If you are concerned, there is no association between artificial
sweeteners and cavities.  In contrast, studies have demonstrated that
Xylitol interferes with bacteria reproduction and aids in the
reduction of cavities.

In regards to the irritation...
Most tooth pastes contain Sodium lauryl sulfate which may cause some
sloughing of the gingiva (perioral dermatitis).  It happens with me,
but is not painful or severe.

I have heard that the artificial flavor that is most commonly
responsible for irritation is cinnamon...but I am unaware of any
problems with Spearmint.

The usage of the two products is slightly different...
Prevident 5000 is only a toothpaste with a higher concentration of
NaF.
GelKam is frequently used with a tray for overnight use in cases of
severe caries risk.  I believe it was originally developed for use
with Head and Neck radiation patients.

I am unaware of another brand of NaF toothpaste without a
sweetener...as most toothpastes have a sweetener to increase patient
acceptance.

Prevident 5000
Active Ingredient:
   Sodium fluoride 1.1% (w/w)
Other Ingredients:
   Purified water, sorbitol, hydrated silica, PEG-12, tetrapotassium
pyrophosphate, sodium lauryl sulfate, mint flavor (Spearmint flavor
only), xanthan gum, sodium benzoate, fruit flavor (FruitasticTM*
flavor only), sodium saccharin, titanium dioxide (FruitasticTM* flavor
only), FD&C Blue #1 (Spearmint flavor only), D&C Red #33
(FruitasticTM* flavor only).