Polarised light micrograph of crystals of xylitol. This is a five-carbon sugar alcohol which tastes sweet and is found in fruit, fungi, vegetables, birch trees and coconut husks. Substituting xylitol for sucrose in the diet inhibits tooth decay because, unlike other sugars, it is not fermented to acid by oral bacteria. These bacteria continue to metabolise nitrogen-containing substances in our food and saliva thus raising the pH and increasing remineralisation of tooth enamel. Xylitol is used to make dentally safe lozenges, chewing gum, pill-coatings and tooth- paste. Magnification: x9 at 35mm size.