How do we get cavities from candy and why do our teeth turn gray/blackish?

Tooth decay, often referred to by the scientific term dental caries, is a condition in which the minerals that form the enamel or outer surface of the tooth are dissolved and tooth enamel is demineralized. The outer surface of tooth enamel is covered by a coating of “plaque” that consists mainly of bacteria, such as streptococcus mutans. Tooth decay occurs when simple sugars and certain fermentable carbohydrate-rich foods are digested by these bacteria to form acids which dissolve minerals such as calcium and phosphate found in tooth enamel. Eating sugary foods increases the production of these corrosive acids and increases the chances of dental decay. If this process of demineralization of tooth enamel proceeds to the dentin (layer of tooth below the enamel) and pulp (layer below the dentin which contains blood vessels and nerves) this results in advanced dental caries or cavities and discolorization of the tooth. Saliva helps to wash away sugars and buffer the effects of the acid formed in the fermentation process by bacteria in plaque, and therefore helps to counteract this demineralization process. We can prevent tooth decay by brushing and flossing our teeth regularly to thoroughly clean away food debris and plaque. We can further control dental decay by eating a proper diet and avoiding an excess amount of candy, sweets and other sugary foods.