The high-speed revolution: a practical guide to friction grip burs

Since the advent of the contra-angle high-speed handpiece in 1949, dental burs have become the ubiquitous means of dental hard tissue preparation. They are extensively used in the removal of existing restorative materials and the shaping and finishing of newly placed ones. Efficient preparation of these substrates is achieved by working at high speed, that is a cutting speed of 200,000 revolutions per minute.¹ There are two types of dental handpieces that can deliver such a rotational speed: the high-speed handpiece (otherwise known as air rotor or air turbine), and the speed-increasing handpiece, colloquially referred to as the ‘red ring’ handpiece.¹ The latter instrument became more popular during the COVID-19 pandemic because it may reduce the amount of aerosol produced during use, which was thought to be beneficial in limiting the potential spread of viral particles into the atmosphere of the dental clinic.² Furthermore, its other advantages have been recognized for many years. The speed-increasing handpiece is powered by a constant output electrical motor, and so, the instrument produces a constant torque, that is, the ability of the bur to continue to rotate when placed against the substrate being prepared. This contrasts with the air turbine, which relies on the pressure of the air supply to the dental unit to power the instrument. Pressure fluctuations, especially seen in clinics housing many dental chairs operating at the same time, will reduce the torque, and therefore, cutting efficiency, of the bur driven by the air turbine compared to speed-increasing handpieces.³ Furthermore, a bur in a speed-increasing handpiece runs more truly, without the vertical displacement (‘pecking action’) that is seen with an air turbine, so increasing the potential for a smoother preparation surface¹ and reduces crack initiation in the surface of the substrate being prepared, particularly a brittle material such as dental enamel.