|Year : 2015 | Volume
| Issue : 3 | Page : 6-12
Fundamentals and history of implant dentistry
Tamal Kanti Pal
Department of Periodontics, Guru Nanak Institute of Dental Sciences and Research, Kolkata, West Bengal, India
|Date of Web Publication||31-Dec-2015|
Tamal Kanti Pal
Professor and Head, Department of Periodontics, Guru Nanak Institute of Dental Sciences and Research, 157/F, Nilgunj Road, Panihati, Sodpur, Kolkata - 700 114, West Bengal
Source of Support: None, Conflict of Interest: None
| Abstract|| |
The practice of implant dentistry was not there a few decades ago It has its long historical retrospectives. The quest for rehabilitation of edentulous ridge has intrigued mankind since ancient times. The period from the time of Egyptian and Mayan civilizations to 1930s was unique when clinicians attempted to replace a missing tooth utilizing various materials. The spark of inquiry began from mid-1930s with the advent of an alloy named “vitallium;” attempts have been made to utilize this new material as an implant. Thereafter, in early 1950s, a good deal of fundamental and clinical research started taking place. These research data had given a boost to the tremendous growth of the practice of using dental implants made of vitallium that practically exploded to reach every general practitioner's clinic across the globe. Critical understanding of bone physiology, drilling protocol, implant design and surface texture, initial implant stability, single-stage implant surgery, and immediate loading of implants are the few factors based on which modern implant practice has become a predictable treatment modality for the replacement of missing teeth.
Keywords: Fibrous encapsulation, HA-coating, immediate loading, osseointegration
|How to cite this article:|
Pal TK. Fundamentals and history of implant dentistry. J Int Clin Dent Res Organ 2015;7, Suppl S1:6-12
| Introduction|| |
Loss of teeth leads to many edentulous situations. This creates many problems like loss of aesthetic look, deterioration of chewing efficiency, and problem of speech. All these three problems lead to handicapping situations. As a result, replacement of lost teeth becomes a necessity. Attempts have been made since the time of Egyptians and Mayan civilizations to reproduce a tooth-like object that can be inserted into the jaw bone. Newer innovations have led to biologically compatible materials.
| Historical Perspectives|| |
The dental implantology can be traced back to earlier civilizations [Table 1]., It can, thus, be divided into seven eras [Table 2]. The year 1937 - a remarkable period known as the “dawn of the modern era” - can be credited to Venable et al. for his role in the invention of an alloy material named vitallium, a mixture of cobalt, chromium, and molybdenum. Thereafter, in 1939, Strock  did animal experimentations using this unique metal alloy and confirmed its biocompatibility. This was a wonderful material of choice and practically dominated the world of implantology in both dental and medical fields for decades. The earlier popular form or design of the dental implant was flat or blade-like. Blade form design was introduced to utilize the narrow alveolar ridge which was undergoing resorption as this narrow ridge does not support the placement of root form implant. From 1960s till the early parts of 1980s the popularity of these dental implants reached its zenith. The significant and major contribution during this period was from a German dentist Leonard I. Linkow who earned fame for his unilateral subperiosteal implants to start with and subsequently, for his invention of blade-vent implants in 1967.
| Recognition of Implant Dentistry|| |
The research data on dental implants were practically nonexistent in 1972.,,,, The American Dental Association (ADA) took a cautious attitude toward dental implants and entitled Natellia et al. to look into the matter in regard to the feasibility of dental implants for clinical use. The report stated that “there is an obvious limited acceptance of dental implants by the profession and this is a point of international concern.” They further wrote “dental implantology has progressed in the past 20 years and has, in many respects, reached a plateau. The scope of dental implantology will be clear only when systematic experimentations and further reporting define some current conceptions.”
In 1974, the ADA recommended , that “dental endosseous implants be considered as being in the new technique phase and in need of continuing scientific inquiry…endosseous dental implants not be recommended at this time for routine clinical use.” However, in early part of 1980s, the Council on Dental Materials and Device of the ADA provisionally accepted the endosseous dental implants based on some selected criteria and cautions. In 1986, only one endosseous implant, the Biotes (Nobelpharama, Gothenburg, Sweden), was accepted by the ADA. Even up to this period, the ADA believed that there was a need for continued scientific review and recommended restricted use of them for routine clinical use. In 1988-1989, three more implant systems received provisional approval by the Council on Dental Materials and Devices; these are IMZ-Interpore Osseintegrated implant system (Interpore International, Skypark Circle, Irvine, CA92714). Oratronics Blade Implant system (Oratronics Inc Corporation, 405 Lexington Avenue, New York, NY 10174). Core Vent Implant System (Core Vent Corporation, 14821 Ventura Boulevard, Encio, CA 91436).
At this point of time, second National Institute of Health (NIH) Implant Consensus Conference was held in Bethesda (1988). From then, Food and Drug Administration exercised its control by employing extensive, rigorous, and sophisticated animal and human tests of dental implant devices prior to marketing.
The transatlantic wave of interest in implant dentistry reached many rich countries throughout the world. Among Asian countries, Japan, Hong Kong, and South Korea were the early initiators in this regard. Among the developing countries, India was no way less than Indonesia in the practice of using tooth implant. Lot of activities took place in India and Japan on the platforms of dental societies as well as societies concerning biomedical engineering, biomaterials, and artificial organs [Table 3a] and [Table 3b].
|Table 3A: Emerging era of Implantology in India (1988-1993),,,,,,,,,,,,,,,,,|
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| In Quest of an Ideal Implant Substrate|| |
For a successful implant therapy, the implant substrate material needs to be biologically acceptable by the body. Neither should it cause any deleterious effects on the body nor should the body elicit any kind of immunological resistance against it. The search for the ideal material was on ever since we came to know that leaching of element, be it in a single metal or in an alloy, takes place in our body. It was first noticed with stainless steel and subsequently with vitallium (cobalt-chromium-molybdenum) so rapidly in medical orthopedic fields that material scientists in collaboration with biologists started searching for some suitable materials that can satisfy the need of an implant clinician. A lot of laboratory research and animal tests were done in search a novel implant substrate.
In 1951, Leventhal  did a unique experiment with titanium screws on rat femoral model. After inserting the titanium screws he went on sacrificing the rats at 6, 12, 16 weeks and found that with the passage of time the screws became increasingly tight. At one specimen of 16 weeks, the screws were so tight that the femur was fractured while making an attempt to remove the screw. This study showed that the titanium can be used in bone surgery for the need of joining the fractured ends. He had not performed any experiment on jaw bone of any animal showcasing the future prospective of his research work could be applicable as dental implant. A decade later, Swedish anatomist Prof. P. I. Branemark found that titanium is an ideal metal for making dental implant as it adheres to bones.
| Osseointegration|| |
1952 onwards, Prof P. I. Branemark  and his coworkers, at Goteborg, Sweden, were doing research on vital microcirculation of blood in mammalian hard tissues especially on fibular model of rabbit. They also started experiments with commercially pure titanium (cp Titanium) fixtures in root form in early 1960s. They made titanium screws and implanted them in dog's jaw bone and allowed to heal for a prolonged period of time under gingiva. Interestingly, it was observed that all the titanium screws older than 16 weeks were fastened to the dog jaw bones to the extent that the dogs weighing 20-25 kg were demonstrated to be suspended through tying a single implant with a metallic wire. It was so fascinating and convincing that the world of implantology took its right turn leaving aside the case reports on personal experiences or clinical observations only. The work of Branemark et al., was published in 1969. They scientifically proved that it was possible to establish a direct bone-to-titanium contact at optical microscopic level. Schroeder et al. in 1976 (English version in 1981) confirmed also this nature of interface on undecalcified ground sections. Branemark et al. in 1985 coined a new term “osseointegration” for this unique interface and defined as “a direct structural and functional connection between ordered, living bone and the surface of a load carrying implant” [Figure 1].
|Figure 1: scanning electron microscopic view of the implant-bone interface|
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Since then, titanium and its various alloys have been in use in the dental implant industry. It has got a strong affinity to react with oxygen and form an oxide layer (TiO, TiO2, TiO3) over the surface within milliseconds. This oxide layer, a kind of ceramic in nature, covers the metal and restrict its interactions with peripheral surroundings; it nevertheless protects the subjacent metal body in many ways from corrosion due to external reasons. This has given an extraordinarily unique characteristic of titanium in terms of its extensive clinical use. Many other materials that are known to be biologically inert were also tested. Among them, ceramics and carbon are worth mentioning. Many workers have used these materials as implant substrates but because of physical, mechanical, chemical, electrical differences these materials could not be permanently considered as an implant material. Above all inertness, thermal conductivity, modulus of elasticity, brittleness, and surface reactions to bond with bone are few notable differences. High-density polymers were also tried but their relative low strength and high ductility did not allow them to be considered as an implant material.
| Implant Surface|| |
Branemark worked with smooth polished surface and showed how beautifully implant-bone interface can be made if proper surgical protocol is followed. The interface that he termed “osseointegration” has been challenged by some other workers in the Netherlands. Researchers have raised questions about the status of osseointegration as an ideal titanium–bone interface. The union referred to as osseointegration between the bone and the implant is a kind of a tight junction that is not a chemically bonded one. The best interface, perhaps, would be when two bone ends join each other. Experimentally, the same can be seen in case the bone is subjected to physical trauma (osteotomy induced) and the healing takes place uneventful [Figure 2]. Employing various modern techniques, it was revealed that there exist up to 100 Å noncellular and noncollagenous proteins like fibronectin, laminin, and osteonectin at osseointegrated interface., The presence of these substances should not be regarded as ideal union with implant to its neighboring bone. Meanwhile the unique biocompatibility and bonding characteristics of calcium hydroxyapatite (HA) to bone were revealed by many researchers , and there have been many reports documenting the ability of HA-coating of implant to bond with bone., This bonding possesses a chemical fixation between the implant and the bone; the new bone is deposited directly onto the surface of implant coating, thus making the implant fixed with the surrounding bone. The chemical nature of bonding of implant to the bone can be attributed by means of coating the surface of titanium with calcium HA. Accordingly, de Groot et al. in 1987 reported a technique of plasma spraying of HA to deposit a thin (in µm) and dense layer onto the surface of titanium substrate [Figure 3]. Bond strength of such apatite coating with the substrate as well as the influence of coating process on fatigue properties of the substrate were measured,. Animal studies showed similar favorable histological reactions to apatite coatings. Pal et al. (1993), investigated the same contention through rabbit transcortical femoral model. They utilized calcium HA developed from extracted human teeth, and prepared the plasma-sprayed HA-coated titanium screws (size = 1.6 mm diameter × 4 mm length) [Figure 4]. Surgically these screws were inserted into rabbit femur bone and after various time intervals these specimens were sectioned parallel to long axis to implants (hemisection) while the implants were seated into bone with special microtome. Optical microscopy revealed the chemical bonding of HA coating (of implant) to the surrounding bone after 12 weeks and 16 weeks [Figure 5]. This kind of interface was given a name “osseocoalescence” or “biointegration” by Daculsi (1990). The predictable early healing of such HA-coated implant was faster than that of machined smooth implants and the finite element computer modeling was conducive to bone physiology [Figure 6]. The HA-coated titanium dental implant system gained popularity for its faster bony adaptation, absence of fibrous tissue seams, firmer implant bone attachment, reduced healing time, and increased tolerance of surgical inaccuracies and inhibition of metal ion release., Later, Pal and Pal (1993, 1995), had given clinical trial of HA-coated cp titanium dental implants to many edentulous patients spanning from 1992 to 1996, and the clinical report of 25 years of HA-coated titanium implant survival is awaiting. However, there have been reviews made by Kido and Saha (1996) on its microbiological susceptibility, resorption, fatigue and fracture in long-term applications. Clinical research has portrayed the main problem associated with porous surface: The bacterial colonization. In recent days, HA coating is imparted on the apical and middle part of the implant leaving the cervical third of the body in order to avoid bacterial contaminations from implant-gingival junction.
|Figure 2: scanning electron photomicrographs of (a) 12 weeks subperiosteal osteotomy wound surface of a rabbit femur showing joining of a new bone with the wound margin (arrow). (b) note the formation of new trabeculae (double arrows) 2 mm below the cortical surface|
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|Figure 3: scanning electron microscopic view of the smooth surface of titanium (a) and after coating with HA (b)|
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|Figure 4: scanning electron microscopic view of HA-coated cp titanium screw (size = 1.6 mm × 4 mm) suitable for rabbit femur as per the american society for testing and materials (ASTM)|
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|Figure 5: optical microphotograph of interface of HA-coated titanium implant (Ti) and bone (B). note HA-coating (HA) is intimately bonded to bone (red arrow). the haematoxylin (violet) stain occupies the space between implant and HA-coating created through tissue processing|
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|Figure 6: finite element modeling of alveolar housing for implant shows overall area is free from stress concentration except at the entry point of implant in the cortical bone|
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| Paradigm Shift in Protocol|| |
The surgical implant protocol, based on the fact that the nature had to be imitated as closely as possible, was mainly followed by blade implant systems. The procedure utilizes a high-speed drilling for making bone channels to accommodate the blades. The high speed itself disrespect the bone cells (osteocytes) and eventually all bone cells would be charred and ultimately die. This gives an enormous insult to bone as a whole and a heavy task to manage the load of dead tissue debris from around the implant by the macrophages. The clearance of the periimplant area all through the length of implant creates a significant gap that leads to a certain degree of clinical mobility. All these sequential events do not allow new bone cells (osteoblast) to form satisfactorily from the traumatized bone wall and will not deliberately promote new bone formations. This phenomenon of formation of fibrous interface between implant and bone was desired by the then implant clinicians led by Linkow. This was how he used to claim that the fibrous interface mimics periodontal ligament and this fibrous encapsulation acts as a shock absorber and protects the implant from occlusal overload. The periodontal ligament is a highly specialized tissue in terms of its orientations, innervations, and vascularizations. The fibers of a periodontal ligament are aligned perpendicular to the root surface (commonly described as the long axis of tooth), whereas in implants, these are arranged in parallel to the implant surface. Moreover, innervations and vascularization in these fibers are very poor. These implants, thus, was not a recommended subject in any of the university courses and curriculum throughout the world.
In the pre-Branemark era (1978-1998), the implants were used to be loaded following surgical insertion with a view to generate some amount of occlusal force to play at implant-bone junction. This would initiate the formation of fibrous tissue around the implant. The procedure put forward by Branemark et al. was entirely opposite to the technique prevalent at that time. On the contrary, they advocated a long delay of loading implant for 3-8 months and allowing it to heal under gingiva that would not allow fibrous tissue to form around the implant. They also emphasized the fact that the growth of fibrous tissue at the implant-bone interface was deleterious as it magnified the harmful effects of stresses that were generated at the implant-bone interface.
With the advent of a new concept of bone-implant interface, established by Branemark et al. through an evidence-based human clinical trial, the old concept gradually started to wear off. The new critically analyzed documentary reports encompassing highest ever sample size at that point of time raised a vibrant wave of interest and excitement among general dental surgeons for starting dental implant practice at their private clinics. The conceptual shift of paradigm from fibrous encapsulation around the implant to direct implant-bone contact has been well-understood by the professionals. Practically all dental clinicians then started switching over to the new era of implant dentistry. The protocol of Branemark, though very strict and rigid, was appreciated by and large in the late 1980s and 1990s in order to tender a predictable treatment modality to our edentulous patients. The implant dentistry, thus, became an easy solution for a problem of edentulousness.
A couple of clinical points were highlighted “in the studies of Branemark's technique”. The biggest being the two stages of surgeries to allow the implant to completely heal in an environment of no mechanical and microbial disturbances. The aseptic/sterile surgical protocol brings about the assurance of noninfection of the operative procedure during insertion. The skilled low rotary speed with profuse cold irrigation for osteotomy ensures atraumatic bone drilling and respects all the bone cells. This is also one of the greatest contributory factors of predictable healing. The only delay of at least 3-8 months before implant loading and, of course, the second surgery to uncover the implant top, have been, somehow, not appreciated both by clinicians and patients by and large.
| Changes in Clinical Protocol|| |
The facts that two NIH consensus conferences on dental implants were held for a period of 10 years indicate how much priority was given to this treatment modality. The clinical world of implantology was sailing smoothly on the concept of Branemark's implant strategy. But in 1997, Dr. Serge Szmukler-Moncler won the first prize for his research work on immediate implant loading at the meeting of the European Association for Osseointegration. Same year in November, Prof. G. Favero and Prof. A Piattelli organized the world convention exclusively focussed on immediate loading for one day and a half in Venice, Greece. About 300 delegates from around the world participated in this conference  and witnessed the introduction of a newer implant technique where a mandatory waiting for submerged implant healing was not a necessity. The initial stability is a primary prerequisite; the stability is attributed through the strength of coronal part of the alveolar bone where more of the thick trabecular bone are present compared to the middle and apical thirds [Figure 7]. It is the clinician's duty to see that the trabeculae are made engaged for tight contact of implant body by judicious and precised drilling protocol.
|Figure 7: optical photomicrographs of vertical sections of human cadaveric alveolar bone to show the width of trabecular bone at various levels of coronal, middle, and apical thirds. note that the trabecular width decreases toward apical direction with concomitant increase of marrow spaces|
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In 1998, the first review of the literature on immediate loading implants was published. The next year, Prof. Branemark, the father of osseointegration, overturned his recommendations for immediate loading by publishing his first paper on immediately loaded mandibular implants.,,
With these understandings of fundamentals on dental implantology, the practice of dental implants is in full swing among the dentists, and this predictable treatment modality has now become a routine treatment procedure in our day-to-day clinical practices for the management of the problem of missing teeth.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2], [Table 3a], [Table 3b]
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