There are enormous differences in opinion regarding the best methods for shaping root canals. A review of the literature reveals virtually no agreement on a variety of fundamental clinical issues. There is ongoing controversy regarding the sequence of canal preparation, working length, and the use of patency files. There is vigorous debate related to the question of how large to prepare the apical foramen. There is no consensus regarding deep shape, or what is the appropriate percentage taper of a canal that ensures a root canal system can be both three-dimensionally cleaned and filled. There is confusion trying to identify and integrate the best technologies and instruments.
In the final analysis, although science and basic research can illuminate our clinical endeavors, ultimately, it is by our clinical actions that our success as a healing profession is measured. Fortuitously, Dr Herbert Schilder described the most predictably successful concepts for shaping canals, cleaning in three dimensions, and filling root canal systems.1–2 Complete endodontics promotes the retention of critically essential teeth and is the cornerstone of restorative and reconstructive dentistry. Schilderian endodontics continues to serve as a powerful beacon of light to guide any clinician on the journey toward greater clinical confidence and success.
Schilder’s genius was how he used a series of instruments to carve the shape and sequence the preparation. Schilder described his Envelope of Motion technique, where a series of precurved reamers were selected, utilized from the smaller to bigger sizes, and rotated so they would randomly cut dentin on the withdrawal stroke. Schilder also emphasized the sequence of preparation where he removed restrictive dentin from the coronal two-thirds of the canal before initiating procedures in the typically more complicated apical region of the canal. Especially in longer, smaller diameter, and more curved canals, the tips of these 0.02 tapered instruments were typically loose within the coronal two-thirds of the canal, whereas the larger, stronger, and more active portion of each instrument would desirably engage and cut dentin. Following pre-enlargement procedures, files were completely loose within the body of the canal and could be more predictably directed apically.
Schilder’s shaping objectives are the standard against which all other preparation techniques are measured. Over many years, the pre-enlargement technique has grown in popularity, as this method for shaping canals has proven to be predictably successful. However, the method Schilder described frequently required many instruments, several recapitulations through a series of files and reamers, and as such, is perceived to be difficult and time-consuming. To address this perception, the ProTaper system (Dentsply Tulsa Dental Specialties) was developed to both duplicate and simplify the Schilder technique.3
A unique feature of the ProTaper files, compared to other file systems, is each instrument has changing percentage tapers over the length of its cutting blades. In use, this progressively tapered design replicates the Schilderian Envelope of Motion technique and serves to significantly improve flexibility, cutting efficiency, and safety.4 Another feature of the ProTaper instruments relates to their convex, triangular cross-section, which enhances the cutting action while decreasing the rotational friction between the blade of the file and dentin.5 ProTaper files have a changing helical angle and pitch over their cutting blades, which reduces the potential of an instrument from inadvertently screwing into the canal.6 The ProTaper files each have a noncutting, modified guiding tip. This feature allows each instrument to safely follow the secured portion of a canal, while the small flat on its tip enhances its ability to find its way through soft tissue and debris.7 The ProTaper system is comprised of three Shaping and five Finishing files (Fig. 1).
The shaping files
Shaping File No. 1 and Shaping File No. 2, termed S1 and S2, have purple and white identification rings on their handles, respectively. The S1 and S2 files have D0 diameters of 0.17 mm and 0.20 mm, respectively, and their D14 maximal flute diameters approach 1.20 mm. The Auxiliary Shaping File, termed SX, has no identification ring on its gold-colored handle and, with a shorter overall length of 19 mm, provides excellent access when space is restrictive. The SX file has a D0 diameter of 0.19 mm and a D14 diameter approaching 1.20 mm. The Shaping files have increasingly larger percentage tapers over the length of their cutting blades, allowing each instrument to engage, cut, and prepare a specific area of the canal and perform its own 'crown down' work. Because SX has a much quicker rate of taper between D1 and D9 as compared to the other ProTaper Shaping files, it is primarily used after the S1 and S2 files to more fully shape canals in coronally broken down or anatomically shorter teeth.
The finishing files
Five Finishing files named F1, F2, F3, F4, and F5 have yellow, red, blue, double black, and double yellow identification rings on their handles corresponding to D0 diameters and apical tapers of 20/07, 25/08, 30/09, 40/06, and 50/05, respectively. From D4–D14 each instrument has a decreasing percentage taper which serves to improve flexibility, reduce the potential for dangerous taper-lock, and reduce the potential to needlessly overenlarge the coronal two-thirds of any given canal.
ProTaper shaping technique
Endodontic outcomes are improved when instruments pass through the access opening, effortlessly slide down smooth axial walls, and are easily inserted into the orifice. The potential to consistently shape canals and clean root canal systems is significantly enhanced when the coronal two-thirds of the canal is first pre-enlarged, followed by preparing its apical one-third (Fig. 2).8
Figs. 2 & 3: Sequencing the preparation facilitates shaping canals and cleaning root canal systems. Complete endodontic treatment is the foundation of perio-prosthetics (Fig. 2).The canals of this mandibular molar were shaped with ProTaper files and three-dimensionally filled. Note the flowing shapes, apical onethird curvatures, and multiple portals of exit. (Fig. 3; Courtesy of Dr Jason West, Tacoma, WA, USA)
Scout the coronal two-thirds
When straightline access is completed, the pulp chamber may be filled brimful with a viscous chelator. Based on the pre-operative radiographs, ISO 0.02 tapered sizes 10 and 15 hand files are measured and precurved to match the anticipated full length and curvature of the root canal. However, in this method of canal preparation, these instruments are initially limited to the coronal two-thirds of a root canal. The 10 and 15 hand files may be utilized within any portion of the canal until they are loose and a smooth reproducible glide path is confirmed. The loose depth of the 15 file is measured and this length transferred to the ProTaper S1 and S2 files.
Shape the coronal two-thirds
The secured portion of the canal can be optimally pre-enlarged by first utilizing S1, then S2. Prior to initiating shaping procedures, the pulp chamber is filled with a full strength solution of NaOCl. Without pressure, and in one or more passes, the ProTaper Shaping files are allowed to passively “float” into the canal and 'follow' the glide path. To optimize safety and efficiency, the Shaping files are used, like a brush, to laterally and selectively cut dentin on the outstroke. A brush-cutting action creates lateral space, which will facilitate the Shaping file’s larger, stronger, and more active cutting blades to safely and progressively move deeper into the canal. Strategically, this brush-cutting action can be used to eliminate cervically positioned triangles of dentin, more effectively shape into fins, isthmuses, and canal irregularities, or to relocate the coronal aspect of a canal away from furcal danger. If any ProTaper file ceases to easily advance within the secured portion of a canal, withdraw it, and recognize that intrablade debris has deactivated and pushed the instrument off the wall of the canal. Upon removing each Shaping file, visualize where the debris is located along its cutting blades to better appreciate the region within the canal that is being prepared. Following the use of each Shaping file, irrigate, recapitulate with a 10 file to break up debris, and move it into solution, then re-irrigate. Without pressure, and in one or more passes, S1, then S2, is used in this manner until the depth of the 15 hand file is reached.
Scout the apical one-third
When the coronal two-thirds of the canal is shaped, then attention can focus on apical one-third procedures. With the pulp chamber filled brimful with a viscous chelator, the apical one-third of the canal is fully negotiated and enlarged to at least a size 15 hand file, working length confirmed, and patency established. At this time, a decision must be made between whether to finish the apical one-third with rotary or hand instruments. If a new and straight 15 file can gently 'slide' and passively 'glide' to length, then rotary instruments will generally follow this confirmed and reproducible glide path. However, certain canals exhibit anatomical challenges that necessitate a reciprocating handle motion in order to move precurved 10 and 15 files to length. When there is an irregular glide path, then the apical one-third of a canal may be advantageously finished with precurved manual ProTaper instruments.
Shape the apical one-third
When the apical one-third of the canal has been secured, then the pulp chamber is filled brimful with NaOCl. The ProTaper sequence is to carry the S1, then the S2, to the full working length. Float, follow, and brush as previously described until the terminus of the canal is reached. S1, then S2, will typically move to length in one or more passes depending on the length, diameter, and curvature of the canal. Following each ProTaper file, irrigate, recapitulate with a 10 file, then re-irrigate. After using the Shaping files, particularly in more curved canals, working length should be reconfirmed, as a more direct path to the terminus has been established. At this stage of treatment, the preparation can be finished using one or more of the ProTaper Finishing files in a non-brushing manner. The F1 is selected and passively allowed to move deeper into the canal, in one or more passes, until the terminus is reached. When the F1 achieves length, the instrument is removed, its apical flutes are inspected, and if they are loaded with dentin, then visual evidence supports, the shape is cut. Following the use of F1, flood the shaped canal with irrigant, recapitulate, and confirm patency, then re-irrigate to liberate debris from the canal. Fully shaped canals hold an effective volume of irrigant that, when activated (EndoActivator, Advanced Endodontics), can potentially circulate, penetrate, and clean into all aspects of the root canal system.9
ProTaper finishing criteria
Following the use of the 20/07 F1, the ProTaper Finishing Criteria is to gauge the size of the foramen with a 20/02 tapered hand file to determine if this instrument is snug or loose at length. If the 20 hand file is snug at length, then the canal is fully shaped and, if irrigation protocols have been followed, ready to pack. Following the use of F1, if the 20 hand file is loose at length, then gauge the size of the foramen with a 25/02 tapered hand file. If the 25 file is snug at length, then the canal is fully shaped and ready to pack. If the 25 file is short of length, proceed to the 25/08 F2 and, when necessary, the 30/09 F3, the 40/06 F4, and the 50/05 F5, gauging after each ProTaper Finisher with the same D0 correspondingly sized hand file. If the 50 hand file is loose at length, then use alternative NiTi rotary or manual files to finish the apical extent of these larger, easier, and more straightforward canals. ProTaper shapes are easy to fill utilizing a ProTaper matching gutta percha master cone in conjunction with a warm vertical condensation technique (Fig. 3). As an alternative, a well-shaped canal can be readily and completely filled with a ProTaper carrier-based obturator. The ProTaper sequence is always the same regardless of the tooth or anatomical configuration of the canal being treated (Fig. 4). In many cases, it’s as easy as one, two, three, or in endodontic language, purple, white, yellow.
Fig. 4: This chart summarizes the ProTaper shaping technique. The ProTaper sequence is always the same regardless of the length, diameter, or curvature of the canal.
Evidence for clinical success
A clinical investigation of the ProTaper technique, emphasizing method of use, was conducted on mesial canals of extracted mandibular molar teeth using µCT-Analysis. In this particular study, horizontal sections from different radicular levels were analyzed using µCT slices and volume renderings. The green color represented the anatomical contours before instrumentation, whereas the red color indicated the shape after instrumentation. The results from this investigation are clinically relevant, and a portion of the data is available for review (Figs. 5a–5d). The advantages of the Shaping files to brush laterally and selectively cut dentin on the outstroke are summarized below:
1. The Shaping files were essentially loose within a canal during the majority of their work.
2. The coronal aspect of the canals were safely relocated away from an external root concavity.
3. A brush-cutting action achieved a centered preparation and maximized remaining dentin.
4. The Shaping files physically contacted over 90% of the internal walls of the canals.
Figs. 5a–d: This figure shows horizontal μCT sections through the coronal one-third of the root. Note the successful relocation of the canals at this level (Fig.5a). This figure reveals horizontal μCT sections through the middle one-third of the root. Note the ProTaper shapes are round and centered within the root (Fig. 5b). This figure shows horizontal μCT sections through the apical onethird of the root. Note the ProTaper shape perfectly includes the original canal diameter (Fig. 5c). This figure compares before and after instrumentation with the S1, S2, and F1 files. Note the shapes are full, smooth flowing, and centered, and the files have physically contacted virtually all the internal anatomy (Fig. 5d).
There is a continuous parade of new files that come to market annually. All of these file systems are claimed to be superior, in one way or another, due to alleged improvements in metallurgy, cutting efficiency, safety, and simplicity. Regrettably, when any given set of rotary files is used incorrectly, either intentionally or unintentionally, then the message delivered is flawed, irrelevant, and fails to honestly disclose true clinical performance. In these times of unprecedented claims, it would be wise to pause and remember those early pioneers, like Dr Herbert Schilder, whose relevant contributions helped create the biological and clinical foundation on which we stand. For new technologies to be meaningful, clinical results must hold up to scientific scrutiny, compliment time-honored principles, and work successfully in the hands of countless dentists. The ProTaper concept provides a set of instruments with unique geometries that, when sequenced and used correctly, affords extraordinary efficiency and safety.10 This shaping method has enabled both inexperienced and experienced dentists to consistently duplicate the most predictably successful concept ever described for preparing a canal. The ProTaper system unites the most enduring shaping method of the past with the greatest advancements in technology and fulfills the age-old adage, “Everything old is new again.”
The author wishes to acknowledge and thank Dr Lars Bergmans and his research group, BIOMAT Research Cluster, Catholic University of Leuven, Belgium, for their valuable time and expertise performing the ProTaper µCT-analysis.
Editorial note: A complete list of references is available from the publisher. This article was originally published in Endo Tribune US, Vol. 3, Issue 3, 2008.
Dr Clifford J. Ruddle can be reached at +1 800 753 3636 or www.endoruddle.com.