MODEL RELEASED. Toothache. Woman holding an ice pack to her face to numb the pain from one of her teeth. Toothache is in most cases the result of tooth decay (dental caries). This is caused by bacteria which remain as a plaque on the teeth and which produce an acid that slowly destroys the tooth. Toothache occurs when decay is so advanced that the bacteria infect the living pulp" inside the tooth, causing pain. Dental treatment involves drilling out the affected area and inserting a filling into the tooth."