Reducing bacteria in the mouth is a good thing. Recent evidence shows that chewing gum reduces the amount of bacteria in the mouth. Researchers determined that 10 minutes of chewing gum provided the maximum benefit. After 10 minutes the benefits decreased as bacteria attached to the gum were re-released into the mouth. By removing bacteria from the mouth, oral hygiene improves. This leads to a decrease in plaque buildup and helps promote good breath.
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0117191