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ORIGINAL ARTICLE
Year : 2018  |  Volume : 8  |  Issue : 2  |  Page : 99-105

Determination of apical constriction and apical foramen using electronic apex locator in vivo: Comparison between vital and nonvital teeth


1 Department of Endodontics and Conservative Dentistry, D.A.V.(c) Dental College, Yamuna Nagar, Haryana, India
2 Department of Pedodontics and Preventive Dentistry, Post Graduate Institute of Dental Sciences, Rohtak, Haryana, India

Date of Web Publication5-Apr-2018

Correspondence Address:
Dr. Gaurav Aggarwal
H. No. 536, Sector 17, Huda, Jagadhri, Yamunanagar - 135 003, Haryana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/sej.sej_35_17

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  Abstract 

Introduction: The aims of the present study were (1) to compare the in vivo accuracy of electronic apex locator (EAL) to locate the apical foramen and apical constriction (AC) in vital and nonvital teeth and (2) to measure and compare the distance between the AC and apical foramen based on EAL readings and those obtained by direct observation under stereomicroscope following extraction of the tooth.
Materials and Methods: A sample of 40 teeth scheduled for extraction independent of the study from patients in the age range of 45–65 years was selected and divided into two groups (Group I – vital and Group II – nonvital). The AC and apical foramen were located using Root ZX II (J. Morita Corp, Kyoto, Japan) in both the groups and then by direct observation under stereomicroscope following extraction.
Results: Fischer's exact test found no statistically significant difference in the ability of EAL to locate AC and apical foramen when compared between vital and nonvital teeth. Likewise, no statistically significant difference was found in the distance between the AC and apical foramen as measured by EAL in vivo and that measured by direct observation under stereomicroscope following extraction in vital (P = 0.412) and nonvital (P = 0.719) teeth (paired t-test).
Conclusion: The study supports that EAL measures the location of AC and apical foramen with similar accuracy in vital and nonvital teeth. Furthermore, the distance between the two is reliable when compared with the actual distance observed under stereomicroscope supporting its widespread usage in clinical endodontics.

Keywords: Apical constriction, apical foramen, electronic apex locator, nonvital teeth, root ZX II, vital


How to cite this article:
Aggarwal G, Bogra P, Gupta S, Jindal A, Jain N. Determination of apical constriction and apical foramen using electronic apex locator in vivo: Comparison between vital and nonvital teeth. Saudi Endod J 2018;8:99-105

How to cite this URL:
Aggarwal G, Bogra P, Gupta S, Jindal A, Jain N. Determination of apical constriction and apical foramen using electronic apex locator in vivo: Comparison between vital and nonvital teeth. Saudi Endod J [serial online] 2018 [cited 2018 Apr 22];8:99-105. Available from: http://www.saudiendodj.com/text.asp?2018/8/2/99/229352


  Introduction Top


Accuracy of working length determination in endodontics is very essential for the success of the treatment. Working length is defined as the distance from the coronal reference point to the point at which canal preparation and obturation should terminate.[1] Apical constriction (AC) considered as the apical limit of canal instrumentation and obturation is not only the narrowest part of canal but a morphologic landmark that helps to improve the apical seal when the canal is obturated.[2] This AC (minor diameter as described by Kuttler, 1955) usually widens to take a funnel shape ending into the apical foramen or major diameter.[3] It is difficult to locate either the AC or apical foramen. When the apical foramen is located, the position of the AC can be estimated; if the AC is not present. The preparation and obturation will usually be within the confines of the root. Accurate working length estimation is actually an attempt to debride and obturate closer to the apical foramen and not beyond it in any case.[4] Distance between minor and major diameter has been found to be 0.5 mm in the age group of 25 years and 0.65 mm in the age group of 55 years.[3] Anatomical studies of the apical third of the root canal have shown that the apical foramen coincides with root vertex in only 17%–46% of the cases.[5]

Seltzer et al. were the first to report greater success in terminating cleaning and obturating the root canal system just short of the radiographic apex, rather than overfilling or underfilling.[6] Since many years, various methods such as tactile sensation, conventional, or digital radiography have been used for determining root canal working length but all with a questionable success. This inaccuracy in determining the precise location of AC along with the increasing concern about radiation exposure and lack of three-dimensional representation in radiographs has led to the introduction and development of the electronic apex locators (EALs) and its increasing usage by the clinicians performing endodontic procedures.

Advancements in technology have led to the introduction of Root ZX. It is a gold standard apex locator that was initially introduced between 1991 and 1994 by Kobayashi and Suda. It uses the ratio method for determining the minor diameter position. It allows for the simultaneous measurement of impedance at two frequencies – high (8 kHz) and low (400 Hz); a quotient of impedance is then calculated and expressed as a position of the file in the canal.[7] The Root ZX has been exhaustively tested for accuracy in many clinical conditions, with many studies reporting 95%–100% accuracy.[8] Root ZX II (J. Morita Corp, Kyoto, Japan), one of the most evaluated EAL, is an updated version of the original Root ZX EAL with original electronic components being used with the addition of a new external casing.[9],[10]

Structural alterations in root apex of the nonvital teeth, electric conductivity of dentinal wall, pathological alteration in the apex of the tooth with apical periodontitis,[9] different impedance values between necrotic pulp and vital pulp due to the destruction of periodontal ligament [11],[12] may result in erroneous readings with the EALs. Furthermore, very few studies have taken vitality into consideration.[11],[12],[13],[14],[15],[16] Some studies have found statistically no difference in the accuracy of EAL to locate the AC and apical foramen in vital and nonvital cases [11],[13],[14],[15],[16] while some studies have found a significant difference (P< 0.05).[12]

Hence, the present study was undertaken with the following purposes: (1) to compare the in vivo accuracy of EAL to locate the AC and apical foramen and AC in vital and nonvital teeth, and (2) to measure and compare the distance between AC and apical foramen based on EAL readings and those obtained by direct observation under stereomicroscope after extraction of the tooth.


  Materials and Methods Top


A sample of 40 single-rooted teeth with mature apices from forty healthy adult patients in the age range of 45–65 years scheduled for extraction due to periodontal or prosthodontic reasons independent of the study were randomly selected from the Department of Oral and Maxillofacial Surgery, DAV (c) Dental College and Hospital, Yamuna Nagar. Patients with heart pacemakers or with a contributory medical history, obliterated canal, fractured tooth, teeth with more than one canal, teeth with open apex, apical resorption, apical pathosis, previous endodontic treatment, broken crowns/caries below the level of gingiva, and prosthetic crowns were excluded from the study. The approval for the study was taken from the institutional ethical committee. Written informed consent was obtained from each patient. Two standardized periapical radiographs with paralleling technique, one in buccolingual projection, and other with 30° mesial angulation were taken for each tooth to allow proper selection. The teeth were initially tested with cold test and then electric pulp tester (Digitest pulp vitality tester, Parkell products, USA) for evaluating the pulp sensibility. The final confirmation was done only after opening the pulp chamber and accordingly categorized into two groups: Group I (vital) and Group II (nonvital) of 20 teeth each. After administration of local anesthesia (2% lignocaine hydrochloride with adrenaline 1:120,000, Indoco Remedies Ltd., India), teeth were isolated with rubber dam. Caries and existing metal restorations were removed and standard access preparation was carried out using carbide burs (SS white, USA) in such a way that a straight-line access to the root canal was achieved. The cusps were flattened with a sterile diamond wheel stone (Mani, Tochigi, Japan) using a high-speed handpiece for reproducible reference points.

Once the canal was located, coronal flaring was done till Gates Glidden drill #3 (Mani, Tochigi, Japan) and the contents of the canal were grossly extirpated. After that, the canals were irrigated with 3% sodium hypochlorite (Prevest DenPro, India). The pulp chamber was gently dried with sterile cotton pellets and the excess irrigant in the chamber and canal was removed. The AC and apical foramen of the tooth were then located using EAL “Root ZX II” (J. Morita Corp, Kyoto, Japan) according to manufacturer's instructions. A size 15 K-file (Mani, Tochigi, Japan) was inserted until the meter read 0.5 mm in the middle of the green zone and was then advanced with a slow clockwise turn until the word Apex began to flash. The silicone stopper on the inserted file was set to the nearest already flattened cusp as a mark of reference. The file was taken out and the two readings – apex reading (a) and 0.5 mm reading (b) were measured individually. The difference of the file length between the apex reading and 0.5 mm reading was calculated and noted down (c) using the following formula: (c = a-b). The file was reinserted to the already known length till 0.5 mm reading and was then fixed in the canal with Glass ionomer cement (GC Universal Restorative, GC Corporation, Japan) with the silicone stopper set to the nearest already flattened cusp as a mark of reference. The file handle was removed using a tapered fissure bur at high speed. Subsequently, the rubber dam was removed, and the tooth was extracted with the file cemented in place. The extracted tooth was stored in 3% sodium hypochlorite for 15 min to clean the tooth of any organic and residual debris. It was then stored in 0.9% normal saline at room temperature and used within 1 week.

The apical foramen of the teeth was located under surgical microscope (Labomed India Private Limited, India) at 40 X magnification and the sectioning of the tooth was done according to the location of the foramen. If the foramen was located somewhat mesial or distal side of the apex, the longitudinal sectioning was done mesiodistally; if it was buccally or lingually, the cut was made accordingly. The plane of the cut was made in the same plane as the greatest curvature of the root. The initial penetration of the root to the file was made 8–10 mm from the apex of the extracted tooth using a fine diamond Bur. The dentin was removed till the root canal and file became visible and only a thin layer of dentin remained over the root canal. This thin dentin was then removed with a thin explorer tip. The apical portion was observed carefully and then photographed under the stereomicroscope as depicted in [Figure 1]. The images were then analyzed with Image Tool 3 software (University of Texas Health Science Center at San Antonio-UTHSCSA)[9] to measure the distance between file tip to the AC (d), file tip to the apical foramen (e), and the distance between actual AC and actual apical foramen (f) [Figure 2]a. The distance between tip of file to apex reading (g) was then calculated in relation to EAL mathematically (g = e + c).
Figure 1: Stereomicroscopic views of sectioned samples, original magnification ×40. (a-c) Few samples of Group I (vital). (d-f) Few samples of Group II (nonvital)

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Figure 2: Schematic diagrams showing (a) actual distance between apical constriction, apical foramen and tip of the file; d = actual distance between apical constriction to tip of the file; e = actual distance between apical foramen to tip of the file; f = actual distance between apical constriction to apical foramen. (b) Measurement of canal width at various points to determine apical constriction

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All the distances were measured in mm, and then, the readings of file tip were given a –ve sign if the file was coronal (short) and + ve sign if the file was apical (long) to AC and apical foramen. If AC was a slot and not a point, then the apical end of the AC was considered. If the AC was not well defined in the sample, the canal width was taken at every 0.25 mm and the shortest distance was taken as the AC [Figure 2]b.

A few of the stereomicroscopic images with different file positions have been shown in [Figure 3]. Any tooth (n = 6) in which the file left the canal curvature or in which the canal curvature was in more than one plane, thereby, raising the file from the dentinal bed during dentin removal was rejected [Figure 4] and replaced with the new samples.
Figure 3: Stereomicroscopic views of sectioned samples, original magnification ×40. (a-c) Few samples with apical constriction as marked by a white arrow. (d-f) Few samples with file position out of apex

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Figure 4: Stereomicroscopic views of rejected samples, original magnification ×40. (a) Sample in which file left the canal curvature. (b) Sample in which file got raised from the dentinal bed

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The results were then statistically analyzed using Fischer's exact test, paired t-test, and independent t-test at 5% level of significance. The statistical analysis was done using SPSS (Statistical Package for Social Sciences) Version 16.0 Statistical Analysis Software, Chicago, SPSS Inc.


  Results Top


Results are summarized in [Table 1], [Table 2], [Table 3]. Independent t-test at 5% level of significance showed no significant difference between vital and nonvital teeth (P = 0.323) in determining the actual distance between AC to the tip of the file. However, Root ZX II recorded the AC more precisely in nonvital (−0.05 mm) than vital teeth (0.08 mm) [Table 1].
Table 1: Mean and standard deviation of distances measured by electronic apex locator, actual distances measured under stereomicroscope, and their comparison between vital and nonvital teeth

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Table 2: Accuracy of electronic apex locator to locate apical constriction and apical foramen in vital and nonvital teeth

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Table 3: Comparison of electronic apex locator distance between 0.5 mm reading to apex (c) and actual distance between apical constriction and apical foramen (f) in vital and nonvital teeth

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Accuracy of actual distance between AC to file tip was 100% for both vital and nonvital teeth when measured at the level of ±0.1 mm. However, it reduced to 55% in vital and 35% in nonvital teeth when accuracy was checked at +0.25 mm, but results were statistically nonsignificant (P > 0.05) [Table 2].

Root ZX II recorded the distance between 0.5 reading and apex to be 0.53 mm for vital teeth and 0.59 mm for nonvital teeth. This distance came out to be close to the actual distance measured between AC and apical foramen when directly observed under stereomicroscope which shows the accuracy of the EAL to be clinically acceptable for both vital and nonvital teeth. However, the difference was not statistically significant (vital [P = 0.412] and nonvital teeth [P = 0.719]) [Table 3].


  Discussion Top


Apical foramen and AC are more conceptual than actual as they cannot be located clinically.[4] Ideal apical limit for the working length has been recommended as the AC in most of the studies.[3],[17] Studies have shown that best results were obtained when the procedure terminated short of the radiographic apex in vital cases while in nonvital cases, this distance was shorter than vital, keeping in view the bacterial toxins and infected dentinal remnants remaining in the apical portion of the canal that might jeopardize the apical healing.[4] Nevertheless, whatever the apical limit, the measuring device used should be precise and reliable. Very few previous studies have evaluated the performance of EAL in vital and nonvital teeth in vivo.

A sample of 40 single-rooted teeth with mature apices from forty healthy adult patients in the age range of 45–65 years scheduled for extraction independent of the study was selected and divided into two groups (Group I – vital and Group II – nonvital). The AC and apical foramen were located using Root ZX II in both the groups. The manufacturers of more recent EALs claim that their products can locate the AC and detect the canal terminus. Thus, the present study used AC as a landmark by fixing the file with GIC up to that point. As it is difficult to locate AC both clinically and radiographically, samples were directly observed under stereomicroscope to precisely locate the actual position of AC, and apical foramen and comparison were made with the EAL readings for both vital and nonvital teeth.

In the present study, when accuracy of EAL to locate the AC in vital teeth was checked at ±1.00 mm and ±0.25 mm levels, it reduced from 100% to 55% [Table 2]. Previously conducted in vivo studies have showed an accuracy ranging from 72% to 100%.[11],[12],[18],[19],[20] The results of the present study are in general agreement with Dunlap et al.,[11] Pommer et al.,[12] and Sharma and Arora.[19] However, the results are in disagreement with Tselnik [20] and Stöber [18] which might probably be due to the difference in sample size and difference in reference point to measure the actual working length.[18]

When accuracy of EAL to locate the AC in nonvital teeth was checked at ±1.00 mm and ±0.25 mm levels, it reduced from 100% to 35% [Table 2]. Various in vitro studies showed an accuracy level varying from 76% to 100%.[11],[12],[21],[22],[23],[24] The results of the present study are in agreement with various authors.[11],[12],[23],[25] However, the results are in disagreement with Duh [24] probably due to the reason that AC was studied as such without cementation of the file in their study which could cause errors during measurement due to file movements.

The present study found accuracy of EAL to locate AC to be 90% in vital and 75% in nonvital teeth within +0.50 mm, but the difference was statistically insignificant [Table 2]. However, Pommer et al.[12] found statistically significant difference on comparing vital and nonvital teeth which may be due to the different EAL (apex finder) used for the study. Furthermore, there was a large difference in the sample size within the groups, i.e., 105 in vital and only 47 in nonvital. Dunlap et al.[11] found an accuracy of 88.3% within +0.50 mm and 100% within +0.75 mm in vital teeth while an accuracy of 76.47% within +0.50 mm and 88.3% within +0.75 mm in nonvital teeth. Minor difference in values from the present study might be due to the smaller sample size.

On measuring accuracy of EAL to locate the apical foramen at +1.00 mm and +0.25 mm levels, a reduction from 100% to 55% was found in vital teeth [Table 2]. Various authors reported an accuracy ranging from 82.7% to 100% when EAL was used to locate the apical foramen.[9], 13, [26],[27],[28] The results of the present study are in agreement with Pagavino et al.[27] and Arora and Gulabivala.[28] However, the results are in disagreement with Piasecki et al.,[9] Mayeda et al.,[13] and Shabahang et al.[26] probably due to the difference in reference point where the file was cemented,[9] difference in sample size, and different EAL used.[13]

On measuring accuracy of EAL to locate the apical foramen at +1.00 mm and +0.25 mm levels, a reduction from 95% to 35% was found in nonvital teeth [Table 2]. In various in vitro studies, when EAL was used to locate the apical foramen in nonvital teeth, the accuracy varied from 81.87%–100%.[9],[13],[28],[29] However, the results are in disagreement with Arora and Gulabivala [28] and Guise et al.[10] probably due to the use of gelatin as embedding media and a different EAL (Endex).[28]

Piasecki et al.[9] found accuracy to determine apical foramen with Root ZX II within +0.5 mm to be 100% in vital and 83% in nonvital groups. Mayeda et al.[13] got an accuracy of 88.2% within +0.5 mm in vital and 93.7% within +0.5 mm in nonvital teeth. Arora and Gulabivala [28] compared accuracy by Endex and RCM Mark II EAL and found both to be more accurate in vital (94%) than in nonvital teeth (81.8%) within +1.00 mm as tolerance level. In the present study, no statistically significant difference was found in the ability of EAL to locate the apical foramen at different levels when comparison was done between vital and nonvital teeth [Table 2].

Overinstrumentation beyond the apical foramen would definitely cause undesirable inflammatory response, extrusion of debris, and unnecessary trauma to the patient leading to discomfort and flare-up. Keeping this in view and considering all the values out of apex to be inaccurate, accuracy of EAL to locate the apical foramen was found to be 30% within −0.50 mm and 35% within −1.00 mm in vital teeth, and 30% within −0.50 mm and 40% within −1.00 mm in nonvital teeth [Table 2].

Kuttler [3] gave the most comprehensive anatomical microscopic study of the root tip and found the distance between the major and minor diameter to be in the range of 0.524–0.659 mm. Melius et al.[30] also found the mean distance between the two to be 0.594 mm. The present study found almost similar findings. The mean distance between 0.5 reading and apex with the EAL in vital and nonvital teeth was found to be 0.53 mm and 0.59 mm, respectively, and mean distance between actual AC and apical foramen of tooth when directly observed under stereomicroscope was found to be 0.47 mm and 0.56 mm, respectively [Table 3]. Whether such a small amount of inaccuracy in working length can have any clinical significance needs to be correlated with other clinical studies. However, these results are in disagreement with Jung et al.[31] who found the mean distance between 0.5 mark and major foramen to be 0.26–0.29 mm but with a different EAL. The use of an in vitro model to determine the length could have influenced the results in their study as it is not so easy to mimic the clinical conditions. Moreover, ×21.2 magnification was used instead of ×40 which was used in the present study.

In the present study, when the distance between 0.5 mm mark and apex as found by EAL was compared with the actual distance between the two (AC and apical foramen), no statistical significant difference was found. Reliability of 0.5 mark and apex reading in both vital and nonvital teeth with EAL was found to be acceptable and accurate.


  Conclusion Top


The results of the study demonstrate that EAL (Root ZX II) measures the location of AC and apical foramen with similar accuracy in vital and nonvital teeth. Furthermore, the distance between the two is reliable when compared with the actual distance observed under stereomicroscope supporting its widespread usage in clinical endodontics.

Acknowledgment

I would like to thank Dr. S. Vijay Singh, Professor and Head, Department of Endodontics and Conservative dentistry, DAV Dental College, Yamunanagar, Haryana, for allowing this study in his department.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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