牙齿

Adult teeth are classified into four types by shape and function. Incisors, with their chisel shape, cut food; canines, pointed and sharp, tear and pierce. Premolars and molars feature broad crowns and rounded tips for grinding and crushing. Together, these 32 permanent teeth work to physically break down food during digestion.

Primary teeth, or deciduous teeth, begin erupting around six months of age, with all 20 milk teeth emerging by 24 months. Permanent teeth typically appear by age 12, starting with first molars around age 6. As permanent teeth enlarge, roots of primary teeth are absorbed, allowing them to shed and make room for the adult dentition.

Odontogenesis, or tooth formation, begins around the sixth week of embryonic development and progresses through three stages. The bud stage involves initial tooth germ formation in the developing jawbone. The cap stage differentiates the tooth germ into enamel organ, dental papilla, and dental sac. The bell stage shapes the tooth and differentiates ameloblasts and odontoblasts, which form enamel and dentin respectively.

The dental formula is a concise notation representing tooth type and number in one half of the mouth. The human permanent dental formula is 2-1-2-3, meaning two incisors, one canine, two premolars, and three molars per half. This formula is doubled to represent both sides and is valuable in dentistry, anthropology, and veterinary medicine for recording dental traits.

Wisdom teeth, or third molars, are the final set of molars emerging in late adolescence or early adulthood, typically between ages 17 and 25. They may cause complications like impaction, infection, and crowding due to insufficient jaw space. Some people never develop wisdom teeth, a trait potentially inherited through genes like PAX9 and MSX1 that control tooth development.

With age, teeth may become discolored, worn, and less sensitive from lifetime use and exposure to substances like caffeine and tobacco. Reduced saliva production increases risk of tooth decay and gum disease. Periodontal disease is the primary cause of tooth loss in adults over 35. Good oral hygiene, balanced diet, tobacco avoidance, and regular dental check-ups maintain healthy teeth and gums throughout life.

Endodontics focuses on preventing, diagnosing, and treating dental pulp diseases, typically involving root canal treatments. Orthodontics corrects teeth and jaw alignment using braces and aligners, improving oral function and aesthetics. Periodontics addresses prevention, diagnosis, and treatment of periodontal disease and dental implant placement, maintaining the health of tooth-supporting structures. These specialties complement the major organs of the digestive system by ensuring proper food breakdown begins in the mouth.