Integrating Endodontic Goals, Principles and Techniques
The goal is to always maximize the chances of success. To date, the principles required for success include removal of all compromised pulp tissue and any bacteria invading that tissue retaining as much tooth structure as possible consistent with that principle. To attain success, the instrumentation techniques employed should reflect those principles as much as possible. To the extent the techniques deviate from those principles, success will be compromised. With these insights, we have the means to judge the impact of the endodontic techniques we use.
Hand instrumentation with varying degrees of apical pressure applied using stainless steel K-files typically applied with a watch winding motion: This is a traditional method of instrumentation that is most familiar to dentists. Being manually applied, it has an increased chance tends to produce hand fatigue and take a longer time to complete the instrumentation process. We can modify hand instrumentation by employing K-reamers rather than K-files, instruments that encounter less resistance as they negotiate through the length of the canals, reducing to some degree hand fatigue and procedural time. Less resistance produces a superior tactile perception aiding the dentist in differentiating a tight canal where tugback is present from hitting a solid wall where no initial tugback is present. Rotary instrumentation manufacturers take note of the advantages of the fewer and more vertical orientation of the reamers’ flutes in shaving dentin away from the canal walls and incorporate that design in all their rotary systems.
When our tactile perception tells us that we are encountering resistance during the penetration of extremely tight canals, our wrist watch motion may be modified into a clockwise twist and pull motion with mild apical pressure applied. In these situations the best irrigant to use is 17% EDTA, a chelating agent that softens the canal walls reducing the resistance the preferred reamers encounter on the way to the apex. Noting the reduced resistance that reamers encounter compared to K-files, resistance is further reduced by incorporating a flat along the working length of the reamers starting with a 15/02. The flat reduces canal engagement while creating two vertical cutting edges that shave the dentin away in both the clockwise and counterclockwise motion further decreasing the procedural time for instrumentation.
Instrumentation of canals using the same relieved K-reamers in a 30o handpiece oscillating at 3000-4000 cycles per minute: A 30o arc of motion mimics the manual watch-winding motion. A shorter arc of motion removes less dentin per cycle, but overall is much more efficient than manual because of the high cyclic frequency. First applying unrelieved reamers through a 10/02 and relieved reamers thereafter, in the oscillating handpiece optimizes the creation of a well-defined pathway to the apex. A major advantage of 30o oscillation is an arc of motion that generates, at its worst, stresses far below the threshold for instrument separation. Given this margin of safety, the unrelieved and relieved stainless steel reamers can be vigorously applied to all the canal walls in a uniform manner performing the function of “internal routing” that cleanses the canals in three dimensions in a way that reflects the original canal anatomy in larger form. 30o oscillation is superior to manual watch-winding where an arc of motion easily exceeding 30o coupled to the negotiation of a curved canal with apical pressure applied can lead to instrument separation. It is the dentist’s awareness that separation is a possibility that limits its usage to the more central portions of canals where resistance is the least, reducing the chances of breakage, but also compromising the cleansing and shaping process. The concern for separation increases significantly when manual is replaced by rotation be it continuous or interrupted otherwise known as reciprocation.
Continuous rotary instrumentation employing NiTi reamers (and they are reamers):
Highly flexible, NiTi reamers will follow a glide path created by the means already discussed. The more defined that glide path the less the engagement along length. When employing rotary NiTi, it is of paramount importance to minimize excessive engagement as much as possible to reduce the amount of torsional stress the rotary instruments are exposed to. To minimize excessive engagement, the glide path is often further modified by creating straight-line access and then employing a crown-down sequencing of instrumentation that provides for deeper access, by less tapered instruments. These steps reduce engagement along length, but do so at the expense of the remaining tooth structure violating a basic endodontic principle of dentin preservation.
Rotary instrumentation can reduce dentin loss by shaping the canals to lesser diameters reducing the number of instruments employed in crown-down preparation and speeding up the instrumentation process. Staying centered would still be considered appropriate to reduce the stresses that might occur if the dentist vigorously applied these rotary instruments into the isthmuses and narrow buccal and lingual extensions that are often present. In fact, the thinner the NiTi instruments, the more flexible they become and more easily deflect off the canal walls with minimal removal of dentin, especially true when a space exists into which these instruments can deflect, something that is common in the bucco-lingual plane. The flexibility of NiTi generally considered an advantage is a disadvantage in the pursuit of three-dimensional shaping. For sure, rotary shaping will produce visually appealing obturation on x-ray, but that pleasing image may not reflect effective cleansing in the bucco-lingual plane.
Interrupted rotation, known as reciprocation, moderates the torsional stresses of continuous rotation thereby reducing the potential for instrument separation. While torsional stress can be reduced by asymmetric rotations (reciprocation) both continuous and interrupted rotations are equally subject to cyclic fatigue where the amount of curvature and the radius of the curve define the amount of cyclic fatigue imposed with each rotation. While interrupted rotations reduce the amount of torsional stress generated compared to continuous rotations, it has minimal impact on cyclic fatigue. The interrupted pattern of reciprocation makes it less efficient than continuous rotation requiring more cycles to reach the apex and generating more cyclic fatigue in the process.
To the extent that rotary NiTi continuous or interrupted require straight-line access, crown-down preparations and centered shaping, these systems are not consistent with the principles of thorough cleansing with the least loss of tooth structure. Somewhere along the line, the preservation of the instruments took precedence over the long-term success of the tooth. For rotary NiTi to be consistent with these principles, it would require their implementation without the need for exaggerated straight-line access and without the need for crown-down preparations. To date, no rotary NiTi system has been introduced that can safely work in this fashion. We introduced the SafeSiders HF, a rotary system with a helical flat along its working length, a design that reduces the engagement of the instruments with the canal walls as they negotiate to the apex. This is not a cure-all, but it does reduce the engagement and resistance of the rotary instruments as they negotiate to the apex. The result of this design reduces torsional stresses and cyclic fatigue resulting from the fewer rotations needed to reach the apex.
Despite these improvements, complex canal anatomy can still impede apical progress putting greater demands upon the instruments and exposing them to unacceptable amounts of torsional stress and cyclic fatigue. This situation does not represent a dead-end where the typical option is to employ rotary with smaller pecking motions and a lighter but longer touch required to reach the apex. Rather, I simply go back to using the stainless steel relieved reamers in the oscillating handpiece to widen the canals sufficiently so the helically relieved rotary instruments subsequently reach the apex without encountering excessive stresses. Unlike crown-down preparations, the stainless steel reamers are limited to 02 tapers preserving tooth structure as they open up the canal spaces for the safe use of rotary instrumentation. I think of this sequence of events as a form of “integration”, the utilization of 30o oscillation of 02 tapered relieved stainless steel reamers, an approach virtually immune to separation, wherever and whenever I sense the potential for excessive stresses generated when shaping canals via rotary NiTi.
Advertising impacts what we buy and use. It is the goal of advertising to shift our choices to the products that the advertisers represent. When those advertising organizations are so big that they monopolize our consciousness, our choices often become dependent upon what we have been told before we gain personal experience and even after we gain personal experience, we may be told that any shortcomings in the systems is our deficiency of use and not the systems and too often we accept that appraisal. The whole point of this particular post as well as previously written ones is to stimulate our imaginations so our ability to apply common sense has a much broader base that introduces approaches we had not considered.
Regards, Barry