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Year : 2016  |  Volume : 6  |  Issue : 3  |  Page : 131-135

Apical Gutta-percha cone adaptation and degree of tug-back sensation after canal preparation

1 Department of Restorative and Prosthetic Dental Sciences, College of Dentistry, King Saud Bin Abdulaziz University for Health Sciences; King Abdullah International Medical Research Center (KAIMRC), National Guard Health Affairs, Riyadh, Saudi Arabia
2 Department of Restorative and Prosthetic Dental Sciences, College of Dentistry, King Saud Bin Abdulaziz University for Health Sciences; King Abdullah International Medical Research Center (KAIMRC), National Guard Health Affairs, Riyadh, Saudi Arabia; Department of Conservative Dentistry, Jordan University of Science and Technology, Irbid, Jordan
3 King Abdullah International Medical Research Center (KAIMRC), National Guard Health Affairs; Department of Medical Education, College of Medicine, King Saud Bin Abdulaziz University for Health Sciences; Riyadh, Saudi Arabia
4 Department of Restorative and Prosthetic Dental Sciences, College of Dentistry, King Saud Bin Abdulaziz University for Health Sciences; King Abdullah International Medical Research Center (KAIMRC), National Guard Health Affairs; Division of Endodontics, King Abdulaziz Medical City, National Guard Health Affairs, Riyadh, Saudi Arabia

Date of Web Publication29-Aug-2016

Correspondence Address:
Ahmed Jamleh
College of Dentistry, King Saud Bin Abdulaziz University for Health Sciences, National Guard Health Affairs, P. O. Box 22490, Riyadh 11426
Saudi Arabia
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1658-5984.189355

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Aims: The aim of this study was to investigate the degree of tug-back after canal preparation with respect to the Gutta-percha-occupied area (GPOA). Materials and Methods: Roots of twenty premolar teeth were prepared till size 35/0.04, then GP cones of same size and taper were adapted to root canals and the degree of tug-back sensation was scored as loose, slight, adequate, and strong. Root canals were filled with GP and AH26 sealer, and then sectioned horizontally 1 mm from the apical end at three levels. GPOA and its sum from the three levels sum of GPOA (sGPOA%) were calculated using digital stereomicroscope. Statistical Analysis: At each sectioned level, GPOA% was compared with the score of tug-back sensation using one-way ANOVA at a 5% significance level. Multiple pairwise comparisons were performed using Tukey test. Results: Tug-back sensation was present in all canals, described as slight, adequate, and strong in 4, 8, and 8 canals, respectively. Among the tug-back scores, quantitative analyses of GPOA% showed significant differences at 2- and 3-mm levels. The strong tug-back with sGPOA of 76.5 ± 11.1% was significantly higher than that of slight tug-back. Conclusions: Under the conditions of this study, the tug-back scoring system can be applied to determine the amount of GP adaptation inside the root canal. Strong tug-back sensation showed the highest GP adaptation although at least one-fifth of the apical canal region was left unfilled.

Keywords: Distance, Gutta-percha adaptation, Gutta-percha-occupied area, tug-back

How to cite this article:
Jamleh A, Awawdeh L, Albanyan H, Masuadi E, Alfouzan K. Apical Gutta-percha cone adaptation and degree of tug-back sensation after canal preparation. Saudi Endod J 2016;6:131-5

How to cite this URL:
Jamleh A, Awawdeh L, Albanyan H, Masuadi E, Alfouzan K. Apical Gutta-percha cone adaptation and degree of tug-back sensation after canal preparation. Saudi Endod J [serial online] 2016 [cited 2023 Feb 1];6:131-5. Available from: https://www.saudiendodj.com/text.asp?2016/6/3/131/189355

  Introduction Top

Root canal obturation is an essential stage of endodontic treatment, with the goal of tightly sealing the canal space after chemomechanical debridement using core filling materials such as Gutta-percha (GP) along with biocompatible endodontic sealer.[1],[2],[3] The obturation quality is commonly evaluated by different criteria and methods such as radiographs,[4] dye and bacterial leakage,[5],[6],[7] and cross-sectional analysis of the space filled with GP.[8],[9],[10],[11] Moreover, overextrusion of root filling materials into periapical tissues should be avoided to increase the probability of treatment success.[12]

Several root canal filling techniques are currently utilized to attain adequate obturation quality.[13] Cold lateral compaction is one of the most common techniques frequently taught in dental schools.[14] It is widely accepted among clinicians because of its benefits of controlling the placement of GP in the root canal and cost-effectiveness.[15] In this technique, a GP cone consistent with the prepared canal diameter at the working length (WL) is supposed to closely adapt and seal the apical portion of the canal in three dimensions.[1],[16] Clinically, the adaptation of GP was proposed to be inspected by the feeling of “tug-back” during GP cone selection [11] which is usually confirmed by taking dental radiographs. According to the American Association of Endodontists, tug-back is defined as slight frictional resistance of a master point to withdrawal when seated at least in two dimensions.[17] In the literature, tug-back has been described by terms such as slight resistance,[18] good tug-back,[11],[19] good deal of pulling force,[20] and resistance to displacement.[21] A recent study evaluated tug-back sensation as either present or absent and reported that its presence is correlated with improved apical GP cone adaptation.[11] However, the degree of tug-back, when present, was not clearly reflected.

Clinically, the degree of resistance required to remove GP might address the amount of GP adaptation onto canal walls. Therefore, the present experiment was conducted to investigate the degree of tug-back after canal preparation with respect to the real GP-filled space apically.

  Materials and Methods Top

Twenty human premolar teeth with single straight canals, extracted according to the treatment plan and for reasons not related to this experiment, were stored immediately in distilled water and used in the current study. The teeth were radiographed buccolingually and mesiodistally to confirm the canal shape. The teeth were inspected under a digital microscope to detect any anatomic irregularities, open apex or fractures, which indicated exclusion from the study.

The apical half of the root was embedded in and stabilized with light-body impression material, and the coronal half of the root was covered by a mixed autopolymerizing resin (DuraLay, Reliance Dental Mfg. Co., Worth, IL, USA). After the resin was set, the impression material was removed; in this manner, a tooth-resin assembly was produced with apical area of the root fully exposed.

Afterward, the tooth was decoronated to a level that maintained a root length of 12 mm as inspected by a digital caliper. This left a flat surface to standardize the root length, guarantee a straight-line access, and provide a reference plane. Root canals were negotiated by 20 K-file that would bind no <2 mm from the canal length; otherwise, the tooth was excluded. The roots were maintained in a wet environment until the next procedure.

WL was defined by introducing 10 K-file into the canal and was set 1mm short of the apical foramen. The root canals were prepared with K3 rotary file system (SybronEndo, Orange, CA, USA) using a digital torque control motor (DTC, SybronEndo, Orange, CA, USA). Each K3 instrument had a rubber stopper fixed with cyanoacrylate adhesive 11 mm away from the tip to critically control the WL during canal preparation. Instruments of 40/0.06 and 35/0.06 were used to prepare the coronal and middle part of the canal and 30/0.04 and 25/0.06 instruments to prepare the middle-apical part. Final preparation was done with 25/0.04, 30/0.04 and 35/0.04 instruments sequentially for 10 s in in-out motions. Recapitulation was done using 10 K-file, and each canal was irrigated with 2 ml of 2.5% sodium hypochlorite. In case the instrument had not reached the predetermined length, the same instrument was reintroduced after irrigation and recapitulation. At the end, the canal was irrigated with 2 ml of 17% ethylenediaminetetra-acetic acid solution for one minute and then rinsed with normal saline solution. Canals were prepared by one operator.

The canal fluid was aspirated by a disposable syringe and a needle, then a matched 35/0.04 GP cone (DiaDent, Cheongwon, Korea) was inserted to WL. Tug-back sensation was assessed based on a 4-level scoring system as follow: (0) No tug-back sensation: The cone was loose at the WL, (1) slight tug-back sensation: The cone could be removed from the canal with very small resistance, (2) adequate tug-back sensation: The cone required some resistance to be removed from the canal, and(3) strong tug-back sensation: There was a need for a considerable force to remove the cone.

After GP cone placement, two operators who were calibrated and trained previously in the scoring system and blinded to the coded specimens assessed the tug-back sensation. An interevaluator reliability analysis using the Kappa statistic was performed to determine consistency among the operators. An agreement was reached by discussion between the two operators in the event of discrepant tug-back scores.

Afterward, the canal walls were dried with absorbent paper points and covered with AH26 sealer (Dentsply, Maillefer, Switzerland), and GP was placed passively inside the root canal. Coronally, the excess GP was seared off and the opening was filled with 3 mm temporary restorative material (Cavit, 3M ESPE Dental AG, Seefeld/Oberbay, Germany). The roots were kept in an incubator for 48 h at 37°C and 100% humidity to allow the sealer to set.

After that, the root was horizontally sectioned 1 mm from the apical end using a diamond disc. The resulting cross section of the root was then observed under digital stereomicroscope (Leica EZ4 HD, Leica Microsystems, Singapore) to record an orthoradial image named “1-mm image.” After imaging, one more 1-mm apical sectioning was performed, and another image of the root cross section was recorded as “2-mm image.” A third cross-sectional image of the root was taken 3 mm away from the original apex after sectioning 1-mm portion and saved as “3-mm image.” The magnification power to observe these sections was set at ×25.

At each level, the GP-occupied area (GPOA) was measured by another blinded operator using ImageJ software (available as freeware from http://rsb.info.nih.gov/ij/). The operator traced peripheries of the canal lumen and the GP to measure their areas, and then the area of GP was divided by that of canal lumen to result in GPOA%. Furthermore, the distance % (D%) parameter, indicating the proximity of GP to root canal walls, was obtained through dividing the diameter of GP by the distance between the closest opposing points on the prepared canal walls crossing the GP center [Figure 1].
Figure 1: Schematic drawings showing cross-sections of a root canal lumen before preparation (a) after preparation (b) and after Gutta-percha cone placement (c) the black arrow represents distance measurement between the closest opposing points at the canal walls that crosses the circle center

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The sum of GPOA% (sGPOA) and sD% was calculated by averaging from the values of three sectioned levels. The GPOA% at each sectioned level as well as sGPOA% and sD% were compared with the score of tug-back sensation using one-way ANOVA. Multiple pairwise comparisons were performed using Tukey test. The statistical tests were performed at a 5% significance level using the SPSS version 20 software (SPSS Inc., Chicago, IL, USA).

Using ANOVA test, sample size calculation was conducted using a significance level of α =0.05 and a 90% power to detect a minimum GPOA% difference of 30% between the four tug-back scores. The common standard deviation within a group was assumed to be 15%.

  Results Top

The means GPOA% at 1-, 2-, and 3-mm levels are shown in [Table 1].
Table 1: The gutta percha-occupied area (GPOA) and distance (D) values shown with respect to tugback sensation scores as means GPOA% and D% at the 3 levels, and sums GPOA% and D% (sGPOA% and sD%, respectively)

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The interoperator reliability for the tug-back scoring was found to be a Kappa value of 0.78 (P < 0.001). Of the 20 canals tested for tug-back sensation, no canal demonstrated loose GP (score 0). However, 4 canals had the GP sensed with slight tug-back (score 1), 8 canals with adequate tug-back (score 2), and 8 canals with strong tug-back (score 3).

Among the tug-back scores, quantitative analyses of GPOA% showed significant differences at 2- and 3-mm levels where score 1 had significantly lower GPOA% than score 3 (P = 0.03 and 0.04, respectively). In term of D%, only at 2-mm level, significant differences were found between tug-back scores 1 and 2 (P = 0.004) and scores 1 and 3 (P = 0.01).

In the presence of slight tug-back (score 1), sGPOA% was 61 ± 18.1% which was significantly lower than that with strong tug-back (score 3) of 76.5 ± 11.1% (P = 0.01). The adequate tug-back (score 2) had a sGPOA% comparable with tug-back scores 1 (P = 0.06) and 3 (P = 0.55). The sD% showed significant differences between scores 1 and 2 (P = 0.03).

  Discussion Top

There were only a few studies probing tug-back sensation;[11],[16] therefore, the present study was designed to examine the degree of tug-back sensation and visualize apical adaptation of the GP matched cone under direct observation in straight canals prepared with rotary nickel titanium (NiTi) instruments.

Clinically, selecting a GP cone that fits the WL is a major step in performing lateral compaction. In the present study, although the selected GP cone was consistent in size and taper with the final endodontic instrument used to prepare the canal, the degree of tactile tug-back sensation was found to be different. Thus, tug-back sensations were scored and their respective sGPOA percentages were analyzed. The strong sensation of tug-back revealed the highest sGPOA%, compared to slightand adequatetug-back sensations.

Comparing GPOA% at 1- and 2-mm levels among the tug-back scores, no significant differences were reflected [Table 1]. This might be attributed to the apical location of calculating GPOA%, which is not mechanically prepared and is difficult to obturate.[22],[23],[24] Therefore, additional parameter (D%) was considered in this study to evaluate the physical adaptation of the master cone. Tug-back sensation is the result of GP contacting with two opposing walls mainly in the area prepared with the NiTi instrument. Further analysis by measuring the D% was performed to show the proximity of the GP cone to the canal walls at the three levels. Although the differences were not significant, slighttug-back had the lowest D%, followed by adequate and strong tug-back sensations. Nevertheless, analyses of GPOA% and D% showed that tug-back sensation can in fact indicate the degree of GP adaptation. These results are supported by Yoon et al. findings.[11] Meanwhile, another study found that the master cone adaptation was not accurately reflected by means of the tactile sensation.[16]

Apical sealing is necessary to prevent passage of microorganisms and their by-products apically.[25],[26] This condition is achieved by having an intimate contact between the GP and the canal walls in three dimensions. The results suggest that adaptation of GP at the apical region can be assessed by tug-back sensation or the resistance felt on GP removal. The parameter sGPOA% should be regarded as the overall GP fitness at the apical area in this study. Presence of slight tug-back had the lowest sGPOA%, followed by that of adequate tug-back and then that of strong tug-back. This might highlight the clinical importance of having strong tug-back sensation to guarantee the maximum GP adaptation. However, even a strong tug-back does not reveal a perfect canal seal apically. The results demonstrated that more than one-fifth of the apical canal region was left unfilled in spite of the tug-back sensation. This was in line with the finding of a previous study that showed up to 20% of the apical region was not filled even in the presence of tug-back sensation.[11] Similarly, Eguchi et al.[8] found that with master GP cone in place, around 20% of the area had voids at 1.5 mm from the anatomical apex. Therefore, matched GP cone alone cannot assure a complete canal seal in the apical region.[22],[23],[24] Thus, even with a strong tug-back, it is still important to seal the areas not occupied with GP using an endodontic sealer and by applying heat to plasticize GP in lateral or vertical compaction techniques.[11],[27]

As with any study, there are certain limitations where caution must be taken when interpreting the results. This investigation was based on scoring the sensed tug-back as the force needed to remove GP from its place. This might vary between the operators and thus the scores given could be subjective. However, careful attempts were made to prevent this discrepancy by training the two operators for calibration to do this procedure, and reaching an agreement between them after discussing the sensation in each canal. Furthermore, influence of GP cone adaptation on the quality of the apical seal was visualized and assessed quantitatively at the examined levels in this study. However, further investigation is required to relate the volume of unfilled region after performing obturation with tug-back sensation.

Within the limitations of this study, the tug-back scoring system can be applied to determine the amount of GP adaptation inside the root canal. Strong tug-back sensation showed the highest GP adaptation although at least 20% of the apical canal region remained unfilled. This might pose a challenge while determining the quality of apical seal solely relying on the degree of tug-back sensation. From a clinical standpoint, it is highly preferable to take additional steps to establish an optimal canal seal, especially at the apical region.


We would like to thank Dr. Alireza Sadr for his contribution in reviewing the manuscript.

Financial support and sponsorship

This work was supported by a research grant (RC/15/107/R) from King Abdullah International Medical Research Center (KAIMRC) and National Guard Health Affairs, Riyadh, Kingdom of Saudi Arabia.

Conflicts of interest

There are no conflicts of interest.

  References Top

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