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ALVEOLAR BONE

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Part I

BONE

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BONE TISSUE

Bone tissue is a specialized form of

connective tissue and is the main element of the skeletal tissues.

is composed of cells and an extracellular matrix in which fibers are embedded.

is unlike other connective tissues in that the extracellular matrix becomes calcified.

http://en.wikipedia.org/wiki/Bone_tissue

2 Types of bone tissue:

1. Compact (Cortical) bone

2. Spongy (Cancellous) bone

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FUNCTIONS OF BONE1. Support: provides framework that supports and

anchors all soft organs.

2. Protection: skull and vertebrae surround soft tissue of the nervous system, and the rib cage protects vital thoracic organs.

3. Movement: skeletal muscles use the bones as levers to move the body.

4. Storage: fat stored in the interior of the bones. Bone matrix serves as a storehouse for various minerals.

5. Blood Cell Formation: hematopoiesis occurs within the marrow cavities of the bones.

http://en.wikipedia.org/wiki/Haematopoiesis

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CLASSIFICATION OF BONE

Bone may be classified in several ways:

Developmentally Histologically By shape

Endochondral bone Compact (Cortical) Bone

Long bones

Intramembranous bone

Spongy (Cancellous) Bone

Short bones

Flat bones

Irregular bones

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A. endochondral bone• Where bone is preceded by a cartilagenous

model that is eventually replaced by bone In a process termed endochondral ossification.

B. intramembranous bone• Where bone forms directly w/in a vascular,

fibrous membrane.

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CHEMICAL PROPERTIES OF BONE 60 % Inorganic

material is formed from

carbonated hydroxyapatite.

25 % Organic material mainly composed of

Type I collagen. The organic part is

also composed of various growth factors:

glycosaminoglycans, osteocalcin, osteonectin, bone sialo protein, osteopontin and Cell Attachment Factor.

“Oral Anatomy, Histology, and Embryology”

Composition of bones

Inorganic Sub-stances

Organic Sub-stances

Water

15% Water

ORGANIC MATRIX OF THE BONE

Bone is formed by the hardening of the matrix, entrapping the cells. When these cells become entrapped from osteoblasts they become osteocytes.

The organic matrix of bone

is about: 90% collagen 10% non-collagenous

proteins.

Organic Components of the Bone Matrix

CollagenNon-col-lagenous proteins

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Non-collagenous Proteins of Bone are a heterogeneous group which vary from

entrapped serum protein to glycoproteins play a role in mineralization. The main non-collagenous proteins

comprise the: Proteoglycans Glycoproteins Bone Gla-containing proteins Serum proteins

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collagen. Contributes towards the important

biomechanical properties of tissue in terms of resisting loads and providing necessary resilience that prevents fractures.

The dominant collagen in bone is Type I. Intrinsic collagen

collagen as secreted by osteoblasts. Extrinsic collagen

Collagen formed by adjacent fibroblasts.

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SHARPEY’S FIBERS

Sharpey's fibers are the terminal ends of principal fibers (of the periodontal ligament) that insert into the cementum and into the periosteum of the alveolar bone.

A study on rats suggests that the three-dimensional structure of Sharpey's fibers intensifies the continuity between the periodontal ligament fiber and the alveolar bone (tooth socket), and acts as a buffer medium against stress.

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CELL TYPES IN BONE

Osteoblasts are mononucleate cells that are responsible for bone formation

Osteocytes When osteoblasts become trapped in the matrix they secrete, they

become osteocytes. Bone-lining cells

Are inactive osteoblasts that cover all of the available bone surface and function as a barrier for certain ions

Osteoprogenitor cells relatively undifferentiated cells found on or near all of the free

surfaces of bone, which, under certain circumstances, undergo division and transform into osteoblasts or coalesce to give rise to osteoclasts.

Osteoclasts is a type of bone cell that removes bone tissue by removing its

mineralized matrix and breaking up the organic bone

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RESORPTION AND FORMATION OF BONE DURING REMODELLING

Resorption Reversal Formation Resting

http://en.wikipedia.org/wiki/Ossification

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OSSIFICATION

Also called Osteogenesis is the natural process of bone formation There are two processes resulting in the formation

of normal, healthy bone tissue: Endochondral (Intracartilaginous) Bone

Ossification The formation of bone in which a cartilage template is

gradually replaced by a bone matrix, as in the formation of long bones or in osteoarthritic ossification of synovial cartilage.

Intramembranous Bone Ossification the development of bone from tissue or membrane, as in the

formation of the skull.

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Sutural Bone Growth variable and irregularly shaped bones in

the sutures between the bones of the skull.

ALVEOLAR BONE

ALVEOLAR BONE

Also called as alveolar process

The specialized bone structure that contains the alveoli or sockets of the teeth and supports the teeth.

If the teeth are lost the alveolar process disappears

It is composed mainly of two parts:

alveolar bone proper Supporting bone

http://www.answers.com/topic/alveolar-bone#ixzz12ko9kyTQ

Alveolar Bone

DEVELOPMENT OF ALVEOLAR BONE

DEVELOPMENT OF ALVEOLAR BONE

Alveolar bone develops from the dental follicle

The ectomesenchymal cells of the dental follicle differentiate into osteoblasts and lay down the matrix called osteoid

Some osteoblasts become embedded in the matrix and are called osteocytes

Near the end of the 2nd month of fetal life, mandible and maxilla form a groove that is opened toward the surface of the oral cavity

As tooth germs start to develop, bony septa form gradually. The alveolar process starts developing strictly during tooth eruption.

GROSS MORPHOLOGY OF BONE

Morphology -is a branch of bioscience dealing with the study of the form and structure of organisms and their specific

structural

Alveolar Socket Also called Dental

alveolus are sockets in the

jaws in which the roots of teeth are held in the alveolar process with the periodontal ligament.

Alveolar socket of the second premolar tooth in a bovine maxillary bone.

Interdental Septa “Septa” – in Latin, it

means “fence” or “wall”

Are plates of bone that separate each individual sockets from one another.

Interradicular Septa Are thin plates of bone

that separate the roots of multi-rooted teeth

Cribriform Plate also called as bundle bone Is the compact layer of

bone lining the tooth socket (alveolar socket)

Reflects the sieve-like appearance produced by numerous Volkmann’s canals passing from the alveolar bone to the PDL (periodontal ligament).

Numerous Sharpey’s Fiber pass through it.

ALVEOLAR PROCESS is the thickened ridge of

bone that contains the tooth sockets on bones that bear teeth.

The alveolar process contains a region of compact bone adjacent to the periodontal ligament called Lamina dura.

Maxilla and Mandible Are the tooth-bearing

bones

Lamina Dura this part which is

attached to the cementum of the roots by the periodontal ligament.

Is the bone lining the alveolus

In clinical radiographs, it commonly appears as a dense white line.

Lamina Dura

Radiographic appearance of alveolar bone proper as ‘Lamina Dura’

FUNCTIONS OF THE BONE

FUNCTIONS OF ALVEOLAR BONE

Protection Alveolar bone forms and protects the sockets for the teeth.

Attachment It gives the attachment to the periodontal ligament fibers, which

are the principle fibers. These fibers which enter the bone are regarded as Sharpey’s fibers.

Support It supports the tooth roots on the facial and on the palatal/lingual

sides.

Shock-absorber It helps absorb the forces placed upon the tooth by disseminating

the force to underlying tissues.

STRUCTURE OF THE ALVEOLAR BONE Cortical Plate Spongiosa /

Spongy Bone

http://www.google.com.ph/imgres?q=cortical+plate+of+alveolar+bone&num=10&um=1&hl=tl&biw=1018&bih=414&tbm=isch&tbnid=WKjYn2hOmQJweM%3A&imgrefurl=http%3A%2F%2Fwww.medicine.uiowa.edu%2Fanatomy%2Fdental%2Foralhist%2FOHWIN%2Funit2%2F_ii-01.html&docid=VZHNS3piimFp2M&w=300&h=452&ei=x1WATpi2BoTBiQf3_-W3Dg&zoom=1&iact=hc&vpx=89&vpy=48&dur=483&hovh=100&hovw=64&tx=101&ty=176&sqi=2&page=1&tbnh=100&tbnw=64&start=0&ndsp=12&ved=1t%3A429%2Cr%3A0%2Cs%3A0

a) outer cortical platesb) a central spongiosa c) bone lining the alveolus (bundle bone)

CORTICAL PLATE

Outer bony plate of varying thickness, which is the outside wall of the maxilla and mandible, covered with periosteum

Continuous with the lamina cribriformis at the orifice of the alveoli – alveolar crest

Consists of haversian systems (osteons) and interstitial lamellae

Thicker in the mandible than maxilla

Generally greater on the lingual than on the buccal/facial

ALVEOLAR BONE PROPER OR LAMINA

An inner, heavily perforated bony lamellae, forming the alveolar wall

In radiograph, appears as radioopaque line distinct from the adjacent spongiosa – Lamina Dura

Contains osteons like other cortical bone, but is distinguished by the presence of Bundle Bone

SPONGIOSA

Are spongy (or cancellous/trabecullar) bone between the 2 bony plates and between the lamina cribriformis of adjacent teeth or roots

Consists of delicate trabeculae, between which are marrow spaces, filled mostly with fatty marrow

Regions of maxillary tuberosity and the angle of mandible, erythropoietic …

VASCULAR SUPPLY OF ALVEOLAR BONE

VASCULAR SUPPLY OF ALVEOLAR PROCESS

Alveolar process of the maxilla Anterior and posterior alveolar arteries

(branch from the maxilla and infraorbital arteries)

Alveolar process of the mandible Inferior alveolar arteries (internal) Periosteal branches of submental and

buccal arteries (external)

PERIODONTAL DISEASE

PERIODONTAL DISEASE

http://en.wikipedia.org/wiki/Periodontal_disease

Periodontal disease is a type of disease that affects one or more of the periodontal tissues: Alveolar bone Periodontal ligament Cementum Gingiva

While many different diseases affect the tooth-supporting structures, plaque-induced inflammatory lesions make up the vast majority of periodontal diseases and have traditionally been divided into two categories: gingivitis or periodontitis

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HISTOLOGICAL ARRANGEMENT OF MATURE BONE

Mature bone is composed of: Compact bone Spongy Bone

http://www.physioweb.org/skeletal/bone_tissue.html

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COMPACT BONE Also called as Cortical bone As its name implies. . .

“cortical” bone forms the cortex or outer shell of most bones.

“compact” bone is much denser than cancellous bone. Furthermore, it is harder, stronger and stiffer than cancellous bone.

The primary anatomical and functional unit of cortical bone is the osteon.

3 Distinct Layering of Compact Bone: Circumferential lamella Concentric lamella Interstitial lamella

Functions: facilitates to support the whole body protect organs provide levers for movement store and release chemical elements, mainly calcium.

http://en.wikipedia.org/wiki/Bone_tissue

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3 DISTINCT LAYERING OF COMPACT BONE:

Circumferential Lamellae enclose the entire adult bone, forming its

outer perimeter

Concentric Lamellae make up the bulk of compact bone and form

the basic metabolic unit of bone, the osteon

Interstitial Lamellae interspersed between adjacent concentric

lamellae and fill the spaces between them

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SPONGY BONE

Also called Cancellous bone or Trabecular bone Compared to compact bone, cancellous bone has a

higher surface area but is less dense, softer, weaker, and less stiff.

Cancellous bone is highly vascular and frequently contains red red bone marrow where hematopoeisis occurs.

The primary anatomical and functional unit of cancellous bone is the trabecula.