The best jews-harp player I know is Lindsay Porteous from Fife.

He realized many years ago that either the front teeth or the jews harp had to go.

So he had his front teeth out to enable him to keep on playing.

There are descriptions from the nineteenth century of players having to give up because of neuralgia caused by the vibrations transmitted through the upper jaw.

The less common type where the frame is a flat plate rather than a forged rod don't need to be gripped between the teeth, but the tang can still give them a damaging whack.

The south-east Asian bamboo ones should be safe - held between the lips and no metal moving parts - but they're rather quiet.