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Best of Fives for Dentistry > Dental materials > Flashcards

Dental materials Flashcards

1
Q
  1. What does an enamel bonding agent consist of?
    a. Unfilled resin
    b. Filled resin
    c. A mixture of resins, acetone and ethanol
    d. Wetting agents or resins
    e. Prime and bond mixture
A

 A. Unfilled resin
 Enamel bonding agents consist of unfilled resin.

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2
Q
  1. Etched enamel does not need ‘wetting’ before enamel bonding agent is applied. Why is ‘wetting’ not required?
    a. Etched enamel has a high surface free energy
    b. Etched enamel has low surface free energy
    c. The enamel bonding agent has a low surface tension
    d. The negative charge in the enamel bonding agent is attracted to the positive calcium ions in the etched enamel
    e. The negative charge in the enamel bonding agent is attracted to the positive fluoride ions in the etched enamel
A

 A. Etched enamel has a high surface free energy
 The high surface free energy prevents the requirement for ‘wetting’. Fluids with a low surface free energy require ‘wetting’.

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3
Q
  1. What is the bond strength achievable using enamel bonding agents on etched enamel (1MPa = 1kg/mm2)?
    a. 0.1 MPa
    b. 5 MPa
    c. 30 MPa
    d. 80 MPa
    e. 250 MPa
A

 C. 30MPa
 A good bond strength achievable with enamel bonding agents is 30 MPA.

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4
Q
  1. What is the appropriate stress caused by the polymerisation contraction of composite when it is setting?
    a. 0.1 MPa
    b. 5 MPa
    c. 30 MPa
    d. 80 MPa
    e. 250 MPa
A

 B. 5 MPa
 The approx. stress caused by polymerisation contraction when setting is 5 MPA.

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5
Q
  1. Which one of the following is not an advantage of an enamel bonding agent over a dentine bonding agent?
    a. Decreased marginal leakage
    b. Better colour stability
    c. Increased bond strength
    d. Easier to apply
    e. Decreased moisture sensitivity
A

 E. Decreased moisture sensitivity
 Decreased moisture sensitivity is not an advantage of enamel bonding agent over dentine bonding agents. Enamel bonding agents are extremely moisture sensitive.

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6
Q
  1. Which one of the following statements is correct about a dentine primer?
    a. It etches dentine
    b. It increases the surface free energy (wets) dentine
    c. It removes the smear layer
    d. It bonds to composite
    e. It bonds to dentine
A

 B. It increases the surface free energy (wets) dentine.
 Dentine primers increase the surface free energy (wets) dentine.

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7
Q
  1. Which one of the following is true about a dentine ‘conditioner’?
    a. It thinly coats collagen fibrils with resin
    b. It thickly coats collagen fibrils with resin
    c. It bonds to composite
    d. It raises the surface free energy of dentine
    e. It removes the smear layer
A

 E. It removes the smear layer
 The main function of the conditioner is to remove the smear layer.

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8
Q
  1. The usual enamel bonding agent resin is:
    a. HEMA (hydroxyethyl methacrylate)
    b. Bis-GMA (bisphenol A glycidyl methacrylate)
    c. PENTA (phosphonate penta-acrylate ester)
    d. Dimethylmethacrylate
    e. Polymethylmethacrylate
A

 B. Bis-GMA (bisphenol a glycidyl methacrylate)
 The usual enamel bonding agent resin is Bis-GMA.

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9
Q
  1. The solvent which is used to aid dentine wetting in dentine bonding systems is:
    a. Water
    b. Ethanol or acetone
    c. CCl4 (carbon tetrachloride)
    d. Ethylene
    e. A low-molecular-weight resin
A

 B. Ethanol or acetone
 The solvent which is used to aid dentine wetting in dentine bonding systems is ethanol or acetone.

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10
Q
  1. The number of steps in dentine bonding is:
    a. 1
    b. 2
    c. 3
    d. 4
    e. Varies
A

 E. Varies
 There are many different systems on the market for dentine bonding, so the number of steps is variable.

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11
Q
  1. What is the bond strength between dentine and composite when dentine bonding agents are used?
    a. 1 MPa
    b. 5 MPa
    c. 100 MPa
    d. 500 MPa
    e. 1000 MPa
A

 B. 5 MPa
 The bond strength between dentine and composite when dentine bonding agents are used is 5 MPa.

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12
Q
  1. Which one of the following statements is true about the resin in a dentine bonding agent primer?
    a. It is hydrophilic
    b. It is hydrophobic
    c. It is viscous
    d. It has a high molecular weight
    e. It has high surface tension
A

 B. It is hydrophobic
 The resins used in a dentine bonding agent primer are hydrophobic.

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13
Q
  1. What is the percentage of copper in a high copper dental amalgam alloy?
    a. 2-12%
    b. 12-32%
    c. 32-52%
    d. 52-70%
    e. 70+ %
A

 B. 12-32 %
 The percentage of copper in a high copper dental amalgam is between 12% and 32%.

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14
Q
  1. Zinc is often used to improve the properties of amalgam. What happens to a zinc-containing low copper alloy if moisture gets into it?
    a. The alloy corrodes
    b. The alloy contracts
    c. The alloy is reduced
    d. The alloy expands
    e. None of the above
A

 D. The alloy expands
 If a zinc-containing low copper alloy is invaded by moisture it expands.

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15
Q
  1. What happens to a zinc-containing high copper alloy if moisture gets into it?
    a. The alloy corrodes
    b. The alloy contracts
    c. The alloy is reduced
    d. The alloy expands
    e. None of the above
A

 E. None of the above
 If a zinc-containing high copper alloy is invaded by moisture there is hardly any change.

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16
Q
  1. Which one of these is a lathe-cut spherical alloy mixture?
    a. Hybrid
    b. Admixture
    c. Gamma 2
    d. Non-gamma 2
    e. Gamma 1
A

 B. Admixture
 Admixed amalgam contains both lathe-cut and spherical-cut particles.

17
Q
  1. Why is tin added to amalgam?
    a. It decreases the reaction rate and gives adequate working time.
    b. It decreases corrosion
    c. It scavenges water molecules
    d. It increases filling strength
    e. It decreases setting time
A

 A. It decreases the reaction rate and gives adequate working time.
 Tin is added to amalgam to decrease the reaction rate and enables the clinician to have increased working time.

18
Q
  1. Which one of these chemical compositions is the gamma 1 phase?
    a. Ag3Sn
    b. Ag2Hg3
    c. AgCu
    d. Cu6Sn5
    e. Sn7Hg
A

 B. Ag2Hg3
 Ag3Sn + Hg  Ag3Sn + Ag2Hg3 + Sn7Hg
 Y + Hg  Y + Y1 + Y2
 Sn7Hg + AgCu  Cu6Sn5 + Ag2Hg3
 Y2 + AgCu  Cu6Sn5 + Y1

19
Q
  1. Which one of these chemical compositions is the gamma 2 phase?
    a. Ag3Sn
    b. Ag2Hg3
    c. AgCu
    d. Cu6Sn5
    e. Sn7Hg
A

 E. Sn7Hg

20
Q
  1. What is the greatest disadvantage of using amalgam in posterior teeth?
    a. Mercury toxicity
    b. Poor aesthetics
    c. Sound tooth tissue requires removal for retention
    d. Increased incidence of cusp fracture
    e. Decreased lifetime of restoration compared with other materials
A

 C. Sound tooth tissue requires removal for retention.
 As amalgam has no chemical bond to the tooth (unlike composite restorations) it requires mechanical retention, therefore it requires further tooth removal to retain the restoration.

21
Q
  1. How long does it take for amalgam to form a bond with the tooth?
    a. 3 minutes
    b. 3 hours
    c. 3 days
    d. 3 weeks
    e. 3 months
A

 E. 3 months
 Amalgam takes three months to produce a bond with a tooth.

22
Q
  1. Which of the following statements regarding the properties of casting gold alloys is correct?
    a. The gold content increases on going from soft type I alloy to an extra hard type IV alloy.
    b. The corrosion resistance increases on going from a soft type I alloy to an extra hard type IV alloy.
    c. The strength increases on going from a soft type I alloy to an extra hard type IV alloy
    d. The ductility increases on going from a soft type I alloy to an extra hard type IV alloy
    e. None of the above statements is correct
A

 C. The strength increases on going from a soft type I alloy to an extra hard type IV alloy.
 Type I soft casting gold has 85% gold whereas extra hard type IV alloy have only 65%. This alters the properties of the alloy and the corrosion resistance the ductility decreases on going from a type I alloy to an extra hard type IV alloy.

23
Q
  1. What is the typical particle size in microfilled composite, in micrometers?
    a. 0.04
    b. 0.4
    c. 4
    d. 40
    e. 400
A

 A. 0.04
 The typical particle size of a microfilled composite is 0.04 micrometres.

24
Q
  1. What is different about a hybrid composite?
    a. It is a mixture of composite and compomer
    b. It includes a mixture of Bis-GMA and TEG-GMA (triethylene glycolglycidyl methacrylate)
    c. The filler particles are a combination of silicon dioxide and glass
    d. It is a mixture of composite and glass ionomer
    e. It contains both large and small filler particles
A

 E. It contains both large and small filler particles
 D defines a compomer which is a mixture of composite and glass ionomer. Almost all composite have silicone dioxide and glass filler particles, not just hybrid composite. There is no such mixture as a composite and a compomer.

25
Q
  1. What is the most important property of a posterior composite?
    a. It requires a single cure
    b. It is dual cured
    c. It is very heavily filled
    d. It is very lightly filled
    e. It flows very easily during placement
A

 C. It is very heavily filled.
 Single or dual cure is not an important property of a posterior composite. The important properly is that the composite is heavily filled so that it can withstand the heavy occlusal forces placed on it. Lightly filled composites can easy flow composites are more commonly used in the anterior region.

26
Q
  1. Which one of the following materials should not be used with composites?
    a. Kalzinol
    b. Zinc phosphate
    c. Vitrebond
    d. Fuji glass ionomer
    e. Poly-F
A

 A. Kalzinol
 Kalzinol prevents bonding of composite to enamel and dentine in a cavity.

27
Q
  1. What is the maximum thickness of composite which can be cured by a curing light?
    a. 0.5mm
    b. 1mm
    c. 2mm
    d. 4mm
    e. 6mm
A

 C. 2mm
 The maximum thickness which can be cured is 2mm. Anything thicker than this and your composite will have a ‘soggy bottom’, and will not be stable as a restoration.

28
Q
  1. Which one of the following events does not occur as a result of microleakage at the composite margin?
    a. Secondary caries
    b. Loss of restoration
    c. Sensitivity
    d. Enamel fracture
    e. Staining
A

 D. Enamel fracture
 The restoration can debond and be lost a result of microleakage. Also air and fluid leakage can lead to sensitivity, and staining can occur, especially if coloured food leak around the margins.

29
Q
  1. Which one of the following is not released from glass ionomer when it sets?
    a. Zinc
    b. Aluminium
    c. Fluoride
    d. Calcium
    e. Sodium
A

A. Zinc
B. Zinc is not released from glass ionomer when it sets. Aluminium, fluoride, calcium and sodium are released during the setting process.

30
Q
  1. When fluoride ions leach out of glass ionomer, what replaces them?
    a. Aluminium ions
    b. Hydroxyl ions
    c. Sodium ions
    d. Carbonate ions
    e. Silicate ions
A

 B. Hydroxyl ions
 Hydroxyl ions replace the fluoride ions which leach out during the setting process.

31
Q
  1. Which one of the following statements about the curing of composite is true?
    a. Exposure time of 2-3 seconds is needed for polymerisation with visible light.
    b. Before light activation, the base and catalyst are mixed.
    c. Lights of both blue and red wavelength are equally effective in polymerisation.
    d. Light from an argon laser with activate polymerisation.
    e. Light from a lithium laser will activate polymerisation.
A

 D. Light from an argon laser with activate polymerisation.
 Light from an argon laser usually between 20 and 40 seconds will cure composite.

32
Q
  1. Which one of the following composite fillers is radiopaque?
    a. Quartz
    b. Lithium aluminium silicate
    c. Colloid silicate
    d. Barium glass
    e. Carbon fibre
A

 D. Barium glass
 Barium is a radiopaque material and is used frequently in radiographic investigation. The most common use is barium enemas. However, this technique is in decline with the increase in computed tomography (CT) scanning.

33
Q
  1. Which one of the following is the best choice of restorative material to achieve a moderate to high strength restoration that allows fluoride leaching and has good aesthetics?
    a. Hybrid ionomer
    b. Composite
    c. Compomer
    d. Amalgam
    e. Glass ionomer
A

 A. Hybrid ionomer
 Hybrid monomers have found popularity as restorative materials and as cements for crowns and fixed prosthesis. They contain about 80% glass ionomer and 20% resin. The hybrid ionomer releases the fluoride present in the aluminosilicate glass constituent, which is dissolved by the acid present in the mixture. Ongoing research has shown that these restorations release considerable amounts of fluoride during their service in the mouth. The tricure characteristics of hybrid ionomers makes them ideally suitable for the repair of opaque restorations that have become carious during service. These materials are ideal for the repair of crowns, as well as for repairs in any restorative situation with inadequate light access to allow a light-cured material to cure properly. Hybrid ionomers do not require a bonding agent for retention. They bond to dentine naturally by means of a calcium-carboxylate ion bond. Some manufacturers have suggested using primer before placement of the hybrid ionomer; however this does not appear to be needed. Ongoing research is showing that the direct contact between the hybrid ionomer and the tooth structure causes high amounts of fluoride to be released into tooth structure. Thus hybrid ionomers are one of the most adequate choices for restoring teeth in patients who have a high caries risk.

 Compomers are easier to use than hybrid ionomers, but some of their characteristics are not as desirable as those of hybrid ionomers. Compomers require a bonding agent for adequate retention to dentinal surfaces. The bonding agent reduces the amount of fluoride that can penetrate into the dentine. However, compomers release considerable amounts of fluoride from their external surfaces into the oral environment. These materials are popular for restoration of children’s posterior teeth. Because compomers are easy to use, and release fluoride, they are nearly ideal for placement in voids in crown preparations resulting from removal of old silver or composite restorations (so-called fillers). These materials release less fluoride than hybrid ionomers, but more than typical resin-based composites, most of which release few or no fluoride ions.

 Conventional glass ionomers continue to be popular for restoring teeth and for cementing crowns and fixed prostheses. Glass ionomer release considerable amounts of fluoride into tooth structure, as well as into the oral environment. In fact, research has shown them to release more fluoride than any other caries-preventive material. The working characteristics of glass ionomer as a restorative material make it more difficult to use than hybrid ionomer or compomer. Nevertheless, when glass ionomer is used, practitioners can expect it to release considerable amounts of fluoride.

34
Q
  1. Which one of the following properties is higher for micro-hybrid composites than for micro-filled composites?
    a. Modulus of elasticity
    b. Water absorption
    c. Thermal expansion
    d. Creep
    e. Polymeric shrinkage
A

 A. Modulus of elasticity
 An elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance’s tendency to deform elastically (ie non-permanently) when a force is applied to it. The elastic modulus of an object is defined as the slope of its stress-strain curve in the elastic deformation region.

35
Q
  1. Regarding adhesion of composite restorations to tooth structure, which one of the following statement is true?
    a. Bonding forms a hybrid layer with enamel.
    b. Bonding to enamel is achieved by the application of an acid etchant followed by the application of a bonding agent and then composite resin.
    c. The bonding agent forms a micro-mechanical bond with the enamel but a chemical bond with the dentine.
    d. Most dentine-bonding agents bond better to a dry surface.
    e. Bonding occurs better without rubber dam.
A

 B. Bonding to enamel is achieved by the application of an acid etchant followed by the application of a bonding agent and then composite resin.
 B describes the most common pathway for placing a composite.

36
Q
  1. Which one of the following statements applies to packable composites?
    a. Their depth of cure allows bulk polymerisation, which has been shown to be clinically effective.
    b. Their wear rate is dissimilar to that of amalgam.
    c. They are radiolucent
    d. They have similar or slightly less polymerisation shrinkage than all purpose composites.
    e. They exhibit more wear than compomers.
A

 A. Their depth of cure allows bulk polymerisation, which has been shown to be clinically effective.
 The packable dental composites can be polymerised in bulk and are clinically very effective.

Best of Fives for Dentistry (6 decks)

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