By Barry L. Musikant, DMD
The safest ways to effectively shape canals must include the safety of the instruments meaning most prominently that they predictably stay intact. Without such assurances, the shaping and cleansing of the canal will be compromised in multiple ways. The most obvious way to assure the integrity of the instruments is to minimize the amplitude of motion they are subject to. We want to avoid the torsional stresses and cyclic fatigue that are generated when instruments are used in rotation be it continuous or interrupted. One effective way to do this is the implementation of a 30º reciprocating handpiece that oscillates at 3000-4000 cycles per minute.
Please note that an arc of motion that is limited to 1/12 of a circle, or 5 minutes on the face of a clock (Fig 1), can afford high frequencies of motion without any concern for instrument separation.
The integrity of the instrument by itself does not mean that the canals will be automatically well cleansed. It simply means that they will stay intact. However, it is a good starting point in employing a system where the dentist is confident in that they can use the instrument against all the walls of canals that are often highly oval and sheath-like in cross-section along a good portion of their length. We all know the alternative of using greater tapered rotary NiTi. Straight-line access, wider coronal openings, and the imposition of a conical shape are necessary to reduce the possibility of instrument separation. In the process, the practitioner needlessly weakening the remaining tooth structure; imparting reduced chances of long term success.
For best practices use an 02 tapered stainless steel modified reamers through a 20, rather than K-files, are used to shape the glide path. Manual usage of these instruments are generally limited to the first and thinnest instrument negotiated to the apex. With the proper measurement made via the apex locator, the first reamer negotiated to the apex manually is attached at that level to the 30º reciprocating handpiece and oscillating at 3000-4000 cycles per minute is worked vigorously and uniformly against all the walls of the canal. The key distinction here is the use of reamers rather than K-files. Reamers have fewer and more vertically oriented flutes. Incorporating a flat they are commercially known as SafeSiders (Fig 2) and due to their design encounter far less resistance along the length of a canal when negotiating to the apex. Vertical flutes, unlike the horizontally oriented flutes of a K-file, tend to glide through any debris present in the canal rather than impacting it apically and losing length. With the first clockwise motion of the modified reamers, dentin is shaved away further reducing the engagement of the instrument along length and reducing apical resistance in the process.
The design differences between a K-file (Fig 3) and modified reamers are far from trivial. In reality, they create a basis for a far simpler, safer more effective way to shape canals. The creation of the glide path has essentially been a manual task. By employing a 30º reciprocating handpiece generating an extremely rapid watch winding motion the hand fatigue associated with the manual use of K-files, is eliminated and the process of shaping the canal to a minimum of 20 is dramatically reduced. This feature alone is highly desirable for any dentist wishing to increase his/her productivity. However, the advantages extend beyond reduced time requirements and the elimination of hand fatigue. Because separation virtually disappears as a possibility, the dentist gains the confidence to use these instruments with vigor in both the mesio-distal and bucco-lingual planes.
Heretofore, the idea of purposely going off center to touch the broader extensions of pulp tissue most often found in the bucco-lingual plane would be an open invitation to an increased incidence of instrument breakage. Consequently, as has been documented, tissue often remains in these broader extensions untouched by the instruments that are imparting a conical shape at the expense of thinning the dentin too much in the mesio-distal plane. The modified reamers in the process of working vigorously in the bucco-lingual plane do the equivalent of creating straight-line access in the mesio-distal, but limited to the broader bucco-lingual dimension. Undercuts are removed giving the dentist a far greater ability to remove tissue ensconced in the extended bucco-lingual plane.
Up to this point we are talking in general terms about the design features of modified reamers and the way they are used to facilitate the creation of the glide path. Now let’s talk about the most challenging type of case one might face, a highly calcified tooth with long curved roots. Our definition of highly calcified must actually have some small level of patency otherwise no instrument could penetrate into a space that literally does not exist. So what we are really saying is that the modified reamer is designed to encounter the least resistance. An essential feature of such a design is a cutting tip. Used manually with a watch winding motion, the thinnest and most highly flexible reamer has no chance of auguring its own canal. We would immediately know via a lack of tugback that we are hitting a wall and no patency exists in the direction of the instrument’s tip. This is our signal to remove the instrument from the canal and place a small 1 mm or less 45º bend on the tip of the instrument and with a light and short twist and push motion seek out a patent pathway. This is the best anyone can do short of creating our own pathway that would be counterproductive to the success of the treatment we are providing.
Assuming the tip of the bent instrument finds a patent pathway, in the presence of 17% EDTA, we would then proceed with our manual watch winding to gain further depth. These initial stainless steel reamers are so flexible that they will take substantial curves without further need for prebending. Our only concern is once again encountering an abrupt curve that would be identified by hitting an obstacle that eliminated tugback at which point we would have to rebend our instrument. The modified reamers are far superior in determining whether or not a wall is being encountered due to the reduction in engagement along length. Used in this manner, the dentist has a greater capability of negotiating to the apex with the thinnest SafeSider than an equally thin K-file. Having now reached the apex, the instrument is attached to the reciprocating handpiece without removing it from the canal’s most apical position and oscillating at 3000-4000 cycles per minute widens the canal without distortion to dimensions larger than itself allowing to the subsequent instruments all used in the 30 reciprocating handpiece to negotiate to the apex almost effortlessly. The result is a glide path open to a minimum of 20, producing a shape that reflects the original canal anatomy on larger form.
At this point in the shaping of the canal we now employ our Tango-Endo Instrumentation System, appropriately named because it consists of two more instruments, a shaping instrument and a finishing instrument (Fig 4). These instruments too are used in a reciprocating handpiece that produces a 45º arc of motion and oscillates at 3000-4000 cycles per minute. Unlike the SafeSider handpiece that accepts the plastic manual handles, the Tango-Endo System employs a latch attachment. The purpose of the latch handpiece is due to the flute design of the Tango-Endo system. The flutes of the Tango-Endo System, are designed to more vigorously remove dentin in the bucco-lingual plane than the initial instruments used with in the SafeSider system with complete safety when confined to a short arc of motion. They would be subject to breakage if used with a greater arc of motion that could only be generated manually. It would be counterproductive to allow this to happen and then explain to dentists why it occurred. By eliminating the potential for greater arcs of motion the system becomes safer and even more rapid in its use.
Together the initial instruments in the SafeSider system define the glide path to the point where the more aggressive flute design of the Tango-Endo System can kick in to do the final shaping. Tango-Endo instruments also are available in large and extra large for wider canal spaces. However, let us not discount the ability of the Tango instruments to work all the walls of the canal in a uniform manner routinely widening its dimensions beyond its own. It is the ability to widen the canals beyond its own dimensions in the mesio-distal and bucco-lingual planes that is the key to both the SafeSiders and the Tango instruments.
What is offered here is a system that eliminates our fears of separation, in turn allowing us to use the instruments far more aggressively and doing so from the very beginning with an automated reciprocating handpiece that does away with hand fatigue throughout the entire shaping and cleansing process. A feature that naturally follows from a system that so dramatically reduces torsional stress and cyclic fatigue to the instruments is the savings that occur now that the dentist knows that he/she can reliably use the instruments several times before replacement.
A benefit that may mean more in the long run, but not generally appreciated on a day-to-day basis is the data from many research studies disassociating short arcs of motion from the production of dentinal microcracks. As well as the creation of greater tapered shaping associated with a reduction in the resistance to vertical fracture. Both these negative consequences are associated with greater tapered rotating NiTi instrumentation whether the rotation is continuous or interrupted.
The story is a good one. Reduce costs, dramatically reduce iatrogenic events, save time, eliminate hand fatigue and instrument separation and proceed with much lower procedural stress. I think that’s a good deal.