Dental problem- back upper molars have shifted down to bottom, what to do?

Shifting molars: When upper molars have shifted down, it is usually because the lower opposing molars are missing or were extracted. This movement downward is called super eruption. There can be several solutions. If the opposing teeth are missing, then the shifted molars have no function and could be extracted. If you wish to keep the teeth because there are opposing teeth that have shifted, orthodontics (braces).

Dental exam: When molars drift downward in the upper arch, they usually bring bone with them. If you are missing the opposing molars and decide to remove the upper ones, you may need to remove some jaw bone as well to allow space for future prosthetic devices

See a dentist: for evaluation, x-rays and treatment. Unfortunately, that is what happens when you are missing an opposing molars. Good luck.