#D3/S2/W3
#Endo

Goals of instrumentation

chemo-mechanical debridement
goal is not to scrape every internal surface but facilitate penetration of irrigants, medicaments and adequate obturation

• instrumentation (shaping) provides appropriate shape to root canal to allow cleaning and obturation of root canal system
• with current technology unshaped canals can neither be cleaned nor filled
• root canal preparations must be appropriate length, shape, size

Working length

• need to always clean entire length of canal
• e - radiographic apex
• b - physiological apical constriction
  
• Dummer et al. 1984
• traditional constriction is only 40-50%

Chugal et al 2003

• 1mm failure of working length increases persistent disease chance by 14%

Steps to use apex locator

• after LA, RD, access, locating canals, +- coronal flare
• determine estimated WL from radiograph
• ensure stable reference point (flattened cusp)
• establish patency using hand files
• remove excess moisture
• use a #10 purple hand file
• attach lip hook and file clip
• slowly progress hand file beyond estimated working length
• once beyond apex, withdraw until long reading stops
• note down working length and reference point
• confirm with WL radiograph

Artery forceps

• get patient to hold phosphor plate, keep frame on

Clinical Case

Glide path

• smooth radicular tunnel from canal orifice to physiological terminus
• minimal size loos no.10 endodontic file
• compulsory, achievable with hand and or rotary/reciprocating instruments
• benefits
  • reduces torsional stress during root canal instrumentation with rotary instruments
  • allows for better preservation of original canal shape
    • failure to preserve the original canal anatomy is associated with post treatment endodontic disease (Gorni and gagliani 2004)

Glide path complications

• perforations, transportations
• instrument fractures

Hand files

• 
• size (#6-#25 mostly)
• length (21, 25, 31)
• taper (2%)
• repeating colours
  • pink grey purple (06 08 10)
  • W Y R B G Black (15, 20, 25, 30, 35, 40)
• D0 - D16, cutting edge
• stainless steel
  • iron and carbon mixed with chromium

K files

• square, rhomboid, triangular cross section wire twisted into shape
• stiff and strong
• approx 45% helical angle
• cut on downwards stroke
• used in watch winding and balanced force technique
  • 180 clockwise to engage dentine, 120 counterclockwise with apical pressure to shear off engaged dentine
• 
  H files
• micro-ground rather than twisted, circular shape
• more aggressive
• efficient cutting when used with quarter turn then push/pull
• will fracture if rotated when bound
• usually used for a curved part of canal or clear a ledge
• 

Technique

• hand files are standard
• #10 is suitable
• only performed once working length confirmed
• optional corone pre flare (larger tapered rotary instrument such as 25/06 m2 in coronal half only)

Why is NiTi good

• 
• fewer procedural errors
• easier to learn
• faster

Hand instrumentation

Step back technique

• prepare apex with a small instrument
• enlarge to desired size (usually #20 or #25 k file )
  • called the master apical file MAF
• prepare with larger sizes, each 1mm shorter than previous
• refine preparation shape with MAF
• often requires coronal flaring with destructive gate glidden burs to ensure straight line access
• 

Crown down technique

• opposite of step back
• large files coronally first, then small files advancing apically
• allegedly reduced debris extrusion and results in less straightening
• similar to how modern rotary/recip systems are used