endodontic file systems – characteristics...aae endodontic case difficulty assessment form and...
TRANSCRIPT
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Endodontic File Systems –Parameters that Influence File
Characteristics
Amsterdam, 12th October 2019Janine Conde, R&D Director
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Characteristics of the endodontic file
Other influencing variables
Clinical perfomance
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Characteristics of the endodontic file
Other influencing variables
Clinical performance
• Standard indications: size, length & taper• Characterization of cross-section • Flute, pitch & helix angle• Material and heat treatments
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The standard indications: length, tip size & taper – What’s missing?
handle measuringlines active part
length
tip size
taper
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Taper: Cairo, Paris or London?
Pyramid: Constant taperISO standard
Eiffel tower: Progressive taper
Lipstick building: Regressive taper
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There is a lot of information hiding in the cross-section… • Cross-section area & core area
• Variability of cross-section along the working length• Size & shape of flutes• Off-centering• Number of cutting edges• Angle of cutting edge (rake
angle)
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How strong is my core?
• Cross-sectional area and corecross-sectional area will bedifferent depending on the shapeof the cross-section
• Ideally the cross-sectional corearea increases toward the tip
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Space for debris to reduce ‘filling’ the flutes
• Depth of the flutes• Shape Cross-section (Triangle has
more space for debris removalthan square)
• Move the center of the cross-section out of the center of the rotational axis• Leading cutting edge creates chips
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How can I see how well it will cut?
-45° cutting angle – scraping actionMore efficient with filing motion
-30° cutting angle
Negative and positive rake angle/cutting angle
+20° cutting angle – cutting actionMore efficient with rotating motionMultiple cutting edges will reduce the force you can
apply on one edge
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Flute, pitch & helix angle have a big impact
pitchhelix angle flute
• Flute: Groove between cutting edges• Pitch: Distance between the same
points on the cross-section• Helix angle: Angle between the
cutting edge and the axis of rotation
Helix angle should be variable to avoid screwing
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The tip will guide the file and enlarge the canal
• Non-cutting, partially cutting or cutting, depending on proximity of flute to the tip and cutting angle of leading edge
Non-cuttingtip
Cuttingtip
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File System – additional factor: work volume
0
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6 8 10 15 20 25 30 35 40 45 50
ISO sizes up to ISO 50+ 11%
+ 50%
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Hard and cutting or soft and blunt?
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If all canals were straight, stainless steel files would have better results than nickel-titanium
DeformationDeformation
Stre
ss
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The two main phases of Nickel Titanium
Austenitic material: stiff and elastic, willreturn to shape after bending
Superelasticmaterial Af < RT
Shape memory material Af > RT
Martensitic material: soft and bendseasily, will keep shape until heated
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The transition temperature can be modifiedto get the desired properties
Martensitic (low T, soft) phase
SE wireM-wireBlue wireGold wire
Nickel Titanium properties are influenced by heat treatment, mechanical history and chemical composition
Simplified schematic of phases in different wire types (R-phase not illustrated)
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The colour of the wire is a consequence of the titanium oxide thickness
The wavelengths of light that is reflected from the surface depend on the thickness of the titaniumoxide layer.
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Characteristics of the endodontic file
Other Influencing Variables
Clinical Performance
• Motion: Sense & speed of rotation• Torque limiting motor• Canal anatomy• Speed and depth of insertion
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Motion: Sense & Speed of rotation
• Continous rotation or reciprocating
• Increasing speed leads to highercutting efficiency but alsoincreases risk of fatigue breakage
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Torque limiting motor
• If the torque goesover a definedvalue the motorgives a sound/stops/autoreverses• Torque limit
should not have any influence on the act of shaping
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Canal anatomy
AAE Endodontic Case Difficulty Assessment Form and Guidelines
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Avoid engaging to much of the file at the same time & limit applied force
The area of engagement can be limited by limiting depth of insertion
Depending on the taper shape the area of engagement may already be predefined
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Characteristics of the endodontic file
Other Influencing Variables
Clinical Performance
• Cutting efficiency• Flexibility and torsional strength• Fatigue resistance• Screwing effect• Final shape
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The geometrical factors influencing cuttingefficiency
Positive cuttingangle
Negativecuttingangle
High offsetCenteredcross-section
Single cuttingedge
Multiple cuttingedges
increasing cutting efficiency
Deep & large flutes
Shallowand smallflutes
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Understanding cutting efficiency
• Positive cutting angle & single cutting edge -> best cuttingaction
• High offset & large, deep flutes -> best evacuation of debris
• Minimize file engagement and clean the flutes regularly
• Increasing speed of rotation of the file increases efficiency (but also risk of breakage)
• Insertion depth should be smalland force applied should belimited
Duration of wave [s]
Force [N]
Total duration to reach the apex [s]
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Flexibility & torsional strength
Large cross-sectional core area
Small cross-sectional core area
High offsetCenteredcross-section
High pitch/lowhelix angle
increasing flexibility
increasing torsional strength
Low pitch/high helix angle
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Fatigue resistance
High canal curvature
Straight canal
HeatTreatedmaterial
increasing number of cycles to failure
increasing risk of fatigue breakage
Non-HeatTreatedmaterial
Small cross-sectional area / file size
Large cross-sectional area / file size
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Screwing effect makes you feel less in control
Constant Helix angle
Variable Helix angle
High pitch/lowhelix angle
Stronger screwing effect
Low pitch/high helix angle
Positive cuttingangle
Negativecuttingangle
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Final shape
Transportation, ledges and perforation may occur if files are too stiff
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The Clinical Outcome is a Result of ManyVariables…
Clinical Performance
Other influencingvariables
Characteristics of the endodontic file
• Observable Performance• Outcome
• Canal dimensions & state• Clinicians Implementation
• Geometrical variables• Material
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Questions?