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Authors:Dr. Anil Dhingra,Dr. Saurabh,Dr. Harkanwal Kaur Bhullar.

ABSTRACT 

AIM:
The aim of the study was to compare the incidence of root cracks observed at the apical root surface and/or in the canal wall after root canal instrumentation with 3 single-file systems, WaveOne, Reciproc and OneShape versus the ProTaper Next.


MATERIAL AND METHODS:
One hundred Twenty extracted mandibular First Premolar with straight roots will select and divided into 4 groups (n=30). The root canals will be coronally flared with Gates-Glidden drills and then instrumented to the full working length with the ProTaper Next, Waveone, OneShape, Reciproc File as per manufacturers’ instruction. The apical root surface and horizontal sections from the apex will be observed under a magnification.

RESULTS:
Statistically significant difference was found [p<0.05] in group 1 [OneShape] at 2mm when compared with other three groups. And no statistically significant difference was found between all the groups at 4 and 6 mm. Therefore One Shape exhibits more number of cracks at apical 2mm when compared with Reciproc ,Protaper Next and WaveOne.
Instrumentation with rotary nickel-titanium (NiTi) instruments could potentially cause dentinal cracks, which may have the potential to develop into fractures. Cracks after canal instrumentation were detected either in horizontal sections cut at different levels along roots or at the apical root surface.1.
Recently, a new generation of NiTi files has been introduced with a variable cross-sectional design and a different working motion, which completes canal preparation with only one instrument like WaveOne, Reciproc and One Shape single file systems.4.

WAVE ONE
[Dentsply Maillefer (Ballaigues, Switzerland)] Single use, reciprocating motion, and M-Wire alloy manufacturing are the main characteristics of these instruments. Another unique design feature of the WaveOne files is they have a reverse helix and 2 distinct cross-sections along the length of their active portions. In 3 engaging/disengaging cutting cycles, the file will turn 360°, which promotes inward movement and hauling debris out of the canal.11
Reciproc files (VDW, Munich, Germany), single use in reciprocating motion are made of M-Wire NiTi alloy subjected to an innovative thermal treatment process to increase flexibility of the instrument. The Reciproc files have an S-shaped cross-section, 2 cutting blades, and a continuous taper over the first 3 mm of their working part followed by a decreasing taper until the shaft.11
OneShape files (Micro-Mega, Besanc¸ onCedex, France) are used in a traditional continuous rotation motion. They have a triangle cutting edge in the apical part, 2 cutting edges in the coronal part, and a cross-section that progressively changes from 3 to 2 cutting edges between the apical and coronal parts; this design offers an optimal cutting action.11.
PROTAPER NEXT rotary files by Dentsply Maillefer (Ballaigues, Switzerland) are made with proven M-Wire NiTi. These instruments are recommended to be used with a brushing motion, away from external root concavities, to facilitate flute unloading and apical file progression.
Thus the purpose of the present study was to compare the incidence of root cracks observed at the apical root surface and/or in the canal wall after root canal instrumentation with 3 single-file systems WaveOne ,Reciproc, OneShape with Multiple-file system, The ProTaper Next upto file X2.

MATERIAL AND METHODS:
Sixty mandibular premolars were selected.They were divided into 4 experimental groups (n = 15) the root canals were first coronally flared with Gates-Glidden drills and then Instrumented to the full working length with: OneShape [Group 1], Reciproc [Group 2], Protaper Next [Group 3] and WaveOne [Group 4]. The apical root surface and horizontal sections 2, 4, and 6 mm from the apex were observed under a microscope. The presence of cracks was noted.[Figure 1]

     
[A] [B] [C]
Figure 1: Stereomicroscopic views of coronal section at 2mm [A], 4mm [B] and 6mm[C] level from the apex.


STATISTICAL ANALYSIS
The Chi-square Test and Mann-Whitney Test was performed to compare the appearance of cracked roots between the experimental groups using SPSS 20 Software.  

RESULTS
Statistically significant difference was found [p<0.05] in group 1 [OneShape] at 2mm when compared with other three groups. And no statistically significant difference was found between all the groups at 4 and 6 mm.[Table 1]. Therefore One Shape exhibits more number of cracks at apical 2mm when compared with Reciproc, Protaper Next and WaveOne. [Graph 1].

TABLE 1: Summary Of Mean And Standard Deviation Of Presence Of Microcracks In All The Four Groups

 

GROUPS 2MM 4MM 6MM
Oneshape 1.5±0.45 2.5±.61 4.2±0.61
Reciproc 0.33±0.61 0.67±.32 1.3±0.54
Protaper NEXT 0.07±0.26 0.17±0.29 .17±0.42
WaveOne 0.27±0.59 0.47±0.62 0.47±0.35


GRAPH 1: Graphical Representation Showing the Number Of Cracks Present At The 2mm Horizontal Section From The Apical End

 

 


  DISCUSSION
The coronal flaring with #2 Gates-Glidden drills (with a 0.7-mm diameter) working in a continuous rotation motion in the coronal part of the canal did not cause cracks.
It is remarkable that Protaper Next- multiple file system used in this study caused less damage when compared with all the single file systems .This is due to its modified tip design and a brushing motion, away from external root concavities, to facilitate flute unloading and apical file progression.
It has been reported that during the instrumentation procedure, the stresses generated at 1 mm short of the AF were merely one third of the stress at more coronal levels.
The OneShape caused more root cracks than other instruments. It has been reported that during the instrumentation procedure, the stresses generated at 1 mm short of the AF were merely one third of the stress at more coronal levels. The OneShape file work in a continuous rotation motion and caused more number of cracks respectively.
WaveOne and Reciproc files work in a reciprocating movement similar to the balanced force technique and caused  less number of cracks.The reciprocating movement minimizes torsional and flexural stresses and reduces canal transportation.Furthermore, the reciprocating motion showed significantly higher resistance to cyclic fatigue.
As opposed to continuous rotation file cutting action, the Protaper Next has an off-set rectangular cross-section which causes smooth apical advancement of the file into the canal space.

CONCLUSION
Nickel-titanium instruments may cause cracks on the apical root surface or in the canal wall. The Protaper Next, WaveOne and  Reciproc files caused less cracks than OneShape files.

REFERENCES
1.Bier CAS, Shemesh H, Tanomaru-Filho M, et al.The ability of different nickeltitanium rotary instruments to induce dentinal damage during canal preparation. J Endod 2009;35:236–8.
2. Shemesh H, Bier CAS, Wu MK, et al. The effects of canal preparation and filling on the incidence of dentinal defects.IntEndod J 2009;42:208–13
3. Shemesh H, Roeleveld AC, Wesselink PR, et al. Damage to root dentin during retreatment procedures. J Endodontics 2011;37:63–6.
4. Shemesh H, Wesselink PR, Wu MK. Incidence of dentinal defects after root canal filling procedures. IntEndod J 2010;43:995–1000.
5. Yoldas O, Yilmaz S, Atakan G, et al. Dentinal microcrack formation during root canal preparations by different NiTi rotary instruments and the Self-Adjusting File. J Endod 2012;38:232–5
6. Adorno CG, Yoshioka T, Suda H. Crack initiation on the apical root surface caused by three different nickel-titanium rotary files at different working lengths. J Endod 2011;37:522–5.
7. Adorno CG, Yoshioka T, Suda H. The effect of root preparation technique and instrumentation length on the development of apical root cracks. J Endod 2009; 35:389–92.
8. Adorno CG, Yoshioka T, Suda H. The effect of working length and root canal preparation technique on crack development in the apical root canal wall.IntEndod J 2010;43:321–7.
9. Liu R, Kaiwar A, Shemesh H, et al. The incidence of apical root cracks and apical dentinal detachments after canal preparation with hand and rotary files at different  instrumentation lengths. J Endod 2013;39:129–32.
10. Wilcox LR, Roskelley C, Sutton T. The relationship of root canal enlargement to finger-spreader induced vertical root fracture. J Endod 1997;23:533–4.  

 

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