Root Canal Orifice Openers

Instruments for working with materials and modelling

In prosthodontics and orthodontics, a wide range of devices is used to create models and work with wax, plaster, and impression materials.

• Spatulas: available with a single-sided flat working part, as well as double-sided with a curved surface.
• Plaster and impression knives: designed for trimming polymerized material and removing excess plaster. Plaster knives have a rigid blade and a metal plate at the end for opening flasks. Lancet-shaped and disc-shaped instruments are used for processing impression materials, allowing the silicone to be cut and drainage grooves to be made.
• Wax knives: used for portioning and thermal processing of wax. They feature a cutting part (blade) and a spatula. The handle is made of thermally insulating material, as the instrument requires heating over a burner. The working part can be flat or feature a depression.
• Carvers: specialized cutting instruments for the final processing of wax patterns, ceramics, and plastics. Le Cron and Bielle carvers are the most demanded.

Impression trays

These instruments are used for the intraoral application of material to obtain a negative imprint of the prosthetic bed. The framework is made of metal or plastic, replicating the anatomy of the jaw.

Trays are classified by size (for children, adults, narrow jaws) and purpose (standard, for functional impressions, for edentulous jaws, for jaws with distal extension defects).

Main types

1. Perforated trays: multiple openings facilitate the escape of excess material and its mechanical retention upon removal from the oral cavity.
2. Non-perforated trays: feature a smooth surface and a bordering retention rim. They are significantly easier to clean and sterilize.
3. Segmental trays: used when it is sufficient to capture only a local area of the dentition (anterior or posterior). Non-perforated variants are mostly used for posterior regions, while perforated ones are used for anterior regions.
4. Customizable / split trays: used in implant prosthetics (double impression technique). A channel is formed in the primary impression (using a bur or punch), which is filled with wash material to secure the impression copings.

Instruments for debonding prosthodontic appliances

Specialized forceps, elevators, and crown removers are used to remove cemented prostheses.

Prosthodontic crown forceps Equipped with diverging beaks. Retention grooves, sintered diamond grit, or rubber pads are applied to the inner surface. This prevents slipping and protects the veneer of crowns from scratches. S-shaped forceps are used for the upper jaw, while those bent on the edge or flat are used for the lower jaw.

Crown removers

• With direct force transmission (e.g., Treymann): used for weak retention, transmitting manual force directly.
• With an active mechanism: Copp's crown remover (spring-loaded) exerts excessive single-impact force, which can deform the prosthesis. Instruments with a sliding weight are safer as they allow the impact force to be controlled.

Prosthodontic elevators The flattened working part is inserted past the gingival margin of the crown. Force is transmitted by rotating the handle. They are available as anterior, lateral, and universal (cross-shaped) types.

Instruments for tooth extraction (surgical forceps)

Forceps for tooth extraction operate on the lever principle. They consist of beaks (for grasping), handles (for hand fixation), a hinge (joint), and sometimes an intermediate shank. To prevent slipping, the beaks have grooves or a diamond coating, and the handles have a knurled surface.

Classification by extraction target:

• For roots: in the closed position, the beaks meet completely, ensuring a secure grip on the narrow root remnant.
• For teeth with preserved crowns: the beaks do not meet, leaving a gap depending on the anatomical width of the tooth.

Anatomical modifications:

• Upper jaw: straight forceps are used for incisors and canines. Forceps with an obtuse beak-to-hinge angle are used for premolars and molars. Bayonet instruments with elongated handles are used for third molars.
• Lower jaw: beaked forceps (bent on the edge) are used. For restricted mouth opening, forceps bent on the flat are used.

What else to study on this topic

• Prosthodontic micrometer: principles of spot material correction
• Occlusal lock and articulating paper forceps: registering contacts
• Solder tweezers (reverse-action tweezers): holding components during thermal processing
• Anatomical differences of extraction forceps for each jaw quadrant

Other topics in «Chapter 3. Dental Instruments»

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