| Abstract|| |
Aim: To use Atomic Force Microscope and Energy Dispersive X-ray Spectroscopy to evaluate the effect of 5% NaOCl, 17% EDTA and triphala on ProTaper and iRaCe rotary Ni-Ti instruments.
Methodology: A total of eight Ni-Ti rotary files, four files each of ProTaper - S2 (Dentsply) and iRaCe - R3 (FKG DENTAIRE) were used. Three out of four files each from ProTaper and iRaCe were immersed in 5% NaOCl, 17% EDTA and Triphala separately for five minutes. The Roughness average (Ra), Root Mean Square (RMS) and Mean Height of Roughness Profile Elements (Rc) of the scanned profiles were then recorded using AFM and the elemental composition was evaluated with EDS. Data were analyzed by Student's t test, One Way ANOVA and Duncan's Multiple Range Test.
Results: Topographic irregularities at the nanometric scale were observed for all files. Files immersed in EDTA and NaOCl showed highly significant surface roughness than untreated files.
Conclusion: Short-term contact with 17% EDTA and 5% NaOCl can cause significant surface deterioration of ProTaper and iRaCe rotary NiTi files. AFM proves to be a suitable method for evaluating the instrument surface.
Keywords: Atomic force microscopy; energy dispersive X-ray spectroscopy; EDTA; Nickel-Titanium instruments; NaOCl; triphala
|How to cite this article:|
Prasad PS, Sam JE, Kumar A, Kannan. The effect of 5% sodium hypochlorite, 17% EDTA and triphala on two different rotary Ni-Ti instruments: An AFM and EDS analysis. J Conserv Dent 2014;17:462-6
|How to cite this URL:|
Prasad PS, Sam JE, Kumar A, Kannan. The effect of 5% sodium hypochlorite, 17% EDTA and triphala on two different rotary Ni-Ti instruments: An AFM and EDS analysis. J Conserv Dent [serial online] 2014 [cited 2020 Jul 14];17:462-6. Available from: http://www.jcd.org.in/text.asp?2014/17/5/462/139842
| Introduction|| |
Nickel-titanium alloys were developed in the early 1960's by W. F. Buehler, a metallurgist at the Naval Ordnance Laboratory in Silver Springs, Maryland, USA.  Considering its property of superior elasticity and resistance to torsional fracture, Walia et al. introduced nickel-titanium endodontic rotary files to the field of endodontics. These properties help Ni-Ti instruments to negotiate and prepare curved root canals without early permanent deformation unlike stainless steel files. 
The Ni-Ti alloys used for manufacturing the endodontic files contain approximately 56% (wt) nickel and 44% (wt) titanium.  Though NiTi instruments have many advantages, incidence of instrument separations are not uncommon in clinical use.  NiTi rotary instruments fracture in two different ways: Fracture because of torsion and fracture because of flexural fatigue.  The endodontic files are in constant contact with the irrigants during the cleaning and shaping procedures. Even short-term contact with these irrigants can cause alterations in the surface of NiTi instruments.  Sodium hypochlorite is the most commonly used endodontic irrigant whose antimicrobial effectiveness is based on its high pH (pH > 11). There is a contact between rotary NiTi instruments and the NaOCl solution during clinical use and cleaning and sterilization procedures. Nygaard - Ostby introduced ethylene diamine tetraacetic acid (EDTA) to the field of endodontics, in 1957, and recommended the use of 15% EDTA solution with a pH of 7.3. Since then, EDTA has been used as the most common chelating solution, which reacts with calcium ions in dentin and form soluble chelates.  The constant increase in antibiotic resistant microbial strains and the side effects caused by the use of synthetic drugs and also the hazards associated with irrigants such as NaOCl has prompted researchers to look for safer, more biocompatible and patient friendly herbal alternatives. Among the herbal alternatives, triphala has been very much promising. Triphala has shown the most significant antibacterial efficacy against the Enterococcus fecalis biofilm.  Triphala has been proven to be safe and containing active constituents that have beneficial physiologic effect and also having curative properties such as being antioxidant, anti-inflammatory and radical scavenging. Triphala is an Indian ayurvedic herbal formulation consisting of dried and powdered fruits of three medicinal plants Terminalia bellerica, Terminalia chebula, and Emblica officinalis. 
Scanning electron microscopy has been widely used for surface analysis of NiTi rotary endodontic instruments. , Recent studies have been done to evaluate the surface topography of these instruments with the help of atomic force microscope (AFM). Atomic force microscope facilitates the imaging and analysis of surface topography with little or no sample preparation. It gives the 3-dimensional surface topography of specimens with high spatial resolution. ,,, Energy-dispersive X-ray spectroscopy (EDS or EDX) is an analytical technique used for the elemental analysis or chemical characterization of a sample. It relies on the investigation of an interaction of X-ray excitation and a sample. It identifies and characterizes semi-quantitatively, the chemical elements present in deposits found on instrument surfaces. Many studies have been conducted to analyze the surface of rotary NiTi endodontic files using EDS. ,
The aim of the present study is to evaluate the effects of NaOCl, EDTA and Triphala on the nano-structure surface of Protaper and iRaCe rotary NiTi endodontic files using AFM and EDS.
| Materials and methods|| |
A total of eight nickel-titanium rotary endodontic files, four files each of ProTaper - S2 (DENTSPLY, Switzerland) and iRaCe - R3 (FKG DENTAIRE, Switzerland) were used for this study. The irrigants used were 5% NaOCl (Azure Research Lab Pvt. Ltd, India), 17% EDTA (Prime Dental Products Pvt. Ltd, India) and Triphala (IMPCOPS, Chennai, India).
AFM (5500-Agilent Technologies, USA) belongs to the scanning probe microscopy family and can reconstruct three-dimensional surface topography images in real time. A sharp tip attached to a flexible cantilever probes the sample surface. The cantilever deflects in the z-direction as a result of the surface topography during tip scanning over the sample surface. This deflection in the cantilever is detected by a photodiode through a laser beam focused on and reflected from the rear of the cantilever. AFM records data of the samples in digital form as sets of x, y and z values. ,,
In EDS (Bruker, USA), a high-energy beam of charged particles such as electrons, or a beam of X-rays, is focused into the sample being studied. The incident beam may excite an electron in an inner shell, ejecting it from the shell while creating an electron hole where the electron was. An electron from an outer, higher-energy shell then fills the hole, and the difference in energy between the higher energy shell and the lower energy shell may be released in the form of an X-ray. The number and energy of the X-rays emitted from a specimen are measured by the EDS. As the energy of the X-rays is characteristic of the difference in energy between the two shells, and of the atomic structure of the element from which they were emitted, this allows the elemental composition of the specimen to be measured.
The cutting flutes of the three files each from ProTaper and iRaCe were immersed in the three different irrigating solutions separately for 5 minutes. These immersion groups were then let to air dry at room temperature. One file each from ProTaper group and iRaCe group were evaluated without immersion in the irrigants and were kept as the control. The files were then attached to a metal holder using adhesive tapes. Nine areas of the surface were analyzed on a 3-mm section taken at the middle portion of the files.
The AFM images of the tested samples were then recorded using the contact mode of the AFM under ambient conditions. A total of nine perfect squares of 2 × 2, 5 × 5 and 10 × 10 micrometers were examined on every sample, which was then unitized to 1 × 1 micrometer for statistical analysis. The roughness average (Ra), root mean square (RMS) and mean height of roughness profile elements (Rc) of the scanned profiles were then recorded. These parameters depict the vertical topography of the instrument surface and an increase in these value means that there are alterations caused by the irrigants. The three-dimensional images were processed using the Picoimage software. The weight percentage of the elements present on the surface of the samples was evaluated using the Energy-Dispersive X-ray Diffraction Spectroscopy.
Data was analyzed using the computer software, Statistical Package for Social Sciences (SPSS) version 10. Data derived is expressed in the mean and standard deviation. Student's t test was used to compare the mean values between ProTaper and iRaCe groups. One-way analysis of variance (ANOVA) was performed as parametric test to compare different treatments. Duncan's multiple range test was also performed along with ANOVA as post-hoc test to elucidate multiple comparisons between treatments. For all statistical evaluations, a two-tailed probability of value < 0.05 was considered as significant.
| Results|| |
The three-dimensional AFM images of the surfaces of all the Protaper and iRaCe instruments including new and those immersed in the three different irrigants showed topographic irregularities at the nanometric scale. The control group images of Protaper files were different compared to iRaCe control instruments. Ra, RMS and Rc values of new Protaper files were significantly lower compared to iRaCe files (P < 0.05). The new and Triphala immersed iRaCe files did not differ significantly, but had a very highly significant difference with NaOCl and EDTA immersed iRaCe files (P < 0.001) [Table 1]. Though both the Protaper and iRaCe show significant surface roughness properties, iRaCe group showed higher values of surface roughness (Ra, RMS and Rc) than the Protaper group [Table 1] and [Table 2]. Among the immersed files, the maximum Ra value was observed for NaOCl immersed iRaCe files and minimum Ra value was observed for Triphala immersed Protaper files.
| Discussion|| |
The mechanical instrumentation of root canals alone cannot sufficiently disinfect the canal space regardless of whether stainless steel or NiTi instruments are used. The ideal irrigant or combination of irrigants should destroy the bacteria, dissolve the necrotic tissue, lubricate the canal, remove the smear layer and not irritate the healthy tissues.  Sodium hypochlorite, as an irrigant encompasses many desirable properties required for an ideal root canal irrigant. 
EDTA creates a stable calcium complex with the dentin mud, smear layer or the calcific deposits present along the canal walls.  Triphala has shown significant antibacterial efficacy against the Enterococcus fecalis biofilm.  Triphala has been proven to be safe, containing active constituents that have beneficial physiologic effect and also having curative properties such as being antioxidant, anti-inflammatory and radical scavenging. 
The Nitinol used in the manufacture of endodontic instruments contain approximately 56% (wt) nickel and 44% (wt) titanium.  The manufacturers of nickel-titanium (NiTi) root canal instruments have come up with different methods, which focus on altering the surface of the alloy as well as altering the alloy microstructure in order to enhance the efficacy and the longevity of the NiTi instruments. 
In the present study, middle region of the cutting flutes was selected for evaluation based on the ease of specimen mounting and focusing on the atomic force microscope. Since the aim of our study was to evaluate the effect of irrigants on the instrument surface, the region to be evaluated on the cutting flutes was assumed to be less significant. One important surface characteristic, as claimed by the manufacturers of iRaCe, is that of electro-polishing, which is a method commonly employed for corrosion resistance and surface finishing of most metallic medical equipments.  The EDS analysis of our study specimens revealed the presence of tantalum (Ta) on the surface of new iRaCe files, which was not present on the surface of new ProTaper files. The presence of this noble metal on the surface of iRaCe files may be attributed to the electro-polishing procedure.
Sodium hypochlorite is known to be corrosive to metals causing, selective removal of nickel from the NiTi instrument surface leading to micro pitting. It is supposed that these microstructural defects can lead to areas of stress concentration, crack formation and finally leads to the weakening of the instrument surface.  The cutting efficiency of stainless steel files is significantly reduced by EDTA as a result of slight corrosion. 
In the present study, AFM was used for evaluation of surface topography of ProTaper and iRaCe files. AFM was selected for the present study as it is a sensitive and reliable technique that offers a suitable means for the acquisition of qualitative and quantitative data concerning the surface topography of rotary NiTi files. AFM can reconstruct a three-dimensional image of the surface topography in real time. ,,
In the present study, both the untreated ProTaper and iRaCe files showed surface deterioration at the nanometric scale. It is assumed that the presence of surface irregularities on NiTi files make them more prone to corrosion and fracture. Manufacturing defects present in NiTi files can also play a role in the process of corrosion. In our study, both iRaCe and ProTaper files have demonstrated considerable amount of instrument surface deterioration, which can attribute to the milling marks present on the file surface that act as crevices and thereby initiate corrosion. 
The present study showed higher surface roughness values for new iRaCe files when compared with the new ProTaper files. The fact that both files were from different manufacturers could be a reason for such minute disparity in the surface roughness values between the files. A significant increase in surface roughness has been shown for NaOCl and EDTA immersed iRaCe when compared to the NaOCl and EDTA immersed ProTaper sample files. The initial roughness profile of the study NiTi files has proportionally changed the intensity due to the immersion in the different irrigants.
A previous study done using AFM to evaluate EDTA and sodium hypochlorite immersed ProTaper files have shown significant surface alterations on the surface of EDTA immersed files when compared to NaOCl immersed study files.  This result is in accordance with our study signifying high surface deterioration potential of EDTA when compared to NaOCl, which may be attributed to the lower pH of EDTA. As of date, there are no published data regarding the use of AFM to evaluate the effect of any herbal irrigant on rotary endodontic files. In our study, sodium hypochlorite and EDTA immersed iRaCe files have shown a significantly higher surface roughness values when compared to the Triphala immersed iRaCe files. The fact that triphala is a less reactive hydrocarbon compound when compared to other study irrigants could be a reason for this difference.
In the present study, only the cutting flutes were immersed in the irrigants, so as to avoid any bias that may occur due to the interaction of different metals, which are present in the shank of the instrument. The energy dispersive x-ray microanalysis (EDS) has shown that the cutting and non-cutting sections of ProTaper files was made of NiTi alloy, while the shank was made of gold-plated brass. 
The EDS analysis showed that the surface of new ProTaper and iRaCe files had almost the similar amount of nickel, titanium and oxygen components. The sodium and chlorine elements present on the surface of these NiTi files are due to the immersion in sodium hypochlorite. The EDS result also showed a decrease in the weight percentage of nickel and titanium with a corresponding increase in the weight percentage of sodium and chlorine elements. The analysis on the nanoscale supplied evidences of the necessity of manufacturers to adjust processing parameters to minimize and prevent the irregularities on the surface of these instruments. To enhance the performance, durability and safety of root canal instruments, alteration in the inherent metallic properties like heat treatment can also be considered. 
| Conclusions|| |
Within the limitations of this study, it can be concluded that:
- Short-term contact with 17% EDTA and 5% NaOCl can cause significant surface deterioration on the surface of ProTaper and iRaCe rotary NiTi endodontic files.
- Electropolished iRaCe files did not show any resistance to surface deterioration when compared to ProTaper files on immersion in irrigants.
- AFM can be considered as a suitable method for quantifying and evaluating the surface characteristics of endodontic instruments.
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Pramod Siva Prasad
Department of Conservative Dentistry and Endodontics, Rajas Dental College, Kavalkinaru, Thirunelveli, Tamil Nadu
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]