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Author: Nancy Arbree, D.D.S.

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)
Dahl, button or intramucosal implant

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)
Subperiosteal impant

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)
Transosteal or staple implant

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)
Blade implant

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)
Ramus frame implant

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)
Branemark implant

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)
IMZ implant

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)

TABLE 1 HISTORY OF DENTAL IMPLANTS
1530 Pare-transplantation
1887 Harris-lead root with platinum pin fused to porcelain crown
1890 Pajme - silver capsules with porcelain crowns
1893 Early Egyptians/pre-Colombian skull with carved stone tooth (reported by Andrews)
1905 Scholl - corrugated porcelain tooth
1909 First reports in the U.S. literature
1913 Greenfield - Boston, MA - endosseous crib of iridio-platinum
1920's Dag - variation of orthopedic screw
1921 Tompkins-implanted porcelain teeth
1930's Development of chrome alloys, modern dental implant technology and terminology
1934 Venable and Stuck described electrolytic passivity of Vitallium (cobalt-chromium alloy) in bone
1937 Adams patented a submergible, cylindrical screw implant with a rounded bottom, smooth gingival collar and healing cap
1937 Strock - vitallium screws in root form - first long term success (15 years)
1938 Skinner and Robinson - buccolingual traverse implant for denture retention
1939 Secord and Breck - bond between bone and metal described
1940 Dahl - mucosal inserts - Germany - Intramucosal or button implant (maxilla)
1940 Dahl conceived subperiosteal implant
1940's Leger - Dorez's four-piece implant
1948 Goldberg and Gershkoff - subperiosteal implant (Vitallium)
1953 Behrman and Egan - implantation of magnets
1953 Sollier, Chercheve and Small - vertical transfixation (transosteal) implant
1963 Seidenberg and Lord - vitallium thimbles
1965 Lew described the concept of "self-tapping" implants
1966 Linkow - endosseous blade-vent implants
1967 Cowland and Lewis - vitreous carbon material first described
1967 Roberts - blade implant
1968 Lam and Poon - acrylic resin root implant
1969 Hodosh, Povar and Shklar - dental polymer implant (methacrylate with or without cancellous freeze-dried calf bone)(TUSDM)
1970 Cranin and Dennison - blade implants
1970 Roberts and Roberts - ramus frame implant
1973 Voss and Wallechlager - vitreous carbon implants
1977 P.I. Branemark reported on his implant research (since 1952) and changed implant dentistry to what it is today
1979 Denissen and Groot - calcium hydroxyapatite root implants
1980 Core Vent System (now Dentsply, Inc.)
1981 Weiss and Rostoker - endosseous "fiber-metal" implant
1981 ITI dental implant system (non submerged implant system)
1982 McKinney and Koth - single-crystal sapphire endosteal dental implant
1984 Cat-scan design of subperiosteal implants (eliminated need for bone impression)
1985 Driskell/Stryker/Bicon dental implant system
1986 The year that the root form implants superseded the blade implant as "most frequently placed type of implant"
1987 Kirsch, Babbush, Mentag - IMZ implant - U.S.A.
1987 Sinus “lifts”
1988 Nerve transposition
1989 Pterygoid implants
1991 GTR
1995 Distraction osteotomies
1997 Consensus on sinus grafting

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.

3.1. Conditions for application of criteria:

  • Only osseointegrated implants should be evaluated with these criteria.
  • The criteria apply to individual endosseous implants.
  • At the time of testing, the implants must have been under a functional load.
  • Implants that are beneath the mucosa and in a state of health in relation to the surrounding bone should preferably not be included in the evaluations but reported as complications.
  • Complications of an iatrogenic nature that are not attributable to a problem with material or design should be considered separately when computing the percentage of success. This category includes such problems as impingement on the mandibular canal and intrusion into the sinus and nasal cavity.

3.2. Criteria for Success:

  • The individual unattached implant is immobile when tested clinically.
  • No evidence of implant periapical radiolucency is present as assessed on an undistorted radiograph.
  • The mean vertical bone loss is less than 0.2 mm annually after the first year of service.
  • No persistent pain, discomfort or infection is attributable to the implant.
  • The implant design does not preclude placement of a crown or a prosthesis with an appearance that is satisfactory to the patient and to the dentist.
  • By these criteria, a success rate of 85% at the end of a 5-year observation period and 80% at the end of a 10-year observation period are minimum levels for success.

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:

5.1. Branemark Implant (NobelBiocare)

  • 4% overall
  • 95%+ mandible
  • 90%+ maxilla
  • By prospective studies. (Same for IMZ and ITI)

5.2. Subperiosteal Implants

  • 5 year: 90-95%
  • 10 year: 65-78%
  • 20 year: 66%

5.3. Staples

  • 5 year: 93%
  • 10 year: 87%

5.4. Vitreous Carbon

  • 5 year: 38%

5.5. Blades

  • 5 year: 49-65-75%
  • 10 year: 50%

5.6. Ramus Frame

  • 4 year: 95%

Smokers have lower success rates:

5.7. Percentage of failures:

  • Nonsmokers: 4.76%
  • Smokers: 11.28%

5.8. Percentage of success:

  • Nonsmokers: 95%
  • Smokers: 89%

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.

TABLE 2: DESCRIPTION OF COMPLICATIONS
I. Swedish Team (Branemark, et al.)
  • Loss of bone anchorage
    • Mucoperiosteal perforation
    • Surgical trauma
  • Gingival Problems
    • Proliferative gingivitis – soft tissue problems
    • Fistula formation
  • Mechanical complications
    • Fixture fractures
    • Fracture of prostheses, gold screws, and abutment screws
II. U.C.L.A. Team (Beumer, Moy) and as reported by Zarb (1989)
  • A. Complications in Stage I Surgery
    • 1. Mental nerve damage - paresthesia
    • 2. Penetration Into a sinus (oral-antral fistula), nasal cavity, or through the inferior border of the mandible
    • 3. Excess countersink
    • 4. Thread exposure
    • 5. Eccentric drills, taps
    • 6. Stripping of threads
    • 7. Jaw fracture (mandible)
    • 8. Ecchymosis: more common in older patients
    • 9. Wound dehiscence
    • 10. Fascial space abscess submental, submandibular, Ludwig's angina
    • 11. Suture abscess
    • 12. Loose cover screw
  • B. Complications in Stage II Surgery
    • 1. Poor selection of fixture height
    • 2. Incorrect fixture placement: more than 35 degrees could not be used prosthetically. This complication is now almost obsolete due to newer abutment systems that have angulated and custom abutments
    • 3. Damaged hexagonal nut on top of fixture
    • 4. Loose abutment
    • 5. Fractured abutment screw
    • 6. Early loading by prostheses
    • 7. Poor air-flow pattern with "high-water" design
    • 8. Aspiration of instruments
    • 9. Thread exposure
    • 10. Fixture (implant) fractures
    • 11. Excess bone resorption
    • 12. Plaque/calculus formation
    • 13. Periodontal problems
    • 14. Poor selection of abutment height
  • C. Prosthetic Complications
    • 1. Insufficient space beneath the fully bone anchored prosthesis
    • 2. Abutments penetrate through alveolar mucosa (unattached tissue)
    • 3. Screw fractures: gold or abutment screws
    • 4. Acrylic resin, porcelain or metal framework fracture
    • 5. Posterior fixture failures in the maxilla
    • 6. Speech problems in the maxilla
    • 7. Cleaning difficulties
    • 8. Loose abutment screws –incidence decreased with the use of the torque control for tightening screws.

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.
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