Healing Abutment Does Not Unscrew: Safest Way to Remove It without Damaging the Implant Threads?

I torqued down a healing abutment at 15Ncm at 2 weeks after uncovery. I have not been able to unscrew the healing abutment in order to proceed with the impression coping. (Source: Dental Implants Discussed by Experts)
MedWorm: Dentistry