(I) The cause of tooth decay is acid, which is produced by bacteria in the mouth. (II) The rate at which bacteria in the mouth produce acid depends on the amount of plaque on the teeth, the composition of the microbial flora, and whether the bacteria of the plaque have been "primed" by frequent exposure to sugar. (III) To keep your teeth healthy, a regular dental hygiene program should be followed. (IV)

[Underlined sentence] Removing plaque with a toothbrush and dental floss temporarily reduces the numbers of harmful bacteria in the mouth, thereby lowering the risk of tooth decay. This practice also makes the surfaces of the teeth more accessible, which enables saliva to neutralize acid and remineralize lesions. If fluoride is present in drinking water when teeth are forming, some fluoride is incorporated into the enamel of the teeth, making [underlined word] them more resistant to attack by acid. Fluoride toothpaste seems to act in another way, by promoting the remineralization of early carious lesions.

In addition to a regular dental hygiene program, a good way to keep your teeth healthy is to reduce your intake of sweet food. The least cavity-causing way to eat sweets is to have them with meals and not between. The number of times you eat sweets rather than the total amount determines how much harmful acid the bacteria in your saliva produce. But the amount of sweets influences the quality of your saliva. Avoid, if you can, [underlined word] sticky sweets that stay in your mouth a long time. Also try to brush and floss your teeth after eating sugary foods. Even rinsing your mouth with water is effective.

Whenever possible, opt for foods with fiber, such as raw carrot sticks, apples, celery sticks, etc., that naturally [underlined phrase] scrape off plaque, acting as a toothbrush. Following these guidelines when consuming sweets and maintaining a thorough oral care routine can significantly reduce the risk of cavities and improve overall dental health.

(Adapted from https://www.verywellhealth.com/tooth-erosion)