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IntroductionThorough cleaning, shaping, and disinfection of the root canal system are the principle steps necessary for successful root canal treatment (RCT). The purpose is to remove all of the pulpal tissue and canal debris from the root canal space while also removing the inner layers of canal wall dentin.1 Years ago, some investigators suggested that we enlarge the canal space to at least three ISO sizes larger than the first file to bind in the apical part of the canal.2,3 This concept assumed such a preparation would remove the inner layers of the dentin walls while allowing the irrigant to reach the entire length of the root canal system.3 In endodontic cases where the canal configuration is relatively straight in its long axis and round in cross-section, this goal might be achieved using conventional hand and rotary-driven endodontic files. However, the cleaning, shaping, and disinfection of canals that are flat and oval-shaped in cross-section, as well as curved canals, represent a significant clinical challenge to endodontic treatment. These canal configurations represent about 25%-50% of root canal systems.4 Many enhancements have resulted in better cleaning and shaping, but investigations using digital subtraction micro-CT and microbiologic assessments have shown our ineffectiveness to adapt to the true cross-sectional shape of all but the most round root canals, leaving almost half of the canal walls untouched by endodontic instruments.5 Until the recent introduction of “adaptive” cleaning/shaping instrument technology, the basic tenets of endodontic treatment have been unattainable.

Adaptive canal cleaning and shapingRotary endodontic files are generally made from a nickel-titanium alloy that makes it possible to shape slightly curved root canals while reasonably maintaining canal morphology. These rotary file designs differ from each other by incorporating different radial land designs, various rake angles, helical pitches, core thicknesses, cross-sectional shapes, and variations of nickel-titanium metallurgy. However, all of these file designs have the same limitations: they are intended to machine the root canal space with rotating blades, creating a round cross-sectional area, while having the potential for file separation and limited ability to irrigate to the working length (WL) of the canal. The recently introduced self-adjusting file system (SAF Endo System [Henry Schein Dental]) dramatically improves the efficacy of root canal instrumentation and disinfection.6 This novel design not only cleans irregularly shaped canals, but also passively and simultaneously supplies an irrigation solution to the entire length of the canal during the shaping process. The SAF instrument is a compressible, thin-walled lattice made from a hollow nickel-titanium cylinder measuring 1.5 mm in diameter (Figures 1A-C). Similar to the preparation prior to the use of rotary files, the canal space is first shaped with a hand or rotary file

The SAF Endo System: adaptive 3-D cleaning, shaping, and disinfectionDrs. Stephen Cohen, Martin D. Levin, and Louis H. Berman describe a recently introduced “adaptive” cleaning/shaping instrument technology

Figure 1A: The SAF is a hollow file designed as an elastically compressible, thin-walled pointed cylinder, 1.5 mm in diameter, composed of a thin nickel-titanium lattice

Educational aims and objectivesThe purpose of this article is to describe a new “adaptive” cleaning/shaping instrument technology that dramatically improves the efficacy of root canal instrumentation and disinfection.

Expected outcomesCorrectly answering the questions on page 39, worth 2 hours of verifiable CE, will demonstrate you can:• describe the “adaptive” cleaning/shaping instrument technology and its design.• discuss how the basic tenets of endodontic treatment are facilitated by this technology.• compare the efficacy of the self-adjusting file system to typical rotary endodontic files.• describe the mechanisms of action of this file system for instrumenting and disinfecting root canals.

Figure 1B: Available in three lengths (21 mm, 25 mm, and 31 mm), the SAF is used as a single instrument to complete 3-D root canal shaping and cleaning

Figure 1C: When inserted into the glide-path, the SAF (magnified view, left) will gently oscillate in an up-and-down motion, radially expanding to apply light, continuous pressure along the entire circumference of the root canal. The abrasive surface of the SAF will achieve gradual enlargement of the root canal. The SAF is extremely flexible and pliable (magnified view, right). It does not impose its shape on the canal, but complies with the canal’s original shape, eliminating the risk of transportation and strip- perforation accidents

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to the WL with a #20 K-file with an 0.04 taper. When the SAF instrument is inserted into the root canal, it compresses to the size of a standard #20 K-file. The SAF instrument is attached to a specially designed handpiece that oscillates the instrument within the canal up-and-down 5,000 times per minute with an amplitude of 0.40 mm; it is this movement that “sandpapers” the walls of the canal. There is no rotational movement used to shape the canal. Because of the metal memory inherent with the nickel-titanium lattice of the instrument, the SAF instrument radially expands within the canal, adapting to the shape of the original canal morphology (an accordion-like effect). The canal space and inner dentin is subsequently cleaned and shaped in three dimensions. To enhance the shaping and disinfection of the canal space, the SAF instrument incorporates an irrigation source through its hollow lattice design, allowing simultaneous irrigation and disinfection of the canal space during the entire cleaning and shaping process. Studies have recently reported that conventional rotary file instrumentation leaves about 60% of the canal walls untouched versus only 17% for the SAF instrument.7

The SAF Endo System specificsSAF instrumentation is intended to be used with a continuous, gentle, up-and-down, “hand pecking” motion of 3-5 mm range, as the specialized handpiece head generates a consistent oscillation. During the use of the SAF System, most of the dentin removal occurs within the first 2 minutes of operation, with less dentin removed thereafter. After the recommended 4 minutes of SAF cleaning/shaping, the apical third of the canal will have been enlarged approximately 3-5 ISO sizes.8 The SAF instrument is intended for single use only, but has ample abrasiveness that will last for up to 30 minutes for any given endodontic case.8 The SAF has been shown to be superior to rotary files in its durability.8 Studies have shown the SAF instrument withstood 650,000 (±15,800) buckling cycles before the first sign of mechanical failure, equivalent to approximately 120 minutes of continuous operation.8 When subjected to functional fatigue-to-failure testing, the first mechanical failure (detachment of one of the lattice arches) did not occur until 29.1 (±1.2) minutes. In no case was there

Figure 2A: The VATEA irrigation system provides a constant flow of fresh irrigant through the SAF lumen. Coupled with the constant agitation of the SAF, continuous exchange of irrigation solution allows shaping and disinfection of the root canal system

Figure 2B: The SAF fits into a special handpiece, which provides the transline (up-and-down) motion of the SAF with the simultaneous and continuous flow of irrigant

a full separation of any components of the SAF instrument.8

In irrigation experiments, no extrusion of solution was detected with continuous use. This was measured by adding the pressure from three sources: the hydrostatic pressure of a column of water in the root canal, stagnating pressure generated by the vibratory effect of the SAF in the fluid, and the piston pressure resulting from the apical thrust of the SAF instrument. The sum of this pressure was calculated at 394.42 Pa, well below the sum of pushing a well-adapted #25 K-file with 1 g of pressure (~199,700 Pa). Even when a syringe needle was inserted with loose adaptation to the canal wall (38% of the canal not free around the needle to allow back-flow), pressure of more than 1,270 Pa will occur, leading to apical extrusion of the irrigant.6 Use of the SAF is not recommended with immature apices or in the presence of a defect such as a perforation or extensive resorption. To facilitate the delivery of the irrigant, a silicone tube is connected to the SAF instrument that leads to the VATEA peristaltic irrigation pump system (ReDent-Nova Ltd). The volume rate of flow of the irrigant can be adjusted from 1 mL/minute up to 10 mL/minute, and is turned on and off by a foot pedal control. The VATEA system can use any irrigant, although sodium hypochlorite is recommended (Figures 2A and 2B).

Challenges: curved and non-round canalsCurved canals are a significant challenge to the chemomechanical preparation of root canal systems. Smaller-

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Figure 3A: Micro-CT analysis of SAF instrumentation in the palatal root of a maxillary molar with curved root canal mor-phology before treatment (red)

Figure 3B: Micro-CT analysis of SAF instrumentation in the palatal root of a maxillary molar with curved root canal morphology after treatment (blue). This is the same tooth as Figure 3A. Note the long axis of the canal is respected along with a high ratio of canal wall treated (Adapted from the Jour-nal of Endodontics, Metzger et al, 3(4):681, Copyright 2010, with permission from Elsevier.)

Figure 3C: Micro-CT analysis, maxillary second bicuspid with extremely flat oval cross section, as seen on buccolingual view. (Figures 3C and 3D reprinted from the Journal of Endodontics, Metzger et al, 3(4):681, Copyright 2010, with permission from Elsevier.)

Figure 3D: Micro-CT analysis maxillary second bicuspid with extremely flat oval cross section, as seen on mesiolin-gual view (same tooth as in Figure 3C)

Figure 3E: Micro-CT analysis after SAF use, as seen in cross sections at 4 mm and 6 mm from the apex. Note original canal morphology is red; after SAF use is blue (Adapted from Metzger et al, J Endod 2010;36:679-690)

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size NiTi rotary files are partially able to clean and shape the apical one-third of the root canal. However, as larger and stiffer instruments are used to broaden the canal preparation, they remove more dentin on the outer side of the curve, leading to probable apical transportation (“zipping”). Complications associated with canal transportation are not only limited to untreated areas of the root canal wall; they may also lead to dangerous thinning of the canal walls and potential future risks of root fracture and/or root perforations. Canals are seldom round in cross-section, but are more often oval or teardrop shaped. Unfortunately, a standard two-dimensional radiographic image does not demonstrate these three-dimensional irregularities. With the advent of laboratory micro-CT scans and the clinical use of cone beam computed tomography (CBCT) systems in the dental office, we have a keener appreciation of the necessity for more precise canal cleaning and shaping (Figures 3A-E). With the incorporation of three-dimensional adaptive canal cleaning and shaping using the SAF Endo System, these common canal irregularities can now be more effectively cleaned and shaped. According to a study by Peters and Paqué,5 conventional rotary files left as much as 49% of the canal surface untreated, while the SAF instrumentation left only 25% of the root canal surface untreated. Micro-CT analysis shows the canal anatomy before instrumentation (Figure 4A), followed by rotary file preparation (Figure 4B). Final analysis reveals the untouched area of the canal using rotary instrumentation (Figure 4C). Micro-CT investigations have also shown how seemingly excellent rotary canal shaping can appear when viewed in a buccolingual dimension (as seen with conventional two-dimensional radiographs). However, if rotated to the clinically unseen mesiodistal direction, many of the canal ramifications can be seen as unaffected by rotary canal instrumentation. These obstacles reviewed above are overcome by adaptive cleaning and shaping using the SAF System.

Bacteriologic considerationsThe ideal microbiological goal of chemomechanical debridement is to completely eradicate intracanal bacterial populations and their toxins. Bacteria (e.g., E. faecalis) persisting after chemomechanical procedures at levels detectable by culture-dependent techniques have been shown to increase failing endodontic treatment outcomes.9 Therefore, the main effort should be to maximize root canal disinfection before obturation. Unfortunately, anatomic complexities may impede thorough root canal disinfection. In a recent investigation by Siqueira et al,9 44 single-rooted teeth with oval root canals were analyzed in vitro after the main canal spaces were first contaminated with E. faecalis. After the use of rotary files with syringe irrigation, 55% of the samples had positive bacterial cultures whereas those canals cleaned and shaped with SAF Endo System had only 20% positive canal cultures remaining, again reinforcing the efficacy of the SAF Endo System over rotary files.

Removal of canal debris and smear layerBesides causing potential periradicular infection and inflammation, remaining soft-tissue remnants smeared together with inorganic debris in the canal will prevent adequate adaptation between the canal wall and root-canal obturation materials. The intimate adaptation of the SAF instrument to the canal walls and the continuous flow of irrigant, especially for oval and irregularly shaped canals, is the primary benefit of the SAF system. In a study10 to

evaluate the removal of canal debris and smear layer with the SAF, single-rooted human teeth were evaluated using a scanning electron microscope (SEM). Similar to hand and rotary instrumentation, the SAF System produced a smear layer when using 3% sodium hypochlorite alone; but when alternated with the application of 17% EDTA, the canals were rendered virtually free of debris and smear layer, with the most pronounced benefit realized in the apical third of the root canal.

Histologic considerationsInfected dentin, soft tissue, and bacterial biofilm can cover an enormous portion of the inner surface of the root canal system and their removal can challenge even the most assiduous cleaning and disinfection protocol.11 It has been well documented that the assessment of canal morphology12 and the true extent of tissue removal and quality of obturation cannot be accomplished by evaluation of two dimensional bucco-lingual radiographic projections. Oval and flat-shaped canals occur in approximately 25% of teeth.13 In a recent investigation, De-Deus, et al (personal communication, 2011) histologically evaluated 12 pair-matched vital mandibular canines slated for extraction whereby the canal spaces were prepared with either the SAF System or rotary-file instrumentation. Only teeth with vital pulps and oval-shaped root canals were included. The SAF System was found to reduce the amount of remaining pulp tissue by 57% compared to conventional rotary files. In addition, 21% of the rotary file prepared canals still contained pulp tissue remnants. The investigators concluded that sodium hypochlorite irrigant, applied with syringe and needle, failed to compensate for the inadequate cleaning by the file itself.

ObturationRoot canal obturation is an essential component of RCT, which aims to prevent future bacterial contamination and recontamination of the canal space. It has been demonstrated often7 that if root canals are not adequately cleaned and shaped before obturation, proper sealing will be jeopardized by the remaining tissue and debris.7 Any debris that prevents the adaptation between the filling material and the canal wall may provide space for bacterial leakage and proliferation. Three-dimensional imaging using high resolution micro-CT scans has greatly improved our understanding of the relationship between complex root canal morphology and failure to thoroughly clean and shape root canal systems using hand and rotary files. In a study7 comparing the obturation efficacy between canals cleaned and shaped with rotary files and the SAF system, lateral compaction of gutta percha cemented with AH26 was evaluated. The results revealed the SAF system allowed as much as 83% of the canal wall to have intimate contact with the obturation material compared to only 55% for rotary files. Because of the irregularly shaped canals prepared using the SAF System, instead of the traditionally tapered-shaped canals, obturation may be more clinically challenging; however, any of the current obturation techniques may be employed, including lateral compaction, carrier-based obturation, and warm vertical compaction. Although a glide path is created using a #20 hand or rotary file prior to the use of the SAF instrument, the resulting apical shape is close to an ISO #30 or #35 K-file. After SAF instrument use, the apical canal shape should be measured by apically gauging with hand files (again, usually a #30 or #35 file should go to full WL). Subsequently, the master cone (or carrier-based obturator) of the corresponding size is selected and cemented

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to WL; lateral or warm vertical compaction of the additional obturation material then continues until the canal space is completely filled.

ConclusionCleaning, shaping, and disinfection of the root canal system are the most important steps in endodontic treatment. Currently, endodontic procedures are performed with hand and rotary instruments that do not adapt to the canal walls and deliver very little fresh irrigant to the root canal space, especially the apical third. Unfortunately, the literature is replete with examples of instrument breakage, poor results with chemomechanical preparation, canal transportation, and over-thinning of the canal walls. Because hand and rotary files are round in cross-section, they often leave more than half of the canal walls untouched and require multiple

sequences of filing and irrigation, all reducing the efficacy of canal obturation techniques. With the introduction of adaptive cleaning, shaping, and disinfection using the SAF Endo System, the reduced effectiveness of rotary filing and their potential for procedural mishaps can be eliminated. Adaptive SAF instruments can conform to the natural shape of each canal, moving in an oscillating up-and-down movement while providing simultaneous irrigation. After establishing the glide path to WL, just one SAF is required to homogenously and circumferentially prepare the canal walls. This paradigm-shifting technology is now in world-wide use, and promises to improve treatment outcomes.

The authors have no financial interest in the products discussed in this article. However, they are all consultants to ENDOVATIONS, a subsidiary of Henry Schein.

References

1. Peters LB, Wesselink PR, Buys JF, et al (2001) Viable bacteria in root dentinal tubules of teeth with apical periodontitis. J Endodon 27(2):76-81.

2. Walton RE, Torabinejad M (1996) Principles and Practice of Endodontics, 2nd edition. Philadelphia, PA: Saunders.

3. Weine FS (1996) Endodontic Therapy, 5th edition. St Louis, MO: Mosby.

4. Wu M-K, van der Sluis LWM, Wesselink PR (2003) The capability of two hand instrumentation techniques to remove the inner layer of dentine in oval canals. Int Endod J 36(3):218-224.

5. Peters OA, Paqué F (2011) Root canal preparation of maxillary molars with the self-adjusting file: a micro-computed tomography study. J Endodon

37(1):53-57.

6. Metzger Z, Teperovich E, Zary R, et al (2010) The self adjusting file (SAF). Part 1: respecting the root canal anatomy–a new concept of endodontic files and its implementation. J Endodon 36(4):679-690.

7. Metzger Z, Zary R, Cohen R, et al (2010) The quality of root canal preparation and root canal obturation in canals treated with rotary versus self-adjusting files: a three dimensional micro-computed tomographic study. J Endodon 36(9):1569-1573.

8. Hoff R, Perevalov V, Eltanant M, et al (2010) The self adjusting file (SAF). Part 2: mechanical analysis. J Endodon 36(4):691-696.

9. Siqueira JF, Alves RF, Almeida BM, et al (2010) Ability of chemomechanical preparation with either rotary instruments or self-adjusting file to disinfect oval-shaped root canals. J Endodon 36(11):1860-1865.

10. Metzger Z, Teperovich E, Cohen R, et al (2010) The self-adjusting file (SAF). Part 3: removal of debris and smear layer-a scanning electron microscope study. J Endodon 36(4):697-702.

11. Ricucci D, Sequeira JF (2010) Biofilms and apical periodontitis: study of prevelance and association with clinical and histopathologic findings. J Endod 36:1277-1288.

12. Scarfe WC, Levin MD, Gane D, et al (2009) Use of cone beam computed tomography in endodontics. Int J Dent 634567. Epub 2010 Mar 31.

13. Wu M-K, R’Oris A, Barkis D, et al (2000) Prevalence and extent of long oval canals in the apical third. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 89:739-743.

Stephen Cohen, MA, DDS, FICD, FACD, is one of the prominent endodontic clinicians in the country and lectures worldwide on endodontics. Dr. Cohen completed his studies in the Endodontic Postgraduate Program at the University of Pennsylvania in 1969, and began his private practice.

From 1970 until 1988, he served as Chairman of the Department of Endodontics at Arthur A. Dugoni School of Dentistry, University of the Pacific, and has continued his commitment to education as an Adjunct Clinical Professor of Endodontics, an Adjunct Clinical Professor of Endodontics in the Department of Preventive and Restorative Dentistry, University of California, San Francisco, and the Director of the Endodontic Post-Graduate program at the Riyadh School of Dentistry and Pharmacy in Saudi Arabia. Dr. Cohen is the senior editor of all nine editions of the definitive endodontics textbook, Pathways of the Pulp, a co-editor of the 10th edition of Cohen’s Pathways of the Pulp and a co-editor of the new textbook, A Clinical Guide to Dental Traumatology. Dr. Cohen is a Diplomate of the American Board of Endodontics, and has held leadership positions in many of the major professional and academic organizations in endodontics. He maintains a full-time endodontic practice in San Francisco.

Martin D. Levin, DMD, is in private practice limited to endodontics in Chevy Chase, MD. He is Adjunct Associate Professor of Endodontics at the University of Pennsylvania and Adjunct Associate Professor, Department of Endodontics, at Nova Southeastern University. At the University of Maryland, he

is a Clinical Associate Professor in the Department of Endodontics, Prosthodontics and Operative Dentistry. At the University of Pennsylvania, School of Dental Medicine, Dr. Levin received the Alumni Award of Merit and served as Chair of the Board of Overseers from 2004-2008, is an ex officio member of the board, and is currently Chair of the Dean’s Council. He is recognized as a Distinguished Practitioner in the National Academies of Practice in Dentistry. He is currently Co-Chair of the Joint Special Committee of the American Association of Endodontists and the American Academy of Oral and Maxillofacial Radiology on Cone Beam Computed Tomography. Dr. Levin is a contributor to the 8th, 9th, and 10th editions of Cohen’s Pathways of the Pulp and the 6th Edition of Ingle’s Endodontics, as well as the author of numerous peer-reviewed articles. He is a recognized expert who speaks both nationally and internationally on advanced technologies in endodontic practice and office operations management. Dr. Levin earned his degree in dental medicine from the University of Pennsylvania in 1972, where he was a member of the Omicron Kappa Upsilon Honor Society. After completing his post-doctoral residency in endodontics at the University of Pennsylvania, he became a Diplomate of the American Board of Endodontics, and a member of the College of Diplomates.

Louis H. Berman, DDS, received his dental degree from the University of Maryland School of Dentistry, and his Certificate in Endodontics from the Albert Einstein Medical Center, a hospital-based endodontic residency program. He is Clinical Associate Professor of Endodontics at the University of Maryland

School of Dentistry and a Clinical Instructor and Guest Lecturer at The Albert Einstein Medical Center. He has lectured internationally in the field of endodontics, and has published in several national dental journals. He is past president of the Maryland State Association of Endodontics and is a member of the Journal of Endodontics Scientific Advisory Board. Dr. Berman is the senior author for the chapter on Diagnosis in the ninth and current tenth edition of Cohen’s Pathways of the Pulp, by Hargreaves and Cohen, and is the editor of the web edition of the current tenth edition this textbook. He is also the senior editor and contributing author of the comprehensive textbook, Dental Traumatology. A Diplomate of the American Board of Endodontics and a Fellow of the American College of Dentistry, Dr. Berman has been in full-time private practice in Annapolis, MD, for the past 28 years.

EP