Properties of Materials Prepared by Dental Materials Department

Properties of Materials Prepared by: Dental Materials Department Yenepoya Dental College, Yenepoya University, Mangalore. 1

Why/How do materials fail? 2

Types of Material Failure n Deformation failure q n Fracture q n A change in shape or size of a component that is sufficient for its function to be lost or impaired. Cracking to the extent that a component is separated into two or more pieces. Corrosion q The loss of material due to chemical action. 3

n Wear q n Surface removal due to abrasion or sticking between solid surfaces that touch Erosion q The wear caused by a fluid (gas or liquid( 4

Material Properties n n n Chemical Properties Physical Properties Mechanical Properties 5

Chemical Properties n Material characteristics that relate to the structure of a material and its formation from the elements. n Cannot be determined by visual observation. 6

Composition q Determined by analytical chemistry techniques percentage of each component Avoid selecting materials by trade names. Try to obtain and understand the composition of materials used in design. 7

Microstructure q q q n Grain size Inclusion Phases Methods to obtain: q q Metallography, Ceramography Chemical etching Microtomy (polymer) Polarized light transmitting 8

Crystal Structure q Method to obtain n q X-ray diffraction Will indicate melting characteristics, mechanical properties, … Corrosion Resistance q Degradation of a material by reaction with its environment 9

Physical Properties n n Characteristics of materials that pertain to the interaction of these materials with various forms of energy and with other forms of matter. Can usually be measured without destroying or changing the material. q Color, density, … 10

n Thermal conductivity q n Should a filling material have good thermal conductivity? Thermal expansion q Is important when dissimilar materials will be fastened and heated, and when materials are locally heated. n n Unit: in. /in. o. F or cm/cm o. C Example: Thermal expansion of restorative materials should match with that of teeth. 11

Thermal expansion: Question Every dimension on the piece must be multiplied by the coef. of expansion factor! 12

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n n n Heat distortion temperature polymers Water absorption polymers Electrical properties Magnetic properties Gravimetric q q Density Specific gravity 14

Mechanical Properties n n n The characteristics of a material that are displayed when a force is applied to the material. Often require the destruction of the material for measurement. “mechanical” indicates the suitability of a material for use in mechanical applications e. g. parts that carry a load, absorb shock, resist wear, . . . 15

Material Properties Chemical Metals Plastics Ceramics Composites Physical Composition Microstructure Phases Grain size Corrosion resistance Inclusions Composition Fillers/additives Crystallinity Molecular weight Flammability Spatial configuration Chemical resistance Composition Porosity Grain size Crystal structure Corrosion resistance Phases Composition matrix: filler Matrix/filler bond Volume fraction of fillers Reinforcement type Chemical resistance Melting point Glass transition (polymers/glasses) Magnetic Electrical Optical Acoustic Gravimetric Color Mechanical Manufacturing considerations Tensile/compressive properties Toughness Ductility Fatigue Hardness Creep resistance Shear strength Available shapes Available sizes Available surface texture Manufacturing tolerances Tensile/compressive properties Heat distortion Pressure-velocity limit Toughness Stress rupture resistance Creep resistance Manufacturing tolerances Stability Available sizes Tensile/compressive properties Fracture toughness Transverse rupture Hardness Available shapes Available sizes Available surface texture Manufacturing tolerances Tensile/compressive properties Fracture toughness Creep resistance Reinforcement orientation Available shapes Available sizes Manufacturing tolerances Stability

It is necessary to understand what these properties mean, how they are measured, and how they should be compared in the selection process. 17