Cavities are holes in teeth due to tooth decay. They are also known as caries. Two major contributors to tooth decay are bacteria and a diet high in sugar and starch.There are over five hundred different types of bacteria that are always present in the mouth.
The bacteria mixes with food and saliva to make a sticky substance called plaque, which fastens to teeth. Foods high in starch add to the stickiness of the plaque, which starts to get hard if it remains on the teeth after 1 or 2 days and turns into tartar or calculus deposits. Bacteria in the plaque turn sugar to acid, which dissolves the tooth structure causing holes or cavities. Due to these factors, dental caries have been described as a "dietobacterial" disease. The parts of teeth that are most vulnerable to tooth decay are where plaque can collect most easily. Plaque settles into the pits and fissures in the tops of teeth, into the areas in between the teeth, and next to the gum line. Where there's plaque, there are bacteria and acid, and sometimes damage of the tooth surface.
The cavity starts in the surface layer of the tooth (enamel) and as it gets deeper, penetrates into the softer inner layer of the tooth (dentin.) In general it's not until the decease reaches the dentin that you will start to notice signs of the cavity. To understand how a cavity works, we really need to have a better understanding of the anatomy of the tooth. A tooth is composed of a couple layers. The outer layer (above the gum-line) is known as the enamel. Enamel is the strongest and most mineralized substance in the body. Beneath the gum-line, a substance called cementum covers the tooth roots. Under the enamel and cementum is the dentin. The dentin is about as hard as bone, and, unlike the enamel, dentin contains nerve endings. Beneath the dentin is the dental pulp. The pulp is a vascular tissue, composed of capillaries, larger blood vessels, connective tissue, nerve fibers, and cells including odontoblasts, fibroblasts, macrophages, and lymphocytes. The pulp is needed to nourish the tooth during its growth and development. After a tooth is fully mature, the only function of the pulp is to let us know if it is damaged or infected by transmitting pain.
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