Year : 2009 | Volume
: 20 | Issue : 4 | Page : 400--403
Canal-centring ability of three rotary file systems in simulated curved canals: A comparative study
Zohreh Khalilak1, Kaveh Alavi2, Nahid Mohammad Zadeh Akhlaghi1, Payman Mehrvarzfar1, Bahareh Dadresanfar1,
1 Department of Endodontics, Dental School, Islamic Azad University, Tehran, Iran
2 Medical School, Iran University of Medical Sciences, Tehran, Iran
Department of Endodontics, Dental School, Islamic Azad University, Tehran
Objective: To compare the canal-centring ability of M two , ProFile and RaCe rotary files, in simulated curved canals.
Materials and Methods: About 30 simulated canals were prepared by M two , ProFile and RaCe rotary files. Pre and post-operative pictures were super-imposed and transportations recorded. Measurements were carried out at five different points: Canal orifice (O); half-way to the orifice in the straight section (HO); the beginning of the curve (BC); the apex of the curve (AC); the end point (EP). Intra- and inter-group comparisons were carried out by Wilcoxon`s signed ranks test and Kruskal-Wallis test respectively, using SPSS 14.0 software.
Results: ProFile did not change canal centricity in any point. RaCe kept centricity at HO, BC, AC and EP. M two changed canal centricity in points BC, AC and EP. M two group kept the centricity significantly less than the other two groups at BC (P = 0.004), AC (P = 0.015) and EP (P = 0.01). There was no significant difference between these three rotary files at HO. However, the difference between RaCe, M two and ProFile was significant at O (P = 0.015).
Conclusion: ProFile and RaCe rotary files remained better centred than M two rotary files
|How to cite this article:|
Khalilak Z, Alavi K, Akhlaghi NM, Mehrvarzfar P, Dadresanfar B. Canal-centring ability of three rotary file systems in simulated curved canals: A comparative study.Indian J Dent Res 2009;20:400-403
|How to cite this URL:|
Khalilak Z, Alavi K, Akhlaghi NM, Mehrvarzfar P, Dadresanfar B. Canal-centring ability of three rotary file systems in simulated curved canals: A comparative study. Indian J Dent Res [serial online] 2009 [cited 2020 Sep 22 ];20:400-403
Available from: http://www.ijdr.in/text.asp?2009/20/4/400/59430
Root canal cleaning and shaping are important phases in endodontic therapy. The objectives of instrumentation include debriding the root canal system, continuously tapering in a conical form, and maintaining the original shape and position of the apical foramen. However, ledge formation, transportation of apical foramen, and non-tapered hourglass-shaped preparation are problems frequently observed after instrumentation in curved root canals.  Cimis et al.  reported that 46% of curved canals exhibited various degrees of apical transportation following instrumentation. To overcome these inconveniences, Nickel-Titanium (Ni-Ti) rotary-shaping techniques were developed more than a decade ago.  They are supposed to be able to maintain the original canal shape without creating severe irregularities such as zip, ledge, or perforation, particularly in narrow curved canals, because of their super-elastic behavior and shape-memory property. 
M two is a rotary file that has two cutting edges which form long, almost vertical spirals, ensuring better control of instrument progression. The backs of the cutting edges are sharp to optimize cutting efficiency and facilitate advancement of the instrument in the canal. M two has maximum space for removal of dentin and minimum radial contact. The core width is designed for maximum flexibility without compromising the instrument strength. The distance between the blades increases from the tip of the file towards the shaft; the pitch is progressive and the space for dentin removal is deeper at the back of the blade, helping to reduce blockage and the accumulation of dentin chips. This increases safety of use. The progressive pitch allows the instrument to proceed towards the apical area safely whilst working more efficiently in the coronal third. 
A number of articles have reported on the shaping ability of ProFile ,,,, and RaCe rotary systems,  whilst to date there is limited published research on the use of M two instruments. However, Schafer et al.  recently showed that M two instruments prepared curved canals with minimal transportation.
The purpose of this study was to compare the ability of the M two rotary root canal files with the ability of ProFile and RaCe rotary file systems to maintain the original canal centre shape of simulated curved canals.
Materials and Methods
A total of 30 resin blocks (Dentsply-Maillefer, Ballaigues, Switzerland) with simulated curved canals of 45 degrees were used in this experimental study. Pre-operative canals were stained with India ink to obtain a clear image of the canal. Three landmarks were made with a round bur in the resin blocks from sidewall to near the inner and outer curve of the canal without penetrating into the canal. These landmarks ensured a precise matching of pre and post-operative images. Pre-operative images of resin blocks in a fixed position were prepared using CanoScan 4200 F (Canon, Tokyo, Japan). The blocks were randomly divided into three groups of 10 each: Group 1 was instrumented with ProFile of .06 and .04 taper (Dentsply-Maillefer, Ballaigues, Switzerland), group 2 with RaCe (FKG, LaChaux- DeFonds, Switzerland) and group 3 with M two (VDW, Munich, Germany). The working length was established with an ISO size 10 file.
Group 1 (ProFile rotary instruments)
Group 1 was instrumented in a crown-down manner as recommended by the manufacturer, with the ProFile 0.06 and 0.04 taper instruments.  Coronal portion of the canal was first instrumented with files number 40.06 and 30.06. Then, files number 25.06 and 20.06 were used two-thirds to three-quarters of the way down the canal. Apical preparation was completed by using file number 25.04 to the full working length.
Group 2 (RaCe rotary file system)
Group 2 was also instrumented in a crown-down manner as recommended by the manufacturer.  Coronal portion of canal was instrumented with files number 40.10, 35.08 and 30.06. Then file number 25.04 was used to prepare the middle portion of the canal. Apical preparation was completed by using file number 25.02 to the full working length.
Group 3 (M two rotary file system)
A.11 taper was used in instrumentation of coronal portion of the canal. The middle third of the canal was prepared using file number 20.06. The files number 15.05 and 25.06 were used to prepare the terminal part of the canal. 
All canals were prepared by the same operator with a hand piece powered by an electric motor control (Endo IT, VDW, Munich, Germany). Upper canal space was filled with Rc-Prep (Stone Pharmaceuticals, Philadelphia, PA) as a lubricant before the use of each instrument. Copious irrigation with saline was performed after the use of each file using a disposable syringe and 27 gauge irrigation needles. Each instrument was used five times before being replaced.
Each block was then scanned in the previous fixed position. Superimposition of pre-and post-operative specimens was aided by holes placed in the sides of the resin blocks [Figure 1]. The superimposed pre-and post-instrumentation stored images were analyzed using the Adobe Photoshop 8 software which magnified the canal images 10 times. Measurements in millimeter were carried out at five different points: At the canal orifice (O); half-way to the orifice in the straight section (HO); the beginning of the curve (BC); the apex of the curve (AC); the end point (EP) [Figure 2]. The increase in canal width due to the instrumentation process was recorded on both the inner and outer sides of the original canal.
Intra- and inter-group comparisons were carried out by Wilcoxon`s signed ranks test and Kruskal-Wallis test respectively, using SPSS 14.0 software. Alpha (á) was set at 0.05 and P less than á was considered statistically significant.
The results are summarized in [Table 1] and [Table 2] and [Figure 3],[Figure 4],[Figure 5],[Figure 6]. Group 1(ProFile) did not change canal centricity in any measured point. Group 2 (RaCe) remained centered at HO, BC, AC and EP. Group 3 (M two ) changed canal centricity in points EP, AC and BC. Group 3 (M two ) was significantly less centered than the other two groups at EP (P is equal to 0.01), AC (P is equal to 0.015) and BC (P is equal to 0.004). There was no significant difference between these three rotary files at HO. However, the difference between RaCe, M two and ProFile was significant at O (P is equal to 0.015).
During instrumentation of curved root canals it is important to maintain the original canal curvature and eliminate the tendency for straightening which can compromise the integrity of the canal; especially at the apex. 
To assess instrumentation of curved canals, clear casting resin blocks were used in this study. These were chosen because the shape, size, taper and curvature of the canal are standardized.  Although the use of simulated canals in resin blocks may not always reflect the action of the instruments in root canals of natural teeth, , it seems to be a simple and useful method for the comparison of the shaping ability of different file systems.
Resin blocks with 45-degree curvature were chosen for this study, because transportation occurs more frequently in canals with acute curves. 
The Ni-Ti files used in the present study were designed to improve various aspects of the properties required for canal preparation instruments, including less canal transportation, intra-canal separations, and procedural steps. ,,
All simulated canals were prepared by the crown-down technique recommended by the manufacturers. The advantage of using a crown-down technique is two-fold. First, initial preparation of this section of the root canal system helps to reduce the number of microorganisms that may be forced into the periapical tissues. Second, early flaring of the coronal part of the preparation may make control of the file easier during preparation of the apical third of the canal. 
A final apical file size of number 25 was chosen because; preparation to size 25 is exceptionally safe in all canals. 
The model used in this study; as was described by Calberson et al.,  allows an analysis of instrumentation in both the inside and outside walls of the canal at five points that is more accurate than comparing pre- and post-instrumentation file positions. Any amount of apical transportation can be identified and evaluated. Here, it was only used to evaluate one aspect of the root canals, but it is also conceivable to perform the experiment with views from various different angles. This is of interest, because root canal curvature does not exist in only one plane.
ProFile instruments remained centered at the all five points. This finding is consistent with the findings of Al-Sudani and Al-Shahrani.  They compared the centring ability of ProFile, K3 and RaCe and concluded that ProFile system remained centred to a greater degree than the other two techniques. These positive characteristics are presumably a reflection of the increased taper of the instruments combined with their planning action during rotation which tend to produce a conical preparation with smooth canal walls. In this study, fracture of instruments occurred in one case in the ProFile group.
RaCe rotary files remained centred at HO, BC, AC and EP. RaCe files transported the canal away from the original axis only at the canal orifice. RaCe files possess a simple triangular cross-sectional shape with alternating cutting edges. Youshimine et al.  suggested that Ni-Ti file systems including less tapered, more flexible instruments like RaCe should be used in the apical preparation of canals with a complicated curvature. Separation of an instrument occurred two times in the RaCe group.
M two rotary files remained centred only at the canal orifice and half-way to the orifice. In contrast with present study, Schafer et al.  demonstrated that canals prepared with M two instruments remained better centred compared with those enlarged with RaCe instruments. None of the M two instruments fractured during preparation. An explanation for the difference between instruments cannot be given with certainty but, again, it may relate to the difference in sizing, subtle differences in design characteristics and production techniques or a variation in the properties of the metals used to create the wire blanks. Schafer et al.  have indicated that the correlation between the bending properties and cross-sectional surface areas of different Ni-Ti rotary instruments are highly significant.
Under the conditions of this study, ProFile and RaCe rotary files remain better centered than M two rotary files in simulated curved canals. However, further research is suggested.
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