# Properties of Dental Materials

 Four major properties of dental materials chemicalphysicalmechanicaloptical forces of metal (ferrous and non ferrous) "electron sea" that glues the ions together uses of metals (ferrous and non ferrous) usually strong, conduct electricity and heat well and are opaque to light forces of ceramics positive or negative ions, coulomb forces composition of ceramics combinations of metals or semiconductors with oxygen, nitrogen, or carbon examples: glass, porcelain, minerals, diamonds forces of polymers covalent, van der waals, H-C bonds Weight of polymers examples of polymers (4) light weight plastics, rubber, polyester, elastomers the mixture of a metal, ceramic and polymer is a composite Stress equation Example:    According to the Centers for Disease Control, the average weight of an American man and woman in 2010 was 195.5 and 166.2 pounds, respectively. Imagine a typical American man wearing shoes with a heel area of 10 square inches and a woman wearing high heels with an area of .25 square inches (1/4 inch per side). When walking, a man’s foot exerts a force of 19.5 pounds per square inch on the surface he is walking on while a woman’s heel would exert a force of 2,659 pounds per square inch. Stress= Force/ Area Stress = Force / Area  195.5/10  =  19    166.2/.0625  =  2659 A and B? P A= compressionB= tension  P= pressure or force? the measure of heat transfer or heat flow thermal conductivity True/False: metals have lower values of conducting heat than plastics and ceramics FALSE; they have higher values Enamel and dentin are ___ conductors of heat and cold poor ____ ____ and their components have the largest coefficient of thermal expansion of any material used in restorative dentistry dental waxes the generation of electrical currents that the patient can feel Galavinism a surface reaction of metals in the mouth from components in saliva or food tarnish the dissolution of metals in the mouth corrosion True/False: computerized systems are the best way to color match for restorative dentistry FALSE; they offer great hope for the future but visual shade selection with the human eye is still the most predictable method available the visible spectrum ranges from ___ to ___ nm 400 to 700 what are the 4 wavelengths shorter than the visible light ultraviolet, x-rays, gamma, and cosmic rays what the 5 waves above the visible spectrum infraredmicrowavestelevisionradioelectrical waves degree of saturation of a shade; light yellow to dark yellow chroma sensation induced from light of varying wavelengths reaching the eye color the property of light source to influence color of objects color rendition dominant color of an object; dominant color: red, yellow, green, blue, etc Hue phenomenon in which the color of an object under one type of light appears to change when illumination by different light source metamerism relative lightness or darkness of a color; white to dark value Guidelines for evidence based shade selection Proper: lighting: distance:  time: environment: preoperative: lighting: 5550* Kdistance: 6-8 inchestime: 3-5 secondsenvironment: neutral environment preoperative: dehydrated teeth are lighter increasing translucency decreases____ value amount, location, and quality varies w person and age determines the amount and direction of light reflected off the facial surface; wears with age; develop texture from adjacent natural teeth surface texture the property of materials that prevents the passage of light opacity A property that allows the passage of light so little distortion takes place and objects may be seen clearly through them. transparency Is a property of substances that permits passage of light but disperses the light so objects cannot be seen through the materials translucency The same object, without changing color may appear different in color under different lighting conditions metamerism strain equation strain= deformation (change in length)/ original length the ratio of stress to strain in the linear or elastic portion of the stress-strain curve elastic modulus the stiffness of a material and is a constant elastic moduli of dental materials elastic moduli of: human enamel: gold alloy: 83,00096,600 the stress at which the material no longer functions as an elastic solid and is higher than the elastic modulus proportional limit used to designate a certain permanent deformation or offset, usually 0.2% (slightly higher than proportional limit) used because proportional limit is difficult to determine yield strength indicates that stress and strain are no longer proportional plastic deformation  higher than plastic deformation on graph the strength at which fracture occurs ultimate strength higher forces applied to a material will cause fracture or rupture ultimate tensile strength indicates the energy absorbed up to the proportional limit resilience indicates the energy absorbed up to the ultimate tensile strength toughness on graph under the elastic modulus until proportional limit resillence on graph between proportional limit to ultimate tensile strength along plastic deformation curve toughness the resistance of a material to indentation hardness knoop hardness scale goes from what to what? hardest material softest material 0-600  softest: acrylic resinhardest: dental porcelain a measure of the consistency of a fluid and its inability to flow. it is a function of time that can be used to measure the working time of a material that undergoes a liquid-to-solid transformation viscosity the percentage of shrinkages or expansion of a material dimensional change Authorarikell ID338415 Card SetProperties of Dental Materials DescriptionMidterm Material 2/7 Updated2018-02-26T23:46:18Z Show Answers