After the second day the abscess burst with pus coming out (fistula). At that stage, the diagnosis of a subperiosteal abscess originating from the fractured right canine seems to be more likely than an allergic reaction.
Palpating a subperiosteal swelling, that means a swelling underneath or within the bone, gives a distinct feeling of firmness and tension under the surface, This is very different from a subcutenous swelling caused by an allergic reaction.
Unfortunately many vets still remove teeth which can be saved. Even though other treatment options are common practice in more advanced veterinary practices. The canine tooth of a dod can be 60mm long and to remove this tooth requires some serious osteotomy (removal of bone to uncover the root).