b. Standard Process. All items must be exposed to enough steam under
pressure to destroy all microorganisms. The autoclave is heated to 250F (121C) and
set at a pressure of 15 pounds per square inch for 30 minutes. [Since water boils at
212F (100C) the required temperature can only be attained by raising the pressure.
Thus, 250F creates a pressure that, at sea level, is equal to 15 pounds per square
inch.] Temperature is thermostatically controlled on autoclaves. Steam has a very high
heat of condensation, and that is why steam can cause so much damage to organic
matter. As steam condenses on a cool instrument in the autoclave, it releases a large
amount of heat energy that destroys microorganisms by denaturation of proteins and
results in sterilization. The actual sterilization time of 30 minutes allows ample time for
the steam to enter the packaging material, which may be paper, plastic, or muslin cloth.
c. Cleaning the Steam Sterilizer (Autoclave). The dental instrument sterilizer
must be cleaned so that all residue and mineral deposits are removed. In addition, the
door hinges should be lightly oiled, as needed, and the power cord and the chamber
door gasket visually checked.
(1) Routine maintenance. Routine maintenance includes cleaning the
exterior surfaces with the mildest of cleaning solutions, rinsing the interior surfaces
thoroughly with fresh water, wiping the surfaces dry to avoid water marks, draining the
water from the chamber, removing the strainer and wiping it to remove sediment
deposits, washing the chamber and trays with a mild detergent solution and cloth,
rinsing the detergent residue away from the chamber and trays with fresh water and
wiping dry with a lint-free cloth, and replacing the strainer.
(2) Removing visible mineral deposits. To remove visible mineral deposits,
a cleaning solution recommended by the manufacturer's instructions is to be used. The
water is drained from the chamber and reservoir. The solution is then poured into the
reservoir and the chamber is allowed to fill until the solution covers the deposits. When
the deposits loosen, they are wiped away. After that, the cleaning solution is drained
from the chamber and reservoir and the chemical residue is removed by flushing with
distilled water and wiping dry.
THE ULTRASONIC CLEANING UNIT
a. Cleaning by Cavitation. The ultrasonic cleaning unit is used in preparing
and cleaning instruments for sterilization. The unit uses high frequency sound waves to
create cavitation. Cavitation is a process of continuous formation and implosion of
microscopic bubbles in a cleaning solution. This creates a gentle scrubbing action that
penetrates all exposed surfaces, leaving them free of all foreign matter. The ultrasonic
cleaning unit does not sterilize an item; it only cleans the item. Rinsing and drying still
must be done before sterilization.