Anatomy and Classification of Teeth
- Dental anatomy is the study of tooth structure, development, appearance, and classification.
- The anatomic crown is the part of the tooth covered in enamel above the cementoenamel junction.
- The crown is mostly composed of dentin, with the pulp chamber inside.
- The anatomic root is found below the cementoenamel junction and is covered with cementum.
- Teeth can be classified as incisors, canines, premolars, and molars based on their function.
- Primary teeth, also known as deciduous or baby teeth, are temporary teeth that are eventually replaced.
- The dental formula for primary teeth in humans is 2.1.0.22.1.0.2.
- Primary teeth include incisors, canines, and molars.
- All primary teeth are later replaced with permanent teeth.
- The Universal Numbering System is used to identify adult human teeth.
- Humans have 32 permanent teeth, with 16 in the maxilla and 16 in the mandible.
- The dental formula for permanent teeth is 2.1.2.32.1.2.3.
- Permanent teeth include central incisors, lateral incisors, canines, premolars, molars, and third molars (wisdom teeth).
- Supernumerary teeth may occasionally form, while hypodontia refers to the development of fewer teeth than usual.
- Male teeth and jaws tend to be larger on average than female teeth and jaws.

Parts of a Tooth
- Enamel is the hardest and most mineralised substance in the body.
- It is primarily composed of hydroxyapatite, a crystalline calcium phosphate.
- Enamel is normally visible and varies in color from light yellow to grayish white.
- The wear rate of enamel is approximately 8 micrometers per year.
- Enamel does not contain collagen but relies on dentin for support.
- Dentin is the substance between enamel or cementum and the pulp chamber.
- It is secreted by odontoblasts in the dental pulp.
- Dentin is porous and yellowish in color, composed of 70% inorganic materials.
- Dentin compensates for the brittleness of enamel and provides support.
- Dentin has microscopic channels called dentinal tubules that radiate outward from the pulp cavity to the exterior cementum or enamel border.
- The diameter of dentinal tubules ranges from 2.5 μm near the pulp to 900nm near the dentino-enamel junction.
- The tubules do not intersect with each other, and their length is determined by the radius of the tooth.
- Dentin can be classified into three types: primary, secondary, and tertiary.
- Cementum is a specialised bone-like substance that covers the root of a tooth.
- It is approximately 45% inorganic material (mainly hydroxyapatite), 33% organic material (mainly collagen), and 22% water.
- Cementum is excreted by cementoblasts within the root of the tooth and is thickest at the root apex.
- Its principal role is to serve as a medium for the attachment of periodontal ligaments to the tooth for stability.
- The dental pulp is the central part of the tooth filled with soft connective tissue.
- It contains blood vessels and nerves that enter the tooth from a hole at the apex of the root.
- Odontoblasts, located along the border between dentin and pulp, initiate the formation of dentin.
- Other cells in the pulp include fibroblasts, preodontoblasts, macrophages, and T lymphocytes.
- The pulp is commonly referred to as the 'nerve' of the tooth.

Tooth Development and Eruption
- Tooth development is a complex process by which teeth form from embryonic cells, grow, and erupt into the mouth.
- Enamel, dentin, cementum, and the periodontium must all develop during appropriate stages of fetal development for a healthy oral environment.
- Primary teeth start to form between the sixth and eighth weeks of embryonic development, while permanent teeth begin to form in the twentieth week.
- Tooth development is divided into stages: bud, cap, bell, and maturation.
- The tooth bud consists of the enamel organ, dental papilla, and dental follicle.
- Tooth eruption is the process in which teeth enter the mouth and become visible.
- Primary teeth erupt from around six months to two years of age, while permanent teeth start erupting around six years old.
- The periodontal ligaments play an important role in tooth eruption.
- Different theories have been proposed for the cause of tooth eruption, with the most widely accepted belief being that the periodontal ligaments provide the main impetus for the process.
- The onset of primary tooth loss has been found to correlate strongly with somatic and psychological criteria of school readiness.

Supporting Structures of Teeth
- The periodontium is the supporting structure of a tooth, attaching it to surrounding tissues and allowing sensations of touch and pressure.
- It consists of cementum, periodontal ligaments, alveolar bone, and gingiva.
- Cementum is the only part of a tooth that is part of the periodontium.
- Periodontal ligaments connect the alveolar bone to the cementum.
- Alveolar bone surrounds the roots of teeth, providing support and creating sockets.
- Alveolar bone forms the alveolus around teeth.
- Osteoblasts create bone, and osteoclasts destroy it.
- Compressive force on a tooth leads to bone resorption, while tension from periodontal ligaments results in bone formation.
- Alveolar bone is modified throughout life.
- Gingiva is the mucosal tissue that overlays the jaws.
- Three types of epithelium associated with gingiva: gingival, junctional, and sulcular epithelium.
- Gingival epithelium is visible in the mouth.
- Junctional epith