SS and NiTi in endo

Question 1

What are the main components of the endodontic instrument?

Answer 1

• tip
• working part
• shank
• shaft
• operative part

Question 2

What is stress?

Answer 2

the resistance force per unit of area of a material against deformation when an external force is applied. Measured in Newtons per square mm

Question 3

What is tensile strength?

Answer 3

capacity of a material to withstand loads that are trying to elongate the material

Question 4

What is yield strength?

Answer 4

stress the material can stand without being deformed permanently

Question 5

What is strain?

Answer 5

the change of original dimension under stress of a material

Question 6

What is elastic limit?

Answer 6

the greatest stress that an elastic solid can withstand without being deformed permanently

Question 7

What is plastic deformation?

Answer 7

the state of permanent deformation that pertain when the load is removed that exceeds a material’s elastic limit

Question 8

What is plastic limit?

Answer 8

the breaking point of a material

Question 9

What are superelasticity and shape memory properties of?

Answer 9

Superelasticity and shape memory are two properties of only nickel titanium

Question 10

What are the different crystal phases of NiTi?

Answer 10

• austenitic
• martensite
• R-phase

Question 11

What are the different crystal phases of NiTi dependant on?

Answer 11

temperature
- austenitic - high temperature
- martensite - low temperature
- R-phase - intermediate

Question 12

What are the properties of austenitic NiTi?

Answer 12

• hexagonal lattice
• less brittle
• higher modulus of elasticity

Question 13

What are the properties of martensitic NiTi?

Answer 13

• body centred cubic lattice
• more brittle
• lower modulus of elasticity

Question 14

Why does NiTi change from austenitic to martensitic?

Answer 14

stress induced, such as during RCT

Question 15

When does NiTi change from martensitic to austenitic?

Answer 15

when stress removed i.e. when file remove from canal

Question 16

What does superelasticity mean for endo files?

Answer 16

the removal of the file from the canal reduces the stress, therefore return to its original form

Question 17

What does memory shape mean for endo files?

Answer 17

the file keeps martensitic phase when stress causes permanent deformation, if heated again, it will return to original austenitic phase

(if the temp the file is under is stable for during martensitic phase the stress will cause permanent deformation)

Question 18

What are the effects of irrigation on NiTi files?

Answer 18

• all irrigation materials could cause alteration of NiTi instruments
• liquid acts as a thermal heat absorber —> cool down
• mechanical properties are not being altered during irrigation