Sugar becomes corrosive to enamel when the bacteria in dental plaque metabolize it and release acid. That is the acid that breaks down enamel and weakens your oral health.
Sugar substitutes, like low-calorie sweeteners, do not have the same effect. In fact, some sweeteners, called polyols, have antibacterial properties.
Some of these substitutes are labeled as sugar alcohols. This is due to the process in which they are derived. They are not broken down by oral bacteria’s and because of this they do not add to the breakdown of oral health by leading to cavities.
An interesting note concerning sugar substitutes in chewing gum can be found here 1998 review article.