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| Tooth in Alveolar Bone
The alveolar process (alveolar bone) is the thickened ridge of bone that contains the tooth sockets or alveoli (alveolus, single) on bones that contain teeth. In humans, the tooth-bearing bones are the maxillae and the mandible.
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Features
The mineral content of alveolar bone is mostly calcium hydroxyapatite, which is similar to that found in higher percentages in both enamel and dentin, but is most similar to the levels in cementum (50%). Like all bone, mature alveolar bone is by weight 60% mineralized or inorganic material, 25% organic material, and 15% water. The minerals of potassium, manganese, magnesium, silica, iron, zinc, selenium, boron, phosphorus, sulfur, chromium, and others are also present but in smaller amounts. It is important to note that alveolar bone is more easily remodeled than cementum, thus allowing orthodontic tooth movement. When viewing a stained histological section, the remodeled alveolar bone shows arrest lines and reversal lines, as does all bone tissue.
Structure
On the maxillae, the alveolar process is a ridge on the inferior surface, and on the mandible it is a ridge on the superior surface. It makes up the thickest part of the maxillae.
The alveolar process contains a region of compact bone adjacent to the periodontal ligament (PDL), which is called the lamina dura when viewed on radiographs. It is this part which is attached to the cementum of the roots by the periodontal ligament. It is uniformly radiopaque (or lighter). Integrity of the lamina dura is important when studying radiographs for pathological lesions.
The alveolar bone or process is divided into the alveolar bone proper and the supporting alveolar bone. Microscopically, both the alveolar bone proper and the supporting alveolar bone have the same components: fibers, cells, intercellular substances, nerves, blood vessels, and lymphatics.
The alveolar bone proper is the lining of the tooth socket or alveolus (plural, alveoli). Although the alveolar bone proper is composed of compact bone, it may be called the cribriform plate because it contains numerous holes where Volkmann canals pass from the alveolar bone into the PDL. The alveolar bone proper is also called bundle bone because Sharpey fibers, a part of the fibers of the PDL, are inserted here. Similar to those of the cemental surface, Sharpey fibers in alveolar bone proper are each inserted at 90 degrees, or at a right angle, but are fewer in number, although thicker in diameter than those present in cementum. As in cellular cementum, Sharpey fibers in bone are generally mineralized only partially at their periphery.
The alveolar crest is the most cervical rim of the alveolar bone proper. In a healthy situation, the alveolar crest is slightly apical to the cementoenamel junction (CEJ) by approximately 1.5 to 2 mm. The alveolar crests of neighboring teeth are also uniform in height along the jaw in healthy situation.
The supporting alveolar bone consists of both cortical bone and trabecular bone. The cortical bone, or cortical plates, consists of plates of compact bone on the facial and lingual surfaces of the alveolar bone. These cortical plates are usually about 1.5 to 3 mm thick over posterior teeth, but the thickness is highly variable around anterior teeth. The trabecular bone consists of cancellous bone that is located between the alveolar bone proper and the plates of cortical bone. The alveolar bone between two neighboring teeth is the interdental septum (or interdental bone).
Pathology
After extraction of a tooth, the clot in the alveolus fills in with immature bone, which later is remodeled into mature secondary bone. However, with the loss of teeth, a patient becomes edentulous, either partially or completely, and the alveolar bone undergoes resorption. The underlying basal bone of the body of the maxilla or mandible remains less affected, however, because it does not need the presence of teeth to remain viable. The loss of alveolar bone, coupled with attrition of the teeth, causes a loss of height of the lower third of the vertical dimension of the face when the teeth are in maximum intercuspation. The extent of this loss is determined based on clinical judgment using the Golden Proportions.
The density of the alveolar bone in a given area also determines the route that dental infection takes with abscess formation, as well as the efficacy of local infiltration during the use of local anesthesia. In addition, the differences in alveolar process density determine the easiest and most convenient areas of bony fracture to be used, if needed during tooth extraction of impacted teeth.
During chronic periodontal disease that has affected the periodontium (periodontitis), localized bone tissue is also lost.
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