A fever that occurs with a toothache may mean an infection has
developed in a tooth or surrounding gums.
An
abscessed tooth 
is caused by an infection that develops in the tissue around a
tooth. When the center of the tooth (pulp) dies
because of damage or tooth decay, mouth bacteria start to overgrow. Bacteria
spread from the root of the tooth to the tissue underneath it, creating a
pus-filled pocket called an abscess.
An abscessed tooth can cause severe pain from the pressure against
the tooth, bone, and nerves. An abscessed tooth may also make your gums swollen
and red. If the abscess is left untreated, the pus may spread to tissues of
your mouth, jaw, and face, causing a fever, bad taste in your mouth, and
swelling in your jaw, face, or neck.
As the infection increases, your jawbone may begin to dissolve to
make more room for swelling of the infected area. As the bone dissolves, it may
relieve pressure and reduce pain, but the infection remains. If too much bone
dissolves, there will be no support for the tooth, and the tooth may have to be
removed.
An abscessed tooth may develop because of gum disease. Gum disease
causes the gums to pull away from the teeth, leaving pockets. If one of these
pockets becomes blocked, mouth bacteria can overgrow and an abscess may
form.
Prompt dental care can help determine the cause of your fever and
keep the tooth from dying.
