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.
– 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.
Functions 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.
•DEVELOPMENT OF ALVEOLAR BONE
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
1 - ALVEOLAR
BONE PROPER
2 -SUPPORTING
ALVEOLAR BONE
A -CORTICAL
PLATE
B -SUPPORTING
SPONGIOSA
ALVEOLAR
CREST
1.5 : 2 mm
C.E.J.
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.
Alveolar Bone proper:
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
Crest
Spongiosa
Interdental
Septum
ALVEOLAR BONE
PEOPER
Molar Alveolus
Out Line
Interradicular
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.
Bundle bone
Sharpey`s fibers
Lamellated bone
PDL
Outer Inner
Anterior teeth
A - CORTICAL PLATES
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.
II-THE SUPPORTING ALVEOLAR BONE:
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
PERFORATED
b++
L+
Lower 45678
Upper 45678
Thin
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
Molar Alveolus
Out-Line
I. R. S. SPONGIOSA
Alveolar Crest
I. D.S. SPONGIOSA
SPONGIOSA
A. B. P.
C. P.
I D S
Alveolar bone proper
Cortical plates
Basal Bone
I R S
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
Cellularity
Hardness
Mineralization
Brittlness
Fatty bone marrow
Osteoporosis
Decreased with age
Increased with age
