Gum is not growing over a tooth implant. Any suggestions?

The implant was placed on the same day as a tooth extraction, on March 30 2016. There is no infection or other abnormalities but the gum is not filling the site and it is still sensitive to cold. I've seen the dentists a few times with this concern, but it looks like he does not know what to do about my gum not growing back. He just replaced a healing cap with a larger one. Are there any treatments to speed up the gum growing?