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Aplied physics/ cosmetic dentistry training


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Aplied physics/ cosmetic dentistry training

  1. 1. APPLIED PHYSICS (Basic Principles) INDIAN DENTAL ACADEMY Leader in continuing dental education
  3. 3. INTRODUCTION All materials made up of atoms These atoms held together by inter atomic forces called cohesive forces. Matter exists in three forms Difference in form is due to difference in energy
  4. 4. Surface tension Wetting Adsorption Colloids Capillary action Adhesion Applied surface phenomena
  5. 5. SURFACE TENSION Referred as surface energy “Increase in energy per unit area of surface” Energy at surface of a solid or liquid is greater than in its interior Inside a lattice all atoms are equally attracted to each other Inter atomic distances are equal and energy is minimal
  6. 6. Where as in outer surface,atoms are not equally attracted in all directions,infact no atoms from out side Higher the bond strength of a substances,greater the surface energy Metallic bonds are stronger and have higher surface energies than Vanderwaals of liquids UNITS:Dynescm Summary:-greater the surface energy,greater the capacity for adhesion
  7. 7. WETTING “The degree of spreading of a liquid drop on a solid surface” Degree of wetting is measured by contact angle “It is the angle formed by the adhesive and the adherent at their surface” Zero degree contact angle indicates complete wetting Values above 90 degree indicates poor wetting
  8. 8. Good wetting promotes capillary penetration and adhesion Indicates strong attraction between liquid and solid surface molecules Important factor in denture retention A more natural appearance is achieved if dentures are wetted by a thin film of saliva Hydrophobic substance are those that exhibit high contact angles with
  9. 9. ADSORPTION “ Process in which a liquid or gas adheres firmly to surface by attachment of molecules to surface of solid or liquid” Thus, reducing their surface free energy Process of adsorption or adhesion to surface of a substance is important in wetting process, in which substance is coated or wetted with a foreign substance such as
  10. 10. Degree to which saliva wet or adhere to surface of a denture depends on tendency for surface adsorption High-energy surfaces such as metals adsorb molecules more readily than low energy surfaces such as waxes. Where, oxides have intermediate surface energies
  11. 11. •COLLOIDS First described by Thomas Graham (1861) Derived from Greek Word Kolla: Glue, Oid: Like Substances with two or more phases Study of small particles and related surface effects in form of surface electrical charge or surface
  12. 12. CLASSIFICATION OF COLLOIDS Dispersed Continuous Type phase phase Solid Liquid Sol Solid Gas Aerosol Liquid Liquid Emulsion Liquid Gas Aerosol (Fog) Gas Liquid Foam Gas Gas Foam
  13. 13. CAPILLARY PENETRATION Penetration of liquids into narrow crevice is known as capillary action Surface energy of a liquid creates pressure that drives liquid into crevices, narrow spaces, and thin tubes
  14. 14. Penetration co-efficient Rate of movement of liquid into a capillary space is related to - Surface tension (ϒ) - Contact angle (θ) - Viscosity (n) i.e. Penetration co-efficient (PC)=ϒCos
  15. 15. Liquid with low viscosity, high surface tension and low contact angle (i.e. good wetting) penetrates more faster Important in adhesion or retention of denture
  16. 16. ADHESION Bonding of dissimilar materials by attraction of atoms or molecule
  17. 17. Classification 1.Mechanical adhesion a. Microscopic penetration b. stresses 2.Chemical adhesion a. Primary forces i. Ionic bonds ii.Covalent bonds iii.Metallic bonds b.Secondary forces (VanderWaals forces)
  18. 18. Diffusion bonding results when one phase penetrates by diffusion into surface of a second phase and forms a hybrid layer. Composite of two materials Several factors affect the strength of an adhesive bond 1. Cleanliness 2. Penetration of surface 3. Chemical reaction 4. Shrinkage of stresses 5. Thermal stresses 6. Corrosive
  19. 19. Forces involved in denture retention 1. Capillary force 2. Wetting of denture base by saliva 3. Thickness of saliva film 4. Surface tension of saliva 5. Viscosity of saliva 6. Atmospheric pressure
  20. 20. PHYSICAL PROPERTIES Considered as the ways that materials respond to changes in their environments Based on laws of mechanics, acoustics, optics, thermodynamics, electricity, magnetism, atomic structure, or nuclear
  21. 21. Classified as I. Mechanical properties II. Thermal properties III. Electrical and Electrochemical properties
  22. 22. Mechanical properties Important in understanding and predicting a material’s behavior under load STREES Internal reaction to external force When a force acts on body, tending to produce deformation, a resistance is developed to this external force application
  23. 23. In a structure, designed as force per unit area Stress = force/area Inversely proportional to cross sectional area and directly proportional to the load
  24. 24. Clinically, it is internal resistance of the body in terms of force per unit area and is equal and opposite in direction of this external force applied. UNITS :Megapascals. (MPa)
  25. 25. TYPES OF STRESSES Depending on type of force, divided into 1.Tension: when body is subjected to two sets of forces that are directed away from each other in same straight line
  26. 26. 2.Compression: Occurs when body is subjected to two sets of forces in same straight line and directed to each other. 3.Shear: Result of two forces directed parallel to each other
  27. 27. STRAINSTRAIN Expressed as change in length per unit length of body when a stress is applied. Dimensionless quantity, expressed as Strain = deformation / original length Hence, each type of stress is capable of producing corresponding deformation in a
  28. 28. Regardless of composition or nature of material, magnitude and type of stress applied to material, deformation and strain result with each other COMPLEX STRESSES: Combination of tensile, shear or compressive stress Hence, whenever, force is applied over a body, complex or multiple stresses are produced.
  29. 29. PROPORTIONAL LIMIT “The greatest stress that may be produced in a material such that the stress is directly proportional to strain” Below proportional limit, no permanent deformation occurs
  30. 30. When stress is removed, structure will return to its original dimensions. Region of stress-strain curve below proportional limit is called elastic region.
  31. 31. Application of a stress greater than proportional limit results in a permanent irreversible strain This region of stress strain curve beyond proportional limit is called the plastic region.
  32. 32. ELASTIC LIMIT “The maximum stress that a material will withstand without permanent deformation” Both proportional limit and elastic limits are often interchangeable in referring to stress involved.
  33. 33. Thus, differ in fundamental concept that, one describes elastic behavior of material whereas other deals with proportionalities of strain to stress in a structure.
  34. 34. YIELD STRENGTH “The stress at which a materials exhibits a limiting deviation from proportionalities of stress to strain” It is a stress at which material begins to functions in a plastic manner.
  35. 35. At this stress a limited permanent strain occurs It is always greater than elastic or proportional limit
  36. 36. MODULUS OF ELASTICITY “The ratio of stresses to strain up to or less than proportional limit” The measures of elasticity of a material is described by this term Also referred to as elastic modulus or Young’s modulus
  37. 37. Represents stiffness of a material within elastic range Determined from a stress strain curve by calculating ratio of stress to strain Elastic Modulus = Stress/Strain It has same units as stress and is usually reported in MPa or
  38. 38. POISSON’S RATIO During axial loading in tension or compression there is a simultaneous axial and lateral strain Hence, within elastic range, ratio of lateral to axial strain is called Poisson’s ratio
  39. 39. In tensile loading, Poisson’s rate indicates that reduction in cross section is proportional to elongation during elastic deformation The reduction in cross section continues until material is fractured
  40. 40. FLEXIBILITIES “the strain that occurs when the material is stressed to its proportional limit”
  41. 41. Relation between maximal flexibility, proportional limit and modulus of elasticity may be expressed as Modulus of elasticity = Proportional limit (P) Maximum flexibility (Em)
  42. 42. Though, some materials withstand high stresses and show minimum deformation, but in some instances where large strain or deformation is needed with a moderate or slight stress.
  43. 43. RESILIENCE Basically an express of energy “The amount of energy absorbed by a structure when it is stressed not to exceed it proportional limit”
  44. 44. The resistance of a material is usually measured in terms of its modulus of resilience, that is the amount of energy stored in a body when one unit volume of a material is stressed to its proportional limit.
  45. 45. Expressed as Modulus of elasticity (R)=Proportional limit (P2 ) Maximum flexibility (2E)
  46. 46. IMPACT Used to describe reaction of a stationery object to a collision with a moving object Depending upon resistance of impact, energy is stored in body without causing deformation or with deformation
  47. 47. Impact strength “The energy required to fracture a material under a impact force” Deformation Once the elastic limit of material is crossed by a specific amount of stress, further increase in strain is permanent deformation i.e. The resulting change in dimension is permanent or material has undergone a permanent deformation. Permanent
  48. 48. STRENGTH It is maximal stress required to fracture a structure Basically three types of strength Tensile strength Compressive strength Shear
  49. 49. It measures collective inter-atomic forces and not individual atomic attraction or repulsion It is not necessarily equal to stress at fracture Flexure strength: Also referred as transverse strength or modulus of rupture. It is collective measurement of all stresses simultaneous applied.
  50. 50. FATIGUE If a structure is subjected to repeated or cyclic stress below its proportional limit can produce abrupt failure of the structure This type of failure is called fatigue Its behavior is determined by subjecting a material to a cyclic stress of a maximum known value and determining the number of cycles that are required to produce failure
  51. 51. STATIC FATIGUE It is a phenomenon exhibited by some ceramic materials These materials support a high static load for long period time and then fail abruptly This type of failure occurs only when materials are stored in a wet environment This property is related to effect of on highly stressed surface of
  52. 52. TOUGHNESS “The energy required to fracture a material” It is a property of the material, which describes how difficult material to break.
  53. 53. BRITTLENESS It is relative inability of a material to sustain plastic deformation before fracture of a material occurs. Generally, it is considered as opposite of toughness
  54. 54. DUCTILITY AND MALLEABILITY Ductility “The ability of a material to withstand permanent deformation under a tensile load without rupture”. A metal may be drawn into a wire and said to be ductile It depends on tensile strength Decreases with increase in
  55. 55. Malleability “The ability of a material to withstand permanent deformation without rupture under compression” Increases with increase in temperature Gold is the most ductile and malleable metal followed by silver, platinum and copper
  56. 56. Measurement of Ductility: three common methods 1.Percent elongation after fracture 2.Reduction in area in the fractured region ends 3.Cold bend test
  57. 57. HARDNESS “It is the ability to withstand permanent deformation in form of indentation load” Several types of surface hardness test
  58. 58. BRINELL HARDNESS NUMBER (BHN) Hardened steal ball is pressed into polished surface of a material under a specified load. Load is divided by area of surface of indentation and quotient is referred to as Brinell hardness number or BHN. BHN = Load / Area of
  59. 59. ROCKWELL HARDNESS NUMBER (RHN) Somewhat similar to the BHN test in that a steel ball or a conical diamond point is used. However instead of measuring diameter of impression, depth is measured directly by a dial gauge on instrument. The RHN test has a wider range of application for material, since BHN test is unsuitable for brittle
  60. 60. VICKERS HARDNESS TEST (VHN) Similar to BHN test Instead of steel ball, a diamond is in shape of a square pyramid The method of analysis of VHN is same as BHN ie., the load is divided by the area of indentation.
  61. 61. The length of the diagonals of the indentation (sides of the diamond) are measured and averaged. Vickers test is used for dental casting gold's. This test is used for brittle materials but is not suitable for elastic materials.
  62. 62. KNOOP HARDNESS TEST (KHN) Diamond indenting tool is used. Its value is independent of ductility of material Values for both exceedingly hard and soft materials can be obtained from this test.
  63. 63. KNOOP and VICKERS tests are classified as Micro hardness tests BRINELL and ROKWELL test are classified as Macro hardness tests. Other tests like SHORE and BARCOL, These are sometimes employed for measuring hardness of rubber and plastics.
  64. 64. ABRASION RESISTANCE Like hardness, abrasion is influenced by a number of factors. Hardness is used to indicate the ability of a material to resist abrasion. Useful for comparing materials in same classification, eg. one brand of cement is compared to another and their abrasion resistance is quoted in comparison to one another.
  65. 65. However, it may not be useful for comparing materials of different classes. The only reliable test for abrasion is via a test procedure
  66. 66. RELAXATION Every element in nature makes an attempt to remain in a stable form. If an element is changed from its equilibrium or stabilized form by either physical or chemical means it tries to come back to its original form. After substances have been permanently deformed, there are trapped internal stresses which cause displacement of the
  67. 67. This condition is unstable Atoms wish to return to their normal positions. This results in a change in shape or contour in the solid as atoms or molecules rearrange themselves. This change in shape due to release of stresses is known as relaxation. The material is said to warp or
  68. 68. RHEOLOGY The study of flow matter is the subject of Rheology Viscosity is the resistance offered by the liquid when placed in motion.
  69. 69. THIXOTROPHIC CREEP Time dependent plastic deformation, which occurs when a metal is subjected to a constant load near its melting point is known as creep. This may be static or dynamic in nature.
  70. 70. STATIC CREEP This is time dependent deformation produced in a completely set solid subjected to a constant stress. DYNAMIC CREEP Refers to the phenomenon when the applied stress is fluctuating, such as in fatigue type
  71. 71. FLOW Although creep or flow may be measured under any type of stress Compression is usually employed for testing of dental materials.
  72. 72. THERMAL PROPERTIES Heat flow through a material Metals tend to be good conductors of heat The rate at which heat flows through a material is expressed as thermal conductivity or thermal diffusivity.
  73. 73. Thermal conductivity(k) It is a measure of speed at which heat travels (in calories per second) through a given thickness of material (1 cm), when one side of material is maintained at a constant temperature that is 10degree C, higher than the other side. Expressed in units of cal cm/cm2 sec 0C.
  74. 74. Thermal diffusivity Thermal conductivity gives an idea of the relative rates at which heat flows through various materials But, fails to take into fact that various materials require different amounts of heat (Calories) to raise their temperatures in an equal amount.
  75. 75. Thus, thermal conductivity alone will not express, how rapidly interior surface under a crown will heat up when exterior surface is heated. The thermal diffusivity (h) of a material (expressed in units of mm2 /sec) is dependent on its thermal conductivity, heat capacity (Cp ), and density (p): H = k (Cp X p )
  76. 76. Co-efficient of Thermal expansion “Change in length per unit of the original length of a material when its temperature is raised 10degreeC” The unit of α can be expressed also as µm/ cm degree C. A tooth restoration may expand or contract more than tooth during a change in
  77. 77. OPTICAL PROPERTIES Color Perception of color of an object is result of a physiological response to a physical stimulus. Sensation is a subjective experience.
  78. 78. According to Grassmann’s laws, eye can distinguish differences in only three parameters of colors. These parameters are dominant wavelength, Luminous reflectance, and excitation purity.
  79. 79. THREE DIMENSIONS OF COLOR Hue : Associated with color of an object Value: It can be separated into light and dark shades. The lightness which can be measured independently of color hue is called value.
  80. 80. Chroma: may be dull or more vivid. Difference in color intensity or strength is called chroma. Represents degree of saturation of a particular of HUE (color) Higher the chroma the more intense and mature is the color. It cannot exist by itself but is always associated with hue and value.
  81. 81. Measurement of color Measured in reflected light by instrumental or visual technique. A popular system for the visual determination of color is Munsell Color System. It is a co-ordinate system, which can be viewed as a
  82. 82. Lines are arranged sequentially around perimeter of cylinder, while chroma increase along a radius out from axis. The value co-ordinate varies along length of cylinder from black at the bottom to neutral gray at the center to white at the top. Clinically color matching is done by use of shade
  83. 83.
  84. 84. Surface finish and thickness When white light shines on a solid, some of the light is directly reflected from the surface, and it remain white light. This light mixes with light reflected from body of material and dilutes color.
  85. 85. As a result, an extremely rough surface appears lighter than a smooth surface of same material. The thickness of a restoration can affect its appearance.
  86. 86. PIGMENTATION Esthetic effects are sometimes produced in a restoration by the incorporation of colored pigments in non-metallic materials. The mixing of pigments therefore involves process of subtracting colors. Usually inorganic pigments rather than organic dyes are used because pigments are more permanent and durable in their color
  87. 87. METAMERISM Objects that appear to be color matched under one type of light but may appear very different under another light source. Quality and intensity of light are factors that must be controlled in matching colors in dental restorations. Colors should be matched in light corresponding to that of
  88. 88. FLUORESCENCE It is emission of luminous energy by a material when a beam of light is shone on it. The wavelength of emitted light usually is longer than that of the exciting radiation. Typically, blue or ultraviolet light produces fluorescent light that is in the visible
  89. 89. Opacity, Translucency, and Transparency The color of an object is modified not only by intensity and shade of pigment or coloring agent but also by translucency or opacity of object. Opacity is a property of material that prevents passage of light. An opaque material may absorb some of light and reflect
  90. 90. Translucency is a property of substances that permits passage of light but disperses light so that objects cannot be seen through material. Some translucent materials used in dentistry are porcelain, composite resins, and dental plastics.
  91. 91. Transparent materials allow passage of light in such a manner that little distortion takes place and objects may be clearly seen through them. Transparent substances such as glass may be colored if they absorb certain wavelength and transmit others.
  92. 92. Conclusion Three interrelated factors are important in long term function of dental materials 1. Material choice 2. Component geometry i.e To minimize stress concentration 3. Component design i.e To distribute stress as uniformly as possible The dental material behavior is dependent on inter-related various properties
  93. 93. REFERENCES 1.Applied dental materials-8th edition- John.Mc cabe and Angus W.G.Walls 2.Clinical aspects of dental materials – Marcia Gladwin 3.Restorative dental materials-Robert G Craig 4.Science of dental materials –Phillips 5.Notes on dental
  94. 94. Thank you For more details please visit