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.

1 History
2 Procedure
3 Complementary procedures
4 Considerations
5 Success rates
6 Failure
7 Contraindications
8 The market
9 Cost
10 See also
11 External links

[edit] History

The Mayan civilisation has been shown to have used the earliest known examples of endosseous implants (implants embedded into bone), dating back over 1,350 years before the famous Per Brånemark started working with titanium. Whilst excavating Mayan burial sites in Honduras in 1931 archaeologists found a fragment of mandible of Mayan origin, dating from about 600 AD. This mandible, which is considered to be that of a woman in her twenties, had three tooth shaped pieces of shell placed into the sockets of three missing lower incisor teeth. For forty years the archaeological world considered that these shells were placed after death in a manner also observed in the ancient Egyptians. However in 1970 a Brazilian dental academic, Professor Amadeo Bobbio studied the mandibular specimen and took a series of radiographs. He noted compact bone formation around two of the implants which led him to conclude that the implants were placed during life.

In the 1950s research was being conducted at Cambridge University in England to study blood flow in vivo. These workers devised a method of constructing a chamber of titanium which was then embedded into the soft tissue of the ears of rabbits. In 1952 the Swedish orthopaedic surgeon, P I Brånemark, was interested in studying bone healing and regeneration, and adopted the Cambridge designed ‘rabbit ear chamber’ for use in the rabbit femur. Following several months of study he attempted to retrieve these expensive chambers from the rabbits and found that he was unable to remove them. Per Brånemark observed that bone had grown into such close approximity with the titanium that it effectively adhered to the metal. Brånemark carried out many further studies into this phenomenon, using both animal and human subjects, which all confirmed this unique property of titanium.

Although he had originally considered that the first work should centre on knee and hip surgery, Brånemark finally decided that the mouth was more accessible for continued clinical observations and the high rate of edentulism in the general population offered more subjects for widespread study. He termed the clinically observed adherence of bone with titanium as ‘osseointegration’. In 1965 Brånemark, who was by then the Professor of Anatomy at Gothenburg University in Sweden, placed the first titanium dental implant into a human volunteer who was a Swede named Gösta Larrson.

Over the next fourteen years Brånemark published many studies on the use of titanium in dental implantology until in 1978 he entered into a commercial partnership with the Swedish defence company, Bofors AB for the development and marketing of his dental implants. With Bofors (later to become Nobel Industries) as the parent company, Nobelpharma AB (later to be renamed Nobel Biocare) was founded in 1981 to focus on dental implantology. To the present day over 7 million Brånemark System implants have now been placed and hundreds of other companies produce dental implants.

[edit] 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 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.

[edit] Complementary procedures

Sinus lifting is a common surgical intervention nowadays. The Oral surgeon thickens the adequate part of atrophic maxilla towards the sinus with the help of bone transplantation or bone expletive substance and as a result of it we enable the implantation.

Bone replacement will be necessary in case of lack of adequately thick bone, which could hold the implant. Substances used during the process of bone replacement can be the own bone of the patient (auto transplantation) or artificially produced bone expletive substance. The intervention can be carried out in the maxilla and mandible as well.

[edit] Considerations

For dental implant procedure to work, there must be enough bone in the jaw, and the bone has to be strong enough to hold and support the implant. If there is not enough bone, be may need to be added with a procedure called bone augmentation. In addition, natural teeth and supporting tissues near where the implant will be placed must be in good health.

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 restorative dentist must first determine what type of prosthesis will be fabricated. Only then can the specific implant requirements including number, length, diameter, and thread pattern be determined. In other words, the case must be reversed engineered by the restoring dentist prior to the surgery. If bone volume or density is inadequate, a bone graft procedure must be considered first.

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.

[edit] 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.

[edit] 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.

[edit] 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 osteoporosis 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. This problem can be minimized by wearing a custom made mouthguard (such an NTI appliance) at night.

[edit] 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, Implant Direct, and Bio-Lok.

Specialists such as oral and maxillofacial surgeons or sometimes periodontists 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.

[edit] Cost

Typically in the United Kingdom a single tooth implant plus crown costs around £2000 or about $4000 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.

In Israel, this procedure (single implant) can cost as little as 5,000 NIS (£625) and in Turkey, a single implant can cost about $800.