Xylitol is an all natural sugar replacement that is healthy for both teeth and gums. It has both antibacterial and antifungal properties and helps to neutralise the pH in the mouth which in turn reduces the chance of tooth decay.
Xylitol is available in all supermarkets, as well as pharmacies, in a fine granular / powder form. Many chewing gums also contain xylitol, but make sure you read the packaging to avoid those that contain the dreaded aspartame too!
I advise chewing 3-4 pieces of xylitol chewing gum per day just until the flavour has gone. This helps to increase the natural saliva flow and improve cleansing in the mouth.