Reciprocating Endodontic Systems

Metal rotary instruments

Rotary instruments for targeted removal of tissues or materials are predominantly represented by burs and cutters (mills).

Carbide instruments Used for preparing hard tooth tissues and working with durable materials (titanium, precious metal alloys, ceramics, plastics, and gypsum). Cutting configurations can be straight, cross-cut, etc. The fewer blades on the working part, the more aggressive and rough the processing will be. For smooth finishing without material cracking, instruments with the maximum number of edges (up to 30) are chosen.

Steel instruments Made from alloyed tungsten-vanadium or hardened stainless steel by stamping (to create cutting edges) or milling (for complex textures). They are inferior in strength to carbide analogues.

• In the clinic: used for removing softened dentin, working with bone tissue, correcting orthodontic appliances and plastic dentures.
• In the laboratory: serve for cutting gypsum, plastics, and primary metal grinding.

To prevent thermal bone burns during surgical procedures (according to Prof. Kirschner's method), steel burs with an internal cooling system are used: fluid is supplied through a channel in the body directly to the working part via nozzles.

Abrasives and polishing instruments

Abrasive properties depend on the size of the coating grains. For diamond instruments, the grit size ranges from 8 to 180 µm (6 types according to the ISO standard, each having its own color code on the shank).

In addition to diamonds, other materials are widely used:

• Corundum grain (Al₂O₃): fixed on a ceramic bond. Used for processing metal, amalgam, acrylic. Produced as abrasives (preliminary processing) and polishers (finishing).
• Silicon carbide (SiC): the binding matrix can be ceramic, silicone, resins, or magnesite. Used for leveling and grinding restorations, enamel, and ceramics.
• Sandstone (SiO₂): on a synthetic binder. Coarse-grained stones are needed for rough processing, fine- and medium-grained silicate coatings for final polishing of composites and plastics.
• Silicone rubbers: chemically stable and non-toxic compounds (formula [-O-Si(R2)-O-]n). Silicone polishers are ideal for final processing of ceramics, amalgam, plaque removal, and enamel polishing.
• Rubber coating: vulcanized rubber for the final finishing of cobalt-chromium alloys and titanium.

There is also a group of instruments without their own abrasive layer (made of felt, fabric, polymers, bristles). They work only in combination with polishing pastes (e.g., GOI paste or diamond grit compounds).

Fabric and brush polishers

For polishing in clinical and laboratory practice, multilayer discs and rotary brushes fixed on mandrels are used.

Multilayer discs:

• Flannel: voluminous, thick, loose discs made of white fabric. Fixed via a metal core with three holes.
• Cotton (calico): layers of white fabric are thinner and more tightly compressed.
• Suede: dense structure of beige/brown leather with a single central hole in the metal core.
• Cloth pleated: white corrugated fabric around a plastic center.

Polishing brushes and felt: Made from pressed felt (filts), natural bristles (soft goat or stiff horse hair), yarn (stiff grey-brown linen, soft white cotton, wool), or wire (copper, steel, silver). They are designed for working with ceramics, metals, and plastics.

Rotary instrument shanks

The shank design strictly depends on the chuck mechanism of the dental handpiece.

1. For turbine handpieces: Smooth shank with a diameter of 1.6 mm without retention points, fixed in a chuck collet. Length varies from 16 mm (pediatric dentistry) to 30 mm (surgery). The end part can be flat or rounded (more convenient for fixation).
2. For contra-angle handpieces: Diameter 2.35 mm. Fixation occurs via a latch connection (lever mechanism). The end part is faceted with a characteristic notch (recess). Length from 15 to 34 mm.
3. For straight handpieces: Smooth shank with a diameter of 2.35 mm (sometimes 3 mm for dental laboratory burs). Held by friction force in the rotating chuck mechanism. The maximum length reaches 70 mm (in surgery).

Some instruments (separation discs, prophylactic polishers) do not have a built-in shank. They require special holders with a connection type matching the handpiece to operate. There are also adapters with a locking clamp that allow turbine burs to be used at low speeds in a contra-angle or straight handpiece.

Working part shape

The instrument shape is selected according to the relief of the treated area. The greatest variety (up to 60 types) is typical for turbine burs.

Clinical and laboratory application of basic shapes:

• Round: opening the pulp chamber, caries preparation (classes I-V), tunnel bone preparation.
• Cylindrical: with a flat end — for opening class I cavities and parallel milling; with a cutting end — for root canal orifice preparation; pointed — for shoulder preparation.
• Conical: fissure formation, safe cavity floor preparation (instruments with a rounded smooth end).
• Inverted cone: removal of old fillings and creation of retention points.
• Pear-shaped and lenticular: smoothing edges, removing fillings, processing cervical areas and plastic structures.
• Separation discs: flat — for cutting; concave — for rough contouring; perforated — for better visual control.

Class and exam questions

What else to study on this topic

• ISO classification of diamond abrasives and color coding
• Features of shoulder preparation with pointed cylindrical instruments
• Methodology for applying polishing pastes with felt and brush discs
• Specifics of separation discs: concave, perforated, and serrated-edge discs

Other topics in «Chapter 3. Dental Instruments»

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.