Which category of instruments only comes into contact with intact mucous membranes?

The correct answer is the category of semi-critical instruments, as these instruments come into contact with intact mucous membranes. Semi-critical instruments are those that are expected to touch mucous membranes or non-intact skin but do not penetrate soft tissue or bone. For instance, intraoral dental instruments, such as mirrors and film holders, fall into this category. These instruments require high-level disinfection after each use to ensure that any pathogens are effectively eliminated before they come into contact with patients during procedures.

In contrast, critical instruments penetrate soft tissue or bone, thus requiring sterilization to eliminate any possible pathogens, as they have the highest risk of infection transmission. Non-critical instruments only come into contact with intact skin, which poses a lower risk of infection and typically only requires low-level disinfection. Disposable instruments are designed for single use and do not require cleaning or disinfection but are not categorized based on the contact they have with mucous membranes.