Question. Where do tooth decay occur? Answer: 90% between the teeth at the contacts. Question: Why does it occur? Answer: Due to the development of bacteria streptococcus mutans Question: How does it occur? Answer: The bacteria eats carbohydrates and excretes an acid PH of approximate 3.5 (very acid) which etched a hole in the enamel. The bacteria is anaerobic and acidophilic - it lives in the etched hole it creates and keeps enlarging the hole until no tooth is left. It likes the enamel-dentin (inside of the tooth) environment. Question: How do we stop it? Answer: Floss the contacts once a day. The floss brings neutral saliva PH to contacts which reduce the acid level (Ph 3.5) and therefore reduces acid etching (holes) from forming an enamel of contact points. The floss also brings oxygen to contact the anerobic bacteria and since aerobic - lives without oxygen), the oxygen kills the bacteria).