Surgical:

Why would the cover screw / extender combination come loose?

There is the possibility, with an implant that has a lead-out bevel, that the implant can be placed with the bevel below the crest of the bone. If this were to happen, it is further possible for the crestal bone to rebound over the top of the lead-out bevel. The extender, then, would not fully seat on the platform of the implant, but would rather stop at the bone that has covered the bevel. In a case like this, the cover screw could then be tightened and it would feel like everything is seated properly. If the bone then resorbs, the cover screw and extender would become loose. When placing a implant with a lead-out bevel to the level of the bone, with the intention of using the cover screw / extender combination, Implant Direct recommends taking an x-ray to verify that the extender and cover screw are fully seated on the platform of the implant.

An additional possibility exists that, if the doctor separates the cover screw and the extender after taking them from Implant Direct’s packaging, that the extender can be placed on the implant upside down. Properly placed, the cover screw should fit inside a recess in the extender with the collar flaring outward from the top of the implant. This would also be evident if a x-ray is taken.