Teeth are hard, calcified structures in the mouth used primarily for biting, chewing, and breaking down food, as well as aiding speech and contributing to facial structure. Humans typically have two sets: 20 primary (baby or deciduous) teeth that erupt between 6 months and 3 years and are later replaced, and 32 permanent (adult) teeth that emerge starting around age 6, including 8 incisors (for cutting), 4 canines (for tearing), 8 premolars (for crushing), and 12 molars (including 4 wisdom teeth for grinding). Each tooth consists of an outer enamel layer (the hardest substance in the body), underlying dentin, a pulp chamber containing nerves and blood vessels, and a root anchored in the jawbone by cementum and periodontal ligament. Common dental issues include cavities (tooth decay from bacterial acid erosion), gum disease (gingivitis or periodontitis causing inflammation and potential tooth loss), tooth sensitivity, cracks, abscesses, misalignment (malocclusion), and wear from grinding or acidic erosion.