Self-adjusting file (SAF) separation in clinical use: A preliminary survey among experienced SAF users regarding prevalence and retrieval methods.

CONTEXT: The self-adjusting file (SAFs) is reported to be resistant to file separation in laboratory tests. No information is currently available regarding SAF separation during clinical use. AIM: To conduct preliminary clinical survey among experienced SAF users in order to establish the prevalence of SAF separation during clinical use and to study how were such cases treated.
MATERIALS AND METHODS: A questionnaire was sent to experienced SAF users to make inquiries regarding incidence of SAF separation and how were such events treated. Only responses from operators who had used 50 SAFs or more were included in the present study. Fisher's exact test was used to compare file separation occurrence.
RESULTS: A total of 2517 SAFs had been used by these operators, and 15 cases of file separation were reported (0.6%). Twelve of these 15 separated files could be retrieved within a few minutes using Hedström files, with no additional dentine removal required. In the three cases in which the separated files could not be retrieved, the separated file segment was successfully bypassed.
CONCLUSIONS: The SAF might separate during clinical use, but the incidence of such an event was low. In most such cases, the separated file segment was easily and quickly retrieved without additional removal of dentin.

INTRODUCTION

File separation is a procedural problem that can occur during root canal treatment.[1] Such problems can occur with hand files[2] and also with nickel-titanium (NiTi) rotary files.[1] The likelihood of breaking a NiTi rotary file could be six times greater than the likelihood of breaking a stainless steel file.[3] When a total of 7159 discarded rotary NiTi instruments, which were obtained from 14 endodontists in 4 countries, were examined, fractures were found in 5% of the instruments.[4] Other researchers have reported file fracture prevalence of 0.9%,[5] 3.3%,[1] 0.3%,[6] 1.8%,[7] 5%[8] and 0.14%.[9] File separation occurred in 40-50% of cases in molar teeth,[12] with the highest prevalence being in the MB canal of these molars [Figure 1a].[12]

Figure 1

Separated rotary instrument vs. separated self-adjusting file (SAF) file. (a) A separated rotary file in the mesial canal of the left first mandibular molar (the three Gutta Percha cones in the furcation area were used to demonstrate a wide periodontal pocket in this area, not related to the separated file). (b) Retrieval of the separated file (“A”), using ultrasonic tips, resulted in a major sacrifice of sound dentin and led to perforation. (c) Separated SAF file. The apical part of the SAF file was torn off and remained in the canal. It was retrieved using a Hedström file that was inserted into the lattice of the apical portion and engaged it, which allowed it to be pulled out

Optimally, one would wish to remove the separated file fragment. Nevertheless, removal of a separated file is often a challenging and time-consuming procedure involving substantial removal of sound dentin [Figure 1b].[10]

When a separated fragment of a rotary file is present, it is usually screwed into the canal, thus making it difficult to remove. When tested in vitro, removal of a separated file fragment required 45-55 min[11] or 36-45 min.[12] One might assume that, in a clinical situation, removal of a separated instrument could take at least that much time or more.

The self-adjusting file (SAF) system (ReDent-Nova, Ra’anana, Israel) consists of a SAF [Figure 2a] that is operated using a special RDT hand piece head that converts the rotation of the micromotor into in-and-out vibrations, with a 0.4 mm amplitude.[1314] An irrigation pump (VATEA, ReDent-Nova, Ra’anana, Israel) is attached by a tube to the hollow file, and the pump provides continuous irrigation throughout the procedure.[1314]

Figure 2

Mechanical damage to self-adjusting file (SAF) files. (a) An intact SAF file. (b) Separated SAF file. The file separated during a root canal treatment in the mesial root of the second right mandibular molar and remained in the canal. It was removed using a canal debrider #30. (c) Arch detachment in an SAF file. (d) Several arch detachments in an SAF file. No metal fragments remained in the canal (the small size of the arches compared to the canal into which the whole file could be inserted)

The SAF differs from all other rotary files. While other rotary files have a central metal shaft with blades and flutes around it, the SAF has no central metal shaft. It is made as a hollow cylinder, 1.5 or 2.0 mm in diameter, the thin walls of which are made of a NiTi lattice; it also has an asymmetrical tip.[1314] The file is extremely compressible, and when inserted into a root canal, the file is claimed to assume the cross-sectional shape of the canal. The SAF has no blades or flutes, and it is operated with a grinding and scrubbing mode of action.[1516]

The SAF is claimed to be highly resistant to mechanical failure, based on laboratory data.[1317] Nevertheless, no data are available to date with regard to the prevalence of SAF separation during clinical use. In addition, no data are available on the ability of operators to retrieve or bypass such separated fragments of the SAF when such separation occurs.

This preliminary clinical survey was conducted to determine the prevalence of SAF separation during clinical use by experienced SAF users and to study how these users addressed separated SAFs when such separation occurred.

MATERIALS AND METHODS

Sample

Because the SAF is a rather new instrument, which is not yet widely used, SAF distributors in various countries were approached to find experienced SAF users. A list of SAF users to whom 50 SAFs or more had been delivered was obtained, and the questionnaire was sent to them.

Questionnaire

The questionnaire consisted of four questions:

What is the quantity of SAFs that have been used in your clinical practice to date? Do you use the SAF for single use or more?

How many SAFs have separated inside the canal?

How many separated SAFs were retrieved from the canal, what retrieval method was used, and how much time did it take?

In the case of nonretrievable separated SAFs, was bypass possible?

Self-adjusting file separation was defined as complete detachment of the apical part of the file, such that it remained in the canal [Figures 1c and 2b].

The operators were also asked to describe in detail:

The method by which they applied the SAF and mainly whether it complied with or differed from the manufacturer's instructions regarding single use of the file and the need to establish an adequate glide path before using the SAF in a given canal;

how the separated files were retrieved and how was the treatment completed, in cases of nonretrievable separated files; and

their type of practice and their training/certification.

The questionnaire consisted of open questions and the answers were interpreted, independently, by two evaluators. When disagreement occurred between them (very rare) the matter was discussed and agreed upon.

Only users who reported that they had already used the SAF system in 50 clinical cases or more were included in the present survey. The survey covered a period of 24 months.

Statistical analysis

Fisher's exact test was used to compare SAF separation occurrence among endodontic specialists versus general dentists, operators who used >100 files versus <100 files and operators who used the SAF as single use or more, with significance set at 0.05.

RESULTS

Fifteen completed questionnaires from SAF users in 7 countries, who had used 50 SAFs or more, were included in this survey. All 15 also met an inclusion criterion that the operator complied with manufacturer's instructions regarding the need to establish an adequate glide path before using the SAF. Thirteen of the 15 operators reported repeated use of the SAF, unless initial signs of mechanical deterioration of the file, such as permanent distortion or tears in the lattice, were detected.

Questionnaires were received from SAF users in Germany, Greece, Israel, Kyrgyzstan, Russia, Slovakia and the USA. These operators had used between 60 and 550 files, with a mean of 168 SAFs per operator. A total of 2517 SAFs were reported in this survey. The results of the survey are presented in Table 1. Six of the responding operators were officially trained and certified as endodontic specialists. The other 9 were general dentists with practices heavily centered on endodontics. All had more than 10 years of experience.

Table 1

SAF file separation incidence during clinical use

The prevalence of SAF separation during clinical use was 0.6% (15/2517). Among the 15 cases of SAF separation, retrieval procedures were successful in 12 cases (12/15). In all of these cases, retrieval of the separated part of the file was performed using Hedström files. One operator reported the successful use of a #30 micro Debrider (Dentsply-Maillefer, Ballaigues, Switzerland). The time required for retrieval of the separated part was 1-3 min. No additional dentin removal was required to accomplish retrieval [Figure 1].

In the three cases (3/15) in which retrieval was not possible, the separated segment of the instrument was bypassed. Stainless steel K files were used to bypass through the hollow file segment and to instrument the canal with copious irrigation of sodium hypochlorite. Obturation was performed using a combination of cold and warm compaction. Sealer and a master cone were inserted, followed by lateral compaction using NiTi finger spreaders (Dentsply-Maillefer). This step was followed by softening the mass of the filling using a hot plugger and further vertical compaction with cold Machtou pluggers (Dentsply-Maillefer). Bypass was possible in all (3/3) of the nonretrievable cases.

When comparing the occurrence of SAF separation between endodontic specialists and general dentists, between those who used >100 files and those who used <100 files and those who used the SAF a single use or more no significant difference was found.

DISCUSSION

The method chosen in the present study to find experienced SAF users for the survey was far from optimal and had its drawbacks. In common surveys, one should calculate the required sample size and verify randomization to validate the results and ensure their representativeness.

Nevertheless, in the case of a new instrument, such as the SAF that is not yet widely used, such measures were not possible. We, therefore, used an alternative, unorthodox method to generate the study sample. This sample of 15 experienced SAF users was apparently nonuniform and included endodontists, as well as general practitioners, whose clinical experience also varied. However, the variety of backgrounds of the SAF users who participated in this survey might be considered as a reflection of the real clinical world. The subjects had only one common denominator: A large number of cases that they treated with the SAF system.

The number of 50 clinical cases was chosen arbitrarily to select people with sufficient clinical experience with the system and who had performed a sufficient number of cases so that there would be likelihood that they had encountered an event of SAF separation, which was expected to be rare, based on the clinical experience of the authors.

Due to the small sample size and the limitations mentioned above, the results of this survey should be considered preliminary and indicative. Nevertheless, in the case of a new instrument like the SAF, it is important to find and publish such initial results; otherwise, the clinician might have only the laboratory data on which to rely[1317] and might thus obtain the wrong impression that this file does not separate. The results of the present study indicated that, in clinical use, the SAF could indeed separate, although the incidence of such separation was low.

The file separation prevalence of NiTi rotary files has been reported to be from 0.14% to 5%.[156789] Such separation represents an as-yet unmet challenge: Manufacturing an unbreakable NiTi rotary instrument.

Major improvements efforts have been based on innovative metallurgy, such as the introduction of the technologies of either the R-phase by SybronEndo, the M-wire by Dentsply or the Hyflex CM NiTi files by Coltene Whaledent; nevertheless, file separation still occurs.[1819] Asymmetrical reciprocation[20] with either regular NiTi files[2122] or with specially designed instruments, such as the WaveOne (Dentsply-Maillefer) and Reciproc (VDW, Munich, Germany), represents another attempt to meet the same challenge. Initial in vitro and clinical studies have indicated a reduced incidence of file fracture.[9222324]

The SAF is also subject to the risks of mechanical failure [Figure 2]. When mechanical failure of the SAF occurs, it is most often in the form of tears in the lattice [Figure 2c and d].[13141725] Such failures might be limited to either: (a) Partial detachment of an arch or strut at one end; or (b) full detachment of an arch.[25] The present study indicated that, in rare cases, true file separation could occur, with the apical part of the file becoming completely detached and remaining in the canal [Figures 1c and 2b].

The first two types of mechanical failure are usually of no clinical consequence, other than having to replace the file. In cases of the partial detachment of an arch, the file should simply be discarded. In cases of full detachment of an arch, the detached arch is easily washed out, using either the action of SAF irrigation and movement[25] or ultrasonic-assisted irrigation.

In contrast with a separated fragment of a rotary file, which is usually screwed into the canal, a detached arch or strut is much smaller than the canal [Figure 2c and d] and is thus easily flushed out.[25] The third case, which consisted of full detachment of the apical part, such that it remained in the canal [Figures 1c and 2b], was termed “SAF separation” and was the subject of this survey.

The results of the present study indicated that SAF separation during clinical use occurred in 0.6% of cases. Retrieval of the separated fragment was possible in 80% of these separation cases, using either a Hedström file or a #30 micro Debrider, which has a shape similar to that of a Hedström file. Such retrieval did not require additional dentine removal and was accomplished within a few minutes. No special additional equipment was needed.

The retrieval procedure of a separated SAF is quite different than the retrieval of a separated rotary NiTi file. The latter is a challenging and time-consuming process,[1112] which frequently requires expertise and substantial removal of sound dentin.[10] Consequently, such removal attempts can lead to procedural failures, such as ledge formation, over-enlargement and transportation of the prepared root canal or even perforation.

In rare cases, retrieval of the separated apical part of the SAF was not possible. Such cases consisted of 0.12% (3/2517) of the entire sample or 20% (3/15) of the cases of separated SAFs. In all of these cases (100%), the endodontic procedure was completed by bypassing the file, which was performed easily through the hollow mesh-like SAF segment.

The present study was designed as a retrospective survey, thus no information was available as to how many times each SAF was used. In the future, a prospective study may be conducted in which detailed record of the use of each file may be followed. This was beyond the scope of the present initial retrospective survey.

The findings of this preliminary survey should be considered indicative and not comprehensive and conclusive. For more conclusive results, further full-scale multicenter prospective studies should be performed. Nevertheless, the results of this survey can currently be considered to offer “the best clinical information available.”

CONCLUSIONS

The results of the present preliminary survey indicated that SAFs could indeed separate during clinical use, even if on relatively rare occasions. In addition, in the rare cases in which file separations did occur, retrieval or bypass procedures were reliable and easy for the operator to perform. No special tools were required, and no excessive dentin removal was required.