When assisting a dentist with a patient who has a history of hepatitis B, you should:

Using standard precautions is essential when assisting a dentist with a patient who has a history of hepatitis B. Standard precautions are a set of infection control practices designed to prevent transmission of infectious agents in healthcare settings, regardless of the patient's known health status. This approach assumes that all blood and certain body fluids may be infectious, and it includes wearing gloves, masks, gowns, and eye protection when appropriate.

By strictly adhering to standard precautions, the dental staff protects themselves and other patients from potential exposure to bloodborne pathogens like hepatitis B. This practice not only enhances safety in the dental office but also promotes a culture of health and hygiene.

Other options like ignoring safety protocols could lead to serious health risks, wearing gloves only when blood is visible could lead to insufficient protection in many scenarios, and using only face masks does not provide adequate barrier protection against all possible routes of exposure. Hence, employing standard precautions is the most effective and responsible approach in this situation.