Dentin chips, pulp tissue fragments, necrotic tissue, microorganisms and intracanal irrigants may be extruded from the apical foramen during the root canal treatment.1 This may be of great concern since material extruded from the apical foramen may be related to post-operative endodontic pain and/or endodontic flare-up.2
There have been several studies that have evaluated the extrusion of intra-canal debris, microorganisms and necrotic tissue out of the apical foramen during instrumentation. Depending on the technique used to prepare the canals, the amount of debris being forced out of the apical foramen may differ. A study done by Al-Omari and Dummer, found that debris extrusion was least with balanced force and crown-down techniques, whereas the most extrusion occurred with techniques involving linear filing motions.3
TF files are made out of nickel titanium (NiTi) that are heat treated and then twisted, not ground. Because they are twisted, their grain structure is maintained and since they are not ground, no surface microfractures occur (which occurs in the grinding process) which obviates the need for surface polishing, thereby maintaining their surface hardness and efficient cutting edges. This process maximizes their flexibility and increases their resistance to cyclic fatigue. There are two file sequences in the TF Adaptive system. The small (SM) sequence contains three files, an SM1 (20 tip and .04 taper), SM2 (25 tip and .06 taper) and SM3 (35 tip and .04 taper). The medium large (ML) sequence contains three files an ML1 (25 tip and .08 taper), ML2 (35 tip and .06 taper) and ML3 (50 tip and .04 taper). Manufacturer recommends the SM sequence used in canals in which a #15 hand file struggles to get to working length. The authors also recommend that the SM sequence be used in canals of narrow width and canals with extreme curvature especially where “strip” perforation is at risk if the canals were to be prepared to a wider dimension. Manufacturer recommends the ML sequence be used in canals in which #15 hand file fits loose at working length or is made to fit loose at working length without risk of “strip” perforation.
Adaptive Motion technology employs a continuous feedback loop from file to motor in which the file motion self adjusts to the intracanal torsional stress. When there is no or minimal load on the file, the motion is a 600° clockwise rotation, where the file accelerates then coasts to an almost imperceptible stop. When there is load on the file the motion is one of reciprocation in which the file rotates clockwise 370° and counter clockwise anywhere from 0° to up to 50°, depending on the load applied to the file.
A single instrument reciprocating technique Wave One (Denstply Tulsa, OK) has been recently proposed in order to save time and simplify the cleaning and shaping of the root canal system. Using a reciprocating motion, the single file prepares the root canal system. Wave One files are made of standard NiTi alloy with M-wire.
Three sizes are available Small # 21 .06 (21 at the tip and .06 taper). Primary # 25 .08 (25 at the tip and 0.8 taper) and Large # 40 .08 with variable taper running along the file from .06 up to .08. The Wave One reciprocation motion operates at 10 cycles per second, allowing a 360° rotation every three reciprocating motion.
The Step Back Technique, which was first described by Clem in 19694, allows the preparation of a distinct apical stop and is divided into two phases. Phase one allows the preparation of the apical constriction of the root canal. During phase two, the remainder of the canal is prepared, gradually stepping back while increasing the file size, thereby producing a continuous taper from apex to orifice.
The purpose of the present study was to measure the amount of dentinal debris extruded through the apical foramen by means of three different instrumentation techniques: Twisted Files (TF) using Adaptive Motion Technology (Kerr Endodontics, (SybronEndo/Kerr Endodontics, Orange, Ca), Wave one (Denstply Tulsa, Oklahoma), a Single file technique using reciprocation and the manual step back technique using hand files (Maillefer, Tulsa. OK).
Material and Methods
A total of 45 extracted human mandibular lower incisors with mature apices, straight root canal and single canal, were selected for the present study. Teeth curvatures were verified according to the Schneider method and only teeth with a curvature (<5°).5 Teeth were stored in a thymol five percent solution until used. Radiographs were taken to verify that the teeth did not have calcifications, were not previously treated and had only a single root canal.
All teeth were standardized to 16 mm in length from the incisal edge to the tip of the root, by reducing it with a straight diamond bur. A #15 K-file was used to standardized the root canal to this size.
Teeth were examined under stereomicroscopy to verify the presence of cracks or root fractures. If present the teeth were excluded from the study.
A modified model used by Montgomery6 was used in this study to collect the extruded debris and irrigants. The container consisted of a pre-weighed Eppendorf’s microtube with two perforations on its cap. One perforation where the tooth was seated and the second perforation was a 1 mm hole designed to release pressure. A second plastic vial (scintillation vial) was used to hold the Eppendorf microtube (with a hole in the lid) in place.
Coronal access was achieved using a round #2 carbide bur. Apical patency was confirmed by inserting a # 10 K-file and visualizing the tip at the apical terminus. The working length was then confirmed to be 16mm. The 45 extracted teeth were randomly assigned to three separate groups of 15 each (n=15). Each group was instrumented by a different canal preparation technique. Apical patency was maintained by using a #8 K-File 0.5 mm extending past of the working length.
TF Adaptive Group:
A #15 K-File was used to determine canal size. Using tactile feel, if the K-file bound before reaching working length, the canal size was deemed to be small. When a #15 K-File reached working length passively, the canal size was deemed to be medium/large. For both groups, the first TF Adaptive file in sequence (SM1/ML1) was slowly advanced in a single controlled motion until the file engaged dentin. The file was then withdrawn from the canal and cleaned using a sterile gauze moistened with alcohol. Two mL of distilled water was used as the irrigant delivered to the pulp chamber and apical patency was confirmed with a #08 K-File. This procedure was repeated until the working length was achieved. The same protocol was used with the remaining two files in each sequence (with the SM2/ML2 and the SM3/ML3) until each file reached working length.
Step Back Group:
The rubber stoppers on the hand files from #15 through #40 were set at 16 mm. The initial root canal preparation was performed in a sequence using an “in and out” motion. Two mL of distilled water was used as irrigation solution in between instruments, placing the irrigation needle (Maxi Probe, Denstply Tulsa, Ok) as deep as possible but no more than 1 mm from working length. A #08 K-file was taken to working length after each irrigation regimen in order to check canal patency. The master apical file was standardized to #40 hand file for each case.
Wave One Group:
The Large 40/08 Wave One file directed apically with an “in-and-out” pecking motion with an amplitude of approximately 3 mm using light apical pressure (as recommended by the manufacturer). After the instrument was removed from the tooth, two mL of water was used to irrigate the root canal. This protocol was repeated continued until the working length was reached.
Once the instrumentation phase was achieved the Eppendorf microtube was placed inside the incubator at 37°C for five days to allow the water to evaporate before weighing the tubes. The micro tubes were checked every day to ensure the sample were not over dried. An electronic balance (Sartorius Cubis, Gottingen, Germany) with an accuracy of ±0.00001 g was used to weigh the samples. Two weight measurements were done before the instrumentation and three measurements were taken after instrumentation. Of the three measurements recorded, an average was obtained and this was compared to the initial measurement to obtain the amount of debris that was extruded.
The amount of extruded debris and preparation times were analyzed statistically using the analysis of variance and post hoc Student-Newman-Keuls test at a significance level of < .05
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Results
The Step-back technique produced significantly more debris compared with the TF adaptive system (P < .05) (Table 1). There was no statistical difference between the TF adaptive group and the Wave One group, even though the Wave One group presented with almost twice the amount of extruded debris.
Discussion
The results of this study showed that apical debris extrusion happens independently of the type of canal preparation system that is used. Step-back technique with hand files extruded significantly more debris when compared with Wave One single file reciprocating NiTi system (p < 0.05). Wave One single file reciprocating NiTi system extruded more debris when compared with TF Adaptive system.
The differences in the amount of debris extruded may be explained by the technique used to prepare the root canal space, the use of reciprocating motion or by the design of the files. As it has been discussed in previous studies,7-10 the cleaning efficacy is enhanced as the cutting ability of an instrument is increased.
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Some of the limitations encountered in this study, previously discussed in other studies,6,7 were the lack of the necessary back pressure to limit the amount of debris that could be extruded provided by the periapical tissues. Without the physical back pressure, the irrigants that were used during the cleaning protocol may have contributed to more debris extrusion through the apical foramen.
The Step Back technique with hand files extrudes debris because of the filing motion used and the apical pressure created during the cleaning and shaping procedures. The design of the files used in Wave One moves debris to the apical area because of its accumulation in the files flutes and by virtue of the reciprocating motion, more debris is extruded through the apical foramen. One of the advantages of adaptive motion is that when debris is created and the TF Adaptive file is free to rotate the debris is chanelled out coronally.
In conclusion, the TF adaptive system, with its unique Adaptive Motion Technology, extruded less debris past the apex when compared with Wave One, although it did not show a statistical difference. However, there was statistical significant difference respect to the amount of debris extruded caused by the Step Back hand file technique when compared to both Wave One and TF Adaptive. OH
David E. Jaramillo, DDS, Associate Professor of Endodontics at the University of Texas Health Science Center at Houston. He can be reached at David.E.Jaramillo@uth.tmc.edu.
Enrique Aguilar, DDS, Clinical Assistant Professor of Endodontics at the Universidad Autonoma de Baja California, Tijuana, Mexico.
Mario F. Leon, DDS, Resident Endodontic Program at the University of Texas Health Science Center at Houston.
Raydolfo Aprecio, OD, Center for Dental Research, Loma Linda University, Loma Linda, CA.
Oral Health welcomes this original article.
References:
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