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Titanium and titanium alloys/ /certified fixed orthodontic courses by Indian dental academy


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  • Ti-O phase diagram required
  • Transcript

    • 1.
    • 2. INDIAN DENTAL ACADEMY Leader in continuing dental education
    • 3. Metals have been used as Biomaterials for many centuries. Around 1565 gold plate was reported to be used to repair cleft palate defects. Gold alloys and their substitutes are formed by a casting process developed by Taggart in 1907. Since then, cast gold restorations have been routinely used in clinical dentistry.
    • 4. With advances in dental porcelain in the 1960s and the significant increase in the price of gold in the 1970s, alternative alloys such as palladium alloys and base metal alloys, were developed. The allergenic and carcinogenic properties of base metal alloys used in dentistry especially nickel and beryllium-based alloys, have fueled controversy.
    • 5. The evolution of titanium (Ti) applications to medical and dental implants has dramatically increased in the past few years because of titanium’s excellent biocompatibility corrosion resistance and desirable physical and mechanical properties.
    • 6. Titanium has become a material of great interest in prosthodontics in recent years. A growing trend involves the use of titanium as an economical and biocompatible replacement for existing alloys for fixed and removable prostheses. However, long term of titanium casting, joining, and porcelain bonding have to be evaluated before this wonder metal can be used routinely in clinical dentistry.
    • 7.
    • 8.
    • 9.
    • 10. Most important deterrent to the use of Ti in dental application is the fact that it is difficult and dangerous to cast, The metal oxidizes so rapidly at elevated temperature that an almost explosive reaction may occur. So that it needs to cast titanium alloy in oxygen atmosphere (vacuum or argon) to prevent excessive oxidation.
    • 11.
    • 12. The physical and mechanical properties of pure Ti and Ti alloys can be greatly varied with the addition of small traces of other elements such as oxygen, iron, and nitrogen. Commercially pure titanium, is available in four different grades
    • 13. ASTM 1 to 1V - based on the incorporation of small amounts of oxygen, nitrogen, hydrogen, iron, and carbon during purification procedure. ASTM committee on materials for surgical implants recognizes four grades of commercially pure titanium and two titanium alloys.
    • 14.
    • 15. The two alloys are Ti-6Al-4V and Ti-6A1-4V extra low interstitial (ELI). Commercially pure titanium is also referred to as unalloyed titanium. All six of these materials are commercially available as dental implants.
    • 16. Ti-6A1-4V Several alloys of titanium are used in dentistry. Of these alloys, Ti 6Al-4V is the most widely used. At room temperature, Ti-6A1-4V is a twophase α+β alloy. At approximately 975°C, an allotropic phase transformation takes place, transforming the microstructure to a single phase BCC β-alloy.
    • 17.
    • 18. Thermal treatments dictate the relative amounts of the α and β phases and the phase morphologies and yield a variety of microstructures and a range of mechanical properties.
    • 19.
    • 20.
    • 21. An extremely reactive metal, titanium forms a tenacious oxide layer that contributes to its biocompatibility and electro chemical passivity. This stable oxide with a thickness on the order of nanoseconds, and it repassivates in a time on the order of nanoseconds.
    • 22. However, titanium-based alloys and alloys containing titanium are prone to gap corrosion and discoloration in the oral cavity. Therefore titanium is electrochemically inactivated by the addition of small percentage of a metal of platinum group to improve the anticorrosion properties of the alloys by inducing a firm passive coating.
    • 23. Palladium was chosen among the platinum group metals, as it prevents corrosion of titanium by the addition of only a small amount (0.15%).
    • 24.
    • 25. The lightly held 3d² and 4s² electrons are highly reactive and rapidly form a tenacious oxide that is responsible for the metal’s biocompatibility. The remaining electrons are relatively stable and tightly bound.
    • 26. There are three general types of titanium base alloys, such as alpha alloys, alpha-beta alloys, and beta alloys, according to the predominant room temperature phases present in the microstructure. At temperatures upto 882°C, pure titanium exists as hexagonal closepacked atomic structure (alpha phase).
    • 27. Above that temperature, pure titanium undergoes a transition from hexagonal closepacked structure (alpha) to a body-centered cubic structure (beta). The metal melts at 1665°C. A component with a predominantly β-phase is stronger than a component with an α-phase microstructure.
    • 28. Alloying elements are added to stabilize one or the other of these phases by either raising or lowering the transformation temperatures. The elements oxygen. aluminium, carbon, and nitrogen stabilize the alpha phase of titanium because of their increased solubility in the hexagonal close-packed structure.
    • 29. For example, in Ti-6A1-4V aluminium is an a stabilizer, which expands the a phase field by increasing the (α+β) to β transformation temperature. Elements that stabilize the beta phase, include manganese, chromium. iron and vanadium. They expand the β -phase field by decreasing the (α+β ) to β transformation temperatures.
    • 30. Vanadium stabilizes the beta phase of Ti-6A1-4V alloy, so that it exists as a combination of alpha and beta phases. The combination of phases gives the alloy strength.
    • 31. The ELI alloys are sometimes used. “Extra low interstitial” describes the low levels of oxygen dissolved in interstitial sites in metal. With lower amounts of oxygen and iron residuals in the ELI alloy, ductility is improved slightly.
    • 32. In general, alpha titanium is weldable, but difficult to form or work with at room temperature. Beta titanium, however, is malleable at room temperature and is thus used in orthodontics. The (α+β) alloys are strong and formable but difficult to weld.
    • 33. Thermal and thermo chemical treatments can refine the post cast microstructures and improve properties.
    • 34. Density 4.5g/cm³ (considerably less than gold or Ni-Cr or Co-C r alloys) Because of the light weight of the titanium and its strength-to-weight ratio, high ductility, and low thermal conductivity would permit design modifications in Ti restorations and removable prostheses, resulting in more functional and comfortable use.
    • 35. The low cost of titanium raw material (USD 22 to 27 per kg) makes titanium material attractive for dental prostheses.
    • 36. The environmental resistance of titanium depends primarily on a thin, tenacious, and highly protective surface oxide film which is about 2O - 50 A°. Titanium and its alloys develop stable surface oxides with high integrity, tenacity and good adherence.
    • 37. The surface oxide of titanium will, if scratched or damaged, immediately reheal and restore itself in the presence of air or water. The protective oxide film on titanium mainly Ti02 (rutile), is stable over a wide range of pHs, potentials, and temperatures, and is specially favoured as the oxidizing character of the environment increases.
    • 38. For this reason, titanium generally resists mild reducing, neutral, and highly oxidizing environments upto reasonably high temperatures. It is only under highly reducing conditions that oxide film breakdown and resultant corrosion may occur. These conditions are not normally found in the mouth.
    • 39. The Coefficient of thermal expansion is a most important factor in bonding of an alloy to porcelain. The difference in the coefficient of the expansion between the alloy and porcelain should be within ±1x10-6 /°C to obtain sufficient bonding strength.
    • 40. Coefficients of thermal expansion of pure titanium and Ti-6A1-4V are 10.37 x 10-6 and 12.43 x 10-6 /ºC, respectively, which are considerably smaller than those of commercial porcelain materials which is about 14 x l0-6 /°C.
    • 41. Titanium is the most corrosion resistant metallic material for implants in present use, but, paradoxically, the self formed protective oxide film on titanium can be affected by excessive use of the commonest preventive agents in dentistry, prophylactic polishing and topical fluoride app1ications.
    • 42. Adhesion of titanium to methacrylate based polymer materials can be increased by plasma treatment.
    • 44. The mechanical properties of titanium and its alloys surpass the requirements for an implant material. Orthopaedic and dental implants require strength levels greater than that of bone and an elastic modulus close to that of bone.
    • 45. The most commonly used and important titanium alloy is Ti-6A1-4V, because of its desirable proportion and predictable producibility. The ultimate tensile strength of spongeous bone is about 83 MPa and cortical bone is about 117 MPa.
    • 46.
    • 47.
    • 48. It is important to note that while the modulus of elasticity of cp grade 1 titanium to cp grade 1V titanium ranges from 102 to 104 GPa (a change of only 2%), the yield strength increases from 170 to 483 MPa (a gain of 180%). Reasons for the changes are related chiefly to oxygen residuals in the metal.
    • 49. The characteristic trend of increasing strength with relatively constant modulus continues when comparing cp titanium with titanium alloys. The elastic modulus of the alloys is slightly higher (113 MPa compared with 104 MPa of cp grade 1V titanium), but the yield strength increases over 60% to 795 MPa for ELI alloys and 860 MPa for Ti-6A1-4V alloys.
    • 50. Titanium has poor shear strength and wear resistance, however making it unsuitable for articulating surface or bone screw applications.
    • 51. Compared with Co-Cr-Mo alloys, titanium alloy is almost twice as strong and has half the elastic modulus. Compared with 316L stainless steel, the Ti-6A1-4V alloy is roughly equal in strength, but again, it has half the modulus.
    • 52. Strength is beneficial because materials better resist occlusal forces without fracture or failure, Lower modulus is desirable because the implant biomaterial better transmits forces to the bone.
    • 53.
    • 54. Titanium and its alloys are inert, have excellent biocompatibility and predictability. The non-alloyed titanium elicits an acute inflammatory response with an increased number of leukocytes around the implant. However, the number of inflammatory cells decrease during the first week and fibroblasts become the major cells in the interfacial tissue.
    • 55. During the first week the implant is surrounded by a fluid space that contains proteins, erythrocytes. inflammatory cells and cell debris. One week after insertion of implants, the size of the fluid space reduces in non-alloyed titanium, for example, ion implanted titanium.
    • 56. The inflammatory cells present in this space seldom adhere to the surface of the nonalloyed titanium and do not appear activated. Non-alloyed titanium implants are surrounded by a thin layer of orderly arranged collagen and elongated fibroblasts.
    • 57. Titanium also provides a surface suitable for the proliferation of several differentiating tissues. Non-alloyed titanium fixtures which are inserted in knee-joints after drilling through the cartilage or synovial tissue heal within the joints and a direct contact with the subchondral bone is established 4 to 6 weeks after insertion.
    • 58. Non-alloyed titanium can also be used intraarticularly as it causes no inflammation in the synovial tissue. Plaque accumulation of titanium or hydroxylapatite (HA) coated titanium is less than on natural teeth because of its high surface energy.
    • 59. Bone formation and its maturation occurs faster on HA coated Ti implants than on noncoated Ti implants. Since enhanced bone growth preceedes by rapid clotting, so the clotting occurs faster on the HA-coated Ti implants than on non-coated titanium implants.
    • 60.
    • 61. Lost wax casting
    • 62.
    • 63. This is a the recently developed investment for casting titanium inlay, crown and bridge. Binder - calcia Refractory -Zirconia
    • 64. There are 2 types of Calcia and mixing liquid. 1. Saturation type (total expansion 2 ± 3%) 2. Delayed expansion type Properties 1. Total thermal and setting expansion found was -1 .5 2.5% 2. The maximum thermal expansion is found at - 900 1200°c
    • 65.
    • 66. Cp titanium - vacuum casting
    • 67. Pure titanium melts at 3,035°F (1,668°C) and reacts readily with conventional investments and gases like oxygen, nitrogen and carbon. In addition because of its low specific gravity, titanium flows less easily that gold alloy when cast in centrifugal casting machine. Therefore, it must be cast and soldered with special equipment in oxygen free environment.
    • 68. New alloys of titanium with nickel that can be cast by more conventional. methods are being developed. They release verity little ionic nickel and bond well to porcelain. New methods of forming titanium crowns and copings by CAD/CAM technology avoids the problem of casting altogether.
    • 69. Lost-wax casting is one of the most widely used methods for the fabrication of metallic restorations outside of the mouth.
    • 70. Three different types of specially designed Ti casting systems are presently available namely A pressure / vacuum casting system with separate melting and casting chamber (Castmatic, Dentaurum) .
    • 71. A pressure /vacuum system with one chamber for melting and casting (Cyclare, J Morita) and vacuum / centrifuge casting system (Tycast. Jeneric / Penetron, and Titaniumer, Ohara)
    • 72. The market price for each system ranges from USD 20,000 to 30,000.
    • 73. A new casting machine for casting of titanium and Ni-Ti alloys was developed by H.Hamanaka et al in 1989. The machine consists of an upper melting chamber and a lower casting chamber with an argon arc vacuum pressure system.
    • 74.
    • 75. The main features that have been developed are as follows: 1) The melting and casting chambers are evacuated to a higher degree by means of an oil diffusion pump. 2) In the casting chamber, a heater has been placed to control the mold temperature; it may be moved up and down with use of the lever outside the chamber.
    • 76. 3) Two types of copper crucibles have been developed - one a split type and the other a tilting type that are changeable. 4) A device for direct suction has been placed at the bottom of the mold for improved castability. 5) The vaccum tank and the compressed argon gas tank have been set to operate more efficiently.
    • 77. 6) With use of the water-cooled electrode and double D.C. electric sources, the capacity for melting alloy is about 100g. 7) A new control system was developed. In this system, after a mold and metal are set on the machine, the upper and lower chambers are evacuated.
    • 78. Then, argon gas is fed into the upper chamber when the “start” button is pushed, and an electric arc begun automatically at the given pressure. After the alloy melts down, the new control system can be started when the “cast” button is pushed.
    • 79. At first. the upper chamber is exhausted for 0 to 1.0 seconds , and then the copper crucible splits or tilts to drop the molten metal. From 0.01 to 0.05 seconds later, the compressed argon gas is injected into the upper chamber. This control system works automatically in accordance with a given program.
    • 80. Advantages of this machine are: As gas in the mold is removed by the mold being heated under a high vacuum, the reaction between the molten metal and the mold decreases.
    • 81. The new control system and the two types of crucibles developed proved very useful for prevention of internal macro-defects in castings and for improvement of castability. Mechanical properties and castability of pure titanium are improved.
    • 82.
    • 83. The initial application of titanium to dentistry was machined Ti dental implants. As an alternative to lost-wax casting, the Procera system (Nobelpharma) with titanium machining has been developed by Andersson et al for the fabrication of unalloyed titanium crowns and fixed partial dentures.
    • 84. The external contour of a titanium crown or coping can be shaped out of a solid piece of titanium by a milling machine, while the internal contour of the titanium crown is spark eroded with a carbon electrode. Single titanium crowns can be fabricated with this method, and multiple unit fixed prostheses can be made by laser welding individual units together.
    • 85.
    • 86. Information on the marginal fit of titanium crowns was unavailable until quite recently. Meyer and Schafers evaluated cast titanium inlay and partial veneer crowns. Heterogeneous results did not satisfactorily withstand comparison to conventional methods. The authors questioned the clinical application of titanium casting.
    • 87. Ida et al reported that, in more than 100 cast titanium crowns made, the fit was inferior to that of silver-palladium crowns but superior to that of nickel-chromium crowns. The criteria used to determine fit were not described.
    • 88. Blackman et al examined the fit of 20 cast titanium copings divided into two equal groups with 45 and 90 degree shoulders. The surface of marginal discrepancy was greatest with the 90 degree configuration. Casting shrinkage occurred particularly along the horizontal axis in the plane of the shoulder. It was concluded that Ti crown copings can be cast with acceptable fitting accuracy.
    • 89.
    • 90. Different methods to join titanium have been investigated. Yamagishi et al examined the mechanical properties of Nd:YAG laser welds of titanium plates (1mm thick) and found that there is a significant relationship between three-point bending strength and the irradiation atmosphere, the irradiation intensity, and the combination of atmosphere and intensity.
    • 91. Laser welding is effective when performed in an argon environment. At the same time, the results are markedly different with various intensities of irradiation.
    • 92. Roggensack et al studied the bending fatigue behavior of titanium joined by laser and plasma welding. No significant differences in fatigue strength could be found between the two methods of welding. Extreme loads led to earlier fatigue in the plasma welded specimens.
    • 93.
    • 94. Even after the recent developments and improvements in casting technology, the challenge of using titanium casting for prosthesis still presents major difficulties. The mechanical properties of cast titanium differ significantly from those of the parent metal.
    • 95. Also, the outer 100 to 200 micro meter of the surface has greater hardness and reduced ductility than the core material. Titanium’s high-fusing temperature and chemical activity are considered primarily responsible for these casting problems.
    • 96. So new techniques like spark erosion (electro erosion) and machine duplication termed “copymilling” have been introduced. Ti-6A1-4V is one of the superplastic alloys that exhibits excellent elongation (more than 1,000%) at a temperature of 800°C to 900°C.
    • 97. This super plasticity deformation is obtained by grain-boundary sliding or dislocation with a fine-grain structure (diameter 4 to 10 micro meters). Ti-6A1-4V is applied to denture framework fabrication.
    • 98. The retention of acrylic resin to the titanium base is an important consideration. Noriyuki Wakabayashi et al confirmed that bond strength between a denture-base resin containing an adhesion-promoting monomer and Ti-6Al-4V alloy that had been airborne particle abraded using aluminum oxide particles was statistically equivalent to that between the same resin and a cobaltchromium alloy casting.
    • 99.
    • 100.
    • 101. Commercially pure (cp) titanium and titanium alloys containing aluminum and vanadium, or palladium (Ti-O Pd), should be considered potential future materials for removable partial denture frameworks.
    • 102. Their versatility and well-known biocompatibility are promising; however, long-term clinical studies are needed to validate their potential usefulness. Currently, when cp titanium is cast under dental conditions, the material properties change dramatically.
    • 103. During the casting procedure, the high affinity of the liquid metal for elements such as oxygen, nitrogen, and hydrogen results in their incorporation from the atmosphere.
    • 104. The usefulness of Ti as a metal for removable partial denture (RPD) and complete-denture frameworks has been evaluated. Removable partial denture frameworks that were 0.70 mm thick had better castability than did 0.35 mm thick RPD frameworks, suggesting that if Ti is used for RPD frameworks, a thicker wax pattern is needed than is used in casting of a conventional denture framework with Co-Cr alloys.
    • 105. In the same study, Ti commonly failed to cast perfect mesh specimens, but Co-Cr alloys did not have this problem.
    • 106.
    • 107. The biocompatibility of titanium is well known in its clinical application in dental and craniofacial implants. Its use has been recently extended to include metal ceramic crowns. Titanium copings can be fabricated by casting or by machine milling.
    • 108. The low coefficient of thermal expansion (CTE) of titanium (about 9 x 10-6/ºC) compared to those of the conventional lowfusing porcelains (about 13 x 10-6/°C) raised the concern of thermal compatibility.
    • 109. Porcelains manufactured to bond to titanium are currently commercially available. The Procera porcelain (Procera, Nobelpharma: Goteborg, Sweden) was formulated for machine-milled crowns processed through the Procera technique, while the Duceratin porcelain (Degussa, South Plainfield NJ) was formulated for cast titanium crowns.
    • 110. The strength of porcelain-fused-to-metal structures is related to mechanical properties of the metal framework, the veneering porcelain, the porcelain-metal interface, and their interactions.
    • 111.
    • 112. There is abundant literature on the adherence of oxides formed at high temperatures on gold alloys, Ni-Cr, and Co-Cr alloys. The oxidation mechanisms and reasons for development of a non-adherent oxide layer while not perfectly understood, are well characterized for Ti and its alloys.
    • 113. Kirmura et al reported the oxidation effects of the porcelain-titanium interface reaction. They concluded that the conventional degassing procedure is not suitable for porcelain-titanium restorations and that the cycle should be below 800°C to minimize the metallic oxide formation on the Ti surface.
    • 114.
    • 115. The use of metals for implants dates back to ancient times. It was not until the 1930s, however, that improvements in metal technology led to an era of expanded surgical use of metallic implants.
    • 116.
    • 117. A successful long-term implant requires biocompatibility, toughness, strength, corrosion resistance, wear resistance, and fracture resistance. Titanium alloys of interest to dentistry exist in three forms: alpha, beta, and alpha-beta. These types originate when pure titanium is heated, mixed with elements such as aluminium and vanadium in certain Concentration and cooled.
    • 118. Titanium and its alloys are important in dental and surgical implants because of their high degree of biocompatibility, their strength. and their corrosion resistance.
    • 119. Pure titanium, theoretically, may form several oxides. Among these . TiO, Ti02 and Ti2 03. Of these, TiO2 is the most stable and therefore the most commonly used under physiologic conditions. These oxides form spontaneously on exposure of Ti to air.
    • 120. When an implant is introduced into the body, complex reactions begin to take place at the oxide/bio environment interface. The oxide film grows as ions diffuse outward from the metal and inward from the environment. The oxide that forms in the body may therefore, be somewhat different than that which forms in air.
    • 121. The rate of formation and composition of this film is important. Titanium, both as a pure metal and as an alloy, is easily passivated, forming a stable Ti02 surface oxide that makes the metal corrosion resistant. This oxide will repair itself instantaneously on damage such as might occur during insertion of an implant.
    • 122. The normal level of Ti in human tissue is 50 ppm. Values of 100 to 300 ppm are frequently observed in soft tissues surrounding Ti implants. At these levels, tissue discoloration with Ti pigments can be seen.
    • 123. This rate of dissolution is one of the lowest of all passivated implant metals and seems to be well tolerated by the body. The clinical significance of this data is substantiated by more than 20 years of clinical experience with pure Ti and Ti 6A1 4V alloys.
    • 124.
    • 125. This reactive group of metals and alloys (with primary elements from reactive group metallic substances) form tenacious oxides in air or oxygenated solutions. Titanium (Ti) oxidizes (passivates) upon contact with room temperature air and normal tissue fluids.
    • 126. This reactivity is favourable for dental implant devices. In the absence of interfacial motion or adverse environmental conditions, this passivated (oxidized) surface condition minimizes biocorrosion phenomena. In situations where the implant would be placed within a closely fitting receptor site in bone, areas scratched or abraded during placement would repassivate in vivo.
    • 127. This characteristic is one important property in vivo. This characteristic is one important property consideration related to the use of titanium for dental implants. Some reports show that the oxide layer tends to increase in thickness under corrosion testing and that breakdown of this layer is unlikely in aerated solutions.
    • 128. Bothe et al. studied the reaction of rabbit bone to 54 different implanted metals and alloys and showed that titanium allowed bone growth directly adjacent to the oxide surface. Leventhal further studied the application of titanium for implantation. Beder et al., Cross et al., Clarke et al., and Brettle were able to expand indications of these materials. In all cases titanium was selected as the material of choice because of its inert and biocompatible nature paired with excellent resistance to corrosion.
    • 129.
    • 130. Proper implant configuration can help effectively control or alter force transmission to remain within physiologic limits of health. The basic metallurgic properties of titanium, particularly its ductility, allow it to be strong and malleable, permitting fabrication of optimal dental implant configurations with little compromise.
    • 131. Relatively high strength is required in a prosthetic metal so it can withstand the mechanical forces and stresses placed on it during short-and long-term function without undergoing unintended permanent deformation or fracture.
    • 132. However, a lower toughness specific to deformation is desired so that one can shape the implant during the manufacturing process, and when appropriate, bend it to accommodate the anatomic conditions found at the host site. These conditions vary, system by system.
    • 133. The strength values for the wrought soft and ductile metallurgic condition (normal root forms and plate form implants) are approximately 1.5 times greater than the strength of compact bone. In most designs where the bulk dimensions and shapes are simple, strength of this magnitude is adequate.
    • 134. Commercially pure (cp) titanium and alloys of titanium exhibit good elongation properties. Elongation is directly related to malleability. Low elongation can result in implant fracture during processing or manipulation at the time of insertion.
    • 135. Titanium and its alloys exhibit moderate yield strengths. Yield strength relates to the magnitude of stress at which a metallic material shows initial permanent deformation. When the yield strength is exceeded, the shape of the implant is altered.
    • 136. Finally, the tensile strengths, the point at which metallic material can fracture in response to an applied load, should be sufficiently high for functional stability of a properly designed dental implant.
    • 137. In general, titanium and its alloys have outstanding strength-to-weight ratios; good yield, tensile, and fatigue strength; and adequate toughness for dental implant systems.
    • 138. The alloy of titanium most often used is titaniumaluminum-vanadium. The wrought alloy condition is approximately 6 times stronger than compact bone and thereby affords more opportunities for designs with thinner sections (e.g., plateaus, thin interconnecting regions, implant-to-abutment connection screw housing, irregular scaffolds, porosities).
    • 139. The modulus of elasticity of the alloy is slightly greater than that of titanium, being about 5.6 times that of compact bone. The alloy and the primary element (Ti) both have titanium oxide (passivated) surfaces. Information has been developed on the oxide thickness, purity, and stability as related to implant biocompatibilities.
    • 140. In general, titanium and alloys of titanium have demonstrated interfaces described as “osseointegrated” for implants in humans. Also, surface conditions where the oxide thickness has varied from hundreds of angstroms of amorphous oxide surface films to 100% titania (Ti02 rutile-form ceramic) have demonstrated osseointegration.
    • 141.
    • 142.
    • 143. Titanium plasma sprayed coating (TPS) The first rough titanium surface introduced Plasma flame spraying technique Coated with titanium powder particles in the form of titanium hydride
    • 144. Porous or rough titanium surfaces have been fabricated by plasma spraying a powder form of molten droplets at high temperatures in the order of 15,000 ºC, an argon plasma is associated with nozzle to provide very high velocity 600 m/sec partially molten particle c titanium powder (0.05 to 0.1mm diameter) projected onto a metal or alloy substrate.
    • 145. The plasma sprayed layer after solidification (fusion) is often provided with a 0.04 to 0.05mm thickness.
    • 146. When examined microscopically, the coatings show round or irregular pores that can be connected to each other. These types of surfaces were first developed by Hahn and Palich, who reported bone ingrowth in plasma spray titanium hybrid powder and plasma spray-coated implants inserted in animals.
    • 147. In addition, porous surfaces can result in an increase in tensile strength through ingrowth of bony tissues into three dimensional features, High shear forces determined by the torque testing methods and improved force transfer into the periimplant area have also been reported.
    • 148.
    • 149.
    • 150. Hydroxyapatite coating by plasma spraying was brought to the dental profession by deGroot. Kay et al. showed with scanning electron microscopy (SEM) and spectrographic analyses that the plasma-sprayed HA coating could be crystalline and could offer chemical and mechanical properties compatible with dental implant applications.
    • 151. Thomas showed an accelerated bone formation and maturation around HA-coated implants in dogs when compared with non-coated implants. HA coating can also lower the corrosion rate of the same substrate alloys. Cook et al. measured the HA coating thickness after retrieval from specimens inserted in animals for 32 weeks and showed a consistent thickness of 50micrometer, which is in the range advocated for manufacturing.
    • 152. The bone adjacent to the implant has been reported to be better organized than with other implant materials and with a higher degree of mineralization. In addition, numerous histologic studies have documented the greater surface area of bone apposition to the implant in comparison to uncoated implants, which may enhance the biomechanics and initial load-bearing capacity of the system.
    • 153. HA coating has been credited with enabling HA-coated Ti or Ti alloy implants to obtain improved bone-to-implant attachment compared with machined surfaces.
    • 154. Implants of solid sintered hydroxyapatite have been shown to he susceptible to fatigue failure. This situation can be altered by the use of a CPC (calcium phosphate coating) along metallic substrates. Although several methods may be used to apply CPC coatings, the majority of commercially available implant systems are coated by a plasma spray technique.
    • 155. A powdered crystalline hydroxyapatite is introduced and melted by a hot, highvelocity region of a plasma gun and propelled onto the metal implant as a partially incited ceramic.
    • 156. One advantage of CPC coatings is that they can act as a protective shield to reduce potential slow ion release from the Ti-6A1-4V substrate. Also, the interdiffusion between titanium and calcium, and phosphorus and other elements may enhance the coating substrate bond by adding a chemical component to the mechanical bond.
    • 157.
    • 158.
    • 159. Cranial prosthesis: Titanium has been recently used in fashioning cranial prostheses (Gordon and Blair, 1974) This metal is a strong but light material that is soft enough to be swaged in a die-counterdie system. Moreover it can be strain hardened and thus become stronger with manipulation. Sheets that are 0.6 1mm thick are adequate and its radiodensity permits most radiographic studies.
    • 160. After the metal prosthesis is shaped, trimmed, and polished, tissue acceptance of the implant is enhanced by anodizing it in a solution of 80% phosphoric acid, 10% sulphuric acid, and 10% water (Gordon and Blair, 1974).
    • 161. Titanium trays offer the best combination of strength and rigidity with the least bulk of any implant material currently available for restoration of mandibular defects. Titanium frameworks are also used for rehabilitation of maxillary and mandibular defects like cleft palate.
    • 162. The osseointegration technique allows the placement of titanium implants in to the orbital bony resin that are capable of supporting a facial prosthesis. The osseointegration procedure, allows titanium implants in to bone to project through the skin, providing points of attachment for prosthetic devices .
    • 163. Titanium implants are used for retention of bone anchored Hearing Aid (BAHA) .
    • 164.
    • 165. Based on their physical properties and biocompatibility, titanium and its alloys have emerged as the metals of choice in dental implant industry. The application of titanium to fixed and removable prostheses is still in the developmental stages. Concerns regarding castability, porcelain bonding, and joining have been reported.
    • 166. Some reports in the literature have indicated problems with castability and porosity. Others have shown that clinically acceptable titanium castings can be produced. Problems associated with porcelain bonding and titanium joining need to be resolved.
    • 167. Attempts to substitute gold alloys with titanium for dental prostheses by the dental industry, laboratories and clinicians, have been a slow process. At present time, use of titanium restorations or prostheses is low because of lack of knowledge of the material among dentists and long-term c1inic follow-up.
    • 168. Titanium is a useful biomaterial. It will probably continue to dominate the implant market in the future. Titanium is economical an readily available, but the technologies of machining, casting, welding and veneering it for dental prostheses are new.
    • 169. Increased use of titanium in prosthodontics depends on research and clinical trials to compare its effectiveness, as an equivalent or superior metal, to existing metals. The future of titanium in dentistry looks promising.
    • 170.
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