1) INTRODUCTION

The alveolar process is the bone that forms and supports the tooth

sockets (alveoli). It forms when the tooth erupts in order to provide the

osseous attachment to the forming periodontal ligament; it disappears

gradually when the tooth is lost. The process of residual ridge resorption

starts soon after the dental extraction / lost following the extraction of teeth,

the bony socket and adjacent soft tissues undergo a series of tissue repair

reactions including acute inflammation. Rapid restoration of epithelial

integration, and connective tissue remodelling. Histologic evidence of

active bone formation in the bottom of the socket and prone resorption at

the edge of the socket are seen as early as 2 weeks after the tooth extraction,

and the socket is progressively filled with newly formed bone in about 6

months. Rapid bone remodelling subsides by this time but continuous bone

resorption may persist at the external surface of the crestal area of the

residual alveolar bone, resulting in considerable morphologic changes of

bone and overlying soft tissues over the years. This phenomenon has been

described as the REDUCTION OF RESIDUAL RIDGES or RESIDUAL

RIDGE RESORPTION (RRR).

2) NORMAL ALVEOLAR BONE PHYSIOLOGY

Alveolar bone is formed during fetal growth by intramembraneous

ossification and consists of a calcified matrix with osteocytes enclosed

within spaces called lacunae. The osteocytes extend processes into

canaliculi that radiate from the lacunae. The canaliculi form an

anastomosing system through the intracellular matrix of the bone, which

brings oxygen and nutrients via the blood to the osteocytes extensively and

travel through the periosteum. The endosteum lies adjacent to the marrow

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vasculature. Bone growth occurs by apposition of an organic matrix that is

deposited by osteoblasts.

The alveolar process consists of the inner socket wall of thin,

compact bone called the:

a) Alveolar bone proper (Cribriform plate).

b) Supporting alveolar bone, which consists of cancellous trabeculae, and

the facial and lingual plates of compact bone. The interdental septum

consists of cancellous supporting bone enclosed within a compact

border.

The alveolar process is divisible into separate areas on an anatomic

basis, but it functions as a unit.

All parts are interrelated in the support of the tooth. Occlusal forces

that are transmitted from the periodontal ligament to the inner wall of the

alveolus are supported by the cancellous trabeculae, which in turn are

buttressed by the labial and lingual cortical plates.

The below diagram show the relative portions of cancellous bone

and compact bone that form the alveolar process.

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Most of the facial and lingual portions of the sockets are formed by

compact bone alone; cancellous bone surrounds the lamina dura in apical,

apicolingual and interradicular areas.

Although the alveolar bone tissue is constantly changing in its

internal organization, it retains approximately the same form from

childhood through adult life. Bone deposition by osteoblasts is balanced by

resorption by osteoclasts during the processes of tissue remodelling and

renewal.

The bone matrix that is laid down by osteoblasts is not mineralized

and is referred to as prebone or osteoid, while new osteoid is being

deposited, the older osteoid located below the surface becomes mineralized

as the mineralizing front advances.

Prior to becoming mineralized, bone matrix collagen becomes coated

or associated with a glycoprotein (or proteoglycan) opaque, granular

substance. It is conceivable that this material together with other matrix

constituents. A similar series of event is believed to occur during dentin

matrix production and mineralization.

Osteoclasts are large, multinucleated cells that are often seen on the

surface of bone within eroded bony depressive referred to as Howship’s

lacunae. The main function of these cells is consisted to be resorption of

bone, when they are active, as opposed to resting, they possess an

elaborately developed ruffled border from which hydrolytic enzymes are

believed to be secreted. These enzymes digest the organic portion of bone,

the activity of osteoclasts and the morphology of the ruffled border can be

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modified and regulated by hormones, such as para hormone and calcitonin.

The origin of osteoclasts is still a matter of speculation and controversy.

Small mononucleated cells have also been described as bone

resorbing cells.

The cancellous portion of the alveolar bone consists of trabeculae

that enclose irregularly shaped marrow spaces lined with a layer of thin

flattened endosteal cells. There is wide variation in the trabecular pattern of

the cancellous bone, which is affected by occlusal forces. The matrix of the

cancellous trabeculae consists of irregularly arranged lamella. Separated by

deeply staining incremental and resorption lines indicative of precious bone

activity, with an occassional haversian system.

Vascular supply – The cribriform plate of the tooth socket appears

radiographically as a thin, radiopaque line termed the lamina dura which is

lost after the loss of the tooth. But when present it is perforated by

numerous channels, containing blood, lymph vessels and nerves which line

the PL with the cancellous portion of the alveolar bone, the vascular supply

of the bone is derived from blood vessels branching off of the superior or

inferior alveolar arteries. These arterioles enter the interdental septa within

nutrient canals together with veins, nerves and lymphatics. Dental

arterioles, also branching off of the alveolar arteries, send tributaries

through the PL and some small branches enter the marrow spacer of the

bone via the perforations in the cribriform plate. Small vessels emanating

from the facial and lingual compact bone also enter the marrow and spongy

bone.

In contrast to its apparent rigidity. Alveolar bone is the least stable of

the periodontal tissues, its structure is in a constant state of flux. The

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physiologic liability of alveolar bone is maintained by a sensitive balance

between bone formation influences. Bone is resorbed in areas of pressure

and formed in areas of tension.

The cellular activity that affects the height, contour and density of

alveolar bone is manifested by three areas:

i) Adjacent to the PL, ii) In relation to the periosteum of the facial and

lingual plates and iii) along the endosteal surface of the marrow

spaces.

3) TOOTH EXTRACTION, WOUND HEALING AND FORMATION OF THE RESIDUAL RIDGE

A specific feature of residual ridge formation is that its essential

components are formed as the consequences to healing of a significant bony

and mucosal wound created by tooth extraction. Histologic studies of

residual ridges indicate that extraction sockets heal with active synthesis of

trabecular bone. Trabecular bone formation reaches the edge of extraction

socket whereas the osteoclastic bone resorption takes place on the surface of

the residual ridge, a combination of which results in a distinct porosity on

the crest of the residual ridge alveolar bone.

Aaron and Sherry described trabecular bone regeneration in the

sheep after localized ablation. The radial arrangement of the developing

bone trabeculae observed in their defects resembled the radial trabecular

pattern observed on radiographs of healing tooth sockets coarse,

birefingement collagen fibres formed a preliminary framework along which

the trabecular were oriented and were fabricated by fibroblasts, marrow

reticular cells and osteoblasts. Trabeculae were absent where this

preliminary collagenous framework is failed to form. Subsequent

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remodeling of the small primary trabeculae produced secondary trabeculae

that resembled the original cancellous bone pattern. The delayed tooth

socket healing often observed in poorly controlled diabetes inevitably

causes a poor alveolar ridge contour. A dense network of collage fibers

normal fills the socket soon after tooth extractions and the defect in diabetes

mellitus may be due to a reduced collagen production and an absence of

these fibers.

Precursor “template” collagen for bone wound healing:

The collagenous extraction socket matrix forms before bone

formation, and it has been hypothesized that this matrix serves as a template

or framework that orientates the forming bone trabeculae. Controversy

surrounds the nature of the collagen molecules that provide this template

function. However, because of its potentials in guiding bone, wound

healing, the major emphasis of current biologic studies of residual ridge

remodelling is directed toward the characterization of this template stage of

bone remodelling.

A two stage process of bone formation is evident in endochondral

ossification, in which cartilage tissue is initially present. Chondrocytes

undergo sequential histo-differentiation, which result in cellular

hypertrophy and apoptasis. The remnant hypertrophic cartilage matrix is

believed to provide the template scaffold for osteoblasts to precipitate bone

extracellular matrix. The template cartilage matrix is eventually resorbed

endochondral synchondrosis of the skull base, and mandibular condyle.

One of the most obvious feature of the healing of tooth extraction

sockets is the absence of precursor cartilaginous tissue. This unique feature

has been described by a general hypothesis that the tissue regeneration is

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considered to be a reiterated process of tissue embryogenesis. In embryos,

maxillofacial bone including tooth bearing alveolar process, is formed

through intramembranous bone formation, which is different from

endochondral ossification. In intramembraneous bone formation examined

in calvaria, the intramembranous bone formation, which is different from

endochondral ossification. In intramembranous bone formation examined in

calvaria, the initial ectomesenchymal cells directly differentiate into

osteoblasts, by passing the deposition and resorption of hypertrophic

cartilage matrix; osteoblasts can directly deposit osteoid tissue, which is

then calcified.

It is of particular interest that recent investigations reported the

transient expression of cartilagenous precollagen type II mRNA during

intramembraneous bone formation type II collagen is a major collagen type

of hyaline cartilage and thus has been long considered to contribute to the

structural integrity of cartilage tissues and provide a template during

endochondral ossification. The involvement of type II procollagen mRNA

in different tissues other than cartilage may suggest some as yet undefined

function of type II collagen unrelated to chondrogenesis.

In recent years, type II collagen has been further investigated and its

two alternative splicing variants of type IIA and type IIB are found to have

differing cell origins. Type IIA is found in noncartilaginous tissues, whereas

type IIB has a strong association with chondrocytes and cartilage tissue

formation. The expression of type II procollagen mRNA has been identified

in the healing extraction sockets in experimental animals by the method of

RNA transfer blot analysis and is situ hyridization.

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Analysis of studies on the uncomplicated healing of extraction

wounds have shown that after the clot formation, granulation tissue is

gradually replaced by connective tissues and later by intramembranous

bone, without cartilage formation. A cluster of cells that are associated with

the early socket wound healing have been shown to express type II collagen

mRNA. A puzzling finding is that investigators have failed to detect the

presence of protein collagen type II by way of immunohistochemical

studies in actively healing extraction sockets. This may be suggestive of

either lack of collagen type II translation or difficulties in detecting this

protein in the healing socket. Some of the questions that need to be

answered in the extraction socket of what are the role of these cells in the

socket healing if type II collagen protein is synthesized. Do systemic or

local factors influence the gene expression pattern during socket healing.

Two-stage process of bone formation:

Cartilage collagen fibrils are composed of a group of different type

of collagen including type II. The surface of this fibril is associated with

small collagen type IX. Because of the exposed perifibril location and the

interactive peptide structure of type IX collagen, it has been postulated that

type IX collagen plays a molecular bridging role in the extracellular matrix

and contributes to formation of a cartilage tissue architecture.

It has been reported that collagen type IX mRNA is also expressed in

early hiealing stage of extraction sockets

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Further analysis of residual ridge remodeling in rats have revealed

that the 1 (IX) collagen mRNA, which was expressed in the extraction

socket, was different and markedly shorter than that of cartilage. The short

form of type IX collagen omits the multiple exons, that encode the Amino

terminal globular domain (in above figure). Therefore this alternation

expression of the short form of type IX collagen, which lacks the interactive

peptide structure, may explain why cartilage tissue is not assumed in the

extraction socket. However, the function of the short form of type Ix

collagen in residual ridge remodeling remains to be classified.

Recent immunohistochemical data suggest that type IX collagen is

present only in the early bone formation stages of extraction socket healing

and seems to disappear during the maturation stages. It has been

characterized in the similar transient expression of the short form of type IX

collagen along with type II collagen is embryonic chicken cornea, in which

the principle orthogonal fiber architecture of the mature cornea is organized

according to the template tissue, primary cornea stroma. Both cornea and

bone posses the similar orthogonal pattern of collagen fibrils. The detailed

molecular assembly of type II and the short form of type IX collagen in

bone remodelling is not elucidated. However, it is tempting to speculate that

the transient matrix containing short type IX collagen may be involved in a

tissue guiding role in alveolar bone repair, as used in avian eye formation.

Transgenic and inactive gene allelic manipulation in experimental animals:

To understand the role of a specific molecule, one can generate

animals harboring an experimentally introduced mutation to the molecule or

inactivate the corresponding gene. Such transgenic animals can provide a

powerful tool to investigate the consequences to the missing biologic role of

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a specific molecule. Several transgenic mice have been generated with

defective type II collagen. The introduced mutated pro 1 (II) collagen

chains appears to be included in a procollagen molecule and prevent folding

into a stable triple helix. Transgenic mice with functionally impaired Type

II collagen result in chondrodysplasia into dwarfism, short and thick limbs,

a short snout, a cranial bulge, a cleft palate, delayed mineralization of bone,

and a severe retardation of growth for practically all bones. Because type II

collage comprises the major constituent of cartilage, the principal

consequence of this mutation is anticipated to cause disorganization of the

growth plate. However, it is interesting to note that both endochondral

bones and intramembranous bones are affected by the Type II collagen

mutation.

Nakata reported the generation of transgenic mice harboring the

minigene of 1 (IX) collagen with an inframe delation of the central

domain. Some homozygons transgenic mice displayed mild proportionate

dwarfism. The vertebral bodies were ovoid in shape as a result of a mild

ossification defect, and the end plate in the mid-dorsal region were

irregular, otherwise, the offspring of the transgenic mice sunlived to their

maturity. After reaching maturity, onset of osteoarthritic changes become

apparent particularly in the anterior part of the weight bearing areas of the

tibia. They reported that even before the histologic onset of osteoarthritis, a

significant decrease in the intrinsic compressive stiffness was found in the

articular cartilage of the transgenic mice. Furthermore, corneas of the

transgenic offspring appeared opaque or irregular and were sometimes

infiltrated by capillary vessels. The opthalmopathy was found in about 15%

of transgenic animals. These results strongly indicate that type IX collagen

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may play diverse biologic roles in various tissues, including localized bone

remodelling.

Recently, 1 (IX) collagen knock-out transgenic mice were

developed. The neogene was inserted in the exon 8 of the 1 (IX) gene by

homologue recombinations, which resulted in the total inactivation of 1

(IX) alleles, including both premolars. Therefore, this animal model allows

an investigation of the functional role of type IX collagen as a potent

element for alveolar bone regeneration. Wild type and homologous mutant

mice were analyzed to elucidate the role of type IX collagen in residual

ridge remodelling. To evaluate alveolar bone repair, the specimens were

obtained at 7 days and 14 days after tooth extraction. The extraction socket

of mice with inactivated 1 (IX) alleles indicated that there was a

considerable retardation in the formation of the trabecular bone pattern as

compared with the healing socket of the control genotypically normal mice.

The results indicated that the trabecular bone pattern was often disturbed in

“knock-out” mice with some formation of cortical bone within the socket.

These data suggest that there may be two distinct bone remodelling

prcoesses. In the trabecular bone remodelling. The presence of type II and

IX collagen precursors seems to be necessary. In the cortical bone

remodelling, type II and IX collagen precursors may not be prerequisite.

Successful socket healing may use the former process, which require the

transient expression of template collagens, including type II and IX.

4) BONE REMODELLING PROCESS

Modelling is the correct word for the microscopic changes in the

bone morphology. Ridge resorption is a misnomer because, resorption is a

part of a process that leads to edentulous bone loss, where atrophy implies a

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passive process. Therefore, the term remodelling is used to describe the

physiological process of bone loss. Since in our topic were are including

even the pathologic process of the bone loss, thus it would be apt to

consider it as residual ridge resorption.

Remodelling of bone involves three stages. This was put forth by

Frost and that has been elaborated on by several investigators since, several

stage of cellular activity can be distinguished:

1. Activation phase.

2. Resorption phase.

3. Formation phase.

Activation : This is the first stage of remodeling persons which begins as a

result of specific local or systemic stimuli. It occurs at the microscopic level

on the surface of the lamellar bone. Whether it could be cortical or

trabecular. Activation stimulation the rest of the resorption process. It

shows the migration of osteoclast precursors to an area of the bone surface

to be resorbed, attachment of these precursor cells, and subsequent fusion of

these cells into multinuclear osteoclasts.

Resorption : The resorption begins, as the osteoclasts adhere to the bone

surface in response to the stimuli. These osteoclasts are probably derived

from the special circulating monocytes. Resorption may occur in the depth

of the haversian system of the compact bone or outside surface of the

trabecular bone. Often this resorption occurs parallel to the stress placed to

bone and it influences the formation process. This process is followed by

the deposition and organic matrix which is responsible for stress resistance

of bone after calcification had occurred. Resorption also occurs in the

absence of stress, but it does so in a less organized manner. This specific

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factor responsible for resorption is yet to be determined. But, there is 8-10

days delay period. The resorbed surface is morphologically identified as

cement line.

Formation phase : It is signalled by the local mesenchymal cells into

osteoclasts which concentrate, or aggregate on the same surface and begin

to lay down the organic matrix.

There are skeletal envelops:

i) Periosteum, ii) Haversian system, iii) Endosteum and iv) Trabecular

system

Each of the skeletal envelops have characteristic bone balance which

is generally not zero.

During this stage osteoblasts differentiate at the sites previously

resorbed and start to deposit osteoid and bone on completion of the phase,

the site enters a resting phase, with no discernibe osteoid remaining

between the lining cells and the mineralized bone. Thus a close anatomic

and functional relationship exists between resorptive and formative cells at

discrete remodelling sites, referred to as Basic Multicellular Unit (BMU) of

bone remodelling. This is, in all likelihood, responsible for the

phenomenon that many treatment of metabolic bone disease developed to

inhibit resorption result in simultaneous inhibition of formation. Numerous

examples of this phenomenon exist, and various schemes have been

devised to selectively affect then the resorptive phase or the formative

phase of the remodelling cycle. The rate of bone remodelling is determined

by the number of BMU operative at any given time. For the normal human

skeleton, activation occurs about once every 10 seconds and the total

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number of BMU in operation at any time has been estimated to be 35

million remodelling is conceivably initiated at a particular site either by

mechanical triggers conveying some type of message to cells initiating

formation or resorption or by unknown sensory mechanisms that indicate to

the cells. The need to initiate a remodelling sequence that bone in a certain

area has to be replaced.

5) HISTOLOGICAL OBSERVATION OF RESIDUAL RIGE RESORBTION

The mandible and maxillary ridges differ in gross appearance from

other surface of the same bone. Generally, the bone surface is smooth and

undulating and contains minute opening into the nutrient canals. Foramina

are larger opening through which vessels and / or nerves of greater diameter

pass. Most foramina are well known anatomic entities. Neither the foramina

nor the minute openings resemble the irregular defects present in the

residual alveolar ridge.

- The gross appearance of the defects ersembles cancellous bone. The

histologic sections confirmed the observation.

Histologically a well defined cortex with a lamelled surface was not

in evidence. Lamellated surface had been resorbed, and the Haversian

systems were undergoing resorption.

- Resorption was a constant factor. An sections with defects showed

periosteal resorption. There was no evidence of repair. There were no

reversal lines in the sections. The resorption penetrated the bone marrow

spaces. The submucosa and periosteum invaded the bone marrow space

replacing the marrow with dense C.T.

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- It was observed histologically, the mandibular ridge resorbs more

readily than the maxillary ridge. However, the mandibular ridges

contained more supporting bone than did the maxillary ridges.

Obviously, the supporting bone offered no resistance to the resorption.

- The resorption continued to expose the cancellous bone to the

periosteum Campbell reported that denture wearing patients

experienced more resorption of the alveolar process them did non

denture wearing subjects.

A study was conducted in 1984: To find out the histologic feature of

edentulous ridge. The objective of the study was to observe the nature of the

edentulous ridge of subjects who were edentulous for varying time periods.

Some of the subjects had worn denture while others had not.

Connective tissue was studied in the ridge crest, buccal and lingual

region. The feature observed were:

1. Thickness, 2. Density, 3. Presence of inflammatory cells, 4. Presence of

an osteogenic periosteum.

Observations:

1. The thickness of C.T. was found to be decreased from the normal in the

ridge crest region in both non denture and denture wearing groups. In

other regions (lingual and buccal) the thickness was considered normal

and no difference was noted between groups except for increased

thickness in the lingual region of the non dentuer wearing groups.

2. The density of connective tissue was increased in non-denture wearers.

But evenly divided between normal and increased in denture wearers.

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3. Inflammation in C.T. was slightly greater in denture wearers group. But

was not a prominent findings.

4. When any type of periosteum was present it was generally fibrous in

nature.

Hence, we conclude that probable during healing process after

extraction of teeth, the thickness of ridge C.T. is decreased while the

density is increased unrelated to the wearing of denture.

In brief, the microscopic studies / histological revealed the following:

1. Varying degrees of keratinization, acanthrosis, thickness, edema and

architectural pattern of epithelium in the same month and between

subjects.

2. Varying degrees of inflammatory cells from clinically normal to frankly

inflammed areas in both denture and nondentuer wearing patients.

3. Lymphocytes, plasma cells, mast cells and osteoclasts.

4. Dense, fibrous connective tissue (sometimes hyalinized) frequently

observed over crestal bone with fibers running parallel to epithelial

surface.

5. A vascular plexus outside the periosteum in areas of bone apposition.

6. Small blood vessels in close contact with the bone margin in areas of

bone resorption, sometimes, in the lacunae with positive correlation

between the degree of inflammation, vascular reactions and bone

resorption.

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7. Marked diapharase activity in areas of bone remodelling either

formation or resorption.

8. AT phase activity in areas of bone formation and acid phosphatase

activity in areas of bone resorption.

9. The lack of evidence of bone resorption in areas which do not have

inflammatory cells.

10. Endosteal bone deposition reinforcing internal structure where external

surface has been affected by resorption.

11. Lack of periosteal lamellar bone on the external surface of the crest of

the ridge.

12. A roughened crestal bone surface which is either actually resorbing or is

inactive, but without versal lines on the external surface of the crestal

bone.

13. Development of secondary Haversian systems in remodelled compacted

endosteal bone.

14. Microradiographic evidence of mandibular osteoporosis including

increased variation in the density of osteons, increased number of

incompletely closed osteons, increased endosteal porosity and increased

number of plugged osteons.

6) FACTORS AFFECTING RESIDUAL RIDGE RESORPTION

As there is wide difference in the individual regarding the rate of the

residual ridge resorption. Some patients show marked change where as

others minimal changes in the ridge form over a period of time.

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According to the literature rate of bone loss is generally greatest

immediately following tooth extraction. Mandibular bone loss occurs at a

more rapid rate when compared to that of maxillary.

Epidemiologic studies are useful in trend finding investigations of

multifactorial diseases. It is entirely possible that RRR is a multifactorial

diseases and that the rate of RRR depends on one single factor but on the

concurrence of two or more factors, which may be called cofactors. Many

years ago, it was suggested that for convenience, possible factors could be

divided with four major categories. This pattern of division was again

revered in 1998 by Leili Jahamgeri with few additions.

1. Anatomic

2. Prosthodontic.

3. Metabolic.

4. Functional.

5. Others.

1. Anatomic :

This includes : a) Size, b) Shape, c) Form, d) Space between ridges,

e) Muscle attachments, f) Action of tongue.

It is postulated that RRR varies in the quality and quantity of the

bone of the residual ridges. It can be said that RRR anatomic factors.

It is the amount of bone which is regard to the time count of RRR. If

denser of bone slower is the resorption.

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Although the broad high ridge may have a greater potential bone

loss. The rate of vertical bone loss may actually be slower than that of a

small ridge because there is more bone to be resorbed per unit of time and

because the rate of resorption also depends on the density of the bone.

Quality of bone : On theoretic grounds if everything is normal. The denser

the bone, the slower the rate of resorption, merely because there is more

bone to be resorbed per unit of time. In actuality everything is never

normal. Every patient is different especially in regard to the metabolic

factors.

Wolf’s law

It postulates that all changes in function of bone are attended by

definite alteration in its internal structure and forces within the

physiological limits are beneficial in their massaging effect. On the other

hand, increased or instained pressure through its disturbance from the

circulatory system produces bone resorption. The amount and frequency of

stress and its distribution and direction are important factors in treatment

planning.

2. Prosthodontic factors

Clinical observations indicate that excessive alveolar bone resorption

can be caused by physiologically intolerable forces produced by functioning

complete dentures.

The inherent denture factors which may affect the supporting

structures include:

i. The occlusal forms of the teeth.

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ii. The alignment of the denture teeth / occlusal pattern.

iii. Deformation of the denture bases.

iv. Materials with which denture teeth are made and

v. The effects of the loss of proper occlusal vertical dimension (over

closure).

i) The occlusal forms : The form of the occlusal surfaces of artificial

teeth, weather of the Anatomic, Non anatomic or 0 degree

configuration, must have some effect on chewing efficiency and on

prices tending to distort the dentuer bases.

- One of the earliest opponents of the anatomic tooth form was French

who coined the term “cusp trauma” as one of the most serious defects

that had to be guarded against in complete denture construction. Soon

after, Sear’s developed his non anatomic tooth form which initiated the

introduction of many new designs to denture teeth throughout the years.

- Although disagreements continues to the advantages of one tooth form

over another. The subject has been removed from the theoretical to a

more scientific level.

ii) Chewing efficiency : Results of early studies on chewing efficiency

with various occlusal forms were contradictory. Thompson and

Trapozzon and Lazzari found anatomic teeth to be more efficient

than non anatomic teeth, whereas Soboik and Manly and Vinton

found no statistical difference between the efficiency of the anatomic

and non-anatomic teeth.

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More recent studies have shown that there is no statistical difference

in the chewing performance in denture teeth with cuspal ranging from 0 to

30 degree.

Aside from studies of chewing efficiency using analysis of

masticated test foods, the use of strain gauges attached to indication of

denture teeth and electromyography has been applied to this problem

Hickey and Asso demonstrated that there was less activity from the closing

muscles when using anatomic (33 degree) teeth than when using 5cm –

Anatomic (20 degree) or non anatomic (0 degree) teeth in tests of chewing

efficiency.

iii) Occlusal pattern – The arrangement of individual teeth in complete

dentures includes a myraid of possibilities ranging from a flat

occlusal plane with 0 degree teeth to a curved configuration which

allows anatomic teeth to guide and pass over each other in close

harmony with mandibular movements.

iv) Denture base deformation – Studies done by Askew and Hoyer

showed that when the mandible with denture was pulled into lateral

and protrusive more deformation was caused under the denture with

anatomic tooth form than with non anatomic tooth form and same

was with acrylic resin denture bases which resorbed the ridge more

than the metal base when used with anatomic teeth than with non

anatomic teeth.

v) Tooth material – the material from which the denture teeth are made

may have some effect on the forces transmitted through the denture

base material to the supporting ridges.

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It is said that porcelain tooth when placed causes more resorbtion of

ridge than acrylic tooth.

vi) Loss of occlusal vertical dimension (over closure) – The loss of

proper occlusal vertical dimension after the insertion of complete

dentures results in the triggering of a cyclic series of event

detrimental to the health of the residual alveolar ridges.

Denture “settling” is one of the most common terms associated with

complete denture prosthetics, yet it has been excluded from prosthetic

glosseries and textbooks. This elusive term implies a sinking of the denture

bases into the supporting structures. Moses described “settling” as a

reorganization of the osseous and mucosal elements underneath the denture

base.

Many authors have observed that overclosure causes the mandible to

be moved or rotated in an upward and forward direction causing occlusal

disharmony and excessive trauma to the anterior region.

Several authors have presented detailed procedures for adjusting the

occlusion to allow for a forward shift of the mandible during over closure

without occlusal interferences. The use of little or no vertical overlap in the

anterior denture teeth has been advocated by authors interested in

preventing trauma to the anterior areas of the mouth.

3. Metabolic Factor and System

General body metabolism is the net sum of all the building up

(anabolism) and the tearing down (catabolism) going in the body. In general

terms, anabolism exceeds catabolism during growth and convalescence,

levels off during most of adult life, and is exceeded by catabolism during

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disease and senoscence. Bone has its own specific metabolism and

undergoes equivalent changes. At no time during life is none static, but

rather it is constantly rebuilding, resorbing and remodelling subject to

functional and metabolic stresses.

The four main levels of bone activity are : 1) Equilibrium, 2)

Growth, 3 ) Atrophy, resulting from decreased osteoblastic activity, as in

osteoporosis and in disuse atrophy and 4) Resorption, caused by increased

osteoclastic activity, as in hyperparathyroidism and in pressure resorption.

Both sides of the equilibrium must be known to understand bone

metabolism. The relative activity of both the osteoblasts and the osteoclasts

must be known. In equilibrium, the two antogonistic actions are in balance.

In growth, although resorption is constantly taking place in the remodelling

of the bones as they grow, increased osteoblastic activity more than makes

up for the bone destruction. In osteoporosis, osteoblasts are hyperactive

whereas in the resorption of hyperparathyroidism, increased osteoblastic

activity is unable to keep up in the increased osteoclastic activity, the

normal equilibrium may be upset and pathologic bone loss may occur. If

either bone resorption is increased or bone formation is decreased, or if both

occur.

Since bone metabolism is dependent on cell metabolism, anything

that influences cell metabolism and specifically, the metabolism of

osteoblasts and osteoclasts is of cells in general and hence the activity of

both the osteoblasts and the osteoclasts. Parathyroid of hormone influences

the excretion of phosphorous in the kidney, and also directly influences

osteoclasts, the degree of absorption of calcium, phosphate and proteins

determines the amount of building blocks available for the growth and

maintenance of bone.

23

One of the most interesting metabolic phenomena concerns the

antagonistic effects of the “Antianabolic Hormones” (the adrenal

glucocorticid hormones including cortison and hydrocortisone). According

to Reifenstein in the young person, there is a relative predominance of

anabolic hormones resulting in continued growth and maturation of the

skeleton, he further states, as people get older, especially women past the

menopause, the anabolic hormones are so reduced that the antianabolic

hormones are in relative excess, with the result that bone resorption may

take place faster than bone formation and that bone mass may be reduced.

Systemic Factors

The influence of these factors can be explained on the statement

given by Glickman. “The status of bone equilibrium is variable, depending

on the physiologic and pathologic process of the entire body for its

regulation, whereas the results of systems disturbance, the microscopic

equilibrium is shifted in favour of bone resorption, a similar condition

prevails in alveolar bone loss of alveolar bone occurs regardless of the

condition of gingival tissue or the structural details of prosthetic appliance”.

Hormone : The three main principal hormones that regulate the plasma

concentration of calcium are:

1. 1,25 dihydroxy cholicalciferol : This is a steroid hormone formed

from vit. D by successive hydroxylation in the liver and the kidney.

Its primary action is to increase the calcium absorption from the

intestine and mobilize this ion from the bone and increase the

absorption from the kidney by approximately 90%.

24

2. Hypophosphatemia : Since low phosphorous concentration in the

incubation medium of bone culture also has been found to enhance

bone resorption; these effects of hypophosphatemia may represent a

direct effect of serum phosphorous on bone to enhance bone

resorption. Recently, however, it has been show that

hypophosphatemia enhances the synthesis of 1.25

dihydroxycholicaliferol, which is the active metabolite of vit. D and

which has been shown to stimulate bone resorption. Thus, it is

possible that the increased resorption seen in person with

hypophosphatema is in past of the result of excess, 1,25

dihydroxycholicalciferol. In any case it is clear that

hypophosphatemia mediates directly, or indirectly a marked increase

in bone resorption. Moreover, in experimental animals suggest that

normal levels of serum phosphorous influence the basal level of bone

resorption through further work is required to be certain of the point.

In addition to these results in experimental animals, it was found be

means of certain studies that hypophosphatemia in a human subject

was associated with increased boner resorption. Since phosphorous is

ubiquitous in nature, hypophosphatemia rarely, if ever occurs as a

result of a deficiency of phosphorous intake. Hypophosphatemia may

occur in patients with duodenal ulcers who are treated with antacids

containing aluminium hydroxide gel, which binds phosphorous and

renders it unabsorbable varying degree of hypophosphatemia are also

seen in patients with impaired of renal tubular resorption of

phosphorus, although we would expect hypophosphatamia of either

glot or renal origin to result in increased resorption further clinical

studies will be necessary to settle this issue. This can be included in

bone loss due to increased resorption.

25

Parathyroid Hormone

Basic research is not definite in disclosing the exact mechanism by

which the parathyroid hormone regulates the calcium-phosphorous balance

in the blood. The chief argument at present is whether the hormone acts as a

direct control on the apposition and resorption of bone or primarily on the

kidneys by influencing calcium resorption by the tubules. When the

parathyroid hormone is injected (hypoparathyroidism), there is an

immediate rise in the renal excretion of phosphate. This disturbs the blood

ca-phosphorous ratio by raising the blood serum calcium level. Then,

phosphates are called from the bone bank by osteoclastic activity.

The parathyroid hormone has another function of maintaining the

blood level of the calcium ion, the calcification of bone tissue will be

retarded to pressure the blood level of the calcium ion. This is related to the

action of vit. D in an antagonistic manner. Parathormone maintains blood

calcium by mobilizing it from the bones by osteoclastic activity. Vit. D

maintains blood calcium by increasing the absorption of calcium from

dietary source in the intestinal tract.

One of the most important systemic factors influencing the rate of

osteoclastic bone resorption is parathyroid hormone (PTH). Under normal

conditions, PTH secretion is controlled by serum calcium concentrations

through a negative feedback mechanism. A slight decrease in serum

calcium concentrations, as for example during the night when little calcium

is being obsorbed from the gut, stimulates the parathyroid glands to secrete

PTH, which in turn stimulates bone resorption, then by delivery more

calcium to the extracellular fluid and closing the feedback loop.

The cause of high PTH secretion can be divided into two categories:

26

1. Primary hyper parathyroidism.

2. Secondary hypoparathyroidism.

Which occurs in a number of different clinical settings. High PTH

stimulates bone resorption and there by causes bone loss. In primary hyper

parathyroidism, the function of the parathyroid glands is abnormal, in that

an abnormally large amount of hormone is secreted and as a result, bone

resorption is increased.

In secondary hyperparathyroidism, there is no abnormality in the

parathyroid glands, the excess PTH secretion is secondary to a fall in serum

calcium concentration and represents an attempt to return the serum calcium

to normal. A fall in serum calcium may be due : 1) Too little Ca being

absorbed from the gut, 2) Too much calcium being excreted in the urine,

and 3) Calcium being lost from extracellular fluid to fetus during the third

trimester of pregnancy.

In all of these causes of secondary hyperparathyroidism. The

parathyroids attempt to maintain serum calcium at the expense of bone

calcium. Decreased external calcium absorption may result from

1) Inadequate calcium intake, 2) small bowel disease, such as sprue, in

which there is impairment of the absorptive process, 3) liver disease which

may impair fat absorption and thereby promote formation of insoluble

calcium soaps, 4) Partial gastrectomy which decreases calcium absorption

as a result of poor mixing of small bovel contents and by other mechanism

and 5) A deficiency of vit. D, which may result from poor fat absorption.

27

Estrogen and Rogen Deficiencies

In general, the sex hormones (Androgenes and estrogens) promote a

protein anabolic action on all tissues including bone. A striking storage of

nitrogen and calcium occurred in individuals with postmenopausal of serile

osteoporosis in one study when these hormones one administered. More

than half of the women over 50 years of age showed Roentgenographic,

evidence of diminishing bone mass in a study by Albright and Reinfestein.

Postmenopausal osteoporosis is the most common form of this

condition, the aging person produces less and less of the Androgens and

ostrogens, which results in faulty protein metabolism for tissue repair.

In estrogen deficiency, the bone loss is not uniform, the amount of

cortical bone does not decrease significantly, whereas the amount of

cancellous bone in the metaphysis of the long bone decrease dramatically,

the information available, to date thus suggests that, with regard to bone

resorption, estrogen deficiency in vivo increase osteoclast numbers. Parallel

with an increase in BMU’s. The increase in osteoclast numbers occurs

primarily on endosteal cancellous bone surface, and estrogen treatment

reverses this effect. Estrogen treatment of estrogen-deficient post-

menopausal women does not change the average depth of the osteoclastic

resorption lacunae which suggests that the resorptive activity of individual

osteoclasts is not affected by estrogen.

Osteoporosis & RRR

Osteoporosis is due to insufficient formation of the organic matrix.

This condition is fundamentally a disturbance of protein metabolism and

involves vitamins, hormone, and nutritional factors. This condition is

28

usually found in edentulous patient. The clinical and pathophysiologic

viscos of osteoporosis has been refined recently to the concept of type I and

type II osteoporosis. Type I osteoporosis is defined as the specific

consequence of menopausal estrogen deprivation, and characteristically

presents the bone mass loss, notably in the trabecular bone. Type II

osteoporosis reflects a composite of age related changes in intestinal, renal

and hormonal function. Both cortical and trabecular bone are affected in

type II osteoporosis. In either case, one of clinical manifestations of

osteoporosis is observed as less radiographic bone density. The maxillary

residual ridge was reported to be significantly smaller in postmenopausal

osteoporotic women while their edentulous mandible remained the same as

the age-matched controls. A knife edged ridge is formed when bone

resorption occurs at the labial and lingual surface of the residual ridge in

preference to the occlusal surface. Postmenopausal women with lower bone

densitometeric scores exhibited a tendency to develop a knife edge ridge in

the mandible.

Islands of langerhans

The failure of these glands to produce sufficient insulin for the

proper utilization of glucose causes diabetes mellitus, the high blood sugar

with the spillover into the urine is well known. The syndrome of poor

healing, low tissue tolerance, and rapid resorption of bone associated with

the diabetic patient is recognized, but the intrinsic causative factors are not.

The explanation for this syndrome is that, in the absence of insulin, a

relative nitrogen starvation amina acids being divested from protein

synthesis. A diabetic controlled by either insulin or diet is not affected by

this mechanism. However, perfect control is rarely possible. Therefore, a

29

word of caution and explanation to diabetic patients is necessary so that

they can appreciate their prosthetic difficulties.

Minor affect of other hormones

Thyroid hormones : The thyroid glands are responsible for the regulation of

the rate of metabolism. Hyperthyroidism increases the metabolic rate so that

a negative nitrogen balance results. Such a balance is equivalent to protein

deficiency, which can be a direct cause of osteoporosis. Thyroxine also has

a direct influence on the kidneys, causing an increased excretion of Ca and

phosphorous. This depletion of Ca and phosphorous results in decreased

bone apposition and increased osteoclastic activity to marshal these

elements from the bone to compensate for their depletion.

Growth hormone : Increases calcium excretion in urine, but also increases

the absorption from the intestine. This effect may be greater than the effect

of excretion with positive calcium balance.

Sex : Women have less bone mass when compared to men.

Age : As the age advances there is decreased bone formation and increased

resorption.

Suprarenal glands : The adrenal cortex produces steroid hormones called

corticoids. One of these, cortison, retards osteogenesis. It was shown

experimentally that administration of ACTII interfered with the healing of

bone in rachitic rats whose treatment consisted of administration of Ca and

Vit. D cortisone and related steroids are antianabolic, may induce the

formation of glucose from noncarbohydrates, and may increase the calcium

loss by direct affect on calcium excretion. The prolonged use and

30

administration of such steroids are considered very dangerous to bone

tissue.

Functional : when force within certain physiologic limits is applied to

living bone, that force, whether compressive, tensile, or shearing brings

about by some unknown mechanism the remodeling of the bone through a

combination of bone resorption and bone formation, the functional factors

of frequency, intensity, duration and direction of force are somehow

translated into biologic cell activity. In as much as the end result is brought

about by cell activity, the metabolic factors are important. However, in that

cell activity is influenced by force, the functional factors are also important.

Evans stresses that mechanical factors constitute just one of several types

of factors that operate in the development and maintenance of the normal

for and size of bone. Henneman and Wallach considered the most

important factor in the stimulation of osteoblastic activity and maintenance

of bone structure in the treatment of osteoporosis to be the stress and strain

of physical activity, even to the point of discomfort.

Force is applied through the teeth to the periodontal fibers, then to

the lamina dura, and then to the rest of the mandible through the trabecular

bone. This force is felt to pass along certain curved pathways called

Trajectories, and it is generally felt that the trabecular structure confirms in

patterns to these trajectories.

The normal forces to the bone are removed along with their resultant

trajectories when the teeth are removed. Hence, it is to be expected that

remodeling of bone will take place when the teeth are removed. Neufeld

found in edentulous patients as compared with dentulous patients that the

trabecular wire finer and the cortex thinner, with the cortex over the crest of

31

the ridge being incomplete in all patients and the over all size quite possibly

smaller. Neufeld also found that instead of the usual trajectories present in

the dentulous mandible, the trabecular pattern in the edentulous mandible

was, in general, random, except that in some specimens the trabecular near

the crest of the ridge were somewhat perpendicular, suggesting the

development of trajectories to the compressive force of a denture.

When are the functional factors of frequency, intensity, duration and

direction physiologic and when are they pathologic? Where is the dividing

line between stimulation and trauma or between disuse and use? The

dividing line is not the same for all patients. What to one patient is

stimulation conducive to bone formation could well be trauma to another

patient, resulting in bone resorption. The functional factors must be

interpreted in conjunction with the metabolic and anatomic factors.

Disuse atrophy and fracture are example of extremes of functional

force.

Disuse Atrophy : the use of natural teeth transmits stresses to the supporting

alveolar process within a certain range, this is physiologically helpful,

serving to increase the density and strength of the alveolar process.

However, pressure exerted on a tooth, which is out a line in the dental arch,

causes traumatic forces to be transmitted to the supporting process. In this,

situation, resorption and reduced density of structure are observed in the

bone, with eventual loosening and loss of the involved teeth.

When natural teeth have lost and no stimulation is provided in the

residual ridge by means of a prosthodontic restoration, the alveolar process,

will be lost through disuse.

32

A large protein deficit followed by metabolic derangements develops

from disuse. The deficiency is in the formation of the new protein matrix

with no disturbance of calcification.

A loss of closing free develops because the mucous membrane and

the periosteum cannot endure the force once received by the teeth, this loss

of internal stimuli and the reduction of closing force are signals for disuse

atrophy and a remodeling of the bone in accordance with Wolf’s law of

Transformation. As Wolf’s law states, briefly, that change in room follows

change in function and that its change is due to alteration of its internal

architecture and external confirmation, in accordance with mathematical

laws.

Disuse atrophy does not result from the direct loss of nonfunctional

bone, but rather from the lack of replacement of bone not needed for

function. Some stimuli are present from the action of the denture. But the

nature of the stimuli is not normal, the response of the bone varies with the

degree, the internal and the tissue tolerance to the stimulation.

Reaction of Bone to pressure and tension : An increase of pressure within

the limits of tolerance leads to bone apposition. As long as pressure does

not interfere with the normal blood supply, nerve supply, and drainage of

the bone tissues. The pressure is resisted. However, whenever pressure

interferes with the blood or nerve supply or with the venous drainage of the

bone, resorption invariably occurs. Normally, the stress of pressure and

tension on bone is transmitted through avascular tissue such as the teeth, the

condylar articulation, the intervertebral disc, and other joints such structure

under pressure are covered by specialized fibrous tissue, fibrocartilage, or

hyaline cartilage. If the pressure is against a vascular tissue covering of the

33

bone such as the periosteum, the blood supply to the bone is aggravated and

it is a target for resorption. The denture bearing bone has a complex blood

supply from two sources, the main supply is internal from the interdental

arteries that pass through canals in the interalveolar septa. After extraction,

if bone loss that slight, the blood supply is not greatly disturbed. However,

if extensive surgical procedure removed large amounts of alveolar bone.

The internal blood supply can be vastly altered by the bone callus. The

other blood supply comes externally from the periosteum. Arteries from the

periosteal network enter the bone as arterioles in the numerous Volkman

canals which open from the outer surface of compact prone.

Interference with the blood supply leads to bone necrosis, the

interference may be due to pressure directly from the bone, or it may be of

inflammatory origin. If inflammation is present, a constant internal capillary

pressure acts to setup resorptive process. The amount of blood supplied to

the prone from within (intrinsic and surgical sequelae) and from without

(periosteal network and denture base) can predispose little or great change

in bone form.

It is tempting to draw definite conclusions about this concept, but it

needs further investigation. However, it does seem to offer a logical

explanation as to why some patients exhibit so little bone loss and some

great loss in a given space of time.

OTHERS

Dietary Factors : During edentulousness the nutritional requirement are not

met with proper attention there will deficiency of the same and this will

affect the residual ridge resorption. This usually happens because of

impaired masticatory efficiency and to complicate further the alveolar bone

34

is over loaded by complete denture where forces generated are transmitted

directly to alveolar prone.

Food are classified as a) Protein, b) Carbohydrates, c) Fats,

d) Inorganic elements and e) Vitamins.

Protein : Protein is necessary to build and maintain tissue and to supply

energy. The necessary daily about requirement of protein is approximately

3 ounce. Aged persons need more than the minimum amount of protein for

the maintenance of tissue health.

Carbohydrate : They provide the chief source of energy. They are related

only, indirectly to bone resorption though association with diabetes and by

substitution for more favourable foods.

Fat : Fats are organic substance that yield heat and energy and only

secondarily build up repair tissue.

Vitamins : Diet must contain vitamins for development, growth and

function of the body.

Vit. A (Carotene) : Deficiency of this causes renal damage by hornification

of the tubules. This damage results in the abnormal loss of phosphorous and

the tubules lose the capacity for reabsorption. The imbalance of the Ca-

phosphorous ratio leads to osteoporosis.

A lowering of Vit. A also has an effect on the osteoblasts so that they

engage in disorderly and uncontrolled activity. The cells adjacent to the

bone modulate to osteoclasts and become active.

35

There is a damage of Hyper vitaminosis A, but experiments are

inconclusive as to the mechanism. Some reports indicate an acceleration of

matrix remodeling while others seem to conclude that excess vit. A

accelerate the activity of the osteoclasts. The general function of Vit. A in

regard to bone is its influence on the activity and position of the osteoblasts

and osteoclasts.

Vit. B Complex : Vit. B complex produces effects in bone similar to a

protein deficiency Chase reported degeneration of bone, enamel and dentin

in rats on a B-complex deficiency diet. Osteoporosis of gingival

inflammation were reduced in dogs by withdrawal of nicotinic acid. This

condition was corrected by addition of this part of the B-complex to diet.

Vit. C : The collagen content of prone is reduced in vit. C deficiency the

lossening of teeth in survey is due both to prone resorption end to

disorganization of the periodontal fibres and members, the periosteum is

affected in a similar way. It thickens, and the cells appear immative and

resemble fibroblasts. This condition may make the periosteum more easily

injured by the denture base sot that inflammatory process are triggered by

the denture base at lower pressure levels.

Vit. D : Deficiencies of Vit. D disturb the Ca-phosphorous balance and

promote prone resorption.

Habits : Habits such as food intake, masticatory, bruxism, sleepswith

denture, holds pipe, sucks fingers, bites nails, nibbles with anterior teeth etc.

can affect RRR.

Biological factors : such as tissue health, saliva content, oral hygiene, oral

bacterial flora, drug or alcohol intake.

36

DIAGNOSTIC AIDS TO DETECT RRR

Many techniques have been used to establish that bone is in fact

being turned over.

1. Radiographic : This procedure is widely used to detect bone

resorption and formation phenomenone by taking periodic

radiographs.

2. Tetracycline labeling : In this tetracycline is injected into the body

through oral or pariental administration and should be repeated the

same after every week for 5 weeks. This tetracycline is taken up by

the bone, only in the new sites of bone formation tetracycline can be

readily identified in the bone, because the resultant tetracycline

calcium chilate formed is fluoroscent and can be viewed by

fluorescence microscopy.

3. Mercury porosimetry : Osteocytes are also capable of bone

resorption (i.e. periosteocytic lacunar bone resorption). This is

evaluated by enlargement of osteocyte lacunae. Therefore, inorder to

determine the quantitative importance of osteocytic resorption. A

method known as mercury porosimetry was used to makes a

comparison between osteocytic and osteoclastic bone resorption. In

this method mercury is introduced into pores by pressure and a

measure of the pore volume as a function of pore diameter is

obtained. Since osteocyte lacunae, canaliculi, and vascular canals

constitute a system of pores, this method can be applied to measure

the volume of different classes of bone pores. Thus with this method

it was able to quantitate osteocyte lacunae canalicular volume, which

37

enlarges as a result of osteoclastic resorption and vascular canal

volume, which enlarges as a result of osteoclastic resorption.

PATTERN OF BONE RESORPTION AND ANATOMICAL CONSIDERATION

Gross anatomic studies of jaw bones have revealed a wide variety of

shapes and sizes of residual ridges. In order to provide a simplified method

of categorizing the most common residual ridge configuration. It has been

described as a system of 6 patterns of residual ridge forms have been

described.

Order I – Pre extraction

Order II – Post extraction

Order III – High well rounded.

Order IV – Knife edge

Order V – Low well rounded

Order VI – Depressed or invested

Even among individuals of the same sex there exist large variations

in the morphologic characteristics of the residual ridge and associated

bones, and these can be related to their original anatomic features. There are

however, certain patterns of resorption and some persistant anatomic

structures that can be recognized from one case to another. These structures

are palpable when they become protruberant, they are the genial tubercles,

the external oblique line and the mylohyoid crest for the mandible or for the

maxilla, the nasal spine, and the pterygoid plates.

The usual changes that take place after dental extraction are those of

a ridge initially wide enough at the crest to accommodate the natural teeth

38

that changes to one that is narrow and sharp, then-flat, and finally concave.

These four stages of resorption correspond to the classification of residual

ridges unable to adequately maintain denture in place.

Group I : High, crestal muscles over non-resorbed ridge

Group II : Sharp atrophic residual ridge.

Group III : Absence of residual ridge and resorption to the level of the basal

bone.

Group IV :Absence of residual ridge and part of the basal bone.

Mandibular changes :

In the anterior region one can observed progressive deterioration of

the lateral bone profile, the angulation of the anterior slope, and the ridge

form, the profile is modified from a pear-shaped appearance to a pointed

one. Soon after teeth are extracted, the anterior slop angulation gradually

loses its perpendicular position with the mandibular plane as the crest of the

ridge moves backward the ridge leads to a flat and round basal bone shape

and more rarely to a concave form where the basal bone itself is involved.

In the premolar molar region, bone loss is more rapid than anteriorly

because of the resorptive nature of the posterior dorsum and a lower

position of reversal lines. Hence bone resorption of the basal bone is more

frequent in this region. Typical patterns of resorption are recognized and

outlined by the presence of this structure that resist resorption, the external

oblique line and the mylohyoid crest, the concavities seen from the different

planes may be present; a lateral dishing of the crest from the cuspid to the

retromolar region and a longitudinal midbody concavity.

39

The dishing of the crest is best revealed by the lateral cephalogram.

In more advanced stages of atrophy these posterior bilateral concavities are

more pronounced, with erosion of the basal bone, they may become

associated with a roundly shaped anterior basal bone, a frequent finding,

described as the sphenoid anteriors basal bone with posterior concavities.

On the medial side of the residual ridge the bone contour forms a gradual

slope toward the mylohyoid crest. In very advanced stages, the concavity

occupies the major portion of the dorsum of the corpus. It is more

commonly located between the dense external oblique line and the

mylohyoid crest.

The position of the teeth in the alveolar basal bone complex may also

play a role in these changes the lingual inclination of the molars and the

more facial position of the premolars, canine and incisors, which result in

the presence of more bone on the lingual side of their roots. Contribute to

the frequent occurrence in resorbed mandibles of another structures, the

paralingual crest. This palpable crest, originating at the myolohyoid crest,

itself extending anteiorly in a downward direction, may become a true

lingual shelf. It may fuse with another structure that becomes protuberant

and palpable in advanced stages of atrophy: the genial tubercles.

Four stages of ridge resorption and classification of deficient residual

ridges:

40

Maxillary changes : Patterns of resorption in the maxilla differ from those

in the mandible. Maxillary ridge resorbs usually more evenly than the

mandibular ones because of larger denture bearing areas, with the palate

providing a more equal distribution of mechanical forces. When the anterior

maxillary bone disappears at a faster rate than the posterior part, it is more

often due to excessive forces originating from natural mandibular incisors

and inadequate posterior prosthetic support.

The lateral cephalogram uncovers an anterior maxillary slope that

represents the external side of the triangle formed by the meeting of the

palate with the anterior ridge. The angulation of this slope relative to the

palatal plane persists much longer throughout the different stages of atrophy

than in the opposing jaw. This particularly could be explained by the natural

protrusion of the anterior maxilla, which is designed to hold incisors that

are normally inclined at 110 degrees with the palatal plane. After dental

extraction and during ridge remodeling, the posterior drift of the anterior

crest does not become as pronounced as in the mandible because of this

advantageous bony artchitecture. An anterior ridge form persists for a

longer period time, the angulation of the slope is affected only in advanced

stages of atrophy when the triangular form disappears and the crest reaches

the same level of the palatal bone or even below this level. In these

instances there is projection of the nasal spine.

41

Residual anterior maxillary triangle and persistence of ori anterior

bone contour slope throughout different stages of atrophy

In the posterior region progressive reduction of the width of the

maxilla takes place as the ridge resorbes. This process is related to the

outward inclination of the maxillary premolars and molars to accommodate

for the lingual angulation of the mandibular teeth, and to the presence of

thin buccal plates more susceptible to resorption than the thicker palatal

ones. The pterygoid plates will become palpable, in advanced stages of

atrophy, their extremities being located below the palate.

Intermaxillary changes

The relationship that existed between the two maxilla when teeth

were present might have undergone a change after ridge resorption, with an

increase of interridge distance as the most obvious change in the vertical

bone, especially in the anterior region.

Sagittal and anteroposterior relationship are also affected. An inverse

ridge relationship and a pseudo prognathic condition will develop with

advanced stages of atrophy. The maxillary ridge will be reduced in size,

whereas the mandibular one will be expanded, when ridge resorbtion

reaches the level of the basal bone. This transformation is favoured by the

natural architecture of both maxilla, the circumference of the crest of the

maxilla being longer than the circumference at its base because of the

outward inclination of the teeth; the reverse is present in the mandible

where the teeth and their supporting tissues are seated over a wider bone

base.

42

Soft tissue changes

Soft tissue changes also occur after teeth are lost and dentures are

worn. A crestal scar bond representing the remnants of the attached gingiva

is usually present all along the crest. It is more prominent and hyperplastic

when some residual ridge remains. It then acts as a protective cushion

between the sharp residual ridge and the denture base. Heavy fibrous tissue

will develop in the tuberosity regions, especially when maxillary molars

were removed at an early age or when the maxillary denture was not

rebased in the first years after teeth were extracted. This tissue puts up the

space left by lost bone.

ANATOMICAL CONSIDERATION

Mental foramen becomes more close to the denture bearing areas, the

alveolar process decreases in size, the change of denture impingement on

the mental nerve increases with bone loss and the nerve is more vulnerable

to the injury during surgical grafting or implantation procedures.

Progressive bone loss leaves the nerve near superior surface of the

mandible.

43

The ultimate result of complete alveolar bone loss is concave

superior surface of the mandible. This concave surface represents the upper

surface of the cortical plate of the mandibular inferior, border. In severe

cases, the genion tubercles may be superior to the crest of the mandible,

pressure on the mucosa on this area cause sharp pain.

Muscle attachments such as buccinator, mentalis, mylohyoid and

genioglossus do not migrate significantly, RRR leaves the muscle

attachments close to the crest of the ridge muscle function will often lift the

muscle and overlying mucosa above the level of the alveolar ridge, thus

reducing the amount of the alveolar bone exposed in the mouth. As the bone

loss progreses in the maxilla the palatal vault becomes relatively more

shallow and redundant soft tissues forms labial to the alveolar crest. The

nasopalatine neurovascular bundle may end up on the crest of the ridge or

anterior to it. Impingement on this nerve by the denture may occur.

However, this is less often a problem when compared to the tough mental

nerve. The shape of the maxilla during RRR is dictated by as many of the

factors as in the mandible. In case where lower anterior teeth occlude with

the upper complete denture. RRR occurs in the anterior ridge where height

decreases to a point of dehiscence between the mouth and the nose. This

usually occurs at or just posterior to the piriform rim of the nose. The

anterior nasal spin may be almost with the level of the alveolar crest. RRR

in the anterior maxilla mostly occurs on the labial and inferior aspect of the

alveolar ridge so that the crest moves posteriorly. Upper lip support is

progressively lost as anterior maxilla decreases in size. This combined with

the relative anterior movement of the mandibular ridge results in an

increasingly Class III facial form and ridge relationship.

44

Posteriorly, as the maxillary tuberosity decrease in height it

approaches the level of the mucosa that is draped from the muco-gingiva

junction on the posterior aspect of the maxillary tuberosity i.e. hamulus.

This change oblitrate the posterior slope of the tuberosity. As the mandible

becomes smaller as the teeth removed, resistance to the fracture is reduced.

Fracture in extremely small edentulous mandibles are especially omnions,

because of the lack of bone mass for fixation and due to the changes in

blood supply. As RRR occurs, major source of blood supply to the

mandible change from centrifugal to centripetal (periosteal) the inferior

alveolar vessels become smaller and less significant in the nourishment of

the mandible. Therefore, the surgical procedure that elevate the mandibular

periosteum compromise the blood supply more as the mandible becomes

smaller.

CLINICAL SIGNIFICANCE

Clinical observations indicate that excessive alveolar bone resorption

can be caused by physiologically intolerable forces produced by functioning

complete dentures.

Changes which have to be considered and taken care while

fabricating the complete denture can be grouped into five major categories.

These are:

1) Appearance (facial and teeth).

2) Efficiency of mastication.

3) Phonetics.

4) Pain and discomfort (Alleviated or initiated, imaginary or real) and

5) Prone and tissue changes.

45

Appearance

Commonly seen men are taller, have greater facial heights and just

more jaw bone to resorb after dental extraction. The ratio of potential units

of bone to resorb to the years of resorption acts in their favour.

But one should not assume. However, that men have an advantages

in treatment over women because men usually have more bone left after the

same number of years of denture wear. Not only the volume of bone but

also its form must be examined. A large residual basal bone does not

necessarily means a more favourable ridge for denture construction or one

superior to a but for the convenience of understanding and implementing

certain parameters so that the proper care is taken for the prevention of the

further residual bone resorbtion. Thus, following Devan’s scientific words.

Its perpetual preservation of what remains of the oral masticatory apparatus

rather than a meticulous restoration of what is missing.

We start with clinical consideration for RRR from impression

procedure

Impression Procedures

Before impression procedure, care has to be taken on selection of

custom made trays.

- If the tray selected is too large, it will distort the tissue around the

borders of the impression away from the bone.

- If it is too small, the border tissues, will collapse inward onto the

residual ridge. This will reduce the support for the denture and prevent

the proper support of the lips by the denture flange.

46

- As we are know the commonly used two procedures for the final

impression procedure are:

1. Minimal pressure technique.

2. Selective pressure technique.

1. The minimal pressure technique with mucostatic principles ignores,

the value of dissipating masticatory forces over the largest possible

basal seat-area. If for example, the patient could develop masticatory

force of 30lb, it is evident that the larger the basal seat area, the less

force would be exerted on each square millimeter of underlying

mucosa furthermore, the form of the mucostatic denture minimizes

the retentive role of the musculature. Today, a large proportion of

dentists make impressions with minimal pressure in order to avoid

distortion of the mucosa and ridge areas which may undergo

considerable pressure otherwise.

2. The principle of this procedure making impression is based on the

being that the mucosa over the ridge is best able to withstand

pressure, as compared to the mucosa covering the midline is thin and

contains very little submucosal tissue. Many fine dentures are made

according to this principle of selective pressure and definitive

judgement on the merits of this approach must be deferred. It must

be emphasized, however, that this technique demands firm, healthy

mucosal covering over the ridge.

- If flabby ridges exist, than decision to make mucostatic, functional or

selective pressure all have to be considered. It can be argued that tissue

tissue will become displaced in occlusal function and therefore, should

47

be improved in a functional state. However, as with all functional

impression techniques, the amount of functional placement is unknown,

the functional movement probably would not be the same in extent or

direction with each functional load because the patient is more often at

rest than in occlusal function, it is not practical to make the impression

of the tissue in a functional state.

- The true mucostatic theory as it relates to impression making may find

advocates who are dealing with the hypermobile ridge crest. The

principle of pareals law as related by Page. However, would have

questionable value here because the excessive tissue movement

encourages denture base movement. This will prevent the equal

distribution of force that the true mucostatic principle purposes.

3. The use of a combined mucostatic and functional impression

technique, the selective pressure impression technique seems to be

the most advantageous for the hypermobile ridge crest, as with most

complete denture impressions, the hypermobile tissue itself would be

recorded at rest with functional placement of border tissue to

enhances denture retention and stability. Many techniques have been

proposed depending upon the severity of the redundancy, and it is

not the intent to suggest a specific impression technique here

Jaw relation

Correct recording of vertical and horizontal relations are equally

important for the preservation of residual bone resorption.

In horizontal relations unless centric relation is established, properly,

the mandibular teeth will not occlude properly with those on the maxillary

48

arch, thus proper occlusion is essential to the health of bony support.

Otherwise during eccentric movement it causes pressure on bone due to

failure of the factor stability. Hence cause resorption of bone.

- Loss of occlusal vertical dimension – the loss of proper occlusal vertical

dimension after the insertion of complete dentures result on the

triggering of a cyclic series of events detrimental to the health of the

residual alveolar ridges.

- Due to excessive interarch distance, because premature striking of teeth

cause recurring trauma to the tissue (i.e. bone and mucosa) and longer

leverage, making the denture more outward to manipulate and more

easily displaced.

- Whenever an excessive amount of bone has been lost from various

causes (sch as periodontal disease, ill fitting denture that have been worn

for many years, partially edentulous months, especially with all the

mandibular posterior teeth gone), it is possible to reduce the denture

space an undesirable amount.

- In narrower knife-edged ridges that cannot be made comfortable in any

other manner may be treated by reducing the occlusal vertical dimension

to trauma and sorners.

Selection and Arrangement of teeth :

Occlusal form : The form of the occlusal surfaces of artificial teeth,

whether of anatomic, non anatomic or 0 degree configuration, must have

some effect on chewing efficiency and force tending to affect the

underlying tissues.

49

The arrangement of individual teeth in complete denture include a

myriad of possibilities ranging from a flat occlusal plane with 0 degree teeth

to a curved configuration which allows anatomic teeth to glide and pass

over each other in close harmony with mandibular movements. Advocates

of cuspless flat plane occlusion, reverse pitch occlusion, and variations of

the reverse pitch occlusion i.e. (pleasure curve) consider such occlusal

schemes to be effective in helping to preserve the underlying ridges.

Proponents of anatomic teeth for complete dentures emphasize

careful settling and selective grinding of the teeth to minimize lateral

stresses and the resulting tissue trauma.

Placement of the posterior teeth. This factor also plays an important,

role while arranging the posterior teeth. It is said that by placing the

posterior teeth on the crest of the ridge, the stress distribution is equally

distributed and reduces the bone resorption. Special attention has to be

given in patient suffering from diabetes, or the above mentioned systemic

diseases.

Tooth material : As it is said the material from which the denture teeth are

made may have some effect on the forces transmitted through the denture

base material to the supporting ridges.

While a complete denture is given against a natural dentition.

Ideally, acrylic teeth are preferred as the porcelain are brittle material

causes attrition of the natural teeth and if porcelain teeth are used than the

occlusal surface have to be covered by gold to prevent much wear and tear.

A very dangerous and traumatic combination of teeth is acrylic resin

posterior teeth on one or both arches and upper and lower porcelain

50

anteriors. Because of the abrasion of the posterior teeth, the anterior teeth

develop interfering contacts during mastication that will continually

traumatic the anterior part of the upper and lower denture foundation. This

is potentially dangerous to the health of the supportive tissues and should

always be considered when selecting the tooth materials.

Size of posterior teeth: the selection of the proper tooth size or mold is

based upon D the capacity of the ridges to receive and resist the forces of

mastication and space available for the teeth and the esthetic requirements.

We considered is the first one. In most complete dentures the lower

ridge offers less support to the forces generated by the occlusal surface of

the teeth. Its smaller area of support and more rapid resorption pattern

progressively narrow and reduce the height of the lower ridge. Because of

this, the use of posterior teeth should favor the lower ridge. For these

reasons the determinants for selection will be based on the lower ridge.

When the lower ridge is strong, well formed and covered by a

generous area of attached masticatory (keratinized) mucosa, the full space

available can be used because this ridge has the capacity to tolerate the

forces of mastication. When the ridge is weak, resorbed, and covered by

only lining mucosa, then the size of the posterior tooth should be smaller.

This will limit the occlusal surface, which in turn will minimize the forces

directed to such a ridge.

The inverse ridge relationship that may result from severe loss of

bone will create problems in constructing the denture and placing teeth. In

order to use the buccal shelf, a stable dentin bearing area, the posterior

mandibular teeth must be placed closes to the vestibular side and the

maxillary teeth outside the ridge it one wishes to correct the crossbite

51

relationship, both dentures consequently will be mounted outside their

original bearing areas.

Dentin base deformation : Forces generated by reaction at the occlusal

surfaces of the denture teeth must be transmitted to the denture base prior to

the ultimate dissipation of these forces in the supporting residual alveolar

ridges.

For degenerative denture ridge patients, there are three types of

denture bases:

1. Resin base.

2. Cast metal base.

3. Processed, resilient lined denture bases.

Sharry, Ashow and Herper used strain sensitive lacquer to study

deformation patterns in bone on skulls (with dentures) when the mandible

was pulled into lateral and protrusive positions. More deformation was

caused under the dentures with anatomic tooth forms than with

nonanatomic forms.

Studies employing electrical strain gauges embedded in various type

denture bases have been conducted to measure deformation occurred during

mastication with anatomic than with nonanatomic teeth and acrylic resin

denture bases deformed much more than did metal bases under similar

situations. One study demonstrated that reducing the occlusal surface area

had no significant effect on deformation whereas reduction of the cusp

angles significantly reduced the deformation of the mandibular denture

base.

52

- After curing the dentures the lab remounting has to be done and

selective grinding for working balancing contacts and for protrusive

balance has to be carried out in order ot remove any interference.

- Lastly after insertion of the denture, the patients have to be recalled on a

regular schedule correct any existing occlusal disharmonies an

encouraging the patient to remove this dentures upon retiring.

Masticatory apparatus therapy

Older edentulous patients frequently suffer from problems involving

the temporomandibular joints and imbalance with spasms of the muscles of

mastication. These conditions should be treated, alleviated, and corrected if

possible before jaw recordings are attempted and new dentures constructed.

Fortunately, this can accompany the tissue treatment.

When these problems exist, the old dentures are duplicated, the

duplicated dentures are then lined with soft resin for impression purposes.

The soft lined dentures are then articulated with a face-bow and centric

relation records. The upper denture is converted via a laboratory duplicators

to a self curing resin base, the occlusion is surveyed, and if nearly correct

and with an acceptable vertical dimension, the dentures are ground in to a

balanced occlusion. When the occlusion is less than acceptable, the lower

denture is removed from the cast and the lining removed the lower denture

is positioned into centric occlusion against the upper denture and luted to it

with sticky wax. The lower cast is lubricated soft lining resin is placed on

the basal surface of the lower denture, the articulation is closed to a

predetermined vertical dimension and the resin is allowed to cure, the sticky

was is removed, the occlusion is checked, and mucin imperfections are

eliminated. By this means, the old lower dentures which has often moved

53

forward into a prognathic relation with collapsed vertical dimension can be

corrected. In doing so we have supported the mandible and maxilla and

established a good centric occlusion and occlusal vertical dimension we

have relieved the strain on the musculature and the temporomandibular

joints.

For a short time, there may be distress in the TMJ or the

musculature, this will cause some resolutions in the apparatus and a shift in

the occlusion with successive treatments, the lower denture can again be

relieved and the repositioning process repeated, progressively obtaining a

better centric relation record and desirable vertical dimension such

treatment may solve the emergency problem quickly while preparing the

patient for new denture.

SURGICAL TREATMENT CONSIDERATION

- Usually the problem associated with denture wearer is one, bone loss

that affects ridge form and increases muscle interferences. Before

hydroxyapatite become available this loss could not be replaced, except

in extreme atrophy when ridge augmentation with bone graft was used,

with all the uncertainties of resorption and inadequate gain of ridge

form.

- Pre prosthetic reconstructive surgery was limited mainly to ridge

extension procedures with muscle reattachment, the outcome of this

surgery was dictated by the contour of the residual bone. These

procedures were very successful. If there was not atrophy, such as in

group I patients, or if the bone loss has affected more the width from the

height of the residual ridge, such as in certain group II cases. But when

very little ridge was left or when only the basal bone remained and the

54

contour was deficient little gain could be expected from extension

techniques unless extensive detachment of the chin and tongue

musculature was done. Hydroxyapatite has opened up a new in

preprosthetic reconstructive surgery. It offers numerous possibilities.

This material not only can be used to reconstruct an ideal ridge form

with less relationships with the help of dependable techniques.

Although, many patients with poor residual alveolar ridges wear

complete dentin successfully, other experience varying degree of difficulty.

Most patients complaints are related to the mandibular C. D. longitudinal

studies indicate that the bone loss associated with the mandible is four times

greater than that associated with maxilla. In extreme atrophy the mandibular

denture can impinge upon the contens of the mental foramen and / or the

inferior alveolar nerve and cause discomfort and parasthesia of the lip. An

extremely atrophic mandible is also more susceptible to fracture. These

problems are especially significant in relatively young patients who can

expect to wear prosthesis for many more years.

- Those have been many attempts to mitigate the problem by various

materials of treatment that incluide:

1) Soft tissue vestibuloplasties to increases the relative height

and extent of the denture foundation.

2) Subperiosteal or endosteal implants to improve comfort and

retention of the denture and preserve the remaining

mandibular bone.

55

3) Augmentations with alloplastic materials such as proplast

calcium aluminate ceramic material to increase the vertical

height of the mandible and.

4) Augmentations with homogenous and autogenous bone and

cartilage in different forms and combinations to increase the

vertical height of the atrophic mandible.

- Tissue augmentations for atrophic mandibles may be divided into the

following categories:

1) Implantation of freeze – dried homogenous bone and cartilage.

2) Implantations of autogenous cancellous bone and /or particular to

marrow in conjunction with some form of tray.

3) Implantation of block sections of autogenous ilac crest or ribs

cortical and cancellous bone.

According to the surgical procedures to be followed by the RR

according to Roger Masella classified as:

Group I High crestal muscles and non resorbed ridge:

Difficulties in achieving stability and retention are not always related

to a deficit of bone. Certain patients with ridges that have resorbed very

little, especially the mandibular ridge cannot be helped a conventional

prosthodontic approach. The tonicity of the muscle and / or their

attachments at the crest of the ridge prevent the development of the

necessary extension of buccal and lingual flanges needed for stability and

retention. Ridge extension procedure is vestibuloplasty may be benefit this

56

group twice the anteriors slope of the mandible is favourable to again of

denture bearing area.

Group II painful atrophic ridge

Most of the problems incomplete denture prosthodontics are of this

type. Usually the ridge has resorbed until the crest made of sharp lingual or

palatal cortical plate, covered by a redundant of tissue that moves with

palpation and is painful to pressure. Many non surgical attempts at treating

the hyperplastic (flabby) ridge have been attempted they range from

mucostasis impression to the use of tissue conditioners. These procedures

have not only partial success since the mucoperiosteum of sharp bony

spicules remains.

Group III – Absence of residual ridge :

Many patients with ridges that have been reduced to the basal bone

may have better masticatory function than those patients in the two previous

groups, the mandibular denture rests on a painless flat or frequently serves

to stabilize the denture may exist these patients with above average muscles

coordination and the capacity to provide the equilibrium of the orofacial

muscles necessary to retain the denture in place, may benefit from the

refinement of excellent prosthodontic treatment using a conventional

approach. However, for those group III patients with a severe functional

handicap a ridge augmentation with implements procedure should be

considered.

1. Vestibuloplasty : The literature is replete with various techniques for

vestibuloplasty. These range from the early technique of ridge

extension with secondary epitheliazation to techniques that

57

emphasize to importance of including the attachments of the muscles

of the floor of the mouth in the dissection. The original description of

the total lowering of the floor of the mouth with vestibuloplasty and

split thickness skin graft was presented by Obwerzer in 1963 which

still serves as the standard approach.

Until the adherent of predictable implant treatment, augmentation

procedure of the edentulous maxilla and mandible focused on

reconstruction of lost R.R and archform for retention of conventional

dentures. Today, our goals for augmentation and reconstruction have

broadened because implant utilization with its advantages of increased

support for function and bone preservation with time, has become the

preferred endpoint of reconstruction, the placement and growth of viable,

healthy mature bone in areas of potential implant placement are now our

primary concerns. Good ridge form and / or soft tissue extensions are still

preferable but are not as critical if an adequate number of implants are

available to support prosthetic. Previously used large scale secondary soft

tissue procedures for improving the denture bearing area, such as

reconstruction of the floor of the mouth and buccolabial vestibule

(vestibuloplasty) with split thickness skin grafting are loss frequently

necessary when implants are first soft tissue manipulates is addressed

relative to implant procedure and is usually more localized, with much less

patient morbidity implants have become or great step forward in our

progress in treating the edentulous maxilla mandible.

58

Maxillary augmentation for utilization of implants:

The severely resorbed maxilla requires bone grafting of the more

common techniques described for maxillary grafting that have been used

with success are:

1. Corticocancellous horseshoe graft obtained from the ilium and fixed

to the maxilla with osteointegrated implants.

2. LeFort I down fracture, with an interpositional cortico cancenllous

graft obtained from the ilium and placed into the antrum and anterior

nasal floor.

3. Corticancellous onlay block graft obtained from the ilum and fixed

to the remaining alveolar and / or maxillary sinus floor with wires or

screws.

4. Particulate autogenous corticocancellous ilium (ACI) mixed with

porous hydroxyapatite (HA) particles and grafted in onlay fashion

and / or into the maxillary antral floor / sinus lift procedure.

Mandibular augmentation

Mandibular augmentation is needed in group III and II cases and

mandibular augmentation for implant utilization is needed when severe

resorption will not allow acceptable fixture height in position because of

lack of adequate bone. Augmentation also is indicated when population of

the implant sites may lead to mandibular fracture or when pathologic

fracture is a concern.

59

The permanence of the bony reconstruction of the mandible has

historically been a problem. pichler and Traunec, in 1948 whole that

clementschitch may have been the pioneer in the construction of the

alveolus of the mandible using blocks of autologous ilium. Many other

followed, using autologous ilium, but it was found that the grafted area

tended to resorts after a four months and had often completely disappeared.

After a few years Obwegeser and Co-workers, introduced the

application of autologous eris in this problem. this graft tended to last

somewhat longer. Thus, the grater proportion of cortex to spongiosa of rib

appeared to suggest that the more cortical bone present in the graft, the

longer the grafted area tended to remain, the grater amount of cortical bone

results with a prolonged resorption and replacement phase while the graft

changes to viable lamellar bone. It appeared possible that if a non

resorbable substance could be substituted for the function of the cortical

bone, the highly osteogenic autoglosus cancellous bone might form a

composite that could last indefinitely Icent and coworkers appeared to

validate this hypothesis by adding dense via to autogenous cancellous bone.

This mixture revealed less than 15% resorption at 4 years after grafting.

Thus, the problem of the retention of the grafted bone for strength of

the mandible has substantially been solved by the addition of dense HA to

the bone graft material. However, when this type of grafting system is used

for implant sites when the implants are to be placed after graft maturation,

the dense HA presents a problem on that it is difficult to through it.

Therefore, dense HA and bone are best used when a graft is to be placed

around a implant.

60

Another splints to substitute the porous form HA for the dense form

as porous can be drilled. It was generally considered that the porous form of

HA would be long lasting it is sometimes reform non resorbed. Hence it

appears appropriate to use porous HA mixed with the bone graft in areas

where implants are to be placed and dense HA mixed with the bone graft

when strengthening only is require.

CONCLUSION

Resorption of alveolar bone seems inevitable when teeth are lost, yet

variability exists between persons. Both between and within the jaws and

over time. It would seem that bone that has undergo higher rates of

resorption initially will continue to resorbs excessively compared with bone

that has undergone lower rates of resorption.

Metabolic differences are undoubtedly most significant in the

response of a given individual to a given stress and account for the

variations among individuals within the same individual at different times.

The state of knowledge is so inadequate that there is no single test or

set of criteria which can be used to determine whether a given patient has a

good bone factor or not. We must rely on clinical judgement. Which is

notoriously poor we revaluate the general nutrition, metabolism and hormal

activity of the patient, sometimes age or sex provides clues. A dental history

of or clinical evidence of inordinate previous bone loss may suggest a poor

bone factors but such bone loss must be evaluated in light of the anatomic

functional and prosthetic factors. The findings although not statistically

significant, suggest that clinical judgement of prosthodontics depends not

only on a profound.

61

Understanding of the myriad of significant technical factors but also on the

understanding of the complex interrelationship of these technical factors

with anatomic metabolic, and functional factors. This is what makes

prosthodontics challenging. This is what makes prosthodontics fun.

62

REFERENCES

1) Lammie G.A. : Reduction of the edentulous ridges. J.P.D., 10 : 605-

611, 1960.

2) Sobolik C.F. : Alveolar bone resorption. J.P.D., 10 : 612-619, 1960.

3) Atwood D.A. : Some clinical factors related to the rate of resorption

of residual ridge. J.P.D., 12 : 411-450, 1962.

4) Ortman H.R. : Factors of bone resorption of the residual ridge.

J.P.D., 12 : 429-440, 1962.

5) Atwood D.A. : Reduction of residual ridges : A major oral disease

entity. J.P.D., 26 : 266-279, 1971.

6) Fenton D.H. : Bone resorption and prosthodontics. J.P.D., 29 : 471-

413, 1973.

7) Keisey L.L. : Alveolar bone resorption of prosthodontics. J.P.D., 25 :

152-161, 1973.

8) Neufeid J.O. : Changes in the trabecular pattern of the mandible

following the loss of teeth. J.P.D., 8 : 685-697, 1958.

9) Wyatt C.L. : The effect of prosthodontic treatment on alveolar bone

loss : A review of the literature. J.P.D., 80 : 362-364, 1998.

10) Atwood D.A. : Bone loss of edentulous alveolar ridge.

11) Kapur K.K. : The effects of complete denture on alveolar mucosa.

J.P.D., 13 : 1030, 1963.

63

12) Turck D. : A histologic comparison of the edentulous denture and

non denture bearing tissue. J.P.D., 15 : 419, 1965.

13) Pietro Kovski : The bony residual ridge in man. J.P.D., 34 : 456,

1975.

14) Enlow D.H. : The remodeling of the edentulous mandible. J.P.D.,

36 : 685, 1976.

15) Paul Mercier : Ridge reconstruction with hydroxylapatite. J. Oral

Surg., 505, 1968.

16) Baylink J.D. : Systemic factors on alveolar bone loss. J.P.D., 31 :

486, 1974.

17) Leka Jahangeri : Current perspectives in residual ridge remodeling

and its clinical implications : A review. J.P.D., 80 : 224, 1998.

18) Curtis A.T. : Autogenous bone graft procedure for atrophic

edentulous mandibles. J.P.D., 38 : 366, 1977.

19) Wendt. C.D. : The degenerative denture ridge-care and treatment.

J.P.D., 32 : 477, 1974.

20) Winkie R. : Essentials of complete denture prosthodontics.

64

CONTENTS

1) Introduction

2) Normal Alveolar Bone Physiology

3) Tooth Extraction, Wound Healing And Formation Of The

Residual Bone

4) Bone Remodelling Process

5) Histological Observation Of Residual Bone Resorption

6) Factors Affecting Residual Ridge Resorption

7) Diagnostic Aids To Defect Rrr

8) Pattern Of Bone Resorption And Anatomical Consideration

9) Clinical Significance

10) Conclusion

11) References

65

CONTENTS

Introduction Functions of Maxillofacial Structures Establishment of Vertical Maxillomandibular Relations for

Complete Dentures Methods of Determining Vertical Relation Physiological Methods Phonetics As a Guide Tests of Vertical Jaw relations with occlusion rims The speaking method The closest speaking space and the free-way space Technique with existing dentures Technique without records or dentures Phonetics in orientation of anterior teeth Labiodental Sounds Dental and alveolar sounds Palatal and velar sounds Patient adaptation in phonetics Palatal contour of the Denture Palatography for proper palatal contour Discussion Conclusion

66