Tooth decay is usually caused by___________

Step 1: Analyze the question The question asks what usually causes tooth decay (dental caries). We need the main biological cause.

Step 2: Explain the concept Tooth decay happens through this process:

1. Food particles, especially sugary and starchy ones, remain on and between the teeth.
2. Bacteria in the mouth (e.g., Streptococcus mutans) feed on the sugar and break it down (metabolize it).
3. This produces acids as a by-product.
4. The acids dissolve the enamel, the hard outer layer of the tooth, and form cavities.
5. If untreated, decay reaches the dentine and pulp, causing toothache.

Step 3: Evaluate each option

• A. Undigested and absorbed food: Wrong. Absorbed food goes into the blood, and undigested food passes down the gut. Neither has any direct role in damaging teeth.
• B. Eating a limited amount of sweetened food: Wrong. A limited amount is not the cause. Frequent or excessive sugar intake is what promotes decay.
• C. The bacteria in the mouth that metabolize sugar to acids: Correct. This describes the actual mechanism of decay.
• D. Eating a lot of proteinous foods: Wrong. Protein is not the fuel for acid-producing bacteria, so it is not a major cause of decay.

Step 4: Answer

Tip: Remember the chain Sugar → Bacteria → Acid → Enamel damage. In WASSCE, if an option mentions "bacteria" and "acid" together in a tooth decay question, it is almost certainly the answer. To prevent decay, brush after meals, reduce sugary snacks, and visit the dentist regularly.