Avoiding Mistakes in Endodontic Techniques

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First of all let me list the endodontic techniques I employ, advocate for and teach.

?They include:

1. Stainless steel twisted reamers both unrelieved and relieved employed in a 30o??handpiece oscillating at 3000-4000 cycles per minute

2. The oscillating handpiece is also employed to activate the irrigants for more effective debridement of the canals

?3. The creation of a canal preparation that rarely exceeds a 30/04 preparation in terms of taper

4. Single-point room temperature obturation using epoxy resin cement?

Why stainless steel relieved twisted reamers?

Stainless steel twisted reamers retain significant strength even fabricated in sizes as thin as an .06/02. If confined to a 30o arc of motion via the oscillating handpiece they are virtually free of breakage regardless of the degree of curvature they may be required to negotiate through. In previous posts, I have gone over in detail why the predominantly vertical flute orientation of the reamers is so much more effective than the predominantly horizontal flute orientation of files. Mechanically, the reamers shave dentin away from the canal walls with the first clockwise stroke of the handpiece. While the short arc of motion limits the amount of dentin that is removed with any single stroke, the process becomes quite rapid and efficient when used at a frequency of 3000-4000 cycles per minute.?

It should also be noted that the description of the reamers used are described as twisted meaning the flutes are a product of twisting the triangular or square wire used to fabricate the instruments rather than having the flutes ground in, a process that avoids the defects that often result from grinding and are a site for the initiation of crack formation that can lead to unpredictable instrument breakage. The short arc of motion so minimizes the torsional stresses and cyclic fatigue that the instruments are exposed to that starting with a 15/02 a flat is incorporated along the working length of the instruments making them more flexible, reducing the engagement and resistance within the canals they are negotiating through and providing for a superior tactile perception of what the tip of the instruments are encountering. Confined to the 30o arcs of motion, the more flexible instruments have an increased ability to adapt to the canal curvatures without distortion. Powered by the oscillating handpiece, hand fatigue is for the most part completely eliminated while speeding up the instrumentation process.

Why 30o rather than full continuous or interrupted (reciprocation) rotations?

While rotary instrumentation has proven to be a rapid way to impart a conical shape to canals, as canal anatomy becomes more complex the chances of instrument separation increase. The dentist has little control over the amount of torsional stress and cyclic fatigue, the two factors causing instrument breakage, that the instruments are be exposed to with the danger of instrument separation increasing as the resistance the instruments are exposed to grows. The dangers of rotating instruments are completely eliminated when using stainless steel relieved twisted reamers confined to 30o arcs of motion.??

The short arcs of rotation reduce the amount of dentin removed per stroke but are compensated by the high frequency of the short arcs (3000-4000 cycles per minute). The key difference is obviously the virtual elimination of the causes of instrument separation. This fundamental difference provides a breath of freedom for the dentist. With instrument separation no longer a concern, the dentist is free to apply the high-frequency oscillating instruments against all the canal walls physically contacting them circumferentially while sonically activating the irrigants that in concert with direct physical contact increase the chances of effective three-dimensional debridement and cleansing.?

Unlike rotary instruments, the oscillating instruments give the dentist the ability to minimize the removal of dentin in what is most often the narrower mesio-distal plane while removing more pulp tissue and bacterial biofilms in what is typically the wider bucco-lingual plane. The preservation of dentin along with more effective canal cleansing is now possible simply because we are no longer worried about instrument breakage. Something that is substantiated in the literature, but not generally appreciated clinically is the fact that with the incidence of instrument separation virtually eliminated, the production of dentinal defects strongly associated with rotary techniques is also minimized, a reduction that is predicated on Newton’s Third Law of Motion that states that two interactive bodies have an equal and opposite effect on each other. This can only be considered a plus.

Do we need preparations that impart a taper greater than 04?

In fact, the better question is whether in many cases do we even need an 04 taper. The whole subject of tapers became an issue with the introduction of rotary instrumentation. Subject to separation, a crown-down technique was devised for their usage limiting the amount of contact any given rotary instrument has with the canal walls. Greater tapers were baked into the system for the sole purpose of reducing the incidence of instrument separation. Over time, tapers greater than 04 became more associated with excessive dentin removal, consequent weaker teeth more prone to vertical fracture.?

Today, rotary is generally limited to tapers not exceeding 04. We should be aware, however, that when we talk about tapers we are really discussing the impact they have on the mesio-distal preparation. One of the many rules of caution suggested by rotary manufacturers is to stay centered with minimal deviation from a straight path to the apex. That the canals may be significantly oval in cross-section with pulp tissue and bacteria present in the buccal and lingual extensions of the canals is not sufficient reason to direct the instruments aggressively in these directions. The need to keep the instruments intact overrules any such movement.?

Considering the oval canal in three-dimensions makes the entire concept of tapers a false notion. Yes, we may have a prepared taper in the mesio-distal plane, but whatever that taper is, it is probably inadequate when applied to the wider bucco-lingual plane of an oval canal, something that is not addressed because of the need to stay centered. A much more constructive approach is to use the 30o oscillating reamers, perhaps of smaller dimensions even in the narrower mesio-distal plane, but definitely smaller than the wider bucco-lingual dimensions of an oval canal.?

What we want to be capable of is the utilization of instruments as internal routers, instruments that can be applied aggressively to all the canal walls removing pulp tissue and bacteria three-dimensionally. Initial internal routing does not require the instrument to be larger than the canal in either dimension. That only becomes a requirement when we want to size the canal to a dimension greater than it had in the unprepared state, rarely exceeding an apical preparation of a 40/02. A canal preparation of a 35/04 tends to be a common sense compromise, a degree of instrumentation that is 95% achieved with 30o oscillating stainless steel twisted reamers and a single 30/04 helically relieved rotary instrument that is only applied to the canal after the canal preparation is sized for minimal resistance to the apex with the impervious oscillating reamers.?

Is single point room temperature obturation effective?

The whole point of obturation is to effectively seal the instrumented space. The whole point of thermoplastic obturation was to maximize the amount of gutta percha in the canal. The more gutta percha present the less sealer along the length of the obturated canals. This may have made sense years ago when the cement used in obturation were particulate in nature, subject to dissolution in the presence of oral fluids. Today, polymer cements such as EZ-Fill Epoxy resins are not subject to dissolution and with the proper application along the length of the canal walls in conjunction with an appropriately sized gutta percha point also coated with the epoxy resin cement will create a three-dimensional seal that is impervious to being washed out by any form of leakage.?

This fact alone precludes the need for any thermoplasticizing of gutta percha. The sealer at room temperature is more flowable than heated gutta percha and rather than undergoing contraction as it cools both the sealer and the gutta percha slightly expand as the materials warm from room to body temperature. The sealer forced laterally into all the nooks and crannies of the canals when the prefitted gutta percha point is inserted into the canal adapts to the canal walls far better than thermoplasticized gutta percha and undergoes expansion rather than contraction upon warming to body temperature. This far easier method of obturation allows the dentist a far simpler and far less expensive way to predictably obturate canals. In past posts I have shown multiple examples of this method of obturation.

In a subsequent post, I’ll talk about the use of the bidirectional spiral in applying the sealer in canals avoiding the potential to drive cement over the apex during its application. I will also talk about when and why to use the Flexi-Post and Flexi-Flange in restoring endodontically treated teeth.

I find asking critical questions directed at the heart of what we do, taking nothing for granted, a way to expand my thinking and reach conclusions that I might not have had I simply accepted the marketing concepts that are devised by those whose goal is to sell product. Most of the approaches I use in the mechanics of instrumentation and obturation we invented ourselves because their absence proved at a minimum to be an inconvenience. I offer them as alternatives to think about and welcome any constructive thoughts regarding these topics.

Regards, Barry