May 1, 2013
by Gianluca Gambarini, MD, DDS and Gary Glassman, DDS, FRCD(D)
File separation via torsional and cyclic fatigue has created the biggest fear and risk for dentists using rotary nickel titanium (NiTi) files for root canal treatment 1-2) Increasing the resistance to file separation has been a focus for new NiTi rotary instrument design and manufacturing. Since 2008, the only way to improve performance and safety of NiTi instruments was to change file design with respect file dimensions, tip configuration, cross-section and flute design. With the development of heat treated Twisted File technology (Axis/SybronEndo, Coppel, TX) and M-wire (Dentsply Maillefer, Ballaigues, Switzerland), instruments produced with the newly treated alloys have been commercialized by aiming at improving their mechanical properties. More recently, a third factor has become important in this search for stronger and better instruments: Movement Kinematics.3
For more than a decade, NiTi Instruments have been traditionally used with a continuous rotary motion, but more recently, a new approach to the use of NiTi instruments in a reciprocating movement had been introduced by Yared1. The CW and the CCW rotations used by Yared were four-tenths and two-tenths of a circle respectively and the rotational speed utilized was 400 rpm. The concept of using a single NiTi instrument to prepare the entire root canal was made possible, due to the fact that a reciprocating motion is thought to reduce instrumentation stress. Recent literature data shows that a reciprocating motion can extend cyclic fatigue resistance of NiTi instruments when compared to continuous rotation4-5, mainly because it reduces instrument stress. As the instrument rotates in one direction (usually the larger angle), it cuts and becomes engaged into the canal, then it disengages in the opposite direction (usually with the smaller angle) and the stresses are therefore reduced. Following these concepts, new instruments have been recently commercialized; Reciproc (VDW, Munich, Germany) and Wave One (Dentsply Maillefer, Ballaigues, Switzerland), which uses specifically developed motors that produce a reciprocating movement (using approximately 150-30° angles).
This reduction of instrumentation stress (both torsional and bending stress) is the main advantage of reciprocating movements, even if it has been shown that a lot of different reciprocating movements can be used. Each one affects the performance and the safety of the NiTi instruments. Therefore, when discussing the advantages and disadvantages of reciprocation, the exact motion should also be mentioned, since the actual angle of reciprocation can have substantial influence on both the clinical and experimental behaviour of NiTi instruments.
Another possible advantage of reciprocation could be better maintenance of original canal trajectory, mainly related to lower instrumentation stress and consequently its elastic return. However, it must be underlined that reciprocation does not affect the inherent rigidity of the instruments. If a quite rigid Niti instrument of greater taper is slightly forced into a curved canal, it will create more canal transportation than a more flexible one, due to its inherent tendency to straighten. Moreover, tip design could strongly influence canal transportation, with a cutting tip being more dangerous that a non-cutting pilot tip.
While reciprocation with NiTi instruments have become very popular in recent years, with a significant number of published articles, some of these studies have shown that there is also inherent disadvantages in the reciprocating movements.
It is well known that a small inadvertent extrusion of debris and irrigants into the periapical tissues is a frequent complication during the cleaning and shaping procedures, both with manual stainless steel and nickel-titanium rotary instrumentation techniques6-7. However, recent studies have shown that commercially available reciprocating instrumentation techniques seem to significantly increase the amount of debris extruded beyond the apex8,9 and, consequently, the risk of postoperative pain. A clinical study comparing Reciproc and NiTi rotary instruments has also confirmed these findings.10
Since reciprocation movement is formed by a wider cutting angle and a smaller releasing angle, while rotating in the releasing angle, the flutes will not remove debris but push them apically. Reciproc and WaveOne motions are very similar (even if not precisely disclosed by manufacturers), and this fact could also explain the higher incidence and intensity of postoperative pain that has been found in recent research studies.10-11
Moreover, both WaveOne and Reciproc techniques use a quite rigid, large single-file of increased taper (usually 08 taper, size 25), which is directed to reach the apex. In many cases, in order to reach the apical working length, reciprocating instruments are used with apically directed pressure, which produces an effective piston to propel debris through a patent apical foramen – and possibly directing debris laterally – making canal debridement more difficult. Since instruments are commonly used without first performing preliminary coronal enlargement, this may result in a greater engagement of the file flutes and, consequently, may produce more torque and/or applied pressure on the file. Moreover, the cutting ability of a reciprocating file is decreased when compared to continuous rotation. Debris removal is also less, thus increasing the frictional stress and torque demand on the file, due to entrapment of debris within the flutes. To reduce this tendency, some authors have advocated the use of NiTi rotary glide-path instruments before using a WaveOne or Reciproc instruments, but in this case, the overall technique is no longer a single file technique but a more complex and more costly technique which utilizes two different types of Niti instruments, glide path instruments and then shapers.12
The TF Adaptive technique has been proposed in order to maximize the advantages of reciprocation while minimizing its disadvantages. By using a unique, patented motion, the innovative TF Adaptive Motion technology, together with an original three file technique, most clinical cases can be treated effectively and safely.
TF Adaptive employs a patented unique motion technology, which automatically adapts to instrumentation stress. When the TF Adaptive instrument is not (or very lightly) stressed in the canal, the movement can be described as a continuous rotation, allowing better cutting efficiency and removal of debris – since cross-sectional and flute design are meant to perform at their best in a clockwise motion.
More precisely, it is an interrupted motion with the following CW-CCW angles: 600-0°. This interrupted motion is not only as effective as continuous rotation in lateral cutting, thus allowing optimal brushing or circumferential filing for better debris removal in oval canals, but also it also minimizes iatrogenic errors by reducing the tendency of “screwing in” that is commonly seen with NiTi instruments of great taper.
On the contrary, while negotiating the canal, due to increased instrumentation stress and metal fatigue, the motion of the TF Adaptive instrument changes into a reciprocation mode, with specifically designed CW and CCW angles which vary from 600 -0° up to 370-50°. These angles are not constant, but vary depending on the anatomical complexities and the intracanal stress placed on the instrument. This “adaptive” motion is therefore meant to reduce the risk intracanal failure without affecting performance, due to the fact that the best movement for each different clinical situation is automatically selected by the Adaptive motor. It is quite interesting that the clinician will hardly perceive the differences in the changing motion due to a very sophisticated algorithm, which permits a smooth transi
tion between the changing angles.
As far as disadvantages of reciprocation are concerned, TF Adaptive motion is a reciprocating motion with cutting angles (CW angles) much greater than WaveOne/reciproc movements. As a consequence, the TF Adaptive instrument is working more with a CW angle, which allows better cutting efficiency and removal of debris (and less tendency to push debris apically and laterally), because the flutes are designed to remove debris in a CW rotation. In such case, TF Adaptive is taking advantage of the use of a motion that is more similar to continuous rotation for optimal debris removal. There are obviously some changes in the angles depending on canal anatomy (the more complex, the smaller the CW angle), but they do not seem to significantly influence the overall result. On the contrary, these changes influence resistance to metal fatigue, since TF instruments used with the Adaptive motion were found to have superior resistance to cyclic fatigue when compared to the same TF instruments used in continuous rotation.13 This explains why TF Adaptive has been shown in a clinical study much better performance than the other commercially available reciprocating instruments.
Additionally, the use of a sequence and the use of more flexible NiTi instruments can also be important factors in determining a lower incidence and intensity of postoperative pain, by reducing the amount of apical transportation and reducing extrusion of debris as the instruments are directed apically. TF instruments have been found to be the most flexible Niti instruments available, being significantly more flexible that Protaper and M2, which are instruments with design and mass very similar to WaveOne and Reciproc. As mentioned before, flexibility is a fundamental property to minimize iatrogenic errors while negotiating canals, both in reciprocation and in continuous rotation. Figure 1 shows that even if the same reciprocating motion was used as in the other reciprocating file systems, the more flexible files (seen with TF files) allow better maintenance of original trajectory with less canal transportation. Therefore, the use of a reciprocating movement does not significantly help a NIti instrument of greater taper to negotiate curved canals with no iatrogenic errors. It mainly helps to reduce instrumentation stress and the risk of intracanal failure.
The TF Adaptive technique is basically a three file technique, designed to treat the majority of cases encountered in clinical practice. Available are two sets of three file systems, one for small calcifying canals and one system for more “standard” and larger canals. In both scenarios, this allows adaquate taper and increased apical preparation. The number of instruments within each sequence can also vary and adapt to canal anatomy, with the last instrument of the sequence used only when a greater apical enlargement is needed due to larger original canal dimensions and/or enhanced final irrigation techniques. The sequences are also different in their shaping concepts. The medium/large canal sequence is a “true” crown-down technique, while the small canal sequence employs a smaller, more flexible instrument (04 taper 20 tip size) to pre enlarge the canal and create a glide path which decreases instrument stress for the next larger size file in sequence. This also allows better maintenance of the original canal trajectory as seen in Figure 2.
The use of a final apical enlargement with a size 35 is not only meant to allow the use of the Endovac (Axis/Sybron Endo, Coppell, Texas) irrigation technique, but to improve canal shaping by touching more canal walls. Figure 3 clearly shows how improved and deeper the apical one-third shape is when a 06 taper 35 tip instrument follows an 08 taper 25 tip instrument. This is why in the majority of cases, two instruments are much better than a single file technique, provided that the second instrument is a flexible one. The superior flexibility allowed by the use of TF technology permits TF Adaptive to follow these criteria, and safely enlarge canals with minimal risk of iatrogenic errors like tooth weakening and canal/apical transportation. The use of a more rigid alloy would have not made this possible, especially in curved canals.
TF ADAPTIVE TECHNIQUE
TF Adaptive is an intuitive, color-coded system designed for efficiency and ease of use. The colour coded system is based on a traffic light (Fig. 4). Start with green, continue or stop with yellow and stop with red. Green means go. Yellow means continue or stop. Red means stop.
CORONAL ACCESS AND GLIDE PATH
1. Place rubber dam.
2. Obtain straight line coronal access with slightly diverging axial walls.
The LA AxxessTM Diamond (Axis/Sybron Endo, Coppell, Texas – Fig. 5) is recommended for access preparation and may be refined with a CT4 diamond coated tip used with the MiniEndo II Ultrasonic Unit (Axis/Sybron Endo, Coppell, Texas) (Fig. 6).
3. Achieve apical patency and establish an apical glide path using #8 hand file, follow that with a #10 hand file and continue at least with a #15 hand file. Glide path may be facilitated with the M4 Safety Handpiece (Axis/Sybron Endo, Coppell, Texas) (Fig. 7) and SlickGelTM (Axis/Sybron Endo, Coppell, Texas) can be used as your lubricant. The pulp chamber should be filled brimful with NaOCl (Sodium Hypochlorite)
CANAL SIZE AND FILE SEQUENCE DETERMINATION FIGURE 8 and 9
SMALL CANALS (SM)
Using tactile feel, if you struggle to get a #15 K-File to Working Length (WL) then the canal size is deemed to be “Small”. Use the Small Pack (one color band) and its instrument sequence.
MEDIUM/LARGE CANALS (ML)
Using tactile feel, if a #15 K-File feels loose at working length then the canal size is deemed to be “Medium/Large”. Use the Medium/Large Pack (two color bands) and its instrument sequence.
ESTABLISH WORKING LENGTH
Using an apex locator (Fig. 10), a radiograph maybe taken to assist in length determination.
TF ADAPTIVE CANAL SHAPING TECHNIQUE
1. Use the “TF Adaptive” setting on your Elements Motor (Axis/SybronEndo, Coppell, Texas) (Fig. 11).
2. Ensure the pulp chamber is flooded with NaOCl or EDTA and make sure the file is rotating as you enter the canal.
3. Slowly advance the Green (SM1 or ML1) with a single controlled motion until the file engages dentin then completely withdraw the file from the canal. Do not force apically. Do not peck.
4. Wipe off the flutes. Deliver irrigant to the pulp chamber and confirm canal patency with a #15 K-File.
5. Repeat steps 3 and 4 using the file you started with until working length is achieved.
6. Repeat steps 3 and 4 with the Yellow SM2 or ML2 until the file reaches working length. If the desired apical size is achieved the sequence is complete. For larger apical sizes, repeat steps 3 and 4 with the Red SM3 or ML3 until the file reaches working length.
IRRIGATE AND DRY
When irrigating with EndoVac, in small canals, you must take SM3 to working length. In medium/ large canals, you must take at least ML2 to working length.
TF Adaptive matching Paper Points may be used to dry the canals.
TF Adaptive matching Gutta Percha or Obturators may be used to obturate the root canal system.
Adaptive Motion Technology is based on a patented, smart algorithm designed to work with the TF Adaptive file system. This technology allows the TF Adaptive file to adjust to intra-canal torsional forces depending on the amount of pressure placed on the file. This means the file is in either a rotary or reciprocation motion depending on the situation. The result is exceptional debris removal with the tried and trusted classic rotary Twisted File design and less chance of file pull-in and debris extrusio
n with Adaptive Motion Technology.
The TF Adaptive file design is based on clinically proven Twisted file technology, which means the file is twisted to shape for improved file durability, features R-Phase Technology to improve file flexibility and provides exceptional debris removal. With TF Adaptive and Adaptive Motion, you get the best of both worlds.
Now that’s “Rotary when you want it, reciprocation when you need it”.OH
Gianluca Gambarini, MD, DDS is full-time Professor of Endodontics, University of Rome, La Sapienza, Dental School. Head of the Endodontic Department International lecturer and researcher. He has focused his interests on endodontic materials and clinical endodontics .He is actively cooperating as a consultant with many manufacturers all over the world to develop new technologies, operative procedures and materials for root canal treatment.
Official member of ANSI/ADA and ISO Commitees for Endodontic Materials. Active member of IADR, Italian Society of Endodontists (SIE) and European Society of Endodontology (ESE), Associate member of AAE. Former Scientific editor of the Italian Journal of Endodontics (G.It. Endo) , official Journal of Italian Society of Endodontists (SIE), he is currently the Country Representative for Italy in the ESE.
He maintains a private practice limited to Endodontics in Rome, Italy
Dr. Gary Glassman graduated from the University of Toronto, Faculty of Dentistry in 1984 and was awarded the James B. Willmott Scholarship, the Mosby Scholarship and the George Hare Endodontic Scholarship for proficiency in Endodontics. A graduate of the Endodontology Program at Temple University in 1987, he received the Louis I. Grossman Study Club Award for academic and clinical proficiency in Endodontics.
The author of numerous publications, Dr. Glassman lectures globally on endodontics, is on staff at the University of Toronto, Faculty of Dentistry in the graduate department of endodontics, and is Adjunct Professor of Dentistry and Director of Endodontic Programming for the University of Technology, Jamaica.
Gary is a fellow of the Royal College of Dentists of Canada, and the endodontic editor for Oral Health dental journal. He maintains a private practice, Endodontic Specialists in Toronto, Ontario, Canada. He can be reached through his website www.rootcanals.ca.
Oral Health welcomes this original article.
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