he's all teeth

[Maybo]

[...]I look up and here comes this f****ng monster dog, must have weighed a hundred and twenty pounds at least, and he's all teeth with slobber flying[...]

Source: Fairy Tale by Stephen King

Does "he's all teeth" mean the dog's showing all his teeth?

 

[teechar]

Yes, showing prominent/big scary teeth. You may want to look up "snarl".

 

[SoothingDave]

It's an exaggeration. He isn't literally "all teeth" but that is what you see and fear when you see him. Everything else is secondary.

 

[Tarheel]

Source: Fairy Tale by Stephen King

Does "he's all teeth" mean the dog's showing all his teeth?

The dog is showing its teeth, yes. But the number of them showing is irrelevant. The point is that it's menacing. The person encountering the dog feels threatened. The focus is on those teeth, which could do serious damage.

Does that help?