What sugar substitute does gum usually use?

Xylitol for anti-cav. Saccharin, sorbitol, xylitol, and a few others. The best one is xylitol because it has anti-cavity properties. It inhibits the growth of cavity causing bacteria and also makes the saliva less acidic, chewing gum also increases salivary flow. Saliva cleanses the teeth and buffers plaque acids. So only chew gum that contains xylitol.
Mannitol an sorbitol. Mannitol and sorbitol are commonly used sugar substitutes. Though they are less cariogenic than sugar containing gums, they are not non-cariogenic.