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An update on non-rotating reciprocating endodontics

The Bi-Directional Spiral thoroughly coats the walls of the root canal and lateral canals without significant cement being forced apically. (Photo: Barry L. Musikant, DMD)
Barry L. Musikant, USA

Barry L. Musikant, USA

Thu. 13 November 2014

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There is an important distinction to be made between systems that involve 360 -degree rotations, be they interrupted or continuous, and systems that purposely minimize rotation to 30 degrees. While a system that undergoes interrupted full rotations is less vulnerable to instrument separation than continuous rotations, it is still a problem and both are associated with the production of dentinal defects where concern exists that they may propagate and coalesce into vertical fractures over time.

Dentists acknowledge separation anxiety by using these rotating systems with a light touch, staying centered with minimal deviation from the conical shapes these instruments impart to the canal. (See Fig. 1.)

By limiting the amplitude of motion to 30 degrees, the torsional stress and cyclic fatigue associated with full rotations is reduced to the point where it virtually is no longer a factor in instrument separation. What this means in practice is the dentist’s ability to use the thinnest 02 tapered stainless steel instrument in his/her arsenal without fear of breakage. For most dentists this immediately leads to the use of K-files, instruments that with their horizontally oriented flute design are inclined to impact debris apically when the push stroke is employed leading to loss of length.

Many of us are familiar with the loss of length that occurs when shaping curved canals with K-files, thinking it is our fault when in fact a good deal of the blame is associated with the instruments’ design. We can drastically reduce the incidence of blockage, minimize resistance along length and shave dentin away far more efficiently if we employ 02 tapered instruments with fewer and more vertically oriented flutes that incorporate a flat along their working length starting with a 15. (See Fig. 2.)

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After the tightest most tortuous canals are negotiated to the apex using our thinnest 02 tapered 06 tipped stainless steel vertically fluted instrument manually, the same instrument is attached to a 30 -degree reciprocating handpiece oscillating at 3,000-4,000 cycles per minute to widen the canal to a diameter larger than the instrument being used without distortion and creating a space where the next instrument in the sequence used in the reciprocating handpiece can reach the apex with minimal resistance.

This capability is utilized because the dentist quickly learns that separation simply will not occur giving him/her the confidence to work these instruments against all the walls of the canal with special attention given to what is often the wider bucco-lingual plane. With each instrument widening the canal significantly beyond its own dimensions, the sequence to any desired dimension is rapid, risk-free and without hand fatigue.

From the point of view of dentin preservation, most of the instrumentation is done with 02 tapered instruments minimizing the amount of coronal tooth structure that is removed when greater tapered instruments are used. Straight-line access, a requirement for rotating NiTi that further compromises coronal dentin, is not a requirement when using the vertically fluted instruments in 30-degree reciprocation, further preserving tooth structure.

Where rotating NiTi prepares a conical shape along length even when the canals are highly oval and sheath-like, the thin 02 tapered stainless steel relieved vertically fluted instruments will produce a space that reflects the original canal anatomy in larger form. If the canal was oval to begin with, the final shape will be oval preserving tooth structure in the mesio-distal plane and extending the preparation to include the buccal and lingual tissue extensions that are present in sheath-like pulpal configurations.

By confining motion to 30 degrees, a number of advantages become available to the dentist:

  • There is a reduction in procedural stress because breakage is no longer a concern.
  • Knowing the instruments are virtually free of breakage, they can be used with vigor against the canal walls assuring a greater degree of cleansing into areas that rotating NiTi does not cleanse effectively.
  • The instruments can be used several times with substantial savings.
  • Short amplitudes of motion are not associated with dentinal defects.
  • Preservation of tooth structure in what is often the thinner mesio-distal plane.
  • No longer a need for crown-down greater preparations that exaggerate the amount of tooth structure removed coronally.
  • The elimination of hand fatigue starting with the first instrument through the final sequence.

With the knowledge that the width of preparations should be a minimum of 30 for effective irrigation, we can prepare an effective well-cleansed space by using just two more instruments after preparing the glide path to a 20. By taking the 30/04 relieved NiTi instrument to within 3 to 4 mm of the apex and then following that up with the 30/02 relieved stainless steel vertically fluted instrument to the apex, we can fit with precision a fine point that when the canal is flooded with epoxy resin cement creates a three dimensional seal.

If desired, we can go up one size to a fine-medium point if we then take the 30/04 to the apex. In both cases the seal is created by the epoxy resin interface present along length via its application with a tool called the Bi-Directional spiral that gives the dentist the ability to flood the canal while at the same time preventing the extrusion of cement beyond its confines. (See Figs. 3a, b.)

If one takes a close look at the Bi-Directional spiral, one sees coronal flutes that drive the cement apically as it rotates. The apical three threads have the opposite orientation as the coronal flutes and drive the cement coronally. The result is two flows of cement that collide three mm from the applicator’s tip driving the cement laterally. The dentist uses the applicator with an up and down motion as it rotates in the slow speed handpiece. Most often, nothing more than a single point is required to produce a three-dimensional fill. This method of obturation is dependent upon the bidirectional spiral and the properties of the cement, including:

  • Physical and chemical bonding to both the gutta percha and the canal walls.
  • Its dimensional stability as it polymerizes.
  • Being a polymer, its resistance to hydrolytic degradation.
  • Being a room-temperature obturation system, the cement and gutta-percha point expand 1.75 percent as it warms from room to body temperature.
  • Is an effective seal in both thin and thick layers.
  • A far lower level of viscosity than the most thermoplasticized gutta-percha.
  • Great penetration of the cement into the dentinal tubules.
  • Its well-documented antibacterial properties.
  • Over 70 years of usage that attest to its effectiveness as an endodontic seal

From a procedural standpoint, the obturation procedures recommended here does away with:

  • The application of excessive force via lateral and vertical condensation that can lead to over extension of the point, the expansion of already existing dentinal defects that in turn can lead to vertical root fracture.
  • The application of heat that can lead to the over extension of obturation material, damage to the periodontal ligament via exposure to excess prolonged heat.
  • The creation of voids as overly compacted gutta-percha rebounds to its original shape after the interface cement has been displaced.

It should be noted here that I am not against the use of lateral or vertical condensation, only the degree of force applied. When creating a space for the placement of auxiliary points, I will never use more force on a spreader than the weight of my hand. I do not want to apply sufficient pressure to distort the gutta-percha, knowing as it rebounds it will create a void. In addition I do not want to add significant stress to the root that may already have preexisting defects or new ones as a result of rotating NiTi instrumentation.

If we consider the two aspects of endodontics, instrumentation and obturation, we can see where techniques can be simplified while adding safety and precision to the procedure. This is the true paradigm shift that has been obscured by the constant introduction of newer rotating NiTi instruments. All the new rotating NiTi entries require some degree of crown down preparation even if a so-called single instrument is used.

The result will predictably be excessive removal of tooth structure in the mesio-distal plane and inadequate preparation in the bucco-lingual plane exacerbated by the dentist’s concern that any deviation from the centered position increases the incidence of instrument breakage. To further alleviate separation anxiety, difficult apical curves are to be first negotiated to a 20 with K-files, a holdover from an earlier time period making initial pathway a tiresome hand-fatiguing proposition.

Vertically fluted instruments unrelieved through a 10 and relieved thereafter with a flat long length used in the 30-degree reciprocating handpiece oscillating at 3,000 to 4,000 cycles per minute eliminate hand fatigue from the start. In the smaller dimensions stainless steel 02 tapered vertically fluted instruments are quite flexible while retaining enough body to effectively remove dentin when directed against all the walls. In these thin dimensions, NiTi by contrast would be way too flexible for effective shaving of dentin when pressed against these walls. (See Fig. 4.)

As we work ourselves up to a 30 preparation, one might think that particularly in curved canals the stainless steel instruments are too stiff to negotiate without distortion. To understand why this is not a problem one must realize that the pathway has already been well-defined by the previous use of thin highly flexible stainless steel instruments that have widened the canal space beyond their own dimensions creating a pathway that less flexible instruments can follow. Furthermore, the instruments used to negotiate the canals are relieved with a flat starting with a 15 making them more flexible just when unrelieved comparably sized instruments might become excessively stiff. Most important, the amplitude of motion confined to 30 degrees keeps the instruments centered on the down stroke preventing distortion and can then be applied to all the walls on the upstroke.

The idea is to replace complex with simple, unpredictable with predictable while preserving as much tooth structure as possible, maintaining the integrity of the dentin and virtually eliminating instrument separation as a concern thus making the procedures safer, less stressful and more effective and ultimately costing far less in its applications.

 

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