|Year : 2016 | Volume
| Issue : 2 | Page : 142-146
Comparative evaluation of sterilization efficacy using two methods of sterilization for rotary endodontic files: An in vitro study
Naveen Kumar Kommmineni1, Swami Ranga Reddy Dappili2, Padakandla Prathyusha1, Pallelrala Vanaja3, Kasa Veera Kishore Kumar Reddy1, Done Vasanthi1
1 Department of Pedodontics and Preventive Dentistry, C.K.S. Teja Institute of Dental Sciences, Tirupati, Andhra Pradesh, India
2 Department of Conservative Dentistry and Endodontics, C.K.S. Teja Institute of Dental Sciences, Tirupati, Andhra Pradesh, India
3 Department of Pedodontics and Preventive Dentistry, S.V.S. Dental College, Mahabubnagar, Telangana, India
|Date of Web Publication||5-Jul-2016|
Naveen Kumar Kommmineni
Department of Pedodontics and Preventive Dentistry, C.K.S. Teja Institute of Dental Sciences, Tirupati - 517 507, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
Context: Sterilization will be effective only when all the bacterial spores are destroyed. The transmission of pathogens from one patient to another via contaminated devices has been a high-profile issue in infection control.
Aims: The purpose of this study was to investigate the sterilization efficacy using two methods of sterilization using rotary endodontic files: Autoclave, chemical sterilization using two solutions (chlorhexidine and glutaraldehyde).
Materials and Methods: The study was carried out on 60 new pre-sterilized rotary nickel titanium files contaminated with commercially available Bacillus stearothermophillus. The files were sterilized by the two methods and checked for sterility by incubating the files in test tubes containing thioglycollate medium.
Statistical Analysis Used: The Kruskal-Wallis test was used to determine any significant difference between groups. The Mann-Whitney test was used to demonstrate any significant difference between the three agents. The level of significance was set at P < 0.05.
Results: The files sterilized by autoclave were 100% sterile, and those sterilized by chlorhexidine showed 87% sterility and with glutaraldehyde showed only 60% sterility.
Conclusions: The study concluded that the autoclave could be used as best reliable method of sterilization.
Keywords: Autoclave, Bacillus stearothermophillus, chlorhexidine, nickel titanium files, sterilization
|How to cite this article:|
Kommmineni NK, Dappili SR, Prathyusha P, Vanaja P, Reddy KK, Vasanthi D. Comparative evaluation of sterilization efficacy using two methods of sterilization for rotary endodontic files: An in vitro study. J NTR Univ Health Sci 2016;5:142-6
|How to cite this URL:|
Kommmineni NK, Dappili SR, Prathyusha P, Vanaja P, Reddy KK, Vasanthi D. Comparative evaluation of sterilization efficacy using two methods of sterilization for rotary endodontic files: An in vitro study. J NTR Univ Health Sci [serial online] 2016 [cited 2020 Mar 31];5:142-6. Available from: http://www.jdrntruhs.org/text.asp?2016/5/2/142/185453
| Introduction|| |
Sterilization of instruments ensures that they are free of "all microbial life, including microbial spores that are the most difficult of microorganisms to kill."  If the sterilization process is effective in killing bacterial spores, it will also be effective against mycobacteria and all viruses, including herpes simplex virus, hepatitis and HIV. 
Resterilization is "the repeated application of the terminal process designed to remove or destroy all viable forms of microbial life, including bacterial spores, to an acceptable sterility assurance level."  Resterilization of instruments used on one patient for reuse on another has been common practice in dentistry. Some instruments used in endodontic procedures, such as files, reamers, nickel-titanium (Ni-Ti) files, are Class I instruments as defined by the United States Food and Drug Administration and can be reused if sterility can be guaranteed.  However, there is now evidence that the sterilization process is complex and that if strict adherence to an effective protocol is not followed, contamination of instruments may result.
In the past decade, single-use devices (SUDs) have been promoted in many dental and medical practices as a strategy to prevent the transmission of blood- and tissue borne pathogens from patient to patient. This practice has also been influenced by high-profile legal cases that have brought the issue of SUDs to the attention of the media and the public.  However, the use of disposable instruments does not come without a significant cost to the health care system as well as environmental concerns.  Currently, numerous articles address the transmission of blood- and tissue-borne pathogens from one patient to another via contaminated devices. ,, Many studies look at the bacterial and viral contamination of dental and medical instrumentation and the safety of sterilizing and reusing these instruments. , There have also been concerns over the possible transmission of prions by contaminated surgical instruments.  The contact of endodontic files with the peripheral branches of the trigeminal nerve may present a risk of transmission of Creutzfeldt-Jakob Disease (CJD), although there is no evidence of transmission of CJD in dentistry. , Although SUDs have been promoted as a strategy to prevent cross-infection of patients, resterilization of previously used instruments is still common as cost is a significant factor in the decision to reuse instruments in dentistry and oral and maxillofacial surgery.  The practice of reprocessing used instruments is becoming more and more prevalent with the overall goal of saving money and decreasing environmental pollution.  Supporters of resterilization believe that the labeling of some devices as SUDs by manufacturers is done so that they can increase profits and avoid liability with regard to cross-infection of patients on whom their instruments are used.
Modern dental and medical equipment can be intricate and contain small lumens, as in endoscopic equipment, and therefore requires more rigorous procedures to ensure sterilization. Some instruments cannot be consistently and reliably sterilized; because of the risk of cross contamination with these instruments, disposable devices became established in the health care industry. There is still much debate regarding the reuse of instruments in both dentistry and medicine. ,,,
The purpose of this study was to investigate the sterilization efficacy using two methods of sterilization using rotary endodontic files: Autoclave, chemical sterilization using two solutions (chlorhexidine and glutaraldehyde).
| Materials and Methods|| |
A total of 60 new rotary Ni-Ti files from the manufacturer ProTaper (Dentsply-Maillefer, Ballaigues, Switzerland) of standardize size S2 and of length 21 mm [Figure 1] were taken for the study. All the files were placed in an endodontic instrument box and were sterilized at 121°C for 15 min at 15 psi in an autoclave.
|Figure 1: Rotary ProTaper (Dentsply-Maillefer, Ballaigues, Switzerland) files of standardize size S2 and of length 21 mm|
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These files were divided into four experimental groups:
Group-1 15 files sterilized by autoclave.
Group-2 15 files sterilized by chlorhexidine (chemical).
Group-3 15 files sterilized by glutaraldehyde (chemical).
Group-4 control group-15 files subject to no sterilization.
The bacterial spore suspension was prepared by immersing the commercially available Bacillus stearothermophillus strips (SGM Strrip® spore strip biological indicator) into thioglycollate medium (Hi Media Laboratories, Mumbai, Maharashtra) and incubated at 55° for 7 days.
All the presterilized files were contaminated with this suspension in a sterile Petri dish for 5 min [Figure 2]. Following this, the files were transferred to another sterile Petri dish under vacuum hood safety with the help of a sterile tweezer, following which the files were dried in an incubator for 10 min at 37°C and stored in an endodontic instrument box until sterilized by different methods.
|Figure 2: Presterilized files were contaminated with this suspension in a sterile Petri dish|
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The 15 contaminated files in Group A were placed in an endodontic instrument box and subjected to autoclave at 121°C for 15 min at a pressure of 15 psi.
The 15 contaminated files in Group B were placed in a sterile plastic container containing 2% chlorhexidine solution and were left in it for 12 h.
The 15 contaminated files in Group C were placed in a sterile plastic container containing 2.4% glutaraldehyde solution and were left in it for 12 h.
The 15 contaminated files in Group D, which is the control group, were not subjected to any sterilization cycle.
The test tubes containing files were labeled and incubated at 55°C for 5 days after noting the incubation date [Figure 3],[Figure 4],[Figure 5] and [Figure 6]. After 5 days, the test tubes were checked for any turbidity. Presence of turbidity indicated the presence of B. stearothermophillus and that the particular file was not sterilized completely. The test tubes with turbidity were checked and confirmed for the presence of microorganisms by viewing under light microscope after doing Gram's-stain and culture test. The specificity of B. stearothermophillus stains was confirmed with sugar test.
The Kruskal-Wallis test was used to determine any significant difference between groups. The Mann-Whitney test was used to demonstrate any significant difference between the three agents. The level of significance was set at P < 0.05.
|Figure 4: Test tubes containing files sterilized by 2% chlorhexidine solution|
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|Figure 5: Test tubes containing files sterilized by 2.4% Glutaraldehyde solution|
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| Results|| |
The study showed that the endodontic files sterilized by autoclaving in an instrument box at 121°C for 15 min at a pressure of 15 pounds (Group A) showed total sterility. The files subjected to 2% chlorhexidine chemical sterilization (Group B) showed turbidity in two test tubes, showing only 87% of sterilization by this method. The files subjected to glutaraldehyde chemical sterilization (Group C) showed turbidity in six test tubes, showing only 60% of sterilization by this method. The control group (Group D), were not sterilized by any method, showed turbidity in all the test tubes. Statistical analysis of the four sterilized groups showed a statistically significant difference between groups with regard to their efficacies in sterilization (P ≤ 0.05).
| Discussion|| |
Endodontic files are one of the commonly reused instrument in dentistry. In a survey of general dentists in the United Kingdom, Bagg et al.  found that 88% of practitioners reused endodontic files. Smith et al.  compared used endodontic files that had been collected from general dental practices with files from a dental hospital, and found that 76% of the former were visibly contaminated when inspected under a dissecting microscope, as opposed to 14% of those from the dental hospital. These authors also concluded that the cleaning methods used were insufficient to remove the organic material on the endodontic files. They suggested that a cost-benefits analysis would be helpful in determining whether these files would be suitable for designation as single use. The clinical applicability of studies that look at the risk of cross contamination as a result of using contaminated instruments depends on the amount of the pathogen transferred, the infectivity of the pathogen and host resistance.  The ultimate outcome depends on the long-term course of the disease caused by the pathogen. Attention has been focused on bacterial infection, but as the oral cavity is a contaminated environment to begin with, the clinical applicability of the research is difficult to elucidate. There has been public concern over handpiece and waterline contamination issues as these topics were widely covered in the media. There have also been ethical studies looking at the issues of reuse and reprocessing and whether the patient is at risk from these practices.  Resterilization is a controversial issue that has yet to be resolved.
The present study utilized the rotary Ni-Ti files that were widely used and significantly have greater tendency to retain cultivable bacteria that may result retaining more biological debris on them. The design of the rotary file further induces the packing of biological debris with the U-shaped flute design adding to the retention. 
In a busy private practice setting, it is not possible to achieve acceptable sterilization results owing to ignorance and hurry in saving time, insisting a rapid chairside sterilization alternative. So in the present the two chemical sterilization methods were compared for their efficacy.
The present study showed 87% sterilization by immersing the files in 2% chlorhexidine solution for 12 h, which is similar to the results of the study done by Parashos et al.,  and so 2% chlorhexidine solution cannot be relied upon completely to sterilize endodontic instruments.
The present study showed 60% sterilization by immersing the files in glutaraldehyde solution for 12 h, which is similar to the results of the study done by Hurtt and Rossman  and so glutaraldehyde solution cannot be relied upon completely to sterilize endodontic instruments.
Sterilizing instruments is a labor-intensive process that requires careful attention to detail. Reuse of rotary instruments can be a cost-effective measure in the practice of endodontic practice if the safety of patients can be assured. Rotary Ni-Ti files can be safely re-used from an infection control perspective by sterilizing in an autoclave. Yet there seems to be increasing evidence that the sterilization process may not be completely effective due to human, mechanical or microbial factors.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]