To know if a tooth is infected, you would have to notice a few of these signs and symptoms first: - Severe, and quite a persistent toothache that may be throbbing or radiate to the jawbone, ear, or neck - Tooth sensitivity to hot or cold items and temperatures - Tooth sensitivity to any pressure put to the teeth from chewing or biting - Fever - Swelling noticeable in the face or cheeks - Swollen and tender lymph nodes under the jaw or within the neck - Noticing a foul-smelling or foul-tasting salty fluid occurring in the mouth - Issues breathing or swallowing If you begin to notice any of these symptoms, it may be an abscess that has formed in the mouth as an infection. To confirm you have a tooth infection, book an appointment with your dentist for a cleaning and check-up.