The primary reason a surgical face mask must be used during a dental procedure is to:

Using a surgical face mask during a dental procedure is essential primarily to protect the dental healthcare professional (DHCP) from exposure to spatter and potentially infectious materials. During dental procedures, there is often the generation of aerosols and splatter, which can contain saliva, blood, and other pathogens. A surgical face mask serves as a barrier that reduces the risk of inhaling or coming into contact with these contaminants, thereby safeguarding the healthcare provider's health and allowing them to maintain a sterile environment.

While improving patient comfort or keeping the mouth closed may be incidental advantages, these do not capture the critical role of a mask in infection control. The primary focus is on minimizing the risk of infectious disease transmission, which is why the mask is a fundamental component of personal protective equipment (PPE) in the dental setting.