It is not uncommon for teeth to be sensitive following the placement of a filling. Your teeth may be sensitive to hot or cold items, to sweet foods, or simply to air or pressure. Normally the sensitivity goes away on its own within a few weeks.
During this intial phase, however, try to avoid things that cause any sharp sensation. And though you should never be in so much pain that you require a painkiller, it's a good idea to get a regular-strength, over-the-counter pain reliever just in case.
Here are some other common types of sensitivity once a tooth is filled:
Pain around your fillings: If you experience this type of pain you may want to see your dentist again because there's a chance the tooth was not properly repaired.
Pain when your teeth touch: This pain is a distinct pain that happens when your teeth touch. The pain is likely caused by the touching of two different metal surfaces such as the silver amalgam in a newly filled tooth and a silver crown on another tooth. This pain should resolve on its own within a short period of time but, again, if it's persistent you'll need to see a doctor again.
Toothache: Unfortunately if the decay was very deep to the pulp of the tooth, this type of pain may indicate this tissue is no longer healthy and you may have to get a root canal treatment for it.
Referred pain: With this type of pain, you experience pain or sensitivity in other teeth besides the one that received the filling. With this particular pain, there is likely nothing wrong with your teeth and the pain will probably go away on its own.
Allergic reactions to silver fillings (rare): In these rare circumstances, mercury or one of the metals used in the filling causes the allergic response. Symptoms of amalgam allergy are similar to those experienced in a typical skin allergy and include skin rashes and itching. The best solution to this is to ask to have the filling replaced with composite type of filling.
If the tooth pain does not subside within two to four weeks, or if your teeth are particularly sensitive, make sure you contact your dentist. Your dentist will likely suggest you use a desensitizing toothpaste or apply a desensitizing agent to the tooth, or possibly suggest a root canal procedure.