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Dental implant

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A dental implant is an artificial tooth root replacement and is used in prosthetic dentistry. There are several types. The most widely accepted and successful is the osseointegrated implant, based on the discovery by Professor Per-Ingvar Brånemark that titanium could be successfully incorporated into bone when osteoblasts grow on and into the rough surface of the implanted titanium. This forms a structural and functional connection between the living bone and the implant. A variation on the implant procedure is the implant-supported bridge, or implant-supported denture.

Procedure

A typical implant consists of a titanium screw, with a roughened surface. This surface is treated either by plasma spraying, etching or sandblasting to increase the integration potential of the implant. At edentulous (without teeth) jaw sites, a pilot hole is bored into the recipient bone, taking care to avoid vital structures (in particular the inferior alveolar nerve within the mandible).

This pilot hole is then expanded by using progressively wider drills. Care is taken not to damage the osteoblast cells by overheating. A cooling saline spray keeps the temperature of the bone to below 47 degrees Celsius (approximately 117 degrees Fahrenheit). The implant screw can be self-tapping, and is screwed into place at a precise torque so as not to overload the surrounding bone. Once in the bone, a cover screw is placed and the operation site is allowed to heal for a few months for integration to occur.

After some months the implant is uncovered and a healing abutment and temporary crown is placed onto the implant. This encourages the gum to grow in the right scalloped shape to approximate a natural tooth's gums and allows assessment of the final aesthetics of the restored tooth. Once this has occurred a permanent crown will be constructed and placed on the implant.

An increasingly common strategy to preserve bone and reduce treatment times includes the placement of a dental implant into a recent extraction site. In addition, immediate loading is becoming more common as success rates for this procedure are now acceptable. This can cut months off of the treatment time and in some cases a prosthetic tooth can be attached to the implants at the same time as the surgery to place the dental implants.

Considerations

In all cases, what must be addressed is the functional aspect of the final implant restoration, the final occlusion. How much force per area is being placed on the bone implant interface? Implant loads from chewing and parafunction can exceed the physio biomechanic tolerance of the implant bone interface and/or the titanium material itself, causing failure. This can be failure of the implant itself (fracture) or bone loss, a "melting" of the surrounding bone.

The architecture of the case, including the number, length, diameter, and thread pattern must be reversed engineered by the restoring dentist - not the referred to implant placing dentist.

Computer simulation software based on CAT scan data allows virtual implant surgical placement based on a barium impregnated prototype of the final prosthesis. This predicts vital anatomy, bone quality, implant characteristics, the need for bone grafting, and maximizing the implant bone surface area for the treatment case creating a high level of predictability. Computer cad/cam milled or stereo lithography based drill guides can be developed for the implant surgeon to facilitate proper implant placement based on the final prosthesis occlusion and aesthetics.

Success rates

Dental implant success is related to operator skill, quality and quantity of the bone available at the site, and also to the patient's oral hygiene. Various studies have found the 5 year success rate of implants to be between 75-95%. Patients who smoke experience significantly poorer success rates.

Failure

Failure of a dental implant is usually related to failure to osseointegrate correctly. A dental implant is considered to be a failure if it is lost, mobile or shows peri-implant bone loss of greater than one mm in the first year after implanting and greater than 0.2mm a year after that. Dental implants are not susceptible to dental caries but they can develop a periodontal condition called peri-implantitis where correct oral hygiene routines have not been followed. Risk of failure is increased in smokers. For this reason implants are frequently placed only after a patient has stopped smoking as the treatment is very expensive. More rarely, an implant may fail because of poor positioning at the time of surgery, or may be overloaded initially causing failure to integrate.

Contraindications

There are no absolute contraindications to implant dentistry, however there are some systemic, behavioral and anatomic considerations that should be considered.

Uncontrolled type II diabetes is a significant relative contraindication as healing following any type of surgical procedure is delayed due to poor peripheral blood circulation. Anatomic considerations include the volume and height of bone available. Often an ancillary procedure known as a block graft or sinus augmentation are needed to provide enough bone for successful implant placement.

There is new information about Bisphosphonates (taken for osteoprosis and certain forms of breast cancer) which put patients at a higher risk for developing a delayed healing syndrome called osteonecrosis. Implants may be contraindicated in patients who take this class of drug.[citation needed]

Bruxism (tooth clenching or grinding) is another contraindication. The forces generated during bruxism are particularly detrimental to implants while bone is healing; micromovements in the implant positioning are associated with increased rates of implant failure. Bruxism continues to pose a threat to implants throughout the life of the recipient. Natural teeth contain a periodontal ligament allowing each tooth to move and absorb shock in response to vertical and horizontal forces. Once replaced by dental implants, this ligament is lost and teeth are immovably anchored directly into the jaw bone.

The market

There are over 100 dental implant companies available on the U.S. market. Notable companies include Nobel Biocare, Straumann, 3i, Zimmer, BioHorizons, Astra Tech,Ankylos and Bio-Lok.

Specialists such as periodontists or oral and maxillofacial surgeons often play a role in the placement of implant fixtures, however these procedures are not beyond the scope of general dentists or prosthodontists. Regardless of who places the implant, it is most appropriate for either a prosthodontist or general dentist to initiate and coordinate implant service, since they can best assess the merits of this treatment against other prosthetic options.

Cost

Typically in the United Kingdom a single tooth implant plus crown costs around £2000 or about $3500 USD in the United States. Full mouth reconstructions with dental implants can start around $12,000 per arch and can approach $50,000 per arch depending on the complexity of the case.

See also

Associations and organizations

Other sources of information

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