Abutment not engaging the fixture: options?

You could have a faulty implant internal threading. Call Straumann and find out if that specific implant batch had any problems.

Nothing blocking the screw hole or threads?debris?

Just curious, what was covering implant while it was healing? I imagine you had a healing abutment. What do the treads on it look like; are they cross threaded? Does the screw work without the abutment? If internal threads are crossed you may be able to chase them out with something from Straumann.

Legally one could argue that the provider should carry a tap and die set because the consequences of not being able to close the site are horrid compared to just picking up the instrument and solving a cross thread surprise.

The obvious possible problem is that something is blocking/stopping the screw engaging in the thread. I presume you have a reasonable view of the internal fitting surface. However although it sounds strange, it might be worth referring to an endodontist with a microscope to see if they could identify an obstruction. The suggestion to ring the manufacturer is also good. Often manufacturers will produce screw removal kits and in that kit is usually an internal tapping tool to clean/machine the internal thread if it has been damaged. So in your case if there is a thread problem, this type of tool might help correct the issue. Another issue could be that the implant was not true to label (ie a different size) or that somehow the internal thread is not true to label. This would be most unlikely but should be checked. Perhaps the manufacturer will supply a range of their different screws to try – just to check. It would be silly trying to diagnose from the PA you supplied (I never read too much into a radiograph) but I can “imagine” that the internal thread in one implant is narrower and not as deep as the other. But this is most likely radiographic distortion. Otherwise it will need to be up to the manufacturer to sort the issue out.

I could be wrong but the intaglio surface of the implant where abutment winter seat looks smaller than the adjacent implant that will seat. Compatibility or sizing issue?

There looks to be significant bone loss around the two implants. Are you sure you want to restore these anyway? Not sure about the long term prognosis. Maybe just remove, graft and replace.

Appears that bone on the side of the implant facing the other implant is preventing seating you will need to flap it to see the bone and remove what is preventing seating

Check for any debris inside the screw hole. Any obstruction.

going by the provided radiograph these two implants are not the same , number of threads differ and intervals , apically are different. ?? Consider better direct visualization of the internal aspects and multiple radiographs to evaluate the implants and boney healing ....

Remember when you were a kid and someone showed you two pictures that appeared almost identical and you had to determine what was different between the two. These implants are not the same. One has ten threads and the other has eight. Also the internal recess of the implants for the screw differs from one implant to the other. Also please note that on one implant there are three threads from the end of the screw recess to the apex and, on the other implant there are six. So it is possible that there is a broken screw tip in one of the implants. Please let us know the final conclusion.

Have you tried to tighten only an abutment screw into the implant channel? That is, without the abutment?

Yes , have tried to tighten only an abutment screw without an abutment and that itself is a problem. It is just rotating inside the implant.

I am of the opinion that the fixture had not osseointegrated.

The osseointegration might not work because the screw is too big for the bone. Mini implant systems might help in this case.