In the skull, mandible and maxilla, are the two bones which form the jaws. Anatomically mandible can be broadly divided into a horseshoe shaped body and quadrilateral shaped ramus. The superior surface of ramus has the chondroid process anteriorly and condylar process posteriorly, separated by a concave mandibular notch. Whereas, the upper border of the body of the mandible is formed by the alveolar process, which is again horseshoe shaped. The maxilla on the other hand, is a pyramid-shaped bone with palatine process, zygomatic process, frontal process and the alveolar process, which when joined together, is horseshoe shaped. Hence, the part of the maxilla and mandible, that forms and supports the socket of teeth, is known as alveolar process or alveolar bone. Alveolar bone is dependent on tooth for its development and maintenance. Alveolar bone. Mandible and maxilla, like any other bone, are formed of cancellous bone or spongy bone or trabecular bone in the center and surrounded by a dense outer sheet of compact bone. The structure which separates alveolar bone from other bones is the presence of tooth sockets, which are again formed of compact bone. These sockets provide anchorage to the roots of teeth. The portion of alveolar bone between two teeth is called inter-dental septum and the portion of alveolar bone between roots of a multi-rooted tooth is called inter-radicular septum. These septums contain the nutrient canals or the canals of Zuckerkandl and Hirschfeld, which carry the blood vessels and nerves. Now let us study the structure of alveolar bone in detail. On the basis of function, alveolar bone can be distinguished into two parts alveolar bone proper and supporting alveolar bone. Alveolar bone proper is the part, which forms the socket of the tooth and is about 0.1 to 0.4 mm thick. The supporting alveolar bone forms the structure around the alveolar bone proper and it supports the socket of the tooth. There is no clear-cut demarcation between supporting alveolar bone and the body of maxilla or mandible. Let us start with alveolar bone proper. Alveolar bone proper is the dense compact bone surrounding the tooth root forming its socket. When the socket wall is seen under the microscope, it shows numerous perforations. Due to which alveolar bone proper is also called cribriform plate, which denotes an anatomical structure that is pierced by numerous small holes. It is through these perforations that blood vessels and nerves enter and exit the periodontal space. When the alveolar bone is seen in a radiograph, the alveolar bone proper or the socket wall, appears more radio opaque, that is, more white than the adjacent supporting alveolar bone. Due to this, radiographically alveolar bone proper is also called lamina dura, denoting anatomical plate which appears thick. This appearance is just because when x-ray beam passes through the alveolar bone, it has to cross the whole bucco-lingual width. When the beam passes the socket wall it does so tangentially through the dense lamellar bone and therefore appears more opaque. Histologically, alveolar bone proper can be further divided into bundle bone and lamellated bone. Bundle bone. As mentioned previously, the alveolar bone proper forms the tooth socket and provides anchorage to the root. How is this anchorage formed? The root of the tooth is lined by cementum, between the cementum and the tooth socket is the periodontal ligament. In the periodontal ligament are the principal fibers. Principal fibers on one end are embedded in the cementum and on the other end in the alveolar bone proper. So bundle bone is that portion of alveolar bone proper, in which the principal fibers of periodontal ligament are embedded or bundles of sharpey's fibers are present. Lamellated bone. Lamellated bone is that part of the aloveolar bone proper which is formed of compact bone or lamellar bone and has no principal fibers or bundles of sharpey's fibers embedded in it. Supporting alveolar bone. The alveolar bone surrounding the tooth socket forms the supporting alveolar bone. It has two parts, cortical plates and spongy bone. Let us start with cortical plates. Cortical plates consist of compact bone and forms the inner and outer plates of the alveolar process. Cortical plates are continuous with the compact bone of the body of the maxilla and mandible. They are thicker in mandible than maxilla, moreover in mandible they are thickest in buccal side of premolar and molar region. Spongy bone. The area between the cortical plates and the alveolar bone proper is filled with spongy bone. It is formed of trabeculae of lamellar bone, which are present between marrow spaces. Depending on the arrangement of the trabeculae in the spongy bone, alveolar bone can be of two types, type 1 and type 2. In type 1 the trabeculae are regular and horizontal in arrangement, giving a ladder-like arrangement. Type 2 the trabeculae are more irregularly arranged. Type 1 is more commonly seen in mandible, whereas type 2 is more common in maxilla. In anterior maxilla and anterior mandible, the spongy bone may be absent, such that the alveolar bone proper is directly fused with the cortical plates.