An oral hygiene device having an ultrasound transducer 22 and an acoustic waveguide 24 facilitating the transmission of ultrasonic acoustic energy to fluids in the oral cavity is disclosed. Preferred ultrasound operating parameters for operation in aqueous environments and in dental slurries are disclosed. Devices may incorporate a drive motor 16 for oscillating a device head 23, acoustic waveguide 24 and one or more bristle tuft(s) 26 at sonic frequencies, and preferred sonic operating parameters are also provided. Multi-element piezoelectric transducer assemblies 30, 40, and various control and communications features are disclosed. Oral hygiene devices disclosed herein achieve improved plaque and stain removal from the teeth as well as interproximal and subgingival regions, while enhancing the user experience, massaging the gums, stimulating dental tissue, and disrupting biofilm.