I recently placed an implant in #21 site in a 65 year old patient. I took a CT scan and had a surgical guide stent made. My plan was to place the stent and do a flapless procedure. However when I placed the stent, I felt something was off. I laid a horizontal flap and saw that my initial penetration and implant placement had been way off to the lingual. I corrected the position and angulation of the implant. During the procedure I noticed that the floor of the mouth was rising and suspected I had severed an artery and there was a sublingual hemorrhage. I was able to control the hemorrhage with pressure and the swelling gradually subsided. Can anyone give me some insight as to what might have happened here?