I don't think pentasa is a drug that will necessarily put you in remission unless you have very mild crohn's. Typically most doctors put people through a course of steroids first, either prednisone or budesonide, two of which I know, then they put you on a maintenance medication.
It is not very common for crohn's disease patients to be on pentasa. It is equivalent to taking aspirin.
I was on pentasa for about 5 years and it did a very good job of keeping me in remission. It just eventually stopped working for me, and I ended up switching to Remicade, and it has been working just as good or even better than pentasa.