The most common cause of toothache is an infected pulp or nerve. This usually happens in the back molar teeth which are more prone to decay. At this point it is no longer possible to fill the tooth & treatment options are limited to root canal therapy or extraction. When faced with this dilemma patients often ask for my advice.
In the vast majority of cases the best decision is to retain the tooth with root canal therapy. Some patients will comment that if the tooth cannot be seen it is not important to keep the tooth. It is actually the back teeth which do most of the work when chewing. Loss of a back molar tooth will almost certainly reduce chewing efficiency with most chewing being done with the other side.