basic concepts on alveolar bone

2. ALVEOLAR PROCESS
By
Dr. K V N VIDYADHAR

3. INTRODUCTION
BONE
It is a mineralized connective tissue
 The structural organization and composition of
bone reflects the activity of the cells involved in
the formation of the matrix

4. ALVEOLAR BONE
 It is a portion of the maxilla or mandible that supports
and protects the alveoli (tooth socket).
 It is formed when the tooth erupts in order to provide
osseous attachment to the forming periodontal ligament
and gradually disappears after the tooth is lost .

5. PARTS OF ALVEOLAR BONE

6. CLASSIFICATION
 DEVELOPMENTALLY,
 Endochondral bone – where the bone is preceded by a
cartilaginous model which is eventually replaced by
bone.
 Intramembranous bone – where the bone forms
directly within a vascular fibrous membrane.
 HISTOLOGICALLY, mature bone can be divided into;
 Compact (cortical) bone
 Cancellous (spongy) bone

7. Inorganic (65%) Organic (35%)
Hydroxyappatite
Collagen (88-89%) Noncollagenous (11-12%)
BONE
Glycoproteins (6.5-10%)
Proteoglycans (0.8%)
Sialoproteins (0.35%)
Lipids (0.4%)
COMPOSITION

8. DEVELOPMENT
 Alveolar bone is dependent on the presence of teeth for its
development and maintenance.
 At the late bell stage, bony septa and bony bridge start to
form, and separate the individual tooth germs from
another, keeping individual tooth germs in clearly outlined
bony compartment.
 The major changes in the alveolar processes begin to
occur with the development of the roots of teeth and tooth
eruption.

9.  As the roots of teeth develop, the alveolar processes
increase in height.
 At the same time, some cells in the dental follicle also
differentiate into osteoblasts and form the alveolar bone
proper.
 Thus, the size and shape of the individual developing tooth
roots determine the overall structure of the alveolar bone
proper.
 On the other hand, the rest of bony structures in the alveolar
process are achieved by periosteal bone formation.

10. FIG. 9-5 A developing root shown by a
divergent apex around the dental papilla
(arrow), which is enclosed by an opaque bony
crypt.

11. STRUCTURE
The maxilla and mandible of the adult human can be
subdivided into two portions:
(a) The alveolar process that involves in housing the
roots of erupted teeth
(b) The basal body that does not involve in housing the
roots.
Two parts of the alveolar process can be distinguished.
 Alveolar bone proper
 Supporting alveolar bone

12. Ground longitudinal through the mandible showing the alveolar bone.
A = Inner layer of compact alveolar bone lining the tooth socket wall; B
- outer alveolar plate of compact bone (note the spongy bone lying
between the two plates of alveolar bone); C = arbitrary boundary
between the alveolar bone and the body of the jaw.

13. CORTICAL BONE SPONGY BONE
About 85% of bone About 15% of bone
Lesser turnover Higher turnover
Remodel about 3% of its mass each
year
remodel about 25% of its mass each
year
Mechanical/protective role More metabolic function

14. BUNDLEBONE AND CRIBRIFORM PLATE
 Bundle bone is the part of alveolar bone, into which the
fiber bundles of the PDL insert.
 It appears as an opaque line radiographically called
LAMINA DURA.
 Embedded within this bone are the extrinsic collagen fiber
bundles of PDL.

15.  Lining of alveolar bone is fairly smooth in youngsters but
with age, the socket lining become rougher.
 It is referred to as cribriform plate because of perforation
through which the blood vessels, lymphatics and nerves of
PDL pass.

16. FIG. 9-6 The lamina dura (arrows) appears as a thin opaque layer of
bone around teeth, A, and around a recent extraction socket, B.

17. FIG. 9-14 The trabecular pattern in the
posterior mandible is quite variable, generally
showing large marrow spaces and sparse
trabeculation, especially interiorly arrows,).

18. HAVERSIAN SYSTEM
 It is the fundamental functional unit of bone.
 Bone is deposited in layers, or lamellae, each lamella
being about 5ųm thick.
 These lamellae surrounds the Haversian canals in the bone
to form Haversian system
 4 and 20 concentric lamellae within each Haversian
system.
 The Haversian canals are connected by a series of
horizontal ones (Volkmann’s canals).

19. Three distinct types of layering are recognized:
1) Circumferential lamellae enclose the entire adult bone,
forming its outer perimeter.
2) Concentric lamellae make up the bulk of compact bone
and form the basic metabolic unit of bone, the osteon.
3) Interstitial lamellae are interspersed between adjacent
concentric lamellae and fill the spaces between them.

21. PERIOSTEUM
The tissue covering the outer surface of bone is termed
periosteum.
The periosteum consists of:
 An inner layer composed of osteoblasts surrounded by
osteoprogenitor cells, which have the potential to
differentiate into osteoblasts,
 An outer layer rich in blood vessels and nerves and
composed of collagen fibers and fibroblasts.

22. ENDOSTEUM
The tissue lining the internal bone cavities is called
endosteum.
The endosteum consists of:
 An inner layer is the osteogenic layer and
 An outer is the fibrous layer.

23. CELLTYPES IN BONE

24. OSTEOBLASTS
 These are specialized fibroblast -like cells of
mesenchymal origin
 Cuboidal or slightly elongated , uninucleated cells.
 Contain a cytoplasm rich in synthetic and secretory
organelles as rough ER, Golgi apparatus, secretory
granules and microtubules

25.  Secretes- Osteoid
 unmineralized bone matrix
 thickness –5-10  before reaching a level of maturity
conducive to mineralisation.
 consists of type 1 collagen fibres
 There is a lag phase of about 10 days before the
deeper layer of osteoid has matured sufficiently to
undergo mineralisation

27. OSTEOCYTES
These are the entrapped 'osteoblasts’.
- Decreased quantity of secretory organelles
- Smaller size with large nucleus
OSTEOCYTIC OSTEOLYSIS:
- It is the process where the osteocytes causes bone
resorption

28. - Numerous cell processes from the osteocytes run in the
canaliculi in all directions.
- About 25000 osteocytes are found per cubic millimetre of
bone
- They detect stress induced in bone and are regarded as the
mechanoreceptors of bone.

29. OSTEOCLASTS
 They are derived from haemopoietic cells of the
monocyte/ macrophage lineage by fusion of mononuclear
precursors, giving rise to multinucleated cells.
 Osteoclasts are the cells responsible for bone resorption
 Osteoclasts may be up to 100 um in diameter and have on
average 10-20 nuclei.
 The lifespan of osteoclasts is thought to be about 10-14
days.

31. BONE FORMATION
 Formation of bone, which appears to be linked with bone
resorption to maintain bone mass, involves the
proliferation and differentiation of stromal stem cells
along an osteogenic pathway that leads to the formation of
osteoblasts.

33. OSSEOUS TOPOGRAPHY
 The anatomy of the alveolar bone varies from person to
person
 Normally it conforms to the root prominence, with
intervening depressions that taper towards the margin
 The factors that affect the height and thickness of the
facial and lingual bony plates are alignment of the teeth,
angulation of the root to the bone and the occlusal forces.
 Howship’s lacunae : Bony concavities

34. FENESTRATION AND DEHISCENCE
 Isolated areas in which the root is denuded of bone and the
root
surface is covered only by periosteum and overlying gingiva
are termed fenestrations.
 When the denuded areas extend through the marginal
bone, the defect is called a dehiscence

35. REMODELLING AND RESORPTION
 Bone deposition by osteoblasts is balanced by resorption
brought about by osteoclasts during tissue remodelling
and repair.
 Bone resorption is a complex process and appears as
eroded bone surfaces, namely Howship’s lacunae.
 It has been suggested that several chemical mediators like
interlukin-1 and 6 influences the remodelling of the
alveolar bone
During bone resorption three process occur:
 Decalcification
 Degradation of matrix
 Transport of soluble factors to the extracellular fluid

36.  Tencate, described the sequence of events in the
resorptive process is as follows:
- Attacment of osteoclats to the mineralized surface of
bone.
- Creation of a sealed acidic environment through the
action of the proton pump, which demineralizes bone and
exposes the organic matrix.
- Degradation of exposed organic matrix to its constituent
amino acids by the action of released enzymes, such as
acid phosphatase and cathepsin B.
- Sequestering of mineral ions and amino acids within the
osteoclast.

37. Bone remodelling cycle. Pre-osteoclasts are recruited to sites of resorption,
induced to differentiate into active osteoclasts, and form resorption pits. After their
period of active resorption, they are replaced by transient mononuclear cells.
Through the process of coupling, pre-osteoblasts are recruited, differentiated into
active matrix secreting cells, and form bone. Some of osteoblasts become
entrapped in the matrix and become osteocytes.

38. BLOOD SUPPLY
 Inferior and superior alveolar arteries for mandible and
maxilla, respectively and reaches PDL;
 Apical vessels
 Penetrating vessels
 Anastomosing vessels

39. CLINICAL CONSIDERATIONS
 The most frequent and harmful change in the alveolar
process is that which is associated with periodontal
diseases.
 The bone resorption caused by periodontal diseases is
usually symmetrical, occurs in episodic manner, and is
both of the horizontal and vertical type.
 Once lost, this bone is very difficult to regenerate and the
time period of regeneration greatly varies

40.  Regenerating just a few millimetres of bone that has been
lost is the greatest challenge to the periodontists .
 Hence an idea about the alveolar process is necessary to
identify and treat any abnormal changes caused by
periodontitis.

41. Unless we know what’s right
we don’t know what’s wrong