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ORIGINAL ARTICLE
Year : 2022  |  Volume : 25  |  Issue : 4  |  Page : 524-530

Evaluation of dentinal crack propagation, amount of gutta percha remaining and time required during removal of gutta percha using two different rotary instruments and hand instruments - An In vitro study


1 Department of Conservative Dentistry and Endodontics, JSS Dental College and Hospita, Mysore, Karnataka, India
2 Department of Periodontology, Bharti Vidyapeeth Deemed University, Pune, Maharashtra, India

Date of Submission23-Sep-2021
Date of Acceptance31-Jan-2022
Date of Web Publication19-Apr-2022

Correspondence Address:
Dr. S Tejaswi
JSS Dental College and Hospital, Mysore, Karnataka, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_1838_21

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   Abstract 


Background: One of the most important goal of non surgical endodontic retreatment is the successful removal of gutta percha and sealers from the root canal system. A variety of techniques have been recommended for retreatment procedures for the removal of gutta-percha and sealers with or without the help of adjunctive chemical solvents, by using stainless steel hand files or nickel-titanium rotary files, gate glidden burs, heated instruments, ultrasonic instruments, and lasers 1,3. The current advancements in the design of NiTi instruments have proved efficacious in the removal of filling materials from the root canal wall and various studies have also confirmed their cleaning ability and efficacy 4,5. Nevertheless, the use of rotary instrumentation can lead to the formation of dentinal cracks in the root canal dentin. Many researchers have reported the incidence of crack formation and propagation after the procedure with manual, rotary and reciprocating instruments. The behavior of rotary instruments in the generation of defects have been the point of greatest interest during many years 6. These dentinal cracks can be defined as defects with a complete crack line extending from inner root canal space up to the outer surface of the root when the tensile stress in the root canal wall exceeds the tensile stress of dentin 7. Aim: This study was conducted to investigate and to compare the amount of dentinal microcracks formation with various new instrumentation methods and conventional hand filing method. It also looks into amount of gutta-percha removed after retreatment from the canal and the time required for all the instrumentation technique. Methodology: Sixty extracted human maxillary first molars with curved roots were mounted on addition silicone impression material incorporated in an aluminium hollow block, then instrumented using step-back preparation with 35 size K files. Obturation was done using gutta-percha with AH plus sealer. These were stored for 14 days and divided into three groups Mani GPR, Endostar Re Endo and H file and were subjected to retreatment procedures. Retreatment was considered complete when no filling material was observed on the canal wall and the canal was smooth and free of visible debris. The samples were examined under scanning electron microscope and the number of cracks were calculated. The percentage of root canal filling material and time taken was recorded. Statistical Analysis: The data obtained were analyzed by using descriptive statistics, ANOVA (Analysis of Variance), chi-square test and Scheffe's post hoc test through SPSS for window (version 22.0). Result: All the techniques showed similar amount of crack propagation, with no statistical difference between the group. Retreatment done using H Files required more time and removed less material. The coronal third showed less amount of gutta-percha remnants than the apical third in all groups. Conclusion: All the groups showed a similar amount of crack propagation. Less number of cracks were observed in the coronal one third and more amount of cracks were found at the apical third. Endostar RE Endo rotary instrument proved to be most effective and least time-consuming. Hedstrom Files required more time and removed less material.

Keywords: Dentinal cracks, Endostar RE Endo, H File, Mani GPR, NiTi retreatment files


How to cite this article:
Tejaswi S, Singh A, Manglekar S, Ambikathanaya U K, Shetty S. Evaluation of dentinal crack propagation, amount of gutta percha remaining and time required during removal of gutta percha using two different rotary instruments and hand instruments - An In vitro study. Niger J Clin Pract 2022;25:524-30

How to cite this URL:
Tejaswi S, Singh A, Manglekar S, Ambikathanaya U K, Shetty S. Evaluation of dentinal crack propagation, amount of gutta percha remaining and time required during removal of gutta percha using two different rotary instruments and hand instruments - An In vitro study. Niger J Clin Pract [serial online] 2022 [cited 2022 May 22];25:524-30. Available from: https://www.njcponline.com/text.asp?2022/25/4/524/343463




   Background Top


Endodontic therapy has a high success rate ranging from 86%–98%,[1] but despite this high success rate of endodontic treatment, failures may occur in a large number of cases and this could be due to various mishaps during treatment procedures such as incomplete negotiation of canals, improper restorations, which can lead to microleakage and bacterial recontamination, ledges, perforations and transportations that can occur because of improper instrumentation, under or overfilled canals.[1] These can be managed either by surgical or nonsurgical endodontic retreatment.

One of the most important goals of nonsurgical endodontic retreatment is the successful removal of gutta percha and sealers from the root canal system.

A variety of techniques have been recommended for retreatment procedures for the removal of gutta-percha and sealers with or without the help of adjunctive chemical solvents, by using stainless steel hand files or nickel-titanium rotary files, gate glidden burs, heated instruments, ultrasonic instruments, and lasers.[1],[2],[3]

The current advancements in the design of NiTi instruments have proved efficacious in the removal of filling materials from the root canal wall and various studies have also confirmed their cleaning ability and efficacy.[4],[5] Nevertheless, the use of rotary instrumentation can lead to the formation of dentinal cracks in the root canal dentin. Many researchers have reported the incidence of crack formation and propagation after the procedure with manual, rotary, and reciprocating instruments. The behavior of rotary instruments in the generation of defects has been the point of greatest interest for many years.[6]

These dentinal cracks can be defined as defects with a complete crack line extending from inner root canal space up to the outer surface of the root when the tensile stress in the root canal wall exceeds the tensile stress of dentin.[7]


   Aim Top


The objective of this study was to evaluate and compare the dentinal crack propagation in the root canal dentin and to evaluate the amount of gutta percha remaining and the time required for the retreatment procedure when using conventional hand filing and newer hand instrumentation techniques.


   Settings and Design Top


Sixty extracted human maxillary first molars were selected and stored in physiological saline solution throughout all the experimental procedures.[8] Teeth with root fractures, cracks, caries or restorations, severe anatomic variations, and severe calcified canals were excluded. Inclusion criteria included teeth having moderately curved apices and were confirmed using radiovisiography. (VATECH RVG EZ Sensor).

Only molars with one mesiobuccal canal were selected (MB1) and this was confirmed using a radiograph. Radiovisography (RVG) was used to determine the curvature using Schneider method. A straight line was drawn parallel to image and marked as point A. Another second point is marked where the curvature starts to deviate, which is labelled as point B. Point C is marked as the third point at the apical foramen and the angle formed by the intersection of these lines is measured. If the angle is less than 5°, the canal is straight; if the angle is 5°–20°, the canal is moderately curved, and if the angle is greater than 20°, the canal is classified as a severely curved canal[9],[10] [Figure 1].
Figure 1: Preoperative radiograph measuring curvature of root canal using the Schneider Method

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   Materials and Methods Top


Two new NiTi instruments Mani GPR (Mani Inc, Utsonomiya Japan) and Endostar RE (ERE; Poldent Co Ltd, Walsow, Poland) were used in the study along with H Files (Mani Inc; Japan) for the retreatment (Approval from the ethics committee was obtained on 01-03-2018 Ethical clearance no: JSS/DCH/IEC/MD-14).

The roots were embedded in addition silicone set in an aluminum hollow block. The root surface and addition silicone socket were coated with hydrophilic vinyl polysiloxane impression material and the root was repositioned immediately. Access cavity was prepared using 0.8 diamond bur. A size 10 K file was introduced into the canal until it was visible at the apical foramen and the working length was determined 1 mm short of the apex. The initial apical file was 20 K and the canals were enlarged until 35 K file, 3 times the initial size. The master apical file used was 35 K; root canals were prepared using the step-back and balanced forced technique. After each instrumentation, the canals were irrigated with 2 ml 1% sodium hypochlorite using 27 gauge needle then 0.9% normal saline followed by 17% EDTA and final rinse with normal saline. Master gutta percha size was 35 and around four accessory cones were used. The spreader used was no. 20 and this protocol was followed for all the groups. All samples were dried with paper points and obturated with gutta-percha points of the corresponding sizes and AH Plus sealer using lateral condensation technique to cause less impact on the root and to reduce the risk of crack formation at this stage.

Retreatment procedure

All the 60 samples were divided into three groups and subjected to the following instrumentation techniques.

Group 1 (MANI GPR; Mani Inc. Utsomoniya; Japan)

From crown to middle portion of the canal 2, S #50 file was selected. The file was attached on the top of the gutta percha and rotated softly. The file was paused at 1–2 s at around middle of the canal (before the curve).

From middle to apical 4, N/30 was selected. The file was paused at around middle of the canal 0.5–1 mm, short of the apex. The file was moved in pull stroke motion and the debris was removed. The file was used at a speed of 1000 rpm. All the steps were followed according to the manufacturer's guidelines and steps were kept same throughout for all the samples to maintain the standardization.

Group 2 (ENDOSTAR RE; ERE; Poldent Co Ltd, Walsow Poland)

Endostar RE – Endo size 1 was used for the coronal part of the root canal to remove the part of the gutta percha from 1/3 to 2/3 of the canal. Size 4 was used to remove the gutta percha from next part of the canal. The canal was irrigated as required. The working speed of the contra-angle micromotor handpiece was at 150–300 rpm. All the steps were followed according to the manufacturer's guidelines and steps were kept same throughout for all the samples to maintain the standardization.

Group 3 (H FILE; Mani Inc. Japan)

Hand filing was done using H file. Initially no # 15 H file was introduced into the canal till it reached the working length. To remove the gutta percha and sealer, canals were instrumented up to size 40. Retreatment was deemed complete when no more gutta percha and sealers were seen on the last instrument and there were clean dentinal shavings from the root canal.

1% sodium hypochlorite (NaOCl) and 17% ethylene diamine tetraacetic acid (EDTA) were used as irrigants after completion of instrumentation in all the three groups.

Radiograph (Skanray, Mysore India) was taken after gutta percha was removed and the file was checked free of any debris and remaining filling material in the canal.

Sectioning and microscopic evaluation

After retreatment procedure, the teeth were decoronated using a diamond disc under copious irrigation to avoid any formation of cracks formation during this stage and the mesiobuccal root was resected. The roots were cut horizontally at 3 mm (apical), 6 mm (middle), and 9 mm (coronal) from the apex.

Evaluation

The specimens were planted in SEM and the images were taken under different magnification (50×, 100×, and 3000×). The voltage was set to 15 kV, and secondary electrons were bombarded at a working distance of 12 mm and the scan speed was 16 frames per 20 s. Different regions of all samples were checked for a number of dentinal cracks line extending from inner root canal space to the outer surface of the root and also the presence or absence of the remaining gutta-percha was calculated using descriptive and one way ANOVA analysis.

The time elapsed from entering the root canal with the hand file or the engine driven file to the completion of the re-instrumentation was measured using a digital stopwatch (Electronic loudstar timer, Pacer 103) in seconds.

Statistical analysis

All the data were subjected to statistical analysis. One way ANOVA with a P value < 0.05 was used to determine significance and Scheffe's post hoc test was used to find the comparison between the groups. All the statistical analyses were carried out using SPSS for windows version 22.


   Results Top


Endostar RE endo retreatment file and H file showed less amount of dentinal defect in the coronal, middle, and apical region compare to Mani GPR files but there was not much difference between the groups.

ANOVA showed no statistically significant differences between the groups, i.e., (P > 0.05) coronal P = 0.956, middle P = 0.65, and apical P = 0.167.

In the coronal, middle, apical 1/3rd, there is no statistical significance because all groups are showing almost similar amounts of cracks. In coronal 1/3rd, all three groups are showing less amount of dentinal cracks followed by middle 1/3rd and more amount of cracks are seen in apical 1/3rd in all the groups [Table 1] [Graph 1].
Table 1: Comparison of the number of dentinal crack formation between the groups

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Comparison of the mean % of root canal filling material remaining in the coronal, middle, and apical region in all three groups

The value P < 0.05 was set as the significance level.

The mean % of root canal filling material present in Mani GPR (G1), Endostar RE endo (G2), and H file (G3) group is 25%, 10%, and 80%, respectively, in coronal region, 50%, 20%, and 75% in middle region, and 75%, 45%, and 90% in the apical region where H file group shows more amount of gutta percha remaining in the root canal. Endostar RE endo group showed the least amount of gutta percha followed by Mani GPR group. All these groups are showing dissimilar values; hence, the data is statistically significant [Table 2] [Graph 2].
Table 2: Comparison of the mean % of root canal filling material remaining in the apical region in the three groups

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Comparison of retreatment time in seconds among three groups

The mean retreatment time using Mani GPR, Endostar RE Endo, H file were 493.6500, 368.7000, 779.0500, respectively [Table 3].
Table 3: Scheffe Post hoc test: Comparison of retreatment time in seconds within 3 groups

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b) ANOVA

ANOVA showed statistically significant differences between the groups, i.e., 0.001 (P = 0.05 or less).

Endostar RE Endo retreatment files showed less time to remove root canal filling material, followed by Mani GPR retreatment files and H files.

SEM Images of MANI GPR, Endostar RE and H file showing evidence of dentinal microcracks and presence of guttapercha in the root canal wall; distance between the dentinal cracks observed was 11.54 μm in the apical third [Figure 2].
Figure 2: SEM Images of Mani GPR File showing evidence of dentinal microcracks and distance between microcracks 11.54 um in apical third

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SEM Image of Endostar RE Endo File showing evidence of dentinal microcracks and presence of guttapercha in the root canal space; distance between the dentinal cracks observed was 11.45 μm in the apical third [Figure 3].
Figure 3: SEM Images of Endostar RE showing evidence of dentinal microcracks and distance between microcracks 11.45 um in apical third

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SEM Image of H File showing evidence of dentinal microcracks and presence of gutta-percha in the root canal space and distance between the dentinal cracks observed was 4.681 μm in the apical third [Figure 4].
Figure 4: SEM Images of H file showing evidence of dentinal microcracks and distance between microcracks 4.681 um in apical third

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   Discussion Top


Endodontic retreatment has always been the first choice to save the tooth when infected again after the root canal treatment, though it is time-consuming.[11] Advances in the endodontic field have led to the use of NiTi rotary instruments, which are not only effective in root canal shaping but also proved to be efficient and require less time in removing GP/sealer during endodontic retreatment.[11]

Previous studies have shown that manual instrumentation using stainless steel hand files removed root canal filling materials more effectively than NiTi rotary instruments.[5]

Here, in the present study, the less effective removal of debris in the coronal, middle, and apical thirds of the canals by manual instrumentation may be explained by the fact that NiTi rotary instrumentation plasticizes the gutta-percha (GP) through frictional heat. Heat softened gutta-percha (GP) is less resistant and easy to be penetrated and removed.[12]

In the present study, Endostar RE endo showed good results in the removal of gutta-percha, which could be explained by the fact that ERE file system no. 1 and 2 have a square cross-section similar to K-files with four cutting edges and good elasticity. Endostar RE endo no. 3 and no. 4 have S-cross-section with cutting taper or tip diameter of 0.06/30 and 0.04/30, respectively. S-cross section design of No. 3 and No. 4 files provides a positive rake angle with two cutting edges distributed symmetrically, increased pitch length, and more cross-sectional space for enhanced cutting and allowing the debris to move coronally. They also have great cutting ability, a noncutting tip, and a good elasticity,[13] whereas MANI GPR file has only 1 cutting edge and one groove.

The cutting edge of the MANI-GPR is R-Phase NiTi, which is different from the general superelastic NiTi files and becomes permanently distorted to a certain degree in accordance with the curvature of the root canal.[13],[14]

More amount of remaining gutta-percha was present on the apical third compared to the coronal and middle third of all specimens [Figure 2],[Figure 3],[Figure 4], which may be justified by the fact that during cleaning and shaping the master apical file used was 35 k with tip size 0.35 and taper 2%. Nickel-titanium rotary files, Endostar RE endo with tip size 0.30 and taper 4% and Mani GPR file with tip size 0.30 and taper 4% were used as the master apical files for retreatment procedures. Because the tip size of retreatment files was smaller than that of initial master file, it could have caused some gutta percha to remain in the apical third of the root canal, which is evident in the results of the present study. The shape of each canal is different and there will be untouched surface areas at the root canal regardless of the preparation techniques and because of the rotary retreatment files that are used in upward and pecking motion. Hence, after retreatment with rotary NiTi files, the additional circumferential filling should be done using H file.[10],[15]

This study also shows that both hand and rotary instrumentation techniques caused similar dentin defect formation during root canal retreatment, but comparatively less amount of dentinal microcracks was found in H file [Figure 4] compared to rotary files Mani GPR and Endostar RE Endo files. This may be attributed to the less aggressive movements of the hand files in the canal compared with engine-operated files, and also amount of contact of the instrument on the canal is less compared to rotary files. The roots prepared with rotary retreatment files have greater taper as compared to H-files (2% taper); it should be realized that these instruments remove more dentin leading to increased stress on the canal walls. This could be the reason for more dentinal cracks in rotary instrumentation.[16],[17]

Apical one third showed more crack propagation among the three groups because apical enlargement is an important stage of retreatment procedures. In this situation, apical enlargement may have led to the propagation of apical cracks.[18] All the NiTi rotary files caused significantly more apical cracks and crack propagation than the hand files.[5],[19]

In this study in terms of time elapsed from entering the root canal with the hand file or the engine driven file until the completion of the re-instrumentation, one way ANOVA showed a statistically significant result. Endostar Re endo removed gutta-percha faster followed by Mani GPR and more time was required for H file to remove gutta-percha.

In this study, H files left the maximum amount of gutta-percha in the canal, which is more than the Endostar RE and Mani GP Retreatment files.

Limitations

  • Because this was an in-vitro study, scenarios might be changed in clinical situations.
  • Mesiobuccal roots of maxillary molars were only chosen for this study. Incorporation of other roots like palatal and mesiodistal roots would have facilitated more validation of the results.
  • The tooth was kept for incubation after root canal treatment for 14 days but the result cannot be directly correlated to clinical situations where symptoms arise after years. Thus, the incubation period should be more in this study.



   Conclusion Top


Within the limitations of this in vitro study, it can be concluded that

  • Retreatment done using Endostar RE Endo rotary instrument proved to be most effective and least time consuming, followed by Mani GPR rotary retreatment files. Retreatment done using hedstrom Files required more time and removed less material.
  • More amount of gutta-percha remnants was found in the apical third compared with the coronal and middle third.
  • All the experimental groups showed crack formation irrespective of hand or rotary instrumentation technique used.
  • Samples instrumented with Mani GPR showed more crack followed by Endostar RE; least amount of crack propagation was seen in H file. Less number of cracks was seen in the coronal one third and more amount of cracks was found in the apical third.


Acknowledgements

The present study was done in association with University of Mysore Vijnana Bhawan and the study was carried out in Department of Conservative Dentistry and Endodontics, JSS Dental College and Hospital, Mysore.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

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

  [Table 1], [Table 2], [Table 3]



 

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