An aching tooth’s a warning. Often it's a cavity, but not always. Other Toothache Causes... After a filling, a tooth can sometimes be a bit sensitive. It’s a normal reaction that should soon correct it-self. In the morning, an aching tooth could be the result of grinding or tooth-clenching overnight. Not a cavity, but a habit you need to shake. Aches can also come from unfamiliar pressures due to tooth [...]