Instrumentation of Root Canal System Flashcards

1
Q

what is the watch winding motion and when is it used

A

clockwise rotation of 30-60 degrees
anticlockwise rotation of 30-60 degrees
used with small instruments

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2
Q

what is the balanced force motion and when is it used

A

used with larger K files or pro-taper instruments
used in curved canals
clockwise turn of 90 degrees
apply apical pressure
anticlockwise turn of greater than 90 degrees

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3
Q

what is the aim of chemomechanical disinfection

A

shape canal
allow delivery of sodium hypochlorite to working length
create shape to obturate

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4
Q

how is EWL decided

A

by the pre-op radiograph

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5
Q

how is CWL decided

A

by using electronic apex locator or working length radiograph

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6
Q

what is the master file

A

largest diameter file taken to working length and therefore represents the final prepared size of the apical portion of canal at working length

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7
Q

what is the barbed broach file used for

A

used for extripating pulp
the elevated barbs engage the pulp and remove it from the canal
the largest sized broach that will fit freely in the canal is selected

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8
Q

what is the ISO colour code for hand files

A

white - 15 and 45
yellow - 20 and 50
red - 25 and 55
blue - 30 and 60
green - 35 and 70
black - 40 and 80

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9
Q

describe the ISO sized instruments

A

16mm cutting flute
named according to diameter at first rake
0.32 taper over the 16mm

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10
Q

what cross section do K-files cut in

A

square

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11
Q

describe K files

A

cutting edges perpendicular to long axis of instrument

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12
Q

what are the types of ISO files

A

H files
reamer
K files

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13
Q

what does the superelasticity of nickel titanium instruments allow

A

they can be strained more than other alloys before permanent deformation
can be placed in curved canals with less lateral force exerted

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14
Q

what are the components of an endodontic rotary instrument

A

taper
flute
leading/ cutting edge
land
relief
helix angle

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15
Q

what does the positive rake angle provide

A

active cutting action

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16
Q

what does the third radial land do

A

stabilises and keeps instruments centred in canal

17
Q

what does the radial land relief do

A

reduces friction on canal wall

18
Q

what does wide radial land provide

A

blade supporting while adding peripheral strength to resist torsional and rotary stresses

19
Q

name four advantages of nickel titanium over stainless steel

A

increased flexibility in larger sizes and tapers
increased cutting efficiency
good safety in use
more user friendly

20
Q

give four disadvantages of nickel titanium instruments for preparation

A

instrument fracture
expense
access difficult in posterior teeth
unsuitable for complex canal anatomy

21
Q

what is true reciprocation and what does it do

A

mimics manual movement
reduces risks associated with continuously rotating file through canal curvatures

22
Q

what are the guidelines for rotary instrumentation in canals

A

straight line access
sufficient space required to guide non-cutting tip of the rotary instrument
decide whether canal is single or multi canals
must use light touch and lots of sodium hypochlorite

23
Q

what motion is observed in reciproc

A

150 degrees counterclockwise
30 degrees clockwise

24
Q

what size of ISO file is required to go to working length before using R50

25
when is R25 used
in narrow canals where the canal is partially or completely invisible
26
what causes instrument separation
torsional stress (instrument tip larger than canal) flexural stress (cyclic fatigue)
27
what is cyclic fatigue
rotating in free curvature generating tension and compression cycles failure of instrument
28
what probe is used to explore the access cavity and ascertain where the canal is
DG16 probe
29
name steps of modified double flare technique
DG16 probe to find canal flush coronal part of canal with irrigant pass 10K file into canal to ensure free passage use rotary instrument to 2/3rds working length to shape coronal portion irrigate and recapitulate use smaller rotary instrument to move coronal preparation more apically irrigate and recapitulate again use smaller rotary instrument to lengthen preparation place size 10 k file into canal to EWL and place apex locator on and wait til 0 or red band appears CWL should be 0.5-1mm short of apex locator use smaller K file and go to CWL irrigate and recapitulate
30
how is apical tapering achieved
go to CWL with the smallest size file each time you go up a size you move 1mm back from CWL