I need some major dental work done and I would like to find out how
much I could save by having it done outside my home country (Denmark).
To help evaluate the savings I would like to know the cost of a few
typical dental interventions in the following countries: Denmark,
Sweden, Germany, Poland and Singapore.
The "typical interventions" must include:
1) bridge 
2) crown
3) dental implant
4) Non-metallic filling

The cost comparison must include Denmark, Poland and Singapore.
Information on Sweden and Germany would be nice, but is less important
to me.

A friend of mine had done her dental treatments in Turkey. She claims
it had been at the same level as in Europe, but much much cheaper.

Perhaps you can ask the National Dental Centre in Singapore?

http://www.ndc.com.sg/ndc/CrownsBridgesandDentures.htm

http://polishmarket.com/next.php?id=10559

http://www.gymuser.co.uk/news/2004/april/story-1229.htm

I would just ask them what they will charge you........

http://polmedico.com/kontakt_e.htm

i don't know the actual money figures, but my close friends from
russia and particularly kiev have told me that dental services there
are excellent and cost literally 10% or less than what they cost in
the US and elsewhere.

The information you provided is not sufficent for an reliable answer.
It would be important to know, what kind of crown, bridge (involves
how many teeth?) implant you needed.

Thorough information about the different qualities, makes, and
subsequent cost at least for the German market is given on the site:

http://www.kisro.de

Please keep in mind that dental treatment often involves post care
activity, so choose a place, where you can return often.