A dental dam is basically a small sheet of latex which acts as a barrier between the vagina or anus and the mouth during oral sex (dental dams get their name because they are used during dental surgery such as root canals). Dental dams were originally only available in translucent-white latex; however, manufacturers are now adding different colours, shapes and sizes as dental dams become more populare as a sex aid.
Dental dams are an extremely effective means of preventing infection from vaginal or anal secretions. There is little data available on rates of infection after use of the dental dam. There are a few important concerns which may reduce the effectiveness of the barrier. Before you use the dam, lightly rinse it off with warm water. Dry with a towel. Then check to be sure the dam is free of holes or breakage. You can check the dam before you use it by holding it up to light or seeing if water is able to pass through it. Finally, ensure that only one side of the dam comes in contact with the genitals, and that the dam is used only once. Otherwise you are defeating the whole purpose of using the dam in the first place.
Only use water-based lubricants when using dental dams.