There is research out there on what is in Behcet's sores (from biopsies in the mouth, gut, genitals, skin, eyes) and also what is in periapical abscesses. Meaning what specific immune response is there. In both there are more of the gamma delta T lymphocytes as opposed to the alpha beta T cells. Gamma delta T lymphocytes make up only about 5% of the T cells. Their role is not as clearly defined as the alpha beta T lymphocytes. Embryonically, they originate from the same area as the lining of the gut, mouth, genitals, eyes and the teeth. (And also the eustachian tube and part of the inner ear where my wife has experienced some documented hearing loss. And also half of the pituitary gland, in which she has also had problems and the thyroid) In autoimmune diseases, what it is named has everything to do with what the target is that the body decides to attack. Arthritis- joints, MS- nerves, Lupus- connective tissue, Behcet's- endothelium of blood vessels, but only in certain places and smaller vessels, Wegners/Takayasu's - larger vessels. Why the certain targets is still a big mystery. But I see the target in Behcet's as all coming from the same embryological origin, of which teeth are a part of that.
There are other factors that are common to PA abscesses and Behcet's sores like Vascular endothelial growth factor (VEGF). I need to look back in my notes to remember what the others are.