Instruments for mechanical canal preparation
Several groups of instruments are used for dentin preparation and shaping the canals.
- Flexicut file (Flexicut File): Optimal for obliterated and severely curved pathways. The triangular cross-section of the nickel-titanium or steel blank reduces the bending moment. The smooth tip without cutting edges prevents the formation of false passages and ledges.
- Hedstroem file (Hedstroem File): A highly abrasive instrument for wall smoothing and rounding of slit-shaped canals. Works exclusively with filing motions. Rotation greater than 45° is unacceptable — the cutting edges screw into the dentin, leading to fracture. In fine sizes (008–015), the edges are flattened to reduce stress.
- Rat-tail file (RASP): Features a tapered shaft with spirally notched teeth (up to 1/3 of the diameter in length). Used for loosening the walls before using reamers. The operation is performed with filing motions and minimal rotation.
Separately, machine orifice openers are distinguished:
- Type B1 (Reamer B1): A flame-shaped alloy steel bur with 4 blades. Used with a contra-angle handpiece (up to 1200 rpm) to create straight-line access.
- Type B2 (Reamer B2): A spirally twisted plate made of chromium-nickel steel. Operates in the middle and coronal thirds (up to 800 rpm). Strictly contraindicated in curved canals due to the risk of perforation.
Auxiliary arsenal and cleaning
Instruments not intended for mechanical dentin preparation include root canal broaches (Broaches). They are made of oxidized steel and replicate the shape of a pulp extractor.
- Depth gauge: A smooth cone with a rounded tip. Necessary for locating canals, checking patency, and radiographically determining working length.
- Miller needle: Has a square cross-section. Used for medicamentous treatment.
- Round needle (for cotton pellets): Equipped with notches to hold cotton, serves for drying and introducing medications.
For final cleaning from dentin chips and micro-fragments of pulp, an endodontic brush (Endobrush) is used. Its spirally arranged bristles, when rotated in the handpiece, create a vortex air flow, evenly distributing medications.
Instruments for obturation and filling
The final stage requires precise placement of filling materials. For pastes, paste carriers (Paste carrier) are used — conical spring spirals or screw-like blades. They operate at speeds up to 800 rpm. Spring models are equipped with a damper at the base to protect against breakage and prevent air embolism. Important rule: the size of the paste carrier is chosen one step smaller than the last working instrument.
For working with gutta-percha, the following are used:
- Plugger (Plugger): Features a tapered shaft and a flat (end-cut) tip. Necessary for the vertical compaction method and thermoplastic delivery. The flat end ensures adequate pressure transmission.
- Spreader (Spreader): Distinguished by a pointed tip. Used for lateral compaction of gutta-percha points against the walls, ensuring tight obturation.
Fragment removal and post placement
If an instrument breaks in the canal, specialized systems are used, for example, MEITRAC from MEISINGER. The process includes two stages:
- Trephine bur (a tube with a cutting edge): forms bone space and provides access to the fragment.
- Extractors: collet clamps securely grasp the freed fragment and remove it.
If the coronal part of the tooth is severely destroyed, intracanal posts are used. Their installation requires a strict protocol: widening the canal with a reamer, preparing the seat with a countersink, forming the bed with a calibrated drill, checking with a verifier, injecting cement with a paste carrier, and final screwing with a socket wrench.
Organization of work and length control
Treatment safety depends on accuracy. The working length is measured using a millimeter endodontic ruler, against which the instrument must fit snugly and without bending.
To fix the length, stops (silicon stops) are used:
- Elastic (rubber, silicone): May have curve direction markers, but are prone to accidental shifting.
- Metal spring stops: Free from this drawback, they sit securely on the shaft, withstanding loads up to 600 grams.
To pre-bend steel files for canal curvature, a special bender with rollers is used. Storage is organized in endodontic modules (for sterilization and organization) and endostands (with an antiseptic sponge for cleaning during work).
Briefly: answers to topical questions
What effects does ultrasound produce during endodontic root canal treatment?
Ultrasound during root canal treatment creates a cavitation effect in the canal lumen. Ultrasonic systems operate at an oscillation frequency of 20,000–30,000 Hz. A mandatory operating condition is the constant supply of irrigant and cooling. Before using vibration systems, preliminary manual enlargement of the root canal to size 20 must be performed.
What instruments are used for root canal orifice enlargement?
For widening root canal orifices, the following are used:
- Root canal orifice enlarger, type B1 (Reamer B1) — an instrument with a flame-shaped working part, designed for orifice enlargement and creating straight-line access.
- Gates-Glidden burs — a bur with a short teardrop-shaped working part on a long thin shaft.
- Peeso (Largo) reamers — an instrument with an elongated working part transitioning into a rigid shaft.
- Beutelrok reamers — types 1 and 2.
- Orifice Opener.
What methods of root canal obturation with gutta-percha exist?
The following methods of root canal obturation with gutta-percha exist:
- Cold lateral compaction of gutta-percha — filling with paste and multiple cones.
- Warm vertical compaction method — introduction of heated gutta-percha from a special syringe followed by compaction in the canal.
- Obturation with pre-heated gutta-percha outside the canal — using the Thermafil system, the OBTURA II injection system, and analogues.
- Obturation with softened gutta-percha — softened gutta-percha, including chemically softened (e.g., in chloroform), is condensed using a vertical compaction plugger.
Plugger has a flat end (for vertical pressure). Spreader has a pointed end (for lateral displacement).
Class and exam questions
Why does a Hedstrom file fracture?
Fracture is most often associated with technique violation — rotating the instrument in the canal by more than 45°. Sharp edges screw into the dentin and jam.
What is the difference between a plugger and a spreader?
A plugger has a flat end-face tip and is used for vertical condensation. A spreader has a pointed tip and is necessary for lateral compaction of gutta-percha.
What is the maximum permissible speed for a B1 orifice opener?
When working with a type B1 orifice enlarger, the rotation speed in the contra-angle handpiece must not exceed 1200 rpm to avoid perforations.
How to prevent air embolism during obturation?
For this purpose, it is recommended to use spring spiral lentulo pastes fillers, which effectively remove air when injecting paste, and also to take an instrument one size smaller than the last bur.
What else to study on this topic
- Complications when violating indications for the B2 rotary canal enlarger
- Operating principle of collet extractors in the MEITRAC system
- Mechanism of vortex canal cleaning using Endobrush
- Rules for pre-bending instruments taking into account tooth anatomy
- Algorithm for preparing the root space for a post: from reamer to verifier
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Other topics in «Chapter 3. Dental Instruments»
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