Spore Test Failure

The most common reason for spore test failure is not due to mechanical failure, but is actually due to operator error.

If your autoclave has failed a spore test, this is a good time to review your sterilization procedures with your staff.

Observe the technician who is responsible for sterilizing the handpieces and/or instruments and look for the following problem areas:
  • Is The Autoclave Being Overloaded?
    Refer to the manufacturers specifications and make sure the technician is not putting in too many items at one time.

  • Is The Right Temperature Being Achieved & Maintained?
    Inadequate Temperature: Set the temperature control knob so that it reaches and maintains 270-degrees (or manufacturers specifications).

    Check on it periodically during the cycle to make sure this temperature is not fluctuating more than a couple of degrees.

    If the temperature varies widely or the unit cannot maintain the manufacturer recommended temperature look for troubleshooting guides on this site for your unit.

  • Is The Right Amount Of Pressure Being Reached & Maintained?
    Inadequate Pressure: The chamber pressure should be maintaining approximately 30psi (or manufacturer specifications).

    If pressure cannot be maintained within the recommended range, check the troubleshooting guides on this site for your unit.

  • Is The Cycle Being Allowed To Run For The Right Amount Of Time?
    Inadequate Time: The normal processing cycle varies somewhat by the autoclave manufacturer. Follow the manufactures guidelines.

    Shortening the cycle endangers everyone, so don’t.

    If the temperature varies widely or the unit cannot maintain the manufacturer recommended temperature look for troubleshooting guides on this site for your unit.

  • Improper Packaging Of Instruments
    Follow Manufacturers Recommendations)

If any of the above shortcuts are being taken because the autoclave cannot keep up with your demand, it is time to either increase your inventory of handpieces and/or instruments, or get a second autoclave, or an autoclave that processes them faster.

How Is Sterilization Confirmed?

Sterilization can only be confirmed by testing for the survival of spores after a complete cycle in the autoclave.

After a spore strip is processed in a sterilizer, it is mailed to a monitoring service.

In a laboratory setting, the spore strip is aseptically removed from its protective envelope and placed in a tube of culture media. It is then incubated for 7 days.

For each of the 7 days, the tube of culture media is inspected for cloudiness.

If the spores are live and have not been killed, cloudiness is noted in the culture media. If no cloudiness is noted in the culture media, then sterilization is confirmed.

Is Chemical Monitoring Sufficient?


CHEMICAL MONITORING uses heat sensitive chemicals (not spores) to assess the physical conditions during the sterilization process.

Chemical monitoring involves the use of indicators that change color when exposed to certain temperatures.

Examples include autoclave tape, special markings on bags and pouches, and, chemical indicator strips, tabs or packets.

If a Chemical Indicator Changes Color, Has Sterilization Taken Place?


A chemical indicator only assesses the physical conditions (e.g., temperature) present during the cycle.

When a sterilizer reaches the required temperature, it causes the chemical indicator to change color; however, it does not indicate how long the temperature was maintained. Keep this in mind:

Temperature + Pressure + Time = Sterilization

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