Definition: Alveolar Bone is a Part Of The Jaw Bone (Mandible Or Maxilla) That

Form The Sockets And Support The Teeth In Their Position. All types of bone are composed of outer sheet of compact bone enclosing

medullary cavity. Functions:1. Support the root of the tooth.2. Act as a media for the embedded fibers of periodontal ligament. Physical Properties :1. Bone is a Calcified Connective Tissue.2. Bone is an Elastic Tissue.3. Bone is a Highly Vascular Tissue.4. Bone is a Highly Remodeling Tissue.

Chemical composition:1- Inorganic component 67%. 2- Organic Component 33% → 28% Collagen Type I. → 5% Ground Substance.

1- After breakdown of epithelial root sheath, cementoblast cells differentiated on the newly formed root dentine and begin to secrete cementum.

2- At the same time, alveolar bone begin to develop.3- At the same time, fibroblast cells differentiated from

Ectomesenchymal cells of dental sac and begin to form collagen fibers of PL.

4- one end of collagen fibers become embedded into the alveolar bone and the other end embedded within the cementum.

5- the embedded part of collagen fibers within both cementum and bone are termed:

Sharpy’s Fibers.

1-Alveolar Bone Proper :A- Bundle bone: facing

socket.B-Compact bone. 2- Supporting Alveolar

Bone:A- Cortical plate (compact

bone): a- Outer cortical plate: facing

lip and check. b- Inner cortical plate: facing

tongue.B-spongy bone.

Alveolar crest

1-Inter-dental septum:Part of alveolar bone found between two adjacent teeth.2-Inter-radicular septum:

Part of alveolar bone found between roots of tooth.3-Alveolar crest:It is the margin of alveolar bone. 2

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Definition:Alveolar bone proper is apart of alveolar bone that form the inner thin wall of the socket facing the root.Terminology:● Alveolar bone proper is perforated by numerous opening that transmit blood vessels and nerves to periodontal ligament.● for this reason, the alveolar bone is termed Cribriform Plate.● Crebriform Plate is an outer manifestation of canals run within the alveolar bone termed:

Zuckerkandl & Hirschfeld canalsStructure:● Bundle bone facing the periodontal ligament.● Lamellar bone (compact) beside bundle bone.

Cribriform plate Zuckerkandl & Hirschfeld canals

DentinBone PL

Cementum

1-Alveolar Bone Proper :Composed of two parts of bone:A- Bundle bone: ● Bundle bone is layer of bone facing the periodontal ligament.● Composed of highly calcified bone.● Sharpy’s fibers of PL are inserted within it.● Contain two types of fibers: 1- Intrinsic fibers. 2- Extrinsic fibers ( from

PL).● Appear more radio-opaque line around the tooth in X-

ray so++++

Bundle bone is termed Lamina Dura .● Loss of bundle bone leads to loss of tooth. B-Compact bone (lamellar bone): ● Lamellar bone is a layer of compact bone adjacent to bundle

bone.● The main function is to support the bundle bone.

Lamina Dura CRIBRIFORM PLATE

Supporting Alveolar Bone

Outer Cortical Plate:It is a bony plate forming the outer surface of alveolar bone Facing lip and check.

Inner Cortical Plate:It is a bony plate forming the inner surface of alveolar bone Facing the tongue.

Alveolar Crest

Alveolar Bone Proper

Spongy Bone (Spongiosa):

It is a bone forming the main bulk of alveolar bone between the cortical plate and alveolar bone proper

A- Cortical Plate :Both Outer and inner Cortical Plates are Composed Of Compact

Bone.Compact bone is composed of :1. Haversian System: as concentric lamellae (8-20 lamella).2- Interstitial lamellae lie among Haversian lamellae.3- Outer and inner circumferential lamellae on the bone

surface.4- Periosteum adjacent to oral mucosa. B- Spongiosa:- Spongiosa form the main bulk of alveolar bone. Spongiosa is composed of bony trabeculae with more bone

marrow spaces and rich blood supply.- Maxilla contain more spongiosa with rich blood supply than

mandible, so wound healing is better in maxilla.- Thickness of Spongiosa varies according to the tooth type,

Example, mandibular incisors have no or little Spongiosa.

1- Bundle bone

3- Spongiosa

2- Lamellar bone

Cementum

Periodontal ligament

Dentine

Alveolar Bone Tooth

SPONGY BONE

Osteoblast cellsDefinition:Osteoblasts are connective tissue cells responsible for formation of bone.Origin:Osteoblast cells of alveolar bone are originates from Ectomesenchymal cells of dental follicle.Site:Osteoblasts are found within the periodontal ligament covering the alveolar bone in a layer termed periosteum.Functions:1. Formation and secretion of collagen fibers of bone.2. Calcification.

LM.:Shape: branched oval cellsNucleus: Nucleus is rounded and centrally located. Active cells: have open-faced nuclei. Rested cells: have close-faced nuclei.Cytoplasm: Basophilic cytoplasm.Cytoplasmic processes:Cytoplasmic processes of osteoblast are in contact with the adjacent cell.EM.:1- Active cells: RER., Mitochondria, GC, secretory vesicles. Open faced nucleus. Active cells more seen in younger tissue.2- Less active cells: Cell organelles is reduced. Less active cells that enclosed within the bone are termed osteocyte.

Definition:Osteoclast is a Multinucleated Gaint Cell That Resorb Bone.Origin:Fusion of Blood Monocyte. Site:On the Site of Bone Resorption in a Depression Termed Hawships

Lacuna.Hawships Lacuna result from the Resorbing Action of Osteoclast cells

Osteoclast cells.

Functions: Resorption of Bone Tissue For:1- Remodeling (Bone Turnover).2- Eruption of Teeth.3- Removing Alveolar Bone After Tooth Extraction. LM.:• Shape: Large Cells.• Nucleous: Multinucleated cells (8-20 nuclei).• Cytoplasm: Acidophilic Cytoplasm ( red).Osteoclast Cells Contain: 1- Acid Phosphatase Enzyme.2- Collagenase Enzyme.3- Protease enzyme.Electron microscope:1- little RER. 2- Golgi complex.3- Numerous mitochondria and Lysosomes.4- Ruffled border: Border Of The Cell Facing The Resorbing Bone Appeared Striated. Function of Ruffled border: Increase The Surface Area of the working side.5- Clear zone: The region of cytoplasm adjacent to the ruffled border are not contain cell

organelles but contain actin and myosin for adhesion of the cell with Hawshyp’s lacuna.

Clear zoneRuffled border

A- Bone decalcification:Removal Of Calcium By The Action Of :

Acid Phosphatase Enzyme (from osteoclast).B- Organic matrix degradation:Collagen Breakdown Into Protein Occurred By The Action Of:

Collagenase Enzyme(from osteoclast).Protein Breakdown Into amino acids by the action of :

Protease Enzyme(from Osteoclast).C- Clearance:Clearance of the west products Into Blood Stream By The Action Of:

Blood Monocyte.

Area of pressure: Bone Resorption.

Area of Tension: Bone Deposition.

1- Resorption occurs to the bundle bone of alveolar bone proper facing the periodontal ligament.

2- Resorption occurs to the compact bone and become replaced by new layer of bundle bone.

3- Resorption occurs to the spongiosa facing alveolar bone proper and become replaced by new layer of compact bone.

NB: Both Bundle Bone And Lamellar Bone Of Alveolar Bone Proper Must Be Of Normal Thickness.

NB: Loss Of Bundle Bone Means Loss Of Tooth.

1- Bone Formation Occurs To The Bundle Bone Facing The Periodontal Ligament Leading To Increased Thickness.

2-Resorption occurs to the bundle bone of alveolar bone proper facing the lamellar bone and replaced by compact one.

3- Resorption occurs to the compact bone facing the spongiosa and replaced by spongy bone.

NB: Both Bundle Bone And Lamellar Bone Of Alveolar Bone Proper Must Be Of Normal Thickness.

NB: Loss Of Bundle Bone Means Loss Of Tooth.

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