Physical Properties

Question 1

What is the Melting and freezing temperature for dental material

Answer 1

It is the temperature at which the material melts or freeze

Question 2

What is the heat of fusion for dental material

Answer 2

It is the amount of heat in calories, required to convert 1 gm of the material from solid to liquid state

Question 3

What is the latent heat of fusion for dental material

Answer 3

It is the liberated heat as the liquid is cooled to solidify

Question 4

What is the thermal conductivity for dental material

Answer 4

It is the quantity of heat in calories per second passing through a body of 1 cm thickness when the temperature difference is 1 Celsius

Question 5

What is the unit of thermal conductivity

Answer 5

The unit is cal / sec / cm

Question 6

Which better in thermal conductivity metals or plastics

Answer 6

Metals are better thermal conductors then plastics

Question 7

Importance of thermal conductivity

Answer 7

Thermal conductivity it might be a disadvantage in the case of large restorative materials ( gold or amalgam ) —> it may result in pulp irritation

Question 8

In the case of pulp irritation as a result from thermal conductivity - which material should be used ?

Answer 8

• in this case the dentin layer must be saved —> so in such cases a base material must be used —> as an example “ metallic denture base “

Question 9

What is the specific heat

Answer 9

It is the quantity of heat in calories required to raise the temperature of 1 gm of substance 1 celsius

Question 10

Importance of specific heat

Answer 10

It is important to define the amount of heat required to apply on a mass to raise the temperature to the melting point !

Question 11

What us the Thermal diffusivity

Answer 11

It is the rate of heat diffusion in a body ( the rate at which the body with non-uniform temperature approach a thermal equilibrium )

Question 12

What is the Coefficient of thermal expansion ( CTE )

Answer 12

It is the change of length for each change in temperature —> change of length unit for each one celsius

Question 13

Importance of CTE “ coefficient of thermal expansion “

Answer 13

• There must be a close match between CTE of tooth structure and restorative material
• if there is a high difference of ECT between the material and tooth structure , it will result in either expansion or contraction which will break the seal between them , leading to marginal leakage , discoloration hypersensitivity and recurrent caries
• close match between ECT of ceramic and metal is needed in ceramo-metal restoration
• crazing in denture teeth as a result of ECT mismatch

Question 14

What is the meaning of “ value “ in colour dimensions ?

Answer 14

• It describes the lightness or darkness of the colour
• ⬆️ value means lighter colour
• ⬇️ value means darker colour

Question 15

What is the meaning of “ chroma “ in dolour dimension

Answer 15

It means the intensity / strength of the colour

Question 16

What is the meaning of “ Hue “ in colour dimension

Answer 16

It means the colour itself —> blue , red , green

Question 17

What is the meaning of transparency in physical properties

Answer 17

• It is a property based on light transmission and absorption so the material can be distinguished
• it allows the passage of the light so that an object can be clearly seen through them
• for example “ glass “

Question 18

What is the meaning of translucency in physical properties

Answer 18

• It is a property based on light transmission and absorption so the material can be distinguished
• it allows the passage of some light and scatter the rest or reflect the rest

Question 19

What is the meaning of opacity in physical properties

Answer 19

• It is a property based on light transmission and absorption so the material can be distinguished
• it prevents the passage of the light as it absorbs all the light and therefore an object cannot be seen through them

Question 20

Define the “ absorption “

Answer 20

• as a light passes through a material , the material absorbs part of the energy of the light ,
• the intensity of of the light decrease and the energy of the material increase , and the light will not be transmitted through the material
• ⬆️ absorption —> ⬆️ opaque

Question 21

Define the “ transmission “

Answer 21

• it is a light passing through an optical medium without attenuation
• total transmission occurs in transparent material
• when part of the light is transmitted and the other is reflected ( diffuse transmission ) the material appears translucent

Question 22

Define the “ scattering “

Answer 22

• it occurs when the light rays passing through a medium and obstruct by any different inclusions
• it will be redirected in other direction away from the observers eyes
• it is important in the rough composite surfaces

Question 23

Define the “ refraction “

Answer 23

• it is the change in direction of light bending as they enter another medium
• it results from the difference in the refractive indices of two media as well as the difference between the speed of light in air and another medium

Question 24

The importance of “ refraction “

Answer 24

• refractory index is a characteristic property of the substance
• a perfect match of refractory indices of the components of resin composite or ceramic will result in transparent material , whereas a large difference will result in opaque material

Question 25

Define the “ reflection “

Answer 25

• most of objects are visible because they reflect light to our eyes
• when light fall on perfectly smooth surface it will be reflected in one direction
• when light fall on a rough surface it will be reflected in all directions
• its importance comes when a highly smooth and polished surface mimic the natural tooth appearance

Question 26

Define the “ light “

Answer 26

It is a polychromatic and consists of various wavelength