A dental sealant is process by which we place a very small layer of bonding material into the grooves of an adult tooth. While any tooth could technically be sealed, we primarily use sealants for upper and lower first molars.
We most often place sealants in children who are 5-7 years old, as this is the age where the first molars tend to erupt. We seal these molars because they are the teeth that will be in the person's mouth the longest, and as such it's important to protect these teeth from decay early on. Adults who have a high rate of cavities can also have sealants placed, but it's much more common to use sealants in children.
No. We will roughen the grooves in the tooth to improve bonding, but we rarely need to use local anesthetic for the procedure.
Whether or not a tooth should be sealed depends upon a number of factors including the child's cavity rate, oral hygiene and the depth of the grooves. If a tooth has very shallow grooves, then sealants are less important vs. teeth that have very deep grooves that will tend to capture and trap food debris and bacteria.