The alveolar process may be defined as that part of the maxilla and the mandible that forms and supports the sockets of the teeth. It developed with the eruption of teeth and disappears or lost after tooth extraction

ALVEOLAR PROCESS

BASAL BONE  Alveolar (bone) process: is that part of the maxilla and the mandible that forms and supports the sockets of the teeth.  Basal Bone. it is the bone of the facial skeleton which support the alveolar bone.  There is no anatomical boundary between basal bones and alveolar bone.  Both alveolar process and basal bone are covered by the same periosteum.  In some areas alveolar processes may fuse or masked with jaw bones as in (1) Anterior part of maxilla (palatal). (2) Oblique line of the mandible. * Alveolar process is resorbed after extraction of teeth.

Functions of alveolar bone

– Houses and protects developing permanent teeth, while supporting primary teeth. – Organizes eruption of primary and permanent teeth. – Anchors the roots of teeth to the alveoli, which is achieved by the insertion of Sharpey’s fibers into the alveolar bone proper (attachment).

– Helps to move the teeth for better occlusion (support). – Helps to absorb and distribute occlusal forces generated during tooth contact (shock absorber). – Supplies vessels to periodontal ligament. •DEVELOPMENT OF ALVEOLAR BONE

•Near the end of the second month of fetal life, the maxilla as well as the mandible form a groove that is open towards the surface of the oral cavity. •Tooth germs develop within the bony structures at late bell stage. •Bony septa and bony bridge begin to form and separatethe individual tooth germs from one another, keeping individual tooth germs in clearly outlined bony compartments. As roots develop, the alveolar process increases in height. Also, the cells in the dental follicle start to differentiate into periodontal ligament and cementum. At the same time, some cells in the dental follicle differentiate into osteoblasts and form alveolar bone proper.

Anatomically, no distinct boundary exists between the body of the maxilla or the mandible and their respective alveolar processes.

In some places, the alveolar process is fused with and partly masked by, bone that is not functionally related to the teeth.

In the anterior part of the maxilla, the palatine process fuses with the oral plate of the alveolar process.

In the posterior part of the mandible, the oblique line is superimposed laterally on the bone of the alveolar process. As a result of its adaptation to function, two parts of the alveolar process can be distinguished, the alveolar bone proper and the supporting alveolar bone.

 After eruption of the teeth, the alveolar bone gradually takes out its adult form.

As a result of its adaptation to function, Mature adult bone is classified into:  1- Alveolar bone proper. a- Bundle Bone. b- Lamellated bone.

 2- Supporting alveolar bone. a- Cortical plates of compact bone. b- Spongy Bone. MACRO-ANATOMY ACCORDING TO FUNCTION

C.E.J. 1 - ALVEOLAR BONE PROPER 1.5 : 2 mm

2 -SUPPORTING ALVEOLAR ALVEOLAR BONE CREST

A -CORTICAL PLATE

B -SUPPORTING SPONGIOSA  Alveolar Bone proper: It consists of thin lamellae of bone that surrounds the roots of teeth and gives attachment to the principle fibers of PDL.

It is perforated by many openings that carry branches of the intra-alveolar nerves and blood vessels into the periodontal ligament and thus may be called the cribriform plate (Anatomical name).

The alveolar bone proper consists of: A- Bundle Bone. B- Lamellated compact Bone.

 Bundle bone is that part of the alveolar process into which the fiber bundles of the periodontal ligament insert.

• It is called the lamina dura (radiologic term) because of an increased radio-opacity.

• This apparent density is due to thick bone without trabeculation that X-rays must penetrate, and not to any increased mineral content.

•The term bundle bone is chosen because the bundles of the principal fibers of the periodontal ligament continue into the bone as Sharpey`s fibers (which, as in cellular cementum, are mineralized only at their periphery).

ALVEOLAR BONE PEOPER Alveolar Crest

Molar Alveolus Out Line Spongiosa

Interradicular Septum Interdental Septum  Lamellated bone lies adjacent to the bundle bone layer. It is formed of lamellae that are arranged parallel to the surfaces of adjacent marrow spaces, or form Haversion system.

Lamellated bone

Bundle bone

PDL Sharpey`s fibers

A - CORTICAL PLATES Anterior teeth

Outer Inner II-THE SUPPORTING ALVEOLAR BONE:

It is the bone that surrounds the alveolar bone proper and gives support to the sockets of the teeth.

Supporting alveolar bone consists of: A- CORTICAL PLATES OF COMPACT BONE: -That forms the outer and inner plates of the alveolar processes. These are continuous with the compact layers of the maxillary and mandibular body. - These are generally much thinner in the maxilla than in the mandible. -Buccal cortical plate is thin, at upper posterior teeth region (may be absent). -They are thickest in the premolar and molar regions of the lower jaws especially on the buccal side. - In the maxilla, the outer cortical plate is perforated by many small openings through which blood and lymph vessels pass. - In the anterior region of both jaws, the supporting bone usually is very thin, no spongy bone is found, and the cortical plate is fused with the alveolar bone proper. The cortical plates consist of:

1- Longitudinal lamellae which are formed of calcified connective tissue and osteocytes, which are parallel with the periosteum or endosteum.

2- Haversion system which is formed of Haversion canals that run parallel to the long axis of the bone and contain blood vessels. These canals are surrounded by concentric lamellae of bone from 4 to 20 in number.

3- Osteocytes in their lacunae are present between these calcified bone lamellae and are connected with each other through their projecting canaliculi.

4- Volkmann's canals connect the haversion canals with the external surface of the bone and the marrow spaces. While, the transverse canals connect between two haversion canals.

B. SPONGY (Cancellous) BONE:

- It fills the area between the cortical plates and the alveolar bone proper.

-It is formed of trabeculae of bone surrounding the medullary spaces that contain the bone marrow.

-The trabeculae of the spongy substances are made up of varying number of closely adjoining lamellae with lacunae and osteocytes in between.

-Continuous with spongiosa of the jaws.

-At alveolar crest spongiosa may be absent.

-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 little number of trabeculae.

Posterior teeth

Thin b++ 45678 L+

Upper 45678

PERFORATED

Lower 45678 -The study of roentgenograms permits the classification of the spongiosa of the alveolar process into two main types:

TYPE I: The interdental and interradicular trabeculae are regular and horizontal in ladder like arrangement. This arrangement is seen mostly in the mandible.

TYPE II: Show irregular arranged numerous fine delicate interdental and interradicular trabeculae. This arrangement is more common in the maxilla. From the apical part of the socket of lower molars, trabeculae are seen radiating in slightly distal direction.

- The marrow spaces of the alveolar process may contain hematopoietic marrow, but usually they contain fatty marrow. By age red bone marrow change to fatty bone marrow except in areas like in the condylar process, in the angle of the mandible, in the maxillary tuberosities, and in other foci where hematopoietic cellular marrow is found frequently even in adults.

Alveolar Bone Peoper Alveolar Crest Molar Alveolus Out-Line SPONGIOSA

I. R. S. SPONGIOSA A. B. P.

C. P.

I. D.S. SPONGIOSA Cortical plates

Alveolar bone proper

I D S

I R S

Basal Bone  Osteoid: non mineralized bone always present at the formative surface of bone, but usually as a very thin layer.

 Osteon: It is the structural unit of compact bone. It is a dense compact cylindrical unit underlying cortical bone. Osteon consists of long cylinders that run parallel to the long axis of the bone.

 Structure of an osteon 1) lamellae 2) Haversian’s canal 3) canaliculi or perforating canals 4) lacuna: contain osteocytes (mature bone cells) Age changes of the alveolar bone  Vasularity  Resliancy Decreased with age  Cellularity

 Hardness  Mineralization Increased with age  Brittlness

 Fatty bone marrow

 Osteoporosis