Which of the following is an example of a critical instrument used in radiology?

A critical instrument in the context of radiology and dental practice is one that penetrates soft tissue or bone and has a high risk of transmitting infection. Scalers are used to remove calculus and plaque from teeth and can come into contact with blood and saliva during procedures. This direct interplay with the internal tissues and fluids of patients categorizes scalers as critical instruments that must be sterilized after each use to prevent cross-contamination between patients.

In contrast, X-ray films primarily serve as a medium to capture images and do not directly penetrate tissues, although they do require careful handling to prevent contamination. Protective gloves are classified as personal protective equipment and are single-use items designed to prevent the clinician from direct contact with patients and the instruments rather than being classified as critical instruments themselves. Dental chairs, while important for patient care and comfort, do not involve direct interaction with body tissues in a way that presents a risk of infection transfer and are, therefore, not considered critical instruments.