Hormones with Ovaries??

This may be a stupid question but I'm hoping someone here will know.

I had a total hysterectomy and he took my tubes but left my ovaries. So my understanding was that I wouldn't need any hormone replacement. Then when I picked up my prescriptions, on week 3, I'm supposed to start using a vaginal cream(Estrace).

Does anyone know if this is something I'll just use for awhile or is this a permanent thing?

From what I found on web MD, it's only for about 3 mo.

My Dr recommends Estrace to be continued for life. He says it helps with vaginal health, to help prevent dryness. He says that the amount of estrogen in it is low and it stays in that area and doesn't get into the bloodstream.