It's for oral sex. It is placed over the womans vagina and the man licks the dental dam to provide pleasure for the female.
Dental dam, a device used to protect the mouth during oral sex, is made of the same latex as used in condoms. Dental dam can be purchased at any adult/safer sex stores.
the dental dam your dad had to use on your mom?
It is a device placed in the mouth to isolate a tooth during a procedure so not to get any saliva or water on the tooth. :) Dental dam is a rubber membrane which prevents bacteria and saliva getting in the area that is worked on, especially when the dentist is using materials that are sensitive to moisture. They are fixed with a bracket and no pain is experienced. Here's a video showing the use of a dental dam - http://www.checkdent.com/en/videos/what-is-a-dental-dam-106.html
A piece of dental dam.
Before applying a dental dam, you should assemble a few essential items: the dental dam itself, a frame to hold the dam in place, lubricant for easier placement, and any necessary clamps or forceps to secure it around the tooth. Additionally, having scissors on hand for trimming the dam and a saliva ejector can help maintain a dry working area. It's also helpful to have a mirror and light source for better visibility during the procedure.
A dental dam
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see:http://www.sexualityandu.ca/adults/sti-4.aspx
The tooth behind the one you're working on
A "dam" is a block or impediment, which holds material in place and/or prevents its motion. The typical dam is a large structure, usually concrete, that blocks a waterway. It may be designed to retain water (a reservoir) or to create hydroelectric power. Other dams can restrict the flow of air, or other fluids (the dental dam used in dentistry).The word dam (related to dame) is also applied to a female parent in some animals.
You can purchase dental dams online through mass retailers like amazon.com and medical or healthy supply websites. Dental dams can be expensive so be sure to shop around to get the best deal.
How a dam is used to make electicity The dam holds back water from a river or similar.