My guess is that the dent below the lip is probably a type of suture pucker, especially so in the following circumstance:
Incision inside the mouth to perform the genio where what was detached to do it had to be re-attached (sewn back up) but where (some of) the sewing went into (some) superficial tissue. Basically, suturing back the tissue needs to be really deep to the tissue (periosteum) directly over the bone. If the needle used to suture the periosteum back up catches on to a piece of soft tissue superficial to that, it might leave an indent.