The removal and shaping of tooth structure is an essential aspect of restorative dentistry. Initially this was a difficult process accomplished entirely by the use of hand instruments. Dental handpieces and rotary instruments were developed to simplify this procedure. Even though high-tech solutions for removal hard dental tissues such as laser, ultrasound vibrations, chemical dissolution are being advocated, the use of dental bur held in dental handpieces is still a most widespread standard procedure.
DENTAL HANPIECES
The irst rotary instruments were drill or bur heads that were twisted with the fingers for crude cutting of the tooth tissue. The first dental engine to provide enough power to spin the bur with sufficient speed for tooth cutting was developed in 1871 by Dr James B. Morrison. Between 1950s and 1960s, maximum developments occurred for improvements in design, mechanical operation and speed of the handpieces.
Nowadays there are basically three handpieces
(ig. 17.1, 17.2).
1. High-speed handpiece (or turbine).
2. Low-speed contra-angle handpiece.
3. Low-speed straight hand-piece.
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Fig. 17.1. Types of dental handpieces
Low-speed handpieces need to be attached to a micromotor for working (ig. 17.3). There are two types of micromotors.
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Fig. 17.2. Dental handpieces working parts: a - head of high-speed handpiece; b - hole for bur shank at the top of low-speed straight handpiece; c - head of low-speed contra angle handpiece (note the different diameter of hole for bur shank in high-speed and low-speed)
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Fig. 17.3. Micromotor and two types of low-speed handpieces
1. Air-driven motor (or air motor).
2. Electric-driven motor (or electric motor).
DRIVING MECHANISMS
There are basically three driven mechanisms for bur rotation in handpieces: ► Belt-driven mechanism: rotary power is transferred by a belt which runs from an electric engine. Power is transferred from the straight handpiece