Alveolar Bone (2)

ALVEOLAR BONE ITS

RELEVANCE IN PROSTHODONTICS

CONTENT

Topic Page no.

Introduction 3-6

Systemic influences on alveolar bone 7

Effects of hormones 8-9

Effects of vitamins 10

Effects of drugs 10

Prosthodontic considerations of alveolar

bone in relation to

Complete denture 12

Single complete denture 12

Removable partial denture 13

Fixed partial denture. 14

Implants. 15

Combination syndrome 16-18

Conclusion 19

References 20-21

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Introduction

According to Glossary of prosthodontics alveolar bone is defined as

bony portion of mandible or maxilla in which roots of teeth are held by

fibers of periodontal ligament. A.R Tencate states that alveolar bone is that

portion of maxilla and mandible which forms & supports roots of teeth. It

forms when tooth erupts, to provide the osseous attachment to the forming

periodontal ligament and disappears gradually after tooth is lost.

It is extremely important to the dental practitioner, as almost all his

treatment procedures can be successful only if the bony support remains

intact. The success of complete denture, partial dentures, implants is

dependent on degree of stability that the underlying bone can maintain.

Residual Ridge Resorption

Alveolar bone has one of the highest metabolic rate, owing to nearly

continous masticatory stress applied to it through tensile forces transmitted

throught periodontal ligament.

Residual Ridge Resorption is chronic, progressive, irreversible,

cumulative, multifactorial, biomechanical disease that results from a

combination of anatomic, metabolic and mechanical determinants.

After teeth loss, alveolar bone undergoes rapid remodeling. Which

results in bone loss.

Amount of bone loss varies among individuals and depends on

- Age

- Sex

- Nutritional status

- Medical conditions

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- Original shape

- Size and location of alveolar process

Factors affecting rate at which bone is lost

Anatomical – size of ridge following extraction

- type of residual bone

- type of mucoperiosteum

- Location with in oralcavity

Metabolic - Age

-Sex

-diet

-harmonal status

Functional - Frequency, direction and amount of force applied to

ridge.

Prosthetic factor - type of denture base,

- forms and type of teeth,

- interocclusal distance.

Osteoclasts have the function of eliminating bone i.e. no longer

adapted to mechanical forces. At the site of bone formation, osteoblasts

differentiate from precursor cells of connective tissue. The mechanisms

which determine bone formation at any given site are unknown. They must

be varied and determined on a genetic and functional basis.

Osteoblasts form osteoid tissue which will be followed by

mineralization. It always lags behind production of bone matrix and

therefore in such areas a superficial layer of osteoid tissue is always seen. A

peptide called osteoclastic activating factor is found in lymphocytes and is

capable of increasing AMP and osteoclastic activity and reducing

osteoblastic activity at target site.

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The exact mechanism by which osteoclasts may act to resorb the bone

is not clear. The osteoclasts may liberate enzymes which dissolve the

organic matrix and remaining inorganic salts. May then be dissolved by

chelating agents such as EDTA, C.AMP in cells may play some role in bone

resorption.

The initiation of resorption is not completely known. It may be due

to dying or dead osteocytes that stimulate the connective tissue, resulting in

osteoclast’s in the area.

Thomas, Stahl and Pendleton consider alveolar ridge resorption as

normal biologic process that increases with age.

Bones have an intrinsic growth pattern as stated by TOWNSLEY in

1948 and it is possible that the alveolar bone may have a hereditary

resorption pattern.

- In 1971, Atewood described RRR as “MAJOR ORAL DISEASE

ENTITY” characterised by loss of oral bone after the extraction of teeth.

- The size, shape and tolerance of residual ridges provides the basis of

stability, retention, support of complete denture.

- New Feld reported “ In some of specimens studied, the trabecular pattern

was arranged in a such a way that it indicated that there was some

adaptation of structure of bones to presence of an appliance in region

near the superior surface of alveolar process”.

- Atewood reported “ A complete abscence of periosteal bone over

residual ridge in all specimens studied”.

- Clayton. F. Parkinson in 1978 stated that i) Arch width of maxilla is

less than mandible in molar region by 6 - 7 mm ii) Alveolar resorption

rate is highest in early stages of edentulism and slows with loss of bone,

longevity of edentulism and the attendant wearing dentures.

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- Antje. Tallgren in 1972 stated that mean reduction in lower anterior

ridge height is approximately four times as great as that of upper ridge.

- Tallgren stated that RRR

According to Atwood D.A.

Class – I – Pre extraction

Class – II – Post extraction. Immediately following exfoliaition of tooth

with, the labial and lingual alveolar process remaining

Class – III – High well rounded. The sharp edges will be rounded OFF by

the external osteoclastic activities leaving a high well rounded

residual ridge.

Class – IV – Knife edge . As resorption continues form both labial and

lingual aspects the crest of ridge becomes increasingly narrow

finally results in knife edge.

Class – V – Low well rounded. The knife edge shortens and finally

leaving

low well rounded or flat ridge.

Class – VI – Depressed . Further resorption leaving only the thin cortical

bone in lower border of body of maxilla

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1damping effect of the mucosa

Winkler observed thatRRR Anatomical factors Bone resorption factors Force factors

Time Bone formation factors Damping Effect+ +

Age changes

Age changes in alveolar bone are similar to those occurring in

remainder of skeletal system.

These include – osteoporosis

- decreased vascularity

- reduction in metabolic rate

- reduction in healing capacity

- Bone resorption may be increased or decreased and the density of

alveolar bone may increase or decrease depending on its location. There

is greater irregularity in surfaces of alveolar bone facing the PDL with

advancing age.

- Older persons is likely to have more alveolar ridge resorption than a

younger person.

- In aged, resorption is not compensated by production of bone, resulting

in senile osteoporosis. In persons over 70 yrs of age, 25% of bone may

be engaged in bone resorption.

REIFENSTEIN in 1950 stated that osteoporosis may be normal after

menopause. Alveolar ridge may show resorption in connection with

osteoporosis.

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Influence of systemic diseases

1. Protein deficiency – causes loss of alveolar bone which is the result

of inhibition of normal bone forming activity.

2. Acute starvation results in osteoporosis and reduction in height of

alveolar bone.

3. In hyperpitutarism (acromegaly) marked over growth of alveolar

bone causes increase in size of dental arch.

4. Ridge resorption is associated with hyperparathyroidism and

vonrecklinghausen’s disease due to increased bone loss.

a. Radiological findings of hyperparathyroidism are alveolar

osteoporosis with closely meshed trabeculae, widening of PDL space

and loss of laminadura.

5. Complete loss of laminadura occurs in paget’s disease, Fibrous

dysplasia, osteomalasia.

6. Diabetes mellitus shows rapid alveolar bone loss.

7. In acute, sub acute leukemia, marrow of alveolar bone exhibits

localized areas of necrosis, thrombosis of blood vessels, leukocytic

infiltration and replacement of fatty marrow with fibrous tissue.

8. In agranulocytosis, osteoporosis of alveolar bone with osteoclastic

resorption, necrosis of alveolar bone and heamorrhage in the marrow

occur.

9. Mercury intoxification leads to destruction of alveolar bone.

10. Other chemicals such as phosphorous, arsenic and chromium may

cause necrosis of alveolar bone.

11. Benzene intoxification also leads to destruction of alveolar bone.

12. Hypophoshatasia, an inherited disease causes premature loss of

alveolar bone surrounding decidous incisors by 10 months of age.

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Effect of hormones

Hormones such as androgens, estrogens and somatotropin exert a

definite influence on growing alveolar bone, but their effect on adult bone is

not clear.

- PTH has direct action on adult bone, which is responsible for

maintainence of normal blood calcium levels of 10-11 mg%

- PTH has 4 main sites of activity namely 1) kidney 2) bone 3) intestine 4)

lactating mammary gland.

- PTH is probably the most important of harmones in so far as RRR is

concerned.

- In alveolar bone PTH liberates both calcium and phosphate. When PTH

is active, calcium and phosphate ions move from alveolar bone to

plasma. But it is not known whether PTH acts directly or through

osteoclasts.

- When circulating PTH is high, it leads to osteoporosis which in turn

leads to resorption of alveolar ridge. A decrease in PTH level results in

increase formation of bone hence resorption of alveolar bone is reduced.

Calcitonin – It has antagonist action compared to PTH.

Estrogen : Estrogen deficiency causes increased bone resorption activity

where as surface of residual ridge alveolar bone in oestrogen deficiency and

its replacement therapy seem to affect the activity of residual ridge bone

remodelling at the molecular level.

Osteoporosis is predominant side effect of menopause which is due to

decrease of oestrogen production.

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Although the osteoporotic change of maxilla – mandible occur elderly

patients in a fashion similar to that of metacarpal bone and vertebral bone.

NISHIMURA et al. reported that, although bone height showed no

differences, the knife edge morphologic features of mandibular residual

ridge was statistically associated with osteoporotic changes in 2nd vertebrate

bone.

Effects of vitamins on alveolar bone :

1. Hypervitaminosis D- causes generalized resorption changes in bone

including alveolar bone.

2. Avitaminosis D causes decreased concentration of blood phosphate

and retarded calcification.

3. Chronic hypervitaminosis A- WEINMANN & SICHER in 1955

noted that above condition leads to bone resorption in supporting

bone of the alveolar process in those regions most subject to stress.

4. Hypovitaminosis A- leads to overall bone growth retardation and in

later stages endochondral bone growth ceases entirely.

5. Hypovitaminosis C leads to SCURVY. It causes failure of collagen

production in bone. Production of osteoid is deficient and hence

calcification is restricted. However, bone resorption continues and

eventually bone becomes thin and fragile, which is prone for fracture.

It is characterized by decreased activity of fibroblasts, osteoblasts,

odontoblasts, which ultimately effects collagen production.

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EFFECT OF DRUGS

A generalised decrease in alveolar bone mass is associated with

chronic corticosteroid therapy, anticonvulsant therapy, long term high dose

heparin therapy and alcoholism.

PROSTHODONTIC CONSIDERATIONS OF ALVEOLAR BONE :

In relation to complete denture :

Alveolar bone is the basic support for the complete dentures. It

provides most of the vertical support. After loss of teeth, re-constructive

process leads generally to loss of bone in the area and the formation of

compact lamellae at surface.

Histologically, socket is filled with immature bone by the end of 2nd

month. But there is some quantitative loss when healing is uneventful; when

primary clot fails to form. The denuded bone necrotizes and is elminated by

resorption. This loss in quantity during healing after extraction is one of the

reasons – awaiting period of 6 weeks to 2 months is advocated prior to

placement of dentures.

Another reason is to allow the immature bone to replace the young

connective tissue.

Continuous presence of dentures is capable of exerting pressure of

sufficient intensity to produce resorption. This is true in mandibular arch,

since gravity exerts a steady pull on denture. A complete denture is

potentially capable of exerting steady pressure that can interrupt the blood

supply. For this season the dentures should be removed at least for 8 hours a

day.

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“WEINMAN – SICHER” reported that “whether intermittent

pressure is tolerated or even beneficial or whether it too leads to loss of

bone depends entirely on its affects on blood circulation.

Boucher stated that “ prominent alveolar ridges with parallel buccal

and lingual walls may also provide significant retention by increasing

surface area between denture and mucosa there by maximizing interfacial

and atmospheric forces.

Factors that influence the form and size of supporting bone include.

1) Original size and consistency.

2) Person’s general health.

3) Forces developed by surrounding musculature.

4) Severity and location of periodontal disease.

5) Surgery at time of extraction.

6) Relative length of time different parts of jaws have been

edentulous.

K. W. Tyson, J. C. Mcford stated that in case of flat ridges

1. Their should be increased free way space by 2 – 3 mm

2. Impression should cover as much area as possible

3. Peripheral form of polished denture should be in hormone with

buccinator muscle.

Ashman stated that ridge preservation can be done by

1. Advanced extraction therapy (AET)

In this after extraction introduction of synthetic graft in to the

socket was done followed by suturing. He observed that their was

not change in height and width of the bone

2. Replacement therapy – An alloplast graft was placed in an

extraction socket, or in combination with titanium threaded

implant immediately after extraction

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RESORPTION PATTERN

Single complete dentures :

In upper jaw the premaxillary area is frequently subjected to more

resorption when the patient is wearing a complete denture which occludes

with natural anterior lower teeth.

If magnitude of major force of occlusion is great i.e., no partial

denture fitted, the alveolar bone will be resorbed in that area, leaving a soft

flabby ridge of tender inflamed tissue.

Even when free end saddle partial denture, has been fitted, it is

inevitable that once any resorption has taken place, the major forces of

occlusion will again be thrust on the anterior teeth to be dissipated in upper

jaw through the premaxillary edentulous ridge.

However carefully the complete denture for upper and lower ridges

are made with occlusal forces concentrated in posterior region rather than

anterior bringing the teeth in to occlusion will often thrust upper denture

upward and forward on unstable, tender premaxillary tissues. This is one of

the most irrevocable injuries done to mouth by dentures.

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Removable partial denture and fixed partial denture :

The radiographic interpretation aspects that are the most pertinent to

RPD & FPD construction, are those relative to prognosis of remaining teeth

used as abutments.

i) Quality of support from alveolar bone of an abutment tooth is of

primary important because the tooth will have to withstand greater

stresses loads when supporting RPD & FPD.

Abutment teeth providing total abutment support to RPD & FPD,

will have to with stand a greater load than before and especially

greater horizontal forces. It is minimized by establishing

harmonious occlusion and by distributing horizontal forces among

several teeth through the use of rigid connectors. Properly

designed tooth borne removable prosthesis should provide

bilateral stabilization against horizontal forces.

ii) Abutment teeth adjacent to distal extension bases in RPD’s are

subjected not only to vertical and horizontal forces but to torque

also because of tissue supported base. Vertical support and

stabilization against horizontal movement with rigid connectors

and just as important as they are with a tooth borne prosthesis.

In addition, abutment tooth adjacent to the extension base will be

subjected to torque in proportion to design of retainers, size of

denture base, tissue, support by base and total occlusal forces

applied.

iii) In RPD, if alveolar bone support is adequate a posterior abutment

should be retained if at all possible in reference to a tissue

supported extension base.

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iv) In case of RPD & FPD teeth with insufficient alveolar support

may be extracted if their prognosis is poor and other adjacent teeth

may be used to better advantage as abutments.

v) Radiographic interpretation also serve as an important function if

used periodically after the placement of RPD and FPD. Further

bone changes of any type suggest traumatic interference from

some source.

Radiographic observations made are

1. Alveolar bone crest resorption

2. Integrity of thickness of laminadura

3. Evidence of generalized horizontal bone loss

4. Evidence of vertical bone loss

5. Widened pdl space

6. Density of trabeculae of both arches

7. Crown and root ratio.

Ante’s law states that for fixed partial dentures the pericemental area of all

abutment teeth supporting the FPD should be equal to or greater than the

pericemental area of the teeth to be replaced.

For removable partial dentures it states that combined pericemental

area plus mucosal area should be equal to or greater than pericemental area

of missing teeth.

INDEX – AREAS are those of alveolar bone support that disclose the

reaction of bone to additional stress. The reaction of bone to additional

stress in index areas may be negative or positive. With evidence of a

supporting trabecular pattern, a heavy cortical layer and a dense lamina

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dura, or reverse response with the former, patient is said to have +ve bone

factor, meaning ability to build additional support where ever needed. With

the later patients is said to have negative bone factor meaning inability to

respond favourably to stress.

In FPD general alveolar bone levels with particular emphasis on

abutment teeth should be observed. Any widening of PDL space and loss of

intact of laminadura due to destruction of cribriform plate should always be

correlated with occlusal prematurities or occlusal trauma. An evaluation can

be made of thickness of cortical plate of alveolar bone around teeth and of

the trabeculation of bone.

Implants :

When we talk of implants in relation to alveolar bone first one should

think about OSSEOINTEGRTION. It is defined as direct structural and

functional connection between ordered, living bone and the surface of a load

carrying implant.

COMBINATION SYNDROME

Definition: The Glossary of Prosthodontic Terms defines combination

syndrome as "the characteristic features that occur when an edentulous

maxilla is opposed by natural mandibular anterior teeth, including loss of

bone from the anterior portion of the maxillary ridge, overgrowth of the

tuberosities, papillary hyperplasia of the hard palatal mucosa, extrusion of

mandibular anterior teeth, and loss of alveolar bone and ridge height beneath

the mandibular removable partial denture bases, also called anterior

hyperfunction syndrome.

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A few years later, further characteristics were added to the

combination syndrome : loss of vertical dimension of occlusion, occlusal

plane discrepancy, anterior spatial repositioning of the mandible, poor

adaptation of the prosthesis, epulis fissuratum, and periodontal changes.

However, these changes are not generally associated with combination

syndrome. (Palmquist Sigvard et al)

When natural anterior teeth are remaining in the mandible opposing a

maxillary edentulous arch results in combination syndrome. These changes

are: - (Kelly Elswarth)

i) Loss of bone from the anterior part of the maxillary ridge.

ii) Overgrowth of tuberosities

iii) Papillary hyperplasia in the hard palate.

iv) Extrusion of the lower anterior teeth.

v) The loss of bone under the partial denture base.

In spite of his emphasis on the negative role of the Mandibular RPD,

Kelly wrote: "The early loss of bone from the anterior part of the maxillary

jaw is the key to the other changes of the combination syndrome".

Dorland's illustrated Medical Dictionary defines "syndrome" as 'a set

of symptoms which occur together; the sum of signs of any morbid state; a

symptom complex". "Combination syndrome" is not included among

hundreds of syndromes listed in

the dictionary. From this review of

the literature it seems obvious that

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"combination syndrome" does not meet the criteria to be included in such a

list.

Prevention of Combination

Syndrome:

Try to avoid maxillary

edentulous arches with

mandibular natural teeth situation.

Authors do not advocate removal of lower anteriors, but rather to

retain the weak posterior teeth as abutments by means of endodontic

and periodontic techniques.

Endosseous implants, hemi section, root amputation can be done to

preserve lower molar.

An overlay denture on lower may avoid combination syndrome.

Surgical excision of flabby (hyperplastic) tissue, papillary hyperplasia

and enlarged tuberosities. This allows the distal end of the occlusal

plane to be raised to the proper level. (Cynthia P. Thiel et al)

Covering maximum area in lower partial denture.

Covering retromolar pad where muscle and raphe attachments

prevent or reduce resorption, and covering buccal shelf is necessary to

retard bone loss.

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conclusion

Now we all know the importance of alveolar bone in dentistry. But it is well

for us to understand the still further physiology of bone. It is especially

necessary to remember the factors such as harmones, vitamins, pressure, age

which may all or separately produce ridge resorption.

Unless until mechanism of bone resorption is understood little

progress will be made in prosthodontic therapy. When alveolar bone loss

can be controlled, it will be possible to offer the patient dentures with a

greatly increased chance of success.

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\

REFERENCES

1. Winkler Sheldon “Essentials of complete denture prosthodontics”. 2nd

Edition.

2. Sharry J.J. “Complete denture prosthodontics”, 3rd edition.

3. Bernard Levin “Impressions for complete dentures”.

4. Carl E. Mish “Contemporary Implant Dentistry”, Second Edition.

5. Ortman L.F. et al, 1992. “Bioelectric stimulation and residual ridge

resorption”. J. Prosthet. Dent; 67 : 67-71.

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6. Israel Harry 1979. “Evidence for continued apposition of adult

mandibular bone from skeletalized materials”. J. Prosthet. Dent; 41 :

101-104.

7. Atwood D.A., Coy W.A., 1971. “Clinical, cephalometric and

densitometric study of reduction of residual ridges”. J. Prosthet. Dent.,

26 : 280-295.

8. Atwood D.A., 1971. “Reduction of residual ridges : A major oral

disease entity”. J. Prosthet. Dent., 26 : 266-279.

9. Mercier Paul, Lafontant Roger, 1979. "Residual alveolar ridge atrophy:

Classification and influence of facial morphology". J. Prosthet. Dent.,

41: 90-100.

10.Baylink D.J. et al., 1974. “Systemic factors in alveolar bone loss”. J.

Prosthet. Dent., 31 : 486-505.

11.Kelsey C.C., 1971. “Alveolar bone resorption under complete denture”.

J. Prosthet. Dent., 25 : 152-161.

12.Wical K.E., Swoope C.C., 1974. “Studies of residual ridge resorption.

Part-II. The relationship of dietary calcium and phosphorus to residual

ridge resorption”. J. Prosthet. Dent; 32 : 13-22.

13.Sones American Diana et al, 1986. “Osteoporosis and mandibular bone

resorption : A prosthodontic perspective”. J. Prosthet. Dent., 56 : 732-

736.

14.Atwood Douglas Allen 1958. “A cephalometric study of the clinical

rest position of the mandible”. J. Prosthet. Dent., 8 : 698-708.

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15.Palmquist Siguard et al. 2003. “The combination syndrome : A

literature review”. J. Prosthet. Dent; 90 : 270-5.

16.Kelly Ellswarth 1972. “Changes caused by a mandibular removable

partial denture opposing a maxillary complete denture”. J. Prosthet.

Dent., 27 : 140-150.

17.Palmer C.A. 2003. “Gerodontic nutrition and dietary counseling for

prosthodontic patients”. Dent. Clin. N. Am., 47 : 355-371.

18.Wical K.E., Brussee P., 1979. “Effect of calcium and vitamin D

supplement on alveolar ridge resorption in immediate denture

patients”. J. Prosthet. Dent; 41 : 4-11.

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