The classification was given by Spaulding and is based on the contact with different tissue types to determine whether sterilization or disinfection is needed.

1. Critical items: that touches sterile areas of the body or enters the vascular system & those that penetrate the oral mucosa. Eg, scalpels, curettes, burs and files.

Instruments in this category must be sterilized and stored in appropriate packages. Single use items must be properly discarded.

2. Semi critical items: that touch mucous membrane but do not penetrate tissues. Eg. Amalgam condensers and saliva ejectors. These items should be sterilized, however if this is not feasible high level disinfection or disposal is required.

3. Non critical items:  that do not come in contact with oral mucosa but  are touched by saliva or blood contaminated hands while treating the patients. Eg. Light switches, counted tops & drawer pulls on cabinet. These should be properly disinfected.

Once the sterilization is complete we should assure its efficacy. This can be achieved by using various chemical and biologic indicators. These will be discussed under the following heading "sterility assurance".