There is no question that over the last two decades dental implants have revolutionized tooth replacement and the practice of dentistry. The concept of dental implants is not new, the earliest recorded attempts of their use were discovered in the Mayan civilization dating back to 600 A.D. Today’s highly successful dental implants consist of root replacement for a natural tooth, to which a crown is attached, just like the teeth in your mouth when you smile, there is no visible difference. In addition they do not decay and are relatively free from developing gum disease. As with most treatment modalities in dentistry today, this not only involves scientific discovery, research and understanding, but application in clinical practice. The practice of implant dentistry requires expertise in planning, surgical placement and crown fabrication; it is as much about art and experience as it is about science. It also requires teamwork between you, the patient, your dentist, an implant surgeon and dental technician. This is an overview article on implant dentistry, more on individual topics will follow in future issues to provide you with the knowledge you need to make informed choices together with your dental health professionals.
Teeth essentially can be thought of as having two main parts, the crown, the part above the gum tissues, and the root, the part that is suspended in the bone by the periodontal ligament (peri-around, odont-tooth) which keeps the tooth in place. A dental or endosseous implant (endo – inside, osseous – bone) is actually a root replacement, but unlike the root of a tooth it becomes anchored in the bone of the jaw, formerly occupied by a tooth or teeth. The amazing thing about currently used dental implants is that they actually fuse with, or “integrate” into the bone, a process known as “osseo-integration” (osseo-bone, integrate – to become part of). They are for the most part made of commercially pure titanium, a metallic substance used for many years in medicine and dentistry because it is not rejected by the body, being osteophilic (bone loving). The actual process of osseo-integration is essentially a biochemical fusion of living bone cells and bone substance to an oxide layer that forms on the surface of the titanium.
As with many scientific advances the discovery of osseo-integration was happily, quite by chance! In 1952, Dr. P. I. Branemark, a Swedish orthopedic surgeon was studying healing in the bones of a rabbit limb. He inserted a small optical chamber through which healing changes in the minute blood vessels of the bone could be observed. When the study was completed it was noted that the optical chamber, made of titanium had fused to the bone and could not be removed. Nearly all currently used dental implant systems in their multiple shapes and sizes utilize this magical bone loving property of titanium.
One of the many successful applications of osseo-integration has been in dentistry with the development of dental implants; root form replacements for missing teeth. Significantly, the application of implants in dentistry was researched for approximately 25 years before becoming available for clinical use in dental practice. Dental implants were first introduced for people who had lost all their teeth and who had great difficulty stabilizing or tolerating dentures, largely because they had lost so much jaw bone upon which dentures rest. Because dental implants fuse to the bone they stabilize it and prevent further bone loss. Resorption, is a normal and inevitable process in which bone is lost when it is no longer supporting or connected to teeth. Only dental implants can stop this process and preserve the bone.
Since their introduction into dental practice in the late 1970s dental implants have undergone many improvements in design. Today most implants are placed for either single or multiple tooth loss. The implants first used in the pioneering “Branemark” system were basically a one size fits all design. The original implants were all the same width, circumference, with only the length being variable. The original surfaces of the implants were machined smooth and polished. It was well known that integration is best in the densest bone, generally in the front part of the lower jaw.
Clinical use and research have led to modifications of implant design and improvements such as the following:
- Improved surface characteristics — from the initial smooth and polished surfaces to the current, acid etched sandblasted, nanotech surfaces. This technical advance significantly increases the microscopic surface area of implants and thereby markedly improves the degree of attachment to bone. This also increases the success rates of osseo-integration, even where bone quality is less dense.
- Improved shapes and sizes for different tooth size replacements — Implants are made in different widths which together with improved surface characteristics provide for maximum bone to implant contact. They can therefore more easily carry the same forces as are applied to natural teeth. For example, back molar teeth have one or more roots to withstand higher biting forces necessary for chewing. Implants have likewise been developed to mirror these functions. Teeth in different areas of the mouth are designed differently to accommodate different functions.
- Improvements in design for aesthetics — connections from implants to crowns have improved to make the teeth look perfectly natural as they emerge from the gum tissues to mimic natural teeth exactly. Materials used are essentially the same as for regular crowns to imitate natural aesthetics, function and durability. Crowns are either directly connected to the implants themselves by tiny invisible screws in the back non-visible parts of the teeth, or are cemented over little tooth like receptors just like regular crowns.
There are now more than 40 different types of what can now be termed traditional or standard implants available today. There are also two others, mini and micro-mini implants. Mini implants are like traditional implants but usually smaller in diameter where as micro-mini implants are a variation of the now more traditional implant design, but smaller, narrower and more screw like in appearance, they are more temporary in nature and designed to be easily removed.
Single tooth replacements: use one implant and as the name suggests support a single crown.
Multiple tooth replacements: multiple missing teeth can be replaced with multiple implants supporting fixed bridgework as small as a 3-unit bridge supported by two implants, or with multiple implants supporting a greater number of teeth. Usually a minimum number of 4-8 implants are needed to replace a full arch (jaw) of teeth, 10 or more crowns by fixed bridgework.
Combinations of fixed and removable bridgework: generally where implants are used to support a section of fixed bridgework, to which is attached a removable section.
Over-dentures: where two or more implants, either standard or mini-implants, are placed to provide stabilization of the denture and preserve the underlying bone. Whereas most traditional full dentures press directly on the gum and bone causing bone loss by resorption, implant supported over-dentures protect the bone. Over-dentures are now considered the standard of care by the American Dental Association for the patients who have lost all of their teeth in one or both jaws.
Anchorage for tooth movement (orthodontics): Implants, either standard, mini, or micro-mini implants, are now being used to provide very stable and non-movable anchor units to allow quicker and easier tooth movement.
Temporary bridgework: utilize micro-mini implants which are later removed when the permanent implants are healed and teeth permanently replaced. They ensure that at no time will a person be without teeth and can therefore be socially comfortable and functional.
Your dentist will select the type of implant that has been evaluated for bio-compatibility, supporting research and to provide tooth replacement.
Immediate implant placement: More recently and in the right circumstances it has become possible to remove teeth and immediately place dental implants into the sockets. The preconditions include that there is sufficient healthy bone left into which to place an implant following tooth removal, and that the socket can accommodate an implant of approximately the same size as the tooth root removed.
Immediate implant loading: Immediate “loading” refers to the ability to not only place an implant into a socket but also to place a crown on the implant simultaneously. This procedure engenders more risk and skill and can only be carried out if the situation is appropriate. One of the keys to success of this technique is to make sure that the crown of the tooth is completely free of movement. If it is not the implant will not integrate or fuse successfully to the bone. This is more difficult to achieve for single tooth replacement than it is for multiple teeth; they can be splinted or joined together, much like pickets in a fence, thereby guaranteeing rigidity.
Implants are more challenging for dental clinicians to achieve acceptable aesthetic results in highly visible areas like the front of the mouth, particularly in people who show not only teeth but the gum tissues as well. In such cases the whole tooth/gum tissue complex must be recreated including the “papillae” (the pink gum tissues that fill the triangular spaces between the teeth in health). It is here that knowledge and experience really come to the forefront with correct prior assessment and diagnosis of the situation being paramount together with knowledge of what can be achieved. Other challenges include creating or generating bone and/or gum tissues where insufficiency exists. Both of these can be accomplished in today’s world quite predictably with a variety of grafting, regenerative and plastic surgical techniques.
A collaborative team approach is necessary to correctly assess your situation and plan the right personalized treatment options for you. While implants are highly successful in the right place, they may not be for everyone or every situation. In the right situation implant success rates in the high nineties have been consistently shown by vigorous research. Even in areas of poor bone quality and amount, success albeit slightly more limited, is quite common.
There are many other types of highly successful dental tooth replacement systems, like fixed or removable bridgework. Sometimes implants can be used in combination with, or to support fixed or removable bridgework.
Implant success is critically dependant upon:
- Careful assessment, diagnosis, and understanding of the site where implant replacement is sought and how the site relates to the function of the rest of the teeth
- The judgment, clinical experience and collaborative efforts of the implant team — dentist, surgeon and technician
Once integrated and functional, implant supported crowns — complete tooth replacements can last a lifetime.