Do you have x-rays before you had your wisdom teeth removed? Quite often if the periodontal ligament isn't explicitly removed during the time of an extraction, a 1mm cap of bone will simply grow over the top of the extraction site, leaving a cavitation in the bone. If you've had dry sockets this is pretty much guaranteed. Unless you've had abscesses around these teeth, the probably size and shape will be where the roots of the original teeth were. But it's not possible to see the exact size and shape of the lesion normally on x-ray, just a rough guide.
As for alternate therapies, don't waste your time or money on o-zone injections or less invasive therapies. Dentists probably shouldn't even offer them. A cavitation is literally an area of dead/gangrenous bone/hole. You don't want to inject anything in this, just surgically clean it out. Any dentist that places implants should in theory be well equipped to deal with cavitations, as the method of cutting down the bone with very low speed drills, and inducing bleeding in the socket is basically identical to what is done during cavitation surgery . Just without the final stage of actually placing an implant.
I can understand being anxious, I think I was before my operations, but it's not really that bad. You will have a sore mouth for a few days, but they heal up pretty fast.