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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
Human teeth function to mechanically break down items of food by cutting and crushing them in preparation for swallowing and digesting. As such, they are considered part of the human digestive system. Humans have four types of teeth: incisors, canines, premolars, and molars, which each have a specific function. The incisors cut the food, the canines tear the food and the molars and premolars crush the food. The roots of teeth are embedded in the maxilla (upper jaw) or the mandible (lower jaw) and are covered by gums. Teeth are made of multiple tissues of varying density and hardness.
| Human tooth | |
|---|---|
 | |
 Diagram of a human molar showing its major constituents | |
| Details | |
| Identifiers | |
| Latin | dens |
| TA98 | A05.1.03.001 |
| TA2 | 2818 |
| FMA | 75150 |
| Anatomical terminology | |
Humans, like most other mammals, are diphyodont, meaning that they develop two sets of teeth. The first set, deciduous teeth, also called "primary teeth", "baby teeth", or "milk teeth", normally eventually contains 20 teeth. Primary teeth typically start to appear ("erupt") around six months of age and this may be distracting and/or painful for the infant. However, some babies are born with one or more visible teeth, known as neonatal teeth or "natal teeth".
