Instrumentation of the root canal system Flashcards
What is the function of instrumentation
• It removes infected soft and hard tissue
• It gives disinfecting irrigants access to apical canal space
• It creates space for the delivery of medicaments and subsequent obturation
It retains the integrity of radicular structures
What is the function of the chemical preparation
Irrigate to kill microorganisms
Remove the smear layer
What is the function of the mechanical preparation
Prepare shape
Allows irrigant to flush out debris and microorganisms
What are the chemomechanical aims
Shape the canal
Allow delivery of sodium hypochlorite to working length
Create a shape that makes it easier to obturate
What are the challenges of root canal preparation
• The root canal system is very complex which can make it difficult to get the irrigant there
• The number, length, curvature and diameter of canals can vary considerably
Vertucci’s classification shows this
What is the estimated working length
○ Length at which instrumentation should be limited
Obtained by measuring pre-operative radiograph to determine distance between coronal ref 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 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 types of instrument motions
filing reaming (warning) watch-winding balanced force motion envelope motion
What is watch winding
○ Back and forward oscillation of 30 to 60 degrees
○ Use light apical pressure
○ Effective with k files
Useful for passing small files through canals
What is balanced force motion
○ Insert file and engage into dentine with a quarter turn clockwise
○ With continued apical pressure turn the other way with a half turn anticlockwise
Do this a few times before removing file
What is the irrigation protocol
- EDTA 17% for 1 minute to remove the smear layer
- Sodium hypochlorite 3%, 30ml for 10 minutes
- Do a slow injection and do not use the thumb
Revise restorative synopsis and chemomechanical disinfection section
What are barbed broach instruments
- Used for extirpating, NOT enlarging
- Formed from a tapered round shaft by lifting up portions of metal of the shaft almost at a right angle to the shaft
- Must not engage the canal walls
- Extremely fragile instrument and will break easily if misused
- The elevated barbs engage the pulp tissue and remove it from the canal
The largest size broach which will fit freely in the canal is selected
Describe the iso color coding
○ Pink = 06 ○ Pale pink = 08 ○ Purple = 10 ○ White = 15 ○ Yellow = 20 ○ Red = 25 ○ Blue = 30 ○ Green = 35 Black = 40
Describe the iso sized instruments
○ All have 16mm cutting flutes
○ Each file is named according to its diameter at the first rake angle
○ Taper is 0.32 over the 16mm or 0.02 per mm
Diameter at D2 = apical size + 0.32mm
Describe Hestrom files
- Machined steel bank
- Used in a filing motion, cuts on withdrawal
- Good cutting efficiency but can cause iatrogenic damage, can easily separate as well
- No longer used for canal preparation
Useful for removing gutta percha or fractured instruments in cases of retreatment
Describe Reamer files
- Manufactured by twisting a tapered triangular shaft
- Cutting edges nearly parallel to long axis
- 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 may break
Describe K files
- Manufactured by twisting, or grinding a square tapered shaft
- Cutting edges almost perpendicular to the long axis of the instrument
- 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. This is repeated circumferentially until canal enlarged
Do not use larger instruments too quickly
Describe nickel-titanium alloy
- It has a high resistance to fatigue
- It has super elasticity
What is the advantage the super elasticity of NiTi
○ This means it can be strained more than other alloys before permanent deformation
○ It allows NiTi files to be placed in curved canals with less lateral force exerted
§ This means less transportation, zipping and ledging if used correctly
More centrally placed preparation in harmony with the original canal shape
What are the components of an endo rotary instrument
- Taper = diameter change along the working surface
- Flute = groove to collect dentine and soft tissue
- Leading/cutting edge = forms and deflects dentine chips
- Land = surface extending between flutes
- Relief = reduction in surface of land
Helix angle = angle cutting axis forms with long axis file
What is the advantage of NiTi vs SS
- Increased flexibility in larger sizes and tapers
- Increased cutting eficiency
- If used appropriately good safety in use
Can be more user friendly with less instruments in simple sequences
What is the disadvantage of NiTi prep
- Instrument fracture
- Expense
- Access can be difficult in posterior teeth if head of the handpiece is large or patient cannot open their mouth very wide
Unsuitable for complex anatomy
Describe S files
S1 = coronal third S2 = middle third S3 = an axillary file sometimes used to open up an orifice, can be used instead of gates gliden
