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Sterility Assurance

Begin with the End in Mind


When the goal is sterility assurance, there are no short cuts and the process must be started with a clear vision of direction and destination; the plan for success is to begin with the end in mind (Figure 1). Covey’s simple quote from his book, The 7 Habits of Highly Effective People should be a guiding principle for sterilization. Every step that happens--from instrument cleaning, packaging, sterilization, monitoring, storage, and delivery--must be in alignment for quality assurance.

Sterilization describes a process that destroys or eliminates all forms of microbial life and is carried out in healthcare facilities by physical or chemical methods. Steam under pressure, dry heat, ethylene oxide (EtO) gas, hydrogen peroxide gas plasma, and liquid chemicals are the principal sterilizing agents used in healthcare facilities.1

The predominate sterilization method used in dentistry is the time-honored technique of steam sterilization. Advantages of steam sterilization include its non-toxic approach, rapid cycle time, and that it is highly efficacious, cost effective, easily monitored, and with strong penetrability.

What is Monitoring?

According to CDC Guidelines, monitoring of sterilization procedures should include a combination of process parameters, specifically mechanical, chemical, and biological. Combined, these parameters evaluate both the sterilizing conditions and the procedure’s effectiveness.2

The first monitoring tool is mechanical, which includes assessing cycle time, temperature, and pressure by observing the gauge, digital displays, or printout on the sterilizer and noting these parameters for each load. Correct end point response does not ensure sterilization, but incorrect readings can be the first indication of a gross equipment malfunction.

Chemical indicators (CIs) provide information about certain conditions within the package, but do not provide sterility assurance of the load. The internal and external CIs use reactive ink that changes color to assess one or more of the physical parameters (i.e., time, temperature, saturated steam) to which the instruments were exposed during the cycle. Single-parameter indicators provide information on only one parameter, while multiparameter indicators measure two to three parameters and provide a more complete evaluation of the sterilization conditions. While these chemical indicators do not necessarily prove sterility, they allow an early warning system for processing errors and they can help identify procedural errors. Every package should be examined by the clinician opening it, and an assessment should be made as to the acceptability of the end point response of the CI; any package indicator that fails to display the correct change and intensity of color should not be used and must be reprocessed.

Biological Indicators

Biological indicators (BIs) commonly use highly resistant spores (i.e., spore test) to challenge the sterilization process. Since they are more resistant and are usually present in greater numbers than are the common microbial contaminants found on instruments, destruction of these organisms will indicate destruction of other potential pathogens. While all three types of monitoring are important to the quality assurance process, biological monitoring is considered the gold standard for sterility assurance.

The most commonly used forms of BIs in dentistry are spore strips and self-contained spore vials. Spore strips are small pieces of filter paper impregnated with nonpathogenic bacterial spores (e.g., Geobacillusstearothermophilus and Bacillus atrophaeus) encased in a protective glassine envelope. After processing, the spore test envelope is sent to a laboratory where the paper strip is aseptically transferred to a test tube containing sterile culture media and then incubated. Self-contained vials have a glass ampule of sterile media, which is encased in a plastic vial with a spore strip inside. After sterilization, the vial is crushed--allowing the media to come into contact with the spore strip and then incubated. With either the strips or vials after incubation, if the pH indicator in the growth media changes the color from purple to yellow, this is an indication of a positive culture (i.e., spore growth) and meaning a failed test. It is recommended that a control be conducted with every BI test.

Three options are available for monitoring sterility assurance in the dental office: mail-in sterilization monitoring services to a third-party testing laboratory (i.e., private companies or dental schools), in-office 24-hour monitoring systems, and a newly released in-office 10-hour monitoring system. While some offices prefer use of a professional lab for testing verification (i.e., gram staining) and third-party documentation of results, others appreciate the convenience in-office processing provides, with a direct turnaround time and without the challenge of mailing and waiting for results. It should be noted that in-office monitoring systems can only be used with steam (autoclave) sterilizers; mail-in monitoring services can provide results for steam, dry heat, chemical vapor, and EtO.

(Continued from page 1 )

Guidelines for Sterilization  

The CDC guidelines state: Correct functioning of sterilization cycles should be verified for each sterilizer by the periodic (at least weekly) use of BIs. Consideration should be given for more frequent testing if the sterilizer is used multiple times each day or with use of a variation of sterilization cycles. Users should follow the manufacturer's directions concerning the appropriate placement of the BIs in the sterilizer; the preferred area for the BI placement is in the least-effective zone of the sterilizer--often near the door or the middle of the load near the drain.

In addition to conducting routine biological monitoring, equipment users should perform biological monitoring for the following occurrences:

  • Whenever a new type of packaging material or tray is used;
  • After training new sterilization personnel;
  • After a sterilizer process failure is indicated by a failed (positive) BI+;
  • After a sterilizer has been repaired;
  • After any change in the sterilizer loading procedures;
  • During initial use of a new sterilizer;
  • After relocation of an existing sterilizer; and
  • After electrical/power source failure.

The Importance of Compliance

In several studies, dental practices have demonstrated variability in sterilization compliance. For example, 68% of respondents believed they were sterilizing their instruments but did not use appropriate chemical sterilants or exposure times, and 49% of respondents did not challenge autoclaves with biological indicator.3 Other investigators using BIs have found a high proportion (15% to 65%) of positive spore tests after assessing the efficacy of sterilizers used in dental offices.4 In one study of Minnesota dental offices, operator error--rather than mechanical malfunction--caused 87% of sterilization failures.5 Common factors in the improper use of sterilizers include chamber overload, low temperature setting, inadequate exposure time, failure to preheat the sterilizer, and interruption of the cycle.

On December 8, 2011, the Supreme Judicial Court of Massachusetts affirmed the final decision and order of the Board of Registration in Dentistry, suspending the license of a dentist who failed to conduct and record weekly spore testing. The dentist’s failure constituted dental malpractice. The entire summary of Chadwick vs. Board of Registration in Dentistry case #SJC-10831 is available on the Internet.

In March, a health center in Wisconsin contacted the families of eight school children who were treated in a mobile clinic with potential exposure to blood-borne pathogens due to use of improperly sterilized instruments. Some of the instrument packages used during treatment displayed failed chemical indicators that would have identified either a procedural or processing sterilization error.

Documenting Sterilization

An accurately detailed and consistent documentation establishes accountability for sterilization. The information to be included with each sterilization cycle includes:

  • Sterilizer identification (serial) number;
  • Full date;
  • Operator identification;
  • Duration and temperature of the sterilization cycle (if not provided by a machine printout) (Figure 2);
  • Description of the general contents of the load;
  • Test results of biological monitoring (pass or fail);
  • Repair and preventive maintenance procedures; and
  • Special notes citing conditions outside of normal procedures, i.e. different operators or load content.

Clinicians should refer to state or local regulation guidelines for the length of time such documentation should be retained.


Effective sterilization is critical to safety and optimal patient care. Proper functioning of the sterilization process should be routinely monitored and documented using mechanical, chemical, and biological methods.

*General Manager & Director of Education, Crosstex International, Englewood, CO.



  1. Rutala WA, Weber, DJ et al. Guideline for disinfection and sterilization in healthcare facilities, 2008; Available at: http://www.cdc.gov/hicpac/pdf/guidelines/Disinfection_Nov_2008.pdf. Accessed March 1, 2012.
  2. KohnWG, Collins AS, Cleveland JL, et al. Guidelines for infection control in dental healthcare settings – 2003. MMWR Recomm Rep. 2003. Available at http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5217a1.htm. Accessed March 1, 2012.
  3. Gurevich I, Dubin R, Cunha BA. Dental instrument and device sterilization and disinfection practices. J Hosp Infect 1996;32:295-304.
  4. Smith A, Dickson M, Aitken J, Bagg J. Contaminated dental instruments. J Hosp Infect 2002;51:233-235.
  5. Hastreiter RJ, Molinari JA, Falken MC, et al. Effectiveness of dental office instrument sterilization procedures. J Am Dent Assoc 1991;122:51-56.
  6. Wahlberg, D. Access says 8 children givendental care with improperly sterilized instruments. Wisconsin State J 2012; March.Available at: http://host.madison.com/wsj/news/local/health_med_fit/access. Accessed March, 2012.


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