Question 1

A new addition silicone impression material is tested for linear dimensional change upon setting.The result of -0.34% indicates that _____ took place within 24 hours after setting.

Accepted Answer

The negative value (-0.34%) represents a shrinkage in linear dimension, indicating that the material decreased in size after setting. Therefore, the correct choice is B, linear shrinkage. The other options are not applicable to the information given.

Question 2

Which of the following is an electrical property of interest in the mouth?

Accepted Answer

Galvanism refers to the electrical current generated when two different types of metals come into contact in the presence of saliva, which can cause discomfort or a metallic taste in the mouth. The other options listed are mechanical or physical properties, not electrical.

Question 3

For which of the following materials do dimensional changes occur during setting as a result of a chemical reaction?

Accepted Answer

Elastomeric impression materials undergo dimensional changes during setting due to a chemical reaction between the base and catalyst components. Wax patterns and gold restorations do not experience dimensional changes during setting as they solidify without undergoing a chemical reaction.

Question 4

Which of the following dental restorative materials has the greatest thermal conductivity?

Accepted Answer

Gold alloys have the greatest thermal conductivity among the listed dental restorative materials, allowing heat to pass through them more easily.

Question 5

Which of the following restorative materials has a linear thermal coefficient of expansion that is smaller than that of human teeth?

Accepted Answer

Ceramics have a smaller linear thermal coefficient of expansion than human teeth, making them a better choice for restorative materials as they are less likely to expand and contract at a different rate than the surrounding natural teeth, which could potentially cause damage or failure of the restoration over time. Dental amalgam, composites, and unfilled acrylics and sealants all have higher coefficients of thermal expansion than human teeth.

Question 6

Given a schematic sketch of two opposing teeth,one with a temporary aluminum alloy crown and the other with a gold crown,the electrolyte would be the:

Accepted Answer

Saliva acts as the electrolyte in the oral environment, facilitating the flow of ions between the two different metal crowns, which can lead to galvanic corrosion.

Question 7

Cavity varnishes and liners are ineffective as thermal insulators because they:

Accepted Answer

Cavity varnishes and liners are applied in very thin layers, which makes them ineffective as thermal insulators regardless of their material properties.

Question 8

Because the thermal expansion of a restorative material usually does not match that of the tooth structure,a differential expansion or contraction occurs that may result in leakage of oral fluids between the restoration and tooth.

Accepted Answer

This statement is true as most restorative materials have a different coefficient of thermal expansion compared to the tooth structure which causes differential expansion or contraction resulting in leakage of oral fluids between the restoration and tooth.

Question 9

Percolation is thought to decrease with time following insertion of which of the following dental restorative materials?

Accepted Answer

Percolation decreases with time in dental amalgam restorations because the material undergoes a process called "self-sealing" where corrosion products fill the gaps at the margins, reducing microleakage.

Question 10

Dimensional change usually is expressed as a percentage of:

Accepted Answer

Dimensional change is usually expressed as a percentage of an original length or volume, as it compares the change in dimension to the initial dimension.

Question 11

_____ is used as a measure of heat transferred.

Accepted Answer

Thermal conductivity is used as a measure of heat transferred. Linear coefficient of thermal expansion measures the change in length or volume of a material due to a change in temperature. Galvanism is the production of electric currents from chemical reactions. Absorption is the process of a substance taking in another substance. Adsorption is the attachment of molecules or particles to a surface. None of these other options directly measure heat transfer.

Question 12

The thermal coefficient of expansion _____ uniform throughout the entire temperature range and is usually _____ for liquids than solids.

Accepted Answer

The thermal coefficient of expansion is not uniform throughout the entire temperature range due to the complex behavior of materials as they heat up or cool down. It is usually higher for liquids than solids because liquids are more responsive to temperature changes, allowing them to expand more readily.

Question 13

Which of the following dental restorative materials has a linear coefficient of thermal expansion closest to teeth?

Accepted Answer

The answer of Which of the following dental restorative materials...

Question 14

Which of the following terms indicates concentration of molecules at the surface of a solid or liquid?

Accepted Answer

Adsorption refers to the concentration of molecules or particles at the surface of a solid or liquid. This can include physical adsorption (where the molecules are held by van der Waal forces) or chemisorption (where the molecules are bound by chemical bonds). Corrosion refers to the degradation of a material due to chemical reactions with its environment. Hydrophilic refers to a substance that has an affinity for water, while absorption refers to the uptake of a substance into another material (e.g. the absorption of a liquid into a sponge).

Question 15

With regard to wettability and water,a low contact angle indicates:

Accepted Answer

A low contact angle indicates that the material is hydrophilic, meaning it has a strong affinity for water and readily wets the surface. A high contact angle (greater than 90°) indicates that the material is hydrophobic, meaning it repels water and does not wet the surface easily. Choice B and E are incorrect as they suggest the opposite of what a low contact angle indicates. Choice C is only partly correct, as it describes the definition of a high contact angle rather than a low one.

Question 16

_____ occurs as the result of a discrepancy between the linear thermal coefficient of expansion between teeth and the restorative material if there is no bonding.

Accepted Answer

Percolation occurs due to the difference in thermal expansion between teeth and restorative materials, leading to gaps and fluid movement when there is no bonding.

Question 17

_____ refers to the uptake of liquid by a bulk solid.

Accepted Answer

Absorption refers to the process of liquid being taken up by the bulk solid. Adsorption, on the other hand, refers to the adhesion of molecules to a surface, while hydrophilic and hydrophobic refer to the affinity of a substance for water.

Question 18

Which of the following restorative materials have thermal conductivity that is most similar to tooth structure?

Accepted Answer

Composites have thermal conductivity that is most similar to tooth structure. Dental amalgam has higher thermal conductivity, while gold alloys have lower thermal conductivity. Zinc phosphate and zinc oxide-eugenol cements have even lower thermal conductivity than gold alloys.

Question 19

Which of the following choices encourage good wetting?

Accepted Answer

The answer of Which of the following choices encourage good...

Question 20

The volumetric dimensional change is equal to _____ times the linear dimensional change.

Accepted Answer

The volumetric dimensional change is equal to three times the linear dimensional change, as volume changes with the cube of the linear dimension.

Quiz 2: Properties of Materials