How common is it to get a gag reflex with dentures?

Very.: Unless you are a severe gagger , having your dentist shorten the end of your denture near your throat on an upper denture to help. If you are a severe gagger, then then a denture without the center section anchored by implants will do the trick.

It Really varies: If one goes from removal partial dentures to full dentures, the transition is much easier than from natural teeth to full dentures. There is an enormous variance of how well different individuals accommodate to full dentures. Some adapt easily and others never are comfortable with them. Gagging is one of the problems but most adapt well in time. Implants never cause this problem.

Very: Very common , especially early on. Ask your dentist to check the end of the denture and the back corners for overextension. Often an adjustment can solve the problem. Many times it is also a "mind over matter" situation. If no luck with your general dentist, seek the advice of a prosthodontist -- they are specialists in dentures.

Fairly common: But this can be corrected by adjusting the length of the denture that extends onto the roof of your mouth.