SURFACE TREATMENT OF IMPLANTS

Dr. Padmashini Gnanam Post Graduate Student Batch 2012-2015 Department of Prosthodontics including Crown and bridge and Implantology Sri Ramakrishna Dental College and Hospital

Introduction

A dental implant is an artificial tooth root that takes the form of a screw. It supports restorations resembling a tooth or a group of teeth. The efficiency of an implant depends on its capacity to provide mechanical support, withstand loads, cyclic loads (fatigue) and wear. On the biological front; toxic, inflammatory, allergic reactions should not occur. Aspects like osseointegration, osteolysis or bone remodelling has to be considered. Per-Ingvar Brånemark, proposed that titanium (Ti) implants integrate such that the bone is laid very close to the implant without any intervening connective tissue. The major factor that determines the success of dental implantation is osseointegration. (the titanium dioxide, TiO2, layer permanently fuses with the bone)Geometrical design, the surface treatment, and the surgical technique are also essential in evaluating the performance of a specific implant.

Introduction

The initial period of osseointegration of Titanium & its alloys is the critical point for promoting the anchoring of dental implants. The implant/tissue interface is influenced by numerous factors, including surface chemistry and surface topography of the foreign material. Surface modifications have been applied to metallic biomaterials on macroscopic, microscopic and nano level in order to improve mechanical, chemical, and physical properties such as wear resistance, corrosion resistance, biocompatibility and surface energy.On the macroscopic level surface roughness influences the mechanical properties of the titanium/bone interface, through mechanical interlocking of the interface.Microrough surfaces enhances the mechanical retention between two surfaces, by sand-blasting, acid etching shot peening, or laser peening method.

Mechanism of osseointegration

Blood clot

Clot transformed by phagocytes (1st to 3rd day)

Procallus formation (containing immature fibroblasts and phagocytes)

Dense connective tissue (differentiation of osteoblasts and fibroblasts)

Callus formation

Fibrocartilagenous callus

Bony callus (penetration and maturation)

Implant Biomaterials

Biomaterials are those materials that are compatible with the living tissues. Biocompatibility is dependent on the basic bulk and surface properties and biomaterials. Materials used for fabrication of dental implants can be categorized in two different ways: 1. Chemical basis - metals, ceramics 2. Biological basis - biodynamic materials: biotolerant, bioinert, bioactive

Factors affecting implant biomaterial

1. Chemical factorsThree basic types of corrosion - General, pitting and crevice. 2. Surface Specific Factors The events at the Bone-Implant interface can be divided into • The behavior of the implant material • The host response 3. Electrical Factors • Physiochemical methods • Morphologic methods • Biochemical methods4. Mechanical Factors • Modulus of elasticity • Tensile or compressive forces • Elongation • Metallurgy

Metals and Alloys

• Titanium• Cobalt-Chromium-Molybdenum Based Alloys• Iron-Chromium-Nickel Based Alloys • Other Metals and Alloys

Ceramics

Ceramics are nonorganic, nonmetallic, nonpolymeric materials manufactured by compacting and sintering at elevated temperatures. They can be categorized according to tissue response as: • Bioactive: Bioglass/Glass ceramic • Bioresorbable: Calcium phosphate • Bioinert: Alumina, zirconia and carbon

Ceramics

• Aluminum, Titanium and Zirconium Oxides • Bioactive and Biodegradable Ceramics based on Calcium Phosphate

• Bioactive Ceramics • Carbon and Carbon Silicon Compounds• Bioactive Glass Ceramics

Polymers and Composites

Biomedical Polymers

The more inert polymeric biomaterials include—

Polytetrafluroethylene (PTFE), Polyethyleneterephthalate (PET), Polymethylmethacrylate (PMMA), Ultra high molecular weight polyethylene (UHMW-PE), Polypropylene (PP), Polysulfone (PSF) and Polydimethyl siloxane (PDS) or Silicone rubber (SR)

Surface modifications of titanium implants

Surface roughness has been identified as an important parameter for implants and its capacity for being anchored in bone tissue.Commercially available implants have been categorized according to the roughness value (Sa) into 4 groups by Albrektsson & Wennerberg in 2004 into- • smooth (Sa < 0.5 μm) • minimally rough (Sa = 0.5-1.0 μm) • moderately rough (Sa = 1.0-2.0 μm) • rough (Sa > 2.0 μm).

Based on the scale of the features, the surface roughness of implants can be divided into- • Macro • Micro • Nano

Methods for evaluation of Surface Roughness

1) Mechanical Contact Profilometers

2) Optical Profiling Instruments Focus Detection Systems Confocal Laser Scanning Microscopy White Light Interferometer

3) Scanning Probe Microscopes

Classification of Surface treatment

Classification -1 Ablative/Subtractive processes- Eg: Grit Blasting, Acid Etching, Anodisation, Laser peening Additive processes- Eg: Plasma Spraying, Electrophoretic Deposition, Sol Gel coating, Biomimetic precipitation

Classification -2 Based on texture obtained, the implant surface can be divided as: Concave texture: mainly by additive treatments like hydroxyapatite coating and titanium plasma spraying. Convex texture: mainly by subtractive treatment like etching and blasting

Classification -3 Based on the orientation of surface irregularities, implant surfaces are divided as: Isotropic surfaces: have the same topography independent of measuring direction. Anisotropic surfaces: have clear directionality and differ considerably in roughness.

Classification -4 Physicochemical: modification of surface energy, surface charge and surface composition to improve the bone-implant interface. Morphological: alteration of surface morphology and roughness to influence cell and tissue response to implants Biochemical: increased biochemical interaction of implant with bone

Macro-Surface ModificationsImplant design and topographyThread shapeThread depthThread widthThread pitchThread helix angleAmount of forceFavorable forceCrestal moduleRough or Smooth neckMicrothreadsMachined surface

Implant design and topography

Thread shape is determined by the thread thickness and thread face angle. Available shapes -- V-shape, square shape, buttress, reverse buttress and spiral. Thread shape determines the face angle. Face angle is the angle between the face of a thread and a plane perpendicular to the long axis of the implant.

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Thread depth is defined as the distance from the tip of the thread to the body of the implant. Thread width is the distance in the same axial plane between the coronal most and the apical most part at the tip of a single thread.

Thread pitch The distance from the center of the thread to the center of the next thread, measured parallel to the axis of a screw. In implants with equal length, the smaller the pitch the more threads there are.In a single-threaded screw, lead is equal to pitch, however in a double threaded screw, lead is double the pitch and in a triple-threaded lead is triple the pitch. An implant with double threads would insert twice as fast the single threaded and the triple threaded would only need a third of the required time for a single threadThread helix angleConstant pitch of 0.8mm. The double and triple threaded implants had twice and triple the thread helix of the single-threaded implant, respectively. According to FEA study, the implant stability appeared to be the single-threaded one. The triple threaded was found to be the least stable.

Amount of force Functional occlusal loading on an implant triggers the remodeling of the surrounding alveolar bone. A mild load induces a bone remodeling response and reactive woven bone production. However, excessive load result in microfractures which in turn causes osteoclastogenesis Favorable forces Three types of loads are generated at the interface --compressive, tensile and shear forces. An ideal implant design should provide a balance between compressive and tensile forces while minimizing shear force generation.

Crestal ModuleThe neck of the implant is called crest module In this area the bone density is thicker and therefore helpful to achieve implant primary stability. If loading on a particular bone increases, the bone will remodel to become stronger. If the loading on a bone decreases, the bone will become weaker because no stimulus is present.

Rough or Smooth neckOriginally crest module was always smooth. The use of a smooth neck on rough implants --decreases plaque retention because the coronal portion of the implant was not embedded in bone. When the smooth portion of the implant is placed under the bone crest, increased shear forces are created resulting in marginal bone loss and eventually more pocket formation. When an implant with a smooth neck is selected, it should be placed over the bone crest.

Micro threadsRecently, the concept of microthreads in the crestal portion has been introduced to maintain marginal bone and soft tissues around the implants. In presence of a smooth neck, negligible forces are transmitted to the marginal bone leading to its resorption. The presence of retentive elements at the implant neck will dissipate some forces leading to the maintenance of the crestal bone height accordingly to Wolff’s law. fMicrothreaded implants increase bone stress at the crestal portion when compared with smooth neck implants.

Machined surface

Lathing, Milling, Threading Machined implant surfaces are characterized by more grooves and valleys which provide mechanical resistance through bone interlocking. Properties of machined surface depends upon manufacturing tools, tool pressure, bulk material, thickness and temperature choice of lubricant and machining speed . Typical Sa values for machined surfaces are 0.3-1.0 μm. The surface oxide consists of a 2-10 nm thick mostly amorphous layer of TiO2 Disadvantage – osteoblastic cells are rugophillic—they grow along the grooves existing in the surface Hence a long waiting time (3-6 months )

Cell adhesion to a machined implant surface- SEM analysis

Micro-Surface Modifications1. Sand blasting2. Grit blasting3. Shot peening4. Acid etching5. Dual acid etching6. Sand blasting and acid etching SLA7. Other chemical treatments• Solvent cleaning• Alkaline etching• Passivation

Micro-Surface Modifications

8. Electrochemical treatments• Anodic oxidation /anodization is the chief anodic technique. • Biocoat – colour anodization• Biodize – alkaline grey anodization• Biobright -- electropolishing• Electrophoresis and Cathodic HA depositions are the cathodic techniques9. Laser treatments – Laser peening10. Vacuum treatment• Plasma treatments - plasma deposition method and plasma surface modification• Ion implantation method11. Thermal treatments

Micro-Surface Modifications

• Plasma spraying -- Titanium plasma spray (TPS) • Sputter deposition -- Radio frequency sputtering (RF),Magnetron sputtering• Sol-gel coated implants • Biomimetic precipitation • Electrolytic deposition • Ultrasonic spray pyrolysis

SandblastingSmall grits in chosen shape and size are forced across implant surfaces by compressed air that creates a crater. Surface roughness is dependent on the bulk material, the particle material, (size, shape, speed density), duration of blasting, air pressure, and distance between the source of the particles and implant surface. Blasting media --Alumina (Al2O3) or silica (SiO2) Surfaces blasted with 25 μm particles were rougher than machined surface and smoother than 75 μm and 250 μm blasted surfaces. Typical Sa values range from 0.5-2.0 μm Goals of sand blasting: 1) Cleaning the implant surface and increasing its bioactivity. 2) Roughening surfaces to increase effective/functional surface area. 3) Accelerate osteoblasts adhesion and proliferation 4) Producing beneficial surface compressive residual stress. 5) Exhibiting higher surface energy, higher surface chemical and physical activities. Enhancing fatigue strength, fatigue life, due to compressive residual stress.

Sandblasted titanium implant surface with 250-600μm

Grit blasting Surface of the implant is bombarded with hard dry particle or particles suspended in a liquid, through a nozzle at high velocity by means of compressed air. Roughness produced on the surface of Ti depends upon the size of the particle. Blasting material must be chemically stable and biocompatible and must not hamper osseointegration. Ceramic particles such as alumina, silica, Titanium oxide, calcium phosphate particles are used. Blasting media is embedded in the implant surface. Residue particles have been released into the surrounding tissues and interfered with osseointegration.Shot peening Modified method of grit blasting but has more controlled peening power, intensity and direction. It is a cold working process in which the surface of a part is bombarded with small spherical media called „shot‟. It is used primarily for introducing compressive stresses in the material‟s surface. Depends greatly on the size of the particle used. Alumina particles in the size (25-75 μm) -- surface roughness (0.5-1.5 μm)Particles of size (200-600 μm) -- roughness (2-6 μm) Glass particles of size (150-230 μm) -- smooth surface with Ra value of 1.36 μm

Acid-etching Immersing it in strong acids (e.g., nitric acid, hydrochloric acid, hydrofluoric acid, sulfuric acid, and their mixtures) for a given period of time, creates a micro-roughness of 0.5–3 μm. The surface is pitted by removal of grains and grain boundaries of the implant surface. It also cleans the implant surface, e.g., removes deposits. The typical Sa values are 0.3-1.0 μm (Fig.22).

Acid etched titanium implant surface in a mixture of HCl, HNO3 and H2SO4

Dual acid-etched techniqueImmersion for several minutes in a mixture of concentrated HCl and H2SO4 heated above 100 °C can be employed to produce a micro rough surface. This enhances the osteoconductive process through the attachment of fibrin and osteogenic cells, resulting in bone formation directly on the surface of the implant.Sandblasted and acid etched surface (SLA) SLA – (Buser) Sand blasted, Large grit, Acid etched. SLA combines sandblasting and acid-etching. In SLA protocol, the titanium dental implant surface is first sandblasted with large grits 250 - 500 μm, making the surface grossly rough. Then, the implant is acid-etched by HCL/H2SO4. Acid etching leads to micro texturing and cleaning.

SLA surface treated titanium implant

Other Chemical Treatments Solvent cleaningRemoves oils, greases and fatty surface contaminants remaining after manufacturing process. Organic solvents (aliphatic hydrocarbons, alcohols, ketones or chlorinated hydrocarbons), surface active detergents and alkaline cleaning solutions.Alkaline etching Treatment of titanium in 4-5 M sodium hydroxide at 600°C for 24 hours produce sodium titanate gel of 1 μm thick, with an irregular topography and a high degree of open porosity. Boiling alkali solution (0.2 M sodium hydroxide, 1400°C for 5 hours) produce a high density of nanoscale pits on the titanium. When the alkali treatment is preceded by etching in hydrochloric acid/sulfuric acid, porosity of the final surface is found to increase. Passivation treatmentsFor obtaining a uniformly oxidized surface to improve corrosion resistance. Immersion of titanium for a minimum of 30 minutes in 20-40 vol% solution of nitric acid at room temperature. After passivation, surface of the implant should be neutralized, thoroughly rinsed and dried. Nitric acid passivation has no major influence on the overall surface topography of titanium surfaces. In addition to nitric acid passivation, heating in air at 400- 600 °C or ageing in boiling deionized water for several hours can be used as an alternative passivation treatments (heat treatment) .

Electrochemical treatments

Anodic oxidation Produces roughness, porosity and chemical composition for improved biocompatibility. The anodic oxide can have interconnected pores (0.5–2 μm in diameter) and intermediate roughness (0.60–1.00 μm). In addition, anodic oxide can be flat layer or tubular and can have amorphous or anatase phase. Titanium can be anodically oxidized in a) acid (sulphuric acid and b) non-acid electrolytes like a) sodium phosphate and isopropyl phosphate in ethylene glycol, b) ammonium pentaborate, and c) calcium acetate and calcium glycerophosphate.Calcium and phosphorus are deposited on the titanium oxide during anodization from a bath containing calcium acetate and glycerophosphate and are useful for the formation of HA.The oxides usually grow at the rate of 1.5 – 3 nm/V (also called as growth constant) in the various electrolytes.

Anodised surface

Biocoat -- (colour anodization) Titanium is immersed into an electrolyte and connected as an anode leading to the formation of an oxide film at the surface.Biodize -- (alkaline grey anodization) Similar to the Biocoat however the specific electrolyte allows the formation of thicker TiO2 layers in the range of micrometers.Biobright -- (electropolishing) Titanium is immersed into an electrolyte and is connected as an anode leading to the dissolution of the titanium material. Innosurf Modification of the Biobright process. The removed layer of titanium is in the range of 5 to 30 micrometers. The thickness of the layer to be dissolved depends on the starting roughness of the material. Electropolishing eliminates surface contaminants.

Electrophoresis

Electrophoretic deposition (EPD)HA powders dispersed in a suitable solvent and coatings are obtained by applying voltages of the order of 20- 200V. The coating density is improved by a further sintering at 600°C or above. Using this method, small particles as well as large particles can be deposited.Advantages Simplicity and low cost Ability to coat with uniform thickness, wide range of thicknesses, complex shapesEase of chemical composition control. Disadvantage -- Post-coating sintering at about 800°C.Mechanism -- Two steps. 1st -- the migration of particles (which acquire positive charge) under the influence of an electric field applied to a stable colloidal suspension. 2nd -- deposition on the metallic substrate. Driving force of the deposition process is the applied electric field. Depending on the mode and sequence of voltage applied, the electrophoretic deposition can be carried out at i) constant voltage or ii) dynamic voltage.

Electrochemical cathodic deposition Calcium phosphate coatings are formed on the titanium cathode from a bath containing dissolved calcium and phosphorus compounds. Concentrations of calcium and phosphorus in the electrolyte, pH of the electrolyte, cathodic current density, time, processing temperature and pressure are the parameters influencing the type of calcium phosphate deposit. Pulsed electrochemical deposition -- produce CaP coatings on porous titanium substrates under milder conditions (pH 4.4, 25°C) but post-treatment with sintering under vacuum at high temperatures between 300 and 800°C was required.Galvanostatic technique was used to produce HA

Laser Treatments

Laser is an micromachining tool to produce a 3-D structure at micrometer and nanometer level. Generates short pulses of light, of single wavelength, providing energy focused on one spot. Advantages• Rapid andextremely clean• Suitable for the selective modification of surfaces. • Allows the generation of complex microstructures with high resolution. • No chemical treatments are done. Only the valley and parts of the flank of the implant threads is laser treated while the remaining part was left as machined. Flank portion (smooth surface) to minimize the incidence of peri-implantitis. High risk to expose to the microorganism and plaque. Valley part of the implant threads has the rougher surface.

Laser Peening no contact, no media and contamination free. High intensity (5-15 GW/cm2) nanosecond pulses (10-30ns) of laser light beam (3-5mm width) striking the ablative layers generate short-lived plasma which causes a shock wave to travel into the implant.The shock wave induces compressive residual stress that penetrates beneath the surface and strengthens the implant, resulting in improvements in fatigue life and retarding in stress corrosion cracking occurrence.The average surface roughness of the laser treated acid-etched implant was 2.28 μm

Vacuum treatment

Glow-discharge treatment (cold plasma treatment) is based on the action of a low-pressure electrical discharge on the surface of the implant. Two types - plasma deposition method and plasma surface modification. In Plasma deposition -- glow discharge is used to deposit the coating material from a separate solid target (sputter deposition) and/or by reactions in the gas phase (reactive sputtering or plasma polymerization). In Plasma surface modification -- exposure of sample surface to a glow discharge in order to obtain a specific modification of surface properties.

In Ion implantation method Surface of the implant is bombarded with high energy ions (approximately 100 KcV to 1 McV range). Ions will penetrate the surface of implant to typical depths of approximately 0.1-1 μm. Ion implantation is controlled by varying the concentration of ions and their energy.

Thermal treatments

Commercially pure titanium can be thermally annealed up to 1000°C to form oxide layer composed of anatase and rutile structures of TiO2. The titanium oxide that is formed on the surface is crack-free and uniformly rough. Average roughness when the titanium is annealed at 600 °C and 650 °C for 48 hours was 0.90 and 1.30 μm, respectively.Average roughness of untreated sample was 0.08 μm. Thermal treatment at 600°C and 650°C for 48 hours is considered appropriate for implanted materials.

Plasma spraying

Titanium Plasma Spray (TPS) A gas plasma stream is first created by having an electrical arc between a finger-type tungsten cathode and a nozzle-type copper anode inside the plasma torch. Inject titanium powders into a plasma torch at high temperature. The titanium particles are projected on to the surface of the implants where they condense and fuse together, forming a film about 30μm thick. The thickness must reach 40-50μm to be uniform. TPS coating has an average roughness of around 7μm.

Sputter deposition

Atoms or molecules of a material are ejected in a vacuum chamber by bombardment of high-energy ions. Useful technique for the deposition of bioceramic thin films Drawback -- deposition rate is very low and the process itself is very slow The deposition rate is improved by radio frequency magnetron sputtering. Radio frequency sputtering (RF) -- used to deposit thin films of CaP coatings on titanium implants. Magnetron sputtering – is a thin-film technique as it allows the mechanical properties of titanium to be preserved while maintaining the bioactivity of the coated HA.

Electrophoretic Deposition

Colloidal particles such as hydroxyapatite 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. EPD can produce HA coatings ranging from <1 to >500μm thick. Advantages Low cost and simple methodology Produces coatings of variable thicknesses High deposition rateAbility to coat irregularly shaped or porous objectsDisadvantages Need for post deposition heat treatment to increase the density of the coating. (1200˚C)

Sol-gel coated implants

Deposits thin coatings with homogenous chemical composition onto substrates with large dimensions and complex design. A system that joins both materials has the mechanical advantages of the underlying (metallic) substrate and biological affinity of HA. Advantagessimple and low cost procedurehigh mechanical strength and toughness of titanium alloys

Biomimetic deposition

Deposition of hydroxyapatite and other calcium phosphate substrates on surfaces of implant materials in simulated body fluid (SBF) under physiological conditions of temperature and pH.Incorporation of drugs and growth factors makes the implants osteoinductive and osteoconductive. Ca–P coating requires an immersion period of about 14 – 28 days with replenishment of SBF solution. The Ca/P ratio for HA biomimetic coating was 1.51 The thickness of HA coatings -- 20 to 25 μm.

Electrolytic deposition

The porous surface can be uniformly coated still maintaining the original composition of the material. The thickness can be as low as 1μm and even of nanometer thickness. The Nanotite implant has a 20nm HA compound attached to the surface. The HA nanoparticles are prepared by mixing phosphoric acid and calcium nitrate with a CaP ratio of 1.67 in the presence of a liquid crystalline phase containing surfactants, water and insoluble organic solvents. The liquid crystalline phase works as a template hindering the particle growth and limiting the particle size to around 5nm. After the particles are formed, the liquid crystalline phase is dissolved and the particles are deposited onto the Ti implants by a dip coating technique and dried. The surfactants are absorbed during the coating process and burned away at 55°C for 5 minutes in an atmosphere of nitrogen. This resulted in the nanocrystalline HA thin layer being deposited on the implant surface.

Ultrasonic spray pyrolysisGroup of processes for particle production which are based on precursor atomization, aerosol transport through a temperature and atmosphere regulated reactor. Used in the production of nanopowders.Particle morphology is the result of -- droplet size (1-100μm), precursor concentration, operating temperature and evaporation rate. Inside the furnace, the following steps are assumed to be taking place- 1. Evaporation of the solvent 2. Diffusion of solutes 3. Precipitation 4. Decomposition 5. Densification Three main process steps (aerosol generation, thermal decomposition, nanopowder collection).

Nano-Surface Modifications

Organic nanoscale self-assembled monolayers Involves adsorption and self-assembly of single layers of molecules on a substrate. Molecular self-assembly of alkane phosphate SAMs on metal oxides like TiO2 and Al2O3. The hydrophilicity of these alkane phosphate SAMs can be modified with a hydroxy-terminated end group. When smooth and rough titanium surfaces coated with hydroxy-terminated (hydrophilic) and methyl-terminated (hydrophobic) alkane phosphate SAMs were exposed to human fibroblasts, more fibroblasts were found on smooth surface. Surface wettability was much less important than surface roughness.

Hydrogels on Titanium Surface

A hydrogel is a network of polymer chains that swell in aqueous solution. It is composed of long polymer chains connected by cross-links. The cross-links may be biodegradable or non-biodegradable and are formed by ionic interactions between polyelectrolyte chains. Cross-linking of polymer molecules or polymerization can be achieved by photo-polymerization, changes in temperature, radiation, self-assembly, or cross-linking enzymes. Hydrogels undergo responsive swelling by absorbing solvent when placed in an aqueous solution (solvation). Swollen hydrogels can absorb many times their own weight in water and can switch between swollen and collapsed forms (Fig.29). Properties of hydrogels are high biocompatibility, biodegradability, and ability to incorporate biomolecular cues (due to high permeability for oxygen, nutrients, and water-soluble metabolites).

Titanium Nanotubes

A nanotube is a tube-like structure at the nanometer-scale (10-9 m). Contain at least two layers, or more measuring about 3–30 nm in outer diameter. Bilayered nanotubes were closed at both ends.Chemical synthesis of titanium dioxide (TiO2) nanotubes by anodization technique. The thickness and structure of the oxide layers formed (amorphous or crystalline) depends on the applied potential between the electrodes, duration of anodization process, and the chemical composition of electrolyte used. Depending on the anodizing conditions, the crystal structure can be anatase, a mixture of anatase and rutile, or rutile A completely different growth morphology leading to self-organized and ordered nanotubular, nanoporous structures of TiO2 has been obtained when electrolytes containing fluoride ions and suitable anodization conditions were used. These nanotube-like pores possess higher surface energy and wettability compared to un-anodized titanium.

Typical morphology obtained in-(A) acidic fluoride or HF electrolytes (B) glycerol/fluoride electrolytes, (C) ethylene glycol/fluoride electrolytes. (D) Tubes grown by a different approach: rapid breakdown anodization (RBA)

Bioactive Surface Coatings

1. Bioactive glass coatings 2. Hydroxyapatite (HA) Coating 3. Calcium-Phosphate Coating 4. Titanium Nitride Coatings 5. Fluoride treatment 6. Biologically active drugs • Bisphosphonates • Simvastatin • Antibiotic coating -- Gentamycin Tetracycline-HCl

1. Bioactive glass coatings silica-based bioactive glasses are slowly resorbing synthetic osteoconductive materials which are able to form strong chemical bond with bone. The coating withstands an external stress of 47MPa, and adequate for load bearing application. Double glass coating -- to solve the problem of differences in thermal expansion coefficients. Application of a ground layer prepared from inert glass with a thermal expansion coefficient close to that of Ti6Al4V provided good adhesion to the substrate. Ground coating in combination with more surface reactive glass coatings , embedded with hydroxyapatite and/or bioactive glass particles or a sol-gel-derived silica coating, Reactive plasma spraying or processing with infra-red laser have also been attempted to create bioactive glass coatings on titanium and its alloys. Titanium implants coated with bioactive glass (BAG) were integrated into host bone without a connective tissue capsule and greater osseointegration and high removal torque in comparison to the control uncoated titanium implants.

2. Hydroxyapatite (HA) Coating HA osseointegrates faster and stronger than untreated titanium so it is coated on the surface of titanium implants. The resulting composite material combines the mechanical advantages of titanium and superior bioactivity and biocompatibility of HA.HA is usually coated onto the surface of a titanium dental implant through plasma spraying, ion beam assisted deposition. All these techniques require sophisticated and expensive equipment and involve the use of high temperatures. Biomimetic processes overcomes the above problems.HA coating has two major advantages.- 1. Faster osseointegration leads to earlier stabilization of the implant in surrounding bone. 2. Stronger bonding between implant and bone extends the functional life of the prosthesis

3. Calcium-Phosphate Coating Accelerates bone formation around the implant and produces effective osseointegration. Various processes available -- chemical, electrochemical and physical – ion beam dynamic mixing technique (IBDM), Radio- frequency magnetron sputter technique, biomimetic deposition, electrochemical deposition are a few examples.

4. Titanium Nitride Coatings Treatment is known as Plasma nitriding or PVD coating with TiN. Titanium nitride has high surface hardness and mechanical strength. Titanium nitriding increases corrosion resistance and surface hardness of the exposed implant surfaces. Methods of titanium nitriding -- gas nitriding, plasma nitriding by plasma diffusion treatment, plasma-assisted chemical vapour deposition, pulsed DC reactive magnetron sputtering and closed field unbalanced magnetron sputter ion plating.

5. Fluoride treatment Titanium is very reactive to fluoride ions, forming soluble TiF4. The chemical treatment of titanium in fluoride solutions enhances the osseointegration of dental implants. 6. Biologically active drugs Bisphosphate-- improve implant osseointegration and they are antiresorptive agents. Simvastatin -- induces bone morphogenetic protein (BMP) that promotes bone formation. Antibacterial coatings -- provides antibacterial activity to the implants.a) Gentamycin --local prophylactic agent b) Tetracycline-HCl -- decontamination and detoxification of contaminated implant surfaces.

Summary

The surface roughness values produced in each type of surface modification technique-

Conclusion

Despite conflicting reports regarding the effect of and micro- and/or nano-topography on the osseointegration of dental implants, the prevailing philosophy is that they may significantly influence the bone growth and attachment to implant surfaces and ultimately improve the success of dental implants and the rapid return to function. The exact role of surface chemistry and topography on the early events of the osseointegration of dental implants remain poorly understood. These techniques have greatly influenced the quality of clinical service in implant prosthodontics.