|Year : 2016 | Volume
| Issue : 1 | Page : 2-6
Redefining the implant surfaces: A journey from passive to active surfaces
Smriti Kapur Dewan, Monika M Sehgal, Aman Arora, Nitika Gupta
Department of Prosthodontics, D.A.V Centenary Dental College, Yamuna Nagar, Haryana, India
|Date of Web Publication||14-Mar-2017|
Smriti Kapur Dewan
Department of Prosthodontics, Room No. 5, D.A.V Centenary Dental College, Yamuna Nagar, Haryana
Source of Support: None, Conflict of Interest: None
The use of implants in the oral and maxillofacial skeleton continues to expand and since then implant surfaces have been modified in various ways to improve biocompatibility and accelerate osseointegration, which results in a shorter edentulous period for a patient. This article reviewed several methods that are widely used to modify the topography or chemistry of titanium surface, including blasting, acid etching, anodic oxidation, fluoride treatment, and calcium phosphate coating. Such modified surfaces demonstrate faster and stronger osseointegration than the turned commercially pure titanium surface.
Keywords: Dental implants, surface modifications and osseointegration, topography
|How to cite this article:|
Dewan SK, Sehgal MM, Arora A, Gupta N. Redefining the implant surfaces: A journey from passive to active surfaces. Saint Int Dent J 2016;2:2-6
|How to cite this URL:|
Dewan SK, Sehgal MM, Arora A, Gupta N. Redefining the implant surfaces: A journey from passive to active surfaces. Saint Int Dent J [serial online] 2016 [cited 2019 May 21];2:2-6. Available from: http://www.sidj.org/text.asp?2016/2/1/2/202123
Response of the tissues to the implant is largely controlled by the nature and texture of the surface of the implant. Compared to smooth surfaces, textured implants surfaces exhibit more surface area for integrating with bone via osseointegration process. The role of surface topography has been the interesting area of investigation in implant dentistry for several years. Some of these have the ability to enhance and direct the growth of bone and achieve osseointegration when implanted in osseous sites. Most implant systems of this category are based on the fact that bone tissue can adapt to surface irregularities in the 1–100 µ range, and that altering the surface topography of an implant can greatly improve its stability. A number ofin vivo studies using endosseous dental implants in human clinical trials indicated that rough surfaces integrate better with the bone than those materials with relatively smooth surfaces. Based on the scale of the features, the surface roughness of implants can be divided into macro-, micro-, and nano-sized topologies. Several methods have been employed to alter the surface topography and surface chemistry of the of the implant materials.
| Surface Treatment|| |
Recently, many works have been carried out on the surface treated commercial titanium implants to enhance the osseointegration function. By increasing the surface roughness, an increase in the osseointegration rate and the biomechanical fixation of titanium implants have been observed., The implant modifications can be achieved either by additive or subtractive methods. The additive methods employed the treatment in which other materials are added to the surface, either superficial or integrated, categorized into coating and impregnation, respectively. While impregnation implies that the material/chemical agent is fully integrated into the titanium core, such as calcium phosphate (CaP) crystals within TiO2 layer or incorporation of fluoride ions to surface, the coating, on the other hand, is the addition of material/agent of various thicknesses superficially on the surface of core material. The coating techniques can include titanium plasma spraying, plasma sprayed hydroxyapatite (HA) coating, alumina coating, and biomimetic CaP coating. Meanwhile, the subtractive techniques are the procedure to either remove the layer of core material or plastically deform the superficial surface and thus roughen the surface of core material. The common subtractive techniques are large-grit sands or ceramic particle blasts, acid etch, and anodization. The removal of surface material by mechanical methods involved shaping/removing, grinding, machining, or grit blasting through physical force. Chemical treatment, either using acids or using alkali solution of titanium alloys, in particular, is normally performed not just to alter the surface roughness but also to modify the composition and to induce the wettability or the surface energy of the surface. As for physical treatment such as plasma spray or thermal spray, it is often carried out on the outer coating surface to improve the aesthetic of the material and its performance. In addition, ion implantation, laser treatment and sputtering alkali/acid etching and ion deposition are also utilized. Thus, in the light of studying the effects of surface treatments, this review only focuses on various methods that have high potentials in improving the performance of titanium implants.
| Pretreatment|| |
Before the surface modification, pretreatment is required to ensure the substrate surfaces are free from contaminations. A pretreatment process is crucial as it provides clean surface, by eliminating undesired defects such as scratch and irregularities. Furthermore, this is done to get better adhesion between substrate and powder leading to more of bone-implant contact. It can have a major impact on the ultimate coating efficacies resulting in minimization of coating time and producing excellent results.
| Type of Surface Treatment|| |
HA coatings were first introduced in the middle 1980s for improved fixation between bone and implant. Since that time, these materials have been extensively used in orthopedic and dental implants. Plasma spraying is commercially the most frequently used method for deposition of CaP coatings, such as HA, onto implant materials to improve their bioactivity. The thickness of HA coatings produced by plasma spray varies from 100 to 300 μm. With plasma spraying processing, the surface area of titanium implant has increased up to approximately six times than the original surface. The arithmetic average roughness (Ra) for HA-coated by plasma spraying process is 5.0 ± 1.0 μm. Several earlier experimental studies have shown a higher percentage of bone-implant contact for HA-coated implants when compared with titanium implants in different species and types of bone. The histological findings demonstrated that the cortical bone reaction to titanium and HA-coated titanium was similar, but the HA-coated surfaces induced more bone deposition in areas on noncortical bone contact than uncoated surfaces. It has been reported that more new bones are formed and grow more rapidly into pores of the surface of alkaline-modified plasma-sprayed implants, and this may be beneficial to reduce clinical healing times and thus to improve implant success rates [Figure 1].
Sputtering process has been shown to be a particularly useful technique for the deposition of bioceramic thin films (based on CaP systems), due to the ability of the technique to provide greater control of the coating's properties and improved adhesion between the substrate and the coating. Scanning electron microscopy showed that the deposited films had a uniform and dense structure. The CaP has been reported to range from 1.5 to 2.6. Thein vitro dissolution appeared to be determined by the degree of the coating's crystallinity. The thickness of HA-coatings produced by sputter process varies from 0.5 to 3.0 μm (Ding, 2003). With sputter processing, the surface roughness of the coating depends on the roughness of the substrate. The arithmetic average roughness (Ra) for HA-coated by sputter process is 3.0 ± 1.2 μm. In a study using TiO2 gritblasted and sputtered CaP implants, the sputtered CaP coatings showed improved initial fixation and healing response when implanted into the trabecular bone of the goat. Further, sputtered CaP-coated titanium implants have shown higher removal torque compared to control uncoated titanium implants after 3 weeks of healing [Figure 2].
Furthermore, known as abrasive blasting, is another technique which is used to create surface topographies on the implant surfaces. In grit blasting, the surface of the implant is bombarded with hard, dry particle, or particles suspended in a liquid at high velocity. Various types of ceramic particles such as alumina, silica, etc., of different sizes, can be used for grit blasting of titanium. This technique is generally employed for descaling and surface roughening of commercial implants thereby increasing the surface area of the implant for better osseointegration. Shot peening is a modified method of grit blasting and is used primarily for introducing compressive stresses in the material's surface. It is most commonly used for producing specific surface topographies on various biomaterials surfaces. Surface topography achieved by shot peening depends greatly on the size of the particle used. Alumina particles in the size range of 25–75 μm result in mean surface roughness in the range 0.5–1.5 μm, whereas roughness in the range of 2–6 μm are reported for surfaces blasted with particles of size between 200 and 600 μm. Use of fine particle size glass particles of 150–230 μm results in relatively smooth surface with Ra value of 1.36 μm whereas use of coarse alumina particles of 200–500 μm provides a much rougher surface with Ra value of 5.09 μm.
Sandblast, large-grit, and acid etching
Sandblast, large-grit, and acid etching is used to induce surface erosion by applying a strong acid onto the blasted surface. This treatment combines blasting with large grit sand particles and acid etching sequentially to obtain macro-roughness and micro-pits to increase the surface roughness as well as osseointegration. A recent investigation on a two-step chemical treatment (acid-alkali) noticed that optimized morphology and good bioactivity resulted in good osseointegration during the early stage of the implantation. Similarly, He et al. also discovered that the implants treated with blasting followed by the DAE (HCl and H2 SO4) promote better osseointegration during the healing phase, indicating a great improvement in the bioactivities.
Electrophoretic deposition of hydroxyapatite
Electrophoretic deposition (EPD) is a process in which colloidal particles, such as HA nanoprecipitates which are suspended in a liquid medium migrate under the influence of an electric field and are deposited onto a counter charged electrode. The coating is simply formed by pressure exerted by the potential difference between the electrodes. The operational parameters of EPD can be changed to alter HA surface coating morphology and composition. It is of low cost, simple methodology capable of producing coatings of variable thickness, high deposition rate, formation of highly crystalline deposits with low residual stresses and ability to uniformly coat irregularly shaped, or porous objects such as threaded implants due to its high throwing power. EPD can produce HA-coatings ranging from <1 to >500 µ thick.
HA was synthesized by a Biomimetic method using calcium nitrate tetrahydrate. Ca(NO3)2·4H2O and diammonium hydrogen phosphate salts (NH4)2 HPO4 as precursors dissolved in synthetic body fluid solutions at 37°C and pH of 7.4. The HAp samples were uniaxially compacted and calcined for 2 h at different temperatures (560, 750 and 850°C). The powder calcined at 750°C was then sintered for 2 h at different temperatures (1000, 1100 and 1200°C).
The significant findings of this work are: The as prepared HAp powder contains broad peaks of HAp with crystallite size of 25.49 nm. The calcined samples show appearance of extra peaks which corresponds to the decomposition of HAp to other phases. All HAp peaks get clearly dissolved on calcination at 560°C. However, at 750°C β-tricalcium phosphate also appears. The powder is fine in nature.
The idea behind sol-gel synthesis is to “dissolve” the compound in a liquid to bring it back as a solid in a controlled manner. Multi-component compounds may be prepared with a controlled stoichiometry by mixing sols of different compounds. The sol-gel method prevents the problems with co-precipitation, which may be inhomogeneous, be a gelation reaction. Enables mixing at an atomic level. Results in small particles which are easily sinterable. The sol-gel method was developed in the 1960s mainly due to the need of new synthesis methods in the nuclear industry. A method was needed where dust was reduced (compared to the ceramic method) and which needed a lower sintering temperature. In addition, it should be possible to do the synthesis by remote control. According to the different tests conducted, it was found that by matching the substrate roughness to the sol-gel oxide coatings it is possible to make the topography of the implant surface different. Depending on the assumed purpose of the treatment, the surfaces obtained could be appropriate for the implants of either short-term or long-term durability [Figure 3].
| Newer Methods|| |
Nanostructured surfaces enhance the surface area of biomaterials and promote cellular adherence. Zhao et al. stated that porous structures at either micro- or sub-micrometer scale supply positive guidance cues for anchorage-dependent cells to attach, leading to enhanced cell attachment in contrast, the cells attached to a smooth titanium surface by focal contacts around their periphery but as predominant adhesion structures, send repulsive signals from the environment, and lead to retraction of the filopodia back to the cell bodies. These studies have indicated that nanotextured surfaces are better than micro-surfaces. For example, Nano calcium HA-coated titanium surfaces and nano titanium dioxide coated titanium surfaces. They also have a great effect on early events, such as the adsorption of proteins, blood clot formation, and cell behaviors occurring upon implantation of dental implants [Figure 4].
To compensate for the reduced rate of proliferation in the differentiating osteoblasts, the treatment of the cells can be done with growth factors, such as transforming growth factor-B, platelet-derived growth factor, and insulin-like growth factors (1 and 2) which are the promising candidates for this purpose, to enhance the bone healing process locally. Members of the Osteoblasts have demonstrated a biological dilemma where there exists an inverted correlation between proliferation and differentiation rates. Proliferation and differentiation are regulated by growth factors that counteract each other in osteoblasts. This applies to the bone formation around biomaterials. The bone mass, however, is smaller than that around the machined surface, due to the diminished osteoblastic proliferation. This helps in increasing binding sites that specifically stimulate their proliferation, may be a biological strategy.,
| Discussion|| |
The past studies have shown substratum composition, and microtopography has been an important factors influencing growth and differentiation of osteoblasts. All in all, the coating techniques contribute to important positive effects of dental implant application. The present article has been reviewed so as to foresee different methods of roughening implant surfaces and enhanced osseointegration.
A good coating technique has a high impact on the mechanical properties of the dental implants. Of the various techniques available, plasma spraying HA-coatings onto metallic bone implants has shifted the concept of bone implant coatings from passive protecting thin films to active and instructive immobilized layers helping the implant surfaces to accelerate the bone healing process. Blasting is also one popular technique for surface treatments which can easily roughen the implant surface but is inadequate to give credit to the important properties such as bone implant contact, removal torque values, tissues response, and biocompatibilities. Ion implantation technique, on the other hand, is useful to harden the surface of titanium but not applicable for dental implant. It is most useful in orthopedic devices which are subject to articulating or in wear situations. To date, ceramic coatings (CaP, HA, and TiO2) still remain the most popular bioceramic materials in the surface treatments area. Nevertheless, HA is recognized as the best candidate in bioceramics compared to TiO2. It is clearly noted that by altering or modifying the surface texture, namely, the roughness of titanium implants, in particular, desired effects can be obtained such as bone-implant contact, removal torque values, tissues response, and biocompatibility. Thus, most works still favor surface treatment of dental implants via coating and acid etching over other methods in producing good substrate surfaces for osseointegration, with surface roughness ranging from 0.44 to 8.68 µm.
| Conclusion|| |
The new generation dental implants exhibit a large variation in surface properties, both in terms of structural and chemical compositions. It is important that the clinician selects for use in their patients the surfaces that have shown good results in the scientific literature. The majority of currently availablein vitro andin vivo studies seem to indicate that implant surfaces with micro and submicro (nano) topography bring forward benefits to the process of interaction between bone cells and implant surfaces, accelerating, and increasing the quality of bone-implant contact. Finally, based on the state of the art of implant development, it is possible to predict that, within some time, implant surfaces coated with substances with biomimetic capacity will be available for clinical use. In short, a good surface with the right roughness and mechanical properties could lead to better osseointegration for successful dental implants.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]