Circular indentation on forehead
The indentation could be secondary to previous trauma/ localized scleroderma. If it's progressively getting deeper you may benefit from a biopsy or some form of imaging to confirm diagnosis. As far as cosmetic treatment goes, I recommend fat transfer to the forehead (may need a few sessions) to help smoothen out the contour. Botox may also help if you think the indentation is more noticeable when animated. Hope that helps.
Goretti H. Taghva MD
Why you would have a forehead indentation that has developed is not clear. But it can be treated by either a bone cement augmentation or a custom forehead implant, done through a hairline incision.