The evolution of endodontic instrumentation from stainless steel hand files to the intricacies of rotary nickel titanium has advanced the efficiency and predictability of the enlargement of root canals. In recent years, other improvements in instrumentation methods and materials have produced even better results. These advancements include the use of hand and engine driven files along with improved use of metals in a reciprocating motion, including stainless steel and nickel titanium used to accomplish different aspects of instrumentation. A new hybridization technique (Endo-Eze TiLOS) designed and produced by Ultradent Products, Inc. epitomizes this new advancement utilizing stainless steel hand and shaping files to anatomically instrument the coronal and middle third of the tooth, followed by nickel titanium transitional files to instrument the critical zone towards the apex. Finally, hand files are used to size the apical constriction area of the tooth.
The critical factors determining the successful outcome of endodontically treated teeth include the diagnosis of the pre-operative root canal infection, the eradication of pathological microorganisms, the preservation of remaining tooth structure and the maintenance of the “status quo,” enhanced by the protective effect of coronal restoration.1 In order for these factors to be effective, paradigms such as diagnosis, biomechanical preparation, use of temporary dressings between appointments, obturation of the root canal and coronal restoration should be respected.
Concurrently and/or after the process of pulpal necrosis, the pulp chamber and canal orifices corresponding to the main root canal suffer an invasion of microorganisms. Over time and with the decrease in oxygen supply, the entire root canal system suffers contamination and, depending on local and systemic factors, bacterial biofilm can form at the apex, causing damage to the apical periodontal structures.2
Because these microorganisms and by-products are an etiological factor in the development of periradicular lesions/periodontitis, the eradication of these microorganisms and by-products is essential for the repair process. Initially, this process will depend on thorough biomechanical preparation and disinfection of the root canal system.
The main objective of the biomechanical preparation is to clean and shape the root canal to facilitate obturation.3 This stage of endodontic treatment is of great relevance because it determines and reflects the effectiveness and outcome of all subsequent procedures.4 This includes mechanical cleaning, creating space for the delivery of irrigating solutions, medicaments and the creation of the optimal anatomy of the root canal for proper obturation.5
When endodontically treating a tooth, it is important to keep in mind that the canal will have a flattened or ribbon-shaped anatomy, especially in the coronal and middle third, and rarely the conical form and circular base as often assumed.6-8 With many of the current rotary biomechanical systems on the market today, the prepared root canal defaults to a conical shape. But, because this is not the true root morphology of the root, the primary objective of cleaning, shaping and disinfection is not met.
It is based on these anatomical findings that the Endo-Eze AET (Anatomical Endodontic Technology) by Ultradent Products was developed. The AET is an oscillating (reciprocating) instrumentation system, which uses stainless steel instruments similar to the K-type files with a small tip on the active portion (diameter 0.10, .13 and .13 mm) and increasing tapers from .02 to .06 mm driven by the Endo-Eze AET contra-angle. Coupled with a 4:1 reduction motor at a speed of 5,000 movements per minute, these instruments oscillate (reciprocate) 30 degrees and are capable of reaching across the entire coronal and middle third of the canal walls, regardless of the anatomy.9
Because of the small diameter at the tip of the active portion, these files are very flexible and permit instrumentation without deviations, especially in curved root canals.10 The small diameter and tight spirals also prevent excessive removal of dentin and enlargement of the canal. This makes obturation techniques that require excessive enlargement, such as the active lateral condensation or thermoplastic gutta-percha techniques, unnecessary.
Since 1992, the interest in nickel titanium (NiTi) rotary instruments has been growing and represents a revolution in endodontic therapy.11 The kinematics of the NiTi rotary instruments, the high elasticity and the self-centering properties all result in a non-selective circular cutting action along the walls of the root canal.5 Consequently, rather than creating an anatomically correct enlargement, the increased taper produces a canal that is the same shape as the instrument and results in a cone-shaped enlargement with a circular base.12
As previously mentioned, this is not the common root morphology, which is generally flat or ribbon-shaped and more circular in the apical third, or 3-4 mm below the cementodentinal junction.13 As a result, the concept of preparing flattened canals with rotary systems is ineffective and can be detrimental by creating areas of weakness due to over-instrumentation at the points where dentin is thin and leaving necrotic tissue in areas within the canal that are untouched after biomechanical preparation. Such inadequate cleaning and shaping of the root canals are one of the major reasons for failure of endodontic treatment.15
Despite these considerations, the benefits associated with the use of NiTi rotary instruments are generally predictable (a conical prep) and result in a circular-shaped apex.15 Alternatively, the Endo-Eze AET oscillating (reciprocating) system with stainless steel files results in non-circular instrumentation and adapts or follows the natural anatomy of the coronal and middle third of the root canal. However it’s known that when pre-molars are instrumented with the AET system, the apical third is a circular, centered preparation, with a final diameter equivalent to 0.40 mm.12 Therefore, to obtain an apical preparation with a conical diameter and taper to promote the ideal obturation, for both lateral condensation and/or thermoplastic techniques, NiTi rotary instruments should be used.17
Another issue of great concern with regard to NiTi rotary instrumentation is the fracture or “file separation.” Many of the problems associated with NiTi files, such as the formation of steps, ledges, deviations, etc., especially in curved canals, seem to be solved because of the bending, high elasticity and new design of the active part of the rotary NiTi files.18 However, even with the industry’s commitment to offer a wide range of NiTi instruments with diverse designs of the active portion, it has not yet managed to avoid the same fractures.19 Unfortunately, there is no reliable evidence, concrete or circulated, to predict and prevent such accidents. A NiTi rotary instrument may fracture without prior visible deformation and, therefore, visual inspection is not a safe method to assess its condition of operability.20
One of the primary features of NiTi rotary systems is the speed of instrumentation. However, speed invariably results in increased stress, which can cause the instruments to ultimately fatigue and consequently fracture.
Most existing information regarding the correct use of rotary NiTi instruments comes from manufacturers or “opinion leaders” who try to convince clinicians to use a single kit, consisting of a few instruments (three to six files) for all clinical situations. In addition, it is also difficult to extrapolate information provided in studies and research to actual clinical situations. The existing standards do not reflect the clinical situations and dynamics relating to rotary instruments.21 Thus, the clinical situation affects the rotary instrumentation of root canals based on uncertainties and unknowns that invariably lead to fracture of the instrument.
File s
eparation or fracture is perhaps the most common and feared problem when using NiTi rotary instruments. This may come as a surprise to the clinicians, who in their eagerness to improve the quality of biomechanical preparation, are confronted with the difficult and sometimes impossible task of removing a broken instrument from the root canal.22
To avoid such a dilemma, it is essential to begin with hand instruments or oscillating (reciprocating) files in order to create a “glide path.” Basically, this is nothing more than a method of removing all interferences – cervical, middle and apical. This allows the more flexible NiTi files to perform their function with less stress, reducing the risk of binding in the canal and fracturing.23 Being aware of the instrument features, the morphological characteristics of the root canal and the AET technique is of the upmost importance in order to avoid excessive fatigue and instrument fracture.
Based on this information, Ultradent has developed a new system that offers the best of both worlds — Endo-Eze TiLOS Anatomic Endodontic Technology (AET) System. (Fig 1) The concept of hybridizing the system brings together the metal best suited for files in a specific area of the root canal using the safest and most effective mechanical movement. The system utilizes a cleaning and shaping hybridization technique, using the technology and rapidity of the biomechanical systems, while maximizing the intuitive, traditional nature of hand instrumentation. It offers simplicity, reliability and profitability and promotes better results with fewer risks regardless of anatomical variations and pathological conditions. Complications often experienced with other systems, such as ledging, zipping, canal transportation, unnecessary tooth structure removal and file separation, are virtually eliminated.
The TiLOS System consists of three stainless-steel shaping files – purple, white and yellow (similar to the current AET system) -with the respective tip diameters of the active portion (.10, .13, .13 mm) and respective tapers (0.020, 0.030 and 0.040 mm/mm); two hand K-type stainless steel files, #15 and #20; and three NiTi transitional files with an active portion initial diameter of 0.25 mm and tapers of 0.08, 0.04, and 0.02. (Fig 2)
Because of their high elasticity, NiTi transitional instruments are able to adequately prepare the apical portion of the root canal, even in the presence of severe and significant curvatures. It requires, however, enlargement and preparation of the coronal and middle thirds to avoid file separation and fracture.
The AET TiLOS oscillating (reciprocating) stainless steel shaping files do just that – enlarge and prepare the coronal and middle third, creating an anatomically correct glide path for the TiLOS NiTi transitional files to reach the apical areas of the root canal. (Fig 3) By eliminating the interferences, one reduces the risk of the NiTi instrument binding on the walls and curvatures of the root canal (especially the middle third) and reduces stress, fracture, deviations and deformities of the canal. The shaping files simultaneously negotiate the root canal and eliminate all interferences, while at the same time creating a straight-line access of the first two-thirds of the root canal, regardless of diameter, morphology or length. The AET reciprocating stainless steel shaping files replace the familiar Peeso or Gates Glidden reamers that cause indiscriminate cutting and loss of tooth structure.
TiLOS’ hybridization also includes a change from rotational motion to oscillating (reciprocating) motion of the TiLOS NiTi transitional files. (Fig 4) The AET handpiece oscillates (reciprocates) the files 30 degrees in each direction, allowing preparation with the same effectiveness as when rotated but with a less aggressive movement, meaning more control and less file separation in the fragile apical area.24
Although any manufacturer’s NiTi file can be used with the handpiece, the degree of efficiency varies greatly depending on the geometry and flute design. This hybridization (NiTi oscillating/reciprocating) allows NiTi instruments to be used safely in any portion of the root canal and lessens the risk of tip fracture or file separation, and the 30 degree oscillation (reciprocation) greatly reduces the risk of fractures due to torsion and flexural stresses. It should be noted again, however, that before using any NiTi instruments in the root canal, the cervical and middle interference should be eliminated or reduced with the use of the AET stainless steel shaping.
Once the coronal and middle thirds allow a straight glide path, the NiTi transitional files can access the apical third without interferences, stress, fracture and deformations, making instrumentation safer and more effective. This also facilitates thorough irrigation, subsequent cleaning and the placement of gutta-percha with larger diameters, if desired.
The sequence presented in Figure 2 indicates the use of a #15 K-file hand instrument for canal negotiation and determination of a working length (X-ray and/or electronic apex locator). After determining the working length, instrumentation is initiated. In canals with extreme calcification or curves, this step is done using smaller diameter hand instruments such as #10 or #08 K-file. In large root canals, #20 or #25 K-files would be recommended to begin instrumentation. One should always record the apical instrument (A.I.), or first instrument that reaches the working length and meets resistance. In cases of pulp necrosis, the negotiation should be made by third, always thoroughly irrigating the root canal with sodium hypochlorite with each file.
Once the canal is negotiated and the A.I. determined, mechanical reciprocating instrumentation begins using the Endo-Eze AET handpiece. The technique for using the reciprocating shaping files is a circular motion or a forceful upward brushing stroke against the canal walls. Begin with the purple shaping file to 3 mm short of the working length. Recapitulate with the #15 K-file followed by the white shaping file, also 3 mm short of the working length. Recapitulate and follow with yellow shaping file to 6 mm short of the working length. Recapitulate using the #15 K-file.
Next take a #20 K-file to the working length (Fig 5) as verified with an X-ray and/or electronic apex locator. Follow this step with the white shaping file a second time to the working length. Irrigate and recapitulate with the #20 K-file. The apical third is prepared using the NiTi transitional files in the AET handpiece. (Fig 6) Use the #25 NiTi transitional files with tapers 0.08, 0.04 and 0.02 mm/mm, respectively, with no pressure in a crown-down technique until the working length is reached. Depending on the anatomy, this result can occur with file 0.08 or 0.04 or in calcified and curved canals with the #25, 0.02 NiTi file. (NOTE: Always recapitulate and irrigate with 5 ml of disinfection solution between all mechanical files.)
With the A.I. as a reference, the final apical preparation is completed with NiTi hand files up to four to five sizes beyond the A.I. For example, if the A.I. were a #15 instrument, use a NiTi hand file of size #35-#40 to complete the apical preparation. Obturation is accomplished using Ultradent’s Apically Delivered Obturation System in a simple and predictable manner. OH
Dr. Leonardo is a specialist in Endodontics, Regional Board of Endodontics (So Paulo, Brazil), former Head and Chairman, Department of Restorative Dentistry, Araraquara Dental School-UNESP, Master in Endodontics, University of So Paulo; PhD in Pathology, University of So Paulo; Visiting Professor, University of Texas-San Antonio, TX and Invited Professor, U.I.C.- Universitat Internacional de Catalunya, Spain.
Dr. Richard D. Tuttle is in private practice in Layton, Utah. He works with Ultradent Products, Inc., Research and Development, Clinical/ Lab Division Manager and Clinical Applications Advisor.
Reprinted with permission, Dental Tribune America GNYDM Dec, 2009.
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