Properties of Dental Materials

Question 1

Hardness

Answer 1

• the ability of the material to resist abrasion or wear
• hardness of dental materials must only be compared between similar materials
• want hardness to be as similar to enamel tooth structure

Question 2

Viscosity

Answer 2

• resistance to motion of a liquid, controlled by internal friction forces within the liquid.
• we want viscous material bc it will flow into the nooks and crannys.

Question 3

Rheology

Answer 3

The study of how matter flows

Question 4

Thixotropic

Answer 4

• A liquid that becomes less viscous and more liquid under pressure
• Examples of thixotropic materials are prophylaxes paste, resin cements, plaster of paris, and some impression materials

Question 5

Creep and flow

Answer 5

• Creep: TIME-DEPENDENT plastic strain of materials under a static load or constant stress. Example of this is amalgam, as well as some metal bridges.
• Flow: Deformation under static load. Flow is used for amorphous materials such as waxes

Question 6

Thermophysical properties: Thermal conductivity and conductivity

Answer 6

• Thermal conductivity: Measure of how well heat is transferred through a material by the conductive flow
• Conductivity: Occurs when electrons increase their kinetic activity
• Rate of heat flow is dependent on area and temperature gradient across the structure

Question 7

Conductors, insulators, and thermal diffusivity

Answer 7

Conductors: Material with good thermal conductivity

Insulators: materials with low conductivity

Thermal diffusivity: Controls the time rate of temperature change as heat passes through a material

-Dentin and enamel have the low thermal conductivity. Metallic restorations tend to have high thermal conductivity. Because of this sometimes an insulator is needed between dentin and restoration

Question 8

Coefficient of thermal expansion

Answer 8

• Change in length per unit of the original length of a material when its temperature is raised 1 degree celsius

-Dental materials should have the similar coefficients of thermal expansion as of the teeth to avoid micro fracture or leakage around the margins of the restoration

Question 9

Coefficient thermal expansion of dental materials:

Answer 9

• Tooth/ Glass ionomer = 11-12 ppm/c x 10
  -Gold = 14.4
  -amalgam = 22-28
• composite = 28-35
• unfilled resin = 81-92

Question 10

Modulus of elasticity

Answer 10

• a quantity that measures an object or substances resistance to being deformed elastically (i.e., non permanently) when a stress is applied to it

Question 11

Dimensions of color

Answer 11

• Hue: Referred to as the basic color- Dominant wavelength. Hue distinguishes one color from another
• Valuer: Relative blackness or whiteness ( 0=Black, 100=white)
• Chroma: Brightness, saturation. Intensity of the color

Question 12

Bite Forces

Answer 12

• Molar region: 90-200 pounds
• Premolar region: 50-100 pounds
• Canine region: 30-75 pounds
• Incisor region: 20-55 pounds