Different Endodontic Situations Demand Different Approaches
When we choose an endodontic instrumentation system the attributes we want include:
1. Remaining intact as it shapes the canals
2. Effectively removing the bulk of the pulp tissue
3. As little weakening of the root consistent with effective tissue removal.
These attributes are determined by the design and utilization of the instruments and the canals they are shaping. An instrument may remain intact when the canals are fairly wide and straight, but be subject to separation when instrumenting long curved canals. Obviously, there is an interplay between the instruments and the canals being treated, one that we should be trained to recognize to avoid untoward events.
There is a continuum in pulpal anatomy from simple to complex. In the transition from simple to complicated pulpal anatomy, the instruments are likely to be subject to increasing stress as they negotiate to the apex. It becomes imperative for the dentist to recognize the increasing stress to the instruments and take appropriate steps to minimize the obvious iatrogenic potential of a broken instrument as well as the production of dentinal defects that can arise from rotary instrumentation.
From a marketing point of view, procedural speed is desirable and is attained by employing fewer instruments and having them remove dentin more aggressively. The dentist is more productive and earns more increasing the incentives to use these systems. Fewer more aggressive instruments, however, concentrate procedural stress. As long as the canal anatomy is fairly straight-forward, simplified systems deliver the reward of speed without apparent consequences. Without clearly defined criteria, dentists will expand their utilization of “efficient” systems to more and more complicated situations, only stopped when the stresses encountered exceed the torsional resistance and fatigue properties of the instruments leading to separation.
Only after instrument breakage do most of us become aware that what seems a robust system in easy situations can be quite vulnerable in more challenging circumstances. Instrument separation can lead to several types of responses:
1. The dentist may abandon the system for another deemed safer
2. Continue to use the system, but emphasize those steps that increase the safety of the instrument including, single usage, straight-line access, crown-down preparations and more conservative shaping in both the mesio-distal and bucco-lingual dimensions.
3. Greater emphasis placed on enlarging the glide path prior to the use of the designated system.
The concept of increasing vulnerability being the determinant in what to use must lead to instrument separation and is the wrong way to look at the challenges that imo plague us. Rather than having simplified anatomy being the standard to test the safety of an instrumentation system, any system that claims general usage should be subject to the most complicated anatomy first. It must prove itself invulnerable to separation in the most challenging situations. To date no system generating full rotations whether continuous or interrupted has successfully passed this test where canal anatomy includes severe curves, anatomy that subjects the instruments to significant amounts of torsional stress and cyclic fatigue.
With this observation clearly documented in the scientific literature, 30º reciprocation whether applied manually or from a handpiece oscillating at 3000-4000 cycles per minute is a substitute form of movement that is far less likely to induce instrument separation no matter the complexity of the canal anatomy. Even within the category of 30º reciprocation, the design and fabrication of the instruments will have an impact on outcomes. The flutes on a reamer resulting from twisting the wire produces an instrument far less vulnerable to breakage than one that has its flutes ground in. The latter process has been shown to produce metallic micro-cracks that coalesce and propagate under function.
There is a place for ground flutes. They can be machined to be significantly more aggressive to remove tooth structure more quickly, but the tradeoff is less resistance to torsional stress and cyclic fatigue. We gain speed when we employ a more aggressive flute design, but the instrument is now subject to increased stress. To use them where the canals are initially curved and narrow is to invite instrument separation. In these situations the better part of caution dictates the use of twisted relieved stainless steel reamers confined to short amplitudes of motion. The flutes are not as aggressive. A few more instruments may be required to shape the canal to the desired dimensions, but the incidence of separation is virtually eliminated. These are the types of tradeoffs that every dentist should be aware of so he/she knows when and where to employ the system that has the correct combination of safety, efficiency and effectiveness.
In terms of actual systems, where separation is not a concern, I can employ the Tango Endo system composed of a 30/02 and a 30/04 instrument with highly aggressive ground flutes used after the glide path has been enlarged to a 20/02 with stainless steel relieved twisted reamers. Where separation is a concern, I substitute stainless steel twisted reamers sized 25/02 through 40/02 reamers (SafeSiders) after glide path creation to a 20/02 to finish the shaping procedure. Because I have full confidence that the twisted relieved reamers limited to a 30º arc of motion are virtually invulnerable to breakage, I routinely use them vigorously in what is most often the wider bucco-lingual plane preserving tooth structure mesio-distally because of their minimum taper. The result is an endodontically treated tooth that is structurally stronger, less prone to vertical fracture yet debrided more thoroughly.
The combination of 30º reciprocation utilizing 02 tapered relieved reamers does away with the built in paradoxes associated with greater tapered rotary instrumentation. The goal must always be maximum preservation of dentin consistent with the effective debridement and irrigation. Greater tapered rotary instrumentation cannot deliver this combination. By knowing the conditions that provide 30º reciprocating instrumentation with aggressive ground flutes we have developed an efficient adjunct that speeds the shaping process for a large number of teeth. Where those conditions don’t exist, it is comforting to know that the SafeSiders are a combination of effectiveness, efficiency and safety.