|Year : 2014 | Volume
| Issue : 1 | Page : 66-71
Surface topography of dental implants: A review
Varun Dahiya, Pradeep Shukla, Shivangi Gupta
Department of Periodontics and Implantology, D.J. College of Dental Sciences and Research, Modinagar, Uttar Pradesh, India
|Date of Web Publication||19-Apr-2014|
Department of Periodontics and Implantology, D.J. College of Dental Sciences and Research, Modinagar, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Pure titanium (Ti) and Ti alloys are well-established standard materials in dental implants due to their favorable combination of mechanical strength, chemical stability and biocompatibility. The concept of osseointegration was discovered by Brεnemark and his co-worker and has had a dramatic influence on clinical treatment of oral implants. The first generation of successfully used clinical Ti implants, which were machined with a smooth surface texture, now approach 50 years in the clinical use. Since then, implant surfaces have long been recognized to play a vital role in molecular interactions, cellular response and osseointegration and scientists all over the world have developed the second generation implants with surfaces which can accelerate and improve implant osseointegration.
Keywords: Implants, osseointegration, titanium
|How to cite this article:|
Dahiya V, Shukla P, Gupta S. Surface topography of dental implants: A review. J Dent Implant 2014;4:66-71
| Introduction|| |
Replacing lost teeth with dental implants is today a reliable treatment method associated with good long-term clinical results. Different surface modifications alter the surface topography at micro- and nano-meter level of resolution as well as chemical properties, which have shown to be of importance for osseointegration. Research within the field of implantology is still intense and aims at further improving the implant properties to achieve successful treatments for patients with compromised bone as well as developing a surface that provides faster integration to shorten the treatment period.  Dental implant quality depends on the chemical, physical, mechanical and topographic characteristics of the surface.  A major factor that determines the success of dental implantation is osseointegration, which is the stable anchorage of an implant in living bone achieved by direct bone-to-implant contacts (BIC).  Osseointegration derives from the Greek osteon (bone) and the Latin verb integrare (to make whole). 
The main objective for the development of implant surface modifications is to promote osseointegration, with faster and stronger bone formation. This will likely confer better stability during the healing process, which, preferentially, will improve the clinical performance in the area of poor bone quality and quantity. Recently growing micro and nano-technology is rapidly advancing surface engineering in implant dentistry. Surface roughness also has a positive influence on cell migration and proliferation, which in turn leads to better BIC results, suggesting that the microstructure of the implant influences biomaterial-tissue interaction.  Various surface modification methods to improve the osseointegration of a titanium (Ti) dental implant, such as surface-roughening (e.g., sandblasting and/or acid etching) and coating, for example, with hydroxyapatite (HA) Ca10(PO4) 6(OH) 2, to improve the implant's bioactivity. 
The main objective, hence, is to develop effective and practical techniques that create a long-lasting electric field on the implant's surface, in order to promote the implant's osseointegration without incurring the drawbacks of existing surface-treatment methods.
| Implant Surface Topography|| |
Implant surface topography refers to macroscopic and microscopic features of the implant surface. Although commercially pure Ti is the prime material of dental implants, the success rates of different commercially available implant systems vary. Ti implants with adequate roughness may influence the primary stability of implants, enhance BIC and may increase removal torque force.  Ti is the most widely used metallic material for dental subgingival implants, due to its invaluable and outstanding biomedical and biomechanical properties. These are its availability, high biocompatibility, high strength and stiffness and relatively low density. More importantly, Ti implants are known to osseointegrate with living bone tissues. 
Goal of various surface textures and techniques is to enhance bone growth toward the implant surface. A number of in vivo studies have demonstrated that increased surface area on the implant improves BIC after the implant placement. 
The primary aim of the surface texturing or treating the implant surface is to enhance cellular activity and improve bone apposition. Surface topography of an implant can be designed by making porous and/or by coating the implant surface with other suitable materials to increase bone-implant contact since the anatomic surface of bone cannot be controlled.  A number of surface treatments are available to create controlled roughness on the surface of the implants. It is not clear whether the height of surface irregularities is more important than the distance between them and which combination of these factors could improve osseointegration.
Roughness can be produced on the implant surfaces through the addition or subtraction procedures. A plasma arc is a kind of addition process, which involves the deposition of bioactive HA material on the surface of the implants. Polishing, machining and acid etching, on the other hand, are subtraction procedures. These treatments may also be classified into mechanical, chemical, electrochemical, electropolishing, vacuum, thermal and laser methods. 
Implant surface roughness is divided, depending on the dimension of the measured surface features into macro-, micro- and nano-roughness [Figure 1].
Macro-roughness comprises features in the range of millimeters to tens of microns. This scale directly relates to implant geometry, with threaded screw and macro porous surface treatments. The primary implant fixation and long-term mechanical stability can be improved by an appropriate macro-roughness. 
|Figure 1: Scanning electron microscopy images in ×3000 magnifi cation of common surface modifi cations (a) TiOblast™ (b) Osseotite® (c) TiUnite™|
Click here to view
Micro-roughness is defined as being in the range of 1-10 μm. This range of roughness maximizes the interlocking between mineralized bone and implant surface. The use of surfaces provided with nanoscale topographies are widely used in recent years.
Nanotechnology involves materials that have a nano-sized topography or are composed of nano-sized materials with a size range between 1 and 100 nm. Nanometer roughness plays an important role in the adsorption of proteins, adhesion of osteoblastic cells and thus the rate of osseointegration. 
| Methods of Surface Modifications of Implants|| |
The methods employed for surface modifications of implants can be broadly classified into 3 types-mechanical; chemical; and physical. The main objective of these techniques is to improve the bio-mechanical properties of the implant such as stimulation of bone formation to enhance osseointegration, removal of surface contaminants and improvement of wear and corrosion resistance.
Mechanical treatments involve either removal of surface material by cutting or abrasive action, or the surface of the implant is deformed (and/or partially removed) by particle blasting.  The most commonly employed mechanical techniques are machining, polishing and blasting.
The chemical methods of implant surface modifications include chemical treatment with acids or alkali, hydrogen peroxide treatment, sol-gel, chemical vapor deposition and anodization. Chemical surface modification of Ti has been widely applied to alter surface roughness and composition and enhance wettability/surface energy. 
The process of acid treatment serves to remove the surface oxide and contamination which leads to a clean and homogenous surface. The acids commonly used include hydrochloric acid, sulfuric acid, hydrofluoric acid and nitric acid.
The physical methods of implant surface modification include plasma spraying, sputtering and ion deposition.
Methods to alter microtopography
Turning - the original Brånemark (Nobel Biocare) implant was turned Ti screw with no further surface treatment.  It had a minimally rough surface and was for a long time the most used implant with good long-term clinical results. , Scanning electron microscopy analysis showed that the surfaces of machined implants have grooves, ridges and marks of the tools used for their manufacturing. These surface defects provide mechanical resistance through bone interlocking.
Grit-blasting - with various hard ceramic particles such as alumina (AlO3), titanium oxide (TiO2), silica or calcium phosphate is one way of roughening the implant surface. The size of the blasting particles determines the roughness created and the blasting particles should be chemically stable and biocompatible.
Several in vivo studies have shown significantly improved BIC for TiO2 blasted implants when compared to machined ones. ,
Acid-etching - of a surface with strong acids such as HCl, H2SO4, HNO3 and HF creates an isotropic surface that may enhance osseointegration in vivo., The most commonly used solutions for acid etching of Ti includes either a mixture of HNO3 and HF or a mixture of HCl and H2SO4. Acid treatment provides homogeneous roughness, increased active surface area and improved bio adhesion.
Dual acid-etched technique - immersion of Ti implants for several minutes in a mixture of concentrated HCl and H2SO4 heated above 100°C (dual acid-etching) is employed to produce a micro rough surface.  The dual acid-etched surfaces enhance the osteoconductive process through the attachment of fibrin and osteogenic cells, resulting in bone formation directly on the surface of the implant. The dual acid-etched surface produces a microtexture rather than a macrotexture. It has been found that dual acid-etched surfaces enhance the osteoconductive process through the attachment of fibrin and osteogenic cells, resulting in bone formation directly on the surface of the implant. 
Experimental studies have reported higher BIC and less bone resorption with dual acid-etched surfaces compared with machined or titanium plasma-sprayed surfaces. 
Hypothetically the blasting procedure creates a surface roughness for good mechanical fixation and the additional etching smoothens out sharp peaks. Commonly, this combination of techniques creates a moderately rough surface.
Anodization - produces a micro- and or nano-porous oxide layer on the Ti surface. The appearance of the layer from the anodization process depends on current density, concentration and composition of the acids used in the electrolyte solution and the temperature. In vivo studies have demonstrated increased bone response with higher biomechanical and histological values for anodized surfaces compared with machined ones. 
Plasma spraying - is a method where particles, HA or Ti are projected on the surface through a plasma torch at very high temperature. The particles condense and fuse together on the surface thereby creating a coat. Ti plasma spraying has displayed better bone integration in vivo as compared to smoother implants. The advantage of plasma coating is that these coatings give implants a porous surface that bone can penetrate more readily.  Osseointegration was shown to be fastest and most effective for rough surfaces with open structure that varied between 50-400 μm.
Plasma spraying with HA particles creates a 50-200 μm thick coat but with poor adhesion to the bulk material and this is believed to be the reason for the long term negative clinical results of such implants.
Sandblasted and acid etched surface
Commercially available dental implants are usually both blasted by particles and then subsequent etched by acids. This is performed to obtain a dual surface roughness as well as removal of embedded blasting particles. The etching reduces the highest peaks while smaller pits will be created and the average surface roughness will be reduced.
Ti is very reactive to fluoride ions, forming soluble TiF4 by treating Ti dental implants in fluoride solutions. This chemical treatment of Ti enhances the osseointegration of dental implants.
Sputtering process has been shown to be a particularly useful technique for the deposition of bioceramic thin films (based on Ca/P 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. The disadvantages with sputter coating is extensive time consuming, produces amorphous coatings and Ca/P ration of the coating is higher than of synthetic HA.
There are several sputter techniques and a common drawback inherent in all these methods is that the deposition rate is very low and the process itself is very slow. 
Radio frequency (RF) sputtering
RF magnetron sputtering is largely used to deposit thin films of Ca/P coatings on Ti implants. The advantage of this technique is that the coating shows strong adhesion to the Ti and the Ca/P ratio and crystallinity of the deposited coating can be varied easily.
Magnetron sputtering is a viable thin-film technique as it allows the mechanical properties of Ti to be preserved while maintaining the bioactivity of the coated HA.
Nano-roughness and nanostructures
All surfaces possess nano-roughness, however not all of them have defined nanostructures. Nanostructured materials are defined in the literature as materials containing structural elements with dimensions in the range of 1-100 nm.
Some methods to alter nanotopography
During the sol-gel process, a liquid with a specific composition (i.e., the Sol) is converted into a solid gel phase. Thin coatings can be deposited onto a surface by dip- or spin coating techniques. The procedure makes it possible to produce coatings of Ti, HA or combination of both.
Nanocrystalline HA coatings
Nanoparticles of HA is prepared by mixing H3PO3 and Ca (NO3) to a Ca/P ratio of 1.67 in the presence of a liquid crystalline phase. The crystalline phase limits particle growth to ~5 nm. When HA particles have formed, the liquid crystalline phase is dissolved and the particles can be deposited onto a surface using dicyandiamide.
Biologically active drugs incorporated dental implants
Some osteogenic drugs have been applied to implant surfaces. Incorporation of bone antiresorptive drugs, such as bisphosphonate, might be very relevant in clinical cases lacking bone support.
Bisphosphonate incorporated on to Ti implants increased bone density locally in the peri-implant region.  with the effect of the antiresorptive drug limited to the vicinity of the implant.
Other experimental studies using PSHA-coated dental implants immersed in pamidronate or zoledronate demonstrated a significant increase in bone contact area. The main problem lies in the grafting and sustained release of antiresorptive drugs on the Ti implant surface. Increase in peri-implant bone density is bisphosphonate concentration-dependent
Simvastatin, could induce the expression of bone morphogenetic protein (BMP) 2 messenger ribonucleic acid that might promote bone formation. In an in vitro study Yang et al. (2010) showed that simvastatin-loaded porous implant surfaces promote accelerated osteogenic differentiation of preosteoblasts, which have the potential to improve the nature of osseointegration.
Gentamycin along with the layer of HA can be coated onto the implant surface, which may act as a local prophylactic agent along with the systemic antibiotics in dental implant surgery.
Tetracycline-HCl functions as an antimicrobial agent capable of killing microorganisms that may be present on the contaminated implant surface. It also effectively removes the smear layer as well as endotoxins from the implant surface. Further, it inhibits collagenase activity, increases cell proliferation as well as attachment and bone healing (Herr et al., 2008). Tetracycline also enhances blood clot attachment and retention on the implant surface during the initial phase of the healing process and thus promotes osseointegration.
Future directions in implant surface modifications
The adhesion of plasma proteins on the surface of Ti implants has been reported to play an essential role in the process of osseointegration.  Polypeptide growth and differentiation factors and cytokines have been suggested as potential candidates in this regard to stimulate a deposition of cells with the capacity of regenerating the desired tissue.
Growth factors released during the inflammatory phase have the potential of attracting undifferentiated mesenchymal stem cells to the injured site. These growth factors include platelet-derived growth factor (PDGF), epidermal growth factor, vascular endothelial growth factor, transforming growth factor (TGF-β) and BMP-2 and BMP-4.
The surface of Ti dental implants may be coated with bone-stimulating agents such as growth factors in order to enhance the bone healing process locally.
Members of the TGF-β superfamily and in particular bone BMPs, TGF-β1, PDGF and insulin-like growth factors are some of the most promising candidates for this purpose. The effects of recombinant human protein BMP-2 on the osseointegration of Ti implants have also been investigated. PRGF can accelerate bone regeneration in artificial defects and improve the osseointegration of Ti dental implants.
A study by Nikolidakis et al. (2006) investigated the effect of local application of autologous platelet-rich plasma on bone healing in combination with the use of Ti implants with 2 different surface configurations - Ca/P coated and non-coated implants. The role of the osteoinductive TGF-β1 application to Ca/P implant surfaces have been studied in animals using a goat model. Although the possibility of incorporation of a plasmid containing the gene coding for a BMP exists, it is associated with disadvantages related to poor efficacy and a possible undesirable overproduction of BMPs.
| Conclusion|| |
The new generation dental implants exhibit a large variation in surface properties, both in terms of structural and chemical compositions. Ti and its alloys are the materials of choice clinically, because of their excellent biocompatibility and superior mechanical properties. The selection criteria for the first generation dental implants were mainly based on their mechanical properties and corrosion resistance under physiological conditions. The current surfaces have mainly underwent topographical modification and to a lesser extent, alteration in chemical composition. These topographical modifications have boosted the success rate of the implant therapy, especially in patients with poor bone quality sites and have significantly reduced the healing period. The cellular mechanisms involved in this faster and improved osseointegration are yet to be fully determined.
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