Alveolar bone

Alveolar Bone in HealthPart - A- Dr. Ibrahim ShaikhDept. of Periodontology & ImplantologySeminar No. 517/07/2015Guide : Dr. Varsha Rathod

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CONTENTSIntroductionClassificationCompositionDevelopmentStructure of Alveolar BoneMorphology of Alveolar BoneRadiographic Features2

Introduction 3

Periodontium:

The term periodontium arises from the Greek word Peri = around, odont = tooth.

Functional unit of tissues that invest and support the teeth including gingiva, periodontal ligament, cementum & alveolar bone.

Bone is a mineralized connective tissue. It is unique in body in that it exists both as a tissue and as an organ. An example for Organ is maxilla and mandible. Each of the bony organs that are collectively called Skeleton, which is primarily composed of a tissue i.e called bone. Therefore the bony skeleton is constructed from the same basic building material which is called bone mass.

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IntroductionAlveolar process is the portion of the maxilla & mandible that forms and supports the tooth sockets (Alveoli).1

Alveolar process is the part of maxilla and mandible that forms and supports the sockets of teeth.2

Alveolar process is defined as the compact and cancellous bony structure that surrounds and supports the teeth.(AAP) 4CLINICAL PERIODONTOLOGY; NEWMAN, TAKEI, KLOKKEVOLD, CARRANZA; 10TH EDNCLINICAL PERIODONTOLOGY AND IMPLANT DENTISTRY- Jan Lindhe pg:34

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IntroductionTogether with the root cementum and periodontal ligament, the alveolar bone constitutes the attachment apparatus of the teeth.

Forms when tooth erupts to provide osseous attachment to the forming PDL, disappears gradually after tooth is lost.

Develops and undergo remodeling with tooth formation, hence tooth-dependent bony structures.

Size, shape, location and function of teeth determine their morphology.5

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IntroductionAlveolar bone Proper is the thin inner socket wall comprising of compact bone.

Alveolar septum / Interdental septum is that part which separates the individual alveoli.

Cribriform plate histologically the alv. bone proper contains a series of perforations ..cribriform plate.

Bundle Bone is that portion or entity of alveolar bone proper in which the principal fibers of the PDL are anchored.

Lamina Dura A radiological term used to describe the radiopaque line representing the cribriform plate.

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7Introduction

8Introduction

The bone holds the tooth firmly in position to masticate and, for the lower jaw, transmits the muscle-powered movements of the body of the mandible.

helps to move the teeth for better occlusion

supplies vessels for the PDL & cementum

houses & protects developing permanent teeth while supporting primary teeth8

ClassificationDEVELOPMENTALLY,Endochondral bone Intramembranous bone

HISTOLOGICALLY,According to its macrology (density), mature bone can be divided into:Compact (cortical) boneCancellous (spongy) bone9

where the bone is preceded by a cartilaginous model which is eventually replaced by bone. "Endochondral" means "within cartilage. The cartilage is partially or entirely destroyed by the process ofcalcification. The cartilage is then resorbed (reabsorbed), leaving bone in its place.

where the bone forms directly within a vascular fibrous membrane.

Compact Bone: It is dense in texture like ivory, but is extremely porous. This is an adaptation to bending & twisting forces.

Cancellous Bone (Trabecular Bone):It is made up of a meshwork of trabeculae (rods & plates) between which are marrow containing spaces. This is an adaptation to compressive forces.

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Microscopically, bone can be divided into:Lamellar boneFibrous (woven) boneClassification

Most of the bones, whether compact or cancellous, are composed of thin plates of bony tissues called lamellae. These are arranged in piles in a cancellous bone, but in concentric cylinders (Haversian system or secondary osteon) in a compact bone.

It is found in young fetal bone. The collagen fibers have more variable diameter and are irregular in orientation which gives it matted appearance.

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ClassificationRELATED TO IMPLANT DENTISTRYLinkow, in 1970, classified bone density into three categories:

Class I bone structure: This ideal bone type consists of evenly spaced trabeculae with small cancellated spaces.

Class II bone structure: The bone has slightly larger cancellated spaces with less uniformity of the osseous pattern.

Class III bone structure: Large marrow-filled spaces exist between bone trabeculae.11

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ClassificationRELATED TO IMPLANT DENTISTRYLekholm and Zarb, in 1985, listed four bone qualities found in the anterior regions of the jawbone.

Quality 1 : Composed of homogeneous compact bone.

Quality 2 : Has a thick layer of cortical bone surrounding dense trabecular bone.

Quality 3 : Thin layer of cortical bone surrounding dense trabecular bone of favorable strength.

Quality 4 : Thin layer of cortical bone surrounding a core of low-density trabecular bone.12

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ClassificationRELATED TO IMPLANT DENTISTRYIn 1988, Dr. Carl E. Misch proposed four bone density groups D 1 : Dense cortical bone.

D 2 : Has dense to porous cortical bone on the crest &, within the bone, has coarse trabecular bone.

D 3 : Thinner porous cortical crest and fine trabecular bone within.

D 4 : Has almost no crestal cortical bone. The fine trabecular bone composes almost all of the total volume of bone.13

A very soft bone with incomplete mineralization and large intertrabecular spaces, may be addressed as D5 bone. This bone type is most often immature bone in a developing sinus graft.

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Inorganic (65%)Organic (35%)Hydroxyapatite

Collagen (88-89%) Noncollagenous (11-12%) BONE

Glycoproteins (6.5-10%)

Proteoglycans (0.8%)

Sialoproteins (0.35%)

Lipids (0.4%)

Composition

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Alveolar bone is dependent on the presence of teeth for its development and maintenance.

At the late bell stage, bony septa and bony bridge start to form, and separate the individual tooth germs from another, keeping individual tooth germs in clearly outlined bony compartment.

At this stage, the dental follicle surrounds each tooth germ, which is located between a tooth germ and its bony compartment. Even prior to root formation, the tooth germs within bony compartments show continued bodily movement in various directions to adjust to the growing jaws. This movement causes minor remodeling of bony compartment through bone resorption and deposition of new bone.15Development

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The major changes in the alveolar processes begin to occur with the development of the roots of teeth and tooth eruption. As the roots of teeth develop, the alveolar processes increase in height.

At the same time, some cells in the dental follicle also differentiate into osteoblasts and form the alveolar bone proper. The formation of the alveolar bone proper is closely related to the formation of the periodontal ligament and cementum during root formation and tooth eruption.

Thus, the size and shape of the individual developing tooth roots determine the overall structure of the alveolar bone proper. On the other hand, the rest of bony structures in the alveolar process are achieved by periosteal bone formation.16Development

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17Development

A developing root shown by a divergent apex around the dental papilla (arrow), which is enclosed by an opaque bony crypt.

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ALVEOLAR PROCESS

As a result of its functional adaptation, two parts of the alveolar process can be distinguished.Alveolar bone proper 0.1 to 0.4 mm thick (Haversian system and lamellated & bundle bone)Supporting alveolar bone - cortical plate, which consists of compact bone and forms outer and inner plates of alveolar processes.- spongy bone, which fills area between these plates and alveolar bone proper, also known as cancellous bone.18Structure of Alveolar Bone

The maxilla and mandible of the adult human can be subdivided into two portions :The alveolar process that involves in housing the roots of erupted teeth The basal body that does not involve in housing the roots.

The alveolar bone proper is 0.1 to 0.4 mm thick and is consisted of a Harversian system and lamellated and bundle bone. The coronal and apical regions of the alveolar bone proper have a sieve-like structure. These openings connect the periodontal ligament to the bone marrow spaces and correspond to Volkmanns canals through which blood vessels, lymphatic vessels and nerve fibers pass. (Haykshi 1952 & Birn 1966)Openings are not evenly distributed more dense in the crestal than in the middle & apical regions.

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19Structure of Alveolar Bone

Longitudinal ground section through the mandible showing the alveolar bone. A = Inner layer of compact alveolar bone lining the tooth socket wall; B - outer alveolar plate of compact bone (note the spongy bone lying between the two plates of alveolar bone); C = arbitrary boundary between the alveolar bone and the body of the jaw.

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CORTICAL PLATES

20Structure of Alveolar Bone

Structurally, the cortical plate is composed of lingual and facial plates of compact bone.It is dense in nature and provides strength and protection and acts as the attachment for skeletal muscles.The mandibular cortical plate is more dense than the maxilla cortical plate and has fewer perforations for the passage of nerves and blood vessels.

Presence of the oblique line results in shelf like bone process at the buccal aspect of second and third molars20

CORTICAL PLATES

Histologically, cortical plates consist of longitudinal lamellae and Haversian system. In the lower jaw, circumferential or basic lamellae reach the body of the mandible into the cortical plates.

21Structure of Alveolar Bone

At the buccal aspect of the jaws the bone coverage is sometimes missing at the coronal portion of the roots, forming a so-called Dehiscence. If some bone is present in the most coronal portion of such an area the defect is called a fenestration. These defects often occur where a tooth is displaced out of the arch and are more frequent over anterior than posterior teeth.21

SPONGY BONE: Type 1: The interdental and interradicular trabeculae are regular and horizontal in a ladder like arrangement. Type 2: Shows irregularly arranged numerous delicate interdental and interradicular trabeculaeWide variations occur in trabecular pattern which is affected by occlusal forces. Maxilla has more cancellous bone than mandible.Both types show a variation in thickness of trabeculae and the size of marrow spaces. 22Structure of Alveolar Bone

It fills the area between the cortical plates and the ABP. Radiographic studies permit the classification of spongiosa of the alveolar process into two main types;

This type of architecture is seen most commonly in the mandible and fits well into the general idea of trajectory pattern of spongy bone.

Although, functionally satisfactory, lacks a distinct trajectory pattern which seems to be compensated by greater number of trabeculae in any given area. This type of arrangement is more common in maxilla.

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SPONGY BONE: 23Structure of Alveolar Bone

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CORTICAL BONESPONGY BONEAbout 85% of boneAbout 15% of boneLesser turnover than spongyHigher turnoverRemodel about 3% of its mass each yearremodel about 25% of its mass each yearMechanical/protective role More metabolic function

Oral anatomy, histology and embryology; Berkovitz, Holland, Moxham; 3rd ednStructure of Alveolar Bone

In the body as a whole, about 85% of bone is of the cortical variety while about 15% is spongy. However, these figures are likely to vary according to site and age. Although it only occupies a small percentage of bone volume, spongy bone has a far higher turnover rate than cortical bone: cortical bone is said to remodel about 3% of its mass each year, while spongy bone remodels about 25%. The cortical bone functions mainly in mechanical/protective role, while the spongy bone has a more metabolic function. 3

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INTERDENTAL SEPTA:

Consists of cancellous bone bordered by the socket wall cribriform plates of approximating teeth and facial and lingual cortical plates. The mesiodistal angulation of the crest of the interdental septum usually parallels a line drawn between CEJ of the approximating teeth. Distance between crest of the alveolar bone and CEJ in young adults is 0.75-1.49mm (avg.1.08mm). This distance increases with age to an average of 2.81mm. The interdental and interradicular septa contain the perforating canals of Zuckerkandl and Hirschfeld which house interdental or interradicular arteries, veins, lymph vessels and nerves.Structure of Alveolar Bone

The interdental septa are bony partition that separate adjacent alveoli coronally at cervical region, the septa are thinner and here the cortical plates are fused and cancellous bone is frequently missing.

If the interdental space is narrow, the septum may consist of only the cribriform plate.

If roots are too close together, an irregular window can appear in the bone between adjacent roots.

The mesiodistal and faciolingual dimension and shape of the interdental septum are governed by the size and convexity of the crowns of the approximating teeth, as well as by the position of the teeth in the jaw and their eruption.

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Generally the form of the alveolar bone can be predicted on the basis of 3 general principles:

Position, state of eruption, size and shape of the teeth.

Forces applied.

Thickness of bone.Morphology of Alveolar Bone

The position, state of eruption, size and shape of the teeth determine to a great extent the form of the alveolar bone.

When subjected to forces within normal physiologic limits bone undergoes remodeling to form a structure that best resolves the forces applied.

There is a finite thickness below which bone will not survive but will be resorbed.

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The alveolar margin usually follows the contour of the cementoenamel line. The interproximal bone between adjacent teeth that are erupted to the different planes of occlusion will be inclined toward the root of the less erupted tooth. Teeth that are rotated will exhibit a bone margin that is located more coronally and is less scalloped than that of adjacent normally positioned teeth. The size, position and shape of the roots have a major influence upon bone form.Morphology of Alveolar Bone

Thus, scalloping of the bony margin is prominent on the facial aspect of the anterior teeth than the molars. Also between the molars, the interproximal bone is flat buccolingually.27

BUNDLE BONE (Lamina Dura) CRIBIFORM PLATE Bundle bone is the part of alveolar bone, into which the fiber bundles of the PDL insert. The ABP appears as an opaque line called LAMINA DURA. Embedded within this bone are the extrinsic collagen fiber bundles of PDL. Lining of alveolar bone is fairly smooth in youngsters but with age, the socket lining become rougher. It is referred to as cribriform plate because of perforation through which the blood vessels, lymphatics and nerves of PDL pass.Morphology of Alveolar Bone

The apparent density is due to thick bone without trabeculations that x-ray cant penetrate and not due to any increase in mineral content.

The outer cortical plate is covered by a fibrous and cellular periosteum. The inner cortical plate (ABP) contains Sharpeys fibers that are the endings of embedded PDL.

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HAVERSIAN SYSTEM (Bone Organisation) Bone is deposited in layers, or lamellae, each lamella being about 5m thick.

Three distinct types of layering are recognized:

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 are interspersed between adjacent concentric lamellae and fill the spaces between them.Morphology of Alveolar Bone

There may be between 4 and 20 concentric lamellae within each Haversian system, the number being limited by the ability of nutrients to diffuse from the central vessel to the cells in the outermost lamella. The longitudinally running Haversian canals are connected by a series of horizontal ones (interconnecting canals).

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HAVERSIAN SYSTEM (Bone Organisation) In spongy bone the lamellae are apposed to each other to form trabeculae about 50 m thick. The trabeculae are not arranged randomly but aligned along lines of stress so as best to withstand the forces applied to the bone while adding minimal to mass. The trabeculae surround the marrow spaces from which they derive their nutrition and only infrequently are seen to possess Haversian canals.Morphology of Alveolar Bone

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HAVERSIAN SYSTEM (Bone Organisation)

Morphology of Alveolar Bone

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BONE MARROW In the embryo and newborn, the cavities of all bones are occupied by red hematopoietic marrow. The red marrow gradually undergoes a physiologic change to the fatty or yellow inactive type of marrow. In the adult, the marrow of the jaw is normally of the latter type, and red marrow is found only in the ribs, sternum, vertebrae, skull, and humerus.Morphology of Alveolar Bone

However foci of red marrow are occasionally seen in the jaws often accompanied by resorption of bony trabeculae. Common locations are the maxillary tuberosity, the maxillary and mandibular molar and premolar areas, and the mandibular symphysis and ramus angle, which may be visible radiographically as zones of radiolucency.32

PERIOSTEUM The tissue covering the outer surface of bone is termed periosteum.

The periosteum consists of: An inner layer composed of osteoblasts surrounded by osteoprogenitor cells, which have the potential to differentiate into osteoblasts, & An outer layer rich in blood vessels and nerves and composed of collagen fibers and fibroblasts.Morphology of Alveolar Bone

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ENDOSTEUM The tissue lining the internal bone cavities is called endosteum. The endosteum consists of:An inner layer - the osteogenic layer, & The outer fibrous layer.Morphology of Alveolar Bone

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Haversian canal35

Morphology of Alveolar Bone

LAMINA DURA A radiograph of sound teeth in a normal dental arch demonstrates that the tooth sockets are bounded by a thin radiopaque layer of dense bone. Its name, lamina dura ("hard layer"), is derived from its radiographic appearance. This layer is continuous with the shadow of the cortical bone at the alveolar crest.

Radiographic Features

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LAMINA DURA Its radiographic appearance is caused by the fact that the x-ray beam passes tangentially through many times the thickness of the thin bony wall, which results in its observed attenuation. Developmentally the lamina dura is an extension of the lining of the bony crypt that surrounds each tooth during development.Radiographic Features

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ALVEOLAR CREST The gingival margin of the alveolar process that extends between the teeth is apparent on radiographs as a radiopaque line, the alveolar crest.The level of this bony crest is considered normal when it is not more than 1.5 mm from the cementoenamel junction of the adjacent teeth.Radiographs can demonstrate only the position of the crest; determining the significance of its level is primarily a clinical problem. Radiographic Features

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ALVEOLAR CREST The image of the crest varies from a dense layer of cortical bone to a smooth surface without cortical bone. In the latter case the trabeculae at the surface are of normal size and density. In the posterior regions this range of radiodensity of the crest is presumed to be normal if the bone is at a proper level in relation to the teeth. The absence of an image of cortex between the incisors, however, is considered by many to be an indication of incipient disease, even if the level of the bone is not abnormal.Radiographic Features

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CANCELLOUS BONE It is composed of thin radiopaque plates and rods (trabeculae) surrounding many small radiolucent pockets of marrow. The radiographic pattern of the trabeculae shows considerable intrapatient and interpatient variability, which is normal and not a manifestation of disease.The trabeculae in the anterior maxilla are typically thin and numerous, forming a fine, granular, dense pattern, and the marrow spaces are consequently small and relatively numerous. Radiographic Features

The cancellous bone (also called trabecular bone, or spongiosa) lies between the cortical plates in both jaws.

In the posterior maxilla the trabecular pattern is usually quite similar to that in the anterior maxilla, although the marrow spaces may be slightly larger.

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CANCELLOUS BONE In the anterior mandible the trabeculae are some what thicker than in the maxilla, resulting in a coarser pattern, with trabecular plates that are oriented more horizontally.The trabecular plates are also fewer than in the maxilla, and the marrow spaces are correspondingly larger.In the posterior mandible the periradicular trabeculae and marrow spaces may be comparable to those in the anterior mandible but are usually somewhat larger.Radiographic Features

The trabecular plates are oriented mainly horizontally in this region also.

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PART - BCell types in boneMatrix componentsUltrastructural organizationPhysiologic remodelling of alveolar boneBlood supplyThe implant - bone interfaceNormal morphologic variationsSummary42

REFERENCESClinical periodontology; Newman, Takei, Carranza; 9th ednClinical periodontology; Newman, Takei, Klokkevold, Carranza; 10th ednOral anatomy, histology and embryology; Berkovitz, Holland, Moxham; 3rd ednTencates Oral histology- development, structure and function; Antonio Nanci; 6th ednOrbans Oral histology and embryology; S.N.Bhaskar; 10th ednClinical periodontology and implant dentistry; Jan Lindhe; 4th ednOral radiology-principles and interpretation; Stuart C. White; 5th edn43

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