Flow and free running speed characterization of dental air turbine handpieces

Abstract

Objectives: Dental air turbine handpieces have been widely used in clinical dentistry for over 30 years, yet little work has been reported on their performance. A few studies have been concerned with measurement of speed (i.e. rotation rate), torque and power performance of these devices, but neither investigations of functional relationships between controlling variables nor theory dealing specifically with this class of turbine have been reported. This has hindered the development of satisfactory methods of handpiece specification and of testing dental rotary cutting tools. It was the intention of the present work to remedy that deficiency. Methods: Measurements of pressure, temperature, gas flow rate and rotation rate were made with improved accuracy and precision for 14 ball bearing turbine handpieces on several gases. Functional relationships between gas properties, supply pressure, flow rate, turbine design factors and free running speed were identified and equations describing these aspects of behaviour of this class of turbine developed. Results: The rotor radius, through peripheral Mach number, was found to be a major determinant of speed performance. In addition, gas flow was found to be an important limiting factor through the effect of choke. Conclusions: Each dental handpiece can be treated as a simple orifice of a characteristic cross-sectional area. Free running speed can be explained in terms of gas properties and pressure, with allowance for a design-specific performance coefficient.