A dental handpiece is disclosed with a transducer assembly for holding a work tool which is caused to vibrate at substantially a resonant frequency by a variable frequency oscillator (20). The oscillator (20) sweeps through a spectrum of frequencies under control of oscillator control means (24). A maximum in the current flow through the transducer assembly occurs at a resonant frequency and is detected by maximum detecting means (22) which then generates a latch signal to stop the oscillator at substantially that resonant frequency. Hence the oscillator is correlated to the resonant frequency of the assembly, and subsequent changes in the loading conditions on the assembly do not affect the oscillator frequency.