Ultrasonic cleaning agent is mainly vibration water bath. The motion of a liquid in its fuel tank is made by a high frequency transducer.
The actual cleansing actions produced by these units are due to the following phenomena.
One is the water bath solution, because it is driven by the surface of the denture. (of course, even the "sound" unit has created this benefit to some extent. See below.
The other is the "scrub" movement, produced by the rupture of tiny bubbles formed by the intense (ultrasonic) agitation of the solution. When they break up (a process called "cavitation"), they produce small but powerful shockwaves that can relax and clear debris on the surface of the denture.
