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 Table of Contents  
PERSPECTIVE
Year : 2013  |  Volume : 4  |  Issue : 3  |  Page : 87-91

Biological aspects of dental implant; Current knowledge and perspectives in oral implantology


1 Department of Prosthodontics, Shree Bankey Bihari Dental College and Research Centre, Ghaziabad, Uttar Pradesh, India
2 Department of Orthodontics, Institute of Dental Studies and Technologies (IDST), Modinagar, Ghaziabad, India
3 Woodside Specialty Dental Clinic, 51 - 23 queens Blvd, Office 1 Dentist Woodside, NY, USA
4 Department of Periodontics, Institute of Dental Studies and Technologies (IDST), Modinagar, Ghaziabad, India

Date of Web Publication8-Aug-2013

Correspondence Address:
Meenu Goel
Department of Orthodontics, Institute of Dental Studies and Technologies (IDST), Modinagar, Ghaziabad
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2155-8213.116336

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  Abstract 

The utilization of dental implants became a scientifically accepted treatment modality for the rehabilitation of fully and partially edentulous patients. The evolution of dental implants has completely changed dentistry. Implants can offer a number of benefits, from improved esthetics, to reducing bone loss, to improving denture retention for edentulous patients. Branemark et al., was the first person to examined submerged titanium implants with a machined surface in dogs and later called this procedure as osseointegration, which is now defined as "A direct structural and functional connection between ordered, living bone and the surface of a load-bearing implant." Commercially pure titanium is recognized today as a material of choice, since it is characterized by excellent biological and also good mechanical properties. In this comprehensive review, authors have sought to explore various biological aspects of dental implant as pertinent to clinical procedure so as to provide research foundation for the establishment of suitable strategies that can assist in successful implant therapy.

Keywords: Biocompatible materials, dental implants, surface properties


How to cite this article:
Sahoo S, Goel M, Gandhi P, Saxena S. Biological aspects of dental implant; Current knowledge and perspectives in oral implantology. Dent Hypotheses 2013;4:87-91

How to cite this URL:
Sahoo S, Goel M, Gandhi P, Saxena S. Biological aspects of dental implant; Current knowledge and perspectives in oral implantology. Dent Hypotheses [serial online] 2013 [cited 2019 Aug 24];4:87-91. Available from: http://www.dentalhypotheses.com/text.asp?2013/4/3/87/116336


  Introduction Top


Dental implant is an artificial titanium fixture, which is placed surgically into the jaw bone to substitute for a missing tooth and its root(s). In the past 20 years, the utilization of dental implants became a scientifically accepted treatment modality for the rehabilitation of fully and partially edentulous patients. This progress in implant dentistry is clearly based on the principle that end osseous dental implants can be anchored in jaw bone with direct bone-implant contact. This phenomenon was first described by Branemark et al., who examined submerged titanium implants with a machined surface in dogs and later called this osseointegration. [1] Similar findings were described by Schroeder et al., in histological non-decalcified sections of non- submerged titanium implants with a titanium plasma-sprayed surface in monkeys. He termed this functional ankylosis. [2],[3]

Dental implants in their earliest known form date back to antiquity showing that ancient Egyptians used seashells, animal bones or ivory to replace missing teeth nearly 4000 years ago. The earliest known of implants within living patients is accredited to the Mayan civilization in the period around 600 A.D. However, with the fall of these civilizations the technology vanished, with the relatively modern history of dental implants actually beginning in the 1700s. The true birth of modern implantology began in the late 1950s and 1960s, when a number of clinicians were working with metals such as steel and implants of a so-called blade design, which were said to integrate by the formation of a pseudo-periodontal ligament (in truth a connective tissue capsule).

The evolution of dental implants has completely changed dentistry. As implants can offer a number of benefits, from improved esthetics, to reducing bone loss, to improving denture retention for edentulous patients. [4] Today more than 1300 types of oral implants varying in form, material, dimension, interface geometry, and surface properties are commercially available. [5] A tremendous variety of different implant shapes have been developed and clinically tested in the past 20 years. The implant shape will influence the predictability, how often osseointegration is achieved after implant insertion and how osseointegration is maintained over time under long-term functional load. Screw type implants are highly preferred in implant dentistry as offer major advantages compared with press-fit cylindrical implants. [3] In the present review, the authors has sought to explore the current concepts and guidelines available in the literature regarding biological aspects of dental implants.


  Osseointegration Top


In the early 1960s, Branemark and co-workers at the University of Gothenburg started developing a novel implant that for clinical function depends upon direct bone anchorage-termed osseointegration. [1] The first investigator to clearly demonstrate osseointegration was Schroeder from Switzerland. [2] Schroeder worked from the mid-1970s, quite independently from Branemark, with research on direct bone anchored implants. Schroeder's team used newly developed techniques to cut through undecalcified bone and implant with-out previous separation of the anchorage. [6] Other pioneering work on osseointegration was conducted at roughly the same time by the German clinical scientist Schulte (1978). [7]

Osseointegration is characterized as "a direct structural and functional connection between ordered, living bone and the surface of a load-bearing implant." Originally, it is defined as direct bone deposition on the implant surfaces, a fact also called "functional ankylosis." Osseointegration clearly belongs to the category of direct or primary healing. Osseointegration can be compared to direct fracture healing, in which the fragment ends become united by bone, without intermediate fibrous tissue or fibrocartilage formation. Osseointegration unites bone not to bone, but to an implant surface : a0 foreign material. Thus, the material plays a decisive role for the achievement of union. [3] Bone healing in osseointegration is activated by any lesion of the pre-existing bone matrix. When the matrix is exposed to extracellular fluid, non-collagenous proteins and growth factors are set free and activate bone repair. Attracted by chemotaxis, osteoprogenitor cells from the bone marrow and the endocortical and periosteal bone envelopes, migrate into the site of the lesion. They proliferate and differentiate into osteoblast precursors and osteoblasts and start bone deposition on the walls of the defect, the fragment ends, and possibly on the implant surface. At this time osteoclasts are rarely seen and apparently not involved in the process of activation. Once activated, osseointegration follows a common, biologically determined program that is subdivided into 3 stages:


  Incorporation by Woven Bone Formation Top


The primary host response after implantation is an inflammatory reaction elicited by the surgical trauma and modified by the presence of the implant. Initially, a hematoma is formed at the bone-implant interface and may play a role as a scaffold for peri-implant bone healing. The host response consists of platelet activation, migration and activation of inflammatory cells, vascularization, mesenchymal cells and osteoblast adhesion, proliferation, protein synthesis, and local factor composition. From the implant side, an oxidation of metallic implants has been observed. Osteoblasts also attach on the implant surface from day one of implant insertion. A few days after implantation, osteoblasts begin to deposit collagen matrix either in direct contact with the implant surface or directly on the early afibrillar interfacial zone comparable to cement lines, which is rich in non-collagenous proteins such as osteopontin and bone sialoprotein. [3]

The early deposition of new calcified matrix is followed by woven bone formation to ensure tissue anchorage. Peri-implantosteogenesis progresses either from the host bone toward the implant surface (distance osteogenesis) or from the implant toward to the healing bone (contact osteogenesis). [8] Woven bone is often considered as a primitive type of bone tissue and characterized by a random, felt-like orientation of its collagen fibrils, numerous, irregularly shaped osteocytes and at the beginning, a relatively low mineral density. It grows by forming a scaffold of rods and plates and thus is able to spread out into the surrounding tissue at a relatively rapid rate. The formation of the primary scaffold is coupled with the elaboration of the vascular net and results in the formation of a primary spongiosa that can bridge gaps of less than 1 mm within a couple of days. Woven bone usually starts growing from the surrounding bone toward the implant, except in narrow gaps, where it is simultaneously deposited upon the implant surface. Woven bone formation clearly dominates the scene within the first 4-6 weeks after surgery. [3]


  Adaptation of Bone Mass to Load Top


Starting in the 2 nd month, the microscopic structure of newly formed bone changes, either towards the well-known lamellar bone or toward an equally important, but less known modification called parallel-fibered bone. Parallel-fibered bone is an intermediate between woven and lamellar bone : t0 he collagen fibrils run parallel to the surface, but without a preferential orientation in that plane. This is clearly seen in polarized light : l0 amellar bone is strongly birefringent (anisotropic), and parallel-fibered bone is not (isotropic). The linear apposition rate for human lamellar bone amounts to only 1-1.5 μm/day and for parallel fibered bone it is 3-5 times larger. Both types cannot form a scaffold like woven bone, but merely grow by apposition on a preformed solid base. [3]

Adaptation of bone structure to load (bone remodeling and modeling)

Bone remodeling characterizes the last stage of osseointegration. It starts around the 3 rd month and after several weeks of increasingly high activity; it slows down again, but continues for the rest of life. In cortical as well as in cancellous bone, remodeling occurs in discrete units, often called as bone multicellular unit as proposed by Frost. Remodeling starts with osteoclastic resorption, followed by lamellar bone deposition. In cortical bone, a bone multicellular unit consists of a squad of osteoclasts (cutting cone) that form a sort of drill-head and produce a cylindrical resorption canal with a diameter equal to an osteon that is 150-200 μm. The cutting cone advances with a speed of about 50 μm/ day, and is followed by a vascular loop, accompanied by perivascular osteoprogenitor cells. About 100 μm behind the osteoclasts, the first osteoblasts line up upon the wall of the resorption canal and begin to deposit concentric layers of lamellar bone. After 2-4 months, the new osteon is completed. In the healthy skeleton, resorption and formation are coupled and balanced; thus, maintaining the skeletal mass over a longer time period. In the trabecular surface, remodeling starts with an accumulation of osteoclasts that produce an erosion cavity. Some days later, osteoblasts appear and refill the eroded space with new lamellar bone in a couple of weeks. The structural unit that results from this remodeling activity is called a lamellar packet or simply packet. [3],[6]


  Osseointegration of Dental Implants Top


In the jaw bones, the coronal part of the dental implants becomes firmly anchored within compact bone, whereas the apical segment is exposed to cancellous bone and bone marrow. [3]

Primary stability is obtained by congruency and press-fitting, which leads to direct bone-implant contact. Press fitting often causes local overload, with plastic deformation of the lamella and even fissures and microcracks. The local blood supply is disturbed by rupture and compression of vessels. The bone becomes a vascular and necrotic, but still provides stability. When screw-type implants are inserted into cortical bone, a bur is recommended with a diameter that is somewhat larger than the core of the thread. The wall of the bore-hole is then often detectable in the sections and separated from the screw thread by a 50-100 pm-wide gap. At 3 months, it is partially or completely filled by lamellar bone, formed in the second stage of osseointegration. Bone remodeling, finally replaces the avascular areas by mature living bone. Cortical remodeling substantially contributes to the increase in interface between implant and living bone that amounts to 60-70% after 15 months in this material. [3] Cancellous bone contributes much less to the primary stability as bone density is less than the cortical bone. A large compartment of implant surface is exposed to bone marrow, with its ample vascularity and abundance of precursor cells for osteoblasts. Bone-implant contact is achieved by bridging the inter trabecular marrow space by scaffolds of woven bone. Free ends of trabecula or edges and threads of the implant serve as a sort of bridgehead and narrow the span to be covered. Once established, these bony anchors are reinforced by lamellar bone and finally subjected to continuous remodeling, which improves bone quality as well as the orientation and dimension of the supporting elements [Table 1]. [3],[8]
Table 1: Factors that affects osseointegration

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  Prerequisites for Osseointegration Top


Material properties

Osseointegration requires a bioinert or bioactive material and surface configurations that are attractive for bone deposition (osteophilic). Bio inert materials do not release any harmful substances and therefore do not elicit adverse tissue reactions. Titanium is generally recognized as being bio-inert and used extensively in both dental and orthopedic surgery. It is thought to cause a favorable tissue reaction, either by establishing chemical bonds with tissue components (hydroxyapatite) or by promoting cellular activities involved in bone matrix formation. [8] Titanium is a reactive metal in air and aqueous electrolytes. It forms spontaneously a dense oxide film at its surface.

Surface properties

Dental implants with a changed surface configuration have been used for more than 30 years and have been shown to have great long-term success. [9] Chemical and physical surface properties such as ionic composition, hydrophilicity, and roughness play a major role in implant-tissue interaction. Therefore, different alterations of implant surfaces may lead to different and unique chemical as well as physical surface properties and those might lead to different changes in the bone-to-implant reaction (Junker et al., 2009). [5] Implants with such modified surfaces can be loaded at an earlier time following installation than was generally recommended for implants with a turned surface. It provided a better mechanical stability between bone and implant immediately following installation - established by a greater contact area. In addition, it provides a surface configuration that properly retained the blood clot and stimulated the bone healing process [Table 2]. [10]
Table 2: Various methods are used to alter the surface topography of dental implants. These may be subtractive or additive processes

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Transmucosal attachment

The soft-tissue seal around a dental implant provides an essential physiological and biological barrier from the external environment. Endosseous implants are introduced as artificial structures into a site, which is surgically created within mature tissues. The peri-implant tissues provide support that permits the implant to function in a masticatory capacity, which is the result of a wound healing process rather than a developmental one. The soft- and hard-tissues around the implant will react to the surgical injury in a manner that will depend on a number of factors, including the nature of the cells at the implant site, the physical and chemical nature of the implants, and the magnitude of occlusal forces applied to the implants at various stages of the healing process and later during masticatory function. The major distinguishing features between the tooth/periodontium and the implant/periimplant tissue interfaces is the absence of a true periodontal ligament and the cementum layer that anchors the principal fibers of the gingiva and periodontal ligament to the implant. Since implants lack periodontal ligament, forces may be applied to them without noticeable effect on their position within the jaw. Hence, implants can be successfully used as anchorage for orthodontic tooth movement [Table 3]. [11],[12]
Table 3: Histological difference between tooth and implant

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Osseous considerations

Proper stability can be achieved when the marginal or "apical" portion of the site harbors sufficient amounts of compact bone and when the spongious (cancellous) bone contributes with sufficient amounts of trabecula. The cortical portion of the bone wall produces the so called "press fit," namely the collapse of the vasculature. Hence, results in more tight bone implant contact. In the cortical bone region resorption of mineralized, avascular necrotic tissue must occur before new bone can form on the implant surface. In the spongious region of the site, on the other hand, woven bone formation and osseointegration occur early in the process of healing. [6]


  Conclusion Top


The goal of modern dentistry is to return patients to oral health in predictable fashion. The partial and complete edentulous patient may be unable to recover normal function, esthetics, comfort or speech with a traditional removable prosthesis. Hence, implant prove to be a useful treatment alternative. Implant-supported restorations are positioned in relation to esthetics, function, and speech, not in neutral zones of soft-tissue support. An implant stimulates the bone and maintains its dimension in a manner similar to healthy natural teeth; hence it is better than other prosthesis in concerned bone loss cases. Branemark, the pioneer of phenomena osseointegration, lead revolutionary changes in Dentistry, although Schroeder also contributed to the same phenomena and termed it "Functional Ankylosis." Since the early 1980s, experimental and clinical research has focused on the various factors that influence the osseointegration of endosseous dental implants such as material, Surface Configuration, Transmucosal Attachment and bone, and density. These efforts were in part necessary to improve implant anchorage in bone.

The titanium being bioinert is used extensively in both dental and orthopedic surgery and causes a favorable tissue reaction. The implant shape influences the predictability of osseointegration. Screwtype implants are highly preferred in implant dentistry as the implant threads improve the primary implant stability and also the threads seem to play an important role for the load transfer from the implant to the surrounding bone. The periimplant tissue acts as a physiological and biological barrier from the external environment. Histologically, both the gingival and peri-implant tissues had a well-keratinized oral epithelium, which terminated at the crest of the gingival margin, and was continuous with an intrasulcular and junctional epithelium, which faced the enamel or titanium surface. The treatment assessment of implant patient depends on different starting points. The specific aspects for implant treatment planning have to be considered during extra-and intra-oral examination. The available bone at the implant forms an important aspect in treatment planning as the deficiency at site may lead to advancement of conventional implant procedure and change in treatment planning.

 
  References Top

1.Brånemark PI, Adell R, Breine U, Hansson BO, Lindström J, Ohlsson A. Intra-osseous anchorage of dental prostheses. I. Experimental studies. Scand J Plast Reconstr Surg 1969;3:81-100.  Back to cited text no. 1
    
2.Schroeder A, Pohler O, Sutter E. Gewebereaktion auf ein Titan-Hohlzylinderimplantat mit Titan-spritzschichtoberflache. Schweiz Monatsschr Zahnheilkd 1976;86:713-27.  Back to cited text no. 2
    
3.Schenk RK, Buser D. Osseointegration: A reality. Periodontol 2000 1998;17:22-35.  Back to cited text no. 3
    
4.Sawyer GL. The business of mini implants. Dent Econ 2010;4:60-4.  Back to cited text no. 4
    
5.Junker R, Dimakis A, Thoneick M, Jansen JA. Effects of implant surface coatings and composition on bone integration: A systematic review. Clin Oral Implants Res 2009;20:185-206.  Back to cited text no. 5
[PUBMED]    
6.Albrektsson T, Berglundh T, Lindhe J. Historic background and current concepts. In: Lindhe J, Karring T, Lang NP, editors. Clinical Periodontology and Implant Dentistry. 4 th ed. Oxford: Blackwell Munksgaard; 2003. p. 809-20.  Back to cited text no. 6
    
7.d'Hoedt B, Schulte W. A comparative study of results with various endosseous implant systems. Int J Oral Maxillofac Implants 1989;4:95-105  Back to cited text no. 7
    
8.Dimitriou R, Babis GC. Biomaterial osseointegration enhancement with biophysical stimulation. J Musculoskelet Neuronal Interact 2007;7:253-65.  Back to cited text no. 8
[PUBMED]    
9.Wennerberg A, Albrektsson T, Lindhe J. Surface Topography of titanium implants. In: Lindhe J, Karring T, Lang NP, editors. Clinical Periodontology and Implant Dentistry. 4 th ed. Oxford: Blackwell Munksgaard; 2003. p. 821-28.  Back to cited text no. 9
    
10.Wennerberg A, Albrektsson T. Effects of titanium surface topography on bone integration: A systematic review. Clin Oral Implants Res 2009;20:172-84.  Back to cited text no. 10
[PUBMED]    
11.Listgarten MA. Soft and hard tissue response to endosseous dental implants. Anat Rec 1996;245:410-25.  Back to cited text no. 11
[PUBMED]    
12.Misch CE. An implant is not a tooth : a0 comparison of periodontal indices. In: Misch CE, editor. Dental Implant Prosthetics. 1 st ed. St. Louis: Mosby; 2004. p. 18-31.  Back to cited text no. 12
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3]


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