Bone Grafting
Sinus Augmentation | Onlay Grafts
Ridge Expansions | Nerve Repositioning
This page
describes several methods of Bone Grafting. These procedures are usually necessary if
there is not enough bone available to place dental implants or if any vital anatomy is in
the way. Several modalities of Bone Grafting as they relate to Oral Implantology will be
discussed. Some of the picture links will underline these discussions with a graphic
representation of the procedure, however, these images are mostly surgical images and may
be very graphic in nature! Also, it may take considerable time to load all the images if
you are on a slower modem connection.
Why Bone Grafting?
Today, Bone Grafting procedures
have become almost an integral part of Implant Reconstruction. In many instances, a
potential implant site in the upper or lower jaw does not offer enough bone volume or
quantity to accommodate a Rootform Implant of proper size
or in the proper place. This is usually a result of bone resorption that has taken place
since one or more teeth (if not all) were lost. Bone Grafting procedures usually try to
re-establish bone dimension, which was lost due to resorption.
If you click on the button below,
you can see a succession of lower jaws undergoing several stages of resorption:
Many years ago the lack of bone
posed a considerable problem and sometimes implant placement was impossible because of
that. Today, however, we have the ability to grow bone where needed. This not
only gives us the opportunity to place implants of proper length and width (and for
Rootform Implants we always try to go for as long and wide as possible), it also
gives us a chance to restore the esthetic appearance and functionality better.
Grafting Material:
With respect to the Bone Graft
material used, we have to differentiate between several choices. All materials can be
categorized into five different categories:
- Autograft or autogenous bone graft
- Allograft or
allogenic bone graft
- Xenograft or xenogenic bone graft
- Alloplast or alloplastic bone
graft
- Growth Factors
The Autograft
is considered the Gold Standard. It is defined as tissue transplanted from one
site to another within the same individual. It is basically your very own bone taken from
a donor site and placed somewhere else in the body, into the recipient site.
The best success rates in bone grafting have been achieved with autografts, because these
are essentially living tissues with their cells intact. There is no immune reaction and
the microscopic architecture is perfectly matched. The only disadvantage of the autograft
is that it has to be harvested from a secondary site in your body, which usually means
more morbidity and a more complicated surgery, overall. For most grafting purposes
confined to Oral Implantology we can use another part of the jaw (i.e., chin or back
portions of jaw) as an acceptable donor site. This way, we stay surgically inside the
mouth and avoid any extraoral wounds and scarring. Sometimes, however, when there is not
enough bone volume available intraorally, we have to get bone from other parts of the
body, usually your hip bone or your tibia (shin) bone, since these are the most accessible
areas to get larger quantities of bone.
The Allograft
is defined as a tissue graft between individuals of the same species (i.e., humans) but of
non-identical genetic composition. The source is usually cadaver bone, which is available
in large amounts. This bone however has to undergo many different treatment sequences in
order to render it neutral to immune reactions and to avoid cross contamination of host
diseases. These treatments may include irradiation, freeze-drying, acid washing and other
chemical treatments. In the U.S. virtually all donors are being prescreened for
infectious diseases before their bone is even accepted into the tissue banks. After that
the processing of the bone would eliminate virtually any chance of cross-infection.
The Xenograft
is defined as a tissue graft between two different species (i.e. bone of bovine origin).
Tissue banks usually choose these graft materials, because it is possible to extract
larger amounts of bone with a specific microstructure (which is an important factor for
bone growth) as compared to bone from human origin.
The Alloplast
usually includes any synthetically derived graft material not (coming) from animal or
human origin. In Oral Implantology this usually includes Hydroxyapatite or any formulation
thereof.
The Growth Factors
are natural proteins found in our bodies that stimulate growth of certain tissues. With
respect to bone, genetic engineers have been able to isolate and clone Bone Morphogenic Proteins (BMPs), which have been shown to
induce tremendous bone growth in many animal and recently human clinical studies. BMPs may
very well become a potential substitute for autogenous graft material for certain
applications in the future; however, these substances still need to pass FDA approval.
Each of the bone graft materials
is usually developed with a specific purpose or advantage in mind. Some claims made by
tissue banks about a certain bone graft material may sometimes have to be taken with a grain
of salt, until independent research can verify those claims. The main purpose of
using the latter four of the above graft materials is usually to avoid a secondary surgery
for harvesting autogenous bone. Your surgeon will make a decision with respect to the
bonegraft material, based on your individual needs and the latest research in that field.
We will describe several types of
bone grafting procedures below. Each of these modalities will be discussed and
supplemented with images. If you want
to see these images, click on the Show Images buttons.
Some of these images, however, are
surgical images and very graphic in nature.
A. Sinus
Augmentations:
One of the most frequently
applied grafting procedures is the Sinus Augmentation. This procedure is restricted only
to the upper jaw.
As we get older our Para- Nasal Sinuses grow larger in volume and literally
take away valuable bone from the jaw ridge as shown below on the x-rays. This is not a
pathological condition, on the very contrary, it happens to almost every one. This process
is called Pneumatization of the Para-nasal sinuses.
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Above you can see the
para-nasal sinuses of a young patient outlined in red. Here the sinuses are not very
large. Notice the distance between the bottom of the sinus and the top of the ridge
(outlined in blue). |
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This image shows a toothless
lower jaw with two rather large sinuses (outlined in red) on each side of the nose (middle
structure). Notice that there is virtually no space left between the top of the ridge
(blue) and the bottom of the sinus (red). |
Once teeth are lost in that particular area it makes it
difficult if not impossible to place endosseous implants in that area, as you can see on
the right image above. For this particular problem a grafting method was developed to
literally raise the bottom of the sinus back up, graft bone underneath and, thus, create enough space for one or more dental implants.
Compare the two x-rays below.
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Above you can see an x-ray of
a pneumatized or very large sinus again (outlined in red). The top of the upper jaw ridge
is outlined in blue. Notice that there is virtually no room between the bottom of the
sinus and the top of the ridge to place any implants. This patient will need a Sinus
Augmentation. |
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This is the same jaw after
the Sinus Augmentation was performed and the implants placed 6 months following the
augmentation. Notice the location of bottom of the sinus (outlined in red) after the
augmentation and compare it to the image on the left. Here we created enough space for
implants of sufficient length to be placed. |
Click on the button below to see a more detailed
description with images of the Sinus Augmentation Procedure.
This procedure has been performed
successfully for over two decades now and is considered an accepted and predictable
method of bone grafting. The grafting
material being used can be of either of the above mentioned categories. Again autogenous
bone will give you the best and fastest results. However it would take a considerable
volume of bone (5cc to 10cc per side) to perform a typical sinus augmentation; usually
more than can be harvested form intraoral donor sites. Therefore, we sometimes downsize
to an allograft, alloplast or xenograft or a combination (sometimes mixed with a little
autograft) and take into account a longer maturation time. An autograft takes
approximately 4 to 6 months to mature in the sinus, an allograft, alloplast or
xenograft may take 9 months or more.
Sinus Augmentations and implant
placement can sometimes be performed as a single procedure, if enough bone between the
upper jaw ridge and the bottom of the sinus is available to stabilize the implant well. If
not enough bone is available, the Sinus Augmentation will have to be performed first, then
the graft will have to mature for several months (depending on the graft material
used). Once the graft has matured the implants can be placed.
B. Onlay Grafts:
This type of grafting procedure
is designed to re-establish bone, which has been lost in a particular area due to
resorption (which again, has been brought on by previous tooth loss in that area). For our
purposes this procedure is considered an autogenous graft procedure. A piece (or several
pieces) of autogenous bone (usually from the chin or the very back of the lower jaw) is
attached to the site with the bone deficiency. Then the area is closed up and after a
certain healing and maturing period, this piece of bone will eventually be incorporated
into the host bed and become solidly fused, so that at a later time implants can be placed
in that same area.
Larger areas of resorption will
need to be augmented with more pieces of autogenous bone. For those cases we need to go to
the patient’s hip or tibia to get more quantity of bone. This, however, is not a very
frequent occurrence, unless the patient had lost all of his or her teeth for a long period
of time (several decades) and bone resorption is very severe. At that point, however,
other implant modalities can sometimes be chosen (Subperiosteal
Implants, Ramus Frame Implants) to circumvent this
rather aggressive surgical approach.
Below you can see on a stone
model a before and after image of an area in a patient’s upper jaw
that underwent an Onlay Grafting procedure.
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The above image shows
a model of a patient's upper jaw ridge. The red line is an orienting line and shows
approximately how much ridge is missing (area between the line and the existing ridge).
The ridge should actually extend a little further out, because the upper jaw arch is
curved. |
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This is a model of the same
patient's upper jaw approximately 4 months after the Onlay Grafting was performed. Notice
how far out we brought the ridge (even beyond the red indicator line) At this point we can
go back in and place implants in an anatomically and functionally correct position and
also re-contour the ridge somewhat for better esthetics. |
If you click on the button below, you can see the entire
surgical progression of this case, but be aware of the loading times and the surgical graphic content of the material.
C. Ridge
Expansion:
C. Ridge
Expansion:
This is a technique used to
restore lost bone dimension when the jaw ridge gets too thin to place conventional Rootform Implants. This may actually not necessarily be
considered a bone grafting technique in the strictest sense as we will se below.
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Above you can see the
defect in the upper jaw ridge of this patient, due to previous tooth loss. This could have
been prevented if an implant was placed shortly after the extraction or loss of this
tooth. |
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In some instances we can use
the Ridge Expansion technique to regain the lost bone dimension and place an implant in
the proper spot for a good future prosthesis or tooth. Not only will this satisfy the
functional parameters, but also the esthetic ones. |
In this procedure, the bony ridge of the jaw is literally expanded by
mechanical means. A series of Expanders (in cross-section round or D-shaped metal
rods of successively increasing diameter) are being forced into the chosen implant site.
This is accomplished by tapping these expanders into the ridge with a surgical mallet. This will compress the inner spongy part of the
bone and, bulge out the outer cortex, if properly done. At this point an appropriate
implant can either be placed immediately into the created socket or one can place a bone
graft into it first and let it mature for a few months before placing the implant (at this
point it can actually be considered a Bone Grafting procedure since we are adding graft
material).
Click on the button below to see a series of images illustrating the Ridge Expansion
procedure.
D. Nerve
Repositioning:
This procedure is also known as
Nerve Transpositioning or Nerve Lateralization. This procedure is usually indicated when
the nerve and vessel canal inside the lower jaw is riding very high and prevents Rootform Implants of sufficient length from being placed
without injuring the canal. This procedure is limited to the lower jaw and indicated when
teeth are missing in the area of the two back molars or/and the 2nd premolar, with the
above mentioned secondary condition. Since this procedure is considered a very aggressive
approach (there is almost always some postoperative numbness of the lower lip and jaw
area, which dissipates only very slowly if ever), usually other, less aggressive options
are considered first (placement of Blade Implants etc.)
Below you see in a model what a
Nerve Repositioning entails:
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The above image shows a lower jaw and the double red
line shows the approximate location of the nerve and vessel canal (Neuro-vascular canal)
inside the bone. |
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This image shows on a model
what a Nerve Repositioning entails. A window is cut into the side of the jaw, exposing the
nerve and vessel canal. The nerve and vessels (indicated by the wire) are being
‘repositioned’ to the outside somewhat so that the implants could be placed. |
In this procedure we typically remove a cortical (outer)
section of the cheek side of the lower jawbone (as shown above) in order to expose the
nerve and vessel canal. Then we isolate the nerve and vessel bundle (neuro-vascular
bundle) in that area, and pull it out to the side a little. At precisely the same time we
place the implants while we keep traction on the neuro-vascular bundle. Then the bundle is
released and placed back over the implants. The
surgical access is re-filled with bone graft material of the surgeon’s choice and the
area is closed.
Click on the button below to see
images of a typical Nerve Repositioning procedure.
E. Miscellaneous Grafting
Procedures:
This category encompasses all
other grafting procedures. For instance, an implant is immediately placed into the socket
of an extracted tooth. Most of the time there will be a discrepancy between the implant
diameter and the diameter of the socket, which translates into a gap between the wall of
the implant and the bony wall of the socket as you can see in the picture in the FAQ
section How Many Implants Do I Need?. These gaps are
usually filled with bone grafting material (and sometimes covered with a membrane) to prevent soft tissue from growing into this
space.
Another Miscellaneous Grafting procedure would be if an implant were placed into the
bone with an exposure of threads on one of its sides. Most of the time these exposures are
grafted and covered with a membrane. While the implant
integrates in the bone the membrane will allow bone to re-model and re-grow underneath it
without letting any cells from the soft tissues disturb and possibly hinder this process.
Click on the button below to see
an example of this.
Finally when implants undergo
bone loss over time, either due to the lack of plaque control or, more importantly,
mechanical overload (a condition we refer to as Peri-Implantitis)
we can sometimes use bone regeneration and grafting techniques similar to the ones used in
modern Periodontics to restore some of the lost bone on
certain implants.
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