|Year : 2015 | Volume
| Issue : 3 | Page : 34-39
Current concepts of regenerative biomaterials in implant dentistry
Annapurna Ahuja1, Vipin Ahuja2, Kumar Saurav Singh1
1 Department of Periodontics, ITS Dental College, Greater Noida, Uttar Pradesh, India
2 Department of Pedodontics, Manav Rachna Dental College, Faridabad, Haryana, India
|Date of Web Publication||31-Dec-2015|
House no: 204, Dental Panecia, Sector 21-C, Faridabad, Haryana 121001
Source of Support: None, Conflict of Interest: None
| Abstract|| |
The primary objective of any implant system is to achieve firm fixation to the bone and this could be influenced by biomechanical as well as biomaterial selection. An array of materials is used in the replacement of missing teeth through implantation. The appropriate selection of biomaterials directly influences the clinical success and longevity of implants. Thus the clinician needs to have adequate knowledge of the various biomaterials and their properties for their judicious selection and application in his/her clinical practice. The recent materials such as bioceramics and composite biomaterials that are under consideration and investigation have a promising future. For optimal performance, implant biomaterials should have suitable mechanical strength, biocompatibility, and structural biostability in the physiological environment. This article reviews the various implant biomaterials and their ease of use in implant dentistry.
Keywords: Bioceramics, bone graft, implant biomaterials
|How to cite this article:|
Ahuja A, Ahuja V, Singh KS. Current concepts of regenerative biomaterials in implant dentistry. J Int Clin Dent Res Organ 2015;7, Suppl S1:34-9
|How to cite this URL:|
Ahuja A, Ahuja V, Singh KS. Current concepts of regenerative biomaterials in implant dentistry. J Int Clin Dent Res Organ [serial online] 2015 [cited 2019 Dec 5];7, Suppl S1:34-9. Available from: http://www.jicdro.org/text.asp?2015/7/3/34/172943
| Introduction|| |
The replacement of missing teeth with various materials dates back to the ancient period, in the Greek and Egyptian civilizations, where bone, carved ivory, shells, metal, and even animal teeth were used. Many materials were introduced later, but unpredictable failures occurred with them due to the lack of firm attachment. In 1952, Dr. Perr Ingvar Branemark developed a threaded implant design made of pure titanium that showed direct contact with bone. This phenomenon was called osseointegration, defined by the American Academy of Implant Dentistry as “the firm, direct and lasting biological attachment of a metallic implant to vital bone with no intervening connective tissue.” With the emerging concept of osseointegration, devices were designed to mimic, as much as possible, cell interactions that normally take place during bone remodeling. Currently, the implant materials available are diverse. The biomaterials discipline has evolved significantly over the past decades. The goal of biomaterials research has been and continues to be to develop implant materials that induce predictable, control-guided, and rapid healing of both hard and soft interfacial tissues.
Biomaterial by definition is “a non-drug substance suitable for inclusion in systems which augment or replace the function of bodily tissues or organs.” From as early as a century ago, artificial materials and devices have been developed to a point where they can replace various components of the human body. These materials are capable of being in contact with bodily fluids and tissues for prolonged periods of time, while eliciting little if any adverse reaction.
In a practical sense, biomaterials are synthetic polymers, metals, ceramics, and natural macromolecules, that is, biopolymers, which are manufactured or processed to be suitable for use in or as a medical device that comes into intimate contact with proteins, cells, tissues, organs, and organ systems.
Classification of biomaterials on the basis of tissue reaction
In general, there are three terms by which a biomaterial may be described or classified, representing the tissue's responses. These are:
- Bioactive (well-covered in a range of excellent review papers)
The term “bioinert” refers to any material that, once placed in the human body, has minimal interaction with its surrounding tissue. Examples of this kind of material are stainless steel, titanium, alumina, partially stabilized zirconium, and ultra-high-molecular-weight polyethylene. Generally a fibrous capsule might form around a bioinert implant, hence its biofunctionality relies on tissue integration through the implant.
”Bioactive” refers to a material that on being placed within the human body interacts with the surrounding bone and even, in some cases, soft tissue. This occurs through a time-dependent kinetic modification of the surface, triggered by implantation within the living bone. An ion-exchange reaction between the bioactive implant and surrounding body fluids results in the formation of a biologically active carbonate apatite (CHAp) layer on the implant that is chemically and crystallographically equivalent to the mineral phase in bone. Prime examples of these materials are synthetic hydroxyapatite [Ca10(PO4)6(OH)2 or HA], apatite-wollastonite glass ceramic (A-W GC), and bioglass ®.
”Bioresorbable” refers to a material that on placement within the human body starts to dissolve (i.e., is resorbed) and is slowly replaced by advancing tissue (such as bone). Common examples of bioresorbable materials are tricalcium phosphate [Ca3(PO4)2 or TCP] and polylactic-polyglycolic acid copolymers. Calcium oxide, calcium carbonate, and gypsum are other common materials that have been utilized in the last three decades.
Classification of biomaterials:
- For bone regeneration: bone grafts and guided bone regeneration membranes (GBR) [Table 2]
- For enhanced osseointegration: implant surface coatings [Table 3]
Bone graft as biomaterial for dental implant
Bone grafts are the materials used for replacement or augmentation of the bone [Figure 1], [Table 1].
Autogenous bone is derived from the individual for whom the graft is intended. It has long been considered the gold standard for biomaterials applied in bone repair. It consists of two components. The first is a natural anatomical structure for scaffolding cellular invasion and for graft and host site support. The second offers a component of primarily type I collagen that provides pathways for vascularity and resilience. The vitality of such grafts may vary in their duration, some lasting a shorter duration than desired. Such grafts are harvested from the surgical patient, from whom a second surgical wound site must be used. The use of autogenous bone, however, offers the promise of high levels of success while avoiding the possibilities of antigenicity , [Figure 2].
|Figure 2: classification of autogenous bone grafts based on region of procurement|
Click here to view
Bone grafts are harvested from one individual for transplantation in another of the same species as the host. There are three main classifications:
- Freeze-dried; and
- Freeze-dried, demineralized.
They come in different forms: Particulate, gels, and putties. A major advantage of the use of bone grafts is that the material is readily available, without the requirement of a secondary surgical site. They provide a source of type I collagen, which is the sole organic component of bone. However, they do not produce the inorganic calcium or scaffolding necessary for bone regeneration. Allographic bone must be processed to guarantee safety.,
According to various literature synthetic graft material function predominantly as biologic space fillers, and other materials should be considered if regeneration is desired. The chemical composition, physical form, and differences in surface configuration result in varying levels of bioresorbability. The varying nature of available commercial graft materials (porosity, geometries, differing solubilities and densities) will determine the resorption of these calcium phosphate (CaP)-based graft materials.
Xenografts (Anorganic bone)
These are the grafts taken from a donor of another species, that is, naturally derived deproteinized cancellous bone from another species (such as bovine or porcine bone) and prepared by chemical or low-heat extraction of the organic component from, for instance, anorganic bovine bone (ABB). ABB is a biomaterial with major long-term success reports in the bone regeneration literature and it has been extensively used in clinics for over 20 years.
Platelet-rich plasma (PRP) along with bone graft
PRP can be defined as a blood derivate where platelets have a higher concentration above baseline levels. PRP is an inexpensive way to obtain many growth factors (GFs) in physiological proportion and has already been largely applied as a carrier of GFs in different fields of medicine due to its property of favoring tissue healing even in tissues with low healing potential.,
The first evidence of the clinical benefits of PRP in implant osseointegration was reported in 1998 by Marx et al., who studied 88 patients with mandibular defects treated with platelet concentrate and cancellous cellular marrow bone graft. The results showed that PRP allowed a radiographic graft maturation rate 1.62-2.16 times higher than that without PRP at 6 months, and also showed greater bone density.
A particulate bone graft with the addition of PRP is well-vascularized and homogenous in bone density, which can clearly be seen during, for instance, implant installation. Endothelial cell proliferation has been found to be increased in cellular research under the influence of PRP. Fontana et al. found a higher amount of peri-implant bone volume after inserting PRP and laminar test implants into rat tibial sites.
Biomaterial as implant surface coating
- Composite of collagen and HA
Dental implants can be coated with a variety of materials and/or molecules depending on the specific application and requirements. Moreover, as osteoblasts recognize specific molecules, it is possible to coat implant surfaces with immobilized molecules to improve cell attachment, protein deposition, and mineralization. These immobilized molecules include amino acid sequences [arginine-glycine-aspartic acid (RDG)], vitronectin, collagen, functional groups, pharmacological substances (biophosphonates), and antimicrobial agents (e.g., tetracycline).
| Ceramics|| |
Ceramic materials are the most biologically acceptable of all materials. Ceramics are fully oxidized or chemically stable compounds. Because of their chemistry, ceramics are much less likely to produce any adverse effects, compared to metals and polymers, which are not as chemically stable.
The major advantage of ceramics as biomaterials is that they can be produced almost completely inert or with the potential for varying degrees of interaction within the physiological environment. Evidence exists to show that certain ceramic and glass compositions can bond to bone. Ceramics have a very wide application as substitutes for calcified tissues and as aids to bone formation.
In spite of the difficulty of fabricating ceramics into complex shapes, their appeal as implant materials is due to their potentially inert, smooth surfaces and their tissue acceptance. Much attention has been focused on porous ceramics, which allow tissue ingrowth for retention and fixation.
They can be categorized according to tissue response as:
Bioactive: Bioglass/glass ceramics
Bioinert: Aluminum, zirconia, carbon 
| Bioactive Ceramics|| |
Besides uses such as bone substitute and drug delivery vehicle, CaPs have also been considered a good option for implant coatings that may promote accelerated bone healing around implants. CaPs, such as TCP, glass ceramics, and HA are included in this category. With a CaP coating, metallic implants can be alternatively regarded as scaffolds for bone-forming cells that can further enhance early and strong fixation of a bone-substituting implant by stimulating bone formation starting from the implant surface. The most successful method to apply CaP coatings to implants to date seems to be the plasma-spraying technique, due to its high deposition rate and ability to coat large areas.
These are bioactive ceramics first introduced in 1971. Bioglass or Ceravital silica-based glass has additions of calcium and phosphate produced by controlled crystallization. It has high mechanical strength, low resistance to tensile and bending stresses, and extreme brittleness, and can chemically bond to the bone due to the formation of a CaP surface layer.
HA was successfully used as an implant material in 1988 in North America, but was used, to begin with, for the repair of residual ridge resorption, in the 1970s. It is similar to the mineral component of bones and hard tissues in mammals. This material has the ability to be integrated into bone structure and support the growth of the bone. It is thermally unstable, with low mechanical strength in terms of withstanding long-term load-bearing applications.
Plasma-sprayed HA was first used by Herman in 1988. It is the most common coating method for dental implants because almost all the commercial HA coatings are produced by this technique.
Crystalline HA powder is heated to a temperature of 12000-16000°C in a plasma flame formed by an electric arc through which an argon gas stream passes. HA particle size is approximately 0.04 mm. The particles melt and are sprayed onto the substrate, and they fall as drops and solidify. Round, interconnected pores are formed. The coating bonds to the substrate by mechanical interlocking. There is a lot of controversy regarding the ideal thickness of HA coating. Studies show that fractures have occurred in coatings that were more than 0.1 mm in thickness, whereas bioresorption was unacceptably rapid with coatings less thick than 0.03 mm. The ideal coating thickness recommended is 0.05 mm.
| Bioresorbable Ceramics|| |
CaP polycrystalline ceramic materials can be produced by precipitation from aqueous solutions and by solid-state reactions. The main purpose of using CaP ceramics as an implant material is to enable it to be gradually substituted by newly formed bone, or at least to become integrated with the host bone. A major factor in the use of such materials is the control of the size of porosity. Daculsi and Passuti evaluated the effect of porosity in an in vivo experiment on cortical bone in dogs. Three kinds of porosity were tested (between 100 mµ and 600 mµ). The results of this study demonstrated that the porosities up to 100 mµ are efficient for bone ingrowth; however, during the first months of implantation, larger macropore sizes are more suitable for bone ingrowth.
Oxide ceramics were introduced for surgical implant devices because of their inertness to biodegradation, high strength, and physical properties such as color and minimal thermal and electrical conductivity.
High ceramics from aluminum, titanium, and zirconium have been used for root form or endosteal plate form and pin-type dental implants. The compressive, tensile, and bending strengths of such implants exceed the strength of compact bone by 3 to 5 times.
Titanium forms three different oxides spontaneously as tenacious surface oxides on exposure to the air or physiological saline. They are TiO (anastase), TiO2(rutile), and Ti2O3(brookite). TiO is the most stable and is most commonly formed on a titanium surface. This oxide layer is self-healing, that is, if the surface is scratched or abraded during implant placement, it repassivates instantaneously.
A number of studies has been done to compare the osseointegration of zirconia with that of titanium implants. Most studies have revealed no significant differences between the two and found similar attachment of both implants to bone, with similar features ultrastructurally. The periodontal aspect shows less bleeding on probing and less recession with zirconia than with a titanium implant.
| Polymers|| |
Polymeric implants in the form of polymethyl methacrylate and polytetrafluoroethylene were first used in the 1930s. However, the low mechanical strength of polymers has precluded their use as implant materials. These are large, organic macromolecules composed of a regular pattern of many monomers. Cellulose, collagen, agarose, chitin, or hyaluronan form the natural polymeric materials or so called biological polymers. Natural polymers such as collagen have been used for bone tissue-engineering purposes.
Composite of collagen and HA
Skeletal bones are comprised mainly of collagen (predominantly type I) and carbonate-substituted HA, both osteoconductive components. Thus, an implant manufactured using such components is likely to behave similarly, and to be of more use than a monolithic device. Indeed, both collagen type I and HA were found to enhance osteoblast differentiation (Xie et al., 2004), but combined they were shown to accelerate osteogenesis.
These composites also behaved mechanically in a superior way to the individual components. The ductile properties of collagen help to improve the poor fracture toughness of HAs. The addition of a calcium/phosphate compound to collagen sheets has been shown to give higher stability, increasing resistance to three-dimensional swelling compared to the collagen reference (Yamauchi et al., 2004), and it enhanced their mechanical “wet” properties (Lawson and Czernuszka, 1998). This happened even when the collagen was highly crosslinked.
| Metals|| |
Steel and titanium or titanium alloys (i.e., Ti-6Al-4V) are the materials that usually form the basis of metal implants for bone regeneration. The bulk phase of the implants consists of solid metal, while titanium particle coatings create a porous surface, its thickness ranging from a few nanometers to the hundreds of micrometers, depending on the fabrication technique.,
| Future Trends|| |
Synthetic materials for tooth replacement have been in use for many years now that have been developed from selected industrial materials such as metals, ceramics, polymers, and composites. The arrival of nanotechnology and advancements in computer technology has opened up new opportunities for the manipulation of implant surfaces. Nanotechnology approaches require novel ways of manipulating matter at the atomic scale. Currently, there is extensive research wherein techniques to produce nanotechnology-based implants are being investigated.
Nanotechnology-based trends for dental implants consist of surface roughness modification at the nanoscale level to promote protein adsorption and cell adhesion, biomimetic CaP coatings, and the incorporation of GFs for accelerating the bone-healing process.
| Conclusion|| |
Implantology has become an exciting and dynamic force within dentistry during recent years: From a less-than-well-accepted treatment option, it has developed into the current cutting-edge practice in dentistry.
The primary objective of any implant system is to achieve firm fixation to the bone and this could be influenced by biomechanical as well as biomaterial selection. Titanium has long been regarded as a biocompatible implant material and recently, various modifications of its surface have been emerging at molecular and atomic levels that can enhance osseointegratition.
An array of biomaterials is currently in use for implants, with their different characteristics.
Biomaterials, regardless of use, fall into one of four general categories: Metals and metallic alloys, ceramics, synthetic polymers, and natural materials. When a material is placed in the body, there will be a biological response that is mediated by the interaction of the implant through its surface. At the points of contact between cells and biomaterials, there is an exchange of information leading to the activation of specific genes and remodeling. The first step in this response involves the adsorption of specific proteins, lipids, sugars, and ions that can activate cell mechanisms to induce either acceptance or rejection of the implant by determining which and how many cells populate the surface.,
For example, bioinert materials allow close approximation of the bone on their surface, leading to contact osteogenesis. These materials allow the formation of new bone on their surface, and ion exchange with the tissues leads to the formation of chemical bonding along the interface, that is, bonding osteogenesis.
Bioceramics, besides being of aesthetic value, have biomimetic properties and have also been incorporated for better bone implant contact. Recent materials such as composites, polymers, bioceramics, and biomaterials are under consideration and investigation, such as cell-based bone graft substitutes; these use cells to generate new tissue alone or are seeded onto a support matrix (e.g., mesenchymal stem cells) and have a promising future.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]