Numbness after an implant procedure is the result of nerve disturbance / irritation during the placement procedure. It can also be caused during administration of local anesthesia if the needle touches the main nerve branch (this type is temporary and usually resolves in 6-8 weeks).
The degree of nerve disturbance from implant placement and how long the numbness will last depends on the type of nerve injury. If mild and very superficial, it usually resolves in 6-8 weeks. If moderate, then partial or almost complete return of sensation may happen up to 9 months. If severe injury, then it may be long term or permanent numbness.
You should ask the surgeon who performed the procedure about any unusual findings during surgery, the length of the implant used, and their opinion. If there is concern of implant impingement on the nerve, a cone beam CT can be done to assess the position of the implant and either remove it or back it out to eliminate pressure on nerve.