DMS Glossary

Question 1

What is compressive strength?

Answer 1

the stress required to cause fracture, making a material no longer fit for purpose

Question 2

What is elastic modulus?

Answer 2

• the stress requires to cause a change in shape
• rigidity
• stress/strain ratio
• Young’s ratio

Question 3

What are brittleness and ductility?

Answer 3

the dimensional change experienced before fracture occurs

• brittle materials experience minimal dimensional change before fracture
• ductile materials can experience considerable dimensional change before fracture

Question 4

What is hardness?

Answer 4

the resistance of a material’s surface to indentation or abrasion

Question 5

What is the initial gradient on a stress-strain curve indicative of?

Answer 5

• elastic modulus
• steeper the gradient the more rigid the material

Question 6

What is the change in gradient on a stress-strain curve indicative of?

Answer 6

proportional limit

Question 7

What is the end point on a stress strain curve indicative of?

Answer 7

fracture stress

• the point at which a material fails

Question 8

What is creep?

Answer 8

the gradual increase in permanent strain experienced under prolonged application of stress beyond the elastic limit

Question 9

What is stress?

Answer 9

The deforming force measured across a given area

• can be tensile, compressive, shear or torsional
• stress = F/A

Question 10

What is a stress concentration point?

Answer 10

An abrupt change in the geometric shape of a material that leads to higher stress at that point

• common in endodontic files

Question 11

What is strain?

Answer 11

The response of a material to stress

• the amount of deformation a material undergoes
• strain = ^L/L

Question 12

What is elastic limit

Answer 12

a set value representing the maximal strain that can be applied to a material allowing the material to return to its original dimensions

Question 13

What is elastic deformation?

Answer 13

reversible deformation that does not exceed the elastic limit

Question 14

What is plastic deformation?

Answer 14

permanent bond displacement occurring when the elastic limit is exceeded

Question 15

What is plastic limit?

Answer 15

the point at which a plastic deformed material breaks

Question 16

What is cyclic fatigue?

Answer 16

the generation of tension/compression cycles in a material freely rotating in a curvature
- experiences both tension and compression
- results in work hardening
- ultimately ends with failure of material

Question 17

What is torsional fatigue?

Answer 17

the generation of strain within a material when different areas are subjected to varying rotational stresses

Question 18

What is shape memory?

Answer 18

alloys which can be deformed at one temperature but when heated or cooled they return to their original shape

Question 19

What is viscosity?

Answer 19

a measure of a material’s ability to flow

• determines a material’s potential for making close contact with tissues