Biomaterials for dental implants --.pptx

Description of biomaterials used in implants

1. Biomaterials for Dental Implants- Part 1 Neeraj Prasad 2nd Year PG Dept of Prosthodontics

2. Contents Part 1:- Defintions Introduction History Physical and Mechanical Properties Corrosion Toxicity Metals and Alloys Ceramics Part 2:- Carbon and Carbon Silica Compounds Zirconia Polymers Composites Surface Characterizations Coatings Tissue Interactions Sterilization

3. Definitions (GPT-9) Biomaterial - any substance other than a drug that can be used for any period of time as part of a system that treats, augments, or replaces any tissue, organ, or function of the body. Biocompatible - capable of existing in harmony with the surrounding biologic environment

4. Introduction Biocompatibility profiles of biomaterials used for replacement or augmentation of biological tissues - critical concern in healthcare disciplines Dental implant-prosthetic reconstruction environment and functionality Chemical and mechanical environmental conditions

5. Biocompatibility - basic bulk & surface properties of the biomaterial Manufacturing, finishing, packaging, delivering, sterilizing and surgical placement must be adequately controlled to ensure optimal success Re-emphasized by concept and practice of osteointegration of endosteal root form implants

6. Biomaterials & Biomechanics complementary The physical, mechanical, chemical, and electrical properties of the basic material components must always be fully evaluated These properties provide key inputs into the interrelated biomechanical and biological analyses of function.

7. It is important to separate the roles of macroscopic implant shape from the microscopic transfer of stress and strain along biomaterial–tissue interfaces. The macroscopic distribution of mechanical stress and strain is predominantly controlled by the shape and form of the implant device.

8. The localized microscopic strain distribution is controlled more by the basic properties of the biomaterial (e.g., surface chemistry, microtopography, modulus of elasticity ) and by whether the biomaterial surface is attached to the adjacent tissues.

9. The desire to positively influence tissue responses and to minimize biodegradation often places restrictions on which materials can be used safely within the oral and tissue environments. Designs are often evolved for specific biomaterials because of the imposed environmental or restorative conditions.

10. History of materials and design Biocompatibility- appropriate response to a material (biomaterial) within a device (design) for a specific clinical application. Metallic and non-metallic implantable materials have been studied in the field of orthopedics since the turn of the twentieth century

11. History of materials and design 1960s - emphasis on inertness and chemically stable in biological environment Eg: High-purity ceramics of aluminum oxide ( Al 2 O 3 ), carbon, carbon-silicon compounds and extra-low interstitial–grade alloys 1970s biocompatibility was defined in terms of minimal harm to the host or to the biomaterial. The importance of a stable interaction then moved into central focus.

12. History of materials and design 1980s - Bioactive substrates intended to positively influence tissue responses, and also emphasis on chemically and mechanically anisotropic substrates combined with growth ( mitogenic ) and inductive ( morphogenic ) substances. Biomaterials are being constituted, fabricated, and surface modified to directly influence short- and long-term tissue responses.

13. Research now focuses on surface science and technology, mechanics and biomechanics of three-dimensional structures, pathways and processes of wound healing along biomaterial interfaces, and the description of the first biofilms that evolve on contact with blood or tissue fluids.

14. Physical and Mechanical Properties

15. Compressive, Tensile, Shear stresses All fatigue failures obey mechanical laws correlating the dimensions of the material to the mechanical properties of the material. Parafunction - detrimental - maximum yield strength, fatigue strength, creep deformability, ductility, and fracture.

16. A recurring problem exists between the mechanical strength and deformability of the material and the recipient bone. Experimentation of polymeric, carbonitic, and metallic materials of low modulus of elasticity - to match properties with existing hard tissue

17. Bone can modify its structure in response to forces exerted on it Implant materials and designs must be designed to account for the increased performance of the musculature and bone in jaws restored with implants. The higher the applied load, the higher the mechanical stress—and therefore the greater the possibility for exceeding the fatigue endurance limit of the material.

18. Fatigue limit of metallic implant materials reaches approximately 50% of their ultimate tensile strength Polymeric systems have no lower limit in terms of endurance fatigue strength Ceramic materials - brittle, no ductility

19. Advantage of Metals: Can be heated for varying periods to influence properties, modified by the addition of alloying elements or altered by mechanical processing such as drawing, swagging, or forging, followed by age or dispersion hardening, until the strength and ductility of the processed material are optimized for the intended application.

20. The modifying elements in metallic systems may be metals or non-metals. A general rule is that constitution or mechanical process hardening procedures result in an increased strength but also invariably correspond to a loss of ductility.

21. Consensus standards for metals (ASTM International [formerly American Society for Testing and materials], International Standardization Organization [ISO], American Dental Association) require a minimum of 8% ductility to minimize brittle fractures.

22. Mixed microstructural-phase hardening of austenitic materials with nitrogen (eg: stainless steels) and the increasing purity of the alloys seem most indicated to achieve maximum strength and maintain this high level of possible plastic deformation.

23. Corrosion and Biodegradation Corrosion : (GPT-9) 1. deterioration of a metal as a result of an electrochemical reaction within its environment; 2. to eat away by degrees as if by gnawing; 3. to wear away gradually usually by chemical action

24. Corrosion and Biodegradation Corrosion is a special concern for metallic materials in because implants protrude into the oral cavity, where electrolyte and oxygen compositions differ from that of tissue fluids. pH can vary significantly in areas below plaque and within the oral cavity. This increases the range of pH that implants are exposed to.

25. Corrosion and Biodegradation

26. Corrosion and Biodegradation Plenk and Zitter - Galvanic corrosion could be greater for dental implants than for orthopedic implants Galvanic processes depend on the passivity of oxide layers - minimal dissolution rate and high regenerative power for metals such as titanium. Passive layer- few nm thick and is usually composed of oxides or hydroxides of the metallic elements that have greatest affinity for oxygen.

27. Corrosion and Biodegradation The risk for mechanical degradation, such as scratching or fretting of implanted materials, combined with corrosion and release into bone and remote organs has been studied Williams suggested that three types of corrosion were most relevant to dental implants: Stress corrosion cracking (SCC), Galvanic Corrosion (GC) and Fretting corrosion (FC).

28. Stress Corrosion Cracking Mechanical Stress + Corrosive environment exposure = failure of metal by cracking FEA Studies show concentration of stresses crest of the bone support and cervical third of implant This tends to support potential SCC at the implant interface area (i.e., a transition zone for altered chemical and mechanical environmental conditions)

29. Stress Corrosion Cracking

30. Galvanic Corrosion It occurs when two dissimilar metallic materials are in contact and are within an electrolyte, resulting in current flowing between the two. The metallic materials with the dissimilar potentials can have their corrosion currents altered, thereby resulting in a greater corrosion rate.

31. Galvanic Corrosion

32. Fretting Corrosion It occurs when a micromotion rubbing contact occur within a corrosive environment Eg: the perforation of the passive layers and shear-directed loading along adjacent contacting surfaces The loss of any protective film can result in the acceleration of metallic ion loss. FC has been shown to occur along implant body–abutment–superstructure interfaces.

33. Normally the passive oxide layers on metallic substrates dissolve at such slower rates that the resultant loss of mass is of no mechanical consequence to the implant. Irreversible local perforation of the passive layer that chloride ions often causemay result in localized pitting corrosion. Such perforations can often be observed for iron-chromium-nickel-molybdenum (Fe-Cr-Ni-Mo) steels.

34. They contain an insufficient amount of the alloying elements stabilizing the passive layer (i.e., Cr and Mo) or local regions of implants that are subjected to abnormal environments. Even ceramic oxide materials are not fully degradation resistant.

35. Corrosion-like behavior of ceramic materials can then be compared with the chemical dissolution of the oxides into ions or complex ions of respective metallic oxide substrates. An example of this is the solubility of Al 2 O 3 as alumina or titanium oxide as titanium.

36. The corrosion resistance of synthetic polymers, in contrast, depends not only on their composition and structural form but also on the degree of polymerization. Unlike metallic and ceramic materials, synthetic polymers are not only dissolved but also penetrated by water and substances from biological environments

37. Toxicity and Considerations Toxicity is related to primary biodegradation products (simple and complex cations and anions), particularly those of higher atomic weight metals.

38. Factors to be considered:- The amount dissolved by biodegradation per time unit The amount of material removed by metabolic activity in the same time unit The quantities of solid particles and ions deposited in the tissue and any associated transfers to the systemic system.

39. The quantity of elements released from metals during corrosion time (e.g., grams per day) can be calculated by using the following formula

40. The critical issue is that the surface represents the “ finished ” form of the implant. The formula is also valid for ceramic materials and for substances transferred from synthetic polymers. Therefore it appears that the toxicity is related to the content of the materials’ toxic elements and that they may have a modifying effect on corrosion rate

41. The transformation of harmful primary products is dependent on their level of solubility and transfer. Chromium and Titanium ions react locally at low concentrations, whereas cobalt, molybdenum, or nickle can remain dissolved at higher relative concentrations, and thus may be transported and circulated in body fluids.

42. Lemons reported on the formation of electrochemical couples as a result of oral implant and restorative procedures He stressed the importance of selecting compatible metals to be placed in direct contact with one another in the oral cavity to avoid the formation of adverse electrochemical couples. The electrochemical behavior of implanted materials has been instrumental in assessing their biocompatibility.

43. Zitter and Plenk have shown that anodic oxidation and cathodic reduction take place in different spaces but must always balance each other through charge transfer. This has been shown to impair both cell growth and transmission of stimuli from one cell to another. Therefore an anodic corrosion site can be influenced by ion transfer but also by other possibly detrimental oxidation phenomena.

44. Charge transfer appears to be a significant factor specific to the biocompatibility of metallic biomaterials. Passive layers along surfaces of titanium, niobium, zirconium, tantalum increase resistance to change transfer processes by isolating substrate from the electrolyte, and provide a higher resistance to ion transfers. Iron, nickel, or cobalt are not as resistant to transfers through the oxide-like passive surface zones.

45. Metals and Alloys

46. Titanium and Titanium-6 Aluminium-4 Vanadium It forms tenacious oxides in air or oxygenated solutions. Titanium oxidizes ( passivates ) on contact with room-temperature air and normal tissue fluids This minimizes biocorrosion (increase in thickness of oxide layer under corrosion testing) If implant is placed within a closely fitting receptor site in bone, areas scratched or abraded during placement would repassivate in vivo.

47. Titanium and Titanium-6 Aluminium-4 Vanadium Various authors concluded that titanium allowed bone growth directly adjacent to the oxide surfaces In all cases, titanium was selected as the material of choice because of its inert and biocompatible nature paired with excellent resistance to corrosion

48. Engineering Properties of Metals and Alloys Used for Surgical Implants

49. Titanium shows a relatively low modulus of elasticity and tensile strength comparitively Creation of sharp corners or thin sections must be avoided for regions loaded under tension or shear conditions.

50. The modulus of elasticity of titanium = 5 times greater than that of compact bone. This property places emphasis on importance of design in proper distribution of mechanical stress transfer Surface areas that are loaded in compression have been maximized for some of the newer implant designs Their ultimate strength and endurance limit vary as a function of their composition.

51. The alloy of titanium most often used is titanium-6 aluminum-4 vanadium. The modulus of elasticity of the alloy is slightly greater than that of titanium-> 5.6 times that of compact bone The alloy and titanium both have titanium oxide (passivated) surfaces. The alloy and the primary element (ie titanium) both have titanium oxide (passivated) surfaces.

52. Titanium and cobalt-based systems are electrochemically similar but several orders of magnitude lower than that in Fe-Cr-Ni-Mo steels or Co-Cr alloys. Electrochemical studies support the selection of conditions in which elemental concentrations would be relatively low in magnitude

53. Titanium is much more ductile (bendable) than titanium alloy - favorable aspect related to the use of titanium for endosteal plate form devices. The need for adjustment or bending to provide parallel abutments for prosthetic treatments has caused manufacturers to optimize microstructures and residual strain conditions

54. Coining, stamping, or forging followed by controlled annealing heat treatments are routinely used during metallurgic processing. However, if an implant abutment is bent at the time of implantation, then the metal is strained locally at the neck region (bent) This is one reason, other than prior loading fatigue cycling, why reuse of implants is not recommended

55. Cobalt-Chromium-Molybdenum–Based Alloy Cobalt-based alloys are most often used in an as-cast or cast-and-annealed metallurgic condition. This permits the fabrication of implants as custom designs such as subperiosteal frames. Cobalt provides the continuous phase for basic properties.

56. Cobalt-Chromium-Molybdenum–Based Alloy Secondary phases based on cobalt, chromium, molybdenum, nickel, and carbon provide strength (four times that of compact bone) and surface abrasion resistance Chromium provides corrosion resistance through the oxide surface; and molybdenum provides strength and bulk corrosion resistance.

57. All these elements and their concentration are critical. Emphasizes the importance of controlled casting and fabrication technologies. Also, minor concentrations of nickel, manganese, and carbon are included Nickel - identified in biocorrosion products Carbon must be precisely controlled to maintain mechanical properties such as ductility.

58. The as-cast cobalt alloys are the least ductile of the alloy systems used for dental surgical implants, and bending of finished implants should be avoided. Implants from this alloy group have shown to exhibit excellent biocompatibility profiles.

59. Iron-Chromium-Nickel–Based Alloys Surgical stainless-steel alloys - long history of use for orthopedic and dental implant devices. Used most often in a wrought and heat-treated metallurgic condition, which results in a high-strength and high-ductility alloy This alloy (for implants) is most subject to crevice and pitting biocorrosion, and care must be taken to use and retain the passivated (oxide) surface condition.

60. Iron-Chromium-Nickel–Based Alloys Use in patients allergic or hypersensitive to nickel should be avoided If a stainless-steel implant is modified before surgery, then recommended procedures call for repassivation to obtain an oxidized (passivated) surface condition to minimize in vivo biodegradation.

61. The iron-based alloys have galvanic potentials and corrosion characteristics. It could result in concerns about galvanic coupling and biocorrosion if interconnected with titanium, cobalt, zirconium, or carbon implant biomaterials. For example, if a bridge of a noble or a base-metal alloy touches the abutment heads of a stainless-steel and titanium implant simultaneously, then an electrical circuit would be formed through the tissues.

62. Long-term device retrievals have demonstrated that, when used properly, the alloy can function withoutsignificant in vivo breakdown. The mechanical properties and cost characteristics of this alloy offer advantages with respect to clinical applications.

63. Other Metals and Alloys Early spirals and cages included tantalum, platinum, iridium, gold, palladium, and alloys of these metals. More recently, devices made from zirconium, hafnium, and tungsten have been evaluated Gold, platinum, and palladium are metals of relatively low strength and high cost.

64. Ceramics

65. Ceramics Ceramics are inorganic, non-metallic, nonpolymeric materials manufactured by compacting and sintering at elevated temperatures. They are divided into Metallic oxides or other compounds.

66. Ceramics Oxide ceramics were introduced for surgical implant devices because of their inertness to biodegradation, high strength, physical characteristics such as color and minimal thermal and electrical conductivity, and a wide range of material-specific elastic properties . In many cases, however, the low ductility or inherent brittleness has resulted in limitations.

67. Aluminum, Titanium, and Zirconium Oxides Used for the root form, endosteal plate form, and pin type of dental implants Compressive, tensile, and bending strengths exceed the strength of compact bone by 3-5 times High moduli of elasticity, and especially with fatigue and fracture strengths - special design requirements

68. Engineering Properties of Some Inert Ceramics Used as Biomaterials

69. Aluminum, Titanium, and Zirconium Oxides For example, the fabrication of a subperiosteal device from a high ceramic should not be done because of the custom nature of these devices, the lower fracture resistance, and the relative cost for manufacturing. These oxide ceramics have a clear, white, cream, or light-gray color, which is beneficial for applications such as anterior root form devices

70. Aluminum, Titanium, and Zirconium Oxides Minimal thermal and electrical conductivity , minimal biodegradation, and minimal reactions with bone, soft tissue, and the oral environment - beneficial Ceramics have exhibited direct interfaces with bone, similar to an osteointegrated condition with titanium. In addition, characterization of gingival attachment zones along sapphire root form devices - localized bonding

71. Exposure to steam sterilization results in a measurable decrease in strength for some ceramics; Scratches or notches may introduce fracture initiation sites; chemical solutions may leave residues; The hard and sometimes rough surfaces may readily abrade other materials, thereby leaving a residue on contact. Dry-heat sterilization within a clean and dry atmosphere is recommended for most ceramics

72. One series of root form and plate form devices used during the 1970s resulted in intraoral fractures after several years of function. The fractures were initiated by fatigue cycling, where biomechanical stresses were along regions of localized bending and tensile loading despite initial positive tests Long-term clinical results clearly demonstrated a functional design-related and material-related limitation.

73. The established chemical biocompatibilities, improved strength and toughness capabilities of sapphire and zirconia, and the basic property characteristics of high ceramics continue to make them excellent candidates for dental implants.

74. Bioactive and Biodegradable Ceramics Based on Calcium Phosphates

75. Bone Augmentation and Replacement The calcium phosphate (CaPO 4 ) materials (i.e., calcium phosphate ceramics [CPCs]) - wide range of uses Early investigations emphasized solid and porous particulates with nominal compositions that were relatively similar to the mineral phase of bone (Ca 5 [PO 4 ] 3 OH).

76. Bone Augmentation and Replacement Microstructural and chemical properties of these particulates were controlled to provide forms that would remain intact for structural purposes after implantation Research led to expansions for implant applications, including larger implant shapes (e.g., rods, cones, blocks, H-bars) for structural support under relatively high-magnitude loading conditions.

77. Bone Augmentation and Replacement Particulate size range for bone replacements was expanded to both smaller and larger sizes for combined applications with organic compounds. Mixtures of particulates with collagen, and subsequently with drugs and active organic compounds such as bone morphogenetic protein, increased the range of possible applications.

78. Endosteal and Subperiosteal Implants 1st series of structural forms for dental implants included rods and cones for filling tooth-root extraction sites (ridge retainers) and, in some cases, load-bearing endosteal implants. Limitations in characteristics soon resulted in internal reinforcement of the CPC implants through mechanical (central metallic rods) or physicochemical (coating over another substrate) techniques.

79. Endosteal and Subperiosteal Implants The numbers of coatings of metallic surfaces using flame or plasma spraying (or other techniques) increased rapidly for the CPCs. The coatings have been applied to a wide range of endosteal and subperiosteal dental implant designs, with an overall intent of improving implant surface biocompatibility profiles and implant longevities

80. Bioactive Ceramics Lower strengths, hardness, and moduli of elasticity than the more chemically inert forms Calcium aluminates, sodium-lithium invert glasses with CaPO 4 additions (Bioglass or Ceravital), and glass ceramics (AW glass ceramic) also provide a wide range of properties

81. Bioactive Ceramic Properties Physical properties are specific to the surface area or form of the product (block, particle), porosity (dense, macroporous, microporous), and crystallinity (crystalline or amorphous). Chemical properties are related to the calcium-phosphate ratio , composition , elemental impurities (e.g., carbonate), ionic substitution in atomic structure, and the pH of the surrounding region

82. Properties of Bioactive and Biodegradable Ceramics

83. The general family of apatites has the following formula:

84. Bioactive Ceramic Properties One of the more important aspects of the CPCs relates to the possible reactions with water . For example, hydration can convert other compositions to HA; also, phase transitions among the various structural forms can exist with any exposure to water.

85. Bioactive Ceramic Properties Steam or water autoclaving can significantly change the basic structure and properties of CPCs (or any bioactive surface), and thereby provide an unknown biomaterial condition at the time of implantation. This is to be avoided through the use of presterilized or clean, dry heat or gamma sterilized conditions.

86. Forms, Microstructures, and Mechanical Properties Particulate HA, provided in a nonporous (<5% porosity) form as angular or spherically shaped particles, is an example of a crystalline, high-purity HA biomaterial Relatively high compressive strengths (up to 500 MPa), with tensile strengths in the range of 50 to 70 MPa.

87. Forms, Microstructures, and Mechanical Properties Dense polycrystalline ceramics consisting of small crystallites exhibit the highest mechanical strength, apart from monocrystalline ceramics free of defects (e.g., single-crystal sapphire implants).

88. Forms, Microstructures, and Mechanical Properties The macroporous (>50 mm) or microporous (<50 mm) particulates have an increased surface area per unit volume. This provides more surface area for solution- and cell-mediated resorption under static conditions and a significant reduction in compressive and tensile strengths

89. Forms, Microstructures, and Mechanical Properties The porous materials also provide additional regions for tissue ingrowth and integration (mechanical stabilization), and thereby a minimization of interfacial motion and dynamic (wear-associated) interfacial breakdown. The strength characteristics after tissue ingrowth would then become a combination of the ceramic and the investing tissues

90. Density, Conductivity, and Solubility Inorganic portion of the recipient bone is more likely to grow next to a more chemically similar material. The bioactive (bioreactive) categorization includes CaPO4 materials such as TCP, HA, calcium carbonate (corals), and calcium sulfate–type compounds and ceramics.

91. Density, Conductivity, and Solubility A chemical-biochemical contact between the host bone and grafted material may be developed, as well as a possible stimulus of bone activity Their limitations have been associated with the material forms that have lower strengths (ie similar to or less than bone)

92. Density, Conductivity, and Solubility The very technique-sensitive fabrication steps related to phase transition and thermal expansion during cooling might cause the final product of CaPO 4 -type coatings to be more or less resorbable.

93. Density, Conductivity, and Solubility Solubility is greater for TCP than for HA. Each increase relative to increasing surface area per unit volume (porosity) and the CPC solubility profiles depend on the environment (e.g., pH, mechanical motion). The larger the particle size is, the longer the material will remain at an augmentation site. (75-mm particles will be resorbed more rapidly than 3000-mm particles)

94. Density, Conductivity, and Solubility Porosity of the product affects the resorption rate Some of the dense HA lacks any macroporosity or microporosity within the particles. The longest resorption rate occurred with the dense nonporous HA type because osteoclasts may attack only the surface and cannot penetrate the non-porous material.

95. Density, Conductivity, and Solubility The greater the porosity is, the more rapid is the resorption of the graft material. For example, clinical observation shows dense crystalline forms of HA may last longer than 15 years in the bone, the macroporous 5 years, and the microporous HA as short as 6 months

96. Density, Conductivity, and Solubility

97. Density, Conductivity, and Solubility The crystallinity of HA also affects the resorption rate of the material. The highly crystalline structure is more resistant to alteration and resorption. An amorphous product has a chemical structure that is less organized with regard to atomic structure.

98. Density, Conductivity, and Solubility The hard or soft tissues of the body are more able to degrade the components and resorb the amorphous forms of grafting materials. Thus crystalline forms of HA are found to be very stable over the long term under normal conditions, whereas the amorphous structures are more likely to exhibit resorption and susceptibility to enzyme- or cell-mediated breakdown

99. Density, Conductivity, and Solubility The purity of the HA bone substitutes may also affect the resorption rate. The resorption of the bone substitute may be cell or solution mediated.

100. Density, Conductivity, and Solubility Cell-mediated resorption requires processes associated with living cells to resorb the material, similar to the modeling and remodeling process of living bone, which demonstrates the coupled resorption and formation process.

101. Density, Conductivity, and Solubility A solution-mediated resorption permits the dissolution of the material by a chemical process. Impurities or other compounds in bioactive ceramics, such as calcium carbonate, permit more rapid solution-medicated resorption, which then increases the porosity of the bone substitute

102. Density, Conductivity, and Solubility The pH in the region in which the bone substitutes are placed also affects the rate of resorption. As the pH decreases (e.g., because of chronic inflammation or infection), the components of living bone, primarily CaPO 4 , resorb by a solution-mediated process (i.e., they become unstable chemically).

103. Current Status and Developing Trends The CPCs have proved to be one of the more successful high technology–based biomaterials that have evolved most recently. Their advantageous properties strongly support the expanding clinical applications and the enhancement of the biocompatibility profiles for surgical implant uses

104. Part 2 Contents Carbon and Carbon Silica Compounds Zirconia Polymers Composites Surface Characterizations/Modifications Coatings Tissue Interactions Sterilization

105. Thank You