Dental Hypotheses

ORIGINAL RESEARCH
Year
: 2020  |  Volume : 11  |  Issue : 2  |  Page : 33--39

A Comparative Evaluation of Four Different Techniques for Determining the Accuracy of Root Canal Working Length: An In Vitro Study


Rakesh Kumar Yadav, Harsh Bhoot, Anil Chandra, Promila Verma, Ramesh Bharti, Vijay Kumar Shakya 
 Department of Conservative Dentistry and Endodontics, King George’s Medical University, Lucknow, Uttar Pradesh, India

Correspondence Address:
MDS, Professor (Junior Grade) Rakesh Kumar Yadav
Department of Conservative Dentistry and Endodontics, King George’s Medical University, Lucknow, Uttar Pradesh
India

Abstract

Introduction: Complete disinfection of root canal is one of the main objectives of root canal treatment. However, complete disinfection is only possible after correct determination of root canal working length. Thus, determining a correct working length is essential for endodontic success. Thus, the present study was conducted with the aim to comparatively evaluate the accuracy of four different techniques in determining root canal working length. Material and Methods: 30 freshly extracted human single-rooted teeth were taken. After sectioning the teeth at the cemento-enamel junction, K-Flexofile with size 10 was used to check the patency of canal and major foramen. Each sample was then subjected to all the four techniques. The four techniques used were conventional radiography, radivisiography, electronic apex locator (raypex 6) and cone beam-computed tomography. After calculating each root canal length of samples, their actual length was measured by using K- Flexofile until its tip became visible through the major foramen. The file was taken out when a magnifying glass showed its tip at the coronal border of major foramen. The adjustment of rubber stop was done according to the occlusal reference, and then the distance between the stop to the file tip was measured. Finally a comparison was done for each sample between the root canal length recorded with the four techniques and the actual length. Results: Mean of absolute differences with respect to actual length was lowest in case of electronic apex locator whereas, it was highest in case of cone beam-computed tomography. Conventional radiography and Radiovisiography had negative mean difference values that showed overestimated canal length. A significant difference was observed between cone beam-computed tomography and the other three techniques respectively (P < 0.05). Conclusion: Raypex 6 apex locator was more accurate than the other three techniques in determining root canal working length.



How to cite this article:
Yadav RK, Bhoot H, Chandra A, Verma P, Bharti R, Shakya VK. A Comparative Evaluation of Four Different Techniques for Determining the Accuracy of Root Canal Working Length: An In Vitro Study.Dent Hypotheses 2020;11:33-39


How to cite this URL:
Yadav RK, Bhoot H, Chandra A, Verma P, Bharti R, Shakya VK. A Comparative Evaluation of Four Different Techniques for Determining the Accuracy of Root Canal Working Length: An In Vitro Study. Dent Hypotheses [serial online] 2020 [cited 2020 Jul 12 ];11:33-39
Available from: http://www.dentalhypotheses.com/text.asp?2020/11/2/33/286348


Full Text



 Introduction



Complete disinfection of root canal is one of the main objectives of root canal treatment. However, complete disinfection is only possible after correct determination of root canal working length. Thus, determining correct working length is essential for endodontic success. A failure rate, ranging from 10% to 50% might result after an observation period of 10 years if the operator fails to determine the correct working length.[1] The definition of working length according to American Association of Endodontists (2003), stated that working length is the distance between coronal reference point and the point at which canal preparation and filling should terminate.[2]

The most important disadvantage of radiography is two-dimensional representation of a three-dimensional object.[3] Technique’s sensitivity and subjectivity are the other shortcomings of radiographic method as elongation or foreshortening of the image, overlapping of the crowns and roots could occur due to incorrect cone angulations and film position.[4],[5] Ionising radiation is the other major issue with this technique.[6]

In the present study, we have used both conventional and digital radiography to determine the working length as the latter has a number of advantages over conventional radiography. The most important being the computer storage of the images as in the case of conventional radiography, the film could distort over a period.[7] Other advantages include the elimination of chemical processing procedure and reduction in radiation dose.[8]

The use of electronic devices to calculate the working length was first proposed by Custer.[9] Suzuki’s investigations led to the invention of first electronic apex locator with the aim to precisely determine root canal length.[10] The studies have shown that apex locators are more accurate than radiographs.[11],[12] Furthermore, there is no radiation involved in case of apex locator. Over the years, many models of apex locators have developed, one of them is Raypex 6® apex locator (VDW, Munich, Germany) which is a new multi-frequency electronic apex locator.

The latest tool used to determine working length is cone beam computed tomography (CBCT). The main advantage of CBCT over periapical radiographs is its ability to show the root canal morphology in three dimensions. Moreover, the apical foramen could not be located in case of two-dimensional radiographs, because of which the radiographic apex had to be used as an apical reference point, which in turn resulted in overestimation of root canal working length.[13] In contrast, the three-dimensional view of CBCT could help the operator locate the apical foramen with more precision.[12],[14] Therefore, the clinician should take advantage of all the information available in pre-existing CBCT scans.[14],[15]

Thus, the conventional techniques and recent advancements, the present study was conducted with the aim to comparatively evaluate the accuracy of four different techniques in determining root canal working length.

 Material and Methods



The study was an in-vitro study, conducted on 30 single-rooted freshly extracted human teeth. They were washed thoroughly under running tap water to remove blood and debris, and were stored in 0.2% thymol solution to prevent dehydration and from becoming brittle.

The selection criteria adopted from Cunha D’ et al.[16] included teeth with fully developed apexes, free of caries, fratures, root resorption, etc., evaluated under Dental Operating Microscope (OPMI PICO 111 Carl Zeiss Meditec AG) calcifications or previous endodontic treatments and without any previous restoration. The teeth were excluded which did not fulfil the selection criteria. The section of teeth was done horizontally at the cemento-enamel junction by using diamond disc to achieve unrestricted access to the canal and to obtain a flat surface for placing rubber stop. The flaring of canal orifices was done using Gates-Glidden drills (Dentsply Maillefer, Ballaigues, Switzerland) of numbers 1 −3. Irrigation of canal was done using 5 ml of saline solution and was dried using paper points. K-Flexofile of size 10 was used to check the patency of the canal and major foramen. After this all the samples were subjected to all four different techniques.

Conventional radiography

Ingle and Bakland (2002) method was used to determine the working length.[17] Parallel technique was used to determine the radiographic tooth length preoperatively. A 15 K-file (Dentsply Maillefer, Ballaigues, Switzerland) with a length 1 mm short (safety allowance) than the tooth length as determined from the preoperative radiograph was placed in the root canal, and a working length radiograph was taken. The difference between the tip of the file and the radiographic apex was measured. The difference thus obtained was added to the original measured length if the file was short of the apex or was subtracted if it was beyond the apex. In order to determine the apical termination of the root canal, 0.5 mm was subtracted from the adjusted length of tooth [Figure 1].{Figure 1}

Radiovisiography

Method used to determine working length through conventional radiography was used for radiovisiography (GENDEX GX S-700, Gendex Dental Systems Hatfield, PA 19440 USA) as well. Radiovisiography machine uses a USB-driven intraoral sensor based on a complementary metal oxide semiconductor (CMOS) technology specially designed for dental use and X-ray exposer setting as per manufactures recommendation. The difference between the tip of the file and radiographic apex was measured using a digital ruler [Figure 1].

Electronic measurements

Raypex 6® apex locator (VDW, Munich, Germany), was used for electronic measurements. Alginate moulds were used to embed the teeth samples.[18] According to the manufacturer’s instructions apex locator was used. K-Flexofile (depending on the width of the root canal) of standard size 10 or 15 was used for measurements. The file was introduced to a point just beyond the major foramen (red ball) and was then retracted slightly to the limit of the fourth yellow bar. Only those readings were considered for evaluation which remained stable for at least 5 seconds. The adjustment of rubber stop was done according to the requirement, and a digital calliper was used to calculate the distance between it and the tip of file.

CBCT measurements

For CBCT measurements, the teeth embedded in alginate mould were used.[18] The CBCT images were obtained with the CS 9300 (Carestream) scanner with a 0.5 mm voxel size. The mould was placed in a consistent position to get a standardized reading for each sample. Exposure time, current amplitude and voltage were set according to manufacturer’s instructions. An experienced radiology personnel took the CBCT images for each sample. Bucco-lingual and mesio-distal sections were obtained for all the samples. In both the sections, full length of the root canal was visualized in a single slice. Measurements were obtained for both the sections by tracing the canal from the coronal reference point to its terminus. Final measurement was the arithmetic mean of both the measurements. No modification was done in the images and the procedures of measurement and alignment for CBCT images mentioned in this study was performed using a specialized software (Trophy Dicom).

After recording the root canal length of each sample with all the four techniques, actual length was recorded [Figure 2].{Figure 2}

Actual length measurements

For actual length measurements, same file used for previous measurements was used. It was inserted within the canal until its tip could be seen through the major foramen. It was then withdrawn until its tip was in line with the most coronal border of the major foramen. The whole procedure was performed under a magnifying glass to improve the accuracy. The distance between the rubber stop and the tip was measured using a digital calliper and was recorded as actual length.

Finally a comparison was done for each sample between the root canal length recorded with the four techniques and the actual length.

Statistical methods

Statistical Package for Social Sciences (SPSS) Version 20.0 software was used for statistical analysis.

Data Processing

Differences between the measurements with the four techniques and actual length was calculated. The negative and positive values thus obtained showed long and short length of actual root canal length.

Data analysis

A one-way repeated measures ANOVA was conducted to determine whether there was a statistically significant difference in accuracy of root canal working length measurement using four different measurement techniques. There were no outliers and the data were normally distributed, as assessed by boxplot and Shapiro-Wilk test (P > .05), respectively. The assumption of sphericity was not met, as assessed by Mauchly’s test of sphericity, χ2(2) = 20.24, P = 0.001. Therefore, a Greenhouse-Geisser correction was applied (ε = 0.672). Finally, Post hoc analysis with a Bonferroni adjustment was done for pairwise comparisons amongst the four techniques.

In addition, the differences between the measurements done with the four techniques and actual length were classified into:

±0.5 mm: Including those differences falling within ±0.5 mm of the actual length.

The chi-squared test was used to compare percentages of ±0.5 mm measurements amongst the four techniques.

The statistical analysis was carried out accepting a level of significance of 5%.

 Results



The mean and standard deviation of differences between the measurements done with the four techniques and actual length is shown in [Table 1]. The least difference was seen in Raypex 6® apex locator group. Conventional radiography and radiovisiography have negative values of mean difference which signifies that they have overestimated the canal length.{Table 1}

[Table 2] shows the frequency of measurements of different techniques falling within 0.5 mm of the actual length. It is 100% in case of electronic apex locator, whereas only 46.7% in case of conventional radiography, the difference being statistically significant (P < 0.05).{Table 2}

[Table 3] shows the frequency of measurements of different techniques that prove long and short with respect to actual length.{Table 3}

 Discussion



Determination of a correct working length is one of the most important steps for a successful root canal treatment as thorough cleaning and filling of the root canal system is only possible after effective execution of this step.[19]

Radiography is one of the most common methods till date to determine root canal working length. In the present study, conventional radiography and radiovisiography were compared and no significant differences were observed between the two techniques which is in accordance with the literature.[19],[20] However several authors have reported the superiority of digital system in uniradicualar teeth.[21],[22] and in cases where larger instruments were used to determine working length, whereas some have confirmed the superiority of conventional radiography when working length was determined with smaller instruments.[23],[24] Due to the difference in digital system used in different studies, it is difficult to assess and compare these findings. In the present study, although no significant differences were observed between the two radiographic techniques, however, radiovisiography was a bit more accurate than conventional radiography in determining root canal working length. It could be attributed to the fact that the file tip was better visualized as contrast and image brightness can be adjusted in case of radiovisiography.

When comparing all included methods for length determination a significant difference was observed between CBCT and conventional radiography as well as Radiovisiography and apex locator groups. The mean of absolute differences between CBCT working length and actual length was +0.36 mm and apex locator it was 0.08 mm whereas in case of conventional radiography and radiovisiography, it was −0.22 mm and −0.15 mm respectively [Table 1]. Positive value indicates that apex locator and CBCT estimated working length within the actual length whereas negative value indicates overestimation of the canal length. When comparing the mean of absolute differences magnitude wise, it is higher in case of CBCT followed by apex locator, conventional radiography and radiovisiography. Positive values in case of apex locater and CBCT are actually more favourable based on the fact that it is not overestimating the canal length and it is a proven fact that instrumentation beyond the apical foramen is associated with a poor prognosis; therefore, it should be avoided.[25],[26] [Table 3] confirms our observations as it clearly shows that conventional radiography, radiovisiography, CBCT and apex locator overestimated the canal length in 53.33%, 60%, 10% and 6.66% of the cases respectively. Our findings are in accordance with other studies which reported overestimation of the canal length with respect to radiography and underestimation with respect to CBCT.[27],[28],[29] Although CBCT is more favourable when compared to other radiographical methods but, one cannot use it as the first choice for working length determination because of potential radiation risks. Furthermore, smallest possible field of view is also recommended and a joint statement was issued recently by American Association of Endodontists and the American Academy of Oral and Maxillofacial Radiology in this context.[30]

When comparing apex locator with CBCT RayPex 6 apex locator was significantly better than CBCT in determining root canal working length. 100% values fall within the 0.5 mm range in case of RayPex 6 apex locator whereas it was only 63.3% in case of CBCT [Table 2]. Thus, it can be concluded that the performance of CBCT was inferior to RayPex 6 apex locator. There are very few studies comparing the two techniques. In a study it was found a mean discrepancy of 0.40 mm between the two techniques.[14] The authors also found a strong correlation between the endodontic working length as measured in the CBCT images and the electronic apex locator measurements. Thus they concluded that already existing CBCT scan can be used in combination with electronic apex locator to determine working length. Another study found a mean discrepancy of 0.51 mm between the two techniques.[15] In the present study, mean discrepancy between the two techniques was found to be 0.28 mm. Although inferior to electronic apex locator, it can be used especially in cases with inconsistent electronic apex locator measurements.

It was evident from the findings in [Table 1], [Table 2] and [Table 3] that Raypex 6 apex locator was more accurate in determining the root canal working length when compared to conventional radiography and radiovisiography. [Table 1] gives the details about the mean of absolute differences with respect to actual length which was 0.08 mm in case of apex locator, −0.22 mm for conventional radiography and −0.15 mm with respect to radiovisiography. [Table 2] shows the number of values falling within ±0.5 mm of actual length which was 100% in case of apex locator, 46.7% in case of conventional radiography and 76.7% in case of radiovisiography. [Table 3] shows that overestimations occurred in only 6.66% of the cases with respect to apex locator whereas in case of conventional radiography and radiovisiography, overestimations occurred in 53.33% and 60% of the cases respectively. Our findings are in accordance with the study done by in which they comparatively evaluated the accuracy of two electronic apex locators with conventional radiography. The two apex locators used were Raypex 5 and Apex NRG XFR. They found that overestimations occurred in 4% of the cases with Raypex 5, 0% of the cases with Apex NRG XFR and 40% of the cases with conventional radiography.[31] ElAyouti et al.[13] found that the frequency of over instrumentation was greater in posterior teeth than in anterior teeth when working with an acceptable in vitro working length radiograph. It could be attributed to the fact that the apical foramen is located laterally in 78 to 93% of posterior teeth.[32] When anatomic apex and apical foramen do no coincide, radiographs have a tendency towards overestimation. To avoid this overestimation, other methods should be considered to determine the working length. Other studies also concluded that complementing radiographic working length determination with electronic apex locator measurements may help to avoid overestimation beyond the apical foramen also much effective in calculating appropriate working length.[3],[33],[12],[34],[35]

 Conclusion



Under the experimental conditions, it can be concluded that Raypex 6® apex locator was more accurate than the other three techniques in determining root canal working length. Furthermore, conventional radiography and radiovisiography overestimated the root canal working length. While measurements made by CBCT were well within the canal.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Ethical approval

Ethical committee approved. The reference number is: 71st ECM II-B Thesis/P36.

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