What, preventation does not exist? True. Neither does the adjective preventative. Please.
The correct form is "preventive". Do not believe those that say that they are equally acceptable. Preventive, as in "preventive medicine", is correct. Preventative is tolerated (not by me, really) just because it has become so widespread, but it is not correct. The fact that many people use it does not make it right, just like the fact that many people use "it's" does not make it a possessive adjective.