Introduction. Abstract

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1 doi: /j x Hard-tissue debris accumulation created by conventional rotary versus self-adjusting file instrumentation in mesial root canal systems of mandibular molars F. Paqué 1, A. Al-Jadaa 1 & A. Kfir 2 1 Division of Preventive Dentistry, Periodontology, and Cariology, University of Zürich Center of Dental Medicine, Zürich, Switzerland; and 2 Department of Endodontology, School of Dental Medicine, Tel Aviv University, Tel Aviv, Israel Abstract Paqué F, Al-Jadaa A, Kfir A. Hard-tissue debris accumulation created by conventional rotary versus self-adjusting file instrumentation in mesial root canal systems of mandibular molars. International Endodontic Journal, 45, , Aim To evaluate the accumulation of hard-tissue debris when using the Self-adjusting File (SAF) system in mesial roots of mandibular molars with isthmuses and to compare it with that occurring when the ProTaper file system was used. Methodology Forty extracted human mandibular molars with joining mesial root canals and an isthmus between the two canals were randomly assigned to two experimental groups and scanned using micro-computed tomography. Root canals in the control group (N = 20) were instrumented using the ProTaper rotary system until F3. Irrigation with 1 ml of 3% NaOCl solution was applied after each instrument. Root canals in the experimental group (N = 20) were prepared using the SAF for 4 min, with continuous irrigation (3% NaOCl, 4 ml min )1 ). After rescanning, canals in both groups were further irrigated with 5 ml of 17% EDTA for 2 min. After final scanning, the per cent value of total canal system volume filled with hardtissue debris was calculated. Statistical analysis was performed using Mann Whitney U-test; the alpha-type error was set at 1%. Results Instrumentation of the root canals with ProTaper left 10.1% (IQR 5.2) of the total canal system volume filled with hard-tissue debris while preparation with the SAF left 1.7% (IQR 1.6). This difference was highly significant (P < ). After subsequent EDTA irrigation, these values were significantly reduced (P < 0.01) to 7.9% (IQR 4.1) and 1.3% (IQR 0.8) in the ProTaper and SAF groups, respectively. Conclusion Preparation with the SAF system resulted in less hard-tissue debris accumulation in isthmus-containing root canal systems compared with instrumentation with ProTaper rotary files. Keywords: accumulated debris, microcomputed tomography, root canal preparation, SAF. Received 14 August 2011; accepted 10 November 2011 Introduction Root canal treatment is aimed to clean the canals and shape them to an adequate geometry. The shape of the prepared canals should optimize the disinfection of the root canals, using irrigants, a task that is particularly Correspondence: Frank Paqué, Department of Preventive Dentistry, Periodontology, and Cariology, University of Zürich Center for Dental Medicine, Plattenstrasse 11, CH 8032 Zürich, Switzerland (Tel.: ; fax: ; frank.paque@zzm.uzh.ch). challenging in the apical region. Additionally, the prepared shape should allow for adequate filling of the root canal system. These goals are commonly achieved using rotary NiTi file systems combined with sodium hypochlorite, which is used as an irrigant. Microcomputed tomography (lct) has been commonly used to evaluate root canal shaping results in terms of the amount of hard tissue removed and per cent of canal wall surface affected by the procedure (Paqué & Peters 2011, Peters & Paqué 2011, Versiani et al. 2011). Recently, lct was also applied to evaluate and measure the amount and extent of hard-tissue ª 2011 International Endodontic Journal International Endodontic Journal, 45, ,

2 SAF lct debris accumulation analysis Paqué et al. debris transportation into canal recesses such as isthmuses and fins. A preliminary investigation (Paqué et al. 2009) evaluated packing of hard-tissue debris into the isthmus areas of mesial roots of mandibular molars when using rotary ProTaper instruments without any irrigation. It was shown that a mean of 29.2 ± 14.5% of the original canal system was filled with hard-tissue debris after such preparation. The use of common syringe-and needle-delivered sodium hypochlorite irrigation, followed by EDTA reduced the accumulation of dentine debris to a mean of 6.9% and 4.9% of the canal volume, respectively (Paqué et al. 2011). The flutes of rotary files are designed to carry the cut dentine chips coronally. Apparently, this does not happen when a free space is available along the length of the canal, as in the case of isthmus or fin adjacent to the main root canal. Recently, a novel file has been introduced, with a different mode of action. This file, called self-adjusting file (SAF; ReDent-Nova, Ra anana, Israel), is claimed to address some of the shortcomings of traditional rotary files by adjusting itself to the canal cross section (Hof et al. 2010, Metzger et al. 2010a). The new file has no cutting edge, nor flutes; dentine removal is carried out in a way similar to the mode of action of sandpaper (Hof et al. 2010). Recent lct analysis of root canals prepared with this file indicated that this new technology allows for a higher per cent of the root canal surface to be affected by the procedure (Paqué & Peters 2011, Peters & Paqué 2011, Versiani et al. 2011). Besides its revolutionary design, the SAF is used with continuous irrigation delivered through the hollow file, using a special irrigation apparatus (VATEA irrigation device; ReDent-Nova). No data are currently available as to the extent of hard-tissue debris accumulation when using the SAF with continuous irrigation. The present study was designed to evaluate the accumulation of hard-tissue debris when using the SAF in mesial roots of mandibular molars with isthmuses and to compare it with that of ProTaper file system. Materials and methods Experimental teeth One hundred and fifty human mandibular first and second molars with fully developed roots were selected from the department s collection of extracted teeth. Teeth had been stored in a 0.1% thymol solution for <1 year at 5 C. Preliminary tomography for selection of teeth Specimens were pre-scanned using a high-resolution lct system (lct 40; Scanco Medical, Brüttisellen, Switzerland) with an isotropic resolution of 72 lm at 70 kv and 114 la. Based on these pre-scans, 40 mandibular molars with joining mesial root canals and an isthmus between the two canals were selected, in which the corono-apical dimension of the isthmus was at least 2 mm. Subsequently, the teeth were randomly assigned to two groups (N = 20 each). Chemo-mechanical preparation of teeth Root canals of the molars were accessed using a diamond-coated bur. Prior to preparation, working length was determined by inserting a K-file size 08 until the tip of the instrument became visible at the tip of the root; working length was determined at 1 mm short of this measurement. Teeth were then mounted on scanning electron microscopy stubs ( T; Bal- Tec AG, Balzers, Liechtenstein) using epoxy resin (Stycast; Emerson & Cuming, Oevel, Belgium). This allowed exact repositioning during repeated scanning procedures. The apices were sealed with sticky wax before the mounting procedure. Prior to further treatment, the teeth were scanned using high-resolution lct with an isotropic resolution of 20 lm. In the experimental group, both mesial canals were prepared using the SAF system (ReDent-Nova) by an operator experienced with the SAF procedure. The canal orifice was flared using size 3 Gates Glidden drills, and a glide path was established using hand files to the extent that a K-file size 20 could be inserted to working length. The SAF file was operated with a RDT3 handpiece head (ReDent-Nova), which was operated at 5000 rpm, resulting in 5000 in-and-out vibrations per min with an amplitude of 0.4 mm (Hof et al. 2010, Metzger et al. 2010a). According to the manufacturer s recommendation, the file was gradually inserted into the canal and used with a pecking motion to working length for 4 min. As determined in pilot experiments, this resulted in a similar apical canal diameter to that obtained with the ProTaper sequence to the F3 instrument. The SAF file was used with continuous flow of 3% NaOCl delivered at 4 ml min )1 through the hollow file, using a VATEA peristaltic pump (ReDent-Nova) that was connected to the file by a polyethylene tube. After 4 min of continuous operation, the canals were dried with paper points and subjected to a second high-resolution scanning procedure with an isotropic resolution of 414 International Endodontic Journal, 45, , 2012 ª 2011 International Endodontic Journal

3 Paqué et al. SAF lct debris accumulation analysis 20 lm. After second scanning, the canals were irrigated with 5 ml of 17% EDTA for 2 min using syringe and needle followed by a final flush with 3% NaOCl to wash out EDTA remnants. Finally, teeth were scanned a third time with an isotropic resolution of 20 lm. In the control group, mesial canals were instrumented using ProTaper instruments (Dentsply Maillefer, Ballaigues, Switzerland) by an operator experienced with the ProTaper procedure. ProTaper SX, S1 and S2 were used to flare the orifice, coronal and middle third of the root canals and to get straight-line access. Care was taken to use SX only in the coronal part and S1 and S2 in the coronal and middle part of the root canals. Subsequently, a glide path was established preparing the canals with K-files size 15 and size 20 to working length. Shaping of the canals was continued using S1, S2, F1, F2 and F3 to working length. After each instrument, canals were irrigated with 1 ml of 3% NaOCl using a 30-gauge side-vented irrigating tip (Max-i-Probe; Hawe-Neos, Dentsply, Bioggio, Switzerland). Apical patency was verified after each rotary instrument using a K-file size 10. Subsequently, the teeth were scanned to evaluate the debris accumulated during instrumentation of the root canals. After the second scanning procedure, canals were irrigated with 5 ml of 17% EDTA for 2 min using the delivery system described previously followed by a final flush with 3% NaOCl to wash out EDTA remnants. Finally, teeth were scanned a third time. Micro-CT measurements and evaluations Three high-resolution scans were performed per tooth as described previously, using a commercially available lct system (lct 40; Scanco Medical): (i) prior to treatment, (ii) after instrumentation and irrigation with 3% NaOCl and (iii) after final irrigation with 17% EDTA and subsequent NaOCL flush. Teeth were scanned at 70 kv and 114 la with an isotropic resolution of 20 lm resulting in slices for each root. The volume of interest was selected extending from the furcation region to the apices of the roots. Although the mounting on SEM carriers ensured almost exact repositioning of the specimens for all scanning procedures, superimposition was subsequently calculated using special software (IPL Register 1.01beta; Scanco Medical). Volumes of matched root canals before and after preparation were calculated using specially developed software (IPL V5.06B; Scanco Medical). Hard-tissue debris was identified and calculated as follows: voxels that were identified as either soft tissue, liquid or air (canal volume) in the preoperative scan but then were filled with radio-opaque material in the postoperative scan were assumed to be filled with hard-tissue debris. Counting those voxels, multiplied with the volume of one voxel thus resulted in volume of apparent hardtissue debris filling the original root canal space. Voxels representing canal wall areas that were removed during instrumentation but then filled with debris could not be included in this calculation, because it is not possible to unambiguously discern between accumulated hard-tissue debris and root canal wall dentine on the scans. For visualization, the voxels that turned from radiolucent to radiopaque reflecting the accumulated hardtissue debris were superimposed on the original root canal anatomy. Accumulated hard-tissue debris could thus be visualized in the complete mesial canal system (Figs 1 and 2). Data generation and analysis The total volume of apparent accumulated hard-tissue debris was calculated in cubic millimetre per total mesial root canal volume. This value was related to the original canal volume leading to data presentation as vol%. Values were rounded to one decimal place. Obtained data were skewed (Shapiro Wilk test). Consequently, values were compared between groups using non-parametric Mann Whitney U-test. The alpha-type error was set at Results Instrumentation of the root canals with ProTaper left 10.1% (IQR 5.2) of the total canal system volume filled with accumulated hard-tissue debris. After preparation with the SAF, 1.7% (IQR 1.6) of the total canal volume was found to be filled with accumulated hard-tissue debris. This difference was highly significant (Mann Whitney U-test, P < ). After subsequent EDTA irrigation, these values were significantly reduced (P < 0.01) to 7.9% (IQR 4.1) and 1.3% (IQR 0.8) for the ProTaper and SAF groups, respectively. The difference between the groups after EDTA irrigation was again highly significant (Mann Whitney U-test, P < ). Discussion Accumulation of hard-tissue debris in the root canal systems in the present study was found mainly in the ª 2011 International Endodontic Journal International Endodontic Journal, 45, ,

4 SAF lct debris accumulation analysis Paqué et al. (a) (b) Figure 1 Microcomputed tomography analysis of a mesial root of a mandibular molar, treated with ProTaper files. (a) (left) Cross sections before, (centre) after treatment and (right) after additional EDTA irrigation. Note: accumulation of radiopaque material in the isthmus. (b) Hard-tissue debris accumulation. (left) canal system before treatment (centre) canal system after treatment and (right) canal system after additional EDTA irrigation. Grey is radiopaque hard-tissue debris that accumulated in the canal as result of treatment with rotary ProTaper file with a syringe-and-needle irrigation. isthmus area (Fig. 1). It was significantly greater when rotary files were used, and the particles could not be dislodged effectively by simple irrigation. This raises two questions: how did the dentine particles get there in the first place and why were they not dislodged by the irrigation? When rotary files are used in canal with a round cross section, the dentine particles that are cut from the canal wall are carried coronally by the flutes of the file, in a manner similar to that of a common mechanical spiral drill. This removal is apparently less effective when the file has no dentine wall on one side, as is the case of a canal adjacent to an isthmus. Rather than being carried coronally or being contained and packed in the file s flute space, the debris was most probably actively packed into the area with the least resistance, namely into the isthmus (Paqué et al. 2009). As to the second issue, two possibilities may be considered. It could be that the dentine particles were large enough to simply get mechanically trapped between the mesial and distal walls of the isthmus. For an alternative one should consider the original contents of root canal recesses such as the isthmuses. It has been demonstrated that when rotary files are used in long oval canals, pulp tissue remains in the recesses (De-Deus et al. 2008, 2010, 2011). These soft-tissue remnants could not be removed from these recesses by simple sodium hypochlorite irrigation, which led De- Deus et al. (2011) to the conclusion that, at least in long oval canals, the notion that the file shapes, the irrigant cleans represents wishful thinking rather than an experimentally established fact. It is conceivable to hypothesize that dentine particles in the present study were actively packed into soft-tissue remnants, thus resulting in composite debris of dentine particles embedded in soft-tissue remnants, which was resistant to the common syringe-and-needle irrigation. To verify this notion, a histological study will be required, which was beyond the scope of the present investigation. The phenomenon of packing hard-tissue debris into isthmuses and similar recesses may be important in two aspects. First such packed hard-tissue debris may potentially interfere with disinfection of these recesses by both preventing the irrigant flow into them as well 416 International Endodontic Journal, 45, , 2012 ª 2011 International Endodontic Journal

5 Paqué et al. SAF lct debris accumulation analysis (a) (b) Figure 2 Microcomputed tomography analysis of a mesial root of a mandibular molar, treated with self-adjusting file (SAF). (a) (left) Cross sections before, (centre) after treatment and (right) after additional EDTA irrigation. Note: absence of radiopaque material in the isthmus. (b) Hard-tissue debris accumulation. (left) canal system before treatment (centre) canal system after treatment and (right) canal system after additional EDTA irrigation. Grey is radiopaque hard-tissue debris that accumulated in the canal system as result of treatment with SAF with continuous irrigation. as by neutralizing the efficacy of the sodium hypochlorite irrigant (Nair et al. 2005, Haapasalo et al. 2007). Second, the debris may interfere with adequate filling of the root canal by preventing contact of the root canal filling material with the canal walls (De-Deus et al. 2008, Metzger et al. 2010b). It was previously established that using rotary files without proper irrigation results in the packing of isthmuses with hard-tissue debris (Paqué et al. 2009). However, even though irrigation between instruments greatly reduced this phenomenon, it was unable to render the isthmus area in the present study free of such debris. Furthermore, a recent study (Paqué et al. 2011) has shown that even when passive ultrasonic irrigation was applied, 50% of the dentine particles still remained in the isthmus area after this vigorous method of irrigation. It should be kept in mind that even passive ultrasonic irrigation is of limited efficacy in curved root canals, as often encountered in mesial roots of mandibular molars. The use of the SAF in similar canals resulted in much less hard-tissue debris accumulation than when rotary files were used. This could be attributed either to avoiding rotary motion in the canals, which most probably caused the packing when rotary files were used, or because of the continuous irrigation that was applied through the hollow file throughout the procedure or both. The mode of action of the SAF may also have contributed to the results. Rotary files have a rotating cutting edge that cuts off dentine particles that may be packed into the isthmus. The SAF on the other hand works like sandpaper: its delicately rough surface comes in close contact with the canal walls with a light pressure produced by the compressed lattice attempting to regain its original form (Hof et al. 2010). The in-andout vibration that is generated by the special handpiece head serves as the motion required to remove material from the canal walls. Dentine is removed as a thin powder that is continuously suspended and carried out by the flow of the irrigant (Hof et al. 2010). This mode ª 2011 International Endodontic Journal International Endodontic Journal, 45, ,

6 SAF lct debris accumulation analysis Paqué et al. of action may explain the results obtained in the present study. It has been recently reported that the SAF system is more likely to remove soft-tissue debris from root canal recesses compared with rotary files (De-Deus et al. 2011). This could have also contributed to the present results, potentially by removing much of the soft tissue that may trap dentine particles that are pushed into it, as suggested above. Siqueira et al. (2010) recently reported significantly better sodium hypochlorite disinfection with the SAF system when compared with rotary files used with syringe-and-needle irrigation in flat oval canals. It is conceivable that the difference in the extent of packing of hard-tissue debris into recesses of flat root canals that was found in the present study could have also potentially contributed to these results. Similarly, it could have contributed also to the better adaptation of root canal fillings to canal walls that was reported by Metzger et al. (2010b). Separate histological studies will be required to test these hypotheses. However, it should be noted here that the SAF system has some inherent problems also, which relate mostly to shaping the canal to a form that can easily be filled. Further research is necessary before this system can be unreservedly recommended to the clinician. Conclusions 1 Preparation of the root canals with the SAF system resulted in less hard-tissue debris accumulation in isthmus-containing root canal systems of mesial roots of mandibular molars compared with rotary files that were used with syringe-and-needle irrigation. 2 The use of a final EDTA irrigation removed some of the hard-tissue debris in both groups but a substantial amount of the debris that was created during instrumentation remained. Acknowledgement This study was supported financially by the ReDent- Nova company, manufacturer of the SAF. References De-Deus G, Reis C, Beznos D, Gruetzmacher-de-Abranches AM, Coutinho-Filho T, Pacionrik S (2008) Limited ability of three commonly used thermoplasticised gutta-percha techniques in filling oval-shaped canals. Journal of Endodontics 34, De-Deus G, Barino B, Quintella-Zamolyi R, Souza E, Fonseca A Jr, Fidel RAS (2010) Suboptimal debridement quality produced by the single-file F2 Protaper technique in ovalshaped canals. Journal of Endodontics 36, De-Deus G, Souza EM, Barino B et al. (2011) The Self-adjusting File optimizes debridement quality in oval-shaped root canals. Journal of Endodontics 37, Haapasalo M, Qian W, Portenier I, Waltimo T (2007) Effects of dentin on the antimicrobial properties of endodontic medicaments. Journal of Endodontics 33, Hof R, Perevalov V, Eltanany M, Zary R, Metzger Z (2010) The Self-adjusting File (SAF). Part 2: mechanical analysis. Journal of Endodontics 36, Metzger Z, Teperovich E, Zary R, Cohen R, Hof R (2010a) The Self-adjusting File (SAF). Part 1: respecting the root canal anatomy A new concept of endodontic files and its implementation. Journal of Endodontics 36, Metzger Z, Zary R, Cohen R, Teperovich E, Paqué F (2010b) 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. Journal of Endodontics 36, Nair PNR, Henry S, Cano V, Vera J (2005) Microbial status of apical root canal system of human mandibular first molars with primary apical periodontitis after one-visit endodontic treatment. Oral Surgery Oral Medicine Oral Pathology Oral Radiology and Endodontics 99, Paqué F, Peters OA (2011) A micro-computed tomography evaluation of the preparation of long oval root canals in mandibular molars with the Self-adjusting File (SAF). Journal of Endodontics, 37, Paqué F, Laib A, Gautschi H, Zehnder M (2009) Hard-tissue debris accumulation analysis by high-resolution computed tomography scans. Journal of Endodontics 35, Paqué F, Boessler C, Zehnder M (2011) Accumulated hard tissue debris levels in mesial roots of mandibular molars after sequential irrigation steps. International Endodontic Journal 44, Peters OA, Paqué F (2011) Root canal preparation of maxillary molars with the Self-adjusting File: a microcomputed tomography study. Journal of Endodontics 37, Siqueira JF, Alves FRF, Bernardo M, Almeida BM, Machado de Oliveira JC, Rôcas JN (2010) Ability of chemomechanical preparation with either rotary instruments or Self-adjusting File to disinfect oval-shaped root canals. Journal of Endodontics 36, Versiani MA, Pecora JD, de Sousa-Neto MD (2011) Flat-oval root canal preparation with Self-adjusting File instrument: a micro computed tomography study. Journal of Endodontics 37, International Endodontic Journal, 45, , 2012 ª 2011 International Endodontic Journal