Final answer:
The most appropriate time for surgical treatment of a patient with mandibular prognathism is following the completion of growth.
Step-by-step explanation:
The most appropriate time for surgical treatment of a patient with mandibular prognathism is E. following the completion of growth.
Mandibular prognathism, also known as an underbite, is a condition where the lower jaw protrudes beyond the upper jaw. The surgical treatment for this condition, called orthognathic surgery, involves repositioning the jaws to correct the bite. Orthognathic surgery is typically recommended when growth has completed, which is usually in late adolescence or early adulthood. This ensures that the surgical outcome is stable and that future growth will not impact the results.