4 - Instrumentation of the root canal system Flashcards
What are the design objectives of instrumentation?
- continuously tapering funnel
- maintain apical foramen in original position
- keep apical opening as small as possible
What is meant by chemomechanical preparation of the canals?
Chemo
- irrigate to kill microorganisms
- removes smear layer
Mechanical
- prepare shape
- flush out
What is the estimated working length?
- estimated length at which instrumentation should be limited
- obtained by by measuring pre-operative radiograph from coronal reference point to radiographic apex then subtracting 1mm
What is the corrected working length?
- length at which instrumentation and obturation should be limited
- obtained using an electronic apex locator or a working length radiograph
What is the master apical file?
- the largest diameter file that is taken to working length
- the width of the apical preparation
What are the different movements used in instrumentation?
- filing
- reaming
- watch-winding
- balanced force motion
- envelope of motion
Describe watch winding.
- back and forward twists of 30-60 degrees
- light apical pressure
- effective when used with K files
Describe the balanced forced technique.
- file inserted into canal
- 1/4 turn CW with pressure, then 1/2 turn CCW with continuous pressure
- complete 2-3x then remove to assess debris and clean file
What is the irrigation protocol?
- EDTA 17% for 1 minute OR
- sodium hypochlorite 3% (30ml for 10mins)
How should you inject irrigation solution into the canal?
With finger, very slowly, do not use thumb
What is a barbed broach?
- tapered file that looks like barbed wire
- used for extirpating not enlarging canals, should be used to engage pulp tissue and remove it
- should not engage with canal walls
- v fragile
What does white indicate on the ISO colour code?
15 or 45
What does yellow indicate on the ISO colour code?
20 or 50
What does red indicate on the ISO colour code?
25 or 55
What does blue indicate on the ISO colour code?
30 or 60
What does green indicate on the ISO colour code?
35 or 70
What does black indicate on the ISO colour code?
40 or 80
What is the cross-section of a K file?
Square
What is a K file?
- manual file used in canal prep
- square cross-section
- cutting edge is perpendicular to long axis of file
- used in filing motion
Why is NiTi used in endodontic files?
- can be strained more than most alloys which prevents permanent deformation
- superelasticity
What are the advantages of using NiTi over stainless steel?
- increased flexibility in larger sizes and tapers
- increased cutting efficiency
- better safety in use
- more user friendly
What are disadvantages of NiTi files?
- instrument fracture
- expensive
- access is difficult in posterior teeth
- unsuitable for complex canal anatomy
Describe true reciprocation.
- mimic manual movement
- reduces risk of rotating files through curvatures
- decreased cutting efficiency so requires more inward pressure
- limited capacity to remove debris from canal
How do you create a glide path?
- straight line access
- explore anatomy for first 2/3 with files 10-25 to resistance
- establish coronal flare
- size 10 to apex with watch winding motion
- irrigate and repeat using larger sizes
What are the angles of reciprocation used in the reciproc system?
- 150 degrees CCW
- 30 degrees CW
What can cause instrument separation?
- torsional stress (friction with canal walls, tip of file larger than canal)
- flexural stress (cyclic metal fatigue)
