between the two apex locators without disturbing the file or electrical connections. The value of the figure on the digital display of the R C M Mark II corresponding to the zero value on the ENDEX was recorded. The file was then removed from the canal and was measured to the nearest 0.25 mm with a graduated metal ruler (No. 64R ruler: Rabone Chesterman, U.K.). The length was noted as L1. The file was replaced into the canal with the R C M Mark II switched on and advanced until the device indicated zero. With the use of the switching box, the ENDEX was brought into the circuit, and the file position corresponding to a zero reading on the R C M was recorded as long, flush, or short. The file was removed from the canal, and its length (L2) was measured as determined by the R C M Mark II. The file was then replaced in the canal to length L 1,
Short
Flush
Long
3 0
49 31
and its position was reconfirmed by the ENDEX. A diluted, light-cured, composite resin (Adaptic LC, Johnson & Johnson Ltd., Maidenhead, U.K.) was introduced around the file in the pulp chamber with a syringe (Centrix Mark II, Hawe-Neos Dental, Gentilino, Switzerland) and was light-cured for 1 minute (Visilux 2 light curing unit, 3M Ltd., Loughborough, U.K.). Further incremental layers of resin were placed and cured. The absence of file movement was checked by leaving the apex locators switched on. Sufficient composite was placed to cover the occlusal surface of the tooth by about 1 mm, and the file was sectioned through this superficial layer with a diamond bur. To confirm that the file had not moved, the original reading of the apex locator was verified by touching the file electrode to the embedded cut surface of the file. The rubber dam was then removed, and a postoperative radiograph was exposed with the file in situ. The tooth was then carefully extracted and stored in 70% 2-propanol isopropyl alcohol for transportation to the Eastman Dental Hospital. In the teeth in which sodium hypochlorite and sterile water were tested, the canals were enlarged apically with H-type files to International Standards Organization (ISO) size 25 (Kerr U.K. Ltd., Peterborough, U.K.) and were filled with the appropriate irrigant. Care was taken to ensure that the irrigant remained below the canal orifice. The evaluation of the position of the file tip in relation to the apical foramen was conducted at the Eastman Dental Hospital. A radiograph was taken of each tooth in the proximal and bucco-lingual planes, and these radiographs together with those from the clinical study were viewed under X2.5 magnification on a masked backlit viewer (Velopex, Medivance Instruments Ltd., London, U.K.). The distance between the file tip and radiographic apex was measured with a pair of electronic vernier callipers (Sylvac S.A., Switzerland) on both sets of radiographs. Adherent soft tissue was removed from the apical two thirds of each root by immersing the teeth in a 1% sodium hypochlorite solution for 30 minutes, rinsing under running water for 5 minutes, and gently air drying. A radiograph was taken to confirm that no
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Table IlL File measurements under different canal conditions for the ENDEX and R C M Mark II* Vital Distancefrom apical (mm) foramen >1 (%)
0.5-1 (%) <0.5 (%)
0.o (%) <-0.5 (%) -0.5--1 (%) >--1 (%) Total (%)
Endex
Necrotic
RCM Mark H
Endex
Pus/exudate
RCM Mark H
Endex
NaOCI
RCM Mark H
1
0
2
2
0
1
(5.6) 1 (5.6) 11 (61.1)
(0) 5 (27.8) 3 (16.7)
(18.2) 4 (36.4) 5 (45.4)
(18.2) 4 (36.4) 5 (45.4)
(0) 1 (16.7) 5 (83.3)
(16.7) 1 (16.7) 2 (33.3)
2 (11.1) 3 (16.6) 0 (0) 0 (0) 18 (100)
0 (0) 6 (33.3) 3 (16.7) 1 (5.5) 18 (100)
o
0
o
(0) 0 (0) 0 (0) 0 (0) 11 (100)
(0) 0 (0) 0 (0) 0 (0) 11 (100)
(0) 0 (0) 0 (0) 0 (0) 6 (100)
0 (0) 1 (16.7) 1 (16.7) 0 (0) 6 (100)
Endex 0
(0) 9 (60) 3 (20)
1 (6.7) 2 (13.3) 0 (0) 0 (0) 15 (100)
Water
RCM Mark H
Endex
RCM Mark H
0
1
1
(0) 2 (13.3) 1 (6.7)
(19.1) 2 (18.1) 4 (36.4)
(9.1) 4 (36.3) 0 (0)
o (0) 0 (0) 0 (0) 12 (80) 15 (100)
o (0) 3 (27.3) 1 (9.1) 0 (0) 11 (100)
0 (0) 3 (27.3) 1 (9.1) 2 (18.2) 11 (100)
NaOCI, Sodiumhypochlorite. *Positive and negativevaluesrepresent long and short files, respectively.Data represent numbersand percentages of canals.
apparent change in file position occurred. The relation between the file tip and apical foramen was then examined at X25 magnification with a stereomicroscope (M400 Makroscope, Wild, Heerbrug, Switzerland). Each root tip was rotated along its long axis so that the foramen was uppermost, and a record was made of whether the file tip was long, flush, or short of the apical foramen. Where the file tip was visible the greatest distance between it and the coronal-most margin of the foramen was measured with the vernier scale on the stereomicroscope. This measurement was the greatest amount that the file tip was extended out of the apical foramen. In those cases where the file tip was short of the apical foramen, the root apexes were demineralized in a 4.75% solution of formic acid (BDH Chemicalsl Leicestershire, U.K.) followed by serial dehydration in ethyl alcohol (BDH Chemicals). They were then cleared in methyl salicylate (BDH Chemicals). The apical anatomy in relation to the file was visualized, and the distance between the file tip and coronal-most margin was recorded under the stereomicroscope as described previously. Results for the R C M Mark II were derived by subtracting the difference in canal length measurements of the two apex locators, L1 and L2, from the actual distance between the file tip and apical foramen as recorded in the laboratory. The following equation shows the relationship: Derived file position = (actual distance between file tip and foramen) - ( L 1 - L2). Data relating the distance of the file tip from the apical foramen with canal contents was analyzed with
and without the presence of sodium hypochlorite. This procedure allowed for the manufacturer's recommendation that the R C M Mark I1 does not function well in the presence of this electrolyte. A chi-squared test was used to compare the difference between the file positions determined electronically and those estimated radiographically. A valid statistical analysis of differences in file positions between teeth with different canal contents was not considered possible because of inadequate numbers in some groups. RESULTS
Twelve teeth were excluded from the study; six teeth fractured during extraction, and six had poor quality radiographs. Consequently 59 teeth with a total of 61 root canals were examined in the laboratory. An overall comparison between actual file position, as determined electronically by the ENDEX and the apparent radiographic position, with the derived file position for the R C M Mark II is presented in Table I. Although the files were judged in many cases (57.4%) to be flush with the radiographic apex, the file tip in fact extended past the coronal-most margin of the apical foramen. More long readings occurred with the ENDEX (80.3%) than with the RCM Mark II (50.8%), and more short readings occurred with the RCM Mark II (49.2%) than with the ENDEX (14.7%). Chi-squared testing indicated a highly significant difference between each technique of canal length determination (p < 0.001). The overall results of the influence of the five different canal contents on the
ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
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Total
Endex
Total minus NaOCI
R C M Mark H
Endex
R C M Mark H
4
4
4
4
17
16
8
14
28
11
25
10
3
0
2
0
8
10
6
10
1
5
1
5
0
15
0
3
61
61
46
46
ability of each apex locator to detect the apical foramen are presented in Table II. A more detailed assessment of the specific measurements from file tip to apical foramen for each apex locator under the different canal conditions is presented in Table III and summarized in Table IV. DISCUSSION The accepted technique for determining working length frequently involves radiographic estimation of a position 1 mm short of the radiographic apex where the main root canal is thought to exit onto the root surface at the apical foramen. 13,26 Radiographs, however, infrequently show the position of the apical foramen or constriction. The findings of the present study agree with others such as that of Olson et al. 27 These findings show that limitations exist in relying on radiographs for accurate length determination. The overall results indicated a large discrepancy between the observed radiographic and actual file positions; radiographs suggest a position shorter than the one that really exists. 8, 28 In general it is agreed that root canals obturated up to 2 mm short of the radiographic apex have improved success rates over those that are either flush, 29 overextended, 3~ 31 or more than 2 mm short 1 of it. Despite the difficulties that occur with the use of radiographs for consistent location of the apical foramen, success rates based on radiographic estimation of working length are relatively high. 32, 33 Nevertheless precise location of the apical foramen would be an advantage and may further improve success rates.
In vivo radiographic assessment of file position alone has been shown to be arbitrary, 34 and results from such studies can therefore be questioned. Studies involving tooth extraction to directly examine the relation between the file tip and root apex require that each file is securely fixed in situ with an appropriate material. Repositioning a file to its measured length after extraction of the tooth may be inaccurate because of differences in path of the file and effect of parallax on relative position of stop and reference point. In this study all precautions were taken to prevent movement of the file tip relative to the root tip. Careful file cementation with dilute resin, sectioning, tooth extraction, and subsequent in vitro processing were conducted to prevent loss or distortion of mineralized tissues apically. In addition, as reported by LeQuire et al., 35 placing the root apexes in a dilute solution of sodium hypochlorite adequately removed adherent soft tissue without altering the hard tissues. The results of the study showed that in the presence of vital tissue, even when hemorrhagic, both the ENDEX and RCM Mark II showed an accuracy of 94.4% within 1 mm of the apical foramen. The ENDEX, however, performed better when accuracy within 0.5 mm was considered (Table IV). The accuracy obtained for each device in the presence of necrotic tissue was identical, although in both cases it was lower than that for vital tissue (Table II). It was unlikely that these results were due to experimental error, because the samples occurred randomly throughout the study. The results obtained in the presence of pus or exudate should be interpreted with caution because of the low sample numbers. It was apparent, however, that the E N D E X provided only long readings, whereas the R C M Mark II gave a greater distribution of resuits (Table III). The presence of sterile water affected the accuracy of both apex locators, particularly when it was measured to within 0.5 mm of the apical foramen (RCM Mark II 27.3%, E N D E X 63.7%). Overall, however, the E N D E X performed better than the R C M Mark II in canals containing this electrolyte. The presence of sodium hypochlorite had the greatest effect on the accuracy of the instruments. Although the manufacturer of the R C M Mark II states that the device will not function accurately in the presence of sodium hypochlorite, it did so in a few cases. On the other hand the E N D E X gave long readings. If, however, readings within 1 mm of the apical foramen were considered, the device was accurate (RCM Mark II 20%, E N D E X 100%). The overall accuracies of the E N D E X and R C M Mark II (91.3% and 84.8%, respectively) within 1 mm
502
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ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
April 1995 Table IV. File measurements for the E N D E X and R C M Mark II within 0.5 mm and 1.0 mm of the apical foramen under different canal conditions*
Distancefrom apical foramen (ram) Within + 0.5 ENDEX Within 1 R C M Mark II
Within + 0.5 Within + 1
Vital (%) 16 (88.9) 17 (94.4) 9 (50) 17 (94.4)
Necrotic (%)
Pus/exudate (%)
NaOCI (%)
Water (%)
Total (%)
Total minus NaOCl(%)
5 (45.4) 9 (81.8) 5 (45.4) 9 (81.8)
5 (83.3) 6 (100) 3 (50) 5
6 (40) 15 (100) 1 (6.7) 3
7 (63.6) 10 (90.0) 3 (27.3) 8
39 (63.9) 57 (93.4) 21 (34.4) 42
33 (71.7) 42 (91.3) 20 (43.5) 39
(72.7)
(68.9)
(84.8)
(83.3)
(20)
NaOCI, Sodium hypochlorite. *Data represent numbers and percentages of canals.
of the apical foramen (Table IV) compare well with those from other in vivo studies in which accuracies range from 1 5 % 34 t o 1 0 0 % . 36 When the results of this study are compared with the only other similar study involving the RCM Mark 1I, 20 a marked difference is seen in overall accuracies obtained within 0.5 mm of the apical foramen. One explanation for this difference may be attributed to the file movement noted in 18.9% of their samples. Furthermore their methodology differed in that the root apex was ground to make measurements of short file positions. This procedure may have led to a loss of orientation and therefore to less accuracy in measurement. The reference point used for the measurement of short files was also different from the present study, whereas that for long files was identical. A recent in vivo radiographic study of the ENDEX 23 found that the device was accurate within 0.5 mm of the apical foramen in 8 9.64% of cases. Another in vivo study 24 using extracted teeth achieved broadly similar results. All their files (100%) 24) were within 1 mm of the apical foramen in both vital and necrotic canals. In the present study the values were 94.4% for vital canals and 81.8% for necrotic canals (Table IV). The results for readings within 0.5 mm were similar for vital canals, 82.4% 24 and 88.9% (this study). The readings within 0.5 ram, however, were substantially different for necrotic canals, 87.5% (value was calculated by authors from figures of Mayeda et al.) and 45.4% (this study). The differences in results may be explained by the different methodology. Mayeda et al. 24 irrigated canals with 5.25% sodium hypochlorite and did not dry the canals before measurement. Additionally their method of measurement relied on grinding to expose the canal and apical foramen. Another explanation may be differences between the apex locators and the manner in which they were used, although the manufacturer's instructions were followed closely.
The greater number of long readings with the ENDEX compared with that of the RCM Mark II in this study suggests that the manufacturer's calibration resulted in an overestimation of canal length. In addition the R C M Mark II gave more short readings, although in a large number of cases (11), sodium hypochlorite was present, and many of these readings were more than 1.5 mm away from the apical foramen. If the short readings are adjusted to exclude the effect of sodium hypochlorite, most of the readings for both devices (ENDEX, 71.7%, R C M Mark II, 43.5%) fall within 0.5 mm of the apical foramen (Table IV). This study confirmed that the sole use of radiographs to establish canal length can be misleading and inaccurate.2O, 34, 37 It appears that a combination of electronic and radiographic methods are more accurate than a single method, which is in agreement with the findings of Keller et al. 38 CONCLUSIONS
The overall accuracies for both the E N D E X and RCM Mark II were well within a clinically acceptable range, 1 mm of the apical foramen, as defined in other in vivo studies. Each device, however, has its limitations, and it appears that neither apex locator nor radiographs are consistently accurate for canal length determination. This study concluded that the E N D E X was accurate to within 0.5 mm of the apical foramen in 71.7% of cases and to within 1 mm in 91.3% of canals tested. The presence of different canal contents and electrolytes had varying effects on the accuracy of each device. The ENDEX, unlike the RCM Mark II, appeared to function consistently in the presence of sodium hypochlorite. In necrotic tissue, however, both devices behaved identically. The accuracy of the ENDEX within 0.5 mm of the apical foramen in the presence of vital pulp tissue or pus was higher than that of the R C M Mark II.
Arora and Gulabivala
ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
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Volume 79, Number 4
It was concluded that the ENDEX appeared more accurate than the RCM Mark II in locating the position of the apical foramen. W e gratefully acknowledge the assistance of Evident Dental Co. Ltd. (London, U.K.) and O s a d a Electric Co. (Tokyo, J a p a n ) t h r o u g h their agents Cottrell and Co. (London, England). T h e authors are also grateful to M i s s Louise T h o m p s o n for expert typing of the manuscript.
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Reprint requests: K. Gulabivala, BDS, MSc, FDS Department of Conservative Dentistry Eastman Dental Institute and Hospital 256 Grays Inn Road London WCIX 8LD U.K.