Alveolar bone

Alveolar bone

By,

M.J.Renganath

M.D.S 1st year

Department of Periodontics

CONTENTS

Introduction

Development and Anatomy

Histologic features

Radiographic features

Pathologies involving loss of Alveolar bone

Alveolar bone & implants

Repair and regeneration

Conclusion

References

Introduction

The term periodontium describes tissues which:

1. Anchor the teeth to the bones of the jaws

2. Provide interdental linkage of the teeth within the dental arch

3. Facilitate epithelial lining of the oral cavity in the region of the erupted tooth.

The developmental, biological and functional unit of periodontium:

1. Gingiva

2. Root cementum

3. Periodontal ligament

4. Alveolar bone proper

Alveolar bone

Alveolar bone is defined as the parts of maxilla and mandible that form

and support the socket of teeth.

CLINICAL PERIODONTOLOGY AND IMPLANT DENTISTRY- Jan Lindhe pg:34

Together 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.

Alveolar bone

Development

Formed during fetal growth by intramembranous ossification and consists of

a calcified matrix with osteocytes enclosed within spaces called lacunae.

During embryogenesis, the skeleton forms by either a direct or indirect

ossification process.

In the case of the mandible and the maxilla, mesenchymal progenitor cells

condensate and undergo direct differentiation into osteoblasts, a process

known as intramembranous osteogenesis.

Alveolar bone lost as a result of an injury, disease, or trauma undergoes a

repair process that is essentially a combination of endochondral and

intramembranous complementary osteogenic processes (Rabie et al., 1996;

Virolainen et al., 1995).

A similar process occurs in most of the bone-related implant site

development techniques, where osteoconduction, osteoinduction, and

osteogenesis are exploited.

Anatomy

Alveolar process consists of:

1. External plate of cortical bone

2. Inner socket wall- Alveolar bone proper

3. Cancellous trabeculae- Supporting alveolar bone

Alveolar process

Cortical bone and cancellous bone

Trabeculae

2 main types

Type1:

The interdental and interradicular trabeculae are regular & horizontal in a

ladder like arrangement.

This type is seen most often in mandible.

Type 2:

Shows irregularly arranged, numerous, delicate interdental and

interradicular trabeculae.

This type is more common in maxilla.

Trabecular pattern of alveolar bone

Haversian system

Consists of the haversian canal and 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.

They provides nutrition to the bone.

Haversian canal

Histologic features

Three types of cells are distinguished:

1. Osteoblasts

2. Osteocytes

3. Osteoclasts

Osteoblasts:

Produce the organic matrix of bone are differentiated from pluripotent

follicle cells.

Comprise a mixed population of preodontoblasts with large nuclei and

fibroblast like cells with small nuclei

Osteocytes:

Arise from odontoblasts which becomes entrapped into bone.

Located in bony lacunae and are connected by long cell projections.

Immature osteocytes are smaller than osteoblasts, but have a similar

structure.

Mature osteocytes have a reduced set of organelles.

Osteoclasts:

Large, multinucleated giant cells, located on the surface pits of the

bone(Howship’s lacunae).

Arise by fusion of hematopoietic, mononuclear precursors of bone marrow.

Resorption of bone is facilitated by acidic phosphatases and other

hydrolytic enzymes.

Osteoblasts and osteoclasts

The combined process of bone formation and resorption by simultaneous

activity of osteoblasts and osteoclasts is called as coupling.

Formation of osteoclasts

Resorption activity

Intercellular matrix

Bone consists of 2/3rd inorganic matter and 1/3rd organic matrix.

Inorganic matter:

Calcium

Phosphate

Hydroxyl

Carbonate

Citrate

Trace amounts of sodium, magnesium and fluorine.

Organic matrix:

Type 1 collagen- 90%

Noncollagenous proteins such as :

• Osteocalcin

• Osteonectin

• Bone morphogenetic protein

• Phosphoproteins

• proteoglycans

Bone morphogenic protein

These are well studied group of growth factors belongs to the transforming

growth factor(TGF-β) subfamily, involved in the process of bone healing.

BMP induces the formation of both bone and cartilage by stimulating the

cellular events of mesenchymal progenitor cells.

However, only a subset of BMPs, most notably BMP 2,4,6,7,9 has

osteoinductive activity.

Guided bone regeneration

Guided Bone Regeneration (GBR) was originally developed by Hurley et al.

in 1959 and Boyne in 1964.

Barrier membranes are used, which are bio-inert materials that serve to

protect the blood clot and prevent soft tissue cells (epithelium and

connective tissue) from migrating into the bone defect, allowing

osteogenic cells to be established.

Barrier membranes could be either resorbable or non resorbable.

Osteoblasts derived from the periosteum and bone are selectively induced

on the osseous defect area, facilitating new bone formation.

GBR using a barrier membrane has become widely used for bone

regeneration of osseous dehiscences and fenestrations and for localized

ridge augmentation and immediate implant placement.

GBR in implant therapy is especially useful for fixture placement with dehis-

cence defects or fenestration defects.

In alveolar ridges with marked facial/buc- cal depressions or in knife-edge

alveolar crests, the position and direction of fix- ture placement is restricted.

Improvement of alveolar ridge morphology becomes possible, however,

with GBR.

Radiographic features

The interdental bone normally is outlined by a thin, radiopaque line

adjacent to the periodontal ligament (PDL) and at the alveolar crest,

referred to as the lamina dura.

Because the lamina dura represents the cortical bone lining the tooth

socket, the shape and position of the root and changes in the angulation

of the x-ray beam produce considerable variations in its appearance.

Radiographic features

Lamina dura

conditions involving loss of Alveolar

bone

The various causes of alveolar bone loss are:

I. Extension of gingival inflammation

II. Trauma from occlusion

III. Systemic factors

IV. Orthodontic treatment

V. Periodontitis

VI. Periodontal abscess

VII. Food impaction

VIII. Overhanging restoration

IX. Adjacent tooth extraction

X. Ill-fitting prosthesis

Extension of gingival inflammation

Most common cause of bone loss in periodontal disease is extension of

inflammation from marginal gingiva into supporting periodontal tissues.

Inflammatory invasion of bone surface and intial bone loss that follows mark

the transition from gingivitis to periodontitis.

the transition from gingivitis to periodontitis is associated with changes in

compostion of bacterial plaque.

In advanced stages number of motile organisms and spirochetes increases.

Mechanism of bone destruction

Factors involved are bacterial and host mediated

Bacterial plaque induces bone progenitor cells into osteoclasts

In aggressive periodontitis, bacterial micro colonies have been found

between collagen fibers and over the bone surface, suggesting a direct

effect.

Host factors released by inflammatory cells are capable of inducing bone

resorption.

These include host produce prostaglandins, IL-1a IL- β and TNF-a.

Pathways of inflammation

Extends along the collagen fiber bundles and follows the course of blood

vessels through loosely arranged tissues around them into the alveolar bone

Interproximally, inflammation spreads to the loose connective tissue around

the blood vessel channels that perforate the crest of the interdental

septum at the center of the crest, towards the side of the crest or at the

angle of the septum.

Also, inflammation may enter the bone through more than one channel.

Spread of inflammation from gingiva directly to PDL is less frequent.

Facially and lingually, inflammation from the gingiva spreads along the

outer periosteal surface of the bone and penetrates into the marrow

spaces through vessel channels in the outer cortex.

It courses from gingiva to the bone, inflammation destroys the gingival and

transeptal fibers, reducing them to disorganized granular fragments

interspersed among the inflammatory cells and edema.

Trauma from occlusion

Trauma from occlusion can produce bone destruction either in the absence or presence of inflammation.

These changes are reversible in that they can be repaired if the offending forces are removed.

However, persistent trauma from occlusion results in funnel shaped widening of the crestal portion of the periodontal ligament, with resorption of the adjacent bone.

These changes, cause the bony crest to have an angular shape.

It represent adaptation of the periodontal tissues aimed at cushioning increased occlusal forces, but the modified bone shape may weaken tooth support and cause tooth mobility.

When combined with inflammation, trauma from occlusion aggravates the bone destruction caused by the inflammation and causes bizarre bone patterns.

Trauma from occlusion

Occlusal force beyond physiological limits

Increased compression& tension of PDL

Increased osteoclasis

Necrosis of PDL and bone

Resorption of bone and tooth structure

Trauma from occlusion

Systemic factors

In recent years, interest has increased in the possible relationship between

periodontal bone loss and osteoporosis.

Osteoporosis is a physiologic condition of post menopausal women

resulting in loss of bone mineral content and structural bone changes.

Periodontal bone loss may also occur in generalized skeletal disturbances

by mechanism that may be totally unrelated to usual periodontal

problems.

Systemic factors

Diabetes mellitus:

A majority of well controlled studies show a higher prevalence and severity

of periodontal disease in diabetic patients than in nondiabetic patients

with similar local factors.

Findings include a greater loss of attachment, increased bleeding on

probing, and increased tooth mobility.

As with other systemic conditions, diabetes does not cause gingivitis or

periodontitis, but evidence indicates, it alters the response of periodontal

tissues to local factors, hastening bone loss & delays post surgical healing.

Alteration in collagen metabolism plays a significant role.

Hyperparathyroidism also known as osteitis fibrosa cystica or Von

Recklinghausen’s bone disease, exhibits loss of lamina dura and giant cell

tumors in the jaws.

Loss of lamina dura may also occur in Paget’s disease, fibrous dysplasia

and osteomalacia.

Reports have suggested that 25-50% of patients with hyperparathyroidism

have oral changes that includes malocclusion and tooth mobility.

Radiographic evidence of alveolar osteoporosis with closely meshed

trabeculae, widening of PDL space, absence of lamina dura.

Orthodontic treatment

Bone resorption occurs when there is increased orthodontic forces beyond

the physiological limits.

Rapid orthodontic movement leads to the insufficient Lag phase period

that tends to resorb the alveolar bone to which the force is directed.

It is more common in adult patients undergoing orthodontic treatment.

Whereas in other side, the single angular defect od interdental craters

could be eliminated by the orthodontic movement of the involved teeth.

Orthodontic relapse, apical root resorption, and crestal

alveolar bone levels-Wendy Sharpe et al

American Journal of Orthodontics and Dentofacial Orthopedics;Volume 91, Issue 3,

Pages 252–258, March 1987

This investigation examined the relationship of postorthodontic treatment relapse to crestal

alveolar bone support and root resorption.

The subjects in the relapse group had undergone longer periods of treatment and

exhibited significantly greater crestal alveolar bone level distances, indicating greater loss

of bone support than that observed in the non-relapse group.

The distances that teeth were translated seemed to affect the extent crestal bone loss

with smaller amounts of tooth translation seemingly more prone to demonstrate tissue loss.

Various Bone destructive patterns in

periodontal disease:

Horizontal bone loss

Vertical/Angular defects

Osseous craters

Bulbous bone contours

Reversed architecture

Ledges

Furcation involvement

Horizontal bone loss

When the bone loss occurs on a plane that is parallel to a line drawn from

the CEJ of a tooth to that of an adjacent tooth, it is called horizontal bone

loss.

It is one of the common pattern of bone loss in periodontal disease.

Significant feature of aggressive periodontitis.

The bone margin remains roughly perpendicular to the tooth surface.

Horizontal bone loss

Localized Aggressive Periodontitis

Localized Aggressive Periodontitis Localized aggressive (formerly “localized

juvenile”) periodontitis is characterized by the following:

1. 1. Initially, bone loss in the maxillary and mandibular incisor and/or first

molar areas, usually bilaterally, resulting in vertical, arc like destructive

patterns.

2. 2. As the disease progresses, loss of alveolar bone may become

generalized but remains less pronounced in the premolar areas.

Localized Aggressive Periodontitis

Vertical bone loss

Vertical or angular defects occur in an oblique direction, leaving a

hollowed-out trough in the bone alongside the root.

The base of the defect is located apical to the surrounding bone.

Resorptive bone patterns may take a vertical or funnel form, resulting in

formation of infrabony defects.

Vertical bone loss usually consists of one or many infrabony pockets,

because the base of the pocket is usually located apical to the crest of the

surrounding bone.

Angular defects are classified on the basis of the number of osseous walls

Vertical bone loss

Bone wall defects

Classified by Goldman and Cohen(1958)

One walled osseous defects where only one wall is present.

The one wall vertical defect is called as hemiseptum.

Two walled osseous defects where two walls are present.

Three walled osseous defects where three walls are present.

Interproximal vertical defects can often be detected radiographically,

whereas radicular surface vertical defects are not readily visible.

Bone wall defects

Interdental osseous craters

Interdental osseous craters are concavities in the crest of the alveolar septa centered under the contact point of adjacent teeth.

As cancellous bone is more vascular and less dense than cortical bone it is likely that, the central cancellous part of a broad alveolar septum will resorb more rapidly than the lateral parts made up of cortical bone forming interdental crater.

Following are the reasons for the high frequency of interdental craters:

a) The interdental area collects plaque and is difficult to clean.

b) The normal flat or even concave faciolingual shape of the interdental septum in lower molars may favor crater formation.

c) Vascular patterns from the gingiva to the center of the crest may provide a pathway for inflammation.

Interdental osseous craters

Bony exostosis

Bulbous bone contours are bony enlargements caused by exostoses,

adaptation to function, or buttressing bone formation which are found

frequently in the maxilla than in the mandible.

Exostosis is a localized harmless idiopathic thickening of bony tissue, whose

cause is unknown.

Depending on their location in the jaws, they are identified as torus

mandibularis (lingual mandibular plate) or torus palatinus (hard palate).

A peculiar condition consisting of bone exostosis has been reported to

occur in some patients after undergoing either a skin graft vestibuloplasty

or an autogenous free gingival graft.

A definitive female sex predilection is characteristic of this condition, which

usually presents in the canine- premolar area of the mandible or maxilla.

Bony exostosis

Reversed architecture & Ledges

Reversed architecture forms when the interdental septum resorbs more

rapidly than radicular bone.

Ledges are plateau-like bone margins caused by resorption of thickened

bony plates.

Furcation involvement refers to the invasion of the bifurcation and

trifurcation of multirooted teeth by periodontal disease.

Reversed architecture

Ledges

Furcation involvement

Fenestration and dehiscence

Fenestrations are the isolated areas in which root is denuded of bone and

marginal bone is intact.

Dehiscences are the denuded areas that extend through the marginal bone.

Dehiscence and fenestration are both associated with extreme buccal or

lingual version of teeth.

It occurs in 20% of all teeth. The defects are very important clinically because

where they occur the root is covered only by the periosteum and overlying

gingiva.

Fenestration and dehiscence

Periodontal abscess

Periodontal abscesses are classified according to location as follows:

1. Abscess in the supporting periodontal tissues along the lateral aspect of

the root.

2. Abscess in the soft tissue wall of a deep periodontal pocket.

The former is related to bone resorption around the tooth due to its

progression in size.

Periodontal abscess

Food impaction

Interdental bone defects often occur where proximal contact is abnormal

or absent.

Pressure and irritation from food impaction contribute to the inverted bone

architecture.

In some cases, the poor proximal relationship may result from a shift in tooth

position because of extensive bone destruction preceding food impaction.

In such patients, food impaction is a complicating factor rather than the

cause of the bone defect

Food impaction

Overhanging restoration

Overhanging restoration either in exaggerated crown margins or in class 2

restorations leads to angular bone loss.

It is most common in class 2 amalgam restorations with overhanging

margins.

Bone loss occurs due to impingement of the gingiva, followed by the

inflammatory process that leads to bone loss.

Over hanging restoration

Adjacent tooth extraction

Normally, tooth extracted adjacent to a tooth will show significant bone

loss in the extraction site.

In case of extraction of a periodontally weakened tooth, adjacent tooth

will tend to show severe bone loss of interdental septa.

More common in delayed extraction of impacted 3rd molar.

Adjacent tooth tends to tilt towards the extracted site.

Extracted adjacent tooth

Ill-fitting prosthesis

Being one of the major factors for periodontal tissue destruction.

Most common in removable partial denture users.

Improper seating and design of the prosthesis could irritate the gingiva that

leads to the sequence of periodontal tissues inflammation.

Long term prosthesis users without periodic evaluation are attributed to this

consequence.

pic

Alveolar bone in implants

Osseointegration is basically a union between bone and the implant

surface.

It is not an absolute phenomenon and can be measured as the proportion

of the total implant surface that is in contact with bone.

Greater levels of bone contact occur in cortical bone than in cancellous

bone, where marrow spaces are often adjacent to the implant surface.

Therefore, bone with well-formed cortices and dense trabeculation offer

the greatest potential for high degrees of bone to implant contact.

The degree of bone contact may increase with time.

Repair and regeneration

Remodelling is the major pathway of bony changes in shape, resistance to

force, repair of wounds.

The bone resorption with bone formation constitutes the remodelling

throughout the life.

Bone remodelling involves osteoblasts and osteoclasts which form and

resorb the mineralized connective tissue of the bone.

Regulation of bone remodelling involves harmones and local factors acting

in an autocrine and the paracrine manner.

Bone contains 99% of body`s calcium ions, Hence the major source for

calcium release when the calcium blood level decreases, which is

monitored by parathyroid gland.

Bone resorption

Decrease in blood calcium

Mediated by receptors on chief cells of parathyroid gland

Release parathyroid hormone(PTH)

Osteoblast stimulation to release il1and il6

Monocytes in bone area

Multinucleated osteoclasts

Resorbs bone

Remodelling

Alveolar bone is least stable of the periodontal tissues because of the

constant state of flux

Internal remodelling takes place by means of resorption and formation

regulated by local and systemic factors

Local factors include functional requirements on the tooth and age related

changes in the bone cells

Systemic factors are hormonal (PTH), calcitonin, vitamin D3

Remodelling affects its height contour and density and is manifestated in

the following:

1. Adjacent to PDL.

2. In relation to periosteum of facial and lingual plates.

3. Along endosteal surface of marrow spaces.

Conclusion

Alveolar bone is of utmost important for the healthy periodontium.

Thorough knowledge about pathologies involving alveolar bone enhances

basic methods in treating them.

Eliminating the bone loss is still being a challenge in treating periodontitis.

A better understanding of cell and molecular biology of developing and

regenerating alveolar bone offers appropriate idea in treating it for

regeneration.

References

Carranza’s clinical periodontology- 11th edition

Periodontology The essentials- H.P.MUELLER

Clinical periodontology and implant dentistry- Jan Lindhe(5th edition)

Chambers TJ: The cellular basis of bone resorption, Clin Orthop, p283, sep

1980.

Elliot JR, Bowers GM: Alveolar dehiscence and fenestration, periodontics

1:245, 1963

Goodson JM et al: the relationship between attachment level loss and

alveolar bone loss, J Clin periodontal 11:348, 1984.