Читать книгу A Practical Approach to Operative Dentistry - Gordon B. Gray - Страница 17

A dental bur is a type of bur or rotary cutter used in a dental handpiece (see Figures 1.3 and 1.4). The burs can be made from steel or tungsten carbide or may be diamond coated. The three parts to a bur are the head, the neck, and the shank.

The heads of steel and tungsten carbide burs contain the cutting blades that remove material. These blades may be positioned at different angles to change the property of the bur. More obtuse angles improve the strength and longevity of the bur, whereas more acute angles produce a sharper blade. Additional cuts across the blades of burs were added to improve their cutting efficiency, but their benefit has been minimised with the advent of high‐speed handpieces. These extra cuts are called crosscuts.

The heads of other commonly used burs are covered in a fine diamond grit, which has a similar cutting function to blades but actually abrades the tooth structure and generates more heat.

There are various shapes of burs that include round, inverted cone, straight fissure, tapered fissure, and pear shaped burs.

Figure 1.3 A range of steel single use burs for intra‐coronal use are shown. In addition, a range of stones and impregnated rubber points are present to smooth and polish restorations.

Figure 1.4 A range of friction grip burs for intra‐coronal and extra‐coronal use. The examples shown are all coated with industrial diamond to make the surface rough and abrade the tooth structure. Similar designs are available made from tungsten carbide that will cut the tooth structure.

Due to the wide array of different burs, numbering systems to categorise them are used and include a US numbering system and a numbering system used by the International Organisation for Standardisation (ISO).

The speed at which these burs operate makes them behave very differently. A bur in an air turbine handpiece will produce a smooth cut with ease, but there will be a high pitched whine while it is operating. A slow‐speed bur may be quieter but will produce a courser cut with a lot more vibration experienced by the patient. It is important to check that the bur is running in a clockwise direction, otherwise the flutes will not engage the tooth structure.

Figure 1.5 Handpieces are held using the pen grip to exert maximum control of the instrument.

Figure 1.6 When a handpiece is substituted for the pen, maximum control of the instrument can be used.

It is important that the operator learns to control the handpieces to prevent hard and soft tissue trauma (see Figures 1.5 and 1.6). This can be prevented by mastering

 Grip on the handpiece

 Finger rest positioning on hard non‐movable tissues

The fine control of the handpiece using the pen grip requires that a stable finger rest is obtained onto immovable tissue such as adjacent or contralateral teeth or hard tissues. It is really important that a finger rest is never placed on mobile soft tissues (see Figure 1.7).