Toothbrush employing acoustic waveguide

Abstract

A power toothbrush ( 10 ) is disclosed having a handle ( 15 ), battery ( 12 ), ultrasonic drive circuit ( 14 ), motor ( 16 ), control unit ( 18 ), and toothbrush head ( 20 ). The toothbrush head includes bristles ( 26 ) and a waveguide ( 24 ) that is operatively connected to an ultrasonic transducer ( 22 ). The waveguide facilitates the transmission of acoustic energy into the dental fluid to achieve improved cleaning and stain removal and improved cleaning in interproximal and subgingival regions. In one embodiment an ultrasound transducer module ( 30 ) includes a plurality of piezoelectric elements ( 32, 34 ) that may be mechanically connected in series, and electrically connected in parallel. One or more contacts ( 36 ) connect the elements, and a waveguide structure ( 50 ). An impedance matching layer ( 38 ) may be provided between the waveguide and the ultrasonic transducer module. The waveguide may be formed from a relatively soft material, for example, a polymer having a hardness between 10 and 65 Shore A.

1 . A method for improving the loosening and removal of dental plaque from dental surfaces in the presence of a dental fluid containing microbubbles having a radius R 0 , comprising:
 propagating ultrasonic waves having a frequency F 0  into the dental fluid under conditions that induce cavitation of the microbubbles in the dental fluid.   
     
     
         2 . The method of  claim 1 , comprising propagating ultrasonic waves into the dental fluid to achieve a resonance formula of F 0 R 0 =3.26, where F 0  is given in MHz and the radius R 0  of the microbubbles is given in microns. 
     
     
         3 . The method of  claim 1 , wherein the ultrasonic waves have a frequency appropriate to resonate microbubbles in the dental fluid having a diameter of between about 1 μm and about 150 μm. 
     
     
         4 . The method of  claim 1 , wherein the ultrasonic waves have a frequency between 20 kHz and 1 MHz. 
     
     
         5 . The method of  claim 1 , wherein the ultrasonic waves propagate from an acoustic waveguide extending from a toothbrush head. 
     
     
         6 . The method of  claim 5 , wherein the acoustic waveguide is acoustically coupled to an ultrasound wave generator disposed on the toothbrush head. 
     
     
         7 . The method of  claim 5 , wherein the acoustic waveguide is acoustically coupled to an ultrasound wave generator disposed in a toothbrush handle. 
     
     
         8 . The method of  claim 5 , additionally comprising vibrating the toothbrush head at a sonic frequency. 
     
     
         9 . The method of  claim 1 , wherein the ultrasonic waves have a pulse repetition frequency of from 0.5 Hz to 10,000 Hz. 
     
     
         10 . The method of  claim 1 , wherein the ultrasonic waves produce a mechanical index in the dental fluid of from 0.01 to 1.9. 
     
     
         11 . The method of  claim 1 , wherein the ultrasonic waves produce a mechanical index in the dental fluid of from 0.51 to 0.9. 
     
     
         12 . The method of  claim 1 , additionally comprising introducing a dentifrice into the dental fluid that facilitates the formation of bubbles having a diameter of between about 1 μm and about 150 μm in the dental fluid. 
     
     
         13 . The method of  claim 1 , wherein the ultrasonic waves additionally induce acoustic streaming to achieve shear stresses of at least about 1 Pa in the dental fluid. 
     
     
         14 . A method for improving the loosening and removal of dental plaque from dental surfaces in the presence of a dental fluid containing microbubbles, comprising:
 propagating ultrasonic waves into the dental fluid under conditions that induce acoustic microstreaming as a result of the action of mechanical pressure changes within the ultrasonic field on the microbubbles in the dental fluid.   
     
     
         15 . The method of  claim 14 , wherein the ultrasonic waves have a frequency of from 20 kHz to 1 MHz in the dental fluid. 
     
     
         16 . The method of  claim 14 , wherein the ultrasonic waves propagate from an acoustic waveguide extending from a toothbrush head. 
     
     
         17 . The method of  claim 16 , additionally comprising vibrating the toothbrush head at a sonic frequency. 
     
     
         18 . The method of  claim 14 , wherein the ultrasonic waves have a pulse repetition frequency in the range from 10 Hz to 10,000 Hz. 
     
     
         19 . The method of  claim 14 , additionally comprising introducing a dentifrice that facilitates the formation of bubbles having a diameter of between about 1 μm and about 150 μm in the dental fluid. 
     
     
         20 . The method of  claim 14 , wherein the ultrasonic waves additionally induce acoustic streaming to achieve shear stresses of at least about 1 Pa in the dental fluid.