Actually, I think there are some overreactions here. If the OP prefers him to shower every day, or clean his teeth twice a day, or whatever, that is one thing. If she dislikes the result of him not doing that, then that's another thing.
I don't clean my teeth every day and on the days I do it I only do it in the morning. I've never had to spend £300 on dental work so I cannot see that these two are connected. I have one small filling I got as a teenager. Mind you, I've not been to the dentist for about 7 years, only been maybe 5 times in my adult life, so if I did go maybe it would be £300, who knows.
And at weekends I don't always shower. Mind you, I don't cycle to work. I do always at least wash and I do tend to use deo (ironically unless I know I am going to be doing something physical, because actually I think it's a waste as it doesn't work anyway).
I've got to the point where I don't need to wash my hair every day, which is fantastic! I used to have to wash it daily but it has changed and now I don't need to.
It's only a fairly recent thing this obsession with washing.
OH has never suggested that I smell, in fact no one has.
The OP is a nanny, constantly telling children to wash their hands - that's fine, and it's about good habits (I am a trained nursery nurse myself) but this does not translate to telling an adult how to behave.
My OH doesn't always wash his hands, but as he says to me - he only held his willy to wee, his willy isn't dirty, he didn't pee on his hands, how is it different to holding/touching any part of his body.
I think hysteria about hygiene is unnecessary.
BUT - I do think that if the OP has preferences and her husband isn't listening to her, that's different. It's an issue of respect and consideration. That is where the issue is, not how often he showers or whether he does as she tells him when she tells him to wash his hands.