L20. Instrumentation of the Root Canal System Flashcards
What is the purpose of instrumentation of the root canal?
- Remove infected soft and hard tissue;
- Creating space for irrigants to access apical space;
- Creating space for medicaments and subsequent obturation;
- Retain the integrity of radicular structures.
What are Herbert Schilder’s design objectives?
- Create a continuously tapering funnel shape;
- Maintain apical foramen in original position;
- Keep apical opening as small as possible.
What is the apical foramen?
An opening at the apex of the tooth where the nerves and blood enter to supply the pulp
What are the risks of over enlarging the apical foramen?
- Extrusion of irrigants into the periapical tissues;
- Effecting the long-term prognosis of the tooth (harder to create an apical seal).
What are the chemical aims of chemomechanical disinfection? [irrigation]
- Kill microorganisms;
- Remove smear layer.
What are the mechanical aims of chemomechanical disinfection? [filing]
- Shape the canal;
- Allow delivery of NaOCl to working length;
- Create shape to obturate.
Why is it important to consider a minimum apical diameter during preparation of a root canal?
To deliver NaOCl to complex structures within the root canal system
What is the estimated working length?
- Maximum estimated length at which instrumentation should be carried out;
- Obtained via pre-operative radiographs (distance between coronal reference point and apex -1mm).
What is the corrected working length?
- Length at which instrumentation and subsequent obturation should be carried out;
- Obtained via electronic apex locator and/ or working length radiograph.
What is the master apical file?
The largest diameter of file taken to working length (therefore represents the final prepared size of the apical portion of the canal)
What are the different types of file motions used in endodontics?
- Filing;
- Reaming (warning);
- Watch-winding;
- Balanced forced motion;
- Envelope of motion.
What is the watch winding technique?
- Back and forward oscillation of 30-60 degrees;
- Light apical pressure;
- Effective with K files;
- Useful for small files.
What is the balanced force technique?
- 90 degrees clockwise;
- Apical pressure;
- With continued pressure, 180 degrees anticlockwise;
- Do this 1-3 times;
- Effective with larger K files and protaper files.
What is the envelope of motion technique?
360 degree rotation around the canal
What’s involved with a modified double flare technique?
- Balanced force;
- Step-back.
What are proper instruments made from?
Nickel titanium
What are barbed broach instruments used for?
Extripating pulp/ materials from the root canal, not to be engaged with canal walls
What is the ISO colour code?
- White (15, 45);
- Yellow (20, 50);
- Red (25, 55);
- Blue (30, 60);
- Green (35, 70);
- Black (40, 80).
N.B. up in 5s but no 65 or 75
What length of cutting flutes do ISO-sized stainless steel instruments have?
16mm
What are Hedström files used for?
GP removal in cases of retreatment (filing motion, cuts on withdrawal)
[can also be used to remove fractured instruments]
Describe the shape, use and angle (to the long axis) of a reamer instrument.
- Triangular cross-section;
- Cutting edge is almost parallel to long axis of instrument;
- Rotated 1/4 to a 1/2 clockwise;
- Cuts as it is advanced.
Describe the shape, use and angle (to the long axis) of a K-file instrument.
- Square cross-section;
- Cutting edge almost perpendicular to long axis of instrument;
- Used in filing or balanced force motion;
- Withdrawn while applying lateral pressure.
What are the advantage of nickel-titanium instruments over stainless steel?
- Superelasticity of Niti;
- Higher resistance to fatigue;
- Better cutting efficiency;
- Good for curved canals without exerting too much lateral force (leading to ledges).
What are the disadvantages of nickel-titanium instruments over stainless steel?
- Can still fracture (usually operator’s fault!);
- Expense;
- Difficult to access posterior teeth;
- Unsuitable for complex canal anatomy.
What is the sequence of protaper files?
- S1 (purple), coronal third;
- S2 (white), middle third;
- Sx (orange), auxiliary orifices;
- F1 (yellow), 0.20mm tip;
- F2 (red), 0.25mm tip;
- F3 (blue), 0.30mm tip;
- F4 (black), 0.40mm tip;
- F5 (yellow), 0.50mm tip.
[S: shaping, F: finishing]
What is true reciprocation, with regards to filing motion techniques?
Equal clockwise and anticlockwise rotation
What type of access should be created when using a rotary instrument? (Gates Glidden/ protaper)
Straight line access
What guidelines must be considered when using a rotary instrument?
- Straight line access (so files don’t go in at too steep an angle);
- Cross-sectional diameter (don’t put too big a instrument into canal too early);
- Root canal system anatomy;
- Speed and sequencing (torque);
- Lubrication and a ‘light touch’ (don’t drive instrument into tooth).
Why is it important to create a glide path?
- Confirm straight-line access;
- Explore anatomy (w small K file);
- ISO-10, watch winding technique and appropriate irrigation;
- Repeat with ISO-15 and 20.
What motion is used in RECIPROC instrumentation (controlled by computer)?
- Like balance force;
- 150 degrees anticlockwise;
- 30 degrees clockwise.
What are the three RECIPROC file sizes?
R25, 40 and 50
What is latency filing?
Use of a small file to just pass through the apical foramen to maintain communication with periapical tissues
What is cyclic fatigue?
- Generation of tension/ compression cycles;
- Leading to fatigue;
- Eventually failure.
Describe the progress to the plastic phase, through torque.
- When an instrument binds, exerted to torque;
- Elastic phase (up to elastic limit) where stress is reversible;
- Elastic limit at 400 degrees;
- After this is the plastic phase where instrument starts to deform;
- The more stress applied, the more likely it is to fracture.
