Types of Oral Implants
Over the past 20 years, Dental
Implants have undergone remarkable changes. Many clinicians designed implants to fit
certain needs and properties. Some of those designs had only a short application period,
whereas others survived to this very day. Dental implants vary in several aspects, such as
shape, place of anchorage (within the bone or on top of the bone), composition, coatings,
etc. This page will shed a little light on the different types of implants that are in use
today, categorize them and explain their most common application.
In general Oral Implants can be
categorized into three main groups:
- Endosseous Implants
- Subperiosteal Implants
- Transosseous Implants
Endosseous
Implants are implants that are surgically inserted into the jawbone.
Subperiosteal Implants
are implants, which typically lie on top of the jawbone, but underneath your gum tissues.
The important distinction is that they usually do not penetrate into the jawbone.
Transosseous Implants
are implants, which are similar in definition to Endosseous implants in that they are
surgically inserted into the jawbone. However, these implants actually penetrate the
entire jaw so that they actually emerge opposite the entry site, usually at the bottom of
the chin. This is also the site, where they are secured with a device similar to a nut and
a pressure plate. It is very similar to a nut and bolt arrangement in ordinary wood
carpentry.
Endosseous Implants are the most
frequently used implants today. They could be further categorized into several
sub-categories; based on their shape, function, surgical placement and surface treatment,
however for our purposes we will only look at several families of these implants.
Below you will see several
thumbnail pictures of implants belonging to certain categories and families. Click on any
of these individual thumbnail images and you will be linked to the area describing that
implant and its category or family:
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| Subperiosteal
Implants |
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Ramusframe
Implants |
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Blade Implants |
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Rootform
Implants |
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Transosseous
Implants |
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To the left you can see a typical
Subperiosteal implant for the lower jaw. This particular implant has a whitish-gray Hydroxyapatite coating on its bone-contacting portion. We
will discuss this coating in more detail in the Rootform Implant
section below. |
Subperiosteal Implants were
already introduced in the 1940s. Of all currently used devices, it is the type of implant
that has had the longest period of clinical application. These implants are not anchored
inside the bone, such as Endosseous Implants, but are instead shaped to ride on
the residual bony ridge of either the upper or lower jaw. They are usually not considered
to be osseointegrated implants. Subperiosteal Implants
have been used in completely edentulous (toothless) as well as partially edentulous upper
and lower jaws. However, the best results have been achieved in treatment of the
edentulous lower jaw.
Indications:
Usually a severely resorbed,
toothless lower jaw bone, which does not offer enough bone height to accommodate Rootform Implants as anchoring devices.
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The leftmost picture shows an x-ray
of a fairly resorbed lower jaw. The next
image shows the same jaw with a Subperiosteal implant in place. |
This implant is custom-made
to each individual jaw. Nowadays, a CT Scan is taken of
the jaw and a computerized modeling machine uses this data to reproduce a
three-dimensional plastic model of the jaw to be treated.
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This image shows a plastic model of
a patient's lower jaw, which was modeled using data from a CT Scan. This model is accurate to the nearest millimeter. |
This model (or a plaster
copy there of) is then used to design the individual Subperiosteal framework on, which is
then cast in metal. Sometimes a coating such as titanium or hydroxyapatite
is applied to the areas that contact the bone, in order to improve its bio-acceptability.
The implant is then sterilized and returned for surgical insertion.
After the implant has been
surgically inserted, only a bar is visible extending from one side of the lower jaw to the
other, onto which a denture can be clipped via an internal attachment mechanism. The
denture can be made approximately two weeks after the surgery and is in general smaller
than a conventional denture. This denture locks into the bar of the implant as shown
below.
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This image represents the Ramusframe
type implants. Its use will be discussed below. |
Ramusframe Implants belong
in the category of endosseous implants, although their appearance might not suggest that
at first. These implants are designed for the toothless lower jaw only and are surgically
inserted into the jaw bone in three different areas: the left and right back area of the
jaw (the approximate area of the wisdom teeth), and the chin area in the front of the
mouth. The part of the implant that is visible in the mouth after the implant is placed
looks similar to that of the Subperiosteal Implant described
above.
Indications:
Usually a severely resorbed,
toothless lower jaw bone, which does not offer enough bone height to accommodate Rootform Implants as anchoring devices. These implants are usually
indicated when the jaws are even resorbed to the point where Subperiosteal
Implants will not suffice anymore.
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Above you can see an x-ray of a severely resorbed mandible. The vertical dimension in the
mid-jaw (1st molar) area is less than 1/4 of an inch. |
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This is the same lower jaw with the implant
in place. The outlines represent the part of the implant which is embedded in bone. The
white mass you see added in is synthetic bonegraft, used to augment the ridges. |
An additional advantage that comes
with this type of implant is a tripodial stabilization of the lower jaw. A jaw as thin as
the one shown above can easily fracture at its thinnest part. The Ramusframe Implant, once
integrated (after a three month waiting period) will also stabilize and protect the jaw
somewhat from fracturing.
The Ramusframe Implant usually comes in a
standard pre-shaped form and needs to be custom-fitted to the patient’s individual
jaw dimension, as shown below:
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Above is a picture of a pre-shaped Ramusframe implant. |
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This is the same implant custom-fitted. |
Once surgically inserted, a bar,
running from one side of the jaw to the other is visible in the mouth. A denture similar
to the one shown for the Subperiosteal Implant above, can
then be attached to the bar.
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Here you can see an
image of a Ramusframe Implant in the patient's mouth immediately after surgery. Notice the
similarity to the Subperiosteal Implant. |
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Above is a picture of a blade implant
specifically designed for the back-most portion of the lower jaw. This implant offers
great anchorage in that particular area. |
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The image above shows a custom-made blade
implant specifically designed for the upper jaw. |
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In contrast, this implant was specifically
and custom-designed for the lower jaw of a patient. Notice the difference in shape to the upper-jaw
implant. These two implants also feature a Hydroxyapatite
coating. |
Each of the three implants
in that row belongs to the family of Blade Implants. However, since these are also
surgically placed into the bone we categorize them also into the Endosseous
Implant category. Blade Implants have a long track record, much longer then the Rootform Implants. Their name is derived from their flat, blade-like
(or plate-like) portion, which is the part that gets embedded into the bone.
Indications:
Blade implants are not used too
frequently any more, however they do find an application in areas where the residual bone
ridge of the jaw is either too thin (due to resorption) to place conventional Rootform Implants or certain vital anatomical structures prevent
conventional implants from being placed. Nowadays, if a certain area of the jaw bone is
too thin and has undergone resorption due to tooth loss it is recommended to undergo a Bonegrafting procedure, which re-establishes the lost bone,
so that conventional Rootform Implants can be placed.
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Here you can see an
x-ray of a blade implant in place. An important anatomical structure (mandibular nerve and
vessel canal) is outlines in black underneath. Notice how the implant was placed to avoid injury to this structure. |
Since the introduction of the Osseointegration concept and the Titanium Screw by Dr. Branemark (see History of
Dental Implants), these implants have become the most popular implants in the world
today. Rootform Implants are also categorized as endosseous implants. These implants come
in a variety of shapes, sizes, and materials and are being offered by many different
companies worldwide. Some clinicians regard them to be the Standard of Care in
Oral Implantology.
Indications:
These implants can be placed
wherever a tooth or several teeth are missing, when enough bone is available to
accommodate them. However, even if the bone volume is not sufficient to place Rootform
Implants, Bonegrafting procedures within reasonable limits
should be initiated, in order to benefit from these implants.
This family of implants has
undergone a tremendous development. They were tested and offered in different material
compositions, since isolated studies have shown that materials other than titanium may
integrate into living bone. Such materials included Aluminum Oxide, Vitallium,
Commercially Pure (CP) Titanium, Titanium Alloys, even Sapphire. Today, the most accepted
material for dental implants is high grade Titanium—either CP Titanium or an alloy thereof. The titanium alloy implants
tend to be stronger than the CP titanium implants. The bone integration shows no
difference to the two different types of titanium.
Further research eventually
introduced titanium implants with different surface treatments. Some implants have an
outer coating of Hydroxyapatite (HA). HA-coated
implants have been shown to initially integrate somewhat faster, however after a year, the
amount of bone contacting the implant surface is roughly the same as measured for the
titanium-surface implants. Other implants have their surface altered through plasma
spraying, aderchims or beading process. This was developed to increase the
surface area of the titanium implant and, thus, in theory, give them more stability. These
surface treatments were also offered as an alternative to the HA coatings, which on some
implants have shown to break loose or even dissolve after a few years.
Other variations dwell on the
shape of the Rootform implant. Some are screw-shaped, others are cylindrical, or even
cone-shaped or any combination thereof. Each implant design has its specific reason or
purpose and your doctor will make the right choice for you, based on your individual
needs.
Below are images and descriptions
of several different types of Rootform Implants.
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This is an example of a commercially pure solid
titanium screw implant. The screw shape usually offers better primary stabilization in
bone of less than ideal density. There are no surface alterations on this implant, hence
its shiny appearance. |
| To the right you can see an example of another
screw-type implant. In contrast to the one above, however, here the surface alteration
becomes apparent. This rough surface is referred to as a Plasma Sprayed Surface.
It offers an increase in surface area over the smooth surface and, thus also more
retention in the bone. Some research has also shown that initial
integration into the host bone is somewhat accelerated through that. |
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To the left is an image of a Titanium Screw
Implant with a Hydroxylapatite (HA) coating (notice the white-gray, rough surface). Beyond
an increase in surface area as compared to smooth surface implants, this surface has also
shown to have an accelerated initial integration, which makes it ideal for quick initial
post-surgical stabilization in weak bone. There is a large range in the quality of
coatings offered. HA coatings from some implant manufacturers have shown to dissolve or
break loose after a while. The surgeon has to be very careful in the selection of a proper
quality coating on an implant. |
| To the right is an image of a cylindrical-type
implant. Notice the absence of the threads. There are, however anti-rotational features,
such as grooves and holes, which prevent rotation during the healing process. This
particular implant also has an HA coating. Cylinder Implants usually require good primary
stabilization at the time of surgery. |
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To the left are two images showing two different
types of tapered, cylindrical implants. One looks like a Christmas tree with fins
projecting out to the sides; the other shows a special surface treatment consisting of
spherical titanium beads. Each of these implants was designed to fulfill a specific
purpose. As research in this field continues, we are assured to see many more shapes,
forms, materials and coatings emerge, each trying to improve upon the last designs. |
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To the left you can
see a typical Transosseous Implant. The plate on the bottom is firmly pressed against the
bottom part of the chin bone, whereas the long screw posts go through the chin
bone, all the way to the top of the jaw ridge inside the mouth. The two attachments that
will eventually protrude through the gums can be used to attach an
overdenture-type
prosthesis. |
Indications:
These implants are not in use
that much any more, because they necessitate an extraoral surgical approach to their
placement, which again translates into general anesthesia, hospitalization and higher
cost, but not necessarily higher benefits to the patient. In any case, these implants are
used in mandibles only and are secured at the lower border of the chin via bone plates.
These were originally designed to have a secure implant system, even for very resorbed
lower jaws.
The Transosseous Implants can
also be categorized into the endosseous implant category. Most clinicians nowadays
however, prefer to use one of the other mentioned implant modalities instead of the
transosseous system.
