It's believed that Mel Gibson got a hair transplant in 2006. Back in 1985, before he got any plastic surgery, he was named the sexiest man alive! He was also voted among the top 50 most beautiful people in the world when he had his luscious locks. His hair transplant maintained and reinforced his natural hairline while also filling the top of his scalp. While he hasn't gone public with his hair transplant, it's hard to not notice the difference in the thickness of his hair.
Mel Gibson is noticeably balding in the before picture, but he magically got his hair back in the after. It's good that he left a little recession in the temporal peaks, otherwise it would look completely unnatural.