Xylitol chewing gum is given to children in schools in Finland, because it prevents cavities. It cannot be digested by oral bacteria. Formerly, there was a special candy tax, which didn't include xylitol candies. The market share of the chewing gum not containing xylitol is only 3%. Connect the dots.
Xylifresh is the only chewing gum that has got the recommendation of the Finnish Dental Association, because its only sweetener is xylitol. The recommended usage is to eat it each time after eating, which is 3-5 times a day. The xylitol will take the place of the sugars in the food, so that the bacteria don't have time to metabolize the food. Stopping the chewing of xylitol will cause the mutans streptococcus to regrow back to its original level, so that they must be suppressed continuously with xylitol. (Eating 10 pieces once a day is less effective than 2 pieces five times a day.)
The birch contains xylane, which is extracted, and so it breaks up to smaller xylosis molecules, which is converted to xylitol by adding hydrogen to it in high pressure, temperature and in the presence of a catalyst, activated nickel. This industrial process (which is dangerous and has caused explosions) makes it more expensive than the other sweeteners, so that most chewing gum manufacturers cut the xylitol with less expensive sweeteners.
The xylosis molecule has the unsaturated carbon-oxygen double bond, or the aldehyde group, in the terminal carbon, which makes it a sugar. Add hydrogen to both ends, and you'll saturate the carbon and get an alcohol. Look at the structure above: there are only saturated carbons bonded to the hydroxyl group. This is why xylitol isn't a sugar, but is easily made from a sugar.
Sources: Hammashuolto - suositukset. http://www.riihimaki.fi/terveyskeskus/hammashuolto3.htm