Mouthplate

Instead of regular human facial features, some Transformers have what looks like a plate affixed to their lower jaw, usually covering up to their nose. While no official name exists for these, they are usually called 'mouthplates ' or 'faceplates' (despite a 'regular' face once being described as a faceplate in the TV series). Two of the most famous examples are those of Optimus Prime and Soundwave.

Often, a Transformer's mouthplate moves when they speak, as if there were a working jaw underneath.

Certain Transformers who sport mouthplates do have regular mouths underneath. Sometimes these mouthplates are even retractable, either in full or partially, to reveal their mouths.

Generation 1
Optimus Prime featured a prominent mouthplate in both cartoon and [[toy form (as do all other G1-based toyline versions). The 20th Anniversary figure featured a mouthplate that was movable via a button on the back of his head that slightly lowered the spring-supported mouthplate to recreate the talking action seen in the cartoons.

Soundwave had a similar mouthplate, but no apparent nose (whether any of his assumed face is visible or not is debatable, considering how visor-esque his eyes are). Like Optimus, both his cartoon and toy form had the mask. No toys have yet been made with a moving mask feature.

Wheeljack's mouthplate was unique in that it was fixed, even in the cartoon. Instead of a movable mouthplate, you knew Wheeljack was speaking because his "ears" flashed.

Many early toys had mouthplates that were simply disregarded in favor of mouths in fictional appearances (barring the occasional toy-accurate rendering). Bumblebee in particular had a mask in toy form, but not in cartoon or comic form. A rare reissue of the toy features a cartoon-accurate face, however, as do most toys of him since. Conversely, as Goldbug, he featured a mask in both cartoon and toy form.

On the other hand, Dead End and Superion have a faceplate on the cartoon even though their toys have mouths.

Hot Spot sometimes has a mouthplate and sometimes he doesn't.