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    Basic Properties of Dental Materials

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    Swetha Raja
    This document summarizes the basic properties of dental materials. It describes the biological properties including biocompatibility as well as mechanical properties such as stress, strain, modulus of elasticity, hardness, and ductility. It also discusses time-dependent properties including creep and flow, as well as thermal, optical, and color properties that are important for dental applications. Finally, it provides an overview of polymers and metals commonly used in dentistry.

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    Basic Properties of Dental Materials

    Uploaded by

    Swetha Raja
    194 views47 pages
    This document summarizes the basic properties of dental materials. It describes the biological properties including biocompatibility as well as mechanical properties such as stress, strain, modulus of elasticity, hardness, and ductility. It also discusses time-dependent properties including creep and flow, as well as thermal, optical, and color properties that are important for dental applications. Finally, it provides an overview of polymers and metals commonly used in dentistry.

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    This document summarizes the basic properties of dental materials. It describes the biological properties including biocompatibility as well as mechanical properties such as stress, strain, modulus of elasticity, hardness, and ductility. It also discusses time-dependent properties including creep and flow, as well as thermal, optical, and color properties that are important for dental applications. Finally, it provides an overview of polymers and metals commonly used in dentistry.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    194 views47 pages

    Basic Properties of Dental Materials

    Uploaded by

    Swetha Raja
    This document summarizes the basic properties of dental materials. It describes the biological properties including biocompatibility as well as mechanical properties such as stress, strain, modulus of elasticity, hardness, and ductility. It also discusses time-dependent properties including creep and flow, as well as thermal, optical, and color properties that are important for dental applications. Finally, it provides an overview of polymers and metals commonly used in dentistry.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    of 47

    Basic Properties of Dental Materials

    Prof. K.A. Wettasinghe

    Biological Properties
    Non-toxic - Patient - Dentist - Staff Non-irritant Non-allergenic Non-mutagenic / carcinogenic

    Mercury Acids - Phosphoric - Hydrochloric - Hydrofluoric Nickel containing alloys Dusts H 2O 2

    Mechanical Properties
    Strain
    Is the change in length that a material undergoes when a force is applied to it It is dimensionless because it has length per units of measurement Is often expressed as a percentage Tension / Compression Elastic / Plastic

    F Stress =F/A

    Strain = l/ l

    Stress
    It is the internal reaction to an externally applied load and is equal in magnitude but opposite in direction to the external load. Force / area N/m2 Compression / tension / shear

    tension

    compression

    torque

    Torsion results in shear strains.

    Fixed end

    Stress-strain relationship
    Stress and strain are not independent and unrelated properties. The relationship between stress and strain is often used to characterize the mechanical properties of a material.

    Stress-Strain relationship
    stress

    Y P T

    strain
    Stress-Strain plot obtained from a simple compressive or tensile test

    Modulus of Elasticity
    Measure of the relative stiffness or rigidity of a material The unit values are those of force per area Modulus of Elasticity=Stress/Strain This only applies the elastic portion of the stress-strain diagram On the diagram the modulus is indicated by the slope of the linear part of the line Youngs modulus of elasticity

    Material

    Youngs Modulus GN/m2


    11.1 11.0 80.0 2.3 20.00 20.00 78-103 36-50

    Enamel Composite filling material Dental ceramic Denture base acrylic Stainless steel Co-Cr alloy Gold alloy Amalgam

    Stress-Strain relationship

    stress

    Y P T

    strain
    Stress-Strain plot obtained from a simple compressive or tensile test P Proportional limit E Elastic limit Y Yield point T Total failure

    Modulus of Elasticity
    Measure of the relative stiffness or rigidity of a material. The unit values are those of force per area.

    Modulus of Elasticity=Stress/Strain This only applies to the elastic portion of the stress-strain diagram On the diagram the modulus is indicated by the slope of the linear part of the line
    Youngs modulus of elasticity

    Material

    Youngs modulus GN/m2


    11.1 11.0 80.0 2.3 20.00 20.00 78-103 36-50

    Enamel Composite filling material Porcelain Denture base acrylic Stainless steel Co-Cr alloy Gold alloy Amalgam

    Ductility - the ability of a material to undergo permanent tensile deformation without fracture
    Malleability - the ability of a material to undergo permanent compressive deformation without fracture or rupture

    Ultimate tensile/ compressive strength


    Material Tensile strength (MPa)
    98 10 48-69 414-828 34-62 28 40 421

    Compressive strength (MPa)


    297 400 310-483 ---200-345 97 150 ----

    Human dentin Human enamel Dental amalgam Gold alloys Composite Unfilled acrylic plastic Porcelain (feldspathic) Nickel-chromium alloy

    Resilience
    The amount of energy a material can absorb before permanent deformation - Area under P

    Toughness
    . before fracture - Total area upto T

    Impact strength
    Application of a sudden force - Charpy - Izod

    Notched specimens

    Fracture toughness Resistance of a material to fracture under a sudden impact or the amount of energy absorbed by a material when it is stressed to a point just shy of its fracture point

    Tear strength Resistance to tearing Fatigue strength Repetitive application of a small load

    Hardness
    Resistance to scratching or denting The value of hardness is referred as the hardness number Depends on the method used for evaluation
    Brinell Vickers Knoop

    Hardness tests

    Brinell

    Vickers

    Knoop

    Increasing hardness for Vickers test

    Abrasion resistance

    Time dependent properties


    Flow/Creep Is an undesirable permanent deformation

    When a constant force is maintained, certain materials continue to permanently deform Compressive stresses that can cause flow is created during biting

    RHEOLOGICAL PROPERTIES
    Science of flow & deformation Mix Fluid paste Solidify - Change of viscosity

    Working time - Time for manipulation Setting time - Reach initial / final set Command Setting

    THERMAL PROPERTIES
    Extremes of temperature inside mouth Thermal conductivity Thermal diffusivity - Rapidity of warming up of a material Thermal expansion Clinical implications - Filling materials - Denture bases

    LIGHT, COLOUR AND AESTHETICS


    Visible light Blue light 380-780nm 470-480nm for LC units

    Primary colours - Blue, green, red

    Transmission of light Refraction Absorption

    Scattering

    Colour: physical aspects


    A colour of an object will depend on,

    Colour of the light source


    Nature of the object

    Metamerism - A colour appear different depending on the light source Fluorescence


    Absorb and emit a different wave length - Teeth absorb UV (400nm) & emit light of 400-450nm

    Colour: Physiological and psychological aspects

    Defective colour vision

    High sensitivity to green Colour fatigue

    Optical illusions

    Measurement of colour
    1. 2.

    HUE

    - Shade

    CHROMA VALUE

    - Saturation of a colour 3.

    - Darkness or lightness of a colour

    Polymers
    Polymer

    Monomer
    Polymerization

    Condensation Reactions
    - A smaller molecule is eliminated

    Free Radical Addition Reactions - No molecules are eliminated

    Activation and Initiation Free radicals very reactive molecules with unpaired electrons H2O2 H2O + O. (R.)

    Activation of initiator - Heat, UV light, chemicals

    Examples - Heat / chemicals for acrylic

    - Benzoil Peroxide and P-toluidine for LC composites

    Polymer Structure & Properties


    - Degree of polymerization - Molecular weight - Physical properties 1) Elastomers or rubbers 2) Hard amorphous polymers
    Tg Glass transition temperature

    Effect of molecular weight


    MW Entanglement Rigidity Strength Tg.

    Effect of cross linking


    Cross linking Harder Brittle Solvent resistant Tg.

    Plasticizers Liquids that penetrate and make it more flexible and rubbery Co-polymers Two or more monomeric units are there - Tailor made properties

    Metals
    Properties of metals
    Hard, lustrous , dense, conductors, opaque, ductile & malleable
    Electro positive - + in solution

    Forming & Shaping of Metals


    1) 2) 3)
    4)

    Casting Cold working Powder Metallurgy - TC burs Electro forming - Electro plating

    Nature of Metallic Bonding


    Loose outer electrons to give positive ions

    Solid metal positive ions held in a cloud of free electrons - High heat & electricity conduction

    Spacing of atoms Crystalline solids - Atoms are regularly arranged in a crystal lattice Unit cell The smallest unit

    14 different C.L.s 1) Body centered cube - Atoms at each corners of a cube and one in the middle

    eg. Iron below 9100C

    2)

    Face centered cube Atoms at each corner and center of each six faces eg. Au, Ag, Cu, Pt, Pd Iron above 9100C Hexagonal Zn, Mg

    3)

    Crystal imperfections
    Defects & impurities strength fractures

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