My upper set are held in by suction, I think the plate is the key to it, mine are a sort of hard plastic with the teeth attached, if the dentist does his job properly when making the impressions of your pallet, the dental lab then make the full top set to fit your mouth correctly. Never had a problem with the top set apart from wear and as you age your gums recede and they become loose, mine needed changing after about 10 years or so. The bottom set are the biggest problem as far as fitting is concerned, because they are only fitted on the gums and any remaining teeth as anchor points. This was all done in the U.K. privately, by a Norwegian dentist who was part of an NHS dental practice.