dear westiebilly11...
the bible OT doesn't say the angels materialized into human bodies. It also says that their offspring were not mere humans. This means that they had their own bodies with angelic dna and that they were capable of reproducing WITH humans. The physical offspring of these unions were destroyed in the flood but the spiritual entity of each was not destroyed they are those call demonic spirits. It is the fallen angels themselves who had the ability to move from the spiritual dimention to the physical dimention (like the resurrected Christ) in an actual body.
These angelic/human offspring have been destroying the earth for a long time and it is they who will inhabit human bodies...that's why it is called demon possession, but demons can be "cast out" and the human "regains" his senses (so to speak). According to the book of enoch these offspring are more or less free to cause destruction to men until sometime before the great judgement when they will be cast into the deepest valleys of the earth to await their fate.
enoch chapter 6