How does dextran and fructose help the bacterium to initiate dental caries? Lab How does dextran and fructose help the bacterium to initiate dental caries? Answer: The polysaccharide clings tenaciously to the teeth and forms dental plaque, in which streptococci reside and ferment fructose with the formation of lactic acid. Learn More : Share this Share on FacebookTweet on TwitterPlus on Google+