Is it possible to have a cavitation or infection at the tip of a root without having ever had an extraction or root canal?

I went somewhere thinking I needed to have one dead tooth extracted and they are saying there is are dark marks at the tips of the roots of all four wisdom teeth (on the OPG x-ray). They say its probably infection/cavitation. I can see the mark by two roots at the bottom but it is so faint and I don't want to have four teeth taken out if I don't need to.
Just wondered if anyone has ever heard of this. I have never had an extraction or root canal and never had any problems with my wisdom teeth - no cavities in them. Just seems so extreme to take them all out.
Could there be any other reason for extremely faint dark marks on a panoramic x-ray? How would you get a cavitation with no cavity, extraction or root canal? Thanks for any advice. Tweet