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Steve writes –

The Tooth Tunes Musical Toothbrush plays two minute pop song clips to help kids count down an appropriate length of tooth brushing time. Suspecting that this used a transducer to conduct the sound through the bristles and into the jaw (bone conductance) I wanted to both know for sure and see how easily it could be hacked, so I bought one and took it apart. Here are photos of that dissection. The audio IC is potted so I suspect it will be hard to change the sound which is played, but I think the transducer itself could make for a fun little toy. The sound quality is decent when the transducer is held directly against the teeth, the head, or any large, flat surface (eg: workbench).

Tooth Tunes Musical Toothbrush dissection – Link.