Toothbrushing, tooth brushing or tooth-brushing? HELP!

[BecauseImWorthIt]

It's important for work - I've written it all three ways and now none of them looks right!

I thought it would be 'toothbrushing' because you do it with a 'toothbrush' - but spellchecker doesn't like that.

TIA

Ah yes - I hate spellchecker. But given my own wobble, that little wavy red line was enough to complete the panic!

I should have thought about the BDA site

thanks