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Year : 2018  |  Volume : 5  |  Issue : 2  |  Page : 50-53

An in vitro evaluation of the efficiency of various disinfection and sterilization methods to decontaminate dental handpieces

Department of Prosthodontics, Azeezia College of Dental Science and Research, Kollam, Kerala, India

Date of Web Publication3-Aug-2018

Correspondence Address:
Sreelekshmi Sreekumar
Department of Prosthodontics, Azzezia College of Dental Science and Research, Kollam - 691 537, Kerala
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jdrr.jdrr_19_18

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Background: Improper decontamination methods employed in the dental clinics to clean dental handpieces often lead to cross-transmission of diseases among patients and dental professionals. Aims and Objectives: The present study evaluates the efficiency of moist heat sterilization using autoclave and disinfection methods such as alcohol and a commercially available disinfectant (Decident™) to decontaminate dental handpieces. Materials and Methods: For the present study, sixty contaminated handpieces were selected and divided into four groups of 15 handpieces. They were then contaminated using a mixture of Streptococcus salivarius, Escherichia coli, and Candida albicans. Sterilization using autoclave and disinfection procedures using a commercially available disinfectant (Decident™) and 70% isopropyl alcohol was done on each group. The handpieces were then subjected to manual scrubbing followed by bacteriological culture. Results: The study revealed that moist autoclave is the best way to decontaminate the dental handpieces. Further, it was shown that proper cleaning of the instrument prior to autoclave, as recommended by the American Dental Association's Centers for Disease Control and Prevention (CDC), is required for 100% efficiency. Statistically significant presence of S. salivarius and E. coli was found in samples disinfected with Decident™ and 70% isopropyl alcohol, respectively. Conclusion: The study revealed that moist autoclave, following the procedures recommended by the CDC, still remains as the gold standard of sterilization of dental handpieces.

Keywords: 70% isopropyl alcohol, autoclave, chemical disinfection, disinfection, sterilization

How to cite this article:
Sreekumar S, Varghese K, Abraham JP, Jaysa J J. An in vitro evaluation of the efficiency of various disinfection and sterilization methods to decontaminate dental handpieces. J Dent Res Rev 2018;5:50-3

How to cite this URL:
Sreekumar S, Varghese K, Abraham JP, Jaysa J J. An in vitro evaluation of the efficiency of various disinfection and sterilization methods to decontaminate dental handpieces. J Dent Res Rev [serial online] 2018 [cited 2022 Jun 27];5:50-3. Available from: https://www.jdrr.org/text.asp?2018/5/2/50/238532

  Introduction Top

Proper infection control is imperative to ensure maximum patient safety and reduce the risk of cross infection.[1] In dental surgical procedures, infection can transmit from patient to dentist, dentist to patient, or from patient to patient.[2],[3] The advent of dental handpieces revolutionized many aspects of dentistry and are widely used in several dental procedures, such as dental prophylaxis, preparing cavities for restoration, odontosections, and osteotomies. Dental handpieces are always subject to microbial contamination, mainly due to (1) the accumulation of debris from dental restorative materials and dental hard tissues; (2) microorganisms from oral cavity, water, and airlines; and (3) accumulation of blood and saliva inside the handpiece chamber.[4] Hence, it is important that dental handpieces should be thoroughly decontaminated before each dental surgical procedure.

Various disinfection and sterilization methods are followed in dentistry. Disinfection methods kill or remove the pathogens, but cannot destroy their spores.[5],[6] In this method, a complete removal of pathogens is not always possible, but it often helps to bring the presence of pathogens to an acceptable level so that it will not result in infection.[7],[8] Applying certain chemicals and use of alcohol are two widely used methods for disinfecting the dental handpieces. Antimicrobial properties of alcohol are widely used for disinfection of dental instruments.[8] The use of 70% w/v isopropyl alcohol provides a low level of disinfection, but it does not remove the microbial spores.[8],[9] Commercially available disinfection pouches are mixtures of ethanol and biphenyl-2-ol in varying proportions, which provide an intermediate level of disinfection.[8] Sterilization is the cleaning of reusable instruments such as dental handpieces that are contaminated with microorganisms by killing or removing them including their spores.[10] However, sterilization procedure does not completely remove the prion proteins, which can potentially cause infection.[11] Hence, for sterilization to be effective, it should be done following proper cleaning of the handpiece, without which even the sterilization procedure will be compromised.[8]

Hence, it is important that the dental handpieces used in everyday dental procedures should be thoroughly decontaminated to provide harmless and clean dental service to the population. According to the American Dental Association's Centers for Disease Control and Prevention (CDC), dental instruments are classified into three categories depending on the risk of transmitting infection, namely critical (should be sterilized), semi-critical (sterilization recommended, but high level of disinfection also accepted if sterilization is not feasible), and noncritical (intermediate or low level of disinfection).[12] As per the CDC recommendation, dental handpieces fall in the critical category and should be sterilized before each use.

Hence, the recommended procedure for safe dental handpiece decontamination is rinsing with water, washing with detergent and drying it, followed by autoclave sterilization.[12] However, mainly due to the tight time schedule in which dental practitioners are working, the often preferred way of decontamination of dental handpieces is disinfection methods rather than sterilization. This compromises the recommended safety procedure. Since there are not many attempts to intercompare the efficiency of these widely used procedures to clean the dental handpieces, this study aims to address that knowledge vacuum.

  Materials and Methods Top

All the materials and instruments used in this study are shown in [Figure 1]. We used sixty dental handpieces in the present study. All the selected dental handpieces were subjected to a microbial challenge of 106 colony-forming unit/ml of a mixture of Streptococcus salivarius,  Escherichia More Details coli, and Candida albicans. The contaminant was applied directly with friction along the entire outer surface of the handpiece. After the contaminant was completely dried out, the handpieces were randomly grouped to the four test groups namely test groups A, B, C, and D, each comprising 15 handpieces. The handpieces belonging to test group A were autoclaved following the standard procedure recommended by the CDC, i.e., first rinse the dental handpieces with water, then wash it with a detergent, and dry it for 10 min and then autoclaved under 121°C for 20 min.[12] Group B handpieces were also autoclaved at 121°C for 20 min, but without rinsing and cleaning with detergent before autoclave. Those belonging to test Group C were kept in a chemical disinfectant pouch (Decident™, Septodont Healthcare India Pvt Ltd, Taloja, Panvel Maharashtra, India) for 15 min as specified by the manufacturer. In test Group D, 70% isopropyl alcohol was applied thrice with friction along the entire outer surface of handpieces for 30 min. After completion of the decontamination procedures, specimens were collected from samples by manual scrubbing along the entire surface using sterile cotton swabs. The collected specimens were transferred aseptically and submersed in sterile test tubes with 1 ml of peptone broth for ascertaining microbial growth. The test tubes were agitated manually for 1 min to disperse the specimens uniformly to the broth. The test tubes were incubated at 37°C for 48 h. Positive cultures obtained were subcultured in nutrient agar, McConkey, and Sabouraud's dextrose agar media for ascertaining the growth of S. salivarius, E. coli, and C. albicans, respectively. The data obtained were then statistically analyzed.
Figure 1: Materials and instruments used in this study. (a) 70% isopropyl alcohol, (b) autoclave machine, (c) Decident™ pouches, (d) dental handpieces, (e) sterilized culture media, and (f) incubator

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  Results Top

[Figure 2] shows the number of times S. salivarius, E. coli, and C. albicans were reported in dental handpieces after doing the four types of decontamination processes described in section 2. Isopropyl alcohol proved least effective in reducing total microbial colonies with only 26.6% reduction in E. coli counts. Of the total samples analyzed, presence of S. salivarius bacteria was positive in 13.3% of samples, E. coli in 73% samples, and Candida species in 6.6% of samples. Decident™ disinfectant has shown 73.3% and 80% success rates in removing the S. salivarius and E. coli counts from the dental handpieces, respectively. Presence of Candida species was not seen in the dental handpieces applied with Decident™ disinfectant. Colonies of S. salivarius were found in one dental handpiece sample when autoclave sterilization method was done without proper cleaning. Autoclave method following the standard protocol proved to be the best method of decontamination with 100% success rate.
Figure 2: Bar diagrams showing the number of samples with the presence of Streptococcus salivarius (blue), Escherichia coli (red), and Candida (green) species after different decontamination methods

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We have done a detailed statistical analysis of the results, which is provided in [Table 1]. Sterilization method following standard protocol, which is considered as the gold standard for the decontamination, is taken as the independent variable, and other methods are statistically compared with it.
Table 1: Statistical comparison of presence of Streptococcus salivarius, Escherichia coli, and Candida in various decontamination methods

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Although S. salivarius was found in B, C, and D test groups, only test Group C was found significantly different from test Group A. This suggests that disinfection method using commercially available Decident™ is not as efficient as the standard autoclave method to remove the S. salivarius from the contaminated dental handpieces. Presence of E. coli was found in 11 of the 15 samples applied with 70% isopropyl alcohol. Statistical analysis suggests that it is significantly different compared with the standard autoclave method (P = 0.0), implying that 70% isopropyl alcohol proved inefficient to completely remove E. coli from the contaminated dental handpieces. Groups B and C showed statistically insignificant presence of E. coli and hence can be ignored. Candida species was found only in a single dental handpiece applied with 70% isopropyl alcohol, but its presence was not found significant in any of the other three methods compared with the standard autoclave method.

  Discussion Top

Effective and efficient infection control has become an essential step to provide safe dental care to patients. To achieve this, various sterilization and disinfection methods are used in dentistry for the decontamination of used dental instruments. Dental handpieces have become an indispensible part of everyday clinical dentistry. Transmission of pathogens through the dental handpieces is one of the important potential routes for the spread of infection. There is a long history of infections transmitted through the dental handpieces that necessitates the need for proper decontamination of the dental surgical instruments prior to use in a patient.[13]

In the present study, we randomly grouped sixty contaminated dental handpieces into four groups and applied various decontamination methods to evaluate its efficiency. Our study agrees with previous studies on this subject that the sterilization process should meet the American Dental Association CDC guidelines for effectively preventing the cross-contamination of diseases through dental handpieces.[1],[3],[4] The present study shows that presence of S. salivarius can be found in dental handpieces if no proper cleaning of the handpieces is done before autoclave sterilization, though it is not statistically significant. There are many studies that point out the importance of prior cleaning of the instruments before autoclaving, as recommended by the CDC, but our study evaluates the efficiency of autoclave sterilization with and without prior cleaning. There are studies[14],[15] that suggest the importance of cleaning of surgical instruments before autoclaving for the best results. These studies and the present one reinforce the importance and critical need to develop rigid protocols for cleaning contaminated objects before autoclave sterilization. Hence, it is an important aspect that dental practitioners should be made aware of the importance of following the proper steps in the autoclave sterilization procedure as recommended by the CDC.

Sterilization methods evolved significantly over the years. The initial version of the steam autoclaves was large in size, but the latest models are very compact with tabletop design. There are a number of recent innovations to improve the efficiency of autoclave, addressing common problems such as the formation of air pockets in the chamber and wet sterilized packages at the end of the cycle. This is addressed by developments such as pulse injection of steam during the process instead of steam entering the chamber all at once.[16] This allows for less mixing of air with steam within the chamber during the sterilization interval. Of late, this type of autoclave has become popular and efficient among dental practitioners. The state-of-the-art sterilizers are called Class B type or the pre- and postvacuum sterilizers.[17] In such sterilizers, a pump housed within the unit creates a vacuum at the beginning of the cycle to prevent mixing of air and steam, thereby ensuring more rapid and efficient penetration of steam to instrument surfaces. The presence of a postvacuum cycle component at the end of the sterilization interval is designed to facilitate drying, thereby providing the clinician with dryer instrument packages at the end of the process. Adopting the latest technological advances in the field of autoclave sterilization will lead to better results.

  Conclusion Top

Our in vitro analysis utilized only sixty contaminated dental handpieces and 15 handpieces each to evaluate the efficiency of each method. This is a major limitation and similar analysis has to be repeated in more number of handpieces to get statistically significant results. Furthermore, in order to access the actual conditions, contaminated handpieces from surgical procedures should be subjected to similar analysis in order to verify the results of this in vitro study.

The following points are the main findings of our study:

  1. Autoclave following standard protocol is the best method for decontamination of dental handpieces. If the recommended cleaning of dental handpieces prior to autoclave procedure, as suggested by the CDC, is not strictly followed, it cannot guarantee 100% sterilization rate
  2. Disinfectant method following 70% isopropyl alcohol is not a reliable way to remove E. coli from the affected dental handpieces
  3. Presence of S. salivarius was found significant in the samples applied with Decident™, a commercially available disinfectant pouch.

Thus, we conclude that autoclaving the dental handpieces still remain as the best decontamination method and it is very important to follow the recommended cleaning procedure prior to autoclave for achieving 100% decontamination rate.

Financial support and sponsorship


Conflict of interest

There are no conflicts of interest.

  References Top

Mohan S, Prajapati VK, Verma SK. Sterilization and infection control measures in dental operatory. Int J Adv Integr Med Sci 2017:2:97-100.  Back to cited text no. 1
McCarthy GM. Risk of transmission of viruses in the dental office. J Can Dent Assoc 2000;66:554-5, 557.  Back to cited text no. 2
Muralidaran S, Muralidaran NP. Evaluation of efficacy of 2% glutaraldehyde for disinfection of hand pieces used in dentistry. J Pharm Sci Res 2016;8:832-4.  Back to cited text no. 3
Offner D, Brisset L, Musset AM. Cleaning of dental handpieces: A method to test its efficiency, and its evaluation with a washer-disinfector lubricator-dryer. Dent Open J 2016;3:10-6.  Back to cited text no. 4
Silva MP, Pereira CA, Junqueira JC, Jorge AO. Methods of destroying bacterial spores. In: Méndez-Vilas A, editor. Microbial Pathogens and Strategies for Combating them: Science, Technology and Education. Badajoz: Formatex Research Center, 2013.  Back to cited text no. 5
Russell AD. Bacterial spores and chemical sporicidal agents. Clin Microbiol Rev 1990;3:99-119.  Back to cited text no. 6
Block SS. Disinfection, Sterilization and Preservation. 5th ed. Philadelphia: Lippincott Williams and Wilkins; 2000.  Back to cited text no. 7
Rutala WA, Weber DJ. Healthcare Infection Control Practices Advisory Committee (HICPAC). Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008. Available from: https://www.cdc.gov/infectioncontrol/pdf/guidelines/disinfection-guidelines.pdf. [Last accessed on 2018 Mar 5].  Back to cited text no. 8
Graziano MU, Graziano KU, Pinto FM, Bruna CQ, de Souza RQ, Lascala CA, et al. Effectiveness of disinfection with alcohol 70% (w/v) of contaminated surfaces not previously cleaned. Rev Lat Am Enfermagem 2013;21:618-23.  Back to cited text no. 9
Sterilization of Dental Instruments Dental Clinical Guidance, Scottish Dental Clinical Effectiveness Programme Online Document. Available from:http://www.sdcep.org.uk/wp-content/uploads/2015/01/SDCEP+Sterilization+of+Dental+Instruments.pdf. [Last accessed on 2018 Mar 10].  Back to cited text no. 10
Sajjanshetty S, Hugar D, Hugar S, Ranjan S, Kadani M. Decontamination methods used for dental burs — A comparative study. J Clin Diagn Res 2014;8:ZC39-41.  Back to cited text no. 11
CDC. Guidelines for environmental infection control in health-care facilities: Recommendations of CDC and the Healthcare Infection Control Practices Advisory Committee (HICPAC). MMWR 2003;52(No. RR-10).  Back to cited text no. 12
Lewis DL, Boe RK. Cross-infection risks associated with current procedures for using high-speed dental handpieces. J Clin Microbiol 1992;30:401-6.  Back to cited text no. 13
Jocobs P. Cleaning-principles, methods and benefits. In: Rutala WA, editor. Disinfection, Sterilization and Antisepsis in Healthcase. Champlain, New York: Polyscience Publications; 1998. p. 165-85.  Back to cited text no. 14
Alfa MJ, Olson N, Degagne P, Hizon R. New low temperature sterilization technologies: microbial activity and clinical efficacy. In: Rutala WA, editor. Disinfection, Sterilization and Antisepsis in Healthcase. Champlain, New York: Polyscience Publications; 1998. p. 165-81.  Back to cited text no. 15
Leiss-Holzinger E, Felbermayer K, Ismic D, Rankl C, Hillmann J, Brandstetter M. A Localized Analysis of the Sterilization Process by Direct Steam Monitoring. IEEE Access. p. 1-1. 10.1109/ACCESS.2017.2753940.  Back to cited text no. 16
Winter S, Smith A, Lappin D, McDonagh G, Kirk B. Investigating steam penetration using thermometric methods in dental handpieces with narrow internal lumens during sterilizing processes with non-vacuum or vacuum processes. J Hosp Infect 2017;97:338-42.  Back to cited text no. 17


  [Figure 1], [Figure 2]

  [Table 1]


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