Dental Materials COPY

Question 1

Q1. What is the main function of dental composites.

Answer 1

Used for Restorative (filling) materials

Question 2

Q2. Dental composites can be used to make impressions of the dental arches, how is this carried out?

Answer 2

Dental impressions are made by placing an appropriate material in a stock or custom dental impression tray, which is designed to roughly fit over the dental arches.

Question 3

Q3. There are two types of dental impression trays, what are they?

Answer 3

Stock tray and custom dental tray (specific to patient)

Question 4

Q4. What does a dental resin composite consist of?

Answer 4

Resin – fibres of high strength and elasticity

Filler – harder type microparticles (quartz/silica)

Coupling Agent – resin and filler chemically to form matrix

Question 5

Q5. A dental resin composite without a filler would most likely result in what of the composite?

Answer 5

Without a filler the resin wears easily, exhibits high shrinkage and is exothermic.

Question 6

Q6. The coupling agent connects the resin and filler chemically to form a matrix, what are the name of the two common microparticle fillers used?

Answer 6

Quartz and Silica

Question 7

Q7. What is needed for the formation of a matrix between the resin and filler?

Answer 7

A coupling agent

Question 8

Q8. The GDC invites patients to ask for a statement of manufacture certificate, failure to offer statement is a criminal offence. What must be presented on the statement?

Answer 8

Patients name and confirmation made for them

Prescribers name and registered address

Technicians name and registered address

Description of the appliances

Confirmation meets legal standards

Question 9

Q9. The end user of the product will be given a leaflet on how to use the product, it is advisable if the process chain is what and why?

Answer 9

Process chain as short and possible

Assume idiot

Time pressures

Not a slave to technology

Simple and reliable

Question 10

Q10. The oral environment must be taken in to consideration when dealing with dental composites, what will the dental composites be subjected to?

Answer 10

Loading to 6 Kg

On/off cyclical forces – fatigue

Chemicals

Temperature fluctuations in microseconds (ice cream -14°C/Coffee 60°C)

Question 11

Q11. What is cyclical forces referred to as?

Answer 11

Chewing

Question 12

Q12. Why is it important for restoration to function within minutes of placement?

Answer 12

It is not acceptable for a patient to not be able to eat/drink for a long period of time, the longer the time taken for the restoration to set may cause retardation of the composite.

Question 13

Q13. What are the 5 common materials used by the dental team?

Answer 13

Gypsum materials (plaster)

Waxes (for dentures)

Alloys (blend of metallic elements)

Polymers

Ceramics

Question 14

Q14. Tests used to characterise materials must meet standards, why?

Answer 14

To protect the user and patient

Question 15

Q15. Who overlooks the standard of materials used?

Answer 15

British Standards Institution (BSI)

International Standards Organisations (ISO)

Question 16

Q16. Pulling type force test is referred to as?

Answer 16

Tensile test

Question 17

Q17. How is strain worked out?

Answer 17

Strain = change in length/original length

Question 18

Q18. What is the expression of the formula σ = F / A?

Answer 18

σ = Stress

F = Newtons

A = mm²

Question 19

Q19. Why is this test not recommended for brittle materials?

Answer 19

Brittle materials do not have a flat surface on the top or bottom, and will result in cracks forming, thus not giving a true recording.

Question 20

Q20. A diametral tensile strength test would be used for what?

Answer 20

Useful for brittle materials where conventional tensile not applicable

Question 21

Q21. What is the expression of the formula σ = 2F/πDL

Answer 21

σ = stress

2F = 2x newtons

Π = pie 3.14

D = diameter

L = length

Question 22

Q22. What is this test referred to as?

Answer 22

Flexural test

Question 23

Q23. What is the expression of the formula σ = 3FL/2bd²

Answer 23

σ = stress

3F = 3x newtons

D = depth

B = breadth

L = length between rollers (support separation)

Question 24

Q24. The box highlighted red represents what?

Answer 24

The red highlight represents the material and its stiffness, it is highlighted to show that the material will remain intact under the right stress/strain measures

Question 25

Q25. What does the purple highlight represent?

Answer 25

The purple highlight represents the outcome when the threshold for the stress/strain measures are overcome, this results in the material losing its elasticity.

Question 26

Q26. What does the green highlight represent?

Answer 26

The green highlight represents the failure force, this is the force where the material is failing to carry out its function.

Question 27

Q27. What does the yellow highlight represent?

Answer 27

The yellow highlight represents the ultimate tensile stress, this is where the material completely fails.

Question 28

Q28. What is represented by yellow highlight?

Answer 28

The yellow highlight represents resilience, the energy absorbed by the material in undergoing plastic deformation up to the elastic limit.

Question 29

Q29. What is represented by the red highlight?

Answer 29

The red highlight represents it ductile ability - able to be drawn out into a thin wire.

Question 30

Q30. What is represented by the blue highlight?

Answer 30

The blue highlight is a measure of toughness, this is the total amount of energy a material can absorb up to the point of fracture. High value = tough, low value = brittle

Question 31

Q31. What is being represented in this graph?

Answer 31

this graph represents fatigue. Application of cyclic loading for a defined number of cycles. Material will eventually fail/survive. Greater the cyclic stress the shorter the cycle.

Question 32

Q32. What is being represented in this image?

Answer 32

The image represents shear bond strength. This test is to test the strength of adhesive and cohesive on materials

Question 33

Q33. What is Ra – arithmetic mean deviation of the surface profile.

Answer 33

This is the measure of the surface roughness which is done by a profilometer. The higher the Ra the rougher the material.

Question 34

Q34. What is the negative of having a high Ra (surface roughness)

Answer 34

A high Ra will increase the chance of more biofilms being present \> this results in the development of periodontal disease.

Question 35

Q35. Why is it important to take thermal conductivity in to account when making materials?

Answer 35

Thermal conductivity is important so that patients can sense something is hot, so they don’t swallow the substance, the more material you have in your mouth (dentures) the less you will be able to naturally feel. Thermal conductivity allows the material to transfer heat through the material at a rate before it is ingested.

Question 36

Q36. Rheological properties, is also known as?

Answer 36

The study of materials flow properties. Such as Composite in syringes, luting cements, veneer trial pastes and impression materials.

Question 37

Q37. What affects the viscosity of a material?

Answer 37

Rate of shear (the pressure being applied) Time (the speed at which the material is coming out)

Question 38

Q38. The graph shows three rheological properties. Which line represents viscosity increase?

Answer 38

Dilatant represents viscosity increase. The material in the syringe must require an increase in shear rate to get the material out,

Question 39

Q39. The graph shows three rheological properties. Which line represents viscosity remains?

Answer 39

Newtonian represents viscosity remains: viscosity remains with constant applied pressure.

Question 40

Q40. The graph shows three rheological properties. Which line represents viscosity decreases?

Answer 40

Pseudoplastic represents viscosity decrease. Viscosity decreases with applied pressure and, unless setting, increases when pressure decreases.

Question 41

Q41. What is one of the negatives of poor corrosion resistance?

Answer 41

Release of toxic element.

Question 42

Q42. Why should thermal expansion and contraction be taken in to account in materials?

Answer 42

Increase in heat can result in expansion of the material and its properties which can result in the material to split. It is therefore important to match the material as closely as possible to the tooth substance being replaced.

Question 43

Q43. Materials are tested before they are used in the clinical environment, how many levels of testing are there and what are they?

Answer 43

Laboratory screening – asses acute systemic toxicity, irritational properties, carcinogenic potential Limited laboratory in vivo usage testing Human randomised controlled clinical trial

Question 44

Q44. What are the requirements for an ideal material?

Answer 44

Non-toxic Non-irritant Harmless to the dental pulp No carcinogenic potential No irritancy

Question 45

Q45. What is gypsum

Answer 45

A soft white or grey mineral consisting of hydrated calcium sulphate. Used in dentistry to make reproductions of impressions called casts, models or dies

Question 46

Q46. What is the purpose of creating a cast?

Answer 46

Purpose of a cast is used to plan treatment and to observe treatment progress.

Question 47

Q47. What Is a die?

Answer 47

A reproduction of a prepared tooth.

Question 48

Q48. What is this CaSO4 2H2O?

Answer 48

Gypsum.

Question 49

Q49. What are three types of gypsum products?

Answer 49

Plaster Stone Improved stone

Question 50

Q50. What is calcination?

Answer 50

The process of heating a solid material to drive off chemically combined components such as H2O and CO2

Question 51

Q51. How do you make β dental plaster?

Answer 51

gypsum must be heated at 110/120 °c

Question 52

Q52. What are the characteristics of the dental plaster material?

Answer 52

Irregular shaped crystals Very porous Random shaped

Question 53

Q53. What are the two forms of plaster?

Answer 53

Type 1 gypsum = impression plaster Type 2 gypsum = model plaster

Question 54

Q55. How do you make α dental stone?

Answer 54

Gypsum must be heated at 125°c with the presence of steam and pressure

Question 55

Q56. What are the characteristics of α dental stone/

Answer 55

More uniform shaped crystals Denser than plaster Larger crystals Smoother particles

Question 56

Q57. What is type 3 gypsum?

Answer 56

Dental stone

Question 57

Q58. How do you make improved stone?

Answer 57

Gypsum along with calcium chloride (30% saturation) must be heated at 100 °c

Question 58

Q59. What are the characteristics of improved stone?

Answer 58

Very dense crystals Cubic or rectangular crystals Large crystals

Question 59

Q60. ADA specification – what are the 5 types of gypsum

Answer 59

Type 1 – impression plaster Type 2 – model plaster Type 3 – dental stone Type 4 – dental stone high strength Type 5 – dental stone, high strength, high expansion

Question 60

Q61. What are Gilmore needles commonly used for?

Answer 60

They are used for a surface penetration test, to measure the setting time of the gypsum material.

Question 61

Q62. The loss of surface gloss can be used as an indication for what?

Answer 61

Setting times. Initial setting 5-7 minutes Final set 30-45 minutes

Question 62

Q63. What is the name of a common retarder used?

Answer 62

Borax

Question 63

Q64. Will a higher water/powder ratio (creates a thinner mixture) result in a longer or shorter setting time?

Answer 63

Longer

Question 64

Q65. Name a common accelerator used for gypsum products.

Answer 64

Potassium sulphate

Question 65

Q66. Will a lower water/powder ratio (creates thicker mixture) result in a longer or shorter setting time?

Answer 65

Shorter

Question 66

Q67. What does increase mixing/decrease mixing of gypsum solution result in?

Answer 66

Increase mixing = shorter set time Decreased mixing = longer set time

Question 67

Q68. What is hygroscopic setting expansion?

Answer 67

The expansion that occurs when gypsum sets while immersed in water

Question 68

Q69. What is normal setting expansion?

Answer 68

The expansion that occurs when gypsum sets in air.

Question 69

Q70. All gypsum products expand normally on setting, out of the 3 gypsum materials, which one expands the most?

Answer 69

1. Plaster – 0.2% ----à 0.3% 2. Stone – 0.08% ----à 0.10% 3. High strength stone – 0.05% -----à 0.07%

Question 70

Q71. How does powder/water ratio affect the strength

Answer 70

High powder/water = strength Powder/high water = decreased strength

Question 71

Q72. What occurs when the gypsum products reach dry strength?

Answer 71

The greatest surface hardness occurs

Question 72

Q73. Of the 3 materials used – which is the weakest to strongest

Answer 72

Plaster Stone Improved stone

Question 73

Q74. Surface detail reproduction: the impression materials viscosity must be what? to obtain less detail but can displace soft tissue.

Answer 73

High viscosity

Question 74

Q75. Surface detail reproduction: the impression materials viscosity must be what? To capture more detail but the tray won’t contain.

Answer 74

Low viscosity

Question 75

Q76. One of the requirements of impression material is for it to repel moisture on its surface, the materials ability to do this is known as?

Answer 75

Hydrophobicity

Question 76

Q77. Dimensional accuracy and stability – what type of trays may cause distortions on the impression material?

Answer 76

Flexible tray

Question 77

Q78. Give two examples of hydrocolloids used in the Dundee dental hospital

Answer 77

Alginate (irreversible) Agar (reversible)