It is interesting that in some situations, an adequate upper denture feels loose once the lower denture has been fixed in place. Usually the lower denture is more mobile than the upper, so the upper feels good relatively. Once the lower is not moving, the upper movement becomes evident.

If you are having problems retaining your upper denture, dental implants would be the answer for you. You could have implants placed, even though your sinus cavity is large. A procedure called a sinus lift is available. In that instance, the floor of the sinus is lifted and a bone graft is placed, this will give you sufficient bone to allow for the implants. This is a fairly straight forward procedure that would be done in the dental chair. Depending on how many implants you have placed, the upper denture could be replaced with a fixed restoration, or you could have an implant retained denture that clips onto the implants (you would not need the palate covered with either solution).

If finances do not allow for you to have the implant procedure done, you should be able to get adequate suction to maintain your upper denture. You should have the extensions of the denture checked to make sure they are not too long, which would decrease suction. The bite should also be checked to make sure that it is not getting loose due to premature bite contacts. After these have been checked and corrected as possible you could have a procedure called a functional reline. Here you would have a soft pliable material placed in you upper denture and would wear it for a few days. The material would adapt to your gums, giving you the optimal fit. The denture would then be processed to acrylic and should have better retention.