The alveolar bone is one of the three types of tissues that support the teeth in the maxillary or mandibular bone. The other two types of tissues that share this function with the alveolar bone are the cementum and the periodontal ligament. This bone is formed with the tooth, supports it and disappears when it is lost. For this reason, it is said of this structure that it is "dependent odonto".
The alveolar bone is located in a structure of the maxillary bones (superior and inferior) that is called “alveolar process” or “alveolus”. The alveolus is the bony compartment that houses the root of the tooth, a bony continuation of the mandible or maxilla that forms a conical cavity.
Alveolar processes, anatomical preparation (Source: Anatomist90 via Wikimedia Commons)
The socket is, then, the conical cavity where the root of the tooth is housed within the maxilla. The alveolus is made up of three bony regions that, from the inside out, are: the cortical plates, the cancellous bone and the alveolar bone itself, whose shape resembles the root suspended in it.
The alveolar bone is perforated and through these perforations the branches of the feeding arteries pass from the cancellous to the periodontal ligament; veins, lymphatic vessels, and nerve fibers also pass. These perforations are called Volkmann conduits.
The alveolar bone, which directly limits the alveolus, together with the periodontal ligament and the cementum, is what is known as the “dental socket joint” or “tooth fixation apparatus”.
The cortical bone, close to the periodontal ligament or alveolar bone itself, is seen radiologically as a dense white line aligned with a dark line, corresponding to the periodontal ligament.
General characteristics
As already mentioned, the alveolar bone is part of the maxillary bones, both upper and lower. Together with the cementum and the periodontal ligament, it forms part of the insertion periodontium.
The maxillary bones are made up of two parts: a) the basal portion or body of the maxilla or the mandibular bone b) and the so-called alveolar processes. After losing a tooth or after an extraction, this bone, which makes up the alveolar processes, is reabsorbed and disappears.
In alveolar processes, the alveolar edges form the walls of the alveoli and follow the curvature of the conical cavity that adjusts to the curvature of the dental arches. The alveoli can be simple or compound, depending on the presence or absence of internal or interradicular septa.
If the tooth has a single root, the socket that houses it is simple and does not have interradicular septa. If the tooth has two or more roots, the socket will have several partitions, depending on the number of roots. Between one dental alveolus and another there is a septum called the “interdental septum”; These septa are made up of alveolar bone.
In response to functional demands, the alveolar bone is constantly renewed, a process that is called bone remodeling. This alveolar bone has a 45-day turnover period. During this process, the bone trabeculae are continually resorbed and reshaped and the cortical bone mass dissolves and is replaced by new bone.
During the degradation of cortical bone, resorption ducts are formed by the proliferation of blood vessels. These ducts, which in the center contain a blood vessel, are later filled with new bone by the formation of lamellae arranged in concentric layers around the blood vessel.
Histology
The alveolar bone is the part of the upper and lower jaw that supports the teeth. It consists of two plates of compact cortical bone separated by a layer of cancellous bone. In some areas the alveolar bone is very thin and does not present cancellous bone.
The spaces between the trabeculae of cancellous bone are filled with bone marrow which is, in early life, a hematopoietic tissue, but which is later replaced by fatty tissue. The shape and structure of the trabeculae is a reflection of the stress support requirements of the area.
The surface of the inorganic part of the bone is lined by osteoblasts, which are responsible for the formation of bone. Those that remain incorporated into the bone mineral are called osteocytes, maintaining contact with each other through the canaliculi. Osteoclasts are responsible for bone resorption.
Compact foil or hard foil
The lamina compact or lamina dura of the alveolar bone is formed from two sources:
-periodontal tissue
-the medullary tissue
The one generated from the periodontal ligament grows by apposition from osteogenic regions of the periodontal ligament. That which comes from the medulla is formed at the expense of the osteoblasts of the adjacent medullary tissue.
The lamina dura is made up of lamellae that run parallel to the alveolar surface and traversed by numerous fibers from the periodontal ligament. These fibers are called Sharpey fibers. Each fiber is accompanied by an arteriole and one or more nerve fibers.
Bone is a dynamic tissue that is continuously being formed and resorbed according to functional requirements. In addition to responding to local needs, bone metabolism is under hormonal control.
Features
The alveolar bone fulfills several functions, among them the following can be named:
- Housing and supporting the teeth embedded in each socket and fixing it by means of the cement and the periodontal ligament to the compact bone or its own alveolar bone.
- Fix the covering fabrics.
- Hold the teeth during the actions of chewing, speaking and swallowing food. Dispel the forces generated by these actions.
- Protects nerves and vessels.
- By containing calcium and other mineral salts, it works as a reservoir for them, especially for calcium.
- In childhood, the bone marrow of the spongy alveolar bone participates in hematopoietic activities, participating in the formation of blood cells that are supplied to the circulatory stream and that serve the entire organism.
References
- Chu, TMG, Liu, SSY, & Babler, WJ (2014). Craniofacial biology, orthodontics, and implants. In Basic and Applied Bone Biology (pp. 225-242). Academic Press.
- Gartner, LP, & Hiatt, JL (2012). Color atlas and text of histology. Lippincott Williams & Wilkins.
- Gulabivala, K., & Ng, YL (2014). Tooth organogenesis, morphology and physiology. In Endodontics (pp. 2-32). Mosby.
- Lindhe, J., Karring, T., & Araujo, M. (2009). Anatomy of periodontal tissues. Clinical Periodontology and Dental Implantology. 5th edition. Buenos Aires: Panamericana Medical, 3-17.
- Zerbo, IR, Bronckers, AL, De Lange, GL, Burger, EH, & Van Beek, GJ (2001). Histology of human alveolar bone regeneration with a porous tricalcium phosphate: a report of two cases. Clinical oral implants research, 12 (4), 379-384.