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Technology and Health Care 00 (2015) 1–9 DOI 10.3233/THC-150895 IOS Press
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Comparative study of root-canal shaping with stainless steel and rotary NiTi files performed by preclinical dental students Mothanna Alrahabi
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Department of Restorative Dental Science, College of Dentistry, Taibah University, Medina, Saudi Arabia Tel.: +966 597674522; E-mail: [email protected], [email protected]
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Abstract. OBJECTIVE: We evaluated the use of NiTi rotary and stainless steel endodontic instruments for canal shaping by undergraduate students. We also assessed the quality of root canal preparation as well as the occurrence of iatrogenic events during instrumentation. METHODS: In total, 30 third-year dental students attending Taibah University Dental College prepared 180 simulated canals in resin blocks with NiTi rotary instruments and stainless steel hand files. Superimposed images were prepared to measure the removal of material at different levels from apical termination using the GSA image analysis software. Preparation time, procedural accidents, and canal shape after preparation were analyzed using χ2 and t-tests. The statistical significance level was set at P < 0.05. RESULTS: There were significant differences in preparation time between NiTi instruments and stainless steel files; the former was associated with shorter preparation time, less ledge formation (1.1% vs. 14.4%), and greater instrument fracture (5.56% vs. 1.1%). These results indicate that NiTi rotary instruments result in better canal geometry and cause less canal transportation. CONCLUSIONS: Manual instrumentation using stainless steel files is safer than rotary instrumentation for inexperienced students. Intensive preclinical training is a prerequisite for using NiTi rotary instruments. These results prompted us to reconsider theoretical and practical coursework when teaching endodontics.
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Received 1 September 2014 Accepted 6 January 2015
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Keywords: NiTi, rotary, stainless steel, resin block, dental students, shaping, root canal, endodontics, dental education, procedural accidents
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1. Introduction
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Cleaning and shaping is an important step in root canal treatment. According to Schilder [1], the optimal canal shape should be a tapering funnel that follows the original shape and curveture of the canal, while retaining the original position of the foramen, keeping it as small as practically possible. To achieve optimal canal shaping, stainless steel instruments have long been used. The sequence of use of such instruments starts from the apical end of the canal and proceeds to the coronal part. Unfortunately, this approach does not fulfill the objectives of shaping a root canal in curved canals and can lead to iatrogenic damage to the original canal [2], such as straightening a curved canal, transportation, zipping, ledging,
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Fig. 1. Simulated root canal.
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2. Materials and methods
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2.1. Simulated canals
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and root perforations [3,4]. The main reason for this is that the stiffness of stainless steel instruments increases with increasing diameter; this is a major factor causing iatrogenic defects [5]. Recently, nickel-titanium (NiTi) instruments have been introduced for root canal shaping. NiTi alloy is a superelastic alloy that provides high flexibility within the instruments and allows one to effectively follow the original path of the root canal [6]. NiTi rotary instruments for endodontic practice have been considered revolutionary tools, as they have substantially reduced the incidence of several clinical problems including the formation of blocks or ledges, transportation, and perforation [7]. NiTi instruments are preferred over stainless steel hand files due to their ability to maintain the original curvature of the canal [8,9]. Due to the higher incidence of procedural errors while using stainless steel files, the success rate of procedures performed with them are also lower than those performed with NiTi rotary files [10, 11]. Even so, stainless steel files are still being used for practical coursework on endodontics at some universities [12]. Despite the significant benefits of using NiTi rotary instruments, there are also certain shortcomings, such as cost and their brittle nature (and thus the possibility of them fracturing), that reduce the use of these instruments among new learners [12–16]. We evaluated the use of NiTi rotary and stainless steel endodontic instruments in canal shaping by undergraduate students. We also assessed the quality of root canal preparation as well as the occurrence of iatrogenic events during instrumentation.
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This study was conducted using simulated root canals (n = 180), fabricated with clear resin blocks (Dentsply Maillefer, Ballaigues, Switzerland). The taper of the canals was 02 and they were 17 mm long (a straight coronal section of 12 mm and a curved apical section of 5 mm). The size of the canal equalled the ISO file size 15# (Fig. 1), and the curvature of the simulated root canals was 40 degrees based on the Schneider method of measuring curvature [17].
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Fig. 2. A mold used in the study.
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2.2. Photographic procedures
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To provide standardized photographs of each canal, a special mold (Fig. 2) was used to position the camera (Nikon D3200, Nikon Inc.) precisely. To improve the color contrast of photos, all canals were injected with black ink before instrumentation. In a standardized manner, a series of photographs of each canal was saved to a computer using a set protocol. The canals were reinjected using red ink postoperatively to define their outlines, and images were taken in the same standard manner. To reduce the margin of error, all photography was performed by the same operator.
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2.3. Instrumentation
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2.4. Assessment of root canal preparation
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The time taken to prepare each canal was recorded, including active instrumentation, instrument changes, and irrigation. Shaping efficiency was evaluated by measuring the amount of material lost at various levels (1 mm [D1], 2 mm [D2], 3 mm [D3], 5 mm [D5], 7 mm [D7], and 9 mm [D9]) of the root canal. Photoshop (Adobe Systems, San Jose, CA, USA) was used to superimpose pre- and post-instrumentation images in two different layers.
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The specimens were divided into two experimental groups (n = 90 each). Simulated canals in the two groups were prepared by 30 dental students at the dental college of Taibah University with no prior experience of root canal preparation. Theoretical information regarding instrumentation using manual stainless steel files and NiTi rotary instruments was provided to the students and this was followed by demonstrations of root canal preparation using stainless steel K files and the step-back technique and ProTaper instruments. Each student was provided with handouts determining the sequence of instruments to be used. Glycerin was used as a lubricant, and 2 mL tap water was used repeatedly as an irrigant after using each instrument. The groups were as follows: group 1 used stainless steel K files (Dentsply Maillefer) up to a size 30 master apical file, and group 2 used ProTaper NiTi rotary instruments (Dentsply Maillefer) up to F2 size.
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M. Alrahabi / Comparative study of root-canal shaping with stainless steel and rotary NiTi files Table 1 Mean preparation times (min ± SD) Group Rotary Ni-Ti Files Stainless steel Files
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Mean prep time 7.33 ± 0.20 17.24 ± 0.42
t = −13.063, P < 0.05.
Percent of ledge occurrence according to instrument
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The removed amount of resin in both the convex (inner) and concave (outer) region of the canal for each 1-mm step was measured using the GSA Image Analyser Software (GSA Image Analyser Software Development and Analytics Bansemer and Scheel GbR, Germany), evaluated as follows: D (difference) = Do (outer resin removed) − Di (inner resin removed).
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Fig. 3. Percent of ledge formation according to study group.
A positive value indicated a prevalence of outer while a negative result indicated a prevalence of inner resin removed. The closer the value was to zero, the more balanced was the preparation.
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2.5. Statistical analyses
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Statistical analyses were carried out using the SPSS software (ver. 20; SPSS Inc., Chicago, IL, USA). To compare results, t-tests and χ2 tests were used. Statistical significance was set at P < 0.05.
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3. Results
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3.1. Preparation time
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The mean time to prepare canals was 7.33 ± 0.20 min with NiTi rotary instruments and 17.24 ± 0.42 min with stainless steel instruments (Table 1), a significant difference between the groups (P < 0.05).
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Table 2 Average, standard deviation, minimum, and maximum of difference in canal shape (in mm) according to study group and the studied location Difference in canal shape (in mm) Studied location Type of file N Average Std. deviation Std. error Minimum Maximum D1 Rotary NiTi 90 −0.031 0.169 0.018 −0.3 0.5 Manual 90 0.064 0.327 0.034 −0.6 0.6 D2 Rotary NiTi 90 0.029 0.145 0.015 −0.24 0.5 Manual 90 0.098 0.383 0.040 −0.6 0.7 D3 Rotary NiTi 90 0.008 0.133 0.014 −0.3 0.25 Manual 90 −0.081 0.403 0.043 −0.7 0.6 D4 Rotary NiTi 90 −0.100 0.185 0.020 −0.5 0.3 Manual 90 −0.329 0.368 0.039 −0.7 0.6 D5 Rotary NiTi 90 −0.131 0.180 0.019 −0.4 0.3 Manual 90 −0.317 0.358 0.038 −0.7 0.63 D7 Rotary NiTi 90 −0.034 0.134 0.014 −0.35 0.22 Manual 90 −0.141 0.342 0.036 −0.75 0.5 D9 Rotary NiTi 90 0.073 0.124 0.013 −0.15 0.3 Manual 90 0.112 0.369 0.039 −0.9 0.7
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Percent of instrument fracture occurrence according to instrument
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Fig. 4. Percent of instrument fracture according to study group.
3.2. Procedural accidents
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We compared the shaping ability between the groups by measuring the amount of material removed from the outer and inner walls of the canal. These measurements also helped to identify canal transportation before and after preparation. The data are presented in Table 2. Statistical analysis revealed that there were no significant differences in canal shape at the D2 and D9 locations at the 95% confidence level, but there were significant differences at D1, D3, D4, D5, and D7 (in terms of both mean and absolute values), being lower in the NiTi group. Transportation of the canal was towards the inner side, as shown in Fig. 5.
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There was a significant difference in ledge formation between the groups (Fig. 3), being more common in the stainless steel group. There was also a significant difference in instrument fracture between the groups (Fig. 4); it was more common in the NiTi group.
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0.098
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0.064 0.008 -0.034
0.029 -0.031 -0.081
-0.100
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-0.329
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Mean (in mm)
Mean Values of Difference in Canal Shape (in mm) according to Studied Location and Study Group
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Fig. 5. Transportation of the canal according to study group.
4. Discussion
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We evaluated the use of NiTi rotary instruments by dental student in preclinical training in an endodontic course. Despite the multiple benefits of using NiTi rotary instruments, the step-back technique using stainless steel files is still a common teaching method in endodontic programs for undergraduate students in most Arab countries. Using simulated canals in clear resin blocks has several advantages for the assessment of root canal preparation procedures [18,19]. Thus, we used such resin blocks to evaluate the performance of students when using NiTi rotary instruments or stainless steel files for root canal preparation. The preparation time was shorter when using the NiTi instruments. This is consistent with the results of several previous studies [20–22]. The most common iatrogenic error detected in root canal therapy performed by undergraduate students using stainless steel files with the step-back technique is ledge formation [23]. Indeed, we found a high incidence of ledge formation when stainless steel files were used, consistent with several previous reports [14,24–26]. A ledge is the result of placing a non-precurved, end-cutting instrument into a curved canal and filing with too much apical pressure [27,28]. A ledge may also result when files shorter than the working length are used, blocking the canal [29]. The presence of a ledge may cause incomplete cleaning and shaping of the root canal system and this may adversely affect endodontic treatment outcomes [3,30]. Instrument fracture is another complication. In the present study, the incidence of fracture was 5.56% for NiTi rotary instruments and 1.1% for stainless steel files, consistent with a previous study [14]. However, some studies have reported no instrument fracture when junior students used NiTi rotary instruments [31,32]. Based on several reports, the incidence of fracture with rotary NiTi instruments ranges from 0.4% to 5% [33–35]. Studies conducted using NiTi rotary instruments with undergraduate students have revealed a high incidence of instrument separation: the percentage varies from 3.7% to 13.3% [14,36–38]. Instrument fractures may result from the incorrect use of NiTi rotary instruments and
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5. Conclusions
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Manual instrumentation was safer than rotary instrumentation for inexperienced students, in that instrument fracture was greater with NiTi instruments than with stainless steel files. Intensive preclinical training is a prerequisite for using NiTi rotary instruments. These results have prompted us to reconsider theoretical and practical coursework when teaching endodontics. Further clinical studies are needed to evaluate the ability of undergraduate students to use NiTi rotary instruments in root canal treatment.
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lack of experience [39,40]; experience is the most important factor influencing defect rates with NiTi instruments [41]. Our study showed the superiority of NiTi instruments in shaping ability, compared to stainless steel files, despite their use by inexperienced undergraduate students. Enlargement was towards the inner wall of the canals, and greater enlargement occurred with stainless steel files. This is consistent with the results of several studies [42–44]. NiTi rotary instruments produce less transportation than stainless steel files; this may be the result of the crown-down preparation technique, which has several advantages over the step-back technique. The high flexibility of NiTi alloys reduces the risk of canal transportation during the enlargement of curved canals [45,46].
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Journal of Endodontics, 1995. 21(3): p. 146–151. Vahid, A., N. Roohi, and F. Zayeri, A comparative study of four rotary NiTi instruments in preserving canal curvature, preparation time and change of working length. Australian Endodontic Journal, 2009. 35(2): p. 93–97. Oikonomou, I., A. Spanaki-Voreadi, and M. Georgopoulou, Procedural errors during root canal treatment performed by undergraduate students in Athens: a prospective study. Int Endod J, 2007. 40: p. 982. Bishop, K. and P. Dummer, A comparison of stainless steel Flexofiles and nickel-titanium NiTiFlex files during the shaping of simulated canals. International Endodontic Journal, 1997. 30(1): p. 25–34. Thompson, S. and P. Dummer, Shaping ability of HERO 642 rotary nickel–titanium instruments in simulated root canals: Part 2. International Endodontic Journal, 2000. 33(3): p. 255–261. Bryant, S., et al., Shaping ability of ProFile rotary nickel-titanium instruments with ISO sized tips in simulated root canals: Part 2. International Endodontic Journal, 1998. 31(4): p. 282–289. Jafarzadeh, H. and P.V. Abbott, Ledge formation: review of a great challenge in endodontics. Journal of Endodontics, 2007. 33(10): p. 1155–1162. LAMBRIANIDIS, T., Ledging and blockage of root canals during canal preparation: causes, recognition, prevention, management, and outcomes. Endodontic Topics, 2006. 15(1): p. 56–74. Nagy, C., et al., The effect of root canal morphology on canal shape following instrumentation using different techniques. International Endodontic Journal, 1997. 30(2): p. 133–140. Greene, K.J. and K.V. Krell, Clinical factors associated with ledged canals in maxillary and mandibular molars. Oral surgery, Oral Medicine, Oral Pathology, 1990. 70(4): p. 490–497. Tu, M.-G., et al., Experiences of Undergraduates Using the Ni-Ti Rotary Technique at the Beginning of the Endodontic Curriculum. Journal of Dental Sciences, 2008. 3(4): p. 199–203. Leonardi, D.P., et al., Undergraduate Students Introduction to Manual and Rotary Root Canal Instrumentation. The Bulletin of Tokyo Dental College, 2012. 53(3): p. 155–159. Pettiette, M., D. Conner, and M. Trope, Procedural errors with the use of nickel-titanium rotary instruments in undergraduate endodontics. J Endod, 2002. 28(3): p. 259. Al-Fouzan, K., Incidence of rotary ProFile instrument fracture and the potential for bypassing in vivo. International Endodontic Journal, 2003. 36(12): p. 864–867. Schäfer, E., U. Schulz-Bongert, and G. Tulus, Comparison of hand stainless steel and nickel titanium rotary instrumentation: A clinical study. Journal of Endodontics, 2004. 30(6): p. 432–435. Baumann, M.A. and A. Roth, Effect of experience on quality of canal preparation with rotary nickel-titanium files. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology, 1999. 88(6): p. 714–718. Gluskin, A., D. Brown, and L. Buchanan, A reconstructed computerized tomographic comparison of Ni–Ti rotary GTTM files versus traditional instruments in canals shaped by novice operators. International Endodontic Journal, 2001. 34(6): p. 476–484. Tu, M.-G., et al., Endodontic Shaping Performance Using Nickel–Titanium Hand and Motor ProTaper Systems by Novice Dental Students. Journal of the Formosan Medical Association, 2008. 107(5): p. 381–388. Mandel, E., et al., Rotary Ni-Ti profile systems for preparing curved canals in resin blocks: influence of operator on instrument breakage. International Endodontic Journal, 1999. 32(6): p. 436–443. Yared, G., F. Bou Dagher and P. Machtou, Failure of ProFile instruments used with high and low torque motors. International Endodontic Journal, 2001. 34(6): p. 471–475. Parashos, P. and H.H. Messer, Rotary NiTi instrument fracture and its consequences. Journal of Endodontics, 2006. 32(11): p. 1031–1043. Gergi, R., et al., Comparison of canal transportation and centering ability of twisted files, Pathfile-ProTaper system, and stainless steel hand K-files by using computed tomography. Journal of Endodontics, 2010. 36(5): p. 904–907. Stavileci, M., et al., Effects of preparation techniques on root canal shaping assessed by micro-computed tomography. Medical Science Monitor Basic Research, 2013. 19: p. 163.
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Liu, S., et al., Cleaning effectiveness and shaping ability of rotary ProTaper compared with rotary GT and manual K-Flexofile. American Journal of Dentistry, 2006. 19(6): p. 353–358. Ehsani M, Z.S., Moghadamnia AA, Mirjani J, An ex vivo study on the shaping parameters of two Ni-Ti rotary systems compared with hand instruments. Iran Endod J, 2001. 6: p. 74–79. Schäfer, E. and R. Schlingemann, Efficiency of rotary nickel–titanium K3 instruments compared with stainless steel hand K-Flexofile. Part 2. Cleaning effectiveness and shaping ability in severely curved root canals of extracted teeth. International Endodontic Journal, 2003. 36(3): p. 208–217.
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Technology and Health Care 00 (2015) 1–9 DOI 10.3233/THC-150895 IOS Press
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Comparative study of root-canal shaping with stainless steel and rotary NiTi files performed by preclinical dental students Mothanna Alrahabi
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Department of Restorative Dental Science, College of Dentistry, Taibah University, Medina, Saudi Arabia Tel.: +966 597674522; E-mail: [email protected], [email protected]
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Abstract. OBJECTIVE: We evaluated the use of NiTi rotary and stainless steel endodontic instruments for canal shaping by undergraduate students. We also assessed the quality of root canal preparation as well as the occurrence of iatrogenic events during instrumentation. METHODS: In total, 30 third-year dental students attending Taibah University Dental College prepared 180 simulated canals in resin blocks with NiTi rotary instruments and stainless steel hand files. Superimposed images were prepared to measure the removal of material at different levels from apical termination using the GSA image analysis software. Preparation time, procedural accidents, and canal shape after preparation were analyzed using χ2 and t-tests. The statistical significance level was set at P < 0.05. RESULTS: There were significant differences in preparation time between NiTi instruments and stainless steel files; the former was associated with shorter preparation time, less ledge formation (1.1% vs. 14.4%), and greater instrument fracture (5.56% vs. 1.1%). These results indicate that NiTi rotary instruments result in better canal geometry and cause less canal transportation. CONCLUSIONS: Manual instrumentation using stainless steel files is safer than rotary instrumentation for inexperienced students. Intensive preclinical training is a prerequisite for using NiTi rotary instruments. These results prompted us to reconsider theoretical and practical coursework when teaching endodontics.
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Received 1 September 2014 Accepted 6 January 2015
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Keywords: NiTi, rotary, stainless steel, resin block, dental students, shaping, root canal, endodontics, dental education, procedural accidents
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1. Introduction
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Cleaning and shaping is an important step in root canal treatment. According to Schilder [1], the optimal canal shape should be a tapering funnel that follows the original shape and curveture of the canal, while retaining the original position of the foramen, keeping it as small as practically possible. To achieve optimal canal shaping, stainless steel instruments have long been used. The sequence of use of such instruments starts from the apical end of the canal and proceeds to the coronal part. Unfortunately, this approach does not fulfill the objectives of shaping a root canal in curved canals and can lead to iatrogenic damage to the original canal [2], such as straightening a curved canal, transportation, zipping, ledging,
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Fig. 1. Simulated root canal.
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2. Materials and methods
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2.1. Simulated canals
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and root perforations [3,4]. The main reason for this is that the stiffness of stainless steel instruments increases with increasing diameter; this is a major factor causing iatrogenic defects [5]. Recently, nickel-titanium (NiTi) instruments have been introduced for root canal shaping. NiTi alloy is a superelastic alloy that provides high flexibility within the instruments and allows one to effectively follow the original path of the root canal [6]. NiTi rotary instruments for endodontic practice have been considered revolutionary tools, as they have substantially reduced the incidence of several clinical problems including the formation of blocks or ledges, transportation, and perforation [7]. NiTi instruments are preferred over stainless steel hand files due to their ability to maintain the original curvature of the canal [8,9]. Due to the higher incidence of procedural errors while using stainless steel files, the success rate of procedures performed with them are also lower than those performed with NiTi rotary files [10, 11]. Even so, stainless steel files are still being used for practical coursework on endodontics at some universities [12]. Despite the significant benefits of using NiTi rotary instruments, there are also certain shortcomings, such as cost and their brittle nature (and thus the possibility of them fracturing), that reduce the use of these instruments among new learners [12–16]. We evaluated the use of NiTi rotary and stainless steel endodontic instruments in canal shaping by undergraduate students. We also assessed the quality of root canal preparation as well as the occurrence of iatrogenic events during instrumentation.
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This study was conducted using simulated root canals (n = 180), fabricated with clear resin blocks (Dentsply Maillefer, Ballaigues, Switzerland). The taper of the canals was 02 and they were 17 mm long (a straight coronal section of 12 mm and a curved apical section of 5 mm). The size of the canal equalled the ISO file size 15# (Fig. 1), and the curvature of the simulated root canals was 40 degrees based on the Schneider method of measuring curvature [17].
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Fig. 2. A mold used in the study.
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2.2. Photographic procedures
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To provide standardized photographs of each canal, a special mold (Fig. 2) was used to position the camera (Nikon D3200, Nikon Inc.) precisely. To improve the color contrast of photos, all canals were injected with black ink before instrumentation. In a standardized manner, a series of photographs of each canal was saved to a computer using a set protocol. The canals were reinjected using red ink postoperatively to define their outlines, and images were taken in the same standard manner. To reduce the margin of error, all photography was performed by the same operator.
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2.3. Instrumentation
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2.4. Assessment of root canal preparation
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The time taken to prepare each canal was recorded, including active instrumentation, instrument changes, and irrigation. Shaping efficiency was evaluated by measuring the amount of material lost at various levels (1 mm [D1], 2 mm [D2], 3 mm [D3], 5 mm [D5], 7 mm [D7], and 9 mm [D9]) of the root canal. Photoshop (Adobe Systems, San Jose, CA, USA) was used to superimpose pre- and post-instrumentation images in two different layers.
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The specimens were divided into two experimental groups (n = 90 each). Simulated canals in the two groups were prepared by 30 dental students at the dental college of Taibah University with no prior experience of root canal preparation. Theoretical information regarding instrumentation using manual stainless steel files and NiTi rotary instruments was provided to the students and this was followed by demonstrations of root canal preparation using stainless steel K files and the step-back technique and ProTaper instruments. Each student was provided with handouts determining the sequence of instruments to be used. Glycerin was used as a lubricant, and 2 mL tap water was used repeatedly as an irrigant after using each instrument. The groups were as follows: group 1 used stainless steel K files (Dentsply Maillefer) up to a size 30 master apical file, and group 2 used ProTaper NiTi rotary instruments (Dentsply Maillefer) up to F2 size.
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M. Alrahabi / Comparative study of root-canal shaping with stainless steel and rotary NiTi files Table 1 Mean preparation times (min ± SD) Group Rotary Ni-Ti Files Stainless steel Files
n 90 90
Mean prep time 7.33 ± 0.20 17.24 ± 0.42
t = −13.063, P < 0.05.
Percent of ledge occurrence according to instrument
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The removed amount of resin in both the convex (inner) and concave (outer) region of the canal for each 1-mm step was measured using the GSA Image Analyser Software (GSA Image Analyser Software Development and Analytics Bansemer and Scheel GbR, Germany), evaluated as follows: D (difference) = Do (outer resin removed) − Di (inner resin removed).
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Fig. 3. Percent of ledge formation according to study group.
A positive value indicated a prevalence of outer while a negative result indicated a prevalence of inner resin removed. The closer the value was to zero, the more balanced was the preparation.
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2.5. Statistical analyses
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Statistical analyses were carried out using the SPSS software (ver. 20; SPSS Inc., Chicago, IL, USA). To compare results, t-tests and χ2 tests were used. Statistical significance was set at P < 0.05.
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3. Results
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3.1. Preparation time
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The mean time to prepare canals was 7.33 ± 0.20 min with NiTi rotary instruments and 17.24 ± 0.42 min with stainless steel instruments (Table 1), a significant difference between the groups (P < 0.05).
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Table 2 Average, standard deviation, minimum, and maximum of difference in canal shape (in mm) according to study group and the studied location Difference in canal shape (in mm) Studied location Type of file N Average Std. deviation Std. error Minimum Maximum D1 Rotary NiTi 90 −0.031 0.169 0.018 −0.3 0.5 Manual 90 0.064 0.327 0.034 −0.6 0.6 D2 Rotary NiTi 90 0.029 0.145 0.015 −0.24 0.5 Manual 90 0.098 0.383 0.040 −0.6 0.7 D3 Rotary NiTi 90 0.008 0.133 0.014 −0.3 0.25 Manual 90 −0.081 0.403 0.043 −0.7 0.6 D4 Rotary NiTi 90 −0.100 0.185 0.020 −0.5 0.3 Manual 90 −0.329 0.368 0.039 −0.7 0.6 D5 Rotary NiTi 90 −0.131 0.180 0.019 −0.4 0.3 Manual 90 −0.317 0.358 0.038 −0.7 0.63 D7 Rotary NiTi 90 −0.034 0.134 0.014 −0.35 0.22 Manual 90 −0.141 0.342 0.036 −0.75 0.5 D9 Rotary NiTi 90 0.073 0.124 0.013 −0.15 0.3 Manual 90 0.112 0.369 0.039 −0.9 0.7
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Fig. 4. Percent of instrument fracture according to study group.
3.2. Procedural accidents
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We compared the shaping ability between the groups by measuring the amount of material removed from the outer and inner walls of the canal. These measurements also helped to identify canal transportation before and after preparation. The data are presented in Table 2. Statistical analysis revealed that there were no significant differences in canal shape at the D2 and D9 locations at the 95% confidence level, but there were significant differences at D1, D3, D4, D5, and D7 (in terms of both mean and absolute values), being lower in the NiTi group. Transportation of the canal was towards the inner side, as shown in Fig. 5.
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There was a significant difference in ledge formation between the groups (Fig. 3), being more common in the stainless steel group. There was also a significant difference in instrument fracture between the groups (Fig. 4); it was more common in the NiTi group.
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0.098
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0.029 -0.031 -0.081
-0.100
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Mean (in mm)
Mean Values of Difference in Canal Shape (in mm) according to Studied Location and Study Group
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Fig. 5. Transportation of the canal according to study group.
4. Discussion
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We evaluated the use of NiTi rotary instruments by dental student in preclinical training in an endodontic course. Despite the multiple benefits of using NiTi rotary instruments, the step-back technique using stainless steel files is still a common teaching method in endodontic programs for undergraduate students in most Arab countries. Using simulated canals in clear resin blocks has several advantages for the assessment of root canal preparation procedures [18,19]. Thus, we used such resin blocks to evaluate the performance of students when using NiTi rotary instruments or stainless steel files for root canal preparation. The preparation time was shorter when using the NiTi instruments. This is consistent with the results of several previous studies [20–22]. The most common iatrogenic error detected in root canal therapy performed by undergraduate students using stainless steel files with the step-back technique is ledge formation [23]. Indeed, we found a high incidence of ledge formation when stainless steel files were used, consistent with several previous reports [14,24–26]. A ledge is the result of placing a non-precurved, end-cutting instrument into a curved canal and filing with too much apical pressure [27,28]. A ledge may also result when files shorter than the working length are used, blocking the canal [29]. The presence of a ledge may cause incomplete cleaning and shaping of the root canal system and this may adversely affect endodontic treatment outcomes [3,30]. Instrument fracture is another complication. In the present study, the incidence of fracture was 5.56% for NiTi rotary instruments and 1.1% for stainless steel files, consistent with a previous study [14]. However, some studies have reported no instrument fracture when junior students used NiTi rotary instruments [31,32]. Based on several reports, the incidence of fracture with rotary NiTi instruments ranges from 0.4% to 5% [33–35]. Studies conducted using NiTi rotary instruments with undergraduate students have revealed a high incidence of instrument separation: the percentage varies from 3.7% to 13.3% [14,36–38]. Instrument fractures may result from the incorrect use of NiTi rotary instruments and
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5. Conclusions
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Manual instrumentation was safer than rotary instrumentation for inexperienced students, in that instrument fracture was greater with NiTi instruments than with stainless steel files. Intensive preclinical training is a prerequisite for using NiTi rotary instruments. These results have prompted us to reconsider theoretical and practical coursework when teaching endodontics. Further clinical studies are needed to evaluate the ability of undergraduate students to use NiTi rotary instruments in root canal treatment.
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Buchanan, A reconstructed computerized tomographic comparison of Ni–Ti rotary GTTM files versus traditional instruments in canals shaped by novice operators. International Endodontic Journal, 2001. 34(6): p. 476–484. Tu, M.-G., et al., Endodontic Shaping Performance Using Nickel–Titanium Hand and Motor ProTaper Systems by Novice Dental Students. Journal of the Formosan Medical Association, 2008. 107(5): p. 381–388. Mandel, E., et al., Rotary Ni-Ti profile systems for preparing curved canals in resin blocks: influence of operator on instrument breakage. International Endodontic Journal, 1999. 32(6): p. 436–443. Yared, G., F. Bou Dagher and P. Machtou, Failure of ProFile instruments used with high and low torque motors. International Endodontic Journal, 2001. 34(6): p. 471–475. Parashos, P. and H.H. Messer, Rotary NiTi instrument fracture and its consequences. Journal of Endodontics, 2006. 32(11): p. 1031–1043. 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