Alveolar Bone Perio

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ALVEOLAR BONE

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Definition Osteogenesis Composition Gross structure of bone microscopic structure of bone Osseous topography Fenestrations & dehiscence

Remodeling ( bone turnover )

Bone changes associated with the orthodontic forces

Blood supply, lymphatic drainage of the bone

References

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BONE:

Bone is a mineralized connective tissue that performs the function of support, protection and locomotion

ALVEOLAR PROCESS :

It is defined as the parts of the maxilla and mandible that form and support the sockets of the teeth.

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OSTEOGENESIS :

The process of bone formation is called osteogenesis.

Endocondral bone formation

Intra- membranous bone formation

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ENDOCHONDRAL BONE FORMATION :

In this type, the bone formation of a cartilagenous model which is subsequently replaced by bone.

Mesenchymal cells become condensed at the site of bone formation.

Some mesenchymal cells differentiate into chondroblasts & lay down hyaline cartilage.

The cartilage is surrounded by a membrane called perichondrium.This is highly vascular & contains osteogenic cells.

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The intercellular substance surrounding the cartilage cells becomes calcified due to the influence of enzyme alkaline phosphatase secreted by the cartilage cells.

Thus the nutrition to the cartilage cells is cut off leading to their death which results in formation of empty spaces called primary areolae.

The blood vessels & osteogenic cells from the perichondrium invade the calcified matrix which is now reduced to bars or walls due to eating away of the calcified matrix. this leaves large empty spaces between the walls called secondary areolae.

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The osteogenic cells from the perichondrium become osteoblasts & arrange themselves along the surface of there bars of calcified matrix.

The osteobleasts lay down osteoid which later becomes calcified to form a lamella of bone. Then another layer of osteoid is secreted & this goes on & on. Thus the calcified matrix of cartilage acts as a support for bone formation.

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INTRA-MEMBRANOUS BONE FORMATION :

In this type of ossification, the formation of bone is not preceded by the formation of a cartilagenous model, Instead bone is laid down directly in a fibrous membrane.

Loose mesemchymal tissue

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At the site of bone formation, mesenchymal cells become aggregated.

Some mesenchymal cells lay down bundles of collagen fibres.

Some mesenchymal cells differentiated into osteoblasts.

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These osteoblasts secrete a gelatinous matrix called osteoid around the collagen fibres.

They deposit calcium salts into the osteoid leading to conversion of osteoid into bone lamellae.

Now the osteoblasts move away from the lamellae & a new layer o osteoid is secreted which also gets calcified

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COMPOSITION : BONE

67% 33%Inorganic Organic

Hydroxyapetite crystals

calcium

phosphates

hydroxyl

carbonate

sodium

magnesium

fluorine

Collagen

type I

Non collagenous

proteins

Osteocalcin

Osteonectin

Phosphoproteins

proteoglycans

Sioloprotein

Bone morphologic

protein

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GROSS STRUCTURE OF BONE ;

Alveolar bone proper

Supporting alveolar

bone

The interdental septum

Periosteum

Endosteum

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It surrounds the roots of the tooth & gives attachment to the principal fibers of the periodontal ligament.

It also known as the cribiform plate as it is perforated by many openings; through which branches of the interalveolar nerve & vessels pass into the periodontal ligament.

Histologically bundle bone & lamellaler bone

ALVEOLAR BONE PROPER :

BUNDLE BONE :

The bone which lines the socket in which sharpey’s fibers are embedded is known as bundle bone.

Contains more calcium salts per units area than other bone.

It also know as lamina dura because of its radiopacity.

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SUPPORTING ALVEOLAR BONE :

It is the bone that surrounds the alveolar bone proper & gives support to the socket.

Consists of cortical plates & spongy bone ( cancellous bone)

CORTICAL PLATES :

Consists of compact bone & form the outer & inner plates of the alveolar process.

Thinner in maxilla than in the mandible.

Thickest in the premolar & molar region of the mandible.

SPONGY BONE:

It is the bone which fills the space between the outer & inner plates &the alveolar bone proper.

Consists of heavy trabeculae with bone marrow spaces.

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THE INTERDENTAL SEPTUM :

Consists of cancellous bone bordered by the socket walls of approximating teeth & the facial & lingual cortical plates.If roots are too close together, an irregular window can appear in the bone adjacent roots.

PERIOSTEUM :

The outside of all compact bone is covered by a thin connective tissue membrane called the periosteum.

ENDOSTEUM :

The internal surface of compact bone as well as the entire surface of the cancellous bone are covered by a single layer of bone cells called the endosteum.

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MICROSCOPIC STRUCTURE OF BONE ;

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OSTEON :

It is the structural & metabolic unit of the lamellar bone.

It consists of haversian canal in the center which harbors a blood vessels.

This is surrounded by concentric, mineralized lamellae to form the osteon; known as concentric lamellae.

Spaces between the different osteon is filled with interstitial lamellae.

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HAVERSIAN SYSTEM :

Consists of the haversian canal & the volkmann’s canal.

Haversian canal located in the center of the osteon.

Volkmann’s canal are the connecting vessels which connect the haversian canal.

FUNCTION: provides nutrition to the bone.

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LAMELLAE :

Made up of osteocytes found within empty spaces called lacunae.

Mainly 3 types:

CIRCUMFERENTIAL LAMELLAE :

They are bony lamellae that surround the entire bone, forming its outer surface.

CONCENTRIC LAMELLAE :

They form the bulk of the bone & osteon.

INTERSTITIAL LAMELLAE :

They are lamellae that found between adjacent concentric lamellae. they fill the space between the concentric lamellae.

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BONE MARROW :

RED BONE MARROW :

Mainly found in the embryo & newborn.

They help in formation on RBCs & WBCs.

In adults, it is found in the ribs, sternum, vertebrae, skull & humerus.

In the oral cavity, it is found in the maxillary tuberocity, the maxillary molars, the mandibular molars, the mandibular premolar areas, the mandibular symphysis & the ramus angle.

Radiographic ally seen as a zones of radiolucencyYELLOW BONE MARROW :

It is a fatty marrow that does not produces red &white blood cells.

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CELLS :

OSTEOBLASTS ;

These are bone forming cells

Origin: pluripotent stem cells

These are mononucleated cells that synthesize collagenous & non - collagenous bone matrix proteins.

It exhibits a high level of alkaline phosphatase on their outer plasma membrane.

When active……. They are plump, cuboidal in shape.

When non-active……. They becomes slight flattened.

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OSTEOCYTES ;

As the osteoblasts secrete the bone matrix, some of the osteoblasts get entrapped in lacunae; they are called osteocytes.

The space in the matrix occupied by an osteocyte is called the osteocytic lacuna.

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OSTEOCLASTS ;

These are bone resorbing cell that are multinucleated , large & generally found in cluster.

Origin: circulating monocytes & local mesenchymal cells.

The osteoclasts are found against the one surface occupying shallow depressions called howship’s lacunae.

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OSSEOUS TOPOGRAPHY :

Normally : prominence of the roots with the intervening vertical depressions that taper toward the margin.

On the labial version ; the margins of the labial bone is thinned to a knife edge &presents an accentuated arc in the direction of the apex.

On the lingual version ; the margins of the labial bone is blunt &rounded & horizontal rather than arcuate.

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FENESTRATIONS & DEHISCENCES :

Isolated areas in which the root is denuded of bone & the root surface is covered only by periosteum & overlying gingiva are termed fenestrations.

When the denuded areas extends through the marginal bone then defect is called a dehiscence.

Etiology… unknown

Predisposing factors… prominent root contours, malposition, labial protrusion of the root combined with a thin bony plate.

Seen more often on facial bone than on lingual bone

More common on anteriorly than posteriorly

Occurs bilaterally

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BONE TURNOVER (REMODELLING) :

The process by which the overall size & shape of bones is established is referred to as bone remodeling.

Alveolar bone is a east stable of the periodontal tissues because its structure is in a constant state of flux.

Influencing factors

local systemicFunctional requirements on the tooth

Age related changes in the bone cells

Parathyroid hormone

Calcitonin

Vitamin D3

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Manifested in 3 areas :

Adjacent to the periodontal ligament.

In relation to the periosteum of the facial & lingual plates.

Endosteum surface of the marrow spaces.

Sequences of resorptive events ;

Attachment of osteoclasts to the mineralized surface of bone.

Creation of a sealed acidic microenvironment through the action of the proton pump, which demineralizes bone &exposes the organic matrix.

Degradation of the exposed matrix by the action of released enzymes such as acid phosphatase & cathespin B.

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Endocytosis at the ruffled border of inorganic & organic bone degradation products.

Translocation of degradation products in transport vesicles & extra cellular release along the membrane opposite the ruffled border. (transcytosis)

Osteoblasts produce osteoid which later calcified.

Bundle bone has the highest turnover rate.

In lamellar, cancellous or spongy bone; half – moon resorption cavity is created by osteoclasts &then filled in with bone matrix by osteoblasts.

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VASCULAR SUPPLY :

Derived from blood vessels branching off of the superior or inferior alveolar arteries.

LMPHATIC DRAINAGE ;

Smallest lymph vessel ……. Lymph capillaries.

All third molars ……. Jugulodigastric lymph nodes.

Mandibular incisors ……. Sub mental lymph nodes.

Rest ……. Sub mandibular lymph nodes.

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BONE CHANGES ASSOCIATED WITH THE ORTHODONTIC FORCES :

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REFERENCES:

Fermin A. Carranza , Newmann , Takei ; clinical periodontology ; 9th edition ; 45 – 51.

Glickman , Fermin A. Carranza , Dr. Odont ; clinical periodontology ; 7th edition ; 62 – 73.

Jan Lindhe , Thorkild Karring , Niklaus P. Lang ; clinical periodontology & implant dentistry ; 4th edition ; 34 – 43.

A. R. Tencate , Antonio Nanci ; oral histology, development, structure & function ; 6th edition ; 111 – 143.

S. I. Bhalajhi ; dental anatomy ,histology, & development ; 1st edition ; 323 – 328.

S. I. Bhalajhi ; orthodontics- the art & science ; 3rd edition ; 183- 185.