Failure to precisely locate the IAN
and MF invites surgical insult by the drills
and the
implant itself. Such insult may cause irreparable damage to the nerve, often felt as a paresthesia (numbness) or dysesthesia (painful numbness) of the gum, lip and chin.
Read more: http://en.wikipedia.org/wiki/Dental_implant
Also, if the symptoms started when the implant was placed, maybe somehow it impinges a nerve and should be removed. Please keep me updated, this is interesting.