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LIST OF CONTENTS
Part I Page
1. Structure of Matter 2
2. Physical Properties 8
3. Mechanical Properties 13
4. Adhesion and Bonding 30
5. Polymers 35
6. Metallurgy 41
7. Tarnish and Corrosion 57
Part II
1. Model and Die Materials 61
2. Investment Materials 68
3. Casting Technology 75
4. Dental Casting Alloys 81
5. Wrought Wires
6. Joining of Metals
7. Dental Amalgam
8. Impression Materials
9. Non Metallic Denture Base Material
10.Direct Aesthetic Restorative Materials
11.Dental Cements
12.Dental Ceramics: Dental Porcelain
1
Structure of Matter
Give short account on:
1. Types of bond.
2. Correlate between the types of bond in ceramics and their properties.
3. Correlate between the types of bond in polymers and their properties
4. Correlate between the type of bond in metals and their properties.
5. Correlate between structure of matter and properties of material.
6. Mention the factors affecting the properties of the materials.
7. Compare between the crystalline and amorphous solids.
8. Give an account on the characteristics of different types of bond.
9. Polymorphism.
10. Amorphous solid.
11. Atomic packing factor.
12. Factors affecting inter atomic distance.
13. Primary bond.
14. Secondary bond.
15. The characteristic features of a material bonded by ionic, covalent and metallic bonds.
16. The characteristic features of ionic, metallic and covalent bond.
State true or false and correct false answer:
1. The higher the atomic packing factor of the material the lower the strength properties.
2. Reconstructive transformation of silica is responsible for the contraction of the investment during heating.
3. The higher the melting temperature, the lower the coefficient of thermal expansion.
4. Amorphous materials have definite melting temperature.
5. The force of attraction between atoms is maximum in the gas state.
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6. Cystalline solids are characterized by short range arrangement of their atoms.
7. Atomic packing factor in body centered cubic is more than that of face centered cubic.
8. The type of bond and the arrangements of atoms specify the properties of the materials.
9. All crystalline materials have the same type of space lattice.
10. An amorphous solid is one in which the molecules tend to be distributed at random.
11. Metals are crystalline in nature.
12. The higher the interatomic bond, the higher the coefficient of thermal expansion.
13. Density of molten alloy is less than that of its crystalline solid.
14. The internal energy of amorphous structure is lower than that of crystalline structure.
15. Polymers have a glass transition temperature.
16. Crystalline solids are characterized by short range of arrangement of their atoms.
17. Transformation of crystobalite to quartz is a reconstructive transformation.
18. The actual strength properties in crystalline structure are higher than their theoretical strength.
19. Polymers have high mechanical properties due to the covalent bond.
20. Materials having higher atomic packing factors usually have higher densities and higher stability.
21. The polymorphic forms of silica have the same crystalline structure.
22. Waxes are characterized by low definite melting point.
23. Van der Wall forces are weak chemical bonds.
24. Face-centered cubic crystals have the highest atomic packing number.
25. Polymers have low melting points and high coefficient of thermal expansion and contraction because its prevailing intramolecular forces are van der Waal forces.
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26. Reconstructive and displacive transformations in silica are reversible processes.
27. Although the polymorphic forms of silica have different properties, they have the same crystalline structure
28. Allotropy is the transformation from one chemical form to the other.
29. Ionic bonds exist in ceramic solids while metallic type of bond governs the behavior of alloys.
Choose the correct answer:
1. Which type of bonding in the material is associated with high electrical and thermal conductivity of the material:
a. Ionic b. Covalentc. Metallicd. Van der Waals
2. In crystalline solids, the high atomic packing factor leads to:a. High thermal coefficient of expansion.b. Flexibility.c. High density.d. High strength properties.
3. Van der Waal forces:a. Ice.b. Secondary bonds.c. Physical and weak.d. Chemical and strong.e. All of the above.
4. Covalent bond:a. Directional.b. Hydrogen atomc. Insoluble in water.d. H2O molecule.e. All of the above.
5. Higher melting temperature is associated with:a. Week atomic bond.b. Strong atomic bond.c. Domination of secondary bondd. All of the above
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Match the following:
1)i. Covalent bond a. Electron transferii. Secondary bonds. b. Involve electronsiii. Metallic bonds. c. Electron cloudiv. Ionic bonds d. Directionalv. Primary bonds e. Physical forces
2)i. Metallic bond a) Sharing of electrons.ii. Covalent bond b) Attraction of dissimilar ions,iii. Ionic bond c) Attraction between free
electrons & positive ionsiv. Combination of bonds d) Insulators when solidv. Hydrogen bond e) Highly directional
f) Polarization of molecules.g) Calcium sulfate.h) Poor thermal conductor.
Complete the following:
1. Body centered cubic system contains……. atoms, while closed packed hexagonal system contains …….. atoms.
2. Space lattice is defined as ………
3. The smallest repeated unit in a space lattice is …………..
4. Ionic bond is the basic bond for ….. while covalent bond is the basic bond for ……….
5. Melting temperature depends on …….. while density depends on ……...
6. The existence of an element in more than one crystalline form is ……………., for example…………………………………
7. In linear polymer, bonding within the molecule is by ……. While that between the molecules is by …………..
8. Characteristic properties of metallic bond are:a)b)c)d)
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9. β-crystobalite is found ………… while α-crystobalite is found at room …… temperature this change is called ………..
10. Waxes have ………… rather than melting point.
11. The internal energy of amorphous structure is ……… than that of crystalline structure.
12. The higher the inter-atomic bond, the ……… the melting temperature and the ……… the coefficient of thermal expansion.
Give reasons for:
1. Metals have high thermal conductivity.
2. Presence of the point defects in crystalline structure increases the strength properties.
3. Ceramics are heat resistant.
4. Opacity of metals.
5. Polymorphic forms of silica have different physical properties.
6. Actual strength is much lower than theoretical strength.
7. Face-centered cubic structures have higher density than body-centered cubic structures.
8. Amorphous structures have higher internal energy than crystalline structures.
9. Elastic moduli of polymers are much lower than metals.
10. Tridymite and crystobalite have different coefficients of thermal expansion although they are chemically the same.
11. Displacive and reconstructive transformation of silica.
12. The melting temperature of the material is directly proportional to its coefficient of thermal expansion and contraction.
13. Materials having higher atomic packing factor usually have higher densities and higher stability.
14. The polymorphic forms of silica have different physical properties but they have the same crystalline structure.
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15. Polymers are so much weaker and more flexible than metals and ceramics.
16. Metals conduct heat and electricity whereas polymers and ceramics do not.
17. Density of molten alloy is less than that of its crystalline solid.
18. Secondary bonds are weak bonds.
19. The insulating capacity of the ionic solids.
20. High melting point of diamond.
Compare between:
1. The properties of meals, ceramics and polymers regarding their atomic
structures.
2. Crystalline structure and amorphous structure.
3. The properties of ceramics and polymers regarding their atomic structure.
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Physical Properties
Give reasons for:
1. The importance of an insulating base under metallic restoration in a deep cavity.
2. The mismatching in coefficient of thermal expansion and contraction between tooth structure and a restorative material may lead to failure.
3. Fluorescent lamps should not be used during shade selection.
4. Shade guide comparison should not exceed five seconds without resting the eyes.
5. Two same color may appear different due to difference in surface texture.
6. The better retention of non-metallic denture base materials is better than that of metallic ones.
7. Thermal diffusivity is more important property than thermal conductivity.
8. The calculated theoretical strength of crystalline materials is much higher than its practical strength.
9. Dead tooth appears less vivid than vital tooth.
10. Close matching of refractive index of tooth structure and aesthetic restorative materials.
11. Presence of scattering centers increases the opacity of an object.
12. Better castability of gold alloys.
13. Insulating base is essential under large metallic restoration.
14. Addition of fluorescing agents to porcelain.
15. Thermal conductivity of dental materials may be desirable or undesirable.
16. Water sorption of acrylic resin is of clinical importance.
17. The high thermal conductivity of metallic denture base materials is an advantage.
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18. Value is the most important color parameter in dentistry.
19. Green object appears black in blue light.
20. Metals have high thermal conductivity.
21. High melting point of diamond.
22. Density of a molten alloy is less than that of crystalline solids.
23. High density of metals
24. The importance of close matching in coefficient of thermal expansion and contraction between tooth structure and a restorative material.
25. Two identical solids, one looks more dull and opaque than the other.
26. Some materials can be easily plastically deformed.
State True or False and correct the false answer:
1. The higher the melting temperature, the less the coefficient of thermal expansion.
2. Thermal conductivity is an advantage for metallic restorative materials.
3. An opaque material can allow the passage of most of light.
4. Atomic bonding is directly proportional to the melting temperature.
5. Allotropy is a physical transformation of an element.
6. The linear coefficient of thermal expansion for isotropic solids is three times the volumetric coefficient.
7. Low value of the tooth structure gives vital look.
8. Scattering of light decreases translucency .
9. Matching of the refractive index between matrix and fillers increases opacity.
10. Increasing the thickness of an object will lead to more opacity and higher value
11. Dead tooth have lower value than vital tooth, thus it appears more vivid and translucent.
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12. Presence of scattering centers decreases the opacity.
13. Dentures of light weight will help the retention of upper denture and allow better castability.
14. Increasing the thickness of an object will lead to more opacity and higher value
15. The higher the melting temperature of the material, the higher its coefficient of thermal expansion and contraction
16. Allotropy is the transformation from one chemical form to other form.
17. Amorphous material has high state of energy than the crystalline materi
18. The higher the strength of interatomic bonds, the stronger and the harder is the material
19. Polymers have low melting points and high coefficient of thermal expansion and contraction because its prevailing intramolecular forces are Vander-Waal's forces.
20. Waxes have a low coefficient of thermal expansion while metals have high value.
21. High thermal conductivity of metallic denture base materials causes thermal shocks and discomfort to the patient.
22. Increased amount of reflected light on an object makes the object to appear shiny.
23. Transparency is decreased by the presence of scattering centers.
24. High density of metallic dentures allows better castability.
25. Rough composite fillings reflect more light than smoothed finished ones.
26. Metamerism is the change of color matching of two objects under different light source.
Compare between:
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1. Transparent and translucent.
2. Fluorescence and phosphorescence.
Give an account on:
1. Thermal conductivity.
2. Color parameters.
3. Differentiate between hue, chroma and value.
4. The clinical importance of:a. Density.b. Coefficient of thermal expansion
5. What are the factors affecting color appearance?
6. What is the clinical significance of:a. Density.b. Scatteringc. refractive indexd. Solubility and disintegration.
7. Discuss why a knowledge and understanding of the physical properties of biomaterials is important in dentistry?
Choose the correct answer:
1. Tooth of low value appears:a. Gray and non vital.b. vital and vivid.c. Yellowish white.
2. Value:a. Is a measurement of color intensity.b. Dominent wave length.c. Most important color factor in tooth color matching.
3. In composite restorative resin, surface gloss decreases with.a. Increases surface roughness.b. Decreases surface roughness.
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c. Increases the intensity of color.
4. Two objects that match color under different light sources are known as:a. Metameric pair.b. Isomeric pair.c. Polymorphic pair.
7. Amorphous solids are characterized by:a. Low internal energy.b. High internal energy.c. Definite shape.d. High fusion temperature.
8. Crystalline solids are characterized by:a. Soften before melting.b. High internal energy.c. High density.d. Lower internal energy.
Complete the following:
a. Tooth of high value appears ……………………………………
b. Increase surface roughnmess in composite resin, …… surface gloss.
c. Two objects that don't match color under different light sources are known as …………
Selected problems:
Problem 1:In the clinical evaluatin of a 2-years old acrylic resin, recurrent caries and marginal discoloration are noted. What most likely caused this problem?
Problem 2:A ceramic crown matches the color of the shade guide but not the adjacent tooth. What most likely caused this problem and how can it be avoided?
Problem 3:A composite filling material may appears gray, non vital and dull. Which variables are involved?
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Mechanical Properties
Give an account on:
1. The difference between internal equilibrium and external equilibrium.
2. Force.
3. Stress and its types.
4. Strain and its types.
5. Draw a stress strain curve showing strong , stiff and brittle material.
6. Draw a stress strain curve showing stiff, ductile, strong and tough material.
7. Draw a stress strain curve showing Flexible, brittle and weak material.
8. Impact strength.
9. Fatigue and creep.
10. The difference between ductile fracture and brittle fracture.
11. State different types of hardness test.
12. Transverse strength test.
13. Determine the type of fracture in rubber and gypsum. Draw stress/strain curve for each.
14. Stress/strain curves. Label and describe the properties that can be derived from the curves below:
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15. Draw and label stress strain curves for different properties:a. Brittle or ductile materialsb. Flexible or Stiff materialsc. Resilient or tough materialsd. Strong or weak materialse. Strong and tough material.f. Strong, rigid, ductile, material.g. Strong, rigid, ductile and hard material.
16. Label the different properties that can be shown on the stress strain curve of material A and material B. How can you describe each material separately.
17. Draw a curve for visco-elastic materials showing different behavior during and after load application.
18. What are the properties that can be derived from stress-strain curve for a material subjected to tensile test (draw and label the curve).
19. How could the following be tested:a. Tensile strength of a brittle material b. Surface hardness of rubber base impression materialc. Fatigue d. Impact strength
20. Draw:i. Labelled stress-strain curve of a strong, rigid, ductile material
showing areas of resilience, toughness and hardness.ii. Strain-time curves of strain-rate sensitive materials.
iii. Stress strain curve for a strong ductile material and define the properties that can be identifical from it.
21. Mention the clinical significance of:a. % elongation b. Resilience.c. Fracture toughnessd. Cantilever bending.e. impact strengthf. Fatigue
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g. Creep
22. Determine the effect of the time of load applied on the properties of each material:
i. Ideal elastic material.ii. Ideal viscous material.
iii. Anelastic material.iv. Visco-elastic material
23. Define and state the clinical importance of:a. Impact strength.b. Fatigue and S-N curve.
24. Draw a curve of viscoelastic material.
25. Differentiate between force and stress.
26. Differentiate between strain and deformation
27. Define A, B, C and D on the curve and mention their importance.
28. Mention the different properties on the following curves.
29. The measurement of the tensile strength of a brittle material.
30. Fracture toughness and its applications.
31. Transverse strength.
32. Fatigue.
33. Hardness (definition, importance, and tests).
34. Definition and dental significance of:a. Modulus of elasticity.b. Hardness
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c. Ductility.d. Impact strength.
35. The modulus of nickel-chromium alloys is about twice that of gold alloys. Is it correct to reduce thickness by one half and have the same deflection in bending?
36. Regarding the strain-time relationship, state the behaviour of materials A, B, C and D on the following curves:
37. A dental component suffers from stress and strain fields generated as a result of loads externally applied. Discuss this statement giving an example of your choice.
38. Define the following and mention their dental applications:a. Impact strength.b. Viscoelasticity.
39. Define and explain the importance of the following mechanical properties in dentistry:
a. Yield strength.b. Resilience.c. Flexure strengthd. Fracture toughness.
40. Give short notes on a restoration in mechanical equilibrium.
41. Fatigue is an important mechanical property of dental materials. Explain.
42. Viscoelasticity and its dental significance.
43. Which mechanical property is usually considered a measure of burnish ability of a soft inlay alloy?
44. Causes of fracture of restorative materials.
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45. What are the properties controlling the burnishability of cast alloy?
46. Why do structure subjected to bending fail on the surface that is increasing in convexity?
47. Is fracture of a restorative material the only indication of failure?
48. Is it possible for a stiff material (high elastic modulus) to fail at a lower stress than a more flexible material?
49. Why is the yield strength of a restorative material is an important property?
50. A small occlusal pit restoration of 4 mm2 surface area having 2 mm depth is subjected to bitting force of 440 N. Calculate the stress within the restoration, the axial strain and the lateral strain knowing that E = 1 GN/mm2 and µ=0.3
51. An orthodontic wire 1.6 mm diameter and 2 mm2 cross sectional area, if 300 N force is applied to that wire find the induced stress within the wire.
52. A tensile force of 200 N is applied to a wire 0.000002 mm2 cross sectional area and 0.1 mm long when the wire is stretched to 0.101 m under that force (elastic deformation) calculate:
i. Stressii. Strain
iii. Mouduls of elasticity
53. A 20 gauge orthodontic wire has a diameter of 0.8 mm and a cross sectional area of 0.5 mm2, if 220 N force is applied to a wire of this diameter find the stress developed.
Complete the following:
1. Stress is ………… and it can be ….., …….. or ……. Units are ………,………… or ………….
2. Deformation is ………….. and it can be ……..or ………Units are …… , ….. or ……..
3. Strain is classified into ………. or ……………..
4. The yield strength is defined as …………
5. Modulus of elasticity is …….. it is a measure of ….. or ……..
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6. Maximal flexibility is defined as …………..
7. A ductile material is characterized by ……………… while a brittle material is characterized by …………………..
8. Measurement of ductility is ……… while a brittle material is tested by ……………………
9. The tensile strength of brittle material is calculated by the equation: ……………………..
10. Resilience is …………. While toughness is ………………..
11. Transverse strength is important in cases like ……….. and …… it can be calculated by ……………. and the deformation is calculated by ………………………………………
12. Fatigue strength is ……………….. while fatigue limit is ………..
13. Impact strength is important in case of ……………………………. It is defined as ……………………………………………………..
14. Hardness is ………… property. The best hardness test employed for brittle materials are ……….. and …….. while for elastic materials, the best test is …………………………………….
15. Flexibility is a …………. relationship while elasticity is a ………. relationship.
16. Creep is defined as ……………………. It occurs in ………….. dental restorative materials like ……… or ……………….
17. Load below proportional limit may cause failure of materials like in case of ………… and ……………….
18. A material that fails under few small cycle loading below its P.L. has a low…………………….i. Impact strength. ii. Creep value.iii. Fatigue strength iv. Tensile strength
19. A material that cannot be easily elastically deformed is called ….. while if it cannot be deformed plastically under tension is called …
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20. Proportional limit is ……………………………………………………. While elastic limit is…………………………………………………………....
21. Fracture of brittle material occurs by ………. While for ductile material, it occurs by ………………….
22. Fracture of the material below the proportional limit under cyclic loading is termed……….
23. Modulus of elasticity depends on ………… and it is not affected by ………
24. Force is defined by four characteristics ……….. , ………,…… and …….
25.Creep can be defined as…………………………………………….
26.Fracture of material below the proportional limit under cyclic loading is termed ………………………………………………………………..
27.Restorations should be designed so that the in-service cyclic stresses are ………………………………….the endurance limit.
28.Materials having their mechanical properties dependent on the rate of loading are termed……………………………………………………………….
29.Ductility is ………………………….it is measured by……………………..
30.Modulus of elasticity represents …………………………………………….., it can be calculated by dividing………………………within…………………
31.The stress equals the force in …………………… and oppose it in …….
32.Hook's law states that………………………………………………..
33.Although both have the same magnitude, the proportional limit describes ……… while the elastic limit describes ………………………………….
34.Modulus of elasticity represents the ……… ………………or ……………..
35.The ductility is ………. ……………..While the malleability is ……………..
36.The total energy required to rupture a material is an indication of its……..
37.The permanent deformation represents a destructive example of deformation if ………………………………, while a constructive example is observed when …………………………………………………………………
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38.The permanent deformation of an impression material when removed from the patients mouth is related to……………………………….
39.Properties related to elasticity are……………………………………………..
40.Properties related to plasticity are……………………………..………
41.Excessive deformation can result from …………………
Match the following:
1. Maximum elastic deformation a) hardness.2. Maximum plastic deformation b) Creep3. Resistance to penetration c) Ductility4. Failure under cyclic loading d) Resilience5. Energy e) Fatigue6. Viscoclasticity
(1) Brittle materials a) Workable and burnishable(2) Ductile materials b) Fracture occurs by crack propagation
c) Fracture at or near P.L.d) Gold alloye) Fracture by necking.
1. Viscoelastic material a) Recovery depends on time2. Elastic material b) Immediate deformation and recovery
c) The lower the rate of loading, the greater will be the permanent deformation.
d) Strain is proportional to stress and independent of time
Choose the correct answer:
1. The energy required to fracture a material under sudden force is …a. Toughness.a. Ultimate strengthb. Resiliencec. Impact strengthd. Non of the above.
2. The ability of the material to withstand permanent deformation under tensile load without rupture is:
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a. Resilience.b. Ductilityc. Yield strengthd. Malleabilitye. None of the above
3. The greatest stress to which a material can be subjected such that it will return to its original dimensions when the load is released is the:
a. Elastic limit of the materialb. Proportional limit of the material.c. Compressive strength of the materiald. Shear e. None of the above.
4. The total work or energy required to rupture a material is:a. Resilience.b. Brittlenessc. Toughness.d. Ultimate strengthe. None of the above
5. Malleability is the property that causes the material:a. To withstand permanent deformation without fracture under tensile
load.b. To withstand permanent deformation without fracture under
compressive load.c. To continue to deform under a given load without the increase in the
load magnitude.d. Non of the above.
6. The amount of energy absorbed by a material when it is stressed to its proportional limit is its:
a. Resilience.b. Proportional limit.c. Modulus of rupture.d. Elastic limit
7. The total energy required to rupture a material under a gradually increasing static loading is the:
a. Endurance limit.b. Toughness.c. Malleability. d. Elastic limit.
8. The strain that occurs when the material is stressed to its proportional is called:
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a. Stress.b. Resilience.c. Deformationd. Maximum flexibility.
9. Fracture toughness of porcelain can be raised by:a. Enhancing crack propagation.b. Interrupting crack propagation.c. Changing the direction of the crack.
10. Modulus of elasticity of a material is related to:a. The heat treatment to which it is subjected.b. The amount of permanent deformation.c. The bond strength between atoms.d. The type of load applied.
11. The endurance limit of any restoration should be:a. Similar to fatigue stresses.b. Higher than fatigue stresses.c. Lower than fatigue stresses.
12. Denture bases made of base metal alloys which have very high modulus:a. Can be used in thick sections.b. Can be used in thin sections.c. Can't be used in thin sections.
13. Ductility of a material is usually measured by its:a. Tensile strength.b. Hardnessc. Yield strengthd. Percent elongation.
14. Creep is associated with:a. Contact angle measurement.b. Distortion of amalgam restorationc. Expansion of the investment mold.d. Coefficient of thermal expansion of a material.
15. Which of the following is a test for measuring hardness:a. Knoopb. Toughnessc. Yield strengthd. Resilience
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16. If load is applied to a rubber impression for a long rather than a short time:a. The permanent strain will be greaterb. The permanent strain will be lessc. Elastic strain will be greaterd. Viscoelastic strain will be less
17. Any internal force that is exerted throughout any unit area of a structure and that resists an external force applied to that area is:
a. Modulus of elasticityb. Stressc. Creep.d. Impact strength
18. Brittle materials are characterized by:a. Ease of burnishingb. Fracture occurs by crack propagationc. Steep slope of elastic range of stress strain curved. Elastic deformation under tensile forces.
19. In which material is the greatest stress generated, when subjected to a force of 100 kg, a material A with cross sectional area = 1 cm2 or a material B with across sectional area = 5 cm2
a. Ab. Bc. The stress is the same
20. Fracture may occur at stress below the proportional limit due to:a. Transverse loadingb. Fatigue loadingc. Creepd. Ductile fracture
21. In 3-point loading test:a. Ductility is important.b. Length and thickness of the beam are critical.c. The resulting deformation in the beam can not be calculated.
22. Which property describes the capability of an impression to be removed from around the teeth without permanent deformation:
a. Maximum flexibilityb. Percent elongationc. Malleabilityd. Stiffness
23. Under slow rate of loading, polymers:
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a. Behave in a ductile manner.b. Show less permanent deformation.c. Behave in a brittle manner.
24. The greatest stress to which a structure may be subjected and return to its original dimensions when the forces are released is the:
a. Proportional limitb. Yield strengthc. Elastic limitd. Modulus of elasticity.
25. Which of the following dental materials have mechanical properties that are time dependent?
a. Human dentin b. Gold alloyc. Dental amalgamd. Alginate hydrocolloide. Rubber impression materials
26. Which of the following are tests for measuring hardness?a. Knoop b. toughnessc. Resilience d. Yield strength
State true or false and correct the false statement:
1. A material is considered to be malleable when it has a low compressive strength.
2. A brittle material is not ductile but it can be malleable.
3. Usually a ductile material is considered as being tough.
4. Rigidity is represented by the slope of the stress-strain curve.
5. If small stone in food fractured the filling during mastication, the filling is considered as have low shear strength.
6. Restorative materials should be used at stresses above their endurance limit.
7. Strain is the internal reaction to the externally applied force.
8. Resilience is the energy absorbed during elastic and plastic deformation.
9. The energy needed to fracture cracked material is called toughness.
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10.Yield strength of a material is much important than its ultimate strength.
11.Diametral compression test is used to measure tensile strength of brittle material while flexure strength test is used for ductile material.
12.Fracture may occur at stresses below P.L.
13.For a restoration to be long standing it should have its endurance limit lower than fatigue stresses.
14.A material can sustain a high static load but may fracture under dynamic load.
15.Brittle materials are characterized by ease of burnishing.
16.Yield strength is the maximum stress the material can withstand before failure.
17. In case of visco-elastic material, the strain is independent of time
18.A material is considered to be malleable when it has a low compressive strength.
19. Resilience is an important criterion of orthodontic wires.
20. Amalgam restorations undergo creep in patient mouth.
21. Porcelain artificial teeth are contraindicated if opposed by natural teeth.
22. Rubber impression must be removed with a sharp snap from patient mouth.
23.Rubber impression easily tears when snaply removed from patient mouth.
24.Fracture may occur at stresses below proportional limit due to creep.
25.Stress is a measure of deformation.
26.The greater the indentation left by the steel ball, the higher the brinell hardness number.
27.Deformation and strain are the internal reaction to the applied force.
28.During adjustment of a wire or a partial denture clasp, the stress applied should be greater than the yield strength.
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29.Maximum flexibility represents the amount of total strain.
30.Tensile strength of brittle materials can be measured through compression.
31.When the yield strength of a material is measured using different % offset, it has the same value.
32.Load on a body should be balanced by an external reaction to be in internal equilibrium.
33.The modulus of elasticity is an important material property that can be changed by cold work but is not affected by heat treatment.
34.A large percentage of elongation is a measure of the ductility of the material.
35.Toughness is the energy required to stress the material under impact load.
36.Above the stress associated with the yield strength, a material does not function as an elastic solid.
37.Most restorations are not classified as clinical failure until fracture has occurred.
38.The flexure strength is the best criterion used to compare long span bridge materials.
39.Brittle materials are not usually weak.
40.Addition of zirconia crystals to porcelain increases its fracture toughness.
41.viscoelastic materials have different moduli of elasticity.
42.The removal of an elastic impression material with a sharp snap from a patient's mouth.
43.High hardness may be desirable or undesirable.
44.The calculated theoretical strength of crystalline materials is much higher than its practical strength.
45.Amalgam and waxes can creep at room temperature.
46.Hardness has an important application in dentistry.
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47.The tear strength of alginate impression material is increased when it is stressed at rapid rate of loading.
48.The force and the stress are the same.
49.The stress is measured by the applied force.
50.Tensile, compressive, shear and complex stresses are pure forms.
51.Under the elastic limit, the strain is elastic.
52.The proportional limit and the elastic limit have the same magnitude but describe different properties.
53.Modulus of elasticity is applied along the entire stress/strain curve.
54.Modulus of elasticity is related to force applied and the type of heat treatment.
55.The tensile strength of a ductile material is measured by diametral compression test.
56.The orthodontic wire must be resilient.
57.The impact strength is the fracture of the material under sudden load.
58.The endurance limit of any restoration must be greater than the biting forces.
59.Brinell hardness test can be used for the brittle materials.
60.In the visco-elastic materials the strain is completely recovered after removal of the load.
61.The high yield strength is more important than the fracture strength.
62.The tensile strength of the brittle materials is measured by diametral compression test.
63.The amalgam filling may deform under the biting forces.
64.The strain of the impression does not recover completely after removal of load.65. Brittle material fractures at or near its ultimate strength
66.Maximum flexibility is the amount of elastic strain, when the material is stressed to its ultimate strength
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67.Low density of the molten alloy is important for its castability.
68.Density is inversely proportional to thermal diffusivity.
69.Transparency is decreased by the presence of scattering centers.
70.For ease of finishing and polishing, a material should have high hardness number.
71.In long span bridge, base metal alloys can be used in thinner sections than gold alloys.
72.The higher the modulus of elasticity of amaterial, the higher the proportional limit.
73.Strain and deformation are interchangeable terms and have unitless values.
74.Below the proportional limit, the strain is always elastic
75.Viscoelastic materials recover completely by time after load removal
76.The fracture toughness of a ceramic material can be improved by interruption of propagating cracks.
77.A restorative material should have a hardness number higher than that of tooth structure.
78.It is possible for stiff material to fail at lower stress than a more flexible material.
79.Fracture of restorative material is the only indication of failure
80.Toughness is an energy related term
81.An ideal viscous material deforms and recovers linearly with time.
82.In case of visco-elastic material, the strain is independent of time
83.To minimize the stresses developed in a material due to external force, the area on which this force acts should be small.
84.Modulus of elasticity is a measure of elasticity in a material.
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85.Ductility is the ability of a material to undergo plastic deformation under compressive loading.
Give reasons for:
1. Brittle materials are not usually weak.
2. Resilience is an important criterion of orthodontic wires.
3. The flexure strength is the best test used to compare long span bridge material.
4. Porcelain artificial teeth are contraindicated if opposed natural teeth.
5. Rubber impression must be removed with a sharp snap from patient mouth.
6. Amalgam restorations undergo creep in patient mouth.
7. Hardness has an important application in dentistry.
8. Actual strength is much lower than theoretical strength.
9. The tear strength of alginate impression material is increased when it is stressed at rapid rate of loading
10. The yield strength is of greater importance than ultimate strength
11. The brittle behavior of a porcelain restoration.
12. An active orthodontic wire can move a tooth over an extended period of time.
13. The fracture of a denture base resin under small cyclic loading.
14. The permanent deformation occurring in amalgam restoration under stresses below the proportional limit of amalgam.
15. An artificial restoration should have a lower hardness number than tooth structure.
16. The removal of an elastic impression material with a sharp snap from the patient's mouth.
17. Addition of zirconia crystals to porcelain increases its fracture toughness.
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18. Amalgam and waxes can creep at room temperature.
Adhesion and Bonding
Choose the correct answer or answers:
1. Spreading of a liquid on a surface indicates thata. The surface has been poorly wet by the liquid.b. The surface energy of the solid is probably quite high and/or the
surface tension of the liquid is quite low.c. The surface energy of the solid is probably quite low and/or the
surface tension of the liquid is quite high.d. The surface has been contaminated by a very low surface energy
material prior to the drop's placement.
2. Metals usually have:a. Poor surface energy.b. High surface energy.c. Low surface tension.
3. The acid etching of enamel leads to the following except:a. Removal of surface debris.b. Increased surface energy.c. Increased surface tension of the adhesive.
4. Thermal stresses may cause failure of the adhesive junction when:a. There is no or slight difference between the joined materials in their
coefficient of thermal expansion.b. There is a large difference in coefficient of thermal expansion.c. Thermal expansion has no effect at all.d. Non of the above.
5. Stresses which may affect adhesion are:a. Transverse stresses.b. Setting stresses.c. Compressive stresses.d. Thermal stresses.
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6. A. Decrease the strength of the adhesive bond.B. Increase the strength of the adhesive bond.
1. Poor wetting.2. Low contact angle.3. Large solidification shrinkage.4. Large differential coefficient of thermal expansion.5. High adhesive viscosity.6. Low surface tension.7. Wide adhesive junction.
7. The force attracting molecules of the same kind across a surface are called:
a. Adhesion.b. Adsorption.c. Surface energy.d. Cohesion.
8. The tendency of a liquid to spread over a solid surface is called:a. Cohesion.b. Chemisorption.c. Surface tension.d. Wetting.
9. Which of the following is not a desirable quality for a dental adhesive?a. Low viscosity.b. Low surface tension.c. Many air bubbles.d. High strength in very thin film.
10. During solidification most liquid adhesives show:a. Expansion.b. Exothermic reaction.c. Contraction.
11. A stronger adhesive junction is obtained when the adhesive is:a. Thicker.b. Viscous.c. Thinner.
12. The adherend is:a. The substrate.b. Cohesive.c. Adhesion.d. Adhesive.
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13. Which of the following factors decrease the surface tension of a liquid?a. Addition of detergents.b. Increase in temperature.c. Increase of impurities.d. None of the above.e. All of the above.
14.Liquids try to decrease its surface tension by:a. Increasing its surface area.b. Minimizing its surface area.c. Adsorption of atoms or molecules.
15. Etching of dentine will lead to:a. Increasing the surface energy of dentine.b. Removal of smear layer.c. Demineralization of dentine surface.d. B and c.e. All of the above.
16. Factors that present difficulties to produce adhesion in the oral cavity:a. Smear layer.b. Heterogeneous composition of enamel and dentine.c. Smooth surface of the prepared cavity.d. A and b.e. All of the above.
17. More natural appearance is achieved if restorative materials are:a. Wet by thick film of saliva.b. Wet by thin film of saliva.c. Not wet.
18. Which of the following is a desirable quality for a dental adhesive?a. High viscosity.b. High surface tension.c. Many air bubbles.d. Thin adhesive film.
State true or false and correct the false:
1. The higher the contact angle, the greater the wetting characteristics of an adhesive on the adherend.
2. The less the contraction of the adhesive during setting, the less will be the stresses and the weaker will be the adhesive joint.
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3. For good wetting, the surface tension of the liquid adhesive should be equal or more than the surface energy of the adherend.
4. Primary bonds yield a stronger adhesive junction than do a secondary bond.
5. Phosphoric acid etching increases the surface energy of the dentine.
6. Thermal stresses have too much effect on the strength of the adhesive junction when there is a big difference in the coefficient between the adhesive and the adherend.
7. The unhomogenesous composition of enamel and dentine is an obstacle toward good adhesion.
8. The smaller the contact angle, the greater the wetting characteristics of an adhesive on the adherend.
9. The adhesive bond of a restorative material to dentin is stronger than that to enamel.
10. For acid-etching of enamel, 70% phosphoric acid is routinely used for 40 seconds.
11. Acid etching decreases surface energy of dentine.
12. Etching of dentine will lead to increasing its surface energy of and removal of smear layer.
13. The higher the contact angle between the adhesive and the adherend surface, the better the wettability
14. The adhesive bond of a restorative material to dentin is weaker than that to enamel.
15. Waxes are not easily wetted because they have low surface energy.
16. Adhesion to wet surfaces of enamel and dentine is better than adhesion to dry surfaces.
17. Dentine poses greater obstacle to adhesion than enamel because it is strongly hydrophobic
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18. Close matching of coefficient of thermal expansion between the adherend and the adhesive is required to decrease stresses at interface.
19. The less the contraction of the adhesive during setting, the less will be the stresses and the weaker will be the adhesive joint.
20. Increasing film thickness of the adhesive decreases the strength of adhesive junction
21. Dentine bonding agent should contain both hydrophilic and hydrophobic materials
22. Most restorative materials bond to tooth structure by mechanical or micro-mechanical means.
23. The contact angle is determined by the viscosity of an adhesive.
24. Fluctuations in temperature produce stresses that affect the strength of an adhesive junction.
Match:
1. Mechanical adhesion a. The point of apposition between an adhesive and an adherend.
2. cohesion. b. Bonding at atomic or molecular level.
3. Interface c. Retention by interlocking4. The classic test for measuring wettability
d. Force attracting molecules of the same kind across the surface.
5. chemical adhesion e. Contact angle.
Give reason for:
1. Surface irregularities prevent an adhesive from completely wetting the adherend.
2. Metals are relatively easy to wet by suitable adhesive
3. Using of the primer after etching the dentin surface.
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Polymers
State true or false and correct the false:
1. At slow rate of loading, polymers behave in a ductile manner.
2. Plasticizers prevent the resin molecules from slipping past one another when the material is stressed.
3. Hydroquinon decomposes giving up free radicals to initiate the polymerization reaction.
4. At rapid rate of loading, polymers may behave in a brittle manner
5. Polymer chains are weakly bonded by secondary forces in all types of polymers
6. Excessive cross-lining increases brittleness of polymers.
7. Addition polymerization reaction requires the presence of activated initiator.
8. Elastic moduli of polymers are much lower than metals.
9. The elastic behavior of some polymers at room temperature.
10. Cross-linked polymers are stronger than non-cross linked ones.
11. Thermoplastic polymers deform easily upon raising the temperature because primary bonds break readily.
12. Addition polymerization can be started by decomposing organic peroxide by heating.
13. Polymerization reactions are associated with increase in volume.
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14. The polymerization reaction is an endothermic reaction.
15. The setting mechanism of polysulphide rubber impression materials, takes place by condensation polymerization.
16. The higher the moelecular weight of a resin, the higher is the strength generally.
17. Termination occurs when two growing chains react to form a stable molecule.
18. An inhibitor of polymerization exerts its effect through increasing the degree of polymerization.
19. External plasticizer is a part of the main polymer chain.
20. Condensation silicone impression materials show less deimensional changes than addition silicone.
21. Plasticizers lower the glass transition temperature of a rigid polymer.
22. During polymerization, chain transfer terminates completely the reaction.
23. It is possible to plasticize a resin that is normally hard and stiff to a condition in which it is flexible and soft.
24. Some polymer chains are terminated before others.
25. Cross linking agent is able to covalently bond different polymer chains at room temperature.
26. Polymers that may soften by heat and solidify on cooling are referred as thermoset polymers.
27. Rubbers have glass transition temperature below mouth temperature.
28. At rapid rate of loading, polymers may behave in a brittle manner.
29. Polymerization reaction is an endothermic reaction.
30. Polymers have low mechanical properties due to the covalent bond.
Define:
1. Plasticizers.
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2. Co-polymerization.
3. Cross-linking agent.
Complete the following:
1. Stages of addition polymerization are…………………………………..
2. At room temperature, the glass transition temperature of a rigid polymer is …………………………………..room temperature.
3. Polymerization reactions are associated with…………………..and ………
4. A polymer is …….. whose smallest repeating unit is called ……
5. Polymers is bonded intramolecularly by ……… while intermolecularly by ………….
6. Polymer chains are held together by ……….. i.e. ………..
7. Elastomers have molecular shape of …………… and its TG is ……………room temperature.
8. Crazing can be defined as ………………, it occurs due to …….. or ………… or ………………
9. Residual monomer in a processed polymer results due to ………..
10. Cross-linked polymer resists action of …………. Which produces …
11. Co-polymerization is …………………………………….
12. Improvements in the properties of denture base resins may be obtained by combining different monomers to form ………………
13. Molecular weight of a polymer is defined as ……………………. while degree of polymerization is defined as ………………………
14. A free radical is …………………………..
15. Addition polymerization reaction can be inhibited by the presence of …………… that will react with ………….. or ………………
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16. Addition polymerization reaction requires the presence of ……….., before initiation occurs, the initiator has to be activated by ………., ………….. or ……………..
Give reasons for:
1. Low softening temperature of polymers.
2. The elastic behavior of some polymers at room temperature
3. The use of activator in a polymer system.
4. Addition polymerization gives rise to better quality polymers than condensation polymerization.
5. Thermoset polymers are stronger than thermoplastic ones.
6. During polymerization, chain transfer does not terminate the reaction completely.
7. Average molecular weight is less important than molecular weight distribution.
8. Care should be taken to avoid incorporation of air during manipulation of polymers.
9. Polymers are sensitive to the rate of loading.
10. The addition polymerization reaction requires the presence of free radicals.
11. Cross-linked polymers have low water sorption.
12. Elastic moduli of polymers are much lower than metals.
13. Excessive cross-linking increases brittleness of polymers
14. Addition polymerization reaction requires the presence of activated initiator .
Choose the correct answer:
1. Single molecules that polymerize to form a resin are referred:a. Homopolymer.b. Copolymer.c. Monomer.
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d. Polymer.
2. Cross-linking:a. Limits the movement of polymer chain upon each other b. Increase flexibilityc. Decrease resistance to action of solventsd. Decrease strength and hardness
3. Below the glass transition temperature, the polymer will be:a. Rubbery.b. Rigid.c. Flexible.d. a and c.
4. In chain transfer reactions:a. The active state is transferred from an activated radical to an
inactive molecule.b. An already terminated chain might be reactivated and continue to
grow.c. Termination takes place by direct coupling of two growing chains.d. Termination takes place by exchange of hydrogen atom from one
growing chain to another.
5. Addition polymerization reaction is characterized by:a. No change in composition.b. Production of a low molecular weight by-product.c. Residual monomer is always left.d. Addition of growing chains is accompanied by evolution of heat.
Compare between:
Condensation polymerization and addition polymerization.
Give an account on:
1. Properties of polymers are time dependent. Discuss.
2. Short notes on:a. Plasticisers.b. Copolymer.c. Retardation and inhibition.d. Cross linking.
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3. Classify polymers.
4. Methods to alter the properties of polymers.
5. How does the structure of polymers affect their properties.
6. Discuss the temperature dependence on properties of polymers with reference to dental applications.
7. Discuss the response of an elastomer to applied stresses.
8. Compare termination by transfer of a hydrogen atom from one growing chain to another and by chain transfer.
9. Factors affecting polymer crystallinity.
10. Termination of a polymerization reaction.
11. Classification of polymers according to stress-strain behavior.
12. Polymer additives and its effect on polymer properties.
13. General properties of polymers.
14. Types of polymerization reactions.
15. Factors affecting properties of polymers.
16. Dental applications of polymers.
17. Stabilizers and inhibitors.
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Metallurgy
Choose the correct answer or answer:
1. You are given two wires with the same diameter and length. One is wrought and the other is cast:a. Cast wire has the greatest percentage elongation.b. Wrought wire has the greatest percentage elongation.c. Cast wire has the highest tensile strength.
2. If dislocations during movement along slip planes are impeded:a. Plastic deformation is inhibited.b. Modulus of elasticity is increased.c. proportional limit and yield strength are increased.d. Ductility is increased.e. a and c.
3.. Coarse grain structure can be obtained by:a. Using mould of low thermal conductivity.b. Heating the metal to just above its melting temperature.c. Addition of nucleating agent.
4. Grain size is:a. Inversely related to strength.b. Directly related to grain number.c. Directly related to nucleating agent.d. Inversely related to grain boundary.
5. Coarse grain structure can be obtained by:a. Rapid cooling of molten metal.b. Addition of nucleating agent.c. Using moulds of higher thermal conductivity.d. Over heating or prolonged heating of the metal during melting.
6. If the movement of the dislocation is easy:a. Plastic deformation is inhibited.b. Modulus of elasticity is decreased.c. Proportional limit and yield strength are increased.d. Ductility is increased.
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7. Metals are characterized by high melting point because of:a. Their cast structure.b. The presence of dislocations.c. The strength of interatomic bonding within the crystalline solid.d. None of the above.
8. In grain boundaries, there is:a. Less accumulation of impurities.b. More tarnish and corrosion resistance.c. Enough surface energy to start the formation of new set of grains.d. Less atomic diffusion.
9. When all slip possible has occurred:a. Ductility is increased.b. Strength is increased.c. The movement of dislocation is easy.d. Fracture of metal occurs.
10. When shaping a structure by sintering:a. It becomes cold worked.b. It becomes in powder form.c. Strong cohesion between particles occurs.d. Melting of solid particles is essential.
11. Wrought wires are:a. Highly stressed structures. b. Plastically formed structures.c. Fibrous structures.d. A and c.e. All of the above.
12. Wrought wires have:a. High strength properties.b. Higher toughness than cast structures.c. Higher modulus of elasticity than cast structures.d. Higher ductility than cast metal.e. Non of the above.
13. Dislocation movement is easy in metals because:a. Metals have less slip.b. Metals have many slip planes.c. Metals have wrought structure.d. Metals have grain structure.
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14. The heating of a metal after plastic deformation to relieve stresses within the grain without changing the shape of the grain is called:a. Recrystallizatin.b. Recovery.c. Aging.d. Restoration.
15. Wrought metals are:a. Cast structure.b. Fibrous structure.c. Cold worked structure.d. Electroformed structure.
16. A substitutional solid solution is obtained only when the constituent atoms:a. Have no chemical affinity towards each other.b. Have difference in atomic size less than 15%c. Have the same type of space lattice.d. All of the above.
17. The super-lattice Au-Cu formed in the gold-copper system is preferred than the super-lattice Au-Cu3 because:
a. It has more strengthening effect.b. It has lower coefficient of thermal expansion.c. It can resist corrosion.d. It is face centered cubic.
18. A homogeneous, mechanically, separable, distinct part of a system is called:a) State b) Matrix c) Phase d) Precipitate.
19. An alloy with a single melting point which is the lowest melting point of the alloy system is called (a, an):
a) Inter-metallic b) Eutectic c) Solid solutiond) Peritcctic
20. Two metals are partially soluble in the liquid and solid condition form: a) Solid solution b) Eutectic alloy c) Inter-metallic compound
21. The number of phases present at any point between the liquidus and solidus lines of an alloy system is usually:
a) One b) Two c) Three.
22. In precipitation hardening, the precipitated phase reduces the mobility of dislocations and thus:i. Increases the strength and hardness of the alloy.
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ii. Decreases the strength and hardness of the alloy.iii. Increases the ductility of the alloy.
23. Grain is related to:i. Casting.
ii. Cold workingiii. Similar orientation of space lattice.
24. In a constitutional diagram in the area below the solidus the metal is:i. Solid.
ii. Liquidiii. Both solid and liquidiv. Amorphous
25. Cold working causes:i. Increase strength.
ii. Increase toughness iii. Increase modulus of elasticityiv. Increase ductility
26. All lattice imperfections increase strength except:i. Vacancies.
ii. Dislocationiii. Grain boundariesiv. Extra atoms.
27. If a gold copper alloy is cooled rapidly from the solidus temperature:i. AuCu and CuCu3 super lattice are formed.
ii. Disordered face centered cubic solid solution is formediii. Ordered solid solution is retained at room temperature.
28. Mechanical properties of metal can be improved by:i. Addition of a grain refiner.
ii. Addition of an alloying element that form a solution iii. Addition of an element that precipitates a new phaseiv. Ordering the orientation of atomsv. All of the above
vi. Non of the above
29. Metals are characterized by high melting point because of:a. Their cast structure.b. The presence of dislocations.c. The strength of interatomic bonding within the crystalline colid.d. None of the above.
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State true or false and correct the false:
1. Rapid cooling from liquid state refines grains.
2. Eutectic alloys are usually ductile.
3. Rapid cooling of gold-copper system produces super lattice structure.
4. An alloy which has the eutectic composition is characterized by having a melting point that is lower than any other alloy in the system.
5. Softening heat treatment of gold alloy should proceed slow cooling if hardening is required.
6. When two metals have chemical affinity to each other, intermetallic compounds may form.
7. Stainless steel alloy is an example of substitational solid solution.
8. Homogenized structures are more corrosion prone than non homogenized one.
9. A coarse grain structure metal is stronger than a finer one.
10. All types of alloys have a melting range.
11. Eutectic alloys have high corrosion resistance.
12. Solid state reactions in metals and alloys do not affect the modulus of elasticity.
13. In gold alloys range of 64-88% An, Au Cu3 superlattice with F.C. cubic fattice forms.
14. Precipitation hardening takes place in gold alloys at temperatures above 700oC.
15. Control of grain size is the only method of altering the mechanical properties of metals and or alloys.
16. Grain refiner in gold alloy increases its strength.
17. Wrought dental alloys usually have higher tensile strength compared to its corresponding cast structure.
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18. The smaller the grain size, the lower the strength.
19. Rapid rate of crystallization produces a large grain size.
20. Cast properties can be regained by heating the wrought structure at lower temperature which allow recovery.
21. In grain boundaries, there is enough surface energy to start the formation of new set of grains.
22. All metals are solids in room temperature.
23. Grain boundaries in polycrystalline metals are amorphous in nature.
24. Elastic deformation becomes difficult in metals if dislocations cannot move.
25. Stainless steel alloy is an example of substitutional solid solution.
26. Eutectic alloys have a high corrosion resistance.
27. Control of grain size is the only method of altering the mechanical properties of metals and/or alloys.
28. Eutectic alloys are formed at any composition but at definite temperature
29. Presence of imperfections in crystalline structure increases the strength properties.
30. Presence of dislocations in crystalline structures increase their strength
properties and decreases deformation.
31. Opacity of metals is due to the presence of valence electrons.
32. Nucleating agents give castings of coarse grain size.
33. During solidification, if the rate of crystallization is higher than the rate of nucleation, coarse grain structure will be formed
34. During shaping of metals, bonding of particles in absence of any liquid is called plastic forming
35. Stress relief procedure should be done after cold working to increase ductility of the wire.
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36. The hardening heat treatment is indicated for structures that are to be shaped or cold worked.
37. In the solidification of an alloy, areas of microscopically heterogenous composition are set up by process called coring.
38. Ordered solid solution is more ductile than disordered one.
39. The greater the number of slip planes, the greater the ductility of a metal
40. The grain size in metals is increased either by the addition of nucleating agents or by rapid cooling from the liquid state.
41. Softening heat treatment of gold alloys increases strength, hardness and decrease ductility.
42. Heterogenous nucleation is associated with foreign atoms.
43. Grain size increases with rapid cooling of a molten metal.
44. Hardening heat treatment of gold alloy would increase its strength
45. Cored structure occur in alloy with wide melting range.
46. An alloy that has the eutectic composition is characterized by having a melting range that is lower than any other alloy in the system.
47. Large grains of an alloy give rise to inferior strength properties.
48. Presence of vacancies within lattice structure would allow atomic diffusion in the solid state to take place.
49. Hardening heat treatment increases rigidity of the material.
50. Cored structure resist corrosion.
51. Softening heat treatment of gold alloy should be performed if hardening is required
52. Eutectic alloy are usually ductile.
53. Cooling curve for a pure metal beginning at a temperature above the melting point will have a horizontal portion during solidification as a result of heat of fusion.
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54. During the process of cold working stresses are applied below the vield strength.
55. Softening heat treatment of gold alloys increases strength, hardness and decreases ductility.
56. AuCu3 play a much important role in strengthening of good alloys than AuCu.
57. Eutectic alloys are usually used in soldering operations.
58. High temperature and sufficient pressure and needed for sintering process.
59. If high strength and hardness are required rapid cooling is needed.
60. A grain boundary is formed between two adjacent growing grains.
61. A dislocation movement is easy in metals.
62. Homogenization needs higher temperature and longer time than annealing heat treatment of cold worked structure.
63. Alloying of metals by formation of solid solutions is a method of strengthening the metal.
64. Cored structure must be eliminated before placement in the oral cavity.
65. Cold working is a mechanical method for shaping of metals at high temperature.
66. Sintering of an alloy particles results finally in shrinkage of the metal
67. Grain boundaries are most resistant to tarnish and corrosion.
68. The elastic deformation stops once there is no more dislocation movement.
69. Modulus of elasticity is greatly affected by the grain size.
70. Atoms at the grain boundaries have higher energy because they interfere with dislocation movement.
71. Mechanical properties of a metal can be improved by rapid cooling of molten alloy.
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72. Cold worked structures should be annealed, otherwise, further working may cause .
73. Gold and copper form substitution solid solution.
74. Slow cooling of gold alloy of 64-88% gold below the solidus temperature increases the strength.
75. Prolonged heating below melting temperature of a cold worked metal result in softer and weaker qualities.
76. The higher strength properties of a quenched metal than that which was slowly cooled.
77. Grain boundaries in polycrystalline metals are amorphous in nature.
78. The energy content of grain proper is higher than that of grain boundaries
79. Elastic deformation becomes difficult in metals if dislocation movement is inhibited
80. Presence of the point defects in crystalline structure increase the strength properties
81. When two metals have chemical affinity to each other, intermetallic compound may form.
Give reasons for:
1. The brittle behavior of eutectic alloy 2. Gold and copper form substitutional solid solution.
3. Slow cooling of gold alloy of 64-88% gold below the solidus temperature increases the strength
4. Cold worked structures should be annealed.
5. Diffusion of atoms occurs more readily along grain boundaries.
6. The yield strength is higher for a material of fine grain size.
7. Occurrence of coring phenomenon in solid solution alloys.
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8. Homogenization process is an essential procedure after casting a solid solution type of an alloy.
9. Au-Cu gives superior properties than Au-Cu3 supperlattice in gold alloys.
10. Cooling curve for a pure metal have a horizontal portion during solidification.
Complete the following:
1. If the dislocation movement along a slip planes are impeded, the plastic deformation is ………………………., proportional limit is ………………… while the modulus of elasticity ………………….
2. Solid solution alloys are the most commonly used in dentistry because:
a) …… b) ……….. On the other hand, eutectic alloys are commonly used in soldering because …………
3. Mention four differences between eutectic and solid solution alloys
a) ………. b) …….. c) ………… d) …………
4. Coring in alloys is ……….. It is undesirable because ……….
5. Casting is performed by ………. While sintering is ………….
6. A cold worked structure has high ………….. and ………….. properties while ………. Is decreased due to ………………..
7. Conditions of substitutional solid solubility are:a)b)c)d)
8. During solidification of an alloy, the first solid to form is rich in the metal of while the last solid is rich in the metal of ………… this results in …….. phenomenon which can be eliminated by …
9. A metal melts at a …….. while alloy melts over a ……. . An alloy can be like a pure metal in this aspect and this alloy is called ……. Which means ………..
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10. In silver-copper alloy system which is used in the dental field in ……….. at the eutectic point ……………, …………. and …….. phases exist, while just below the eutectic point ……. phase only exist.
11. In gold-copper system, AuCu can be formed by solution cooling with ….. space lattice if the % of Au was …… and temperature of ………….. while rapid cooling from 700oC give …… structure.
12. Mechanical properties of metals and/or alloys can be altered by ……….., ……….., …….. the mechanism of each is based on the inhibition of ……………
13. In metals, a good thermal and electrical conductivity is due to ….., while high melting point is due to ………
14. In polycrystalline metals, grain size can be controlled by:a.b.c.
15. Grains meet at …… which represent ……… areas and can be microscopically revealed by ….. and appears as ……. Due to …….
16. In metals, grain size can be controlled by:i.ii.iii.
17.…………… are responsible for plastic deformation of metals. These can be inhibited if they meet:i.ii.iii.iv.
18. A cold worked structure has high …………, ….. and ……. Properties, while …….. is decreased due to ………..
19. The horizontal portion of time-temperature cooling curve of metals is due to ………………..
20. Gold-copper alloy that contains (AuC3) superlattice is not found in dental applications because……………………..
21. Solid solution alloys are the most commonly used in dentistry because:
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a) b) c) d)
22. Grain size shape can be altered by: a) b) c) d)
23. Eutectic alloys are characterized by two interesting features: a) b)
24. Examples of pure metals used in dentistry are ……, ………., …… and …………………………..
25. Metals ionize ……. in solutions.
26. The pure metals used for electroplating are ……… and ………
27. The steps of solidification of metals are ……….. then ………
28. Pure metals crystallize in a tree like form called …….
29. Grain boundaries are ……… and can be easily attacked by impurities.
30. A is …… and B is …….. and it is …… in nature so its resistance to corrosion ………..
31. By the end of recovery stage……… and …….. occur
32. By the end of recrystalization, the metal becomes of ……… and …..
33. Prolonged heating during annealing results in ………
34. The solid solution alloy could be either ……… or …….
35. ……….. is an example of eutectic alloys.
36. Solid state reactions include:1. ………………………………………2. ………………………………………3. ………………………………………4. ………………………………………
Give an account on:
1. Discuss the strengthening mechanisms in case of :
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i. An alloy of composition 80 %gold and 20% copper.ii. An alloy of composition 50% gold and 50% copper.
2. How does the melting of pure metal differ from the melting of an alloy?
3. List several ways in which the yield strength of a metal or alloy may be increased?
4. How can dislocation motion be impeded so as to raise the yield stress?
5. Is it better to have large crystallites or small ones in order to have a high yield stress and ultimate strength.
6. What are the eutectic temperature and composition for the silver-copper system?
7. What is an alloy.
8. Characteristics of a solid solution.
9. Characteristics of eutectic.
10. Correlation between material properties and their microstructure.
11. Solid state reactions.
12. Factors affecting grain size and shape.
13. Draw:
a) Phase diagrams for solid solution and eutectic alloys.
b) Cooling curves for pure metal and an alloy.
14. What is the relation between grain size and number of nuclei of crystallization and what is the relation between yield strength and grain size?
15. Draw a phase diagram of A-B solution alloy system where Tm of A is 1000oC. Tm of B is 1500oC, and label the diagram identifying different phases present. At a temperature of 1400oC and the composition of 30% A, what phases exist? Identify the composition of each one.
16. Draw and label a phase diagram representing gold-copper system subjected to hardening heat treatment.
17. Referring to the gold-copper phase diagram, mention the hardening mechanisms involved in strengthening gold alloys.
18. Cored structure and how to prevent its formation.
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19. Methods of shaping metals and alloys.
20. Different classifications of alloys.
21. Heat treatment of gold alloys.
22. Factors affecting grain size.
23. Super-lattices of gold-copper system.
24. General properties of the metals.
25. Pure metals used in dentistry.
26. Properties of metals
27. Properties that change by annealing.
28. Draw and illustrate how a liquid pure metal solidifies.
29. Explain annealing heat treatment of wrought structures.
30. What does this diagram describe?
31. Grain and grain boundaries.
32. Lattice imperfections.
33. Annealing (definition and stages).
34. What are the differencesbetween metal A & metal B.
35. Discuss this diagramin details.
36. Miscibility of the alloys in the solid state.
37. Types of solid solution alloys.
38. Conditions for substitutional solid solution.
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39. Homogenization.
40. Describe this diagram.
41. Altering of the physical properties of the alloys.
42. Cooling curves of pure metal, solid solution and eutectic (draw only).
43. Solid – solid reaction. Give examples.
Compare between:
1. Solid solution and eutectic systems.2. Coring and homogenization.3. Casting and sintering.4. Cast metal and wrought metal.5. Annealing and homogenization.6. Au-Cu and Au-C3.
Match the following:
1)i. Phase diagram. 1. Relation between composition
and temperatureii. Iron Carbon 2. Relation between time and
temperatureiii. Cooling curve 3. Fine grain structure.iv. Reduce ductility 4. Interstitial solid solutionv. Increase strength 5. Nucleating agent.
vi. Grain size is related to 6. Rate of cooling.vii. Decrease hardness 7. Large grain size.
viii. Increase ductility 8. Cold working 9. Binary alloy 10. Recrystallization.
2)i. Cold working 1. Increase grain size.
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ii. Annealing 2. Decrease grain sizeiii. Recrystallization 3. Not affect grain sizeiv. Grain growth 4. Increase elastic limit
5. Decrease elastic limit6. Not affect elastic limit7. Increase ductility8. Decrease ductility9. Not affect ductility.
Selected problems:
Problem 1:In the metallic crystal lattice, the valence electrons are relatively unbound
to their atomic centers. What properties of metals result from this configuration?
Problem 2:
A person hands you two samples of the same metal, in the first sample (A). She tells you that there are absolutely no flaws in the crystal structure of the metal. In the second sample (B), there are numerous crystal flaws "defects". How do the strengths of (A) and (B) compare, and why?
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Tarnish and Corrosion
State true or false and correct the false:
1. The corrosion resistance of alloys is dependant on heat treatment.
2. Uniform corrosion is generally far more dangerous than localized
corrosion.
3. Passivity means loss of chemical stability of metals and alloys.
4. Difference in composition of the parent alloy and solder alloy, may
develop concentration cell corrosion
5. Lower anode/cathode ratio may lead to localized corrosion
6. To decrease the rate of corrosion, you should paint anode by varnish7. Tarnish is a sign of corrosion in a later stage.
8. Cathodic reactions can be considered to be the primary driving face in electrolytic corrosion.
9. Tarnish layer may be protective and prevent further corrosion.
10. Corrosion tendency of metals and alloys increased when oxygen tension decreases.
11. Galvanic cell corrosion takes place only when two different metallic restorations are present opposing each other.
12. Corrosion resistance of cold worked metals/alloys is lower than cast ones.
13. A solid solution type of alloy is a homogenous structure which is highly a corrosion resistant.
Match the following :
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1. Cathode. a. More prone to corrosion.2. Grain boundary zone. b. Limits reactivity of the alloy.3. Oxidation of dental alloy c. A type of uniform corrosion.4. Difference in electrolytic composition
d. A type of localized corrosion.
e. Driving force in corrosion process.Choose the correct answer:1. In electrolytic cell:
a. Anode has higher electrode potential.b. Cathode has higher dissolution tendency.c. Cathode has higher electrode potential.
2. Due to the difference in composition of the parent alloy and solder alloy the following may occur:
a. Concentration cell corrosion.b. Galvanic cell corrosion.c. Chemical corrosion.
3. If consuming the electrons at the cathode is higher than the production of electrons at the anode.
a. The corrosion rate will be higher.b. The corrosion rate will be lower.c. The corrosion rate will not be affected.
Give reasons for:1. Corrosion resistance of cold worked structures is lower than cast ones.
2. In case of presence of dissimilar metals, we must increase anode/ cathode
area.
3. Cleaning of base metal alloys using household bleaches must be avoided.
4. Causes of concentration cell corrosion in patient's mouth and how to
overcome.
5. The addition of chromium and/or titanium in dental base metal alloys is
essential
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6. All dental base metal alloys should contain chromium and/or titanium.
7. In dental standard, silver is not considered noble metal.
8. Dental amalgam alloy powder contains (Ag-Cu) eutectic alloy should be stored in cool-dry place.
9. Due to difference in composition of the parent alloy and solder alloy, concentration cell corrosion may develop.
10. The cored structure has lower tarnish and corrosion resistance than homogenized one.
11. Rate of corrosion depends on relative position of metals in electromotive
force sense .
12. Proper polishing of dental metallic restoration is a must.
13. Ag/Pd ratio should be adjusted in case of cast gold alloys.
14. Tarnish layer may be protective and prevent further corrosion.
15. Eutectic alloys have low resistance to tarnish and corrosion.
16. Corrosion tendency of metals and/or alloys increases when oxygen tension decreases.
17. A highly stressed metallic structure is prone to corrosion than a non stressed one.
18. Uses of eutectic alloys in patient's mouth should be limited.
19. In cast structure, stress cell corrosion may develop.
20. Localized corrosion is generally far more dangerous than uniform corrosion.
21. Solder joints may corrode in patient’s mouth.
22. All dental metallic alloys should have high tarnish and corrosion resistance.
23. Oral cavity is very conductive to the formation of corrosion products.
Give an account on :
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The different types of corrosion that may occur in the dental amalgam inside and
outside the patient's mouth and how to overcome?
Complete the following:
1. Rate of corrosion in patient's mouth depends on:a…………………………………………….b…………………………………………….c…………………………………………….d……………………………………………..e……………………………………………..
2. Stress cell corrosion may occur due to the presence of …………………… or …………………………
3. Tarnish is …………………………………………………………….While corrosion is ……………………………………………………
4. The passivity is …………………………………………………………It's essential for………………………………………………………….
5. In the oral cavity, presence of different alloys causes ………… corrosion. However, presence of different electrolyte composition causes ……………. corrosion.
6. The elements …………… or …………… should be added to base metal alloys for protecting against ……….. they are responsible for ………………
7. Types of corrosion are…………………………………………………….
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