Instrumentation of RCS Flashcards
Why instrumentation?
- remove infected soft and hard tissues
- give disinfecting irrigants access to apical canal space
- create space for delivery of medicaments and subsequent obturation
- retain integrity of radicular structures
Who invented Chemomechanical disinfection?
Dr Herbert Schilder
Design objective
- create a continuously tapering funnel shape
- maintain apical foramen at original position
- keep apical opening as small as possible
What is Chemomechanical prep?
Chemo
- irrigate to kill microorganism
- remove smear layer
Mechanical
- prepare shape
- flush out
Mechanical aim
- shape canal
- allow delivery of irrigant, ie: NaOCl to WL
- creates shape to obturate
Vertucci classification
Estimated WL
- Estimated WL
- estimated length at which instrumentation should be limited
- obtained by measuring pre-op radiograph to determine distance between coronal reference point and radiographic apex then subtract by 1mm
Corrected WL
- length at which instrumentation and subsequent obturation should be limited
- obtained by thr use of electronic apex locator/ WL radiograph
Master apical file
- largest diameter file taken to WL and therefore represents the final prepared size of apical portion of canal at WL
Type of motion
- filing
- reaming
- watch-winding
- balanced force motion
- envelope of motion
How is watch- winding method?
- back and forward oscillation 30-60 degrees
- light apical pressure
- effective with K files
- useful for passing small files through canals
Balanced force
- insert file and engage CW into dentine 1/4 turn
- with continued pressure, go CC 1/2 turn to strip dentine away
- do this 1-3 times before removing file to remove debris and check file
- remove
- clean
- reintroduce
- working to WL
Modified Double Flare
- incorporating balanced force and step back technique
Reciproc
- modified reciprocation
Irrigation protocol after shaping complete
- 17% EDTA for 1 min
- 3% NaOCl, 30ml for 10 mins
- use index finger, do not use thumb
Barbed Broach
- used for extirpating, not enlarging
- formed from tapered round shaft by lifting up portions of metal of shaft almost at right angle to shaft
- must not engage canal walls
- will break easily if misused
- engage the pulp tissue and remove it from canal
ISO colour code
size 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80
ISO SS sized instruments
- all have 16mm cutting flutes
- named according to diameter
Instrument design
Hedstrom files
- machined steel blank
- used in filing motion, cuts on withdrawal
- good cutting efficiency but can cause iatrogenic damage
- no longer used for canal prep
- removing GP/ fractured instruments in cases of re-tx
Reamer
- tapered triangular shaft
- cutting edge nearly parallel to long axis
- rotate 1/4 to 1/2 turn clockwise to cut as advanced to length
- in contact with the walls of canal in order to be effective
NiTi
- superelasticity
- can be strained more than other alloys before permanent deformation
- allows NiTi to be placed in curved canals with less lateral forces exerted
- ## less transportation, zipping and ledging
Components of Endodontic Rotary
Advantages of NiTi vs SS
- increased flexibility in larger sizes and tapers
- increased cutting efficiency
- more user friendly
- ie: ProTaper rotary
Disadvantages of NiTi prep
- instrument fracture
- expense
- access can be difficult in posterior teeth
- unsuitable for complex canal anatomy
What is true reciprocation?
- mimics manual movement
- reduces risks associated with continuous rotating a file through canal curvatures
- decreased cutting efficiency
- requires increased inward pressure
- limited capacity to auger debris out of canal
Why do instrument separation happen?
Torsional stress
- extensive instrument surface encounters excessive friction on canal walls
- instrument tip is larger than canal section to be shaped
Flexural stress
- repeated cyclic metal fatigue
What is cyclic fatigue?
- freely rotating in curvature
- generation of tension/ compression cycles
- cyclic fatigue
- failure
Torsional fatigue
Modified Double flare
- Gates Glidden and K files
- ensure orifices are filled with irrigants before using K files to check for smooth movement into canal
- doesnt need to be to WL with size 10 and 15, ensure clear passage into the canal
- use GG size 4 at coronal portion to flare coronal portion
- 2/3 of the estimated WL
- with light apical pressure to create smooth flare prep
- after gates 4, use K files 10 to remove excess debris and irrigate
- move on to GG 3, drop the flaring more apically
Apical prep
- light apical pressure with watch winding using size 10
- attach apex locator
- measure length of file that has reached the red band on apex locator
- CWL should be 0.5-1mm short than what is on apex locator
- advance with size 15 to CWL with watch winding motion
- use size 20 until CWL
- irrigation
- using patency file size 10 to ensure no debris accumulation at apical region
- use balanced force for size 25
- size 25 is master apical file (15mm)
- size 30 use 1mm short of WL (14mm)
- size 35, 13mm
- size 40, 12 mm- balanced force technique
- use master apical file, filing motion to smooth the steps at canal
Reciproc file system
- introduce irrigant into orifice and pulp chamber
- size 10 file to 2/3 of WL
- size 15 to 2/3 of WL, watch winding
- irrigate
- start coronal prep with reciproc R25, 2/3 of EWL
- introduce in a pecking motion, 3 pecks and remove debris from the flute
- recapitulate using size 10
- once reach 2/3 of EWL, recapitulate, irrigate and then check CWL
- use size 10 file to EWL, use apex locator
- measure the file and substract 0.5-1mm for CWL
- prep glide path using size 15 set to CWL
- recapitulate with size10 and use as patency file to touch PDL
- R25 to CWL and follow through 3 pecks and irrigate
- patency file to prevent likelihood of blockage and lost of WL
- brush away from furcation if multirooted teeth
- use K file 25 similar to reciproc 25
- attach apex locator and check if it remain in green, check tuck back sensation
- irrigate with activation using manual dynamic irrigation; GP cone towards CWL inwards and outwards
- go through 3% NaOCl for 10 mins
- 17% EDTA 10 mins
- final rince of NaOCl
- try master cone and feel tuck back
Obturation
- dry with paper point until dry
- coating with sealer into canal CWL
- use B spreader to check if accessory cones are needed
- SuperEndo- alpha to separate the GP
- endo plugger and plug to coronal aspect
- ensure well condense, just below level of orifice
- place Vitrebond before perm restoration
