Looks like the original version is driven by a coil electromagnet which deflects rare earth magnets in the brush head. https://www.powerelectronictips.com/teardown-whats-inside-a-...

I am 100% unsure, but if you hold a modern Sonicare toothbrush head up to a refrigerator door the magnetism (if any) is not even strong enough to hold the head to the door. The old models had two dark-black rectangular magnets (many of which I still use to affix postcards to my fridge) and the new ones have light silver circular “magnets”. The ‘how/why’ is well beyond my scope of knowledge.