doi:10.1111/j.1365-2591.2011.02008.x Centring ability and apical transportation after overinstrumentation with ProTaper Universal and ProFile Vortex instruments J. A. González Sánchez, F. Duran-Sindreu, S. de Noé, M. Mercadé & M. Roig Department of Restorative Dentistry and Endodontics, Universitat Internacional de Catalunya, Barcelona, Spain Abstract González Sánchez JA, Duran-Sindreu F, de Noé S, Mercadé M, Roig M. Centring ability and apical transportation after overinstrumentation with ProTaper Universal and ProFile Vortex instruments. International Endodontic Journal, 45, 542–551, 2012. Aim To evaluate morphological changes to the major foramen after overinstrumentation with ProTaper Universal and ProFile Vortex Ni–Ti rotary instruments. Methodology Twenty-eight mesiobuccal canals of maxillary and mandibular first molars were divided into two groups of 14 canals each. The root canals were prepared with ProTaper Universal or ProFile Vortex instruments. ProTaper and Vortex instruments were used until the file tip protruded 1 mm beyond the working length (0.5 mm beyond the major foramen). The major foramen was photographed before and after overinstrumentation with each file of the two systems used. The images were superimposed and evaluated using Adobe Photoshop. The parameters evaluated were canal transportation, centring ability and shape of the major foramen. Transportation and centring ability were calculated in two directions: the direction of maximum curvature (MC) and a direction vertical to the maximum curvature (VC). Measurements of canal transportation and centring ability were analysed by anova followed by post hoc least significance difference (LSD) multiple comparisons. Results No significant differences were observed amongst the different instruments with respect to centring ability in either direction (P > 0.05). The F3 ProTaper Universal instrument was associated with a higher mean values for transportation in the direction of MC (P < 0.05) than the S1, S2 and F1 ProTaper Universal instruments and the size 15, 0.06 taper, size 20, 0.06 taper, and size 25, 0.06 taper ProFile Vortex instruments. The size 30, 0.06 taper ProFile Vortex instrument had a larger mean value for transportation in the direction of MC (P < 0.05) than the S1 ProTaper Universal and size 15, 0.06 taper ProFile Vortex instruments. The S1, S2, F1, F2 and F3 ProTaper Universal files and the size 15, 0.06 taper, size 20, 0.06 taper, size 25, 0.06 taper, and size 30, 0.06 taper ProFile Vortex files produced an oval foramen in 71%, 71%, 85%, 85%, 71%, 71%, 85%, 85% and 89% of the cases, respectively. Conclusions In most samples, the ProTaper Universal and ProFile Vortex files produced transportation of the major foramen and created an oval-shaped major foramen after overinstrumentation. Keywords: apical transportation, centring ability, overinstrumentation, ProFile Vortex, ProTaper Universal. Received 8 August 2011; accepted 12 December 2011 Introduction Correspondence: Miguel Roig, Dentistry Faculty, Universitat Internacional de Catalunya, C/Josep Trueta s/n. 08195, Sant Cugat del Vallès, Spain (Tel.: +34 504 2000; fax: +34 504 2031; e-mail: mroig@csc.uic.es). 542 International Endodontic Journal, 45, 542–551, 2012 The aims of root canal treatment are to eliminate microorganisms, to remove infected and necrotic pulpal remnants and to shape the root canal system in ª 2012 International Endodontic Journal González Sánchez et al. ProTaper Universal and ProFile Vortex order to facilitate irrigation and the placement of a medicament and/or filling material (Haapasalo et al. 2005). At the same time, the procedure should avoid any iatrogenic events, such as fracture of the instruments, transportation of the root canal, formation of a ledge or perforation of the tooth. A number of studies on both extracted teeth and simulated canals have shown that rotary nickel–titanium (Ni–Ti) instruments allow more rapid, more centred, rounder and more conservative shaping of canals than stainless steel instruments (Glossen et al. 1995, Kum et al. 2000, Schäfer & Lohmann 2002). The Ni–Ti rotary instruments that are on the market vary considerably in design. Studies evaluating the cutting efficiency of various tip designs suggest less apical transportation with noncutting tips than those with cutting tips (Dummer et al. 1998, Powell et al. 1998). An increasing taper is directly related to increased cross-sectional area and decreased flexibility (Javaheri & Javaheri 2007). Several other variables, such as canal curvature, root canal anatomy and diameter, might also be involved in changes to root canal morphology (Schäfer & Dammaschke 2006). ProTaper instruments (Dentsply Maillefer, Ballaigues, Switzerland) have a convex triangular crosssectional design with three cutting edges, a negative cutting angle and a flute design that combines progressive tapers within the shaft (Yang et al. 2006). A new design feature of the ProTaper Universal Ni–Ti system is that the tips of the finishing files are more rounded than those of the original ProTaper Ni–Ti system to improve working and shaping ability (Aguiar et al. 2009). Furthermore, the convex lateral surfaces of the F3 to F5 instruments are machined to increase flexibility (Vaudt et al. 2009). The ProTaper Universal instruments performed better than the original ProTaper files evaluated previously, probably because the file tip was changed from the ‘modified guiding tip’ to the ‘rounded safe tip’ (Câmara et al. 2009). ProFile Vortex rotary instruments (Dentsply, Tulsa Dental Specialities, Tulsa, OK, USA) were introduced in 2009. Vortex files are manufactured from modified Ni– Ti raw alloy known as M-wire. M-wire, which was introduced in 2008, is produced by applying a series of heat treatments to Ni–Ti wire blanks. Preliminary evidence suggests that the use of M-wire improves the fatigue lifespan of rotary instruments whilst maintaining the same torsional properties as instruments that have been ground conventionally (Bardsley et al. 2011). ProFile size 25, 0.04 taper files that are manufactured from M-Wire Ni–Ti show nearly 400% more resistance ª 2012 International Endodontic Journal to cyclic fatigue than size 25, .04 taper ProFile files manufactured from SE508 Ni–Ti (Johnson et al. 2008). The system has 0.04 and 0.06 taper instruments in sizes that range from 15 to 50. ProFile Vortex rotary files have a triangular cross section and a specific helical angle without radial lands with a noncutting safety tip (Gao et al. 2010). The effectiveness of various instruments in root canal preparation has been studied after the correct working length (WL) has been determined, which does not take into account the fact that instrumentation might occur beyond the major foramen. It has been shown that the WL was overestimated in more than 50% of premolar samples and 22% of molar samples, although the radiographic WL was located 0–2 mm short of the radiographic apex (ElAyouti et al. 2001). Some authors have shown that electronic apex locators (EALs) provide a more accurate estimation of the WL than radiographs (Pratten & McDonald 1996, Cianconi et al. 2010). For this reason, the use of EALs has been proposed to obtain a more accurate length for the root canal (Pratten & McDonald 1996). However, in in vivo studies, Wrbas et al. (2007) and Stöber et al. (2011a) observed that the file tip passed the major foramen in 20% and 15% of the samples, respectively, when the Raypex 5 (VDW, Munich, Germany) EAL was used. In addition, Wrbas et al. (2007), Shabahang et al. (1996), Dunlap et al. (1998) and Stöber et al. (2011b) observed that, with the Root ZX (J Morita Corp, Tokyo, Japan) EAL, the file tip protruded beyond the major foramen in 40%, 30.8%, 26% and 16.7% of the samples, respectively. Furthermore, Stöber et al. (2011a,b) reported that, with the iPex (NSK, Tochigi, Japan) EAL, the file extended beyond the major foramen in 26.3% of the samples. In addition, some authors have observed that EALs used with rotary Ni–Ti files cannot determine and control the apical extent of rotary instrumentation accurately. Jakobson et al. (2008) found that the autoreverse function of the Root ZX II with the Low-Speed Handpiece unit could not control the apical extent of rotary instrumentation when the auto-reverse function was set to 1. Uzun et al. (2008) observed that, when the auto-reverse function was used, the Tri Auto ZX (J Morita Co., Kyoto, Japan) and TCM Endo V (Nouvag, Goldach, Switzerland) EALs instrumented beyond the major foramen in 60% and 95% of cases of retreatment, respectively. Siu et al. (2009) reported that the rotary Ni–Ti file protruded beyond the major foramen 28.6% of the time for the Root ZX II with the LowSpeed Handpiece module (J. Morita USA, Tustin, CA, USA), 28.6% of the time for the Apex NRG XFR (Medic International Endodontic Journal, 45, 542–551, 2012 543 ProTaper Universal and ProFile Vortex González Sánchez et al. NRG Ltd, Tel Aviv, Israel) attached to the Brasseler handpiece (Brasseler USA, Savannah, GA, USA) and 25% of the time for the Mini Apex Locator attached to the Brasseler handpiece. On the basis of these results, some authors have proposed that, when determining the WL, the instrument should be withdrawn by approximately 0.5 mm from the position given by some EALs (Wrbas et al. 2007, Pascon et al. 2009). However, the range of values of WL obtained with EALs is broad (i.e. the standard deviation is high), and thus, the WL will be underestimated in some cases, although in others it will be overestimated. By following the recommendations of the above-mentioned authors, the WL would be underestimated more frequently; underestimation of the WL can lead to insufficient debridement of the root canal and may jeopardize the outcome of the treatment (Sjögren et al. 1990). In the light of the concerns about overestimation of the WL, it is important to understand the effects of overinstrumentation on the major foramen when the WL has been overestimated. The aim of the study was to evaluate the morphological changes in the major foramen after overinstrumentation with the ProTaper Universal and ProFile Vortex rotary instruments. The null hypothesis was that ProTaper Universal and the ProFile Vortex would demonstrate the same morphological changes to the major foramen when used to prepare the root canal with the file tip protruding 1 mm beyond the working length (0.5 mm beyond the major foramen). Materials and methods Selection of root canals Fourteen maxillary and 14 mandibular molar teeth with complete root formation and no history of endodontic treatment were used. The teeth were extracted because of periodontal disease and comprised a total of 28 mesiobuccal root canals. For the maxillary molars, the main mesiobuccal root canal was chosen, and only mesiobuccal canals from mesial roots that had two separate orifices that terminated in two separate foramina were selected for the mandibular molars. Teeth were only selected if they allowed placement of a size 06 K-file to the major foramen and did not allow passive placement of a size 15 K-file to within 1 mm of the major foramen. The teeth were cleaned, disinfected, immersed in 0.9% saline solution and stored at room temperature. The root canals were 544 International Endodontic Journal, 45, 542–551, 2012 divided equally into two instrumentation groups, such that there was an equitable distribution of canal numbers, canal curvatures and radii between the two groups. Both the ProTaper Universal group and the ProFile Vortex group contained seven mesiobuccal canals from maxillary molars and seven from mandibular molars. The angle of curvature and radius of each canal were determined from periapical radiographs, in accordance with the method of Pruett et al. (1997). The means and standard deviations of the angles and radii of curvature of the root canals in the ProTaper group were 33.8 ± 10.1 degrees and 4.83 ± 1.14 mm, and in the ProFile Vortex group, 31.14 ± 8.32 degrees and 5.21 ± 1.81 mm. A t-test showed no statistically significant differences in these variables between the two groups. Preparation of the model and root canal instrumentation All the teeth were shortened to a length of 18 mm. Each tooth was placed coronally in a customized silicone block, leaving the apical portion of the root visible. The teeth could be removed and repositioned in the block easily to allow instrumentation and irrigation. The silicone block was adjusted with precision on an acrylic base coupled to a stereomicroscope to visualize the position of the major foramen. Each root was illuminated directly and orientated until the major foramen was located in the middle of and parallel to the objective lens, which allowed the entire major foramen to be observed under the stereomicroscope. The major foramen was photographed at 20· magnification using a 35-mm digital camera coupled to the stereomicroscope (pre-instrumentation photograph, [Po0]); (Fig. 1a). The WL was established with a size 06 K-file. The file was introduced into each canal until the file tip became visible through the major foramen under a stereomicroscope at 20· magnification. The file was then withdrawn until the tip was tangential to the major foramen. The silicone stop was adjusted to the nearest flat anatomical tooth landmark, which was chosen as a reference for measurement of the root canal. The distance between the file tip and the rubber stop was measured under a stereomicroscope at 4.5· magnification with a millimetre ruler. Subsequently, 0.5 mm was subtracted from this measurement, and the resulting value was considered to be the WL. ª 2012 International Endodontic Journal González Sánchez et al. ProTaper Universal and ProFile Vortex (a) (c) (b) Figure 1 (a) Pre-instrumentation photograph, [Po0]. (b) Post-instrumentation photograph [Po3], after use of the F1 ProTaper Universal. (c) F1 image [Po3] superimposed over its pre-instrumentation image [PoO]. A customized jig was designed in silicone (Optosil P Plus HERAEUS KULZER, Hanau, Germany) and provided a reproducible position for the digital dental X-ray sensor and cone alignment. A size 15 K-file was placed in the root canal to the WL, and two digital radiographs (Kodak RVG 6100; Kodak, Rochester, NY, USA) were taken of each tooth. The first radiograph was obtained orthoradially. Then, the tooth was rotated through 90, and a second radiograph was taken. The radiographs were transferred to AutoCad 2009 (Autodesk Inc, San Rafael, CA, USA), and the angle and radius of curvature of each root canal were measured. Group A was assigned to preparation with ProTaper Universal instruments and group B to preparation with ProFile Vortex instruments. Both the ProTaper Universal and ProFile Vortex instruments were used with a 16 : 1 reduction handpiece (X-Smart; Dentsply Maillefer) powered by a torque-limited electric motor (X-Smart; Dentsply Maillefer). The instrumentation was carried out in accordance with the manufacturer’s instructions. Vortex rotary files were used at 400 rpm and ProTaper rotary files at 300 rpm. Table 1 shows the instrument sequence for each group. ProTaper Universal A glide path up to a size 20 K-file was created to the WL before instrumentation. The teeth were pre-flared with an SX ProTaper file, which was applied in a brushing motion away from the furcation. Subsequently, a size 10 K-file was introduced passively into the root canal until the file tip protruded 1 mm beyond the WL (0.5 mm beyond the major foramen). The rotary files were withdrawn immediately upon reaching the WL + 1 mm. ProTaper instruments were used up to F3 until the file tip protruded 1 mm beyond the WL (Table 1). ª 2012 International Endodontic Journal Table 1 Instrumentation for each system ProTaper ProFile Vortex Type Length Size 10 K-File Size 15 K-File Size 20 K-File WL WL WL Type SX Length Meet resistance Size 10 K-File WL + 1 mm S1 WL + 1 mm S2 WL + 1 mm F1 WL + 1 mm F2 WL + 1 mm F3 Taper Size 0.06 40 Length Meet resistance 0.06 0.06 0.06 0.06 0.02 Meet resistance Meet resistance Meet resistance WL WL + 1 mm WL + 1 mm 0.06 0.06 0.06 0.06 35 30 25 20 Size 10 K-File 15 20 25 30 WL WL WL WL + + + + 1 1 1 1 mm mm mm mm WL, working length. ProFile Vortex In the second group, the glide path and patency were established in an identical manner to those of group A. The canals were prepared using 0.06 tapered instruments in a crown-down technique, starting with a size 40 file, followed by sizes 35, 30, 25 and 20. It should be noted that only the size 20, 0.06 taper file reached the WL. Subsequently, the root canals were instrumented with size 15, 0.06 taper, size 20, 0.06 taper, size 25, 0.06 taper, and size 30, 0.06 taper files until the file tip protruded 1 mm beyond the WL (Table 1). In both groups, after each instrument had been used and the root canal was irrigated with 2 mL of 5.25% sodium hypochlorite solution using a plastic International Endodontic Journal, 45, 542–551, 2012 545 ProTaper Universal and ProFile Vortex González Sánchez et al. syringe with a 27-gauge closed-end needle (Hawe Max-I-probe; Hawe Neos, Bioggio, Switzerland). In both groups, each instrument was used to enlarge three canals and was then discarded. During the study, three instruments were discarded owing to surface deformation. Digital images of the major foramen (Fig. 1b) were taken post-instrumentation following an identical method to that used for the pre-instrumentation images. The major foramen was photographed after the use of each single instrument. The root canals and the major foramen were dried carefully before each photograph was taken. All photographs were transferred to Adobe Photoshop (Adobe Systems, Inc, San Jose, CA, USA) to outline the perimeter of the major foramen. Photoshop was used to transform each image to 50% transparency and to superimpose each photograph separately over its pre-instrumentation image (PoO) (López et al. 2008). Precision was achieved by marking the apical surface with indelible dye, which allowed the post-instrumentation image to be superimposed over the pre-instrumentation images (Fig. 1c). The superimposed images were transferred to AutoCAD (Autodesk Incorporated), which was used to calculate and pinpoint the centre of gravity (Paqué et al. 2005) (CG; the mean location of all the mass in a system) of each Po0 (Fig. 2). Figure 3 Definition of transportation (T = T¢ ) T¢¢) and cen- tring ability (ratio = T¢/T¢¢ or T¢¢/T¢). Representation of the two directions of measurement: MC, direction of maximum curvature (black line); VC, direction vertical to the maximum curvature (blue line). Image analysis The following parameters were used to evaluate the ability of the instruments to shape the canal: Canal transportation Transportation of the canal after instrumentation was measured in accordance with the method described by Yang et al. (2007). Transportation was calculated for the major foramen in two directions (Fig. 3): the direction of maximum curvature (MC) and the direction vertical to the maximum curvature (VC). Centring ability According to Gambill et al. (1996), the mean centring ratio indicates the ability of the instrument to stay centred in the canal. The centring ability of the instrument was calculated from the ratio of T¢/T¢¢ or T¢¢/T¢ in accordance with the method of Gambill et al. (1996). Centring ability was also calculated in two directions (Fig. 3): MC and VC. A result of ‘1’ indicates perfect centring ability. Figure 2 The superimposed images were transferred to Auto- CAD, which was used to calculate and pinpoint the centre of gravity (CG). 546 International Endodontic Journal, 45, 542–551, 2012 Shape of the major foramen The shape of the major foramen after instrumentation was measured in accordance with the method described by Marroquin et al. (2007). Two measurements of the diameter, defined as wide and narrow, were made for each major foramen. A major foramen ª 2012 International Endodontic Journal González Sánchez et al. ProTaper Universal and ProFile Vortex Table 2 Absolute values (mean ± SD) for transportation (lm) File S1 Transportation +/) S2 +/) F1 +/) F2 +/) F3 +/) V15 +/) V20 +/) V25 +/) V30 +/) Direction of 27.81 22.88 36.64 24.15 42.55 29.83 56.95 45.15 88.95 98.48 27.76 29.90 36.73 42.45 48.05 46.68 73.67 63.46 maximum curvature Direction 5.88 5.07 8.64 5.28 9.68 7.05 17.95 13.59 26.70 14.60 5.60 3.25 7.55 8.43 9.45 7.42 14.94 12.47 vertical to the maximum curvature with a difference equal to or greater than 0.02 mm between the wide and narrow diameters was defined as having an oval instead of a round shape. Analysis of data The values for canal transportation and centring ability were analysed using anova followed by post hoc least significance difference (LSD) multiple comparisons. When the anova test indicated a significant difference, the LSD multiple range test procedure was used to ascertain which means differed from the others. Significance was considered at P < 0.05. (P < 0.05) than the S1, S2 and F1 ProTaper Universal instruments and the size 15, 0.06 taper, size 20, 0.06 taper, and size 25, 0.06 taper ProFile Vortex instruments. The F3 ProTaper Universal instrument had a larger mean value for transportation in the direction of VC (P < 0.05) than the F2 ProTaper Universal instrument. The ProFile Vortex size 30, 0.06 taper instrument had a larger mean value for transportation in the directions of MC and VC (P < 0.05) than the S1 ProTaper Universal instrument and the size 15, 0.06 taper ProFile Vortex instrument. No significant differences were observed amongst the other instruments. Centring ability Results Transportation Table 2 shows the mean values for transportation after instrumentation for each file. The F3 ProTaper Universal instrument had a higher mean value for transportation in the direction of MC (P < 0.05) than the S1, S2 and F1 ProTaper Universal instruments and the size 15, 0.06 taper, size 20, 0.06 taper, and size 25, 0.06 taper ProFile Vortex instruments. The F2 and F3 ProTaper Universal instruments had a higher mean value for transportation in the direction of VC The centring ability (as expressed by the centring ratio) for each instrument in the two directions is detailed in Table 3. There were no significant differences amongst the different instruments with respect to centring ability in either direction (P > 0.05). Shape of the major foramen The S1, S2, F1, F2 and F3 ProTaper Universal files and the size 15, 0.06 taper, size 20, 0.06 taper, size 25, 0.06 taper and size 30, 0.06 taper ProFile Vortex files produced an oval foramen in 71% (10/14), 71% Table 3 Absolute values (mean ± SD) for centring ability (ratio) Centring ability File S1 +/) S2 +/) F1 +/) F2 +/) F3 +/) V15 +/) V20 +/) V25 +/) V30 +/) Direction of 0.341 0.26 0.278 0.26 0.299 0.15 0.307 0.22 0.344 0.25 0.353 0.29 0.307 0.28 0.259 0.19 0.240 0.16 maximum curvature 0.542 0.32 0.563 0.19 0.658 0.19 0.623 0.28 0.546 0.25 0.537 0.26 0.691 0.16 0.724 0.15 0.525 0.28 Direction vertical to the maximum curvature ª 2012 International Endodontic Journal International Endodontic Journal, 45, 542–551, 2012 547 ProTaper Universal and ProFile Vortex González Sánchez et al. (10/14), 85% (12/14), 85% (12/14), 71% (10/14), 71% (10/14), 85% (12/14), 85% (12/14) and 89% (8/ 9) of the cases. In five of the samples, the size 30, 0.06 taper ProFile Vortex file could not pass the major foramen. Discussion The purpose of this study was to evaluate the morphological changes in the major foramen after overinstrumentation with ProTaper Universal and ProFile Vortex rotary instruments. In general, two experimental models are used to evaluate the preparation of root canals with different instruments: (i) simulated root canals in clear resin blocks and (ii) root canals in extracted human teeth. In simulated root canals in resin, the diameter, length and angle of curvature of the root canals are standardized. However, the resin might not represent clinical conditions owing to differences in the surface texture, hardness and cross sectioning of dentine (Bertrand et al. 2001). Moreover, the heat generated by rotary instruments through friction may cause the resin to melt (Rhodes et al. 1999). Extracted teeth provide conditions that are close to the clinical situation (Schäfer & Vlassis 2004). Despite variations in the morphology of natural teeth, efforts were made in this study to ensure comparability of the experimental groups. On the basis of the initial radiographs, the two groups were balanced with respect to the angles and radii of curvature of the canals. The use of an operatordriven instrument rather than a standardized computer-driven instrument has the drawback of introducing operator bias but the advantage of simulating clinical conditions wherein an operator can compensate for the shortcomings of the instrument by modifying digital pressure (Ounsi et al. 2011). It is important to highlight that the present study investigated two types of Ni–Ti rotary instruments. Thus, the results obtained cannot be directly extrapolated to other instruments with different designs (Ounsi et al. 2011). Radiographic evaluation allows only a two-dimensional evaluation of the root canal (Sydney et al. 1991). In this study, as in others, pre- and postoperative photographs of the cross section of the root canal were evaluated, which enabled the most important parameters of root canal preparation, i.e. transportation, centring ability, cross-sectional area and the shape of the major foramen, to be assessed (Hülsmann et al. 2003). 548 International Endodontic Journal, 45, 542–551, 2012 Fourteen canals in each group were used in this study. Six instruments were used for the ProTaper group for each canal and four instruments for the Vortex group. Having used each instrument, the major foramen was measured twice to obtain the direction of maximum deformation and the direction vertical to maximum deformation. Next transportation and centring ability were analysed. Thus, 1164 measurements were obtained for the two groups, and the statistical analysis showed significant differences. For this reason, the sample was not increased. It is important to note that the standard deviations were often quite close to the mean values themselves. This variation indicates that even with the same experienced operator, the outcome is subject to considerable differences. This finding agrees with that observed by Ounsi et al. (2011), who used standardized simulated canals. Thus, having carried out a linear regression on a possible link between the angle and radius of curvature and the transportation of the major foramen (data not shown), no relationship was observed between these variables and transportation. However, it is important to note that all the canals in this study had curvatures ranging from moderate (4/ 28) to severe (24/28), in accordance with Di Fiore et al. (2006). The results might have varied if straight root canals had been used. Gonzalez Sanchez et al. (2010) observed no transportation in the majority of samples when size 08 stainless steel K-Flex files and size 10 stainless steel reamers were used as patency files. Siqueira et al. (2002) reported that using a patency file had no influence on the incidence of flare-ups, even when the file was used by inexperienced practitioners. Torabinejad et al. (1988) noted that accidental overextension of small files during determination of the WL had no significant effect on the frequency of post-endodontic pain. These studies suggest that overextension of small files does not necessarily cause post-endodontic pain (Torabinejad et al. 1988, Siqueira et al. 2002, Arias et al. 2009). It appears that the patency file is not as harmful to periapical tissues as some think (Arias et al. 2009). However, although direct evidence of the potentially negative consequences of overinstrumentation is lacking, it can be speculated that overinstrumentation, with the possible exception of the use of the smallest hand files of size 06–10 for apical patency, should be avoided for the following reasons (Haapasalo et al. 2003). First, large instruments that are passed through the major foramen can result in direct ª 2012 International Endodontic Journal González Sánchez et al. ProTaper Universal and ProFile Vortex trauma to periapical tissues (Haapasalo et al. 2003), and this could increase the incidence of postoperative pain (Siqueira 2005). Second, overinstrumentation usually precedes overfilling because overinstrumentation can destroy the apical stop (Siqueira 2001, 2005). Overextended filling materials can induce pain through mechanical compression of the periradicular tissues (Siqueira 2005). However, most of the materials that are used to fill root canals are either biocompatible or exhibit cytotoxicity only before setting (Siqueira 2001). Therefore, it is highly improbable that most modern-day endodontic materials would be able to sustain periradicular inflammation in the absence of a concomitant endodontic infection (Siqueira 2001, 2005). Third, extrusion of necrotic debris and microorganisms from the root canal into the periapical area might result in persistent infection, such as periapical actinomycosis, and this poses a potential threat to the long-term outcome of the treatment (Siqueira 2001, 2005, Haapasalo et al. 2003). Fourth, creation of an oval foramen instead of a round one might result in a poorer apical seal with a round Gutta-percha master point (complete compensation with a sealer is theoretical) (Haapasalo et al. 2003). In the present study, the rotary Ni–Ti instruments did not maintain the original position of the major foramen in general and thus produced oval preparations. In the authors¢ opinion, it is not a problem of deformation per se, but deformation that normally causes an oval-shaped major foramen, which could hinder root canal filling. The F1, F2 and F3 ProTaper Universal files and the size 20, 0.06 taper, size 25, 0.06 taper, and size 30, 0.06 taper Vortex files created an oval major foramen in 85%, 85%, 71%, 85%, 85% and 89% of cases, respectively. The warm Gutta-percha techniques could fill these oval-shaped major foramina because these procedures can fill other irregularities in the root canal (Bowman & Baumgartner 2002). However, there is no evidence to corroborate that these techniques can fill ovalshaped major foramens correctly after overinstrumentation. In the case of a poor apical seal, percolation of tissue fluids rich in glycoproteins into the root canal system can supply substrate to surviving microorganisms, which can multiply and reach sufficient numbers to induce or sustain a periradicular lesion (Siqueira 2001, 2005). Fifth, in cases of apical transportation, an increase in the size of the major foramen makes it possible for bacteria to receive nutrients from an inflammatory exudate in the periapical area (Haapasalo et al. 2003). ª 2012 International Endodontic Journal In the present study, the ProTaper Universal instruments had a tendency to cause transportation of the major foramen. The findings of this study concur with those of Yang et al. (2007), Kunert et al. (2010) and Javaheri & Javaheri (2007). However, the results of the present study cannot be compared directly with those of the above-mentioned studies, owing to the different area of the root canal under study. Previous studies examined the entire length of the canal (apical third to furcation), whereas the current research focused exclusively on the major foramen. The Glossary of Endodontic Terms of the American Association of Endodontists (2003) defines transportation as ‘the removal of canal wall structure on the outside curve in the apical half of the canal due to the tendency of files to restore themselves to their original linear shape during canal preparation’. Apical transportation may promote the harbouring of debris and residual microorganisms as a result of insufficient cleaning of the root canals. According to McSpadden (2007), less canal transportation occurs when the file that is used has greater flexibility, an asymmetrical cross-sectional design and/ or a radial land. Transportation of the major foramen after preparation with either the ProTaper or Vortex files was evident. This might be explained by the tapers of the instruments used in this study, in conjunction with the sharp cutting edges of these instruments (neither of the systems has a radial land), and the fact that neither of the systems has an asymmetrical crosssectional design (McSpadden 2007). Radial lands are especially effective in supporting the edge of the cutting angle and reducing canal transportation because they help to distribute the pressure of the blades more uniformly around the circumference of a curved canal. This is in contrast to files that lack radial lands, which concentrate all the pressure of the cutting edges on the canal wall and tend to straighten the curvature (McSpadden 2007). The size of the taper is one of the main factors involved in apical root transportation because an increase in the taper reduces instrument flexibility (Schäfer et al. 2003, McSpadden 2007). Schäfer et al. (2003) concluded from their research on the relationship between taper size and flexibility that Ni–Ti files with tapers greater than 0.04 should not be used for apical enlargement of curved canals. Conclusions In most samples, the ProTaper Universal and ProFile Vortex files resulted in transportation of the major International Endodontic Journal, 45, 542–551, 2012 549 ProTaper Universal and ProFile Vortex González Sánchez et al. foramen and created an oval major foramen after overinstrumentation of the major foramen. Disclosure There are no disclosures with possible commercial associations. References Aguiar CM, de Andrade Mendes D, Câmara AC, de Figueiredo JA (2009) Evaluation of the centreing ability of the ProTaper Universal rotary system in curved roots in comparison to Nitiflex files. Australian Endodontic Journal 35, 174–9. Arias A, Azabal M, Hidalgo JJ, de la Macorra JC (2009) Relationship between postendodontic pain, tooth diagnostic factors, and apical patency. 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