By saying one of Toms teeth, you mean his tooth, which is singular.

By singular I mean referring to only one and not more than one. So the choice between WAS and WERE is quite simple, it must also be singular and therefore the answer is WAS.

Take this:

One of the sheep from the herd was black.

AND:

One of the sheep from the herd were black.

See what I mean?

I mean can we correct spelling ? It is Grammar and not grammer.

Next, option 1 is right. ‘One’ is in question not ‘teeth’. so it is singular. But though it is grammatically correct, it doesn’t make much sense symantically though. Why wud Tom’s tooth be loose ?

One of tom’s teeth was loose.

One and was have to agree.

TWO of Tom’s teeth WERE loose.

Reword to make this choice more obvious: One tooth WAS loose.

Thanks

Many WERE loose.