Macro and micro anatomy of the alveolar process
The adult alveolar process is formed of:
1- The alveolar bone proper
The osteoblasts that form the alveolar bone proper are derived from the dental sac.
The alveolar bone proper (ABP) is a thin layer of bone that forms the inner wall of the sockets facing the roots.
Its main function is to furnish a medium for the attachment of the periodontal ligament fibers.
The alveolar bone proper is also called the cribriform plate because it is perforated by many openings that carry branches of the interalveolar nerves and blood vessels into the periodontal ligament. These openings are called Zucker kandle and Hirschfeld canals.
Radiographically, the alveolar bone proper is called lamina dura because it appears radiopaque.
Histologically, the alveolar bone proper consists of two types of bone .
a- Bundle bone :
Which is adjacent to the periodontal ligament. It is formed of bundles of woven bone, but it never matures into lamellar bone.
The principal fiber bundles of periodontal ligament insert into bundle bone as Sharpey’s fibers . Thus, it is very important for tooth support.
A reversal line is usually present separating lamellated and bundle bones.
b- Lamellated bone :
It lies adjacent to the bundle bone layer. It is formed of lamellae that are arranged parallel to the surface of the adjacent marrow spaces, or form Haversion systems.
2- Supporting alveolar bone
It is the bone that surrounds the alveolar bone proper and gives support to the socket of teeth. The supporting” alveolar bone consists of:
a- Cortical plates of compact bone;
They form the outer and inner (labial and lingual) plates of the alveolar process. These are continuous with the compact layers of the maxillary and mandibular jaws.
These are much thinner in the maxilla than in the mandible, and are thickest in the premolar and molar regions of the lower jaw especially on the buccal side.
In the anterior region of both jaws, the supporting bone is usually very thin, no spongy bone is found and the cortical plate is fused with the alveolar bone proper.
• Longitudinal lamellae, formed of calcified ground substance and osteocytes.
• Haversian systems.
It fills the area between the cortical plates and the alveolar bone proper.
Histologically, cancellous bone is usually very dense around the teeth which are subjected to excessive forces of mastication.
Around functionless teeth, the spongy bone shows very wide medullary spaces and few numbers of trabeculae.
The spongiosa of the alveolar process is classified according to roentgenograms study into two main types:
Type I : In which the interdental and interradicular trabeculae are regular and horizontal in a ladder like arrangement. This is seen only in the mandible.
Type II : Shows irregularly arranged, numerous delicate interdental and interradicular trabeculae. This arrangement is more common in the maxilla.
The trabeculae of the spongiosa below the root apices of the lower molars appear as if they are radiating from the fundus of the socket.
The marrow spaces in the alveolar process may contain hematopiotic marrow, but usually they contain fatty marrow.