بسم الله الرحمن الرحيم

Bone is a specialized form of connective tissue. It consists of cells and extracellular substance (matrix and fibers).

Functions 1. Protects and supports vital organs. 2. Serves as a reservoir for calcium and phosphate (containing 99% of body calcium). 3. Contains bone marrow which function in hemopoiesis. 4. Provides for attachment of muscles. 5. Forms the body skeleton.

Physical Properties 1. Yellow in color. 2. Softer than dentin. 3. Lined by soft C.T. containing osteoprogenitor cells. 4. Vascular tissue.

Chemical composition Organic materials + H 2 O 35% Inorganic materials 65%

Inorganic Materials In the form of apatite crystals Calcium Phosphorus Magnesium Citrate Potasium Sodium

Organic Materials Type I collagen. Ground substance of glycoproteins and proteoglycans with small amount of proteins and lipids.

Bone Cells Ostoproginator cells. Osteoblasts. Osteocytes. Osteoclasts (bone resorbing cells )

Bone cells

Types of Bone Lamellated bone Course fibered bone (woven bone) Bundle bone Cancellous Compact Found in embryo Formed during Healing of bone Contains Sharpey’s fibers

Cancellous Bone Sponge-like found in the head of a long bone. Has large marrow spaces. Surrounded by thin spicules or trabeculae.

Spicules are small and short containing one or two lamellae and few osteocytes. Trabeculae are large composed of several lamellae.

Compact Bone Denser than cancellous bone. Its spaces are much reduced in size.

Lamellae are organized in 4 systems: External circumferential lamellae. Internal circumferential lamellae. Interstitial lamellae. Haversian canal systems (osteons).

Woven bone (non-lamellar bone, reticulated bone) Bony tissue characteristic of the embryonic skeleton in which the collagen fibers of the matrix are arranged irregularly in the form of interlacing networks.

Periosteum 1. An outer fibrous layer (collagen and fibroblasts). 2. An inner cellular layer (some collagen and osteogenic cells and osteoblasts).

Endosteum The endosteum is composed of osteoprogenitor cells and only a small amount of connective tissue, covering the surface of bone trabeculae and the medullary surface of cortical bone and haversian canals.

Incremental Lines of Bone: 1. Resting lines. 2. Reversal line.

Collagen fibers of the periosteum become trapped in the calcified bone matrix (Sharpey’s fibers). They are arranged at an angle to bone fibers.

It is a direct continuation of the maxilla and mandible. Is derived from ectomesenchymal cells of the dental follicle.

Each alveolus contains one tooth. Adjacent alveoli are separated by interdental septum consisting mostly of cancellous bone.

Alveolar Bone Alveolar Bone ProperSupporting Alveolar Bone Bundle bone(Sharpy’s fibers) Lamellar bone(compact) Cortical bone(compact) Spongiosa(cancellous)

The part of the alveolus which immediately surrounds the root is the alveolar bone proper (cribriform plate, lamina dura or bundle bone).The rest of the alveolar bone is the supporting alveolar bone.

Lamina dura

Alveolar bone proper The bundle bone which is the most inner part lining the socket. Lamellar bone (compact bone next to bundle bone). Some lamellae are arranged parallel to the surface and others form Haversian systems.

Supporting Alveolar Bone: Cotrical bone on the buccal and lingual surfaces. The intervening cancellous bone (spongiosa) surrounding the alveolar bone proper.

Cortical bone Consisting of well organized lamellae 1. External circumferential lamellae. 2. Internal circumferential lamellae. 3. Interstitial lamellae. 4. Haversian canal system.

The spongiosa is adapted to support the alveolus proper, since its trabeculae are arranged in such a fashion as to resist occlusal force. The spongiosa is absent in the regions of the incisors, where the alveolar bone proper is fused with the cortical plate. In multirooted teeth, the bone septum intervenes between the root is called interradicular septum composed of spongy bone covered by a cribriform plate.

Radiographically; Type I : A sparse ladder-like arrangement (in the mandible). Type II : An apparent haphazard arrangement (in the maxilla).

Type I Type II

The thickness of the cortical plate varies depending upon the location. The cortical plates of the molar regions are thicker than those of the incisor regions.

Aging of alveolar bone A comparison of young and old alveolar bone reveals the following: - The alveolar sockets appear Jagged and scalloped. - The bone marrow appears to have a fatty infiltration. - Osteoporosis indicates loss of some bony elements. - The internal trabecular arrangement is more open, which indicates bone loss.

References Ten Cate oral histology,development and structure and function. Antonio Nancy 7 th ed Berkovitz oral anatomy, histology and embryology. Berkovitz BKB, Maxham B J, Holland G R.4 th ed