Same page but appearing in Google with different titles

[Bio-RadAbs]

I have a page ranking on position 1 for a key phrase. The key phrase is the title of the page as well.

I'll use a mock key phrase to aid my question  - "Teeth and Gums"

So the page is ranking number 1 for "Teeth and Gums" and "Teeth and Gums" is the meta title.

However, I went ahead and did a new search adding an additional keyword to the original search.

When I did a new search adding an additional keyword to the original search, Google has done something weird..

Let's say the search is "Dentistry - Teeth and Gums", Google has ranked my page again as number 1 but changed the title.

The title in the search result is now "Dentistry - Teeth and Gums"

How and why? It's kinda like Google PPC's keyword insertion but the title hasn't got anything weird like {KeyWord: Dentistry}. It's just "Teeth and Gums"

Has this happened to you guys? Any ideas?

[TomRayner]

This is something that was first talked about around February 2011.  SearchEngineWatch provided a great insight into how and why it was happening, which I'd highly recommend reading through.

[Bio-RadAbs]

That explained it, thanks Tom

[TomRayner]

No problem, glad to have helped and hope it's not too much of a frustration for you!

[Bio-RadAbs]

Well, i'm ranking for both so it's all good

However, it has given me an insight to review the keywords driving traffic and amend the page title to a much longer one.