Demineralization is promoted by acidic foods and beverages and by acids from bacterial action on food particles. It is also promoted by the habits of constantly sipping water, or sucking on acidic candies (even sugar-free acidic candies).
In a normal mouth, saliva (with its high concentrations of calcium and phosphate) remineralizes the teeth constantly. In a dry mouth, something else must play that remineralizing role.
A supersaturated remineralizing solution developed by Dr. Athena Papas, D.M.D, Ph.D., Director of the Rubenstein Oral Health Management Clinic at Tufts New England Medical Center, has worked for me as needed since 1996. I find it effective in remineralizing teeth, and I find it soothing to distressed oral tissues. It seems also to help quell candidiasis. As far as safety goes: although a prescription is required, these are fairly innocuous ingredients -- same calcium and phosphate as in normal saliva, but at about 10-fold concentration.
Caphosol is available by prescription only. It is sold now in fully diluted pairs of ampules, which are mixed just prior to use (so that the supersaturated solution does not precipitate out while "on the shelf".)
There are now some competitors to Caphosol, which also describe themselves as supersaturated calcium phosphate solutions. I know of NeutraSal and SalivaMax, both of which offer the lighter weight of a dry powder which is dissolved in water just prior to use. I have used NeutraSal; I like its light form factor, but find it harsher on the mouth than the Caphosol ampules.
I have not yet seen price competition. These products seem to all sell at about the same per-use price, which is (as of 6/2016) an enormous multiple of the cost of the raw ingredients. I am hoping that we will see some real competition in this marketplace, to pull the price down closer to, say, the price of saline solution inhalation ampules, which have similar raw ingredients, similar packaging, and similar regulatory requirements to meet.
The recipe for the original researcher's version of the Caphosol solutions is described, in more detail than anybody but a chemist wants, in US Patent number 5,993,785 Now that that patent has expired, it seems that perhaps a compounding pharmacist might be persuaded to make up some batches in that way (which is targeted toward creating small vials of concentrated A and B solutions, each of which gets diluted by the user to create a large volume of ready-to-use solution).