1. Introduction

Dental Implant:

a prosthetic device of alloplastic material implanted into the oral tissues beneath the mucosal and/or periosteal layer, and/or within the bone to provide retention and support for a fixed or removable prosthesis

Implant dentistry recently had a resurgence due to the work of the Swedish Physician, P.I. Branemark. The uniqueness of Dr. Branemark's work was that he and his colleagues conducted prospective clinical trials involving thousands of implants (2,768) in hundreds of patients (371) to prove the success of their technique. Prior to his work, which began in 1966, this had not yet been done in the field of implant dentistry. Today, other implant systems also have prospective clinical trials to report their success rates.

2. History

Dental implants are not new to dentistry, and have been reported in the U.S. dental literature since 1909. They have been reported as far back as the early Egyptians, but we will not consider here those earlier reports. Implants can be of various types:

1. autoplastic, or an implant from within the same individual;
2. homoplastic, or an implant from the same species;
3. heteroplastic, or an implant from a different species;
4. alloplastic, or an implant from a nonliving material and
5. Combination, i.e., endodontic endosteal implant or the placement of an implant through an endodontically treated tooth into bone. All dental implants described below and used today are of the alloplastic variety.

One of the first implant systems was that of Greenfield, here in Boston, Massachusetts. Other innovators, such as Dag, followed. It was the Introduction of chrome alloys to dentistry in the 1930s that truly revolutionized dental implants. Here was an electrolytically passive substance that was more successful as an implant. In 1936, Veneble and Stuck demonstrated the passivity of Vitallium.

In 1939, Strock made vitallium screws in root forms for dental implants. In 1943 Germany, Dahl developed his button inserts, which are also known as intramucosal implants. These small metal buttons were incorporated into the tissue surface of a complete denture facing toward the patient's tissue. Matching holes were surgically created in the patient's denture-bearing soft tissues at diverging angles so, when the denture was inserted, the buttons engaged and improved the retention (see Figure 1). The only problem with this system was that the patient had to wear their denture all the time or the holes in their mucosa would heal, and insertion of the denture was impossible or caused ulcerations and discomfort. This system is still available today, but it is not very widely used.

Figure 1: The Dahl, button or intramucosal implant (1943)

In 1946, Goldberg and Gershkoff popularized the subperiosteal implant. (Figure 2) This implant is used in the maxilla or mandible, is placed on top of the bone but underneath the periosteum, and usually has four metal posts that project through the soft tissue into the oral cavity. These posts are used to retain a complete denture. This system does not require height of alveolar bone, since the implant is placed on the bone. The success rates for subperiosteal implants are around 90% at 5 years; 65% at 10 years. The possible risk factors are resorption, paresthesia, fracture of the mandible, and soft tissue problems. These are still in use today, but not widely used.

Figure 2: The subperiosteal implant (1946)

In 1953, Behrman and Egan reported implanting magnets in patients' jaws with an attractive magnet inside the patients' complete denture. This is no longer used. Also in 1953, Sollier and Chercheve reported the vertical transfixation implant, or staple implant as it is now known. This implant is tapped from under the anterior mandible and has three, four, five or seven pins that protrude into the mouth. These are used to retain the patient's denture or partial denture.

Figure 3: The transosteal or staple implant (1953)

In 1967, Cowland and Lewis first described the vitreous carbon implant. Poor success rates have made this implant obsolete. Others have tried to use methyl methacrylate (acrylic resin) for implants, with little success.

In 1969, Linkow reported on the use of an implant system still used today though less so: the blade implant. This implant is inserted into the bone and requires very little width of bone to be placed. A post protrudes into the oral cavity for use as an abutment. This is used mostly for partially edentulous patients. Other operators have suggested ceramics for dental implant use.

Figure 4: The blade implant (1969)

In 1970, Roberts and Roberts reported on the Ramus Frame implant. This implant inserts into the mandible in three locations: the ramus on both sides, and the anterior mandible. Running between these three sites is a bar on which a complete denture can be retained. This is still in use today, though less so.

Figure 5: The ramus frame implant (1970)

In 1981, Branemark reported on his success with his implant system, now marketed in the U.S. by Nobel Biocare, USA. Branemark is a physician who discovered his implant by accident when he tried to remove microvascular study chambers from rabbits. The titanium chambers had become incorporated into the rabbits' bone so that they could not be removed. He saw the application of this to dental implants, and coined the term osseointegration, or the apposition of bone in direct contact with an implant with no Intervening layer of connective tissue at the light microscopic level. He then designed an implant system incorporating the technique that made this possible.

Figure 6: The Branemark implant (1981)

In 1987, Kirsch developed a unique concept with his IMZ implant system by incorporating a stress-breaking element called an intramobile element to allow implant connection to natural teeth. His excellent system is also based on prospective clinical research trials. However, connecting implants to teeth is now usually discouraged.

Figure 7: The IMZ implant (1987)

A recent development has been the coating of implants with hydroxyapatite, which some feel enhances the osseointegration by allowing it to occur at a more rapid rate. Although osseointegration occurs more rapidly, there has been no evidence to support that there is better integration with hydroxyapatite over time. (See Table 1)

3. Consensus Conferences

The evolution of dental implants brought some people together at various times both to share ideas and to develop criteria for successful implants. The first major such conference was held at Harvard in June of 1978 and was cosponsored by the National Institutes of Dental Research. This brought together clinicians, researchers and teachers for the first time. The guidelines from this conference were that, to be considered successful, a dental implant should provide functional service for five years in 75 percent of the cases. The objective criteria were:

• Bone loss no greater than one-third of the vertical height of the implant
• Good occlusal balance and vertical dimension
• Gingival inflammation amenable to treatment
• Mobility of less than 1 mm in any direction
• Absence of symptoms and infection
• Absence of any damage to adjacent teeth
• Absence of paresthesia or anesthesia or violation of the mandibular canal, maxillary sinus, or floor of the nasal passage
• Healthy collagenous tissue

Researches since 1978, however, have outdated these criteria. In light of Dr. Branemark and colleagues' success rates of 90 to 91 percent in the maxilla and 96 to 98 percent in the mandible, lower success rates by other implant systems had to be reevaluated. Now, most consider Albrektsson et. al.'s criteria to be justified: 85 percent success at five years and 80 percent success at 10 years.

In 1988, NIH sponsored another symposium, which formally updated to these criteria, and gave indications for all existing implant systems. They recognized three main types of dental implant systems currently being used:

Subperiosteal:

rests on the surface of bone beneath the periosteum.

Transosteal:

mandibular bone plate (staple): penetrates the inferior border of the mandible and projects through the oral mucosa covering the edentulous ridge.

Endosseous:

embedded in the maxillary or mandibular bone and projects through the oral mucosa covering the edentulous ridge.

By these definitions, the blade, the Branemark and the IMZ implant are all endosseous. Today, most successful implants are made out of titanium. In 1986, the root form implant superceded the blade implant as the most frequently placed type of implant.

4. Other Implant Systems

There are several other companies that sell implant systems today. Some of them are:

Nobel Biocare, Inc.
(Branemark Implant and Steri-oss Implant)
777 Oakmont Lane, Suite 100
Westmont, Illinois 60559
(800) 891-9191

The Straumann Company
(ITI Implant)
One Alewife Center
Cambridge, Massachusetts 02140-2317
(617) 868-3800

3i Implant Innovations
3071 Continental Drive
West Palm Beach, Florida 33407
(407) 840-2600

Bicon Dental Implants
1153 Centre Street
Boston, Massachusetts 02130

Most also now have prospective clinical trials with success rates and failure rates although the number of years of follow-up vary. Newer implant companies having shorter study periods. All appear to be very successful.

It is difficult to be familiar with all systems. Specialists such as prosthodontists, oral and maxillofacial surgeons and periodontists often must know and use multiple systems. General dentists can decide how involved they would like to get with each system. When just starting out, it is best to contact your local surgeons and to be familiar with the implant systems they use as well as the one you learned in dental school.

5. Success Rates

The first long-term 15-year study using 895 fixtures in 130 jaws was done by the Branemark group, reporting a success rate of 78-90% in varying sites of anterior and posterior maxillae and mandible. Success rates of maxillary and mandibular implants were also investigated over a 5 to 8 year period where 99.1% success rate was observed for 334 mandibular and 84.9% of 106 maxillary implants. Due to the success rates of the endosteal root form implant, the varieties in designs, materials and concepts arose, yielding other implant systems as ITI, Bicon, and IMZ.

The following are recently reported success rates:

Smokers have lower success rates:

Irradiated patients have lower success rates:

• "In both intraoral and extraoral applications, irradiation decreased implant success rates. The amount of reduction was dependent on the location within the craniofacial skeleton. The implants placed into the irradiated anterior mandible have demonstrated an acceptable implant success rate of 94% to 100% with a minimal risk of osteoradionecrosis. Implant success rates ranged from 69% to 95% n the irradiated maxilla for intraoral applications. Extraoral applications demonstrated excellent implant success rates in the temporal bone (91% to 100%). The rates in the anterior nasal floor have varied from 50% to 100%. The implant success rates in the frontal bone decreased as the length of the studies increased (96% to 33%)." (J Prosthet Dent 79:641-7, 1998)

6. Complications

Nothing is perfect or without complications. Table 2 describes these.

Many of these complications can be avoided with careful diagnosis treatment planning, surgery and prosthetic design.

7. Nutrition and Quality of Life

Many studies have attempted to show that dental implants improve nutrition for patients. This sounds like a compelling argument: if you replace a complete denture with a fixed implant prosthesis, the patient should have better nutrition.

While in fact patients do experience psychological benefits, improved quality of life and more efficient chewing, several nutrition studies found that there was no improvement in nutrition as measured by food diaries and food frequency questionnaires.

8. References

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• Bain, C. Influences of Smoking on the Periodontium and Dental Implants. Dental Update. 24(8):328-30, Oct 1997.
• Sebring NG, Guckes AD, Li S-H, McCarthy GR. Nutritional Adequacy of Reported Intake of Edentulous Subjects Treated with Conventional or Implant Supported Mandibular Dentures. J. Prosthet Dent 74:358-363, 1995
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• Guckes AD, Brahim JS, et al. Using Endosseous Implants for Patients With Ectodermal Dysplasia. JADA 122:59-62, 1991.
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