Year : 2010 | Volume
: 28 | Issue : 1 | Page : 2--5
Comparison of the effectiveness of sterilizing endodontic files by 4 different methods: An in vitro study
R Venkatasubramanian1, Jayanthi2, UM Das1, S Bhatnagar1,
1 Department of Pedodontics and Preventive Dentistry,V S Dental College and Hospital, Bangalore, India
2 Department of Pedodontics and Preventive Dentistry, HOD & Prof. Ragas Dental College & Hospital, Chennai, India
Department of Pedodontics and Preventive Dentistry, V S Dental College and Hospital, Bangalore
Sterilization is the best method to counter the threats of microorganisms. The purpose of sterilization in the field of health care is to prevent the spread of infectious diseases. In dentistry, it primarily relates to processing reusable instruments to prevent cross-infection. The aim of this study was to investigate the efficacy of 4 methods of sterilizing endodontic instruments: Autoclaving, carbon dioxide laser sterilization, chemical sterilization (with glutaraldehyde) and glass-bead sterilization. The endodontic file was sterilized by 4 different methods after contaminating it with bacillus stearothermophillus and then checked for sterility by incubating after putting it in test tubes containing thioglycollate medium. The study showed that the files sterilized by autoclave and lasers were completely sterile. Those sterilized by glass bead were 90% sterile and those with glutaraldehyde were 80% sterile. The study concluded that autoclave or laser could be used as a method of sterilization in clinical practice and in advanced clinics; laser can be used also as a chair side method of sterilization.
|How to cite this article:|
Venkatasubramanian R, Jayanthi, Das U M, Bhatnagar S. Comparison of the effectiveness of sterilizing endodontic files by 4 different methods: An in vitro study.J Indian Soc Pedod Prev Dent 2010;28:2-5
|How to cite this URL:|
Venkatasubramanian R, Jayanthi, Das U M, Bhatnagar S. Comparison of the effectiveness of sterilizing endodontic files by 4 different methods: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2010 [cited 2021 May 8 ];28:2-5
Available from: https://www.jisppd.com/text.asp?2010/28/1/2/60478
Microorganisms induce a variety of infections and diseases in the human body and are largely ubiquitous in nature. Contamination directly or indirectly leads to transmission of infectious agents.  Infection control is a major issue in medicine and dentistry because of concern over communicable diseases transmitted in health care settings. The prevention of cross-contamination of infectious diseases among dental staff and patients is a major concern in dental practice. The purpose of sterilization in the field of health care is to prevent the spread of infectious diseases. In dentistry, it primarily relates to processing reusable instruments to prevent cross-infection.  In endodontics, various instruments like files, reamers, gates glidden drill and peeso reamers are used for cleaning and shaping the root canal system and to eliminate the bacterial population in pulp canal space. Various methods are followed to sterilize these instruments, such as dry heat sterilizer, autoclave, ethylene oxide gas, glass-bead sterilizer or hot-salt sterilizer, etc.  Few studies comparing different methods of sterilizing endodontic files have been done. Hence this study was undertaken.
Aims and objectives
The purpose of this study was to compare 4 methods of sterilizing endodontic files in dental practice and recommend the effective method from among these.
The aim of this study was to investigate the efficacy of 4 accepted methods of sterilizing endodontic instruments:
Autoclaving Carbon dioxide laser sterilizationChemical sterilization (with glutaraldehyde)Glass-bead sterilization
Materials and Methods
The study was performed on 100 K-files, 21 mm long and of size 25. Of these, 20 files were taken as control group, and the remaining 80 files were divided into 4 groups of 20 files each and they were tested for the efficacy of sterilization with different methods: Autoclave, glass bead, glutaraldehyde and CO 2 laser.
100 K-files of size 25, 21 mm long, were taken for this study. All the 100 files included in the study were pre-sterilized in an endodontic instrument box by autoclaving for 30 minutes at 121°C at a pressure of 15 pounds, for standardization to eliminate any bias. The test files were divided into 5 groups of 20 files each and labeled as A (autoclave), B (glass bead), G (glutaraldehyde), L (CO 2 laser) and C (control) and were numbered 1 to 20.
The spore suspension was prepared by immersing the commercially available bacillus stearothermophillus strips into thioglycollate medium broth and incubated at 55°C for 48 hours. Growth that occurred in the test tube was confirmed by doing Gram's stain that showed the presence of gram-positive bacillus stearothermophillus.
All the pre-sterilized files were contaminated with bacillus stearothermophillus in a sterile Petri dish for 5 minutes. After 5 minutes of immersion, 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 minutes at 37°C and stored in an endodontic instrument box till they were sterilized by different methods.
The 20 contaminated files in group A were placed in an endodontic instrument box and subjected to autoclave at 121°C for 15 minutes at a pressure of 15 pounds.
The 20 contaminated files in Group B were taken in 4 batches of 5 files each and wiped for 10 seconds with a 2 x 2 gauze soaked with surgical spirit and placed in the periphery of the glass-bead sterilizer and sterilized for 45 seconds at 240°C.
The 20 contaminated files in Group G were placed in a sterile plastic container containing 2.4% glutaraldehyde solution and were left in it for 12 hours.
The 20 contaminated files in Group L were irradiated for 3 seconds per surface at 10 watts using CO 2 laser system. The laser beam was moved along the length of the instrument during the 3-second period. A sterile tweezer was used to hold the handle of the file and change the surface for exposure.
After completion of sterilization of the files as described, the shaft of the instrument was removed from the handle by means of a sterile autoclaved wire cutter and each file was placed in separate tubes containing thioglycollate medium with the help of a sterile tweezer.
The 20 contaminated files in Group C (control group) were put in separate tubes containing thioglycollate medium by the method described above without doing any sterilization.
The test tubes containing files were labeled with the date and were kept for incubation at 55°C for 3 days. After 3 days the test tubes were removed from the incubator and each test tube was checked for any turbidity in the test tube. Presence of turbidity in a test tube indicated the presence of bacillus stearothermophillus and that the particular file was not sterilized completely. The test tubes were then further kept for incubation at 55°C for 21 days and again checked for growth in a similar manner as described above. 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 bacillus stearothermophillus stains was confirmed with sugar test.
The study showed that the endodontic files sterilized by autoclaving in an instrument box at 121°C for 15 minutes at a pressure of 15 pounds (group A) showed total sterility [Figure 1].
The files subjected to sterilization by glass-bead sterilizer after wiping for 10 seconds with a 2 x 2 gauze soaked with surgical spirit and sterilized for 45 seconds at 240°C (group B) showed presence of turbidity in 2 test tubes. Incomplete sterilization to the range of 10% was observed when the files were sterilized in glass-bead sterilizer [Figure 2].
The endodontic files sterilized by immersing in glutaraldehyde for 24 hours (group G) showed sterilization up to only 80%. This method showed contamination of 4 files after incubation [Figure 3]. The files on sterilization by CO 2 laser for 3 seconds per surface at 10 watts (group L) showed 100% sterility. There was total sterility seen by this method of sterilization [Figure 4]. The control group (group C), for which the files after contamination were not sterilized by any method, showed growth in all the test tubes.
Statistical analysis of the 4 sterilized groups showed a statistically significant difference between groups with regard to their efficacies in sterilization (P ≤ 0.05) [Table 1].
Comparison of the sterilized groups with the control group with regard to their efficacies in sterilization showed that the difference was statistically significant (P ≤ 0.05) [Graph 1]. On comparing the different groups among themselves, it was seen that there was no statistically significant difference among them with regard to their efficacies in sterilization.
There are 3 principal methods currently available for sterilization of instruments: Steam under pressure (autoclave), dry heat and chemiclave. Another method of sterilization, viz., laser, is also available but not widely used. The spores of bacillus stearothermophillus used to contaminate the files in this study are heat-resistant bacterial spores used in many of the previous researches. Many methods have been advocated for sterilization of endodontic instruments. Steam autoclaving and glass-bead sterilizers are among the commonly recommended methods of sterilization. Boyd  stated that moist heat generally kills microorganisms by coagulation of proteins. However, coagulation occurs only when overkill conditions are attained. Less drastic changes such as inactivation of enzymes, changes in nucleic acids and cytoplasmic membrane alterations probably kill microorganisms before coagulation occurs. The present study indicated that complete sterilization was possible by autoclaving the instruments in an endodontic box. This is significantly similar to the findings from studies done by other researchers like Rajkumar et al.,  Hurtt et al.  and Velez et al.  Damaging alterations of proteins by dry heat are the result of oxidation, desiccation and changes in osmotic pressure owing to evaporation of moisture. Dry heat is slower and requires temperatures higher than those used in moist heat sterilization. This study showed that sterilization by a glass-bead sterilizer was up to only 90% and that total sterility was not found even after sterilizing for 45 seconds at 240°C. Incomplete sterilization was in the range of 10%. The present study result was contradictory to that of previous research done by Rajkumar et al.,  but it was the same as that of the research done by Hurtt et al.,  who performed the study with salt instead of glass bead.
The present study showed 80% sterilization by immersing the files in glutaraldehyde solution for 12 hours, which is similar to the results of study done by Hurtt et al.,  and so glutaraldehyde solution cannot be relied upon completely to sterilize endodontic instruments.
The present study used CO 2 laser since it is commonly used nowadays in the dental office for periodontal surgery, endodontic instrumentation and so it can be concluded that it is an effective means of sterilizing endodontic files and can be followed in a dental clinic. Nammour et al.  on the basis of a study concluded that CO 2 laser had a important potential for sterilization. Powell et al.  on the basis of a study stated that all 3 lasers (argon, CO 2 and NdYAG) were capable of sterilizing dental instruments, but argon laser was found to be capable of sterilizing at the lowest energy level. The result of the present study is similar to that of the study done by Hooks et al.  and Adrian and Gross.  A multitude of factors are to be considered in prevention of cross-contamination. Endodontic instruments should be sterilized effectively before use on different patients to prevent cross-contamination.
The present study indicates that autoclaving and exposing to laser give complete sterilization. Glass-bead sterilizer can be used as an alternative when these two methods are not available, but glutaraldehyde cannot be relied upon as a method of sterilization.
Though autoclave is an effective method for sterilizing endodontic files, the time taken by it to sterilize is more, but lasers can sterilize endodontic instruments effectively and also fast. As the use of CO 2 laser is becoming common in dental clinics, it can be used as a routine method and also as a chair side method to sterilize endodontic files in routine clinical practice. Though laser is an effective method of sterilization, further studies have to determine the cutting efficiency and other mechanical properties of endodontic files after repeated exposure to CO 2 laser.
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