Okay, I found the problem, as no one answered, I will leave the solution for this here, it’s very simple, but it can pass totally unnoticed, before combining every object (body, tongue, teeth, eyes…), you need to set a material for each one of them, exemple: lambert 1, lambert 2, lambert 3…Then combine them.
PS: it was quite interesting, as I couldn’t find this detail anywhere in my search.
PS 2: I hope this information would help you.