I have a deep dent across the top of my butt. What can help fill in the dent so I can have an even butt?(photos)

Hello dear!
Thanks for the pictures and provided information as well.
Looks like you could be a good candidate for liposuction and fat transfer, to fix your problem and improve your buttocks, and I think you'll get very good results. 
l recommend you to make an in-person consultation with a board certified plastic surgeon for a proper answer and to talk about your goals and anything you need to know.
Good luck :)

From your photos, it is difficult to tell if liposuction of the pre-sacral area alone would solve your issue, or if liposuction with fat transfer would be optimum.  I recommend being seen in person so you can be evaluated and discuss your options & desires.

You need a combination of liposuction and fat transfer to get the best result. I could not see your lower back area but you might could use some lipo there also to enhance the final look of the buttock. See a surgeon that has experience with lipo and fat transfer. Good luck.