Читать книгу A Practical Approach to Operative Dentistry - Gordon B. Gray - Страница 15

The air turbine or air rotor handpiece is often referred to as the high‐speed drill because it rotates at around 400 000–450 000 rpm (see Figure 1.1). This is known as the free‐running speed, but when the dentist is actually cutting tooth structure it slows down to 250 000–300 000 rpm, and this is known as the cutting speed.

It operates using compressed air, which turns the turbine containing the bur. The first handpiece was designed by John Walsh and first produced commercially by Dr John Borden in the USA in 1950. The handpiece has two main parts:

 The body through which the compressed air and water are channelled

 The turbine that is contained within the head of the handpiece

The turbine is precision made and converts the compressed air into rotational energy. The fins arranged around its periphery are caught by the flow of compressed air and rotate the turbine within the head of the instrument. A bur is held within the central axis of the turbine, and this is then rotated as the turbine turns. The burs inserted into air turbines are known as friction grip burs. Many handpieces now have a fibre optic facility to shine light directly at the tooth being prepared.

Water is also channelled through the handpiece and sprays a mist onto the rotating bur. This has the effect of cooling the bur and the tooth being cut as well as flushing away the cut debris. It is vital that routine maintenance is performed on all handpieces to ensure they are free from abrasive particles that can cause wear in the turbine and allow it to vibrate. Nowadays cleaning and lubrication can be performed in automated machines. The use of a regular maintenance programme will greatly extend the life of these expensive handpieces.

Video 1.1