Hope this helps,
Jossi Stokes, DDS, FAGD
abscess is visible usually in later stages of the condition when
infection has affected and dissolved some of the bone surrounding the
root, leaving a dark area or shadow in that area. Usually, when
visible, the condition has been growing for 6 to 9 months. But
sometimes, in the early stages of an abscess, when the infection hasn't
yet caused too much visible damage, we have to rely on symptoms for the
diagnosis of abscess. Some of those symptoms are: pain to biting,
spontaneous pain (toothache), pain to hot or cold that lingers beyond a
few seconds, or a draining "blister" alongside the tooth. We can even
test the tooth with a mild electric current to see if the nerve
reacts. If it doesn't, it means that the pulp of the tooth has mostly
or totally died and an abscess is forming.
The tooth abscesses because of trauma-injury to face or occlusal trauma due to bruxism(clenching or grinding) , large decay or a large filling.
Early accesses can't always be seen on a x-ray. Specific symptoms and pain
also factor into the diagnosis and treatment. It would be prudent to have
your son seen by a dentist to evaluate the area of concern and make sure
the dentist get a radiograph.