Dental Handpieces

Turbine handpieces: high-speed operation

This is high-speed equipment where the rotation of the working instrument is driven by the kinetic energy of gas. A stream of compressed air under pressure is supplied into the rotor head, spinning the air rotor and the collet — a special mechanism that directly secures and holds the bur.

• Speed characteristics: from 160,000 to 400,000 rpm.
• Instruments: uses exclusively diamond burs with a shank diameter strictly of 1.6 mm.
• Indications: rapid and highly efficient preparation of enamel and unaffected dentin.

Standard clinical models (featuring a characteristic angled shape) and laboratory models (straight, used in dental technician laboratories) are distinguished. To adapt equipment to the Midwest connector standard, quick connectors (adapters) are often used, for example, Unifix.

Mechanical handpieces: contra-angle and straight

Unlike turbine handpieces, these belong to the class of low-speed mechanical devices. They do not have their own turbine and are driven by external electric or pneumatic motors. The bur rotation speed here is significantly lower — from 1,000 to 40,000 rpm, ensuring high precision during operation.

1. Contra-angle handpieces. Optimal for the preparation of necrotic tooth tissues. Used in pairs with carbide burs. Instrument fixation is performed using a latch or push-button collet.
2. Straight handpieces. Attached directly to micromotors connected to the dental unit drive. The main difference is that the fixation mechanism requires burs with an absolutely smooth shank, without latch notches.

Shank features and instrument lengths

The basic principle of restorative and prosthetic dentistry states: the shank design of a rotary instrument is always strictly determined by the type of clamping device of the specific handpiece. You cannot use a contra-angle bur in a straight handpiece and vice versa. All instruments are divided into three large groups depending on the connection type: for turbine, contra-angle, and straight handpieces.

By length, they are classified into:

• Standard instruments (from 44.5 to 53 mm).
• Ultrashort (32 mm).

Some separation and abrasive discs, as well as prophylactic polishers, are produced without a built-in fastening element. To secure them in the handpiece, special mandrels are required. For a contra-angle handpiece, the disc mandrel will have a characteristic notch for the latch, while for a straight handpiece, it will have a smooth straight shaft.

Adapters and finishing instruments

In clinical practice, there is sometimes a need to use a turbine instrument at low speeds. For this purpose, adapters are used, which are installed in a straight or contra-angle handpiece. They are equipped with a locking clamp that solves two tasks simultaneously: it allows for quick instrument replacement and prevents its radial runout during operation. This also helps the clinician rationally reduce the total number of burs.

For the final processing and polishing of dental restorations, specialized polishing discs and brushes are used. They allow achieving ideal smoothness of restorations made from various materials: composites, plastics, dental ceramics, as well as noble and base metal alloys. The working part of the brushes can be made of:

• Nylon.
• Metal wire (steel, copper, or silver).

Class and exam questions

What else to study on this topic

• Classification of turbine handpieces by technical characteristics
• Structure of the rotor assembly and collet mechanism
• Types of Midwest standard quick connectors
• Features of using laboratory turbine handpieces
• Criteria for selecting polishing brush material

Other topics in «Chapter 3. Dental Instruments»

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