Teeth are small, calcified structures found in the mouth that mechanically break down food. They are composed of materials like calcium, phosphorus, and enamel. There are four main types of teeth - incisors for cutting, canines for tearing, premolars for crushing, and molars for grinding food. Plaque buildup can lead to tooth decay from bacteria like Streptococcus mutans producing acid that dissolves enamel over time. Proper oral hygiene through brushing teeth twice daily and regular dental checkups can prevent dental issues.