I have a theory about a working mandible system. It would have four separate small dowel rods cut to the length of each mandible. A wire would be connected to the end of the dowel and would run the length of the dowel. The wire for the bottom dowel rods would run up to meet the wires from the top dowel rods. The wires would go from the top mandible to the persons jaw [who would be wearing the mask] and would be fitted to a chinstrap. Every time the person would open their mouth, the mandible would open. I would attach a spring from the mandible [on the inside of each mandible] to the sintra plate that would be attached to the inside of the mask. This would make the mask close after it would open.
I priced everything around $40 USD and the items came from a local hardware store. I have everything ready, all I need is the sintra and mask.
In theory and on paper, it seems like it would work fine. On a regular latex mask, idk--different story. If animatronic latex was used to make the mask, maybe but I can't say. I never made a mask. I'm in the process of ordering a mask from Mannowar...so maybe I'll try it and see what happens.