Failed immediate implant: thoughts?

Authors

I placed a 3.75x13mm implant immediately after extraction. I used 45Ncm on insertion and achieved primary stability. I grafted with TCP (Beta-tricalcium phosphate). The healing period was uneventful. The patient is a heavy smoker (cigars). After 4 months, I tried to manually unscrew the cover screw and the implant unscrewed with it. What are your thoughts and recommendations?