35, male, I have this dent in my forehead & I’d like to know what caused it? (Photo)

Hi, thanks for your question and photo. From the photo, it appears the muscles of the forehead are contracting to make that line. The lines that form here come from repetitive muscle action of the brow and forehead muscles, and are impacted by one's genetics, side sleeping, and repetitive expression movements like furrowing or squinting. Botox would be a great option to relax the size and the activity of the muscle in this complex. This area is known as the "11s", or the glabella. Hope that helps!