larryfb,
First, I would like to say that I believe you should be covered for fluoride supplementation due to your recent history. Prescrition fluoride toothpaste is a good product. I don't utilize it very often in my patients with reduced salivary flow because in my experience topical fluoride applied via custom fluoride trays are much more effective in protecting the teeth from deterioration and patients prefer them and are much more inclined to follow my instructions.
However in the research I have read there is no significant difference in the benefits of prescription fluoride toothpaste compared with fluoride rinses and/or gels in protecting the teeth if used properly. In my practice, in Canada, I have had few occasions where a patient's insurance has not, at least partially, covered additional fluoride use if presrcibed by a dentist or doctor. In recent memory I have had to write one letter for a patient to their insurer and it resulted in coverage for the patient.
If the letter you send to your insurer is unproductive ask your dentist and/or doctor about alternative fluoride products as you may have coverage for a different method of application.
Please contact me if I can offer any further assistance or answer any questions.
Cheers,
Mike