The 'moon face' appearance results from downward displacement and flattening of the midface, typically seen in Le Fort I, II, and III fractures due to the involvement of the maxilla and midfacial skeleton. In contrast, a zygomatic complex fracture primarily affects the cheekbone (zygoma) without causing the characteristic midfacial flattening or swelling distributed over the entire midface. Therefore, it does not produce the classic 'moon face' appearance. The key point is that Le Fort fractures involve midfacial structural displacement, which leads to the rounded, full facial contour, whereas zygomatic complex fractures do not alter the overall midfacial fullness to the same extent.

Reference: Oral and Maxillofacial Trauma, Peter Kübler, 3rd Edition.