Instrumentation of Root Canal System

Question 1

what is the watch winding motion and when is it used

Answer 1

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

Question 2

what is the balanced force motion and when is it used

Answer 2

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

Question 3

what is the aim of chemomechanical disinfection

Answer 3

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

Question 4

how is EWL decided

Answer 4

by the pre-op radiograph

Question 5

how is CWL decided

Answer 5

by using electronic apex locator or working length radiograph

Question 6

what is the master file

Answer 6

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

Question 7

what is the barbed broach file used for

Answer 7

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

Question 8

what is the ISO colour code for hand files

Answer 8

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

Question 9

describe the ISO sized instruments

Answer 9

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

Question 10

what cross section do K-files cut in

Answer 10

square

Question 11

describe K files

Answer 11

cutting edges perpendicular to long axis of instrument

Question 12

what are the types of ISO files

Answer 12

H files
reamer
K files

Question 13

what does the superelasticity of nickel titanium instruments allow

Answer 13

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

Question 14

what are the components of an endodontic rotary instrument

Answer 14

taper
flute
leading/ cutting edge
land
relief
helix angle

Question 15

what does the positive rake angle provide

Answer 15

active cutting action

Question 16

what does the third radial land do

Answer 16

stabilises and keeps instruments centred in canal

Question 17

what does the radial land relief do

Answer 17

reduces friction on canal wall

Question 18

what does wide radial land provide

Answer 18

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

Question 19

name four advantages of nickel titanium over stainless steel

Answer 19

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

Question 20

give four disadvantages of nickel titanium instruments for preparation

Answer 20

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

Question 21

what is true reciprocation and what does it do

Answer 21

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

Question 22

what are the guidelines for rotary instrumentation in canals

Answer 22

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

Question 23

what motion is observed in reciproc

Answer 23

150 degrees counterclockwise
30 degrees clockwise

Question 24

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

Answer 24

ISO 30

Question 25

when is R25 used

Answer 25

in narrow canals where the canal is partially or completely invisible

Question 26

what causes instrument separation

Answer 26

torsional stress (instrument tip larger than canal)
flexural stress (cyclic fatigue)

Question 27

what is cyclic fatigue

Answer 27

rotating in free curvature
generating tension and compression cycles
failure of instrument

Question 28

what probe is used to explore the access cavity and ascertain where the canal is

Answer 28

DG16 probe

Question 29

name steps of modified double flare technique

Answer 29

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

Question 30

how is apical tapering achieved

Answer 30

go to CWL with the smallest size file
each time you go up a size you move 1mm back from CWL