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Year : 2019  |  Volume : 31  |  Issue : 1  |  Page : 104-109

In vitro comparison of the force required to fracture roots vertically following the use of two instrument retrieval systems

Department of Conservative Dentistry and Endodontics, Sardar Patel Post Graduate Institute of Dental and Medical Sciences, Lucknow, Uttar Pradesh, India

Date of Web Publication19-Jun-2019

Correspondence Address:
Dr. Asit Vats
Sardar Patel Post Graduate Institute of Dental and Medical Sciences, Lucknow, Uttar Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/endo.endo_8_18

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Objective: The objective of this study was to compare the force required to fracture the roots in a vertical direction following the use of two instrument retrieval systems.
Introduction: A vertical root fracture is a longitudinal fracture of the root, extending throughout the dentin from the root canal to the periodontium. The fracture strength of teeth after the application of two systems used for instrument retrieval, i.e. ultrasonic (P5 Booster Company Irrisafe, Satelec ACTEON, North America) and instrument removal system (iRS Switzerland) was compared.
Materials and Methods: Freshly extracted 60 maxillary central incisor teeth with straight roots and single canal were collected. The anatomical crowns of all the teeth were sectioned. The samples were cleaned and shaped with the crown down technique using Pro-Taper (DENTSPLY, Maillefer, USA) rotary instruments up to a size F2. The fracture of rotary file was deliberately induced by the pressure that was applied during rotary motion of F3 file. The samples were then randomly divided into three groups each having 20 teeth, i.e., Groups A, B, and C. Retrieval of separated file was performed in Groups B and C by means of Ultrasonic and Instrument retrieval system, respectively, while no retrieval of separated file was done in Group A. Each sample was then subjected to load by Instron testing machine until the sample got fractured. That load at the time of fracture of each sample was recorded. The data collected from all the samples were then subjected to statistical analysis using ANOVA and Tukey's HSD.
Results: The results showed statistically significant difference among all the groups. The group in which no retrieval system was employed showed the best fracture resistance. The group in which ultrasonic removal system was used showed better fracture resistance as compared to the group in which iRS was used. The fracture resistance of Group A, Group B, and Group C ranged from 265.23–289.66, 114.67–135.66, and 70.56–97.56, respectively, with mean (± standard error) 277.60 ± 1.94, 124.65 ± 1.53, and 84.98 ± 1.76, respectively, and median 276.54, 123.95, and 85.78, respectively.
Conclusion: According to the results of the present study, the difference between the force required to fracture roots vertically after removal of a fracture instrument with the ultrasonic and instrument removal system was statistically significant.

Keywords: Cleaning and shaping, instrument removal system, ultrasonic removal system, vertical root fracture

How to cite this article:
Vats A, Singh AP, Paliwal A, Bhardwaj K, Srivastava S, Chhabra HS. In vitro comparison of the force required to fracture roots vertically following the use of two instrument retrieval systems. Endodontology 2019;31:104-9

How to cite this URL:
Vats A, Singh AP, Paliwal A, Bhardwaj K, Srivastava S, Chhabra HS. In vitro comparison of the force required to fracture roots vertically following the use of two instrument retrieval systems. Endodontology [serial online] 2019 [cited 2020 Apr 2];31:104-9. Available from: http://www.endodontologyonweb.org/text.asp?2019/31/1/104/260539

  Introduction Top

The procedure of root canal treatment comprises of three intricate processes, namely access opening, cleaning and shaping, disinfection, and obturation of the root canal space. Out of all these processes, cleaning and shaping procedures are of paramount importance as it is responsible for eradication of microorganism with the help of irrigants and for subsequently shaping it so that the canal is adequately obturated by an inert filling material.[1]

The cleaning and shaping of root canal involves the use of various files along the walls of dentine. Conventionally, this procedure was performed by various hand files, but these days rotary nickel-titanium files are routinely used in cleaning and shaping of root canal treatment.[2]

Even through NiTi is a versatile alloy with properties such as shape memory, superelasticity, and corrosion resistance, these NiTi files may fracture during instrumentation. These separated instruments make it impossible to clean and disinfect the root canal in the apical area which negatively affects the treatment outcome. Simon et al. concluded that as a consequence of instrument fracture, the access to the apical portion of the root canal is decreased which has deleterious effect on the long-term prognosis on the tooth. Hence, retrieving the separated instrument becomes vitally important in salvaging the tooth and improving its prognosis.[3]

However, the instrument retrieval involves substantial amount of risks. Depending on the technique used complications such as perforation of the root, ledge formation, and transportation of the original canal may occur. It may also result in weakening of the affected root or fracture of an additional instrument,[4],[5],[6] which may in turn also lead to vertical root fracture of the tooth.

The techniques of retrieval of separated files may lead to excessive removal of root dentin, which may reduce root strength by 30%–40% and predispose the teeth to vertical root fracture.

Hence, it is very important to understand the deleterious effect of these techniques on the strength of roots so that suitable methods of removal can be selected. Various kinds of new armamentarium are available in the market for instrument retrieval. Instruments such as Masserann kit, canal finder system, ultrasonic device system, and instrument removal system (iRS) have been used for retrieving separated instrument.[7],[8],[9]

Ultrasonic technique has been reported as being the most frequently used. Ultrasonic method is applicable in most cases and is not restricted to the position of the fractured fragment in the root canal.[10] This unit affords precise working accuracy and has a broad power range and its unique “feedback” system measures tip resistance, regulates tip movement, and reduces the potential for tip breakage.[11]

iRS Switzerland is a new two-component system designed to mechanically engage broken instruments. Each microtube has a small-sized plastic handle to enhance vision during placement, a side window to improve mechanics and a 45° beveled end to “scoop up” the coronal end of a broken instrument. Each screw wedge has a knurled metal handle, a left-handed screw mechanism, and a solid cylinder that becomes tapered toward its distal end to facilitate engaging an obstruction.[12]

Therefore, this study was undertaken to compare the fracture strength of teeth after the application of two systems used for instrument retrieval, i.e., ultrasonic and iRS.

  Materials and Methods Top

Sixty freshly extracted human maxillary central incisor teeth were collected. The teeth were cleaned thoroughly to remove hard, soft debris, and blood. Thereafter, teeth were sterilized in autoclave at 15 lbs. Pressure, 121° centigrade for 30 min and then stored in distilled water at room temperature.

All the experimental teeth were sectioned horizontally with a diamond disk (SS White, Germany) to leave 13 mm root length to standardize the experimental procedure. The cervical third was flared with size 2–4 Gates–Glidden (DENTSPLY, Maillefer, USA) drills using a slow speed handpiece.

The secured portion of the canal can be optimally preenlarged by first utilizing S1 then S2. Before initiating shaping procedures, the pulp chamber was filled with 2.5% of NaOCl (Septodont). Following the use of each shaping and finishing file, irrigations, recapitulation was done with a 10 k file, then canal was prepared up to F2 ProTaper (DENTSPLY, Maillefer, USA). After completion of instrumentation of root canal, 5 ml of 17% EDTA (DENTSPLY, Maillefer, USA) was applied for 3 min, to remove smear layer and the canals were again irrigated with 2 ml of 2.5% NaOCL followed by final rinse with 5 ml of saline (0.9%) solution using an irrigation needle.

Then, the size F3 rotary files were notched to a depth of half of the instrument with a No. 2 round burs, 3 mm from the tip, to facilitate breakage of the file at this point. The instrument was inserted into the canal until resistance was felt and rotated clockwise with pressure to fracture the instrument. Each of the teeth in the experimental groups was radiographed again to ensure that the instrument had fractured in the middle-third of the canal. Then, the samples were randomly divided into three groups of 20 teeth in each group, i.e., Group (A) 20 sample, Group (B) 20 sample, and Group (C) 20 sample.

  • Group A - No attempt to retrieve instrument was done
  • Group B - Separated instrument was retrieved by ultrasonic system
  • Group C - Separated instrument was retrieved using iRS.

Ultrasonic removal system (P5 Booster Company Irrisafe, Satelec ACTEON, North America)

A staging platform was prepared to improve the visibility of the fractured instrument. The GG drills were modified by cutting off the guiding tip using a diamond bur, and a flattened end was prepared at the maximal cross-sectional diameter of the GG (DENTSPLY, Maillefer, USA). Modified GG drills of size 2, 3, and 4 were used until GG 4 contacted the most coronal end of the fractured instrument lightly. The canals were flushed with 17% EDTA (DENTSPLY, Maillefer, USA) for 1 min and dried thoroughly with paper point before the removal procedure was begun.

ProUltra tips of size 3, 4, and 5 ENDO (DENTSPLY, USA) were mounted on an ultrasonic handpiece connected to an ultrasonic unit, at a low power setting to prevent fracture of tips. The tips were activated without coolant to allow visualization of the energized tip around the fractured instrument, and then, the dentine around the fragment was circumferentially trephined around the broken instrument.

Instrument removal system (SSWIS)

The coronal widening of the root fragment was done with GG drills as in the ultrasonic group. After ensuring that the fragment could be visualized, a gutter was prepared around it with a trepan bur. The extractor tube was engaged in the prepared space, and the plunger rod was turned manually in a clockwise direction to grip the fragment. When the tightest grip was felt manually, the entire assembly was rotated in an anticlockwise direction to unscrew the fragment.

All procedures for instrument removal were performed by the same operator. After removal of the instrument, a size 15 K-file was inserted into the canal to confirm that the fragment had been removed from the canal.

Thereafter, the samples were mounted in copper box (15 mm high and 15 mm in diameter) that was filled with self-cure acrylic resin. The blocks of acrylic resin with the prepared roots were stored in 100% humidity until tested. A universal testing machine (Instron) was used to evaluate the force required to fracture the roots.

The root was fixed in the testing machine in such a way that a tip with a diameter of 1 mm moved vertically toward the center of the root. Fracturing was defined as the point at which a sharp drop in force was observed, and an audible cracking sound was heard. At this point, the force was recorded in Newton. All the samples were then subjected to statistical analysis using ANOVA test and Tukey's HSD, and then data were interpolated and interpreted qualitatively.

  Results Top

The present study compares the force required to fracture roots vertically following the use of two instrument retrieval systems. The teeth were randomly distributed in three Groups A, B, and C. In Group A, no attempt to retrieval was done, while in Group B, separated instrument was retrieved using ultrasonic system and in Group C separated instrument was retrieved by iRS. The outcome measure of the study was fracture resistance, measured in Newton. The objective of the study was to compare the fracture resistance between the Groups A, B, and C.

Fracture resistance

The observed fracture resistance (Newton) of three groups is further summarized in [Table 1]. The fracture resistance of Group A, Group B, and Group C ranged from 265.23–289.66, 114.67–135.66, and 70.56–97.56, respectively with mean (± standard error [SE]) 277.60 ± 1.94, 124.65 ± 1.53, and 84.98 ± 1.76, respectively and median 276.54, 123.95, and 85.78, respectively. The mean fracture resistance of Group A was the highest followed by Group B and Group C the least (Group A > Group B > Group C) [Table 1].
Table 1: Fracture resistance (Newton) summary of three groups

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Comparing the mean fracture resistance of three groups, ANOVA showed significantly different fracture resistance among the groups (F = 3366.00, P < 0.001) [Table 2].
Table 2: Comparison of mean fracture resistance of three groups by ANOVA

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Further, comparing the mean fracture resistance between the groups, Tukey's test showed significantly different and lower fracture resistance in both Group B (55.1%) (277.60 ± 1.94 vs. 124.65 ± 1.53, mean difference = 153.00, q = 87.25, P < 0.001) and Group C (69.4%) (277.60 ± 1.94 vs. 84.98 ± 1.76, mean difference = 192.60, q = 109.90, P < 0.001) as compared to Group A [Table 3]. Further, the mean fracture resistance also lower significantly in Group C (31.8%) as compared to group B (124.65 ± 1.53 vs. 84.98 ± 1.76, mean difference = 39.67, q = 22.63, P < 0.001) [Table 3].
Table 3: Comparison of mean fracture resistance between the groups by Tukey's test

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The results for the 3 groups were compared result showed significant differences among all the 3 Groups. The fracture resistance of Group A, Group B, and Group C ranged from 265.23–289.66, 114.67–135.66, and 70.56–97.56, respectively, with mean (± SE) 277.60 ± 1.94, 124.65 ± 1.53, and 84.98 ± 1.76, respectively and median 276.54, 123.95, and 85.78, respectively. The mean fracture resistance of Group A was the highest followed by Group B and Group C the least (Group A > Group B > Group C). These results showed a statistically significant difference when the Group A is compared with Groups B and C (P < 0.001).

  Discussion Top

Cleaning and shaping procedure is an integral part of the root canal treatment. In this procedure, the root canal is thoroughly cleaned, debrided and shaped by the endodontic files so as to prepare it for obturation.

The separation of files in the root canal presents a huge challenge for the clinician as it prevents complete cleaning of the root canal. The results of separation are all the more deleterious if the separated file is not sterilized. Hence, in any case retrieval of the separated file is imperative, if it cannot be bypassed, for the success of root canal treatment. However, this pursuit of retrieval of separated instruments leads to more removal of tooth structure which leads to weakening of the tooth and may ultimately result in fracture of the tooth.

Hence, in this study, fracture resistance of teeth after instrumentation with two different instrument retrieving systems, namely ultrasonic system and iRS has been compared.

The results for the three groups which were compared showed significant differences among all the three groups. The fracture resistance of Group A (control Group) ranged from 265.23–289.66 and was most resistant to fracture since they were not subjected to instrument retrieval procedures.

Trabert et al. concluded that the loss of dentin increases the chances of teeth to fracture. Excessive instrumentation of the root canal, excessive pressure during canal filling, dehydration of dentine and preparation of post space leads to fracture of the teeth.[13],[14],[15],[16]

In this study, both the Groups B and C showed significantly lower values of fracture load as compared to control Group A. Such a result implied that the process of retrieval of instrument either by Group B ultrasonic or Group C iRS did play a crucial role in weakening of the tooth structure.

A study reported relatively good success rates after instrument retrieval technique, but the complications still may occur. The most common complication reported (67%) was root fracture due to excessive removal of tooth structure.[17]

When an attempt is made to remove instruments fractured in the apical one-third of the root canal, tooth integrity might be compromised (Madarati et al., 2009, 2010) and also fragment removal is likely to be unsuccessful (Hülsmann and Schinkel, 1999, Ward et al., 2003b, Shen et al., 2004, Suter et al., 2005).[5],[8],[11],[17],[18]

There are contradictory reports regarding the occurrence of microcracks in the dentin after the use of ultrasonic tips during instrument retrieval or posts removal. The power setting and tip design seem to have an influence on the occurrence of microcracks.[19],[20]

According to this study, the best results among the retrieval system that caused the least weakening of tooth structure was Group B (ultrasonic system) which ranged from 114.67–135.66. The results were statistically significant when compared with Group C (iRS).

Ultrasonic systems work on the principle of ultrasonic vibrations. The ultrasonic vibrations are transmitted to the fractured fragment so that it becomes loose and easier to remove. The better results of ultrasonic systems in our study can be attributed to less invasive action, in which staging platform is prepared at the coronal part of the fractured instrument. Ultrasonic can prove useful for the removal of all kinds of instruments from root canal.[8],[21],[22],[23],[24]

Ultrasonic has been reported as being the most frequently used technique for instrument retrieval. The ultrasonic method is applicable in most cases and is not restricted by the position of the fractured fragment in the root canal, but in a study done by Shen, Peng, Cheung (2004) and Nagai et al. (1986) iRS method was applicable only in teeth with large straight root.[18],[25],[26]

The time required to remove the fractured fragment using ultrasonic varied from 3 to 40 min. The time taken was influenced by the location of the tooth, the root canal shape, position of the fractured fragment in the root canal.[26] However, sufficient coronal enlargement of the root canal to visualize the most coronal aspect of the fractured fragment is generally required.[8]

According to our study, Group C (iRS) ranged from 70.56–97.56 showed worse results as compared to ultrasonic system. That means, it led to more weakening of tooth structure as compared to ultrasonic systems.

The iRS kit is designed to remove metallic objects from the root canals. It is limited in its application because it uses rigid and relatively large trepan burs and extractors to establish straight-line access to the coronal aspect of the separated fragment. However, this leads to removal of a considerable amount of radicular dentin and can cause iatrogenic damage like perforation.[27]

The lower values of iRS reported in our study can be attributed to it is highly invasive action, in which gutter is prepared at the coronal part of the fractured instrument. iRS exposes 2–3 mm or about one-third of the total length of separated instruments.[28] iRS uses rigid and relatively large burs and extractors. Hence, a great deal of dentin is lost in pursuit of attaining straight-line access to the target object.[29]

This study inferred that ultrasonic is indeed a better system of retrieval of instruments with regards to unnecessary removal of dentin and therefore leads to more preservation of tooth structure when compared to ultrasonic system. Therefore, this study concludes definitively that both these systems, (ultrasonic and iRS) significantly hampers the strength and the structural integrity of the tooth. Hence, care and restrain should be exercised before using these systems of instruments retrieval.

This study also stresses the need to carry out more researches and innovations in the field of endodontics instruments so that someday we can finally come up with an instrument retrieval system that not only efficiently retrieves the separated instruments but at the same time makes sure that the tooth is not debilitated in any way.

Although this study has been carried out under strict parameters but considering variations in teeth size, degree of mineralization and subjection of load, further in vitro and clinical studies need to be carried out to standardize all the parameters so that we obtain even more precise results.

  Conclusion Top

In the present study, the ultrasonic removal system has displayed the best results among the two systems tested. This is attributed to less invasive action of ultrasonic system. The other system that was tested was iRS, and it showed inferior results. iRS is particularly detrimental for the structural integrity of the tooth structure, and care should be taken before the use of iRS in the future.

Group A was the highest followed by Group B and Group C the least (Group A > Group B > Group C).

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Table 1], [Table 2], [Table 3]


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