Presented By – Abhishek Gakhar

27rd June 2012

Department of PeriodonticsITS Dental College, Hospital & Research Center

Greater Noida

Moderator- Dr. Kanwarjit Sing AsiPerceptor - Dr. Shivjot Chhina

Alveolar Bone

Bone - Classification - Functions - Composition Alveolar Bone & Alveolar Process Development of Alveolar Bone Functions of Alveolar Bone Structural Elements of Alveolar

Bone -Bone cells

◦ Osteoprogenitor cells – stem cells◦ Osteoblasts – forms bone◦ Osteocytes – maintains bone◦ Osteoclasts – resorbs bone

Content

Bone matrix Sharpey’s fibers Vascular Supply & Lymphatic Vessels Gross Morphology of alveolar Bone. Structures of Alveolar Bone Periosteum & Endosteum References

The hard form of connective tissue that constitutes the majority of the skeleton of most vertebrates.(1)

Second only to cartilage in its ability to withstand stress.

Bone

Bone may be classified in several ways:

Classification of Bone

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 within a vascular, fibrous membrane.

Developmental Classification

COMPACT BONE

• Composed of dense and concentrically arranged bony trabeculae or lamella.

• More solid with fewer cavities.

• Found external to spongy bone

• Presence of haversian system.

Histological Classification

SPONGY or CANCELLOUS BONE

Composed of bone trabeculae or spicules.

Has a simple and less organized architecture.

Has a lattice-work pattern with numerous small cavities.

Found internal to compact bone.

Has no haversian system.

1. Immature bone /Fibrous bone : These have more cells & fibers in them. In humans they are found only in fetus, sockets of alveolar bone, sutures of the skull.

2. Mature bone /Lamellar bone: The type of bone which are composed of thin plates (lamellae) of bony tissue. Most mature human bones are lamellar bones.

MACROSCOPIC CLASSIFICATION

1. 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 is 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.

Functions of bone

65% Inorganic matter (Hydroxyapatite)◦ Mostly Calcium and

inorganic orthophosphate deposited between collagen

35% Organic◦ 28-30% collagen◦ 5-7% non-collagenous

proteins. Osteocalcin Bone Sialoprotein Phosphoprotein Osteonectin Bone morohogenic protein

Composition of Bone

Composition of bones

Inorganic SubstancesOrganic Substances

2/3rd inorganic matrix(2)

Composed of minerals calcium & phosphate, along with hydroxyl, carbonate, citrate & trace amount of other ions,(2) such as sodium, magnesium & fluorine.

Inorganic matrix

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(3)

◦ 10% non-collagenous proteins.

Organic Matrix of the bone

Organic Components of the Bone Matrix

CollagenNon-col-lagenous proteins

◦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.

Collagen

◦ are a heterogeneous group which vary from entrapped serum protein to glycoproteins.

◦ play a role in mineralization.

◦ The main non-collagenous proteins comprise of: Proteoglycans Osteonectin (SPARC)/(BM40) Osteocalcin (BGLAP) Glycoproteins Bone morphogenic proteins Bone Sialoproteins (BSP)

Non-collagenous Proteins of Bone

ALVEOLAR BONE

Alveolar bone or alveolar process is that portion of maxilla and mandible that supports the roots of the tooth.

If the teeth are lost the alveolar process disappears.

It is composed of two parts the alveolar bone proper and the supporting bone.

Alveolar Bone

Since the alveolar process develop & undergo remodeling with the tooth formation & eruption, they are tooth dependent bony structures.(2)

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

It is called processus alveolaris in maxila and pars alveolaris in the mandible bone.

◦ It 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’

Development of alveolar bone

Alveolar bone develops from the dental follicle. (4)

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. (4)

It supports the tooth roots on the facial and on the palatal/lingual sides.

It is the one responsible for the separation of teeth from mesial to distal.

Also contributes to absorption and distribution of occlusal pressure produced in tooth to tooth contact.

Functions of Alveolar process

Bone cells◦ Osteoprogenitor cells – stem cells◦ Osteoblasts – forms bone◦ Osteocytes – maintains bone◦ Osteoclasts – resorbs bone

Bone matrix

Sharpey’s fibers

Vascular Supply & Lymphatic Drainage

Structural Elements of Bone

Stem cells derived from the mesenchyme.(5)

Possess mitotic potential and the ability to differentiate into mature bone cells.

Resemble mesenchymal cells and are spindle-shaped, with pale-staining elongated nuclei and sparse cytoplasm (small amount of rough ER and poorly developed golgi complex).

Mostly found in the inner portion of the periosteum, in the endosteum, and within vascular canals of compact bone.(4)

Osteoprogenitor cells

Uninucleated cells . Synthesize both collagenous and noncollagenous bone

proteins.(6)

Osteoblasts also synthesize the enzyme alkaline phosphatase, which is needed locally for the mineralization of osteoid.

The precursor cell of the osteoblast is the preosteoblast. (7)

Osteoblasts have all the characteristics of hard tissue-forming cells.

When the bone is no longer forming, the surfaces of the osteoblasts become inactive and are called Lining cells.

Osteoblasts

are osteoblasts secreted in the bone matrixes that are entrapped in lacunae.(8)

An osteocyte lies in its own lacuna and contacts its neighboring osteocytes cytoplasmically through canaliculi.

The most important function of osteoblast-osteocyte complex is to prevent hypomineralization of bone by continually pumping calcium back to the bloodstream.(9)

Osteocytes

Derived from a monocytic-macrophage system, which are responsible for bone resorbtion.(10)

They are multinucleated cells with fine, fingerlike cytoplasmic processes and are rich in lysosomes that contain tartrate-resistant acid phosphatase (TRAP).(11)

Osteoclasts lie in resorbtion craters known as Howship’s lacunae on bone surfaces or in deep resorption cavities called cutting cones.

These bone cells can only resorb mineralized bone matrix.

Osteoclasts

Bone matrix consists of organic and inorganic components.(12)

The association of these substances gives bone its hardness and resistance.

The organic component is composed of collagen

fibers with predominately type I collagen (95%) and amorphous material, including glycosaminoglycans that are associated with proteins.(4)

Bone matrix

Osteoid is uncalcified organic matrix.

Inorganic matter represents about 50% of the dry weight of bone matrix.

composed of abundant calcium and phosphorus, as well as smaller amounts of bicarbonate, citrate, magnesium, potassium, and sodium.(4)

Calcium forms hydroxyapatite crystals with phosphorus but is also present in an amorphous form.

Concentrically arranged bony lamellae◦Types of layering (lamella)

Circumferential lamella – external, internal

Concentric/Haversian lamella

Interstitial or Intermediate lamella

Continuous uninterrupted layer found immediately beneath the periosteum around the circumference of the bone.

External Circumferential lamella or Periosteal lamella

INTERNAL CIRCUMFERENTIAL LAMELLA OR ENDOSTEAL LAMELLA

Continuous uninterrupted lamellae immediately surrounding the central medullary cavity.

Layers of bone surrounding the Haversian canal.

Varies from 5 – 20 layers.

Concentric or Haversian Lamella

Found in between haversian systems.

Triangular or irregularly shaped groups of parallel lamella.

May represent lamella left by former haversian systems destroyed during growth and remodelling of bone.

Interstitial or Intermediate lamella

Composed of small central canal (HAVERSIAN CANAL) which is in constant communication with the blood vessels.(4)

Surrounding the canal are concentric bony lamella called haversian lamella.

Haversian system

A bright thin line called CEMENTING LINE separates one haversian system from another.

Haversian systems or OSTEONES (OSTEON) are found underneath the periosteal lamella.

Canals that are not surrounded by bony lamella.(4)

Traverse the bone in a direction perpendicular or oblique to the lamella.

Larger than haversian canals.

Volkmann’s canal

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.(13)

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.

Sharpey’s fibers

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).

Vascular Supply of Alveolar Process

Smallest lymph vessel - Lymph capillaries.

All third molars – Jugulodigastric lymphnodes

Mandibular incisors – Submental lymphnodes

Rest – Submandibular lymphnode

Lymphatic Drainage

GROSS MORPHOLOGY

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.

Interdental Septa◦ “Septa” – in Latin, it

means “fence” or “wall”◦ Are plates of bone that

separate each individual sockets from one another.(14)

Inter-radicular Septa◦ Are thin plates of bone

that separate the roots of multi-rooted teeth.

◦ also called as bundle bone.

◦ A type of alveolar bone so called because of the ‘Bundle’ pattern caused by continuation of principal (Sharpey’s) fibers into it.(1)

◦ 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.

Cribriform Plate

STRUCTURE OF THE ALVEOLAR BONE

a) outer cortical plates

b) 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 aspect.

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.

Spongiosa

Compact bone that composes the alveolus (tooth socket).(1)

It is inner, heavily perforated bony lamellae, forming the alveolar wall.

In radiograph, appears as radio-opaque line distinct from the adjacent spongiosa – Lamina Dura.

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

Alveolar Bone Proper

Layers of differentiated osteogenic connective tissue covers all bone surfaces.

Tissue covering outer surface of bone is termed as Periosteum.(3)

Tissue lining the internal bone cavities is called Endosteum.(3)

Periosteum & Endosteum

Periosteum consist of an inner layer composed of osteoblasts,surrounded by osteoprogenitor cells & an outer layer rich in blood vessles , nerves & composed of collagen fibers & fibroblasts.

The endosteum is composed of single layer of osteoblasts & sometimes small amount of connective tissue.

1)Glossary of Periodontal Terms.

2)FerminA, Carranza, Newmann, Takei; clinical periodontology ;9thedition;45–51.

3)FerminA.Carranza,Newmann,Takei;clinicalperiodontology;10thedition;68–92.

4)R.Tencate,AntonioNanci;oralhistology,development,structure&function;6thedition;111–143

5) Hagel-Bradway S, Dziak R: Regulation of bone cells metabolism, J Oral Pathol Med 18:344,1989

6)Junqueria LC, Carneiro J, Kelley RO: Basic Histology, ed6, Norwalk, Conn, 1989, Appleton & Lange.

References

7)Sicher H, DuBrul EL: Oral Anatomy, ed6, St Louis, 1975

8)Otero RL, Parodi RJ, Ubios AM, et al: Histologic & histometric study of bone resorption , J Periodontal Res 8:327,1973.

9)Schroeder HE: The periodontium, Berlin, 1986, Springerverla.

10)Chambers TJ: The cellular basis of bone resorption, Clin J Periodontal Res 1:120, 1966.

11)Bernard GW, Ko JS: Osteoclast formation in vitro form bone marrow, mononuclear cells in osteoclast-free bone, Am J Anat 161:415, 1981

12) Glimcher MJ: the nature of mineral content of bone & mechanism of calcification, Philadelphia, 1990, Saunders.13) Weinmann JP, Sicher H: Bone & Bones: Fundamentals of bone biology, ed 2, St Louis, 1955, Mosby.14) Heins PJ, Wieder SM: A histologic study of width & nature of inter-redicular spaces in human adult premolars & molars, J Dent Res 65:948, 1986.