What is it?

A rubber dam or dental dam is a rectangular sheet of latex used by dentists, especially for root canal treatment, but also for things like tooth-coloured fillings

What is it used for?

Your dentist uses a hole puncher to make a hole in the sheet for the tooth to be treated, only one hole is punched. The sheet may be marked with dots (with each dot representing a tooth) which make it easier to punch the hole in the right place