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| 2010-22 |
| 22-1 |
ISSN (Print) 1013-9052
EISSN 1658-3558
P.O. Box 52500,
Riyadh 11563,
Kingdom of Saudi Arabia
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Effects of chelating agent (RC - Preparation) on surface characterization of profile nickel-titanium endodontic instruments
Dina
Al-Sudani,DDS, MsEdu
The aim of the present study was to investigate the effect of a chelating agent, RC-prep, on the surface characterization of nickel-titanium endodontic instruments. The instruments were immersed in RC-prep for varying times up to 1 hour. The surface elements analysis of all instruments was carried out using electron microscope fitted energy dispersive x-ray (EDX) analyzer. Surface analysis revealed no significant change in the amount of Ni, Ti and NiO for all the time intervals. However, there was statistically significant increase in the concentration of TiO2, after 5 minutes, ½ hour and 1 hour immersion times. In conclusion, the surface treatment of NiTi files with RC-prep may affect their biocompatibility.
Root canal therapy,
involves a variety of instruments used in conjunction with various intracanal
medicaments such as sodium hypochlorite, H2O2 and
RC-preparation. RC-prep is used for
chemo-mechanical cleaning and shaping procedures. The chemical effects of these intracanal
medicaments on endodontic files may hinder their performance as the chemical
and electrochemical aggressiveness of these different solutions on the
instrument themselves. 1,2
After the pioneering research by Walia et al. 3, which introduced nickel-titanium (NiTi) to the endodontic profession, both nickel-titanium hand and rotary instruments have achieved widespread popularity. A major reason for their selection includes the properties of super-elasticity, shape memory, high corrosion resistance, and superior biocompatibility.3 Despite this interest, a lot of work pertaining to the properties of NiTi instruments still has to be done. Current endodontic practice necessitates that root canal instruments be repeatedly exposed to various sterilization procedures and irrigating solutions. RC-prep is generally accepted as the most effective chelating agent with prominent lubricant properties. It is used to enlarge root canal, remove the smear layer, and as a lubricant during instrumentation with most NiTi automated system. 4 Industrial testing has shown that EDTA is slightly corrosive to AISI 300 series stainless steel. Urea is corrosive to these materials at high temperature.5 Several investigators have demonstrated the correlation between the surface change of chemical composition of NiTi files and some sterilization treatment.6-17 The effects of these clinical practices on the surface of the NiTi endodontic files have not been determined. The purpose of this study was to determine the effect of chelating agent (RC-prep) on the surface characterization of selected nickel titanium instruments.
Fifty new Profile files were* used in the current investigation. The instruments were divided into 5 groups of 10 instruments each. Each group contained 2 instruments from each size (15, 20, 25, 30, and 35). Group I was used as a control and the other groups were exposed to RC-prep** for different time intervals. RC-prep used consisted mainly of 10% urea peroxide and 15% ethylene diamine tetracetic acid. The groups exposed to RC-prep were as follows: Group I (Control): The unused files Group II: The instruments were immersed in the RC-prep for 1 minute Group III: The instruments were immersed in the RC-prep for 5 minutes Group IV: The instruments were immersed in the RC-prep for ½ hour Group V: The instruments were immersed in the RC-prep for 1 hour
Each
file, after being immersed in RC-prep for the varying times at room
temperature, was rinsed in distilled water and allowed to dry at room
temperature on filter paper. Surface
elements analysis (spot analysis) of all the instruments was carried out using
electron microscope fitted energy dispersive x-ray (EDX) analyzer (Link Oxford
Analytic System) under 200X magnification (Fig. 1). The mean value and standard
deviation for each element on the surface was recorded and t-test was used for
comparison among the groups.
Mean and standard deviation for each element (Ni, Ti, NiO and TiO2) which were measured on the files surface before and after exposure to RC-prep are shown in Tables 1 and 2. There was no statistically significant difference (P>0.05) of Ni or Ti concentration for all time intervals Table 1. Moreover, as shown in Table 2 there was no significant change (P>0.05) in the concentration of the nickel oxide (NiO) for all time intervals. There was no significant change (P>0.05) in the concentration of the titanium oxide (TiO2) after immersion for 1 minute. However, there was statistically significant increase (P<0.05) in the concentration of the TiO2 after exposure for 5 minutes, ½ hour and 1 hour (Table 2 and Fig. 2).
The surface elements of
NiTi files were studied after they were exposed to RC-prep, which is generally
accepted as the most effective chelating agent with prominent lubricant
properties in endodontic treatment.4
The results indicated that the surface of NiTi files consisted mainly of
TiO2, NiO, and metallic Ni, while nickel-titanium compounds
constitutes the inner layer. The finding
of the present study parallels the results of some other investigators.
7-9
NiTi files have stable oxide layer on their surfaces that helps to render them corrosion resistant.13 The corrosion resistance of metals and metal alloys is mainly based on passivation phenomenon.13 The passivation of a metal is due to the compact coat, the passive layer, which contains hardly any original metal, but forms a metal oxide layer, "skin," on metal. This oxide layer may be amorphic or crystalline. The passive oxide layer varies in thickness depending on the preparation methods and could be enhanced by modifying the thickness, topography and chemical composition of this oxide layer by different surface treatment.7, 11-13 In our present study, the exposures of NiTi file to RC-prep which contains mainly EDTA and urea peroxide resulted in the increase of the oxide layer. This finding was in agreement with Villermaux et al.12 They showed that nitric acid passivation is recommended for surface treatment of medical devices to remove plastically deformed native oxide layers and replace them by more uniform ones. This improved oxide layer has been shown to be very protective and promising for improving the corrosion resistance and biocompatibility of NiTi, which was reported by many authors.12,13,15 Several in vitro evaluations of the corrosion properties of the alloy have been preformed.13,16,1711,14 Furthermore, it was found that the uniformity of the oxide layer rather than its thickness and composition, seemed to be the predominant factor to explain the improvement of corrosion resistant.7,11,15-17 Sohmura13 also showed that this layer is able to sustain large deformations induced by the shape memory effect. Ni-Ti alloy derives its good corrosion behavior from a homogeneously covered surface of Ni-Ti alloy in the presence of oxygen.
Corrosion
reactions susceptible to occur with clinical use of NiTi are numerous and can
lead to different rates of ionic release ranging from low rates during passive
dissolution to high rate when breakdown of the protective oxide film occurs.16,17 The current study demonstrated that the
surface treatment performed on NiTi had modified the amount of the protective
oxide layer on their surface which promoted their good biocompatibility and
their excellent resistance to corrosion processes. According to several researchers, the
corrosion behavior is directly related to the surface property.16,17
Moreover, this result could be attributed to the effect of RC-prep treatment in
addition to the presence of oxygen which is known to cover the titanium alloy
spontaneously by TiO2 layer.11,14,15,17 However, it was indicated by previous studies7,11,15-17
that the uniformity of the oxide layer, rather than its thickness and composition,
seemed to be the predominant factor to explain the improvement of corrosion
resistance. Further investigation has to be done to study the uniformity of
this oxide layer. From the current
findings, it was concluded that the RC-prep surface treatment performed on NiTi
had enhanced the protective oxide layer which was found in previous studies to
be the predominant factor to explain the improvement of corrosion resistant of
Ni-Ti instruments.
The author would like to express her great appreciation to Prof. S. Kheir for her invaluable insight and discussions regarding this paper.
Address reprint requests to: Dr. Dina Al-Sudani
Endodontics Division
Table 1. The concentration (%) of Nickel (Ni) and Titanium (Ti) before and after exposure to RC-prep for varying duration
Table 2. The concentration (%) of NIO and TIO2 after exposure to RC-Prep for varying duration
Figure 1. Surface elements analysis using energy
dispersive x-ray (EDX).
Figure 2. The concentration (%) of NiO and TiO2 after
exposure to RC-Prep for varying duration. |
