Dental Materials COPY Flashcards
Q1. What is the main function of dental composites.
Used for Restorative (filling) materials
Q2. Dental composites can be used to make impressions of the dental arches, how is this carried out?
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.
Q3. There are two types of dental impression trays, what are they?
Stock tray and custom dental tray (specific to patient)
Q4. What does a dental resin composite consist of?
Resin – fibres of high strength and elasticity
Filler – harder type microparticles (quartz/silica)
Coupling Agent – resin and filler chemically to form matrix
Q5. A dental resin composite without a filler would most likely result in what of the composite?
Without a filler the resin wears easily, exhibits high shrinkage and is exothermic.
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?
Quartz and Silica
Q7. What is needed for the formation of a matrix between the resin and filler?
A coupling agent
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?
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
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?
Process chain as short and possible
Assume idiot
Time pressures
Not a slave to technology
Simple and reliable
Q10. The oral environment must be taken in to consideration when dealing with dental composites, what will the dental composites be subjected to?
Loading to 6 Kg
On/off cyclical forces – fatigue
Chemicals
Temperature fluctuations in microseconds (ice cream -14°C/Coffee 60°C)
Q11. What is cyclical forces referred to as?
Chewing
Q12. Why is it important for restoration to function within minutes of placement?
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.
Q13. What are the 5 common materials used by the dental team?
Gypsum materials (plaster)
Waxes (for dentures)
Alloys (blend of metallic elements)
Polymers
Ceramics
Q14. Tests used to characterise materials must meet standards, why?
To protect the user and patient
Q15. Who overlooks the standard of materials used?
British Standards Institution (BSI)
International Standards Organisations (ISO)
Q16. Pulling type force test is referred to as?
Tensile test
Q17. How is strain worked out?
Strain = change in length/original length
Q18. What is the expression of the formula σ = F / A?
σ = Stress
F = Newtons
A = mm²
Q19. Why is this test not recommended for brittle materials?
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.
Q20. A diametral tensile strength test would be used for what?
Useful for brittle materials where conventional tensile not applicable
Q21. What is the expression of the formula σ = 2F/πDL
σ = stress
2F = 2x newtons
Π = pie 3.14
D = diameter
L = length
Q22. What is this test referred to as?
Flexural test
Q23. What is the expression of the formula σ = 3FL/2bd2
σ = stress
3F = 3x newtons
D = depth
B = breadth
L = length between rollers (support separation)
Q24. The box highlighted red represents what?
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
Q25. What does the purple highlight represent?
The purple highlight represents the outcome when the threshold for the stress/strain measures are overcome, this results in the material losing its elasticity.
Q26. What does the green highlight represent?
The green highlight represents the failure force, this is the force where the material is failing to carry out its function.
Q27. What does the yellow highlight represent?
The yellow highlight represents the ultimate tensile stress, this is where the material completely fails.
Q28. What is represented by yellow highlight?
The yellow highlight represents resilience, the energy absorbed by the material in undergoing plastic deformation up to the elastic limit.
Q29. What is represented by the red highlight?
The red highlight represents it ductile ability - able to be drawn out into a thin wire.
Q30. What is represented by the blue highlight?
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
Q31. What is being represented in this graph?
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.
Q32. What is being represented in this image?
The image represents shear bond strength. This test is to test the strength of adhesive and cohesive on materials
Q33. What is Ra – arithmetic mean deviation of the surface profile.
This is the measure of the surface roughness which is done by a profilometer. The higher the Ra the rougher the material.
Q34. What is the negative of having a high Ra (surface roughness)
A high Ra will increase the chance of more biofilms being present > this results in the development of periodontal disease.
Q35. Why is it important to take thermal conductivity in to account when making materials?
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.
Q36. Rheological properties, is also known as?
The study of materials flow properties. Such as
Composite in syringes, luting cements, veneer trial pastes and impression materials.
Q37. What affects the viscosity of a material?
Rate of shear (the pressure being applied)
Time (the speed at which the material is coming out)
Q38. The graph shows three rheological properties. Which line represents viscosity increase?
Dilatant represents viscosity increase. The material in the syringe must require an increase in shear rate to get the material out,
Q39. The graph shows three rheological properties. Which line represents viscosity remains?
Newtonian represents viscosity remains: viscosity remains with constant applied pressure.
Q40. The graph shows three rheological properties. Which line represents viscosity decreases?
Pseudoplastic represents viscosity decrease. Viscosity decreases with applied pressure and, unless setting, increases when pressure decreases.
Q41. What is one of the negatives of poor corrosion resistance?
Release of toxic element.
Q42. Why should thermal expansion and contraction be taken in to account in materials?
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.
Q43. Materials are tested before they are used in the clinical environment, how many levels of testing are there and what are they?
Laboratory screening – asses acute systemic toxicity, irritational properties, carcinogenic potential
Limited laboratory in vivo usage testing
Human randomised controlled clinical trial
Q44. What are the requirements for an ideal material?
Non-toxic
Non-irritant
Harmless to the dental pulp
No carcinogenic potential
No irritancy
Q45. What is gypsum
A soft white or grey mineral consisting of hydrated calcium sulphate. Used in dentistry to make reproductions of impressions called casts, models or dies
Q46. What is the purpose of creating a cast?
Purpose of a cast is used to plan treatment and to observe treatment progress.
Q47. What Is a die?
A reproduction of a prepared tooth.
Q48. What is this CaSO4 2H2O?
Gypsum.
Q49. What are three types of gypsum products?
Plaster
Stone
Improved stone
Q50. What is calcination?
The process of heating a solid material to drive off chemically combined components such as H2O and CO2
Q51. How do you make β dental plaster?
gypsum must be heated at 110/120 °c
Q52. What are the characteristics of the dental plaster material?
Irregular shaped crystals
Very porous
Random shaped
Q53. What are the two forms of plaster?
Type 1 gypsum = impression plaster
Type 2 gypsum = model plaster
Q55. How do you make α dental stone?
Gypsum must be heated at 125°c with the presence of steam and pressure
Q56. What are the characteristics of α dental stone/
More uniform shaped crystals
Denser than plaster
Larger crystals
Smoother particles
Q57. What is type 3 gypsum?
Dental stone
Q58. How do you make improved stone?
Gypsum along with calcium chloride (30% saturation) must be heated at 100 °c
Q59. What are the characteristics of improved stone?
Very dense crystals
Cubic or rectangular crystals
Large crystals
Q60. ADA specification – what are the 5 types of gypsum
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
Q61. What are Gilmore needles commonly used for?
They are used for a surface penetration test, to measure the setting time of the gypsum material.
Q62. The loss of surface gloss can be used as an indication for what?
Setting times.
Initial setting 5-7 minutes
Final set 30-45 minutes
Q63. What is the name of a common retarder used?
Borax
Q64. Will a higher water/powder ratio (creates a thinner mixture) result in a longer or shorter setting time?
Longer
Q65. Name a common accelerator used for gypsum products.
Potassium sulphate
Q66. Will a lower water/powder ratio (creates thicker mixture) result in a longer or shorter setting time?
Shorter
Q67. What does increase mixing/decrease mixing of gypsum solution result in?
Increase mixing = shorter set time
Decreased mixing = longer set time
Q68. What is hygroscopic setting expansion?
The expansion that occurs when gypsum sets while immersed in water
Q69. What is normal setting expansion?
The expansion that occurs when gypsum sets in air.
Q70. All gypsum products expand normally on setting, out of the 3 gypsum materials, which one expands the most?
- Plaster – 0.2% —-à 0.3%
- Stone – 0.08% —-à 0.10%
- High strength stone – 0.05% —–à 0.07%
Q71. How does powder/water ratio affect the strength
High powder/water = strength
Powder/high water = decreased strength
Q72. What occurs when the gypsum products reach dry strength?
The greatest surface hardness occurs
Q73. Of the 3 materials used – which is the weakest to strongest
Plaster
Stone
Improved stone
Q74. Surface detail reproduction: the impression materials viscosity must be what? to obtain less detail but can displace soft tissue.
High viscosity
Q75. Surface detail reproduction: the impression materials viscosity must be what? To capture more detail but the tray won’t contain.
Low viscosity
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?
Hydrophobicity
Q77. Dimensional accuracy and stability – what type of trays may cause distortions on the impression material?
Flexible tray
Q78. Give two examples of hydrocolloids used in the Dundee dental hospital
Alginate (irreversible)
Agar (reversible)
