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ORIGINAL RESEARCH Table of Contents   
Year : 2009  |  Volume : 20  |  Issue : 3  |  Page : 268-270
Cleaning and shaping curved root canals: Mtwo® vs ProTaper® instruments, a lab comparison


1 Department of Endodontics, Kerman Oral and Dental Diseases Research Center, Kerman University of Medical Sciences, Kerman, Iran
2 School of Dentistry, The University of Queensland, Brisbane, Australia

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Date of Submission21-Dec-2008
Date of Decision28-Apr-2009
Date of Acceptance03-May-2009
Date of Web Publication30-Oct-2009
 

   Abstract 

Objectives: The purpose of this study was to compare root canal preparation in curved canals in molar teeth with the rotary NiTi Mtwo and ProTaper systems in terms of canal shape and smear layer.
Materials and Methods: Mesiobuccal canals of 60 molar teeth with angles of curvature between 25 and 35 degrees were prepared with a torque controlled low speed engine; 30 canals for each system. Each individual instrument was used to prepare four root canals and the time required for preparation was recorded. Standardized radiographs were taken before and following instrumentation and used to determine changes in canal curvature.
Results: There was no significant difference in preparation time between the two systems. No instruments separated during use. The Mtwo system gave a statistically smaller change in canal curvature and thus was better for maintaining the original shape of the root canal, with less transportation (P less than 0.05). The greatest difference was seen for maxillary molar teeth. When prepared root canals were examined by SEM there was no difference between the two systems at the coronal, middle or apical thirds.
Conclusion: Overall, the results of this study suggest that Mtwo instruments are preferable for situations where canals are curved, particularly for maxillary molars.

Keywords: Nickel-titanium files, Mtwo, ProTaper, rotary endodontics, smear layer

How to cite this article:
Kuzekanani M, Walsh LJ, Yousefi MA. Cleaning and shaping curved root canals: Mtwo® vs ProTaper® instruments, a lab comparison. Indian J Dent Res 2009;20:268-70

How to cite this URL:
Kuzekanani M, Walsh LJ, Yousefi MA. Cleaning and shaping curved root canals: Mtwo® vs ProTaper® instruments, a lab comparison. Indian J Dent Res [serial online] 2009 [cited 2019 Apr 25];20:268-70. Available from: http://www.ijdr.in/text.asp?2009/20/3/268/57355
Over the past decade, rotary nickel-titanium (NiTi) instruments have become widely used in endodontics. These super-elastic instruments offer benefits over hand instrumentation for preparing curved root canals, including less transportation of the canal and reduced operating time. [1],[2],[3],[4],[5] In contemporary clinical practice most systems with rotary NiTi instruments follow a "crown down" philosophy. [6] This reduces friction between instruments and root canal walls minimizing the risk of instrument separation during use.

Recently, a new instrument design has been introduced (Mtwo; , VDW, Munich, Germany). These instruments have an S-shaped cross sectional design with a non-cutting tip. The two cutting edges have a positive rake angle to cut dentine effectively. Moreover, the pitch length increases from the tip to the shaft. This design is claimed to eliminate threading and binding in continuous rotation, and to reduce transportation of debris towards the apex.

The basic series of Mtwo instruments includes eight instruments, with tapers ranging between 0.04 and 0.07, and sizes from ISO 10 to 40. The manufacturers claim that a crown down instrumentation sequence is no longer required, since each instrument creates a glide path to the apex for the following instrument, and is used to the full working length to shape the entire length of the canal.

The cross-sectional design of ProTaper rotary NiTi instruments (Densply, Maillefer, Ballaigues, Switzerland) resembles that of a reamer with three machined cutting edges and a convex core. As with the Mtwo, the ProTaper design has positive rake angles, no radial lands, a progressive blade pitch in the apical-coronal direction and a non-cutting tip. [7]

The ability of rotary NiTi instruments to remove dentine and soft tissue pulpal debris during shaping is related to design features of the instrument, particularly the cross-sectional profile and the flutes. [8] The purpose of this study was to compare the shaping ability and cleaning effectiveness of the Mtwo and ProTaper systems, in curved mesiobuccal canals in human permanent molar teeth.


   Materials and Methods Top


A total of 60 extracted human mandibular and maxillary molar teeth with at least one curved mesiobuccal root canal were used. Coronal access was achieved using diamond burs, and the canals assessed for apical patency using an ISO 10 file. Only teeth with intact root apices and a root canal width of ISO 15 in the apical third region were used.

The teeth were embedded in acrylic resin and radiographed with an ISO 15 K file in the curved canal. The same exposure parameters (0.12 sec; 70 kV, 7 mA) were used for all teeth. Using the radiographs, the degree and radius of root canal curvature were determined. Only teeth whose radii of curvature ranged between four and nine mm, and whose angles of curvature ranged between 25 and 35 degrees were included. The selected teeth were then divided randomly into two experimental groups of 30 each, each of which had equal numbers of mandibular and maxillary molars (15 per sub-group).

In the first group, the Mtwo system was used in the selected curved canal, according to the manufacturer's instructions. The instrumentation sequence employed six files, as follows: 0.04 taper ISO 10, 0.05 taper ISO 15, 0.06 taper ISO 20, 0.06 taper ISO 25, 0.05 taper ISO 30, and 0.04 taper ISO 35. All six instruments were used to the full length of the canals, employing a cyclical in-out motion. At the point where the instrument rotated freely in the end of canal, it was removed. Irrigation was performed after each instrument change, with 2.5% NaOCl and 17% EDTA solutions. Each individual instrument was used to prepare four root canals.

In the second group, the selected curved root canal was instrumented using the ProTaper system in a crown down fashion with five instruments in the following sequence: SX at two thirds of the working length (WL); S1 at 1 mm short of the WL, F1 at the WL, F2 at the WL, and F3 at the WL. [8],[9],[10],[11] The same cyclical in-out motion and irrigation protocol was used as with Mtwo instruments. Individual ProTaper instruments were used to prepare four root canals.

The time required for canal preparation was recorded. Means and standard deviations were calculated separately for mandibular and maxillary molars in each of the two treatment groups and differences in preparation time assessed using analysis of variance.

Post treatment radiographs were taken, with the final instrument placed inside the canal, and used to determine the degree of curvature after root canal preparation. As before, means and standard deviations were calculated separately for mandibular and maxillary molars in each of the two treatment groups and differences between groups assessed using analysis of variance and Tukey-Kramer multiple comparisons post-hoc tests.

For SEM examination, crowns of the teeth were removed at the cemento enamel junction, and the selected root removed. To facilitate separation of these roots into halves, they were grooved longitudinally on their external surfaces using a diamond disc and then split using a hammer and chisel. The split roots were then dehydrated in graded ethanol solutions, critical point dried and attached to coded stubs, sputter coated with gold, and examined at 1500X magnification. Images were recorded of the apical, middle and coronal thirds of the prepared root canals.


   Results Top


The various experimental groups were well matched at baseline with no significant difference between any of the four subgroups in terms of canal curvature [Table 1]. No instruments fractured during use. There was no significant difference in preparation time between the two systems, or between maxillary and molar teeth.

Following canal preparation, there was a significant difference in curvature between the four groups (P less than 0.05), with a particularly marked difference in maxillary canals between the Mtwo and ProTaper systems (P less than 0.05). There was a significant difference between mandibular and maxillary canals in the ProTaper system (P less than 0.05), but not in the Mtwo system.

Taking data from individual roots and comparing the changes in curvature during treatment[Table 1] there was once again a significant difference in curvature between the four groups (P less than 0.0001), with a marked difference in maxillary canals between the Mtwo and ProTaper systems (P is equal to 0.001). Maxillary canals prepared with the ProTaper system showed the largest change in curvature of all four groups. There was a significant difference between mandibular and maxillary canals in both the ProTaper system (P less than 0.01), as well as in the Mtwo system (P less than 0.05).

SEM analysis of the root canals showed no differences between groups. Clean dentine surfaces were seen in the coronal and middle thirds, but smear layer and debris remained in the apical third of the root canal with both systems.


   Discussion Top


The results of this study suggest that Mtwo rotary NiTi instruments can prepare root canals in curved roots with significantly less transportation than ProTaper instruments. This difference is particularly apparent in maxillary molars. There was no significant difference between the two systems in terms of the time taken to prepare a canal, even though the techniques differed (Five vs. six instruments in sequence). Likewise, there were no differences in terms of instrument separation during use, and no differences in terms of debridement of the canal at various levels, at the scanning electron microscope level. The finding that coronal and middle third root canal walls are clean following the use of either Mtwo or ProTaper instruments is consistent with other studies, [9] as is the observation that neither system could give clean dentine surfaces free from smear layer and debris in the apical third.

With regard to differences between rotary NiTi instrument systems the better performance of Mtwo files, in terms of less canal transportation, has been noted in other studies which have compared Mtwo and K3 or RaCe files. [5] A previous comparative laboratory study involving Mtwo, ProTaper and K3 instruments [12] showed that Mtwo and K3 instruments gave the least canal changes in canal shape, although there was not a significant difference in transportation or taper between the three systems in that investigation. Another recent study which quantified changes in canal shape noted that ProTaper instruments transport the canal shape more than Hero642 and RaCe instruments and suggested that the ProTaper system should be used in combination with other systems when preparing curved canals. [13] In previous studies, using Mtwo and ProTaper files, instrument separation has been noted at modest frequency (10-20%), [12] unlike the present study where no instrument separation occurred. This may reflect the gentle technique used, and the lack of strong apical forces. Although in this study the Mtwo files were only used to prepare four root canals, recent studies have suggested that these same instruments could be used up to 10 times inside oval canals as long as a light brushing action is employed. [14],[15]


   Conclusion Top


On the basis of the positive results of this study, Mtwo rotary instruments appear useful for cleaning and shaping curved root canal systems, particularly in maxillary molar teeth.

 
   References Top

1.Hulsmann M, Peters OA, Dummer PM. Mechanical preparation of root canals: Shaping goals, techniques and means. Endodont Top 2005;10:30-76.  Back to cited text no. 1      
2.Kum KY, Spangberg I, Chab Y. Shaping ability of 3 profile rotary instrumentation techniques in simulated resin root canals. J Endod 2000;26:719-23.  Back to cited text no. 2      
3.Schafer E, Vlassi M. Comparative investigation of 2 rotary nickel titanium instruments: Protaper versus RaCe: Part 1: Shaping ability in simulated curved canals. Int Endod J 2004;37:229-38.  Back to cited text no. 3      
4.Schafer E, Erler M, Dammaschke T. Comparative study of the shaping ability and cleaning efficiency of rotary Mtwo instruments: Part 1: Shaping ability in simulated curved canals. Int Endood J 2006;39: 196-202.  Back to cited text no. 4      
5.Schafer E, Erler M, Damaschke T. Comparative study of the shaping ability and cleaning efficiency of rotary Mtwo instruments: Part2: Cleaning effectiveness and shaping ability in severely curved root canals of extracted teeth. Int Endod J 2006;39:203-12.  Back to cited text no. 5      
6.Peters OA. Current challenges and concepts in the preparation of root canal systems: A review. J Endod 2004;30:559-71.  Back to cited text no. 6  [PUBMED]  [FULLTEXT]  
7.Berutti E, Chiandussi G, Gaviglio I, Ibba A. Comparative analysis of torsional and bending stresses in two mathematical models of nickel-titanium rotary instruments: Protaper versus Profile. J Endod 2003;29:9-15.  Back to cited text no. 7      
8.Gambarini G, Lasakiewics J. A scanning electron microscopic study of debris and smear layer remaining following GT rotary instruments. Int Endod J 2002;35:422-7.  Back to cited text no. 8      
9.Foschi F, Nucci C, Montebugnoli L. SEM evaluation of canal wall dentine following use of Mtwo and Protaper NiTi rotary instruments. Int Endod J 2004;37:832-9.  Back to cited text no. 9      
10.Veltri M, Mollo A, Mantovani P. A comparative study of Endoflare Hero shaper and Mtwo NiTi instruments in the preparation of curved root canals. Int Endod J 2005;38:610-6.  Back to cited text no. 10      
11.Schafer E. Roentgenographic investi gation of frequency and degree of canal curvatures in human permanent teeth J Endod 2002;28:211-5.  Back to cited text no. 11      
12.Sonntag D, Kook K. Root canal preparation with NiTi systems K3, Mtwo and Protaper. Aust Endod J 2007;33:73-81.  Back to cited text no. 12      
13.Javaheri H, Javaheri GH. A comparison of three NiTi rotary instruments in apical transportation. J Endod 2007;33:284-6.  Back to cited text no. 13      
14.Burklein S, Schafer E. The influence of various automated devices on the shaping ability of Mtwo rotary nickel titanium instruments. Int Endod J 2006;39:945-51.  Back to cited text no. 14      
15.Plotino G, Grande NM. Influence of a brushing working motion on the fatigue life of NiTi rotary instruments. Int Endod J 2007;40:45-51.  Back to cited text no. 15      

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Correspondence Address:
Maryam Kuzekanani
Department of Endodontics, Kerman Oral and Dental Diseases Research Center, Kerman University of Medical Sciences, Kerman
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.57355

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