One of the great challenges in endodontic treatment is the cleaning, shaping and disinfection of the root canal spaces. Since the early 1990s, endodontic cleaning and shaping has transitioned from using hand files to implementing the use of rotary driven instrumentation. These NiTi rotary files, driven by electric handpieces, have made it less fatiguing to do endodontic treatment, because they are very efficient cutting instruments. They are available in multiple files sizes and have variable sequences of use. One of the most significant issues with rotary driven instrumentation is that they do not take into consideration the natural three dimensional anatomy of the root canal space. The rotating blade of rotary driven files can only produce a circular bore, ignoring the fact that most canals are not round in cross-section, but rather have a flat-oval or tear-drop shape. Attempts to overcome this issue by using a "brushing" motion on file withdrawal has been met with limited success (and occasional file breakage), because this has only been effective in the coronal third of the canal, as demonstrated by Paqué et al.1 Using digital subtraction micro-CT analyses as well as microbiologic and histologic assessments have validated our inability to adequately treat the true cross-sectional shape of all but the most round root canals.2-6 In a recent study by Peters et al,2 canals of maxillary molars prepared with rotary instrumentation consistently revealed inadequate cleaning and shaping, with an average of 43% (mesio-buccal roots) and 33% (disto-buccal roots) of the remaining canal space being untouched during instrumentation. In a corroborating investigation, Metzger et al7 found traditional rotary file instrumentation left 60% of the canal walls unaffected with a corresponding 45% of the canal walls untouched by obturation. Furthermore, Paqué et al.8,9 demonstrated that not only does the isthmus area in mesial roots of mandibular molars fail to be adequately cleaned by rotary files, but the rotating files actively pack these recesses with dentin chips that cannot be fully dislodged even with passive ultrasonic irrigation. Because of the lack of adequate contact between the rotary files and the canal walls, it is no surprise that the canal disinfection is limited by the irrigation techniques traditionally used. In a recent investigation by Siqueira et al,6 rotary instrumentation with sequential irrigation resulted in 55% of the canals still having viable bacterial cultures.
Another issue with rotary driven files is their unforgiving potential for file separation when stressed. Although a rare occurrence, this may be due to the clinician not following the manufacturer's recommended instructions or possibly from the file having a manufacturing defect. Regardless, when file separation occurs, it is often non-retrievable and can adversely affect the prognosis of endodontic treatment.
The transitioning from the use of hand files to rotary driven nickel titanium files was a great leap of technology in the field of endodontics; however, over the past 18 years there has been limited success in confronting the limitations and drawbacks of this technology. Adjunctive irrigation devices and recently introduced combined irrigation solutions have been proposed to improve the delivery of the irrigant and to improve the cleaning of anatomical irregularities of the root canal system. Unfortunately, none of these approaches can consistently provide complete tissue debridement and disinfection. A new concept to achieve these goals was presented when the SAF system was introduced into the market.
THE SAF SYSTEM
The recently introduced SAF System® (ReDent Nova, Ra'anana, Israel) has dramatically improved the efficacy of root canal cleaning, shaping and disinfection. This novel design not only cleans irregularly shaped canals with only one instrument, 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 (Fig. 1), and is available in three lengths. The SAF-System incorporates the use of the SAF instrument in a specially designed handpiece (RDT3, ReDent Nova, Ra'anana, Israel) that operates by vibrating with an up-and-down motion, at 5,000 times per minute, with an amplitude of .4mm. There is no rotational movement used to shape the canal. Its unique property allows a continuous flow of fresh irrigant delivered into the canal through the hollow file during the entire mechanical cleaning and shaping process.10
One of the many unique features of the SAF instrument is that its hollow lattice is extremely compressible: it can be compressed from its original 1.5 mm diameter to dimensions as small as a #20 K file (Fig. 2).11 When inserted into a canal with a round cross section, it compresses circularly and symmetrically; however, when inserted into a flat-oval canal, it spreads laterally (bucco-lingually) and assumes the cross sectional shape of that canal (Fig. 3).11 This adaptation occurs without any special action or awareness by the clinician, hence the name Self-Adjusting File.
The wall thickness of the lattice which makes up the file is about 100 µm. When fully compressed mesio-distally, the file has the ability to spread bucco-lingually as far as 2.4mm.12 The instrument also has an asymmetrical tip, which bends more easily to a peripheral direction, a feature that is used to help enable the negotiation of canal curvatures. The canal space and inner dentin are subsequently cleaned and shaped conservatively in three dimensions, thus preserving the natural cross-sectional shape of the canal (Fig. 4).
Another very unique property of the SAF instrument is that its hollow design allows the flow of a constant and simultaneous irrigation. With a thin tubing connected to the irrigation hub of the SAF instrument (Fig. 5), the irrigation is supplied by an automated peristaltic pump, the VATEA (ReDent Nova, Ra'anana, Israel) irrigation system (Fig. 6). Because the SAF instrument has a mesh-like construction, the irrigation creates no internal pressure or compression which can build up within the canal. The motion of the file agitates the irrigant to such an extent that it effectively reaches the apical portion of the canal with sonic activation. Throughout the procedure, the nickel titanium lattice of this abrasive instrument intimately adapts and shapes the canal walls while taking advantage of the simultaneous presence of the irrigant. In an era of controversy with regard to the efficacy of positive and negative pressure irrigation systems, the SAF system may be defined as a non-pressure irrigation system (think of drip irrigation) with sonic activation and scrubbing effect. It is the only system currently available that can concomitantly clean, shape and disinfect the canal spaces three dimensionally.
This filing and irrigation method results in a clean canal surface, even in the cul-de-sac apical portion of the canal, which is commonly considered the most difficult part of the canal to clean.13 Scanning electron microscopy studies15 show a remarkably clean surface even in the apical part of the canal. In a recent micro-CT investigation14 using oval canals, the shapes generated with the SAF System were more complete compared to rotary canal preparation.
Recent studies by Paqué et al9,10 have indicated that the packing of dentin chips into the isthmus, which occurs with rotary files, does not occur when the SAF System is applied in similar canals.9,10 This unique property of the SAF System is most likely due to the removal of dentin as a delicate powder suspended in a continuously refreshed irrigant, as well as to the lack of rotation that would tend to pack the material into the isthmus.
DEBRIS AND SMEAR LAYER REMOVAL
The cleaning efficacy of any root canal instrumentation system is usually measured by the amount of tissue and debris left within the canal. Any remaining tissue remnants may prevent adequate adaptation between the canal wall and root canal filling, resulting in space for bacterial colonization. The adaptation of the file to the shape of the root canal's cross-section, and continuous flow of irrigant, especially in oval, flat canals, is a key benefit of the SAF System. In a study16 to evaluate the removal of canal debris and smear layer, 23 single rooted human teeth were evaluated using a scanning electron microscope. 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 (Figs. 7A & B).
The ultimate microbiological goal of chemo-mechanical preparation is to completely eradicate intra-canal bacterial populations, or at least reduce them to levels enabling periradicular tissue healing. Bacteria persisting after chemo-mechanical procedures at levels detectable by culture-dependent techniques have been shown to negatively influence endodontic treatment outcomes.15 Therefore, efforts should always be directed towards cleaning and shaping strategies that maximize root canal disinfection before obturation.
Unfortunately, anatomic complexities in the root canal system often present physical constraints that pose serious challenges to adequate root canal disinfection. An in-vitro study6 using 44 single-rooted teeth with oval root canals analyzed the disinfecting abilities of rotary driven instrumentation compared to the SAF System. After the main canal spaces were contaminated with E. faecalis, cleaning and shaping using rotary files with syringe irrigation resulted in canals having an incidence of 55% positive bacterial cultures. Canals cleaned and shaped with the SAF System, using the SAF instrument and a constant irrigation source, resulted in canals which had only 20% positive canal cultures, again showing the effective cleaning, shaping and disinfection of the SAF System.
Infected 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.16 Unfortunately, the assessment of tissue removal and disinfection cannot be accomplished by simply evaluating two dimensional mesial-distal radiography. In a recent investigation, De Deus et al6 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 significantly reduce the amount of remaining pulp tissue compared to conventional rotary files. The investigators also concluded that sodium hypochlorite irrigation, applied with a syringe and needle, failed to compensate for the inadequate cleaning of the rotary file itself.
Root canal obturation is an essential component of root canal treatment which aims to prevent future bacterial contamination (or recontamination) of the canal space and periapical tissues. When the root canal spaces are not adequately cleaned and shaped before obturation, proper sealing will be jeopardized by the remaining tissue and debris.17,18 Any debris that prevents the adaptation of the filling material to the canal wall may provide space for bacterial leakage and proliferation. A recent study7 compared the obturation efficacy between canals cleaned and shaped with rotary files versus the SAF System, using lateral compaction of gutta percha cemented with AH26. 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% after the use of rotary files.
Therefore, the efficacy of the SAF System in canal cleaning and shaping is the principle reason why the SAF System results in a more intimately adapted obturation, again allowing endodontic treatment to be managed more three-dimensionally.
Cleaning, shaping and disinfection using the SAF System has been proven in rigorous peer-reviewed studies to be significantly more effective than traditional rotary NiTi instrumentation with syringe irrigation.1-9 Microbiologic sampling of canals infected with E. faecalis, histologic and three-dimensional micro-CT analysis of prepared canal surfaces, and the adaptation of root canal filling materials all suggest that the adaptive technology offered by the SAF System is clearly superior to that of rotary file preparation. Operational errors such as under-instrumentation, canal transportation, over thinning of the canal walls and instrument breakage are greatly reduced or eliminated when using the SAF System. After a glide path to working length is established to a size #20 file with a .04 taper, only one SAF instrument is required to complete the instrumentation, while achieving simultaneous irrigation during the entire cleaning and shaping process. This innovative technology represents the next paradigm shift in how we will be providing endodontic treatment.OH
Louis H. Berman, DDS, Diplomate, American Board of Endodontics, Clinical Associate Professor, University of Maryland School of Dentistry. Berman@AnnapolisEndodontics.com
Stephen Cohen, MA, DDS, Diplomate, American Board of Endodontics, Adjunct Clinical Professor of Endodontics, Department of Endodontics, University of the Pacific Arthur A. Dugoni School of Dentistry.
Zvi Metzger, DMD, Associate Professor in Oral Biology and Endodontology; Chair, Department of Endodontology, The Goldschleger School of Dental Medicine, Tel Aviv University, Tel Aviv, Israel.
Bettina Basrani, DDS, PhD, Assistant Professor, Program Co-Director MSc Endodontics, Department of Endodontics, Faculty of Dentistry, University of Toronto.
Oral Health welcomes this original article.
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