Physical properties of dental materials /certified fixed orthodontic courses by Indian dental academy

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Physical properties of dental materials /certified fixed orthodontic courses by Indian dental academy

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental educationwww.indiandentalacademy.com
  2. 2.  Dentistry is mainly a material science branch To fabricate any prosthesis we MUST know advantages and limitations of those material Proper selection of material So to know the things what we use in routine practice is essentialwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  3. 3.  what are physical properties? Abrasion and abrasion resistance. Viscosity. Structural and stress relaxation. Creep and flow. Color and color perception. Tarnish and corrosion.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  4. 4.  Properties based on laws of, -machanics, acoustics, optics, thermodynamics, electricity, magnetism, radiation, atomic structure or nuclear phenomena. Hue,value,chroma and translucency – based on laws of OPTICS thermal conductivity and coefficient Of thermal expansion – based on laws of THERMODYNAMICS viscosity – related to MATERIAL SCIENCE AND MECHANICSwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  5. 5.  Hardness: index of ability of a material to resist wear or abrasion. In oral cavity, abrasion is a complex mechanism, with interaction of numerous factors. So, hardness can be used to compare similar materials(e.g:one brand of metals with other) but invalid for dissimilar materials(e.g:resins andwww.indiandentalacademy.com metals)www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  6. 6.  A reliable invitro test for abrasion resistance should simulate particular abrasion in vivo due to complex clinical environment, invitro and in vivo tests will differ. For e.g; abrasion of enamel of atooth opposing ceramic crown is affected by; 1.bite force 2.frequency of chewing 3.abrasiveness of diet 4.composition of liquids 5.temperature changes 6.surface roughness 7.phy.props. Of materials 8.surface irregularitieswww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  7. 7. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  8. 8.  Resistance of a liquid to flow. Success of given dental material depends on its properties in liquid state as much as it is in solid state. Dentist has to manipulate many materials in liquid state to achieve successful clinical out comes. E.g; -cements, impression materials, gypsum www.indiandentalacademy.com www.indiandentalacademy.com www.indiandentalacademy.com www.indiandentalacademy.com
  9. 9. Some amorphous materials such as waxes andresins appear solid but they are supercooled liquidsthat can flow,- plastically(irreversibly) with sustained loading or-elastically(reversibly) with small stresses. Rheology :Is the study of deformation and flowcharacterstics of matter. www.indiandentalacademy.com www.indiandentalacademy.com www.indiandentalacademy.com www.indiandentalacademy.com
  10. 10.  Most liquids when placed in motion, resists imposed forces that cause them to moove because of internal frictional forces with in the liquid. Thus viscosity is a measure of consistency of a fluid and its inability to flow. Highly viscous liquids flows slowly compared to less viscous liquids. E.g;zinc poly carboxylate cement and resin cements compared with zn. phosphate cementwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  11. 11.  Liquid occupying space between two plates – lower plate fixed and upper being mooved to right with a velocity V and a force F is required to overcome viscosity.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  12. 12.  Stress: force per unit area that develops with in a structure when external force is applied. Shear Stress = F/A A – area of plates in contact with liquid. Strain: deformation caused by stress. Strain rate = V/D D – distance moved by upper plate relative to lower plate viscosity = shear stress/shear strain ratewww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  13. 13.  Units of measurement: measured in units of Mpa/sec or centipoise(cp) e.g; viscosity of pure water at 20◦C – 1 cp tempered agar(45◦C) – 281,000cp elastomeric impression materials light body(109,000) putty(1,360,000)www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  14. 14.  Used to explain viscous nature of some materials. Based on rheologic behavior, fluids can be classified into; -newtonian, -pseudoplastic, -dilatant, -plastics Nature of this curve for a given material is important in determining best way to manipulate that material. Similarly viscosity is plotted against time can be used to determine working time of a material thatwww.indiandentalacademy.com undergoes liquid – solid transformationwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  15. 15. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  16. 16.  Ideal fluid. Demonstrates - stress α strain. Plot - straight line exhibits constant viscosity. Slope is constant.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  17. 17.  Viscosity decreases with increase in strain rate till it reaches constant value. With increase in strain rate, shear stress rate increases to reach a constant value.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  18. 18.  Opposite to pseudoplastic behavior. Viscosity increases with increase in shear strain rate.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  19. 19.  They behave like rigid body until some minimum value of shear stress is reached. This minimum value is called OFFSET. Exhibits rigid behavior initially, and then attains constant viscosity. E.g; ketchup in bottle.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  20. 20.  Viscosity of most liquids decreases rapidly with increase in temperature and it also depends on previous deformation of liquid. A liquid that becomes less viscous and more fluid under repeated application of pressure is referred to as thixotrophic. E.g; dental prophylaxis pastes, plaster of paris, some impression materials.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  21. 21.  Thixotrophic property often confused with pseudoplasticity. A thixotrophic material does not flow until sufficient energy in the form of impact force is applied to overcome its yield stress. Beyond this point , the material becomes very fluid.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  22. 22.  Dental prophylactic pastes - they will not flow out of a rubber cup until it is rotated against the teeth to be cleaned. Impression materials - does not flow out of an impression tray until placed over dental tissues which is benificial for mandibular impression . Plaster of paris - if stirred rapidly and viscosity is measured, the value is lower than the value for a sample that left undisturbed due to thixotrophic property.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  23. 23. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  24. 24.  A stable substance application of stress displacement of atoms from equilibrium trapped internal stresses permanent deformation (plastic deformation) change in shape and contour of solidwww.indiandentalacademy.comwww.indiandentalacademy.com warps material or distortswww.indiandentalacademy.comwww.indiandentalacademy.com
  25. 25.  The rate of relaxation increases with increase in temperature. E.g;if a wire is bent, it may tend to straighten out if heated to high temperature. At room temperature such relaxation – negligible. Many non-crystalline dental materials (such as waxes,resins,and gels) that when manipulated and cooled can then undergo relaxation(distortion) at elevated temperature. results in inaccuratewww.indiandentalacademy.com fit of dental applianceswww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  26. 26.  CREEP - def: time dependent plastic strain of a material under a static load or constant stress. A metal held at a temperature near its melting point - subjected to constant stress - increase in strain over time. Metal creep usually occurs as the temperature increases to with in a few hundred degrees of melting range.www.indiandentalacademy.comwww.indiandentalacademy.com E.g;creep of amalgamwww.indiandentalacademy.comwww.indiandentalacademy.com
  27. 27.  Amalgam creep – dental amalgam usually contains 42-52% of Hg and begin melting at a temperature only slightly above room temperature. Restored tooth with amalgam clenching and biting periodic sustained stress destruction to dental prosthesiswww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  28. 28. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  29. 29.  Flow : is generally used in dentistry to describe the rheology of amorphous materials such as waxes. Flow of a wax is a measure of its potential to deform under a small static load ,even that associated with its own weight.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  30. 30.  Although creep or flow can be measured under any type of stress, compressive stress is used in testing dental materials. Cylinder of particular dimension subjected to given compressive stress for a specific time and temperature, % decrease in length gives creep or flow.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  31. 31.  Light: electromagnetic radiation that can be detected by human eye. Eye is sensitive to -λ of 400nm(violet)- 700nm(red). The reflected light intensity and the combined intensities of λ’s present in incident and reflected light determines the appearance properties i.e hue, value ,and chroma.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  32. 32.  Cone shaped cells are responsible for color vision. Optic nerve Image on retina is focused, then energy in visual spectrum is converted to electric potential by rods and cones through chemical reaction.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  33. 33.  eye is most sensitive to light in green-yellow region(550nm) and least sensitive at red or blue regions of color spectrum. www.indiandentalacademy.com www.indiandentalacademy.com www.indiandentalacademy.com www.indiandentalacademy.com
  34. 34.  Color fatigue: decrease in eyes response to color because of constant stimulation by single color. Color blindness: defect in certain portion of color sensing receptors. Thus human observers greatly differs in their ability to distinguish colors.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  35. 35. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  36. 36.  Colorimeter : exceptionally sensitive scientific instrument that measures intensity and wave length of light. Advantages : colorimeter is more precise than human eye in measuring slight differences in colored objects. Disadvantages: it is extremely in accurate when used on rough or curved surfaces . eye can differentiate colors seen side by side on smooth or irregular surfaces, whether curved or flat.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  37. 37.  Verbal description of color - not precise to describe appearance of teeth. So three variables must be measured to accurately describe color of tooth or restoration. They are, 1. HUE. 2.VALUE. 3.CHROMA.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  38. 38.  Defined as particular variety of a color, shade or tint. Describes the dominant color of an object. E.g: red, green or blue. Refers to dominant wavelengths present in spectral distribution.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  39. 39.  Identifies the lightness or darkness of color which can be measured independently of hue. E.g:yellow of a lemon is lighter than is the red of a cherry. Teeth can be separated into lighter shades(high value), and darker shades(lower value).www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  40. 40.  Degree of saturation of a particular hue. This is difference in color intensity or concentration of pigment. E.g:yellow of lemon is more vivid than that of banana which is dull yellow. Higher the chroma, more intense the color. In dentistry ,chroma is always associated with hue and value of dental tissues.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  41. 41. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  42. 42.  Hue changes occur in circumferential direction. Value varies vertically. increases towards the top(whiter) and decreases towards bottom(darker or more black). Chroma varies radially. Increases from center outwards.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  43. 43.  used to peform color matching in dental operatory or laboratory to select color of crowns, inlays, veneers etc. Usually neck region is grinded away, because correct shade is determined from gingival half of the tab not from the neck. www.indiandentalacademy.com www.indiandentalacademy.com www.indiandentalacademy.com www.indiandentalacademy.com
  44. 44. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  45. 45.  Objects that appeared to be color matched under one type of light may appear different under other light source. Spectral distribution of light reflected from or transmitted through depends on spectral content of incident light. Common sources – day light, incandescent and fluorescent.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  46. 46. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  47. 47.  The energy that the tooth absorbs is converted into alight with longer wavelengths, in which tooth actually becomes a light source. Natural teeth absorbs wavelength too short to be visible to human eye referred as near U.V.radiation(300-400nm). Emitted color is bluish white with wave length 400-450nm range contributing to brightness and vital appearance of humanwww.indiandentalacademy.com eye.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  48. 48.  Thermal conductivity Is a thermophysical measure that how well heat is transferred through a material by conductive flow. Conduction through metal – crystal lattice vibrations, motion of electrons ,and their interaction with atoms. Measured under steady state conditions (constant T ). Thermal conductivity  area(┴to heat flow ) and temperature gradient acrosswww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  49. 49.  Coefficient of thermal conductivity: is the quantity of heat in calories per second, that passes through a specimen 1cm thick having a cross sectional area of 1 cm sq. when the temperature difference between the surfaces perpendicular to heat flow is 1 k. High conductivity - conductors low conductivity - insulators units of measurement–watt/meter/sec/kelvin.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  50. 50.  Is a measure of the rate at which a body with a non uniform temperature reaches a state of thermal equilibrium. For e.g: the thermal conductivity of ZOE <dentin but thermal diffusivity is twice that of dentin. Thickness of cement base directly related to benefit as insulator.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  51. 51.  Applied e.g’s: - importance of thickness of cement base as thermal insulator. - Difference in thermal conductivity of metallic and resin denture bases.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  52. 52.  Change in length per unit length of a material when its temperature is raised 1˚k. (μm/m˚k) Coefficient of thermal expansion for ENAMEL is 1www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  53. 53. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  54. 54.  Other applications of  - inlay wax removed from tooth or die in warmer area and stored in cooler area. - Denture teeth arranged in wax in warm area and stored in cooler area causing shift in positions of teeth - stresses produced from metal ceramic restorations when porcelain veneer is fired to a metal substrate.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  55. 55. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  56. 56.  Tarnish: the process by which a metal surface is dulled or discolored when a reaction with a sulfide ,oxide, chloride, or other chemical causes a thin film to form. (or) tarnish is observable as a surface discoloration on a metal , or as a slight loss or alteration of the surface finish or luster. ‘Tarnish is often a forerunner of corrosion’www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  57. 57.  Often occurs from formation of hard and soft deposits on the surface of restoration. Soft deposits - plaque, films of bacteria,mucin, stains from pigment producing bacteria, drugs containing iron or mercury, adsorbed food debris hard deposits - calculus. Also from formation of thin films such as oxides, sulfides, chlorides which is anwww.indiandentalacademy.com early indication of corrosionwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  58. 58.  Corrosion: chemical or electrochemical process in which a solid usually a metal,is attacked by an environmental agent, resulting in partial or complete dissolution. (or) it is a process in which deterioration of a metal is caused by reaction with its environment and is not merely a surface deposit.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  59. 59.  Disintegration of a metal by corrosion may occur in mouth because of - warmness and moistness . - fluctuations in temperature. - ingested foods with wide range of PH - acids liberated from localized attachment of debris.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  60. 60.  A tarnish film may intime accumulate elements and compounds that chemically attack metal. For e.g; egg and certain foods containing sulfur . sulfides such as hydrogen, or ammonium corrode Ag,Cu,Hg and similar metals present in dental alloys and amalgam. Specific ions play role in corrosion of certain alloys . For e.g; Oxygen and chloride in corrosion of amalgamwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  61. 61.  Broadly classified into, 1. chemical /dry corrosion. 2.electrochemical/wet corrosion - galvanic corrosion - stress corrosion - concentration cell corrosionwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  62. 62.  Requires presence of water/fluid electrolyte and also a pathway for transport of electrons. Electrochemical cell: composed of 3 components 1. anode.(e.g; dental amalgam) 2 cathode.(e.g; gold alloy restoration) 3. electrolyte.(e.g; saliva)www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  63. 63. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  64. 64.  Anode is a surface or site, on a surface where, +ve ions are formed (surface undergoing oxidation and corroding.) with the production of free electrons. 0 + _ M M + e at cathode, reduction reaction occurs that consumes free electrons produced at anode. + _ 0 + _ M + e M / 2H + 2e H2 / _ _ _ 2H2O + O2 + 4e 4(OH)www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  65. 65.  Electrolyte supplies the ions needed at cathode ,and carries away the corrosion products at the anode. External circuit – path to carry electrons from anode to cathode. For corrosion to be an ongoing process, - production of e at anode must be balanced by consumption in reduction reaction at cathode. Cathodic reaction - primary driving force for electro-chemical corrosion – an important consideration in determining rate of corrosion.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  66. 66.  Classification of metals by their equilibrium values, of electrode potential there by arranging them in the order of their dissolution tendencies in water. Potential value –calculated for a standard state, consisting of one atomic wt. of ions in 100ml of water at 25˚c. The half cell potentials considered as voltage of an E-C cell in which one electrode iswww.indiandentalacademy.com hydrogen electrode designated as 0 potentialwww.indiandentalacademy.comwww.indiandentalacademy.com of choice. and other is elementwww.indiandentalacademy.com
  67. 67. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  68. 68.  If two metals are immersed in an electrolyte, connected by an electrical conductor, - metal with low V - anode - metal with high V – cathode for e.g; E-C cell with Cu and Zn electrodes in aqueous acidic solution Zn becomes anode and undergoes surface dissolution. Magnitude of resulting corrosion influenced by salivary, - concentration of its components - pH - surface tension - buffering capacitywww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  69. 69.  corrosion increase in metal ion content in environment saturation of ions in electrolyte prevent further corrosion metal ceases corroding usually, the dissolved ions from dental restorations removed by food, fluids and brushing, there by corrosion continues.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  70. 70.  An important type of E-C corrosion occurring when combinations of dissimilar metals are in direct physical contact.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  71. 71.  Amalgam restoration on lower tooth opposing upper tooth with gold inlay electric circuit(because of saliva) with potential difference between metals when teeth brought into contact short circuit through alloys sharpwww.indiandentalacademy.com painwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  72. 72. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  73. 73.  When teeth are not in contact - still electric circuit is present due to potential difference between metals. Saliva forms electrolyte and hard and soft tissues forms external circuit. Electric current generated between gold and amalgam restorations, when they are not in contact - 0.5 – 1 μA with potential difference -500mV. Coating with varnish tends to eliminate galvanic shock. www.indiandentalacademy.com www.indiandentalacademy.com www.indiandentalacademy.com www.indiandentalacademy.com
  74. 74.  Single metallic restoration: current also associated with single isolated metallic restoration. Electric cell is generated as a result of potential difference created by two electrolytes - - saliva and tissue fluid. (tissue fluid : used to denote , dentinal fluid, soft tissue fluid, blood that provides a means of external circuit.) because chloride concentration several times higher than saliva, - interior surface of restoration exposed to dentinal fluid will have a more activewww.indiandentalacademy.com electric potential.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  75. 75. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  76. 76.  Associated with heterogeneous composition of dental alloys. Corrosion resistance of multiphase alloys is generally less than that of single phase solid solution. E.g: when alloy containing a two phase micro structural constituents immersed in electrolyte, the lamellae of phase withwww.indiandentalacademy.com attacked and corrosion lower potential are results.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  77. 77.  Solder joints - corrode because of difference in composition of alloy and solder. Impurities - contaminating metals cause corrosionwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  78. 78.  Imposition of stresses increases internal energy of an alloy through elastic displacement of atoms or creation of micro strained fields associated with dislocation then the tendency to undergo corrosion increases called stress corrosion. likely to occur during fatigue or cyclic loading. Electro-chemical cell forms with more deformed regions (anode), less deformed regions(cathode), and saliva. E.g:failure of RPD framework due to cyclicwww.indiandentalacademy.com stresswww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  79. 79.  Occurs whenever there are variations in the electrolytes or in the composition of the given electrolyte with in system. E.g : difference in electrolyte compositon contacting restoration on occlusal and proximal surfaces. Similar type of corrosion occurs due to difference in oxygen concentration between parts of same restoration.www.indiandentalacademy.com E.g : pits in restorations.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  80. 80.  Deepest portion of pit - low o2 concentration because of debris - anode. Alloy surface around rim of the pit - cathode. Crevice corrosion: corrosion at the junction of tooth and restoration because of presence of food debris causing changes in o2 concentration and change in electrolyte.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  81. 81. www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  82. 82.  Metallic and non metallic coatings over gold alloy restorations are ineffective because, -were too thin, -were incomplete, -did not adhere to metal, -were readily scratched, -were attacked by oral fluids. When dissimilar metals in contact, - painting a non conductive film.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  83. 83.  Certain metals develop a thin ,adherent, highly protective film by reaction with environment called passivation. E.g : passivation of iron with chromium and passivation by titanium due to titanium oxide formation Chromium passivated metals – susceptible to stress corrosion and pitting corrosion and certain ions such as chloride will disrupt protective layer.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  84. 84.  Corrosion resistance is very important consideration dental alloys because release corrosion products affect biocompatibility. A guideline that has been employed by manufacturers for many dental alloys is atleast 50% atoms should be noble metals. Palladium – prevents sulfur tarnishing of silver alloys. Base metal alloys susceptible to tarnish with chloride.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  85. 85.  Many base materials below restorations lose the property of insulation when they becomes wet through microleakage or dentinal fluid. Practical method of eliminating galvanic currents - application of varnish. It has been suggested that Galvanic currents may account for many types of dyscrasias such as lichenoid reactions, ulcers, leukoplakia, cancer, and kidney disorders but research has failed to find correlation.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  86. 86.  With the latest advance in material aspect, there is emergence of many materials in dentistry. the complete understanding of the various properties of the materials can make out the suitable material of choice. And this will definitely lead to better quality of treatment.www.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com
  87. 87. THANK YOU FOR WATCHINGwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.comwww.indiandentalacademy.com

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