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 Dental Implants can be categorized into three main groups:
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 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 particular page describing that implant and its category or family:
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 trial. 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 not considered to be <osseointegrated> implants. Subperiosteal Implants have been used in completely edentulous (toothless) 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.
This implant is custom-made to the 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.
This model (or a plaster copy there off) 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 bioacceptability. 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.
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.
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 stabilized (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:
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 Bone Grafting procedure, which re-establishes the lost bone, so that conventional Rootform Implants can be placed.
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 Implant Dentistry.
Indications:
These implants can be placed wherever a tooth or several teeth are missing, and when enough bone is available to accommodate them. However, even if the bone volume is not sufficient to place Rootform Implants, Bone Grafting 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 materials, 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. Some implants have their surface roughened through a plasma spraying process or “beading”. This was developed to increase the surface area of the titanium implant and, thus, give them more stability. These surface treatments were also offered as an alternative to the HA coatings, which on some implants have shown to come off 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.
The above implants are all considered Rootform implants due to their apparent cylindrical shape. To the very left 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.
The implant to its right is also a screw implant with a "plasma-sprayed" surface. This increases the surface area on the implant and thus, the area of bone contact.
The middle implant has a special "beaded" surface, which is also believed to enhance bone contact and initial stabilization.
The two implants on the right are also Titanium Implants (one screw and one cylinder implant), however, these feature 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 been 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 proper quality.
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 above mentioned implant modalities instead of the transosseous system.
