Picture books to help children prepare for treatment

[Arisaig]

DS (3) is due to have a filling, and I want to help him understand what's going to happen, how it might feel, what he can do to cope etc. Does anyone have any recommendations?

I'm trying to find something that uses metaphor (like 'The Big Bag of Worries'), so books aimed at preparing children for hospital treatment might also work. Something involving a character facing something frightening and/or painful, getting through it, and feeling better afterwards.

The Usborne first experience "Going to Hospital" is good-shows taking the gas for anaesthetic etc. It's for an ear problem, but you may be able to use it.
There's also a Mr. Tumble episode with a child having an anaesthetic too.

Thank you DeWe - I'll have a look for it. He loves Mr Tumble so that sounds good too.

Topsy and tim go to the dentist has one of them having a filing, talks through what happens and is very reassuring
The main thing I would say is you remaining calm and reassuring through out, the concept may be quite abstract until your ds is there, too much preparation might make it seem more of a bigger deal if that makes sense - for our boys operations they have always taken a teddy who has got stickers etc just like them, could he talk a teddy too?