GROUP 3 PRESENTATION RHEOLOGICAL PROPERTIES.pptx

Material properties

1. GROUP 2 PRESENTATION NICE NJAMBI CYNTHIA GITHINJI FRANCIS GICHUTHI

2. RHEOLOGICAL PROPERTIES In this lecture we will discuss the science of flow of materials in different various states under stress ,emphasis will be on liquids or fluid behavior .

3. Rheology and viscosity Rheology is the study of flow of liquids under applied stress Viscosity is the resistance a liquid exhibits to flow Liquids that offer low resistance to flow under stress have low viscosities for example water , alcohol, acetone, cavity vanish

4. Liquids that offer very high resistance to flow under shear stress are viscous for example tar , honey ,dental resin composites . Viscosity is measured in unit pose

5. Why study rheology? Most mixed dental materials are fluid pastes which subsequently solidify The mixed pastes are adapted to required shape The setting time of materials initially involves a change in viscosity with time and develop an elastic modulus as solidification proceeds.

6. VELOCITY GRADIENT REPRESENTED IN A GRAPH

7. Shear stress against shear rate

8. Types of flow Newtonian flow –the viscosity of Newtonian fluid is constant and independent of shear rate for example water ,mineral oils Non Newtonian flow – shows no constancy and has 4 different types ; Bingham plastic, pseudo plastic , dilatant ,thixotropic flow

9. Bingham plastic flow –for flow to occur ,the stress must exceeds certain value ,the yield point.eg composite , ketch up Pseudo plastic flow-materials that show a decrease in viscosity as the shear rate increases for example adhesives waxes zinc polycarboxylate cement

10. Dilatant flow-the materials show an increase in viscosity with a an increase in shear rate eg wet sand Thixotropic flow –is where a material becomes less viscous and more fluid under repeated application of pressure

11. MEASUREMENT OF RHEOLOGICAL PROPERTIES Capillary viscometer –the viscosity of Newtonian fluids can be determined by timing their flow in a capillary tube Falling body viscometer –the viscosity cab be calculated from the time taken for a sphere to fall through a fluid

12. Rotational viscometer –the fluid is displaced between 2 cylinders either of which is rotated .the shear rate is obtained from ammeter which determines the torque transmitted through the liquid Parallel plate plastometer – this has 2 discs of the same size of which is the fluid is placed .one plate is made to move towards the other and viscosity calculated from the force applied to move the plate and the rate of movement

13. viscoelasticity Viscoelasticity is where some materials have mechanical properties that relate to both a solid an da liquid There are 2 aspects of viscoelasticity ;creep and stress relaxation

14. Creep is the slow deformation of a set material under constant stress .there are 2 types static creep and dynamic creep Stress relaxation –is the reduction in stress in a material subjected to constant strain

15. Optical properties In restoring oral structures a key characteristic of restorative material used would be their aesthetic compatibility .These materials need to be indistinguishable from natural structures as subtly as possible thus they need to satisfy certain optical criteria. The linkage between electromagnetic spectrum color and dental aesthetics The color is a primary component .the color of an object as sensed by human observer is dependent on a)properties of illumination , b)properties of an object c) properties of observer

16. The human eye can detect EMR in the 400-700 nm range and its more sensitive to light in the green yellow range . Generally EMR is defined by wavelength and intensity . Ultra violet light cant be seen as it falls in the 200-400 nm ,its responsible for sunburns ,skin damage , Although it cant be seen its significant as it was the precursor to the discovery of visible blue light’s ability to act as an activator of certain light curable materials setting reactions

17. Generally the human eye is more sensitive to light in the 550nm wavelength range which is yellow green .and its least sensitive in the red blue wavelength range of the color spectrum

18. Optical parameters Absorption –with the object appearing opaque Transmission- with object appearing transparent Partial transmission and refraction – with the object appearing translucent . The combined intensities of wavelength ,present in incident and reflected light determine the appearance properties of an object

19. Elements of color Hue –distinguish between red /yellow /blue light. Differentiates the small wavelengths within the visible light range Chroma-refers to the degree of saturation of a certain color Value –the scale of lightness or darkness of a color

20. Color measurement Color is measured using various equipment Munsell color system Spectrophotometer Chroma meter Shade guide Is used in the clinic in establishing color matches for tooth colored restorative for example composite

21. Munsell color syste m

22. Diagram of shade guide

23. The most popular method of assessing tooth color clinically is visual shade matching as it is quick and simple to use , Image analysis appears to be the most suitable method of tooth color measurement

24. Metamerism This is a phenomenon whereby an object appears of a different color due to light source differences . Metamerism easily affects patient treatment in terms of choice of restoration colors. its therefore advisable to do all color matching under visible light .

25. Fluorescence This is the absorption of short wavelength light and reemission of a longer wavelength Enamel and dentin strongly absorb 360-380 nm ultra violet and emit 450nm blue light hence giving these tissues a vital appearance under illumination with a significant UV component for example sunlight

26. OPALESCENCE Opalescence - This is where a tooth appears orange in transmitted light and blue in reflected light

27. Ideal optical properties For a dental material to be considered aesthetically adequate.it should posses the following ; 1.translucency 2.color stability 3.pigmentable 4.flouresence for example porcelain 5.stain resistant 6.polishable to a smooth surface

28. Lecture ;Electrochemical properties In this lecture we discuss ,reactions that occur on surfaces of metallic materials while in use in the mouth In the mouth ,metallic materials are exposed to complex environments such as change in ph. ,temperatures.

29. Electrochemical activity In aqueous environment there are found to be electronic and electrolytic conductors .electric conductors include metals /alloys whose free electrons conduct electricity . Electrolytic conductors conduct electricity by movement of ions within the electrolyte which is fluid in this case saliva Metals undergo electrochemical and chemical reactions within the oral environment which results in corrosion Corrosion compounds may accelerate ,retard ,or have no influence on deterioration on the meat surface.

30. Electrochemical cell

31. Electrolytic cell An electrolyte contains anions and cations . when 2 electrolytes are place in the electrolyte an electrical potential difference is established known as a battery A galvanic cell is where electrons are produced at the anode and consumed at the cathode Tarnish –is the surface discoloration on a metal .it commonly occurs from soft and hard deposits of plaque or calculus ,food debris on restorative surface . Corrosion – is the actual deterioration of a metal due to interaction with the environment ;moisture ,atmospheric humidity ,acidic or alkaline solutions

32. Disadvantages of corrosion 1.the products may be biologically harmful 2.causes surface discoloration which is unaesthetic 3.it also weakens the meat significantly and may lead to fracture 4.causes tooth discoloration

33. Types of corrosion Dry corrosion – occurs in absence of water or fluid electrolyte an example is the discoloration of silver by Sulphur (formation of sulfide) like in silver containing gold alloys Wet corrosion –occurs in the presence of water or other liquid electrolyte ,in the oral environment saliva acts as electrolyte .there must be n anode and a cathode This corrosion may be uniform or localized .uniform corrosion occurs if metal ions are removed from the surface evenly .localized can be classified further into 1.galvanic corrosion occurs where 2 dissimilar metals are combined whereas crevice corrosion occurs in crevices of unpolished restorations

34. Diagram of galvanic corrosion

35. Clinical examples of corrosion Electro galvanic corrosion –arises due to differences in composition of a material for example gold inlay containing amalgam . Heterogeneous surface composition –occurs in eutectic alloys of soldered appliances due to their cored structure Difference in composition of electrolytes –If a restoration is covered by a food debris as seen in crevices of unpolished restorations or semi buried dental implant the different fluid environment and oxygen concentration will lead to this type of corrosion. Stress corrosion –in a metal that has been stressed by cold working ,the area of maximum stress becomes more prone to corrosion for example implants screw ,orthopedic plates and screw

36. Protection against corrosion 1.polishing of restorations 2.use noble metals for example gold , platinum , palladium 3.passivation 4. alternative materials 5.Correct application and design of selected metals 6.patient education

37. Electroplating The metallic material that is to be coated is positioned as the cathode of an electrolytic cell The anodic metal dissolves into the electrolyte Electrolyte contains metal ions to be deposited Clinical example include ;copper plating of impressions

38. Electro polishing In this case one aims to get the highest possible luster for a metallic prosthesis .its achieved by positioning the prosthetic material as an anode ,meaning the surface will undergo dissolution in the electrolyte to yield a polished surface

39. Electro polished metal

40. Lecture ;mechanical properties Mechanical properties are an aspect of physical science that deals with energy and forces and their effects on materials. Materials need to have ability to bear forces applied to them . Measure of strength refers to the ability of material to function in the midst of these forces without failure . With this knowledge one is able to understand concept of fractures of restorative materials gaining design modifications that improve the fracture resistance of restorative materials

41. Forces Force is defined as the energy capable of changing the physical state of rest or motion of a body. Stress is the internal resistance of the body to external forces /load Stress=force/area. units are N/m^2 or Pascal’s or Megapascals ( Mpa ) There are 5 different types of stresses ;depending on the different direction of force s .they can be tensile ,compressive ,flexural , shear stress

42. Tensile stress –results when a body is subjected to 2 sets of forces that are directed away from each other in the same straight line Compressive stress –results when a body is subjected to 2 sets of forces in the same straight line but directed towards each other. Shear stress –results when 2 forces are directed parallel to each other .it tends to results in a twisting motion /sliding of one portion of a body over another. Flexural stress –refers to tensile and compressive forces working simultaneously Torsion stress-it refers to twisting /rotational forces around an axis

43. Torsion stress

44. Diagram of types of forces

45. Stress strain curve

46. Stress strain curve When a material is subjected to varying forces it will respond in a certain manner based on whether the material is elastic or rigid .these are some parameters you need to understand in order to move forward Proportional limit-is the stress above which stress is no longer proportional to strain . Proportional line –portion in the stress strain curve which obeys Hooke’s law . Elastic limit –maximum stress a material can stand before it becomes plastically deformed Yield strength and proof stress –is the maximum amount of stress a material can bear without undergoing plastic deformation

47. Reversible strain occurs in the elastic region while irreversible strain occurs in the plastic region . Fracture point is the maximum stress the material can withstand and is the stress at which the material undergoes failure . Strain –is the change in length per unit length of the body when stress is applied . Strain =change per unit length /original length

48. Resilience and toughness Toughness is a measure of maximum amount of material can absorb without undergoing fracture Resilience is the maximum amount of energy a material can withstand /absorb without undergoing permanent deformation . Units for both are ( Mmn /m^3

49. Resilience and toughness

50. Brinell hardness test machine

51. Ceramics undergo elastic deformation Metals undergo both elastic and plastic deformation Polymers undergo elastic deformation Elastic region is the region until the yield point while the plastic region is the area of the curve from the yield point to failure point

52. Elastic modulus –represents the relative stiffness or rigidity of the material within the elastic range .its measures d by the area under the stress strain curve corresponding to proportional limit Elastic modulus =stress/strain units are MPA Poisson’s ratio-ratio of lateral to axial strain within elastic range of a material Ultimate strength is the maximum stress a material can undergo before failure in compression or tension .ultimate strength =maximum load in tension or compression /original x sectional area of test sample

53. Diametral compression test for tension –in brittle materials ie acrylic polymers and ceramics a diametral compression test is used to measures their ultimate tensile strength due to challenges in conducting tensile test without risk of premature fracture

54. Ductility and malleability Ductility –is the ability of a material to withstand permanent deformation under a tensile load without rupture . Malleability –is the ability of a material to withstand rupture under compression as in hammering and rolling into a sheet

55. Hardness Hardness is the measure of the resistance of a material to indentation or scratching . Testing methods include the ; Brinell ,Vickers , Rockwell , Knoop , Barcol, Shore A hardness tests Brinell hardness tests is used to measure hardness of metals and metallic materials .formulae =load /area of indentation Rockwell hardness tests –a steel ball or conical diamond point is used and the depth is directly measured .it has a wider application of material testing

56. Vickers hardness test – similar to Brinell test however instead of a steel ball a diamond square pyramid is used . its suitable for brittle materials used for measuring harness of tooth structure as well . Knoop hardness test –its values are independent of ductility of the materials and values of both exceedingly hard and soft materials can be obtained . Vickers and knoops hardness test are termed as micro indenters and are preferred in evaluation of most dental materials

57. Barcol /Shore A hardness tests –its used specifically for measuring the hardness of rubber and plastics whereas Barcol tester can be used to measure hardness of composites

58. Barcol hardness test machine

59. Vickers hardness test

60. Rockwell hardness test

61. Brinell hardness test

62. Fatigue strength –a structure is subjected to repeated or cyclic stresses below its proportional limit and can produce abrupt failure of the structure . Impact strength- it’s the reaction of a stationary object to a collision with the moving object .the moving object subjects the stationery object to impact energy /mechanical shock /shock loading . There are 2 types of the testers for this the Charpy type impact tester and the izod impact tester

63. Charpy type impact tester

64. Question 2 Materials that have a high compressive strength and low tensile strength are classified as having the property A)Ductility B)fracture toughness C)brittleness D)malleability E)resilience

65. Lecture ;thermal properties THIS TOPIC FOCUSES ON RESPONSE OF MATERIALS TO TEMPERATURE CHANGES TEMPERATURE CHANGES CAN BE MEASURED by thermometers ,thermocouple ,and tactile sense . Temp changes may occur during the setting reaction of some materials during cavity preparations and also the oral environment is exposed to both hot and cold foods in a cyclic manner Thermal conductivity –is the quantity of heat passing through a body one centimeter thick ,within a cross section of one square centimeter when the temperature difference is one degree centigrade .its represented in the units of watts /m/s/degree centigrade

66. Thermal conduction

67. Thermal diffusivity It’s the rate at which a solid with non uniform temperature reaches a state of equilibrium . Its calculated as thermal diffusivity =thermal conductivity /specific heat capacity times density .units are mm^2/sec This parameter is important since; A)prosthesis in the mouth are exposed to non steady state due to eating and drinking hot or cold substances B) a 5.5 degrees Celsius Increase in temperature is capable of causing pulp damage

68. Linear coefficient of thermal expansion COTE This is the change in the length per unit of a material when the temperature Is raised by one degree kelvin

69. Lecture ;Natural dental tissues In this lecture we dwell on dentine and enamel to be specific as the natural dental tissues in humans. We essentially learn them so as to; Understand engineering of these hard tissues in order to make synthetic copies Be biocompatible ,synthetic chemical components should have minimal adverse effects To repair materials should match properties of residual tooth substances and have capability of bonding Assist in understanding manipulation of the tissues in preparation of attaching dental biomaterials

70. Enamel Enamel is the hardest tissue on the body composed of 97%-calcium hydroxyapatite ,1%organic ,2%-water The largest structural unit of enamel is enamel rods consisting of calcium hydroxyapatite crystals which form a key hole appearance Properties of enamel include; 1.has no nerves –biological 2.cannot be renewed

71. 3.darkens with age 4.tensile strength of 10 MPA- mechanical 5.compressive strength of 375MPA -mechanical 6.Elastic modulus of 65-70gGPA –mechanical 7.translucency-optical property 8.lower resilience –mechanical 9.a density of 2.9gm/cm^3- mechanical

72. Dentine Composed of 69%hydroxyappetite crystals ,20%-organic content ,insoluble protein ,11%water When cut it remains as a disorganized layer of dentine and debris that’s referred to as smear layer that presents a challenge to tooth bonding Mechanisms have been established via amino acids in collagen that can form chemical bonds ; 1.polar amino acids

73. 3. Hydroxyl and Sulphur containing amino acids -OH 4.calcium ion groups of the inorganic part for example hydroxyl apatite can as well form chemical bonds DENTINE PROPERTIES INCLUDE; 1)hydrophilic 2)Vital

74. 3)organic 4)energetic 5)forms a smear layer 5-10 micrometers 6)is produced throughout life –biological 7)tensile strength of 50MPA- mechanical 8)compressive strength of 230-300MPA -mechanical 9)softer than enamel

75. 10)does not have a nerve supply but can still be sensitive 11)Density of 2.1gm/cm^3 -mechanical 12) a low thermal conductivity-therma l

76. Dentine and enamel

77. Lecture bio oral environment and biocompatibility Bio oral environment ;main factors that influence a materials survival in the mouth . the following conditions prevail in the oral environment 1. different functional stresses exerted 2. moisture –saliva 3.variable PH 4.temperature changes of 0-60 degrees 5.bacteria and enzymatic action

78. 6)stain 7)wear 8)oral hygiene procedures IDEAL BIOLOGICAL PROPERTIES Biocompatibility ;is the capability of a manufactured materials and devices interacting with body tissues and fluids with no unfavorable reaction

79. Biocompatibility materials should therefore be 1)non toxic 2)Non irritant 3)non –allergenic 4)non mutagenic /carcinogenic

80. Biocompatibility testing before use of dental materials ,They are tested in 3 stages LEVEL 1 TEST/PRIMARY TEST These are screening tests whereby materials are evaluated for systemic toxicity Acute systemic toxicity here is evaluated in animals via a gastric tube of a certain dosage of reacted or hardened dental material The material is studied for 2 weeks and toxic manifestations /death are recorded If more than 50% of animals survive ,the material will have passed stage 1 test In this category we have in vitro tests where cell response is tested in a cell culture ,test tube or flask through direct or indirect contact with material . Cell death extent in this case ,becomes the measurable criterion for cytotoxicity

81. Level 2 tests /secondary test These are evaluation of allergenic and inflammatory potential via injection of the material intradermal /intramuscularly into the test animal .the test animals are then sacrificed at various time intervals and site of implantation examined .these findings are then compared with those of zinc oxide eugenol (negative control )and silicate cement which is a positive control

82. Level 3 test /usage test Conducted in subhuman mammals like primates .cavities are prepared and restored and pulpal reaction evaluated by extracting them at different time intervals and histological sections made sections are examined microscopically for presence of inflammation ,necrosis and evidence of repair ,the reactions are compared to that of zinc oxide eugenol and silicate as the negative and positive controls respectively

83. QUESTION 1 Which is not a thermal property in dental biomaterials ? A)thermal conductivity B)glass transitional temperature C)thermal diffusivity D)specific heat E)coefficient of thermal expansion

84. Question 2 Regarding Crevice corrosion which is true? A)occurs in metal alloys with inhomogeneous composition B)the differential oxygen concentration in crack filled with fluid in the mouth culminates to cathodic process at the bottom of the crevice and anodic process at the surface C)the differential oxygen concentration in crack filled the fluid in the mouth culminates to anodic process at the bottom of the crevice and cathodic process at the surface D)it occurs on polished metallic restorations e)none of the above

85. QUESTION 2 Cote of dental materials should A )Waxes demonstrate the lowest COTE B)is a measure of change in length per unit length for a 1 degree Celsius change in temperature C)dental ceramics exhibit the highest cote value D)should ideally be higher than that of dental tissues E)none of the above

86. Question 3 With regards to perception of color the following is false ? A)the human eye detects red most sensitively B)color fatigue occurs at the cones cells of the retina C)its subjective and physiological in all individuals D)The human eye is most sensitive to light in the green yellow range

87. Question 1 1Concerning electrochemical properties of materials select one which is correct ? A)corrosion and tarnish occur in all types of materials B)corrosion and tarnish can be prevented by passivation or use of noble alloys C)corrosion occurs in metals while tarnish occurs in dental cements D)Corrosion is surface discoloration while tarnish is surface deterioration. E) corrosion and tarnish occur in metals

88. Question 3 ALL THESE ARE TYPES OF ELECTROCHEMICAL CORROSION EXCEPT ? A) DRY COOROSION B) INTERGRANULAR CORROSION C) GALVANIC CORROSION D) HETEROGENOUS CORROSION E) CREVICE CORROSION

89. Study question The following are biological properties of biomaterials except a)bioactivity B)biocompatibility C)fluorescence D)bio functionality E) osseointegration

90. Questions Which is false about of biological materials tests? A)level 3 tests are usage tests B)they are conducted in stages to determine suitability of a biomaterial for an intended function c)they are cheap and easily executed D) level 1 test include cell culture E)clinical trials are the gold standard test

91. Question 1 A dental materials which has a high proportional limit compared with one with a lower proportional limit would have A)a high modulus of elasticity B)greater toughness C)greater ductility D)lower elastic limit E)more resistance to permanent deformation

92. Question 1 If a fluid undergoes increase in viscosity with increasing shear rate the fluid is said to undergo ? a)Pseudoplastic flow b)Plastic flow c)Newtonian flow d)Dilatant flow e) Bingham flow

93. Question 2 Creep A)Under certain conditions is a flow behavior of set solids such as dental amalgam B)Is time independent C)may be static occurring in a solid under cyclic fluctuating stress D)may be dynamic occurring in a solid under constant stress E)under given conditions of stress and temperature is a flow behavior of liquids

94. ANY QUESTIONS ? THANK YOU FOR YOUR TIME

95. Question Which of the following statement is false concerning behavior of light on an interface A)an opaque object that reflects all incident light with the same intensity as received appears black B)any object viewed under different light sources may appear to change color C)opacity is a property in which an object prevents passage of light D)a beam of light on an object may be reflected ,refracted or transmitted E)a beam of light on an object may be absorbed or scattered