Candy, cookies, soft drinks, cakes, doughnuts, and other foods and drinks that are high in sugar are the primary cause of tooth decay. Tooth decay interferes with the salivary glands ability to produce saliva. This creates a cycle where tooth decay reduces the amount of saliva in the mouth. This allows bacteria to remain in the mouth, which exacerbates further tooth decay.
Your gums are vital to maintaining strong and healthy teeth. Saliva protects your gums from bacteria by forming a barrier that keeps the bacteria away. When there is not enough saliva to protect your gums, the bacteria can damage your gums and weaken your teeth. This starts the tooth decay process.