Presently, dental implants are widely used in dentistry. The replacement of lost teeth with dental implants is an effective and acceptable treatment modality. Social recognition and acceptance of implants in dentistry has shown a dramatic increase in recent years. Implant dentistry has evolved dramatically in past few decades to reach the present status. In the following sections we shall read about the historical aspect of dental implants.
Evidence of dental implant treatment in history:
History of dental implant treatment has a centuries-long history. There are evidences available which prove that prehistoric people sought this technology. The Maya civilization has been shown to have used the earliest known examples of endosseous implants (implants embedded into bone). Archaeologists in 1931 found a fragment of female mandible of Maya origin, dating from about 600 AD. This female in her twenties had three tooth-shaped pieces of shell placed into the sockets of three missing lower incisor teeth. It was believed by the archaeologists that these shells were placed after death in a manner also observed by the ancient Egyptians. In 1970, the Brazilian dental academic professor Amadeo Bobbio studied these specimens again. He took series of radiographs of these specimens and noted that there was a compact bone formation around two of the implants which means that these were placed when the women was alive.
The use of root form implants dates back thousands of years. Evidences have shown their use in various civilizations like Chinese, Egyptians and Incas 3.
The modern era of dental implants:
Probably, the first description of the technique of modern dental implants was published by a French dentist, Maggiolo J. According to M.E. Ring, Maggiolo describes a method to implant 18-karat gold alloy, with three branches into the jawbone, and to install a porcelain crown as a superstructure in his book: â€œLe Manuel de lâ€™Art du Dentisteâ€ (1809) 4. During mid 1800â€™s Harris placed a porcelain implant in the jaw bone. The porcelain surface of the implant was made rough with the help of lead coating 4. During later half of 1800â€™s Berry constructed a root-form implant that was lead-free.
During beginning of 20th century research work on dental implants was initiated in different parts of world. Various materials like aluminium, gold, silver, red copper and nickel were used to make dental implants 5. Scholl made a root-form, porcelain implant in 1905 that consisted of corrugated structure 6.
A latticed cage design of dental implant was given by Greenfield in 1909, which was made up of iridoplatinum 7. He also introduced trephine burs to place implant. He was also the first to report dental implant failure due to infection 4. In 1937, Stock at Harvard University introduced Vitallium®, a cobalt-chromium-molybdenum alloy which was used to make implants. The fusion of titanium to bone was first reported in 1940 by Bothe et al 8 which was the beginning of research work on titanium implants. Professor Per-Ingvar BrÃ¥nemark a Swedish orthopedic surgeon in 1952 started his extensive experimental study on microscopic circulation of bone marrow healing and it was shown that titanium implants showed integration to the surrounding bone without any significant reaction to hard and soft tissue 9.
By the mid 20th century, various procedures, techniques and implant designs were introduced. Leonard I. Linkow of New York, in 1964 introduced self-tapping titanium implants. For cases advanced bone loss, Linkow later created a blade implant that eventually became the most widely used implant design in the 1970s 10. So, three type of implant designs used were: subperiosteal, transosteal and blade implants. These techniques are not used widely due to their high cost and unpredictability. Another problem is unpredictable success rate with these systems. Some of these implants functioned reasonably well for years, some began to show signs of failure shortly after insertion 11.
Dahl in Germany (1943), developed 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 patientâ€™s tissue. Matching holes were surgically created in the patientâ€™s denture-bearing soft tissues at diverging angles so, when the denture was inserted; the buttons engaged and improved the retention of the denture. The problem with this design was that the patient had to wear the denture all the time because the surgically created hole in the mucosa would heal denture insertion would be difficult or cause ulcerations in the tissue. This system is rarely used today.
Sub-periosteal dental implants:
Sub-periosteal implant placement was first described as a treatment for the atrophic mandible in 1941 when a Swedish doctor Gustav Dahl placed a metal structure below the periosteum with vertical extensions protruding through the gingiva. These implants are used in advanced alveolar bone resorption, where there may not be enough bone width or height for the more common and routinely placed type of implant: the root form implant. These implants were popularized by Goldberg and Gershkoff in 1946.
Diagrammatic representation of sub-periosteal implant metal framwork
By definition, a subperiosteal implant is a framework specifically fabricated to fit the supporting areas of the mandible or maxilla with permucosal extensions for support and attachment of a prosthesis. Initially mucoperiosteal flap were raised to take a mandibular impression. CT scans were also used to allow CAD/CAM fabrication of the framework, negating the need for impressions. In this system the framework usually rests on the mandible, with no penetration into the bone. The framework consists of permucosal extensions with or without connecting bars and struts. This implant system can be used in advanced atrophic jawbones where patient does not want to get the bone enhancement procedures to be done. 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.
Diagrammatic representation of sub-periosteal implant after mucosal coverage
Due to the high success rates in atrophic mandibles of osseointegrated implants facilitated by the placement of autogenous grafts, subperiosteal implants are no longer used.
This system is used in mandible where the implants run throughout the body of the mandible and a metallic plate is utilised beneath the chin where these implants are attached. The posts projecting in the oral cavity are used to attach removable prosthesis.
There are specific contraindications for this form of implant, including patients having had radiation therapy to the jaws and prosthodontic or esthetic considerations. Because of complexities involved in this system it is no longer used these days.
Diagrammatic representation of trans-periosteal implant
The blade form implants were used in areas where the residual bone ridge of the jaw is either too thin (due to resorption) to place conventional root form Implants or certain vital anatomical structures prevent conventional implants from being placed. When the alveolar ridge is thin, it permits tricortical anchorage 12, i.e. the implant is stabilized by press-fit in both the internal and external bone cortex, as well as the deep cortex. This condition represents the optimum to allow immediate loading with a functional provisional prosthesis.
Here, the bone was split and the blade was inserted into the bone. As the bone formation takes place, these implants get firmly embedded into the bone. Presently these implants are rarely used because we have various bone augmentation procedures with the help of which we can put endosseous root form implants successfully.
Other less popular designs include one that utilized magnet implantation. Behrman and Egan in 1953 reported implanting magnets in patientsâ€™ jaws with an attractive magnet inside the patientsâ€™ complete denture. 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.
Milestones in development of modern implant dentistry:
Concept of osseointegration:
The most important milestone in the modern implant dentistry was the introduction of concept of osseointegration. Professor Per-Ingvar BrÃ¥nemark a Swedish orthopedic surgeon is considered as the father of modern dental implantology. He is one of the pioneers within osseointegration and started developing this method in the early 1960s. In 1982 in Toronto, Canada, he presented his research that began around 15 years earlier to explain the process of Osseointegration, the biological fusion of bone to a foreign material. This foreign material was titanium. He discovered that the titanium is not rejected by the human body; rather, it is integrated into the surrounding bone tissue. This discovery was initially used to treat tooth loss through the use of dental titanium implants which is now used worldwide with great degree of success.
During his research work on rabbits, BrÃ¥nemark serendipitously discovered osseointegration of titanium optic chambers examined during vital microscopy. They found that titanium oculars placed into the lower leg bones of rabbits could not be removed from the bones after a period of healing 13. The BrÃ¥nemark system is now marketed in the U.S. by Nobel Biocare.
Another milestone was the introduction of self tapping implants by Leonard I. Linkow in 1964. He also introduced blade implants which were widely used 10.
In 1976 Dr. Andre Schroeder along with Straumann studied titanium plasma-sprayed hollow endosseous implants and histologically demonstrated the in-growth of bone on the implant surface 14. In this way the surface treatment of implants was introduced.
Immediate implant placement after tooth extraction was reported by Professor Willi Schulte of the University of TÃ¼bingen in Germany. He used vitreous carbon implants. Their research work led to the development of Frialit-2 implant 15.
During 1980â€™s the BrÃ¥nemarkâ€™s concept was widely explored and accepted. It led to further research on implant design and surface properties. Presently, we have numerous implant designs available with different surface properties providing us with one of the most promising treatment modality in dentistry.
Concept of fibrointegration:
This concept was propagated by Weiss 16. According to him there is a fibro-osseous ligament formed between the implant and the bone and this ligament can be considered as equivalent of the periodontal ligament found around natural teeth. The collagen fibers are present at the bone-implant interface and have an osteogenic effect. He advocated early loading of the implants.
Evolution of implant design:
Before we go into the details of the evolution of implant design, let us first discuss the primary requirements of an implant design. Requirements for oral implant design included:
- Maximum surface area for attachment and primary stability;
- Anchoring effect with minor surface irregularities;
- Minimum bone loss on implant site preparation;
- Minimum implant body volume.
The preliminary designed implants had a hollow implant body as a basic design concept. They were parallel in design. Early modifications in the hollow cylinder implants included transverse openings in the side walls and oblique holes at the shoulder. After animal trials, some more modifications were done to modify the design which included the double hollow body cylinder implants and implants with central post, the lower end of which was a hollow cylinder with two fenestrated hollow cylinders on the mesial and distal sides, respectively. Clinical research revealed drawbacks in these designs as under mechanical load the distribution of forces was variable.
Evolution of implant design
The screw type implant concept was based on experience in the field of orthopaedic surgery and other related research. Major advantage of this design was better biomechanical load distribution. These implants were designated as single tooth replacement implants. Other designs introduced included tapered implants and self-tapping implants. Self-tapping implants have been specifically designed for use in bones with poor quality (Type 3 and 4 bone). Presently, most implant companies offer tapered implants.
The designs on the implant surface were also modified to improve the bone to implant contact and primary stability of the implant.
Surface modifications of dental implants:
Modifying the surface of the implants is one of the most effective methods of improving the stability of the implant. Surface modifications of the implant have been shown to enhance the bone formation on its surface 17. Based on the scale of the surface features, the implant surface modification can be divided as macro-, micro- or nano sized topographies 18, 19. The implant surface can be modified by ablative/ subtractive or dditive procedures. Further information about these procedures is available in â€œDental implants: Surface modificationsâ€.
Dental implant has become one of the most widely accepted and used treatment modality in dentistry. From the time of introduction of concept of osseointegration by Professor Per-Ingvar BrÃ¥nemark, till date tremendous research work has taken place in the field of implant dentistry. Surgical techniques have been refined to help clinicians to achieve better primary stability of the implants. The present topic discussed briefly the development and evolution of implant dentistry to its present status. With this knowledge readers are advised to go through other topics like â€œDental implants: Surface modificationsâ€ and â€œDental implant components and Current concepts in implant designâ€.
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