Husband's tooth implant screw fell out 4 weeks after procedure (had a severe infection after the implant). What are his options?

It is unfortunate that his implant failed,but sometimes this happens if an infection occurs.  Here are the options moving forward:1.  Leave the space ( not the best option).2.  Let the area heal, regraft the area with bone,  then place a new implant.3.  If you have adjacent teeth on each side of the space, you can have  a bridge placed (not the best option).  

Implants in general have a very low complication rate, success is over 90%.In your situation it is hard to tell what could have occurred during the surgery that resultedin an implant infection.  I would suggest having a second opinion by a surgeon or a general dentist with a higher degree of expertise look over your case.  It would be advisable tohave an additional CT scan to evaluate the residual bone from the original surgery.In some cases of implant failures I have seen very little damage to surrounding boneand all you may need is some healing time before a new implant is placed.  I wouldalso try not to be discouraged because success of the 2nd placement doesnt decreasebecause the first implant failed. 

Good Afternoon, I would suggest getting to a qualified dentist as soon as possible.  You have to determine what happened.  Sometimes during surgery, if not guided, the dentist can misplace the implant.  A CT scan is only the first step, the next is ACTUALLY doing the surgery guided and planned on the computer so you do not come across surprises or missteps during the procedure.  Another possibility is that the dentist "overheated" the bone during placement.  The next step is to get another CBCT and see what the bone looks like now - sometimes you can place another implant.  You may have to do a bone graft and wait or may be able to place a new implant and graft at the same time.  I would suggest to get to someone that understands guided dental implant placement and grafting and go from there.Best of Luck!