8 - Endodontic materials Flashcards
What are endodontic instruments?
- used in mechanical phase of chemomechanical disinfection
- metal files are used to remove soft and hard tissues
- removes micro-organisms
- creates space to the disinfectants and medicaments
- create the shape for obturation
What causes stress to endodontic files?
Abrupt changes in shape causes higher stress at that point
What is the elastic limit?
The maximum amount of strain that can be applied to the file and it will still return to its original shape
What is plastic deformation?
The file will not return to its original shape as the elastic limit has been exceeded
What is plastic limit?
The point at which the already deformed file breaks
What is cyclic fatigue?
- work hardening of the file when used in a curved canal
- generation of tension and compression cycles
What are the different classifications of endodontic instruments?
- manually operated
- low-speed
- engine driven NiTi rotary
- engine driven instruments that adapt to canal shape
- engine driven reciprocating
- ultrasonic
What makes up stainless steel?
- alloy of iron, carbon and chromium (can contain nickel)
- chromium prevents rusting
How are stainless steel files manufactured?
- machined stainless steel wire cut to cross-sectional shape of file
- twisted (work hardening)
What is nitinol?
- alloy of nickel and titanium
- super-elasticity stops usual metal properties and proportional strain
What is shape memory?
Material scan be deformed and then heated/cooled to return to their original shape
Describe the crystal structure of NiTi.
- has shape memory
- crystal lattice is affected by temperature
- in martensite form it is ductile
- in austenite form it is strong and hard
Define taper.
Diameter change along working surface of instrument
Define flute.
Groove to collect dentine and soft tissues
Define leading edge.
- aka cutting edge
- forms and deflects dentine chips
Define land.
Surface extending between flutes
Define relief.
Reduction in surface of land (modifies friction)
Define helix angle.
Angle cutting axis forms with long axis of file
What are irritants used for?
- facilitate removal of debris
- lubrication
- dissolution of organic and inorganic material
- penetration to canal periphery
- antimicrobial
- biofilm disruption
What is used as an irritant in endodontic treatment?
Sodium hypochlorite
What factors affect the function of sodium hypochlorite?
- concentration
- volume
- contact time
- mechanical agitation
What is the smear layer?
- organic pulpal material and inorganic dentinal debris
- superficial and packing into tubules
- the contamination interferes with disinfection
- prevents sealer penetrating into tubules
How do you remove the smear layer?
- 17% EDTA
- 10% citric acid
- sonic and ultrasonic irrigation
What happens if irritants are mixed?
- can interact and become cytotoxic and carcinogenic
- EDTA and sodium hypochlorite should never mix and the canal should be rinsed between use
