Introduction
The mechanical and biological goals of root canal treatment are the cleaning and shaping of the root canal system. It consists of eradicating residual vital and non-vital pulp tissue and reducing the number of pathogenic organisms, disorganizing the bacterial biofilm, facilitating canal disinfection through irrigation, and giving a suitable conformation for subsequent sealing.1
The Smear layer is a surface film of 1 to 2 μm thickness that contains dentin debris, residual pulp tissue and, bacteria that remain on the dentinal walls following mechanical instrumentation of the root canal. Rotary nickel-titanium instruments (RNT) represent a comparatively new approach to rapid and simplified canal preparation with a uniform taper.2
Protaper Gold instruments have the same geometry as that of Protaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) but offer increased flexibility.3 Mtwo (VDW, Munich, Germany) instruments have an S-shaped cross-sectional design with a non-cutting tip. The two cutting edges have a positive rake angle to chop dentine effectively. The pitch length in Mtwo increases from the tip to the shaft. This design is claimed to eliminate threading and binding in continuous rotation and scale back debris transportation towards the apex. 4 Hyflex EDM, a new generation file system with continuous rotation motion, is manufactured by EDM technique (electro-discharge machining). 5, 6 Scanning electron microscopic images are visualized at higher magnification. The basic principle of working in SEM is that a beam scans the surface of the sample to supply a spread of signals and is collected by a detector. It proved to be a valuable method in the comparison of the volume of debris and Smear layer remnants on the root canal wall after preparation with different instruments. 7
Aim
This study aims to evaluate the Smear layer generated by three rotary instrumentation techniques.
Materials and Methods
Sample selection
30 Single-rooted teeth that, were extracted due to orthodontic and periodontal reasons were collected
Inclusion criteria
Human teeth with single, straight root, single canal and, mature apical foramen that comes under Vertucci class I.
Exclusion criteria
Teeth with caries, cracks, open apices, calcified canals and, other Vertucci classes except class I.
Methodology
Preoperative radiographs of each tooth were taken and they were decoronated standardized to 15mm. A number 10-K file was inserted into all the canals until it could be seen at the apical foramen. The working length was set at 1mm below the apical foramen.
Grouping
The 30 root samples were randomly divided into 3 groups.
Group 1: Cleaning and shaping did with Protaper gold.
Group 2: Cleaning and shaping did with VDW Mtwo.
Group 3: Cleaning and shaping did with HYflex EDM.
Cleaning and shaping
Root canals were initially flooded with 5.25% sodium hypochlorite for each group and shaping was performed with each file system till full sequence for Protaper gold SX - F3. For VDW Mtwo 10 - 25. For HyFlex EDM 10/.05 Glidepath File, 25/~ Hyflex OneFile. The final irrigation protocol was performed by continuous delivery of solutions for 1min each as follows, 5ml of 17% EDTA solution, 5ml of 5.25% NaOCl followed by 5ml of distilled water.
Scanning electron microscopic evaluation
To prevent penetration of debris in the root canal during sectioning, the canal orifices were plugged with cotton pellets and cavit. Teeth were then split for scanning electron microscopy evaluation. One half of each sectioned specimen was used for evaluation and the other half was discarded. Specimens were air-dried and sputter-coated with a gold-palladium layer and observed under a scanning electron microscope. Images were taken at 1, 3 and, 5mm from apex at 1000x magnification.
Results
Table 1
Comparison of 1mm, 3mm, and 5mm in group 1 (Protapergold) with Smear layer generation by Friedman’s ANOVA.
|
Groups at |
Mean |
SD |
SE |
Mean rank |
|
1mm |
3.40 |
0.70 |
0.22 |
1.70 |
|
3mm |
3.60 |
0.84 |
0.27 |
2.05 |
|
5mm |
4.20 |
0.63 |
0.20 |
2.25 |
|
ANOVA Chi Sqr. |
2.2142 |
|||
|
P-value |
0.3350 |
|||
Table 2
Comparison of 1mm, 3mm, and 5mm in group 2 (VDW Mtwo) with Smear layer generation by Friedman’s ANOVA.
|
Groups at |
Mean |
SD |
SE |
Mean rank |
|
1mm |
1.50 |
0.53 |
0.17 |
1.75 |
|
3mm |
1.60 |
0.52 |
0.16 |
1.90 |
|
5mm |
1.90 |
0.32 |
0.10 |
2.35 |
|
ANOVA Chi Sqr. |
4.3333 |
|||
|
P-value |
0.1145 |
|||
Table 3
Comparison of 1mm, 3mm, and 5mm in group 3 (Hyflex EDM) with Smear layer generation by Friedman’s ANOVA.
|
Groups at |
Mean |
SD |
SE |
Mean rank |
|
1mm |
2.80 |
0.63 |
0.20 |
1.45 |
|
3mm |
3.00 |
0.67 |
0.21 |
1.80 |
|
5mm |
3.70 |
0.48 |
0.15 |
2.75 |
|
ANOVA Chi Sqr. |
11.3125 |
|||
|
P-value |
0.0035 |
|||
Figure 1
Show’s that Group 1 (Protapergold) generated a high Smear layer compared to Group 2 Hyflex EDM that generated a moderate Smear layer and Group 3 that showed the least Smear layer values.
Discussion
The Currently used methods of instrumentation, especially rotary instrumentation techniques, produce a Smear layer that covers root canal walls and thus the openings to the dentinal tubules. The Smear layer consists of an organic and inorganic substance that includes fragments of the odontoblastic processes, microorganisms, and necrotic material. 8 The Smear layer interferes with the adhesion or penetration of sealer in a root canal system and may prevent the penetration of gutta-percha. Smear layer removal increases the adhesion of sealer to dentin. 9
Preoperative radiographs were taken to detect calcified or large canals and were discarded from the study. Working lengths were established at -1 mm from the foramen in all samples to standardize. The new Hyflex EDM Files, which is also a successor of Hyflex CM nickel-titanium files have completely new properties and fewer files due to their innovative manufacturing process using electric discharge machining. As a result of the EDM process, the file is extremely flexible and with variable cross-section design (Quadratic at the tip, trapezoidal in middle and triangular cross-section at top) contributes to high breakage resistance and also controls the memory of the material. 10
In this study Protaper gold (Group I), showed the highest amount of Smear layer. Protaper gold has a modified triangular cross-section presenting no active cutting edge with a neutral rake angle. A positive rake angle permits the instrument to cut more aggressively whereas a negative or a neutral rake angle will just grind the root canal wall and instruments with fixed taper aloe dentin chips to accumulate in the coronal part of the file and have a screw-in effect. The greater taper of 0.09 is the reason for increased Smear layer formation. 11
The use of Mtwo files showed significantly less Smear layer formation in all three canal areas compared to HyFlex EDM and ProTaper instruments. This difference in cleanliness between the rotary nickel-titanium files could be attributed to their cross-sectional design. Mtwo files are characterized by a positive rake angle with two sharp cutting edges and have a smaller cross-sectional area which increases its flexibility and a greater chip space allowing increased debris clearance. Also, increasing helical pitch from tip to shaft reduces the transportation and the accumulation of debris towards the apex. 2
Conclusion
Within the limitations of this study, it can be concluded that VDW Mtwo (Group 2) showed better results compared to Protaper gold and Hyflex EDM file systems which showed high levels of Smear layer.
