There's no clear information on what type and variety of bacteria are eliminated with xylitol. When I've tried those products, I would end up with canker sores. Furthermore, the xylitol passes into the intestinal system and can create imbalances there.
The body can respond to artificial sweeteners or sugar substitutes just as it would to sugar, through conditioned reflexes, that develop over years of sugar exposure. This is the Cephalic Response. This can increase inflammation in the tissues dpending on how the body responds. Some artificial sugars can also replace natural sugars in the body and render immune cells ineffective.