Final answer:
Correct use of latex condoms and abstinence are demonstrated methods to prevent HIV spread. Knowing HIV status is vital, but the impact of dental dams on HIV prevention is not as clearly established.
Step-by-step explanation:
Among the listed safer sex precautionary measures, abstaining from sexual contact has been demonstrated to completely prevent the spread of HIV, as it removes any possibility of transmission via sexual fluids. The correct use of latex condoms has been shown to significantly reduce the transmission risk of HIV and other sexually transmitted infections (STIs) when used consistently and correctly.
Knowing one's own and one's partner's HIV status is crucial for taking precautionary measures in the context of a sexual relationship. However the use of barriers such as dental dams during oral sex while theoretically preventive, has not been specifically demonstrated to reduce the spread of HIV to the same extent as the correct use of condoms and abstinence largely due to a lack of comprehensive research in this specific area.