White spot on dental xray, what does this signify?

Hard to say: On x-rays, basically everything you see is either white or a shade of gray. Would need a lot more specifics.

Density: White spots or areas are places where the radiographs could not pass and expose the film. Where your white spots are is a guess and that is why you need to ask the dentist who took your films.

Generally a filling: Most white spots that my patients point to on their radiographs are fillings or a crown or nose / tongue piercing jewelry. X-rays can't penetrate these dense metal objects and they appear very white. However, less dense objects could be areas of dense bone in response to an abscess/infection, partially developed teeth, retained root tips or in rare cases benign or malignant cancers.