This is often caused by a lack of oral hygiene. If proper dental care is not carried out on a daily basis, bacteria can attack healthy teeth and cause tooth decay. Bacteria work their way further and further into the tooth and reach the inner layers of the tooth. Stimuli such as cold water, sweet foods or fruit acids come closer and closer to the nerve in the tooth, causing the familiar toothache. Bacteria can also cause inflammation of the gums. This allows the bacteria to settle in the gum pockets and move deeper and deeper towards the root of the tooth. This also causes toothache.