1) Tooth decay – This is the most common cause of toothache. Small cavities affecting the outer layer (enamel) of the teeth are normally painless. But if the cavity/tooth decay penetrates through the enamel and effects the inner layer (dentin), your teeth becomes sensitive and when taking hot or cold food/drinks you may experience mild to sharp pain. And in the advanced stage, the decay progresses to the inner layer (pulp of the tooth) resulting in shooting, sharp pain. It can also lead to an abscess (pus) at the root tips.
3) Gum disease – Gum infection causes inflammation on gum and bone tissues, which leads to swelling, bone loss around the teeth and a dull pain. This is the advanced stage of gum disease which, can even cause pain in a healthy tooth.
4) Improper oral hygiene – Improper brushing and flossing can lead to plaque build up on teeth. Plaque on teeth for longer time can irritate gums. The bacteria in the plaque react with left over tiny food particles and forms acid. This acid attacks the tooth/teeth, which in turn leads to pain.
5) Teeth grinding (bruxism) – Many people have habit of teeth grinding during sleep. This can wear down your teeth enamel or chip out your teeth and make your teeth sensitive to hot or cold food/drinks.
Excessive pressure put on the teeth during teeth grinding can not only cause pain in the teeth nut also in muscles and jaw joints.
6) Impacted wisdom tooth – Wisdom teeth are the last molars to erupt. When these teeth do not have enough room to emerge or are partially erupted, they are called impacted wisdom teeth. And this impacted wisdom teeth cause pain. It also puts pressure on nearby tooth that even can cause pain.
Also if the wisdom teeth are partially erupted, they are difficult to clean and floss and are more prone to tooth decay.
7) Orthodontic treatment – A treatment to correct, straighten and align teeth. The appliance (braces) that is fixed when undergoing this treatment can be painful during its initial stage, as it puts pressure on teeth to bring them in their correct position.
A toothache may also be caused by a problem that may not relate to tooth or jaw. There are some conditions that are referred to as toothache. For example, during a sinus infection, the pressure from your sinuses is sometimes referred as dull pain in your upper back teeth because of the close proximity to the teeth.