Bone Resorbtion

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Bone resorbtion

Both skulls above are real The one on the right belonged to an elderly person who lost his

teeth many years before he died. When he was young and he had teeth, his skull used to

look like the one on the left. The first thing that jumps out at you is how thin the bone of hislower jaw is in comparison to the bone on the lower jaw of the skull on the left. But another

thing that is not so apparent is the loss of the bone in the upper jaw.

Notice that both skulls are positioned with their lower jaws mounted so that the bone of the

lower jaw is about parallel with the bone of the upper jaws. This tells you that the teeth are

together. Even the skull on the right---if it had teeth. This gives you an idea of the amountof bone that that has been lost since this man had all his teeth extracted. This is the golden

rule in dentistry:

Whenever a tooth is extracted, nature willremove the bone that used to surround it.

When the body removes any tissue, we say that it has been resorbed. Think of resorptionas the "melting" away of the bone after a tooth is extracted. The longer the tooth is missing,the less bone that remains behind. Thus, when a tooth is extracted from a young person, by

the time that person is middle aged, a great deal of bone will be missing. If our friend in the

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image on the left above had all his teeth extracted when he was 30, by the time he reachedthe age of 75, his skull might look like the image below which I have Photoshopped. Note

that without changing the relationship of the upper and lower jaws, he now looks just like

the toothless image above, on the right:

Bone that surrounds a natural tooth is calledalveolar bone. The job of the alveolar bone

is to support the teeth. Once a tooth isextracted, the alveolar bone no longer has a

purpose, and the body resorbs it. Eventually,

the resorption slows down and stops. What isleft behind is the cortical bone, a part of the

skeleton which, like the rest of the skull, may

change shape during life, but never entirely

resorbs without being rebuilt. The corticalbone is like the main beam that supports the

house.

The red ellipse highlights the symphysis of

the lower jaw. The symphysis is made of the densest bone in the human body. Thus, it

generally remains thicker than much of the other cortical bone in the jaw. The symphysisand its surrounding bone is very important to dentists who make dentures and who do

implants. It is often the only bone in the lower jaw that remains high enough to present a

ridge to support a denture.

The image below shows what the floor of the mouth may look like in a person who has been

toothless for twenty or thirty years. The low "hill" in the form of an arch is called the

residual ridge. The ridge is composed of firm gums overlying the bone of the lower jaw.The "gums" in the anterior part of the ridge (at the bottom of the picture) overlay thesymphysis. When we build a denture, it must gain support and stability from the vertical

height of the residual ridge. You can see that there isn't much vertical ridge here to helpstabilize the denture. And this is by no means the worst lower jaw we see on a regular

basis.

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The reason that I have marked the symphysis in the skull image above is to illustrate what

happens even to dense, cortical bone if there are no teeth to maintain it. You are looking atillustrations of a cross section through the middle of the symphysis. The tongue would be to

the left, and the tip of the chin would be at the lowest point of the gray outline of the bone.

The prominent point on the left of each stage illustration is the genial tubercle, which youcan feel with the tip of your tongue in the front of the floor of your

mouth. The genial tubercle is a landmark which never resorbs, since it

represents an important muscle attachment point. It also represents

the level of the soft tissue floor of the mouth. For a full explanation ofthe way the lower jaw changes after the teeth are extracted, including lots of images, click

the icon on the right.

The illustration labeled stage 1 shows the general shape of the bone when teeth are present.

Once the teeth are removed, the alveolar bone above the genial tubercle begins to resorb,

and over the years, the shape of the symphysis progresses through the stages you see here.This process happens all over both jaws, but it is most pronounced in the lower jaw. This is

the reason that so many people cannot wear their lower dentures.

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Lest anyone think that the stage diagram above is some theoretical figment of an anatomist'simagination, the two x-rays above show x-rays of two of my own patient's edentulous

symphyses. This is what an x-ray looks like when you shoot broadside to a patient's chin.

The white stringy things that you see above each ridge are their dentures, which have beenoutlined with lead foil. The shape of the dentures give a fair idea of the extent of the bone

that sticks up and is available as a ridge upon which to rest the denture. The one on the left

has retained a reasonable amount of its vertical height and represents about a stage II

symphysis. The one on the right has lost virtually all of its alveolar bone and has sufferedextensive cortical remodeling since the teeth were extracted. It represents a stage IV. The

point of bone sticking up on the left side of the symphysis of the stage IV is the genial

tubercle.

How fast does bone resorb once a tooth is extracted?

Whenever a tooth is extracted, and no interventions are planned to preserve the bone,

approximately 25% of the bone height above the base of the socket may be lost within the

first year. Within the first three years, as much as 63% of the bone height will be resorbed.The final height of the remaining ridge depends upon the depth of the original socket, and

the presence of adjacent teeth. If there are adjacent teeth present, less bone will be lost. On

the other hand, if multiple teeth are lost, then, over a period of years, bone will be lost down

to the depth of the of the original socket, and even beyond, since the cortical bone willeventually remodel.

Real world consequences of bone resorption.

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The images above are drawn by hand, but they show the real effect of the loss of the teeth.

The image to the left shows the profile of a middle age woman with a full set of teeth. The

center image shows what the patient would look like immediately after the extraction of herteeth. The image to the right shows the what the patient would look like at the same age if

the teeth had been removed about ten years before. If you have ever ridden the subway in

any large city, you have seen people with this type of deformity. They were not born that

way. They have simply lost all their teeth. Visit my page on dentures to see several moreimages of patients who have lost their teeth. Click on the image above to go to the website

of theInternational Congress of Oral Implantologistsfor more on this subject.

Socket Preservation--How the dentist can prevent the loss of bone after extractions

(For dental professionals and students)

Guided tissue regeneration--Technically, the term "guided tissue

regeneration" applies to the use of resorbable or non resorbable membranesto allow for the rebuilding of bone around periodontally involved teeth. The

same term can be applied to the use of resorbable or non resorbablemembranes with a bone graft material to prevent epithelial migration into a

socket during any form of socket preservation procedure.

Both the bone graft and the membrane act as barriers to epithelial migration,

however, the bone graft is secondary to the membrane in this respect, and in

cases in which the membrane is sufficiently supported by the patient'ssurrounding natural bone, the bone graft material may not even be

necessary. This applies mainly to small residual spaces surrounding an

implant that is placed directly into a socket immediately after an extraction.

The reason that guided tissue regeneration works is outlined below.

After a tooth is extracted, the socket fills with blood. The blood clots, and acts as a kind ofscaffold for somatic (from the body) cells to begin the work of healing the wound. Thereare essentially three types of cells that concern us here. Epithelial cells from the gingiva

(the gums), begin to creep down over and into the clot, or over the exposed bone of the

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socket if the clot is not well adhered to the socket bone. These epithelial cells come fromthe top down, and begin creating a new "skin" to heal over the socket. From the bone deep

inside the socket, two other types of cells begin working their way into the deep layers of

the clot to reshape the remaining bone, and to build new bone within the clot. Osteoclasts

are cells who's job is to break down existing bone so that it can be rebuilt to better conform

to the newly toothless environment that the bone will occupy when healed. Osteoblasts arecells which build new bone in the socket.

Thus, when a tooth is extracted, a sort of race begins to see which process "wins". The

osteoblasts and osteoclasts work from the bottom up to reshape and rebuild bone in the

socket, while the epithelial cells work their way from the top down into the socketdisplacing the clot and producing a soft tissue "scar". Bone building is called osteogenesis,

while the process of epithelial cells migrating down the walls of the socket is called

epithelialization. Under the epithelialized layer, another process begins to form tiny blood

vessels and collagen fibers throughout the blood clot. This granulation tissue thenbecomes a soft tissue scar which prevents bone from fully filling the extraction socket.

Because the body builds soft tissue much faster than bone (about a mm per day as opposedto a mm per month), the process of epithelialization and granulation often wins out, fillingthe socket from half to two thirds full of epithelialized collagen scar tissue. If the patient

gets adry socket, the socket may end up as an epithelialized hole in the surrounding bone.

Some patients are lucky and build more bone in their sockets, but many do not.

Dentists have discovered that they can prevent the epithelialization process by filling the

socket with a material which can prevent epithelial cells from migrating into the socket, andthen covering the socket with a membrane. Ideally, these materials should be resorbable

themselves, and replaced by the body's own bone. There are essentially three ways of doing

this. These three techniques have the added advantage of preventing dry sockets after the

extraction.

Socket preservation--three ways to prevent bone loss

1. Rootform ImplantsWhen a tooth is extracted, it is possible to replace it with an artificial tooth

root called animplant. Implants are generally (though not always) made

from titanium and if properly placed, bone will grow around it and actuallyattach to it, a process called osseointegration. An implant is the most

expensive form of socket preservation, but it is always considered the best

thing to do after extracting a functioning tooth since it is the closest thing to a naturaltooth replacement offered by dental science today. The implant may be placed at thetime a tooth is extracted (or if the socket bone has been preserved, it can be placed

later). The dentist drills a perfectly shaped and sized hole in the empty socket, and

screws a titanium "root" into it. This implant is then covered by suturing the gumsover it, and allowed to heal for about six months. Implants are the only

permanent way to prevent bone loss after an extraction.

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Sometimes the dentist will fill in any remaining space around the implant with bonegrafting material, and then cover the implant and the bone graft with a collagen

membrane. Between the implant itself, and the bone graft material, epithelial cells

are prevented from migrating into the socket. During the healing process, the bone

surrounding the titanium implant osseointegrates with the titanium, and the bone

graft material is removed by osteoclasts and replaced with the patient's own bone byosteoblasts. At the end of the healing period, the dentist uncovers the implant and

attaches an abutment to it. The abutment sticks up out of the gums and serves as ananchor for a crown. This combination ofimplant, abutment and crown serves as a

very firm and permanent tooth. With good hygiene, a crown/abutment placed on an

implant can last as long as a healthy natural tooth.

The popularity of rootform implants is growing at an exponential rate. It is

beginning to become popular to extract seriously damaged teeth that were formerly

restorable and replace them immediately with implants which have better long termprognoses. Implants have the additional benefit of not being susceptible to decay

like a natural tooth.

Clickhere to learn how implants are done, how long they taketo do, and how much they cost.

2. Bone GraftsBone grafts are the best non-implant form of socket preservation. Bone grafts are

very effective at preserving bone height, and they also create more bone for an

implant later on. There are three types of bone graft material.

o Xenogenic grafts are made from animal bone, mostfrequently bovine (cattle) or porcine bone. Xenograftsare processed in such a way that all organic material is

removed leaving only the hydroxyapatite component.

(hydroxyapatite is the mineral that makes natural boneand teeth hard.) The bone structure remaining is very

porous and has about the same structure as natural

bone (see image to the right). When you look at an x-

ray of normal human bone, you can see a weblike

pattern in the marrow spaces. The weblike pattern iscalled trabeculation, and it has the same general

pattern as the demineralized bovine bone that you can see on the right.

Xenogenic grafting has been shown to be one of the most effective methodsof creating bone in areas where there is none. Xegenogenic grafts are known

to be osteoconductive, which means that it supports the formation of new

bone by acting as a matrix or scaffolding for extension or apposition of newbone from existing bone (i.e. the patient's own bone). Xenografts also may

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have varying degrees ofosteoinductive potential, which means that inaddition to acting as a simple scaffolding, the graft material may actually

stimulate the patient's own mesenchymal cells to transform into osteoblasts

(bone-forming cells) hastening the replacement of the graft material with the

patient's own bone. Xenograft grafting materials are generally resorbed and

replaced entirely with the pathien's own bone.o Alloplastic grafts are made from synthetic

material such as ceramic material (bioactiveglass), tricalcium phosphate, calcium sulfate

(plaster) and hydroxyapatite, (the hard mineral

that makes up teeth and bones). The mostpopular brand of alloplast today is called

Bioplant (a highly magnified microsphere is seen

in the image to the right). It is made of very thin

microspheres of methyl methacrylate (plastic) which are perforated, andcoated inside and outside with Ca(OH)2. During healing, the osteoblasts

and osteoclasts migrate inside and between the spheres and form new bonewithin and around them. Alloplastic graft material constitutes the second of

the most popular forms of bone grafting material in dentistry. Alloplasticgrafts are known to be osteoconductive and have varying degrees of

osteoinductive potential. Alloplastic materials may, or may not be resorbed

and replaced by the patient's own bone. Plaster always resorbs, but bioactiveglass does not. When not resorbed, the material remains behind as an

implant acting as a sort of scaffolding that is surrounded by the patient's own

bone. Non-resorbable alloplastic bone grafting materials, can be used in

most oral applications, but they are especially good for permanent ridgeaugmentation procedures because the resulting bone is unlikely to further

resorb over time.o Allogeneic grafts-- Allografts are derived from human sources and are

obtained from tissue banks. They are made from freeze dried human cadaver

bone, or bone from living donors such as people undergoing total hip

replacement. The allograft is prepared by treating a section of cadaver bone

to remove all soft tissue, then texturing the bone surface to produce a patternof holes of selected size, density, and depth. It is processed in such a way

that it is well cleaned, sterile, and free of viruses. Allogenic grafting material

is osteoconductive and has a higher osteoinductive potential than xenograftsor alloplastic grafts.

o Autografts are made from the patient's own bone. Bone is taken from adonor site, such as the crest of the pelvic bone and transferred to the surgicalsite where bone is needed. An autograft is considered the gold standard inbone grafting because in addition to being osteoconductive and

osteoinductive, it is known to be osteogenic, which means thatitsupports the

formation of new bone by direct interaction with and stimulation ofosteoblasts (bone-forming cells). This phenomenon is based on the

contribution of the patient's own living cells that are contained in the graft.

Autogenous bone can promote osteogenesis, with the new bone being

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generated from endosteal osteoblasts and marrow stem cells that arecontained within the graft material. An autograft is the most predictable

grafting technique available, however it leaves a second surgical site in need

of healing which causes extra discomfort after the surgical procedure. In

dentistry, bone can sometimes be scavenged from areas adjacent to the

primary surgical site. However, since the advent of the artificial bonesubstitutes, this is rarely done today. On the other hand, whenever an

implant is placed, there is generally some bone "sawdust" in the flutes of thedrills used to create the space for the implant, and this material is often

scraped out of the drills and added to the xenograft or alloplastic grafting

material that the dentist plans to use in the grafting procedure.

The dentist mixes the bone graft granules with the patient's blood and forces it into

the socket immediately after the tooth is extracted. The mixture is held in place

either by tightly suturing the gums over the socket, or by suturing a collagenmembrane over it. Over the course of four to six months, the patient's body resorbs

the artificial bone and replaces it with his or her own. A bone graft is nearly 100%effective at preserving bone height.

3. Collagen PlugsCollagen is a component of connective tissue. The collagen used in dental procedures is

derived from bovine Achilles tendon. Collagen is a connective tissue protein which forms

fibers. It is the elastic material underlying your skin that makes it tough and rubbery. In its

pure form, collagen is not species specific. Cattle have about the same collagen as humans.

Since all other bovine organic material is removed from it during processing, the humanbody does not reject it as it would for foreign tissues. The material is supplied in the form

of a soft, fiberous "plug" in a single use sterile vial . After an extraction, the dentist places acollagen plug into the socket and sutures it in place. The sutures are removed in a week.

A collagen plug is a good deal less expensive than a bone graft, and the procedure for

placing it is easier. This procedure may preserve between 50% and 70% of the original

bone height. Unfortunately, it is a much less predictable method of socket preservation than

bone grafting.

Finally, note that the only way to permanently preserve bone

after a dental extraction is by placing a titanium implant, or byusing non-resorbable alloplastic graft materials in the site.Even well preserved socket bone will eventually resorb over a

period of many years if it is not kept in function. An implant

signals to the body that the bone is in use, and therefore necessary.

This is the body's way of saying "use it or lose it". Alloplastic graftmaterials remain in the socket as a permanent implant material and

act as a scaffolding to maintain the intervening natural bone that

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infiltrates between the alloplastic particles.

Click the image above to go to the companion page of this one. It shows the stages of

resorption of the lower jaw, and explains why granny can't wear her lower denture.

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ARTIFICIAL BONE GRAFTS: PRO

OSTEON

Many medical situations call for a bone graft. Among them are fusions of the spine,

fusions of the joints in the arms and legs, fractures, gaps in bones caused by trauma or

infection, revision joint surgery and oral/maxillofacial surgery.

Americans suffer 5.6 million fractures a year, and surgeons perform nearly half a

million bone graft operations annually. Bone grafts are second only to blood

transfusions on the list of transplanted materials.

In a typical bone graft involving a fracture, bone or synthetic material is shaped by the

surgeon to fit the affected area. It is then held in place with pins or screws that hold

the healthy bone to the implanted material.

Bone grafts provide a framework into which the host bone can regenerate and heal.

Bone cells weave into and through the porous microstructure of the implant. The

implant provides a framework to support the new tissue, blood cells and soft tissue as

they grow to connect fractured bone segments. Bone cells and living cells inside the

graft may also stimulate growth of bone and other tissue.

PRO OSTEON IMPLANT 500

Safe, strong, and cost effective bone grafts are now performed using synthetic

material known as Pro Osteon Implant 500. This substance facilitates the natural

healing process without risking the major drawbacks of previous grafting methods,

(disease transmission, biological rejection, and the additional surgery necessary to

collect the bone for grafting).

Pro Osteon Implant 500, generically called "bone void filler", is a clinically provenmaterial that has changed the way many orthopaedic surgeons do bone grafts. It is

sterile, biocompatible (meaning the bodys immune system does not reject it), and it iseasily sculpted to fill a defect in fractured bones. In some 20,000 procedures using Pro

Osteon, there has not been a single case of rejection. Pro Osteon is fully approved by

the Food and Drug Administration for metaphyseal fracture defects, which are

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typically fractures at the ends of the long bones of the arms and legs, when used with

rigid internal fixation (plates, pins, screws, etc.)

A SAFE SOLUTION FROM THE SEA

What makes this synthetic bone graft material effective? Pro Osteon mimics the

internal structure of human bone. This synthetic material is made by subjecting a

common, non-decorative form to coral to a patented chemical process which converts

the coral to hydroxyapatite, the same mineral content of human bone. The porous,

interconnected structure of the coral remains intact, providing an ideal matrix through

which new bone tissue can grow. One coral head weighting 150 - 200 pounds

provides enough material for hundreds of bone grafts.

After conversion processing, the material is no longer technically coral, but a calcium

phosphate. It retains the porous, interconnected architecture of coral, which is

compatible with human bone stucture. The material is osteoconductive, allowing bone

cells to weave into and through it.

Figure 1: Human Cancellous Bone Figure 2: Pro Osteon

Implant 500

In a typical surgical procedure using Pro Osteon on a long bone, the surgeon

determines the amount of bone graft he needs and shapes the Pro Osteon block to fit

into the damaged area. The graft area is stabilized with a metal plate, screws, or some

other form of internal fixation. This protects the bone graft area so it can grow strong

and durable.

Eventually, the Pro Osteon is replaced by bone, leaving the mended bone as strong as

it was before it was fractured. Healing rates for Pro Osteon compare favorably to

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other products. Pro Osteon needs no special storage or handling. It is simply taken

from the shelf and sculpted to fit the defect.

WHAT ABOUT OTHER PROCEDURES?

The use of Pro Osteon has several advantages over the two other, older bone graft

techniques.

AUTOGRAFT: In an autograft procedure, the bone grafts are taken fromelsewhere in the patents body, typically the pelvis. Thus, two operations must

be done. The patients benefits from having compatible, living cells at work in

the defect area.

The drawbacks, however, can be significant. Among them are chronic, oftendebilitating pain that results from the harvesting operation, blood loss, chance

of infection, and longer hospital stay and recovery time. The second surgery

also adds substantially to the financial cost. Pro Osteon was compared to

autograft in a clinical study for metaphyseal fractures, and the healing time was

the same as the autograft.

ALLOGRAFT: An allograft procedure uses bone from a cadaver. While thiseliminates the need for a second surgery, the grafted bone may be incompatible

with the host bone and ultimately rejected. Allograft also poses a slight but

troubling risk of introducing a variety of viruses, including that cause AIDS or

hepatitis, in the patient. In addition, allograft had worked inconsistently in a

variety of surgical procedures.

OTHER ALTERNATIVES: Several other synthetic graft products have beenapproved by the FDA. Both Pro Osteon and these graft materials have the same

advantages over autograft and allograft. However, only Pro Osteon provides

interconnected pores which allow the Pro Osteon material to become an

integral part of the surrounding bone.

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Artificial graft and implantation methodUnited States Patent 5662700

An intraluminal grafting system includes a hollow graft which has a proximal staple positionedproximate its proximal end and a distal staple adapted proximate its distal end. The system

includes a capsule for transporting the graft through the lumen and for positioning the proximal

end of the graft upstream in a lumen which may be a blood vessel or artery. A tube is connectedto the capsule and extends to exterior the vessel for manipulation by the user. A catheter ispositioned within the tube to extend from the cavity and through the graft to exterior the body.

The catheter has an inflatable membrane or balloon proximate the distal end thereof which is in

communication via a channel with inflation and deflation means located exterior the vessel. Withthe inflatable membrane deflated, the capsule is positioned in the lumen and manipulated to a

desired location. The inflatable membrane is manipulated by the rod away from the graft. The

force exerted by the inflatable membrane and the structure of the staples urges the staples in the

vessel wall, retaining the graft in position. The remainder of the intraluminal grafting system isthen removed from the corporeal vessel.