#D3/S2/W3
#Endo
Canal preparation

• shape of instrumentation provides vehicle for irrigation, medication and obturation
• unshaped canal cannot be cleaned or filled
• files shape and irrigants clean (chemo + mechanical debridement)

Why tapering canal preparation?

• 
• removal of microorganisms and pulp tissue
• allow penetration of irrigants and medicaments
• allow compaction of high quality root filling
• reduce impact on root strength

Technical goals

• tapering funnel from access cavity to apical foramen
• maintain path or original canal and avoid iatrogenic damage
• create sufficient space for irrigation and medication
• strategiccally conserve dentine to facilitate long-term tooth function
• apical foramen kept as small as practical

Traditional techniques

• traditional stainless stell techniques can result in excessive coronal dentine removal
  • predispose to tooth fracture
  • gates-glidden use for coronal flaring lead to increase in subcrestal fractures
    

Canal transportation (technical inadequacy with stainless steel)

• stiff instruments straighten during canal prep
• overprepartion of outer wall (apical third) and inner wall (middle/coronal third)
• transported canal has hourglass shape
• 
• associated complications
  • compromised cleaning
  • obturation with poor apical density/seal
  • perforation (apical or strip)
  • ledging
  • excessive removal or radicular dentine predisposes to root fracture

Nickel titanium files

• extremely flexible alloy
• permits manufacture of rotary instruments with greater taper
• conservative coronal flaring
• smoothly tapered canal shape
• permits enlargement to greater apical sizes with no/minimal apical transportation
• predictable shape facilitates obturation
• 
• Size and Taper
  • 
  • #30 is .3mm
  • taper is % of a mm per mm from the tip
  • most files have cutting surface of 16mm
  • 30/.04 = #30 4% taper
  • apical preparation to .3-.5 improves access for irrigants apically
  • larger apical enlargement may reduce tooth fracture resistance
• Better clinical outcomes with rotary NiTi
  • significantly higher healing rate and lower incidence of procedure errors (cheung and liu 2009)
  • good quality root filling rate significantly increase (Molander et al 2007)
  • requires fewer instrumentation sessions (Koch et al 2012)

Problems

• too expensive
  • endo files shall be single use unless cleaned by validated cleaning process
  • validated protocol using mechnical, chemical and ultrasonic cleaning
• fracture more often?
  • study indicate about the same
  • hand 1.6%, rotary 1.0%

Aetiology of NITi instrument fracture

• torsional fracture
  • tip binds while shaft continues to rotate
  • deformation precedes fracture
  • due to excessive apical pressure / inadequate glide path
  • 
• flexural fracture
  • cyclic fatigue occurs when file rotates in a curved canal
  • work hardening and metal fatigue leads to initiation surface cracks
  • file breaks suddenly without distortion
  • due to substantial file usage
  • 
• 
• Canal curvature
  • small radius of curvature reduces rotary NiTi lifespan
  • 
• number of uses
  • no correlation between number of uses and frequency of fracture
  • single overloading event is most common fracture mechanism
    • abrupt canal curvature
    • clogging of flutes
    • excessive apical force
    • operator experience
  • reuse up to 4 times does not increase fracture incidence (walcott 2006)
  • up to 10 times or 5 molar teeth (plotino 2007)
  • extensive precycling (up to 75% mean fatigue life) will significantly reduce the torsional resistance of NiTi files
• to not fracture
  • light touch only
  • ensure file always moving in canal
  • pulp chamber flooded with sodium hypochlorite
  • replace files sooner after use in narrow or curved canals
  • examine files regularly during use
• caution when
  • acess through crowns
  • sharp canal curvature, joining canals
  • isthmus region between two canals
  • patient factors - closing mouth, jerky movement, falling asleep

Effectiveness of chemomechanical preparation

• mechanical instrumentation reduced bacteria 100-1000 fold but no canals were bacteria free
• instrumentation with Na OCl reduced bacterial number by >99%, with 50% canals culture negative
• inter appointment dress (CH) further reduced bacterial numbers, 75% canals culture negative
• increased apical enlargement reduced bacterial numbers further

Research show

• morphology studies
  • apical canal is wider than 300-350 microns
  • therefore minimum apical preparation of ISO30-35 of larger
• microbiological studies
  • more bacteria removed as apical size increases
• histological studies
  • cleaner apical preparations as apical size increases
• clinical outcome studies
  • SS files to prepare to larger sizes decreased success
  • NiTi increased healing rate with larger apical sizes
  • NiTi higher healing rate with 3 sizes larger than first 2 bind

Larger apical sizes + moderate taper

• irrigant penetration
  • minimum size for effective irrigant penetration is #30 - #35 depending on taper
  • increase in size from ISO 35 to 40 result in 44% increase in irrigant volume delivered to working length

Best NiTi system

• any system or combination that produces moderate taper (~4%) and includes files with tip sizes #30 - 35 and larger
  • then consider secondary factors such as cross sectional shape and manufacturing process (affect flexibility and fatigue life)

Instrumentation Protocols

Glide path/root canal freeway

• essential prior to rotary NiTi instrumentation to prevent canal blockages, ledges, transportation
• small stainless steel hand files
• minimum size #15 / .02 SS hand file to patency
  Patency instrument
• small stainless steel hand file (#10 or #15)
• penetrates up to 1mm beyond working length
• maintains a clear canal
• clears infected debris at apical foramen
• improves delivery of irrigants into apical third
• no effect on post op pain
  Glide path (small SS hand files)
• initial negotiation #6, 8 10 15 hand files
  • precurve file
  • watch winding motion
  • short amplitude in out strokes
  • flooded canal
• use a #10 / 02 hand instrument between every second rotary instrument (recapitulation and maintain patency)
• recapitulation prevents buildup of dentinal debris
• establish working length (apex locator + radiograph)
• rework #15 / .02 SS hand file to working length
  • push pull filing of all walls (circumferential filing)
  • file until loose
    Preliminary coronal flare (preflaring)
• required if #10 or 15 does not slide to working length
• eliminates coronal and middle third interferences
• more accurate apical sizing
• orifice opener (mtwo 25/06 to 2/3 working length)
• gentle brushing action
  Conventional rotation NiTi instrumentation
• touch retract action (keep moving) in a flooded canal
  • 0.5-2mm increments, deeper with each increment
  • reduce fracture incidence
  • do not keep file stationary in one spot
• clean flutes, copious irrigation
• recapitulate with #10 hand file to maintain glide path
• 2-3 passes once at length
• no more than 1/2 rotations at the apex with any pass to prevent apical transportation

**Mtwo![[

• 
• **S shaped cross section
  • Reduced core diameter
  • Increased flexibility
  • Maintains curvature better than ProTaper, RaCe, K3
  • Greater fatigue life in abrupt apical curvature
  • Superior cutting efficiency
• 11mm shaft length
• 16mm vs 21mm working part
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• 
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Master apical file (MAF)

• largest instrument used at the working length
• may be used to determine master GP point size
• apical enlargement size considers removal of debris on root canal wall and allowing irrigants to penetrate the apex

If canal is open to greater than #40

• when canal is open to 35, irrigate can peentrate apically
• further enlargement of the cnaal is unnecessary
• circumferential filing to disrupt biofilm as much as possible
• irrigant activation
• may need to modify obturation technique

Instruments

Ideal properties

• maximum flexibility
• minimise/eliminate canal transportation
• maximum torsional resistance
• maximum fatigue resistance

Niti shape memory alloy

• 
• conventional NiTi are in austensile phase during clinical use (exert a restoring force)
• when cooled with irrigant, transforms to martensite (elastic and deformable) (doesnt exert a restoring force)
• conventional NiTi
  • preferential cutting on apical outer wall, middle third inner wall
  • zipping, elbow formation, apical transportation
• Heat treated NiTi
  • file contains higher proportion of martensite at room and body temperature (no restoring force), no shape memory and therefore no zipping or preferential cutting

Thermomechanical manufacturing of NiTi instrument

• higher martensite content alloys
  • edgefile x7, HyFlex
  • mainly in martensite phase during clinical use
  • extremely flexible
  • improved transportation dynamics
  • improved fatigue resistance
• resistance to torsional fracture was reduce (softer)
• glide path is therefore more important (dont push if file doesn't want to advance)
  

Edgefile X7

• heat treated alloy
• fixed taper instrumens .04
• maximum flute diameter 1mm
• operate at 300-500rpm, torque 2.5-4 Ncm
• smallest file 17/04
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Single file systems - reciprocation

• reciprocating files cut in a counter clockwise direction
  • reciproc F 30 deg R 150 deg
  • Waveone F 50 deg R 170 deg
• potential reduction in fracture risk due to reduced torsional stress and increased cyclic fatigue resistance
• time saving and fewer files
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