|Anatomical terms of bone|
The alveolar process () (also called the alveolar bone) is the thickened ridge of bone that contains the tooth sockets (dental alveoli) on the jaw bones that hold teeth (in humans, the maxilla and the mandible). The curved part of each alveolar process on the jaw is called the alveolar arch.
The alveolar process contains a region of compact bone adjacent to the periodontal ligament (PDL), 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 process has a supporting bone, both of which have the same components: fibers, cells, intercellular substances, nerves, blood vessels, and lymphatics.
The alveolar process is the lining of the tooth socket or alveolus (plural, alveoli). Although the alveolar process is composed of compact bone, it may be called the cribriform plate because it contains numerous holes where Volkmann's 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).
Alveolar bone is 67% inorganic material by weight. The inorganic material is composed mainly of the minerals calcium and phosphate. The mineral content is mostly in the form of calcium hydroxyapatite crystals.
The remaining alveolar bone is organic material (33%). The organic material consists of collagen and non-collagenous material. The cellular component of bone consists of osteoblasts, osteocytes and osteoclasts.
Bone is lost through the process of resorption which involves osteoclasts breaking down the hard tissue of bone. A key indication of resorption is when scalloped erosion occurs. This is also known as Howship's lacuna. The resorption phase lasts as long as the lifespan of the osteoclast which is around 8 to 10 days. After this resorption phase, the osteoclast can continue resorbing surfaces in another cycle or carry out apoptosis. A repair phase follows the resorption phase which lasts over 3 months. In patients with periodontal disease, inflammation lasts longer and during the repair phase, resorption may override any bone formation. This results in a net loss of alveolar bone.
Alveolar bone loss is closely associated with periodontal disease. Periodontal disease is the inflammation of the gums. Studies in osteoimmunology have proposed 2 models for alveolar bone loss. One model states that inflammation is triggered by a periodontal pathogen which activates the acquired immune system to inhibit bone coupling by limiting new bone formation after resorption. Another model states that cytokinesis may inhibit the differentiation of osteoblasts from their precursors, therefore limiting bone formation. This results in a net loss of alveolar bone.
The developmental disturbance of anodontia (or hypodontia, if only one tooth), in which tooth germs are congenitally absent, may affect the development of the alveolar processes. This occurrence can prevent the alveolar processes of either the maxillae or the mandible from developing. Proper development is impossible because the alveolar unit of each dental arch must form in response to the tooth germs in the area.
After extraction of a tooth, the clot in the alveolus fills in with immature bone, which later is remodeled into mature secondary bone. Disturbance of the blood clot can cause alveolar osteitis, commonly referred to as "dry socket." With the partial or total loss of teeth, the alveolar process 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.
Alveolar bone grafting in the mixed dentition is an essential part of the reconstructive journey for cleft lip and palate patients. The reconstruction of the alveolar cleft can provide both aesthetic and practical advantages to the patient. Alveolar bone grafting can also bring about the following benefits: stabilisation of the maxillary arch; aid of eruption of the canine and sometimes lateral incisor eruption; offering bony support to the teeth lying next to the cleft; elevate the alar base of the nose; aid sealing of oro-nasal fistula; permit insertion of a titanium fixture in the grafted region and achieve good periodontal conditions within and next to the cleft. The timing of the alveolar bone grafting takes into consideration both eruption of the canine and lateral incisor. The optimal time for bone grafting surgery is when a thin shell of bone still covers the soon erupting lateral incisor or canine tooth close to the cleft.