Alveolar bone

Dr Jamal Naim

PhD in Orthodontics

Bone and alveolar bone

Periodontium (cont.)

1. Support and protect the skeletal functions.

2. Bone stores minerals, especially calcium and

phosphorous, which are mobilized according to the

body needs.

3. Bone protects the internal organs.

4. Bone marrow manufactures the blood elements.

5. Bone remodeling is responsible for the development,

growth, movements, fracture and repair.

Functions of bone

Structural Constituents

Osteoprogenitor cell

Location: Present in the deepest layer of periosteum

and lining the vascular canals of compact bone.

Origin: It is mesenchymal in origin.

Function: According to the function needed they divide

by mitosis to give any type of bone cells

Morphology: It resembles mesenchymal cell with pale

stained nucleus and little esinophilic cytoplasm.

Osteoprogenitor cell

Bone cells

All types of bone cells are from the same type, the alters there appearance according to there function: this is what is called cell modulation.

Intercellular substance

Types of bone

a.Compact bone

b.Spongy bone

Lamellar bone

a. Compact bone (ivory bone):

It forms the main part of the shafts of the long bone

and covers the cancellous bone e.g. ribs and flat

bones of the skull.

Its lamellae are arranged in 3 patterns:

n Circumferential lamellae

n Havarsian lamellae

n Interstitial lamellae

Compact bone Compact bone

Lamellar bone

Circumferential lamellae:

n outer circumferential lamellae

beneath the periosteum.

n inner circumferential lamellae

adjacent to the endostium

Lamellar bone

Havarsian lamellae:

n It is the unite structure of the compact bone and is

called the Haversian system or osteon.

n The Haversian system if formed of Haversian canal

which is surrounded by (4-

20) concentrically

arranged lamellae.

n The Haversian canal contains B.Vs., nerves, C.T.

and lined by osteoprogenitor cells.

Lamellar bone

n Osteocytes are arranged concentrically in

the osteons (they anastomose with each

others by their process).

n Haversian canals connected to each others

or to the outer surface or to the bone

marrow spaces with Volkmann's canal.

Lamellar bone

Interstitial lamellae:

n The Haversian systems are separated from each

others by the interstitial lamellae.

n They represent the remnants of an old resorbed

and remodeled bone.

Compact bone Compact bone

Haversian system

Bone Trabeculae

Bone Marrow Spaces

Spongy bone

n It is present in the central part of the flat bone.

n It is formed of connected bone trabeculae in the

form of network to give maximum rigidity.

n In between the bone trabeculae, there are bone

marrow spaces

n The bone trabeculae have osteocytes.

Woven bone

This type of bone is characterized by:

n Irregular arrangement of the collagen fibers.

n Great number, large size and irregular arrangement of

the osteocytes.

n Increase in the organic substance and decrease in the

inorganic contents so; it appears radiolucent in X-ray.

n This type of bone is resorbed completely and is replaced

by lamellar bone.

It is referred to the bundles of principal fibers of either the periosteum or PDL continue into the bone as sharpeys fibers.

3. Bundle Bone

Bundle bone

n It is found adjacent to the periosteum and periodontal

ligament (areas of tension).

n It is characterized by the presence of the Sharpey's

fibers.

n It has less number of cells than Woven bone; but more

calcium salts than lamellar bone. So it appears more

radio-opaque and called lamina dura.

n Its fibers are arranged parallel to the socket wall.

Alveolar bone

In X-ray the cribriform plate is referred to lamina dura.

The alveolar process is that bone containing the alveoli.

It consists of:

n an outer (lingual and buccal) cortical plate (compact

bone)

n A central spongiosa (spongous bone) and

n Alveolar bone (bone lining the alveolus), (bundle

bone)

The alveolar bone and the cortical plate meet at the alveolar

crest (1.5 to 2 mm below the level of CEJ).

Alveolar bone

Alveolar bone

Alveolar bone

divided into the:

a. alveolar bone proper

n lining of the tooth socket or alveolus

n bone is also called the cribriform plate because of

the many holes through which Volkmann’s canals

pass (from the alveolar bone into the PDL)

Alveolar bone

n also called bundle bone because Sharpey’s fibers insert

into this bone (Sharpey’s fibers = portion of the

fibers of the PDL)

n

these fibers are inserted at a 90 angle into the ABP –

but are fewer in number than those found at the

cemental surface

n consists of plates of compact bone that surround the

tooth

Alveolar bone

n

varies in thickness from 0.1 to 0.5mm

n can see a portion of the ABP on radiographs lamina

dura

n most cervical rim = alveolar crest – slightly apical to

the CEJ in healthy patients

Alveolar bone

b. supporting alveolar bone

n has the same components as ABP

n but is considered to be cortical and trabecular bone –

different arrangement of bony plates

n cortical bone is made up of cortical plates of compact bone

found on the facial and lingual surfaces

n

plates are usually 1.5 to 3mm thick over the posterior teeth

and can vary over the anterior teeth

Alveolar bone

n trabecular bone is located between the ABP and the plates

of the cortical bone (cross section of mandible)

Alveolar bone

n alveolar bone can be resorbed with age (edentulous)

n the underlying basal bone is less affected with age –

because it does not need the presence of teeth to

remain viable

n loss of teeth + alveolar bone can results in loss in the

vertical dimension of the face – “Popeye” facial

appearance

Alveolar bone

n after tooth extraction the clot is replaced with

immature bone

n later remodelled as mature secondary bone, very

similar process to fracture repair in skeletal bone

Alveolar bone

alveolar crest

alveolar bone

Cortical plate

The alveolar bone is perforated by many foramina to allow blood and nerve supply to the teeth, so it is referred to cribriform plate

Alveolar bone

Hirschfeldcanal

Alveolar bone

Collagen fibers

Alveolar bone

Collagen fibers

Outer compact bone

Spongiosa

Alveolar bone

SpongiosaPDLDentin

Cementum