Final answer:
The appropriate mouth closure method without authorization is needle injector closure, involving the use of a needle injector tool that secures the jaws together.
Step-by-step explanation:
When no authorization has been obtained for a mouth closure method after a person's passing, the most appropriate technique to use is c. Needle injector closure. This method involves the use of a needle injector tool that inserts a barbed wire or pin into the maxilla and mandible, securing the jaws together. It is a common procedure in mortuary science and is considered acceptable when other forms of authorization for more invasive procedures, like suture closure, cannot be obtained. The injector delivers a special adhesive that holds the edges of the wound together, allowing it to heal properly.