Instrumentation of the root canal system Flashcards
What is the purpose of instrumentation of the root canal? (4)
- Remove infected soft and hard tissue
- Give disinfecting irrigants access to apical canal space
- Create space for the delivery of medicaments and subsequent obturation
- Retain the integrity of radicular structures
What do you want to achieve when instrumenting a canal? (4)
- Get all the stuff out
- Widen it to allow you to put bleach in
- Make it easier to fill
- Keep it the same shape as before
What are the design objectives when doing RCT? (3)
- Create a continuously tapering funnel shape
- Maintain apical foramen in original position
- Keep apical opening as small as possible
What is the purpose of the chemo part in chemo-mechanical preparation? (2)
- Irrigate to kill microorganisms
- Remove smear layer
What is the purpose of the mechanical part in chemo-mechanical preparation? (2)
- Prepare shape
- Flush out debris and microorganisms when we irrigate
What is the aim of the mechanical part of chemo-mechanical disinfection? (3)
- Shape the canal
- Allows delivery of sodium hypochlorite to working length
- Creates shape to obturate
What are the possible challenges of root canal preparation? (3)
- The root canal system is very complex
- The number, length, curvature and diameter of canals can vary considerably
- Vertucci classification
What is the estimated working length?
- Estimated length at which instrumentation should be limited. Obtained by measuring pre-operative radiograph to determine distance between coronal reference point and radiographic apex then subtracting 1mm
What is the corrected working length?
- Length at which instrumentation and subsequent obturation should be limited. Obtained by the use of an electronic apex locator and/or working length radiograph
What is the master apical file?
- The largest diameter file taken to working length and therefore represents the final prepared size of the apical portion of the canal at the working length
What are the different types of motion? (5)
- Filing
- Reaming (warning)
- Watch-winding
- Balanced force motion
- Envelope of motion
Explain the ‘watch-winding’ motion?
- Backward and forward oscillation of 30-60 degrees
- Light apical pressure
Which type of file works effectively with a watch winding motion?
- K files
What is the watch-winding motion useful for?
- Useful for passing small files through canals
Explain the balances force tehcnique?
- Insert file and engage clockwise into the dentine 1/4 turn
- With continued pressure go counter clockwise 1/2 turn to strip the dentine away
- Do this 1-3 times before removing the file to remove debris and check the file
- Remove
- Clean
- Reintroduce, working your way to WL
Explain the ‘envelope of motion’ movement?
- Very important
- Remembering that in a lot of endodontic treatment you find that you can place a file in the canal in a particular way but you have to debride dentine 360 degrees round the canal - not just one wall
What is the initiate irrigation protocol for the canal? (3)
- EDTA for 17% for 1 minute
- Sodium hypochlorite 3%, 30ml for 10mins
- Slow injection, Don’t use thumb!
What is a ‘barbed broach’ used for?
- Used for extirpating, NOT enlarging
- Spiky bit of metal - can be used to get rid of bits of debris out of the root canal system
How are ‘barbed broach’ files formed?
- Formed from a tapered round shaft by lifting up portions of metal of the shaft almost at a right angle to the shaft
What MUST barbed broach files not engage?
- Must not engage canal walls
What may happen if a barbed broach file is misused?
- Extremely fragile instrument and will break easily if misused
How do the elevated barbs of the barbed broach instrument work?
- The elevated barbs engage the pulp tissue and remove it from the canal
- Use the largest size broach which will fit freely in the canal selected
What is another name for a K file?
- ISO instruments
How long are the cutting flutes of ISO instruments?
- All have 16mm cutting flutes
What is each ISO file named according to?
- Named according to its diameter at the tip
What is the taper of ISO instruments?
- Taper is 0.32 over the 16mm, or 0.02 per millimetre
What is the diameter of an ISO instrument at the end of the cutting surface closest to the handle?
- Diameter = apical size + 0.32mm
What is the cross-sectional shape of a k-reamer instrument?
- Triangle
What is the cross-sectional shape of a k-file instrument?
- Square
What is the cross-sectional shape of a H-file instrument?
- Comma (,) shaped
What kind of motion is used for a Hedstrom file?
- Used in a filing motion, cuts on withdrawal
Do Hedstrom files have a good cutting efficiency?
- Yes, have a good cutting efficiency but can cause iatrogenic damage
Are Hedstrom files still used for canal preparation?
- No
What are Hedstrom files useful for?
- Useful for removing GP or fractured instruments in cases of retreatment
How are reamers manufactured?
- Manufactured by twisting a tapered triangular shaft
What are the cutting edges of reamers almost parallel to?
- Almost parallel to the long axis
How do we use reamers to allow us to get an effective cut? (2)
- Rotated 1/4 to 1/2 turn clockwise to cut as advanced to length
- Must be in contact with the walls of the canal in order to be effective, must not bind or it will break
How are K files manufactured?
- Manufactured by twisting or grinding a square tapered shaft (square cross-section)
Why must we take care in instrumenting canals with k files, that you don’t try to put big instruments in too quickly?
- As this is how ledges form and how you can create iatrogenic problems or the file can break in the canal
What are the cutting edges of K files like?
- Almost perpendicular to the long axis of the instrument
What kind of motion is used for k files?
- Can be used in a filing motion - advanced to the full working length rotated 1/4 to 1/2 turn clockwise, and withdrawn while applying lateral pressure. Repeated circumferentially until canal enlarged
What are 2 properties of nickel-titanium alloy?
- Shape memory effect after heat treatment
- Super-elasticity
What is meant by super-elasticity of nickel-titanium alloy?
- Can be strained more than other alloys before permanent deformation
What does the super-elasticity of nickel-titanium alloys allow the files to do?
- Allows NiTi files to be places in curved canals with less lateral forces exerted
- Less transportation, zipping and ledging
- More centrally placed preparation in harmony with the original canal shape
What is the ‘taper’ of an endodontic rotary instrument?
- Diameter change along the working surface
What is the ‘flute’ of an endodontic rotary instrument?
- Groove to collect dentine and soft tissue
What is the ‘ledging/cutting edge’ of an endodontic rotary instrument?
Forms and deflects dentine chips
What is the ‘land’ of an endodontic rotary instrument?
Surface extending between flutes
What is the ‘relief’ of an endodontic rotary instrument?
Reduction in surface of land
What is the ‘helix angle’ of an endodontic rotary instrument?
Angle cutting axis forms with long axis of file
What does the ‘positive rake angle’ on an endodontic instrument do?
- Provides the active cutting action of the K3
What does the ‘wide radial land’ on an endodontic instrument do?
- Provides blade support while adding peripheral strength to resist torsional and rotary stresses
What does the ‘radial land relief’ on an endodontic instrument do?
- Reduces friction on the canal wall
What does the ‘third radial land’ on an endodontic instrument do?
Stabilises and keeps the instrument centred in the canal and minimises ‘over-engagement’
What are the advantages of NiTi versus SS instruments? (4)
- Increased flexibility in larger sizes and tapers
- Increased cutting efficiency
- If used appropriately good safety in use
- Can be more user friendly with less instruments and simple sequences
What are the disadvantages of NiTi preparation? (4)
- Instrument fracture
- Expense
- Access can be difficult in posterior teeth
- Unsuitable for complex canal anatomy
What are the 3 protaper rotary instruments?
- S1, S2 and Sx
What is the S1 protaper instrument used for?
- Used for the coronal third of the preparation
What is the S2 protaper instrument used for?
- Is for the middle third of the preparation
What is the Sx protaper instrument used for?
- This is an auxiliary file that you sometimes need to open up the orifice of the tooth (might use before the gates glidden)
What are F files?
- Finishing files
What is an F2 equivalent to?
- F2 has equivalent to an ISO 25 so 0.25mm
- All of the F files have an equivalent K file
What is the downside of F files?
- Downside of these is if have a particularly large root canal and find F5 (tip size of 0.5mm)has not engaged the dentine then perhaps you need to revert to a modified double flare technique to use a 60 or 70 ISO file to prepare the root canal
What is the protaper sequence of the files that you would use?
- K10
- K15
- S1
- (Sx)
- K10
- K15
- S1
- S2
- F1
Then if needed:
- F2
- F3
- F4
- F5
What is true reciprocations?
- This is equal clockwise/anticlockwise turning
- Mimics manual movement
What does true reciprocation reduce the risks of?
- Reduces risks associated with continuously rotating a file through canal curvatures
Does true reciprocation increase or decrease the cutting efficiency?
- Decreases cutting efficiency
What does true reciprocation require an increase of?
- Requires an increase of inward pressure
What does true reciprocation have a limited capacity to do?
- Has a limited capacity to auger debris out of a canal
What are the guidelines for rotary instruments? (5)
- Straight line access
- Cross-sectional diameter (don’t want to put too bug an instrument in too quickly)
- Root canal system anatomy
- Speed and sequencing
- Lubrication and a ‘light touch’
How would you create a glide path? (6)
- Confirm straight-line access
- Explore anatomy
- Always introduce files 10-25 to resistance only (coronal only)
- Coronal flare
- Size 10 with watch winging establish apex
- Irrigate and repeat using sizes 15 (WW) and 20 (BF)
If you get a file stuck in a canal what should you do?
- Don’t panic if get the file stuck just try to use watch winding action to get it out
When using reciproc what is the file controlled by?
- Controlled by a computer motor
Slides on the protocol for reciproc instruments in the lecture
- Go look at the protocol
Instrument separation can be due to Torsional stress or Flexural stress. What is Torsional stress and how does it cause instrument separation?
- Extensive instrument surface encounters excessive friction on canal walls
- Instrument tip is larger than canal section to be shaped (tip may lock, torque exceeds critical level)
Instrument separation can be due to Torsional stress or Flexural stress. What is Flexural stress and how does it cause instrument separation?
- Repeated cyclic metal fatigue (cannot be influenced by clinician)
What is cyclic fatigue?
- Freely rotating in a curvature
- Generation of tension/compression cycles
- Cyclic fatigue
- Failure
Want to use an aseptic technique when undergoing RCT. How can we do this?
- By placing dental dam and by the use of hypochlorite
