Residual Bone Resorption

7/31/2019 Residual Bone Resorption

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1) INTRODUCTION

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

(alveoli). The process of residual ridge resorption starts soon after the dentalextraction / 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

remodeling. Histologic evidence of active bone formation in the bottom of the

socket and bone 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).

The alveolar process consists of the:

a) Inner socket wall of thin, compact bone called the Alveolar bone proper

(Cribriform plate).

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

facial and lingual plates ofcompact bone. The interdental septum consists of

cancellous supporting bone enclosed within a compact border.

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.

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Continuous remodeling of the socket occurs by the action of osteoclast

and the osteoblast. Bone is resorbed in areas of pressure and formed in areas of

tension.

Vascular supply

- Blood vessels from superior and inferior alveolar artery.

- Dental arteriols through PL enter the perforation in the cribriform plate.

- Small vessels emanating from the facial and lingual compact bone also

enter the marrow and spongy bone.

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.

2) TOOTH EXTRACTION, WOUND HEALING AND FORMATION

OF THE RESIDUAL RIDGE

Remodelling of residual ridge occurs as the consequences to healing of a

significant bony and mucosal wound created by tooth extraction. Trabecular

bone formation starts from apex to crest of the 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.

Coarse, birefingement collagen fibres formed a preliminary framework

along which the trabecular and were fabricated by fibroblasts, marrow reticular

cells and osteoblasts. Trabeculae were absent where this preliminary collagenous

framework is failed to form. Subsequent remodeling of the small primary

trabeculae produced secondary trabeculae that resembled the original cancellous

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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 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 initial3


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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 collagenunrelated 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 healingextraction sockets in experimental animals by the method of RNA transfer blot

analysis and is situ hyridization.

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

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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

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 explainwhy 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

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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 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 endochondralbones and intramembranous bones are affected by the Type II collagen mutation.

Nakata reported the generation of transgenic mice harboring the

minigene of1 (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

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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 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

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may use the former process, which require the transient expression of template

collagens, including type II and IX.

3) 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 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, attachmentof 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.

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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 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, inall 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 number of

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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.

4) 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 largeropening 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.

- 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.

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- 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.

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

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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.

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.

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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.

5) 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.

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 :

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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.

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.

Wolfs 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.

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The inherent denture factors which may affect the supporting structures

include:

i. The occlusal forms of the teeth.

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, Sears

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.

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

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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 disease and senoscence. Bone

has its own specific metabolism and undergoes equivalent changes. At no timeduring 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

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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.

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 the18


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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%.

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,

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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.

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 excretionof 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 calcium20


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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:

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

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and by other mechanism and 5) A deficiency of vit. D, which may result from

poor fat absorption.

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 informationavailable, to date thus suggests that, with regard to bone resorption, estrogen

deficiency in vivo increase osteoclast numbers. Parallel with an increase in

BMUs. 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 usually found in

edentulous patient. The clinical and pathophysiologic viscos of osteoporosis has

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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 thespillover 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 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 a23


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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 ofglucose from noncarbohydrates, and may increase the calcium loss by direct

affect on calcium excretion. The prolonged use and 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 boneresorption 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

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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 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.

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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.

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 Wolfs law of Transformation.

As Wolfs 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

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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 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 the27


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residual ridge resorption. This usually happens because of impaired masticatory

efficiency and to complicate further the alveolar bone 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.

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

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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.

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.

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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 asmercury 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 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 edge30


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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 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

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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.

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 veryadvanced 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.

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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.

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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 maxillatakes 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.

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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 theinjury during surgical grafting or implantation procedures. Progressive bone loss

leaves the nerve near superior surface of the mandible.

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

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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 nerveby 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.

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 centripetal37


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(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.

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.

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Thus, following Devans 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.

- 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.

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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 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

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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 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 :

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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.

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 anteriors.

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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 relationship, both dentures consequently will

be mounted outside their original bearing areas.

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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 duringmastication 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.

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

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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, thearticulation 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 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.

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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 contour was deficient little gain could be

expected from extension techniques

Residual Bone Resorption

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