Yes,but as Kent said,you need to add the oral cavity. Without it,the character is just mute or a statue.
Yes, there's plenty of situations where an animation-ready character does not need speak. For example this character could be in a fight sequence where only a black open mouth (no oral cavity) is needed for simple facial expressions barely discernible through motion blur. Mouth cavities with teeth are a lot of work and I only add it when absolutely necessary.
ffnafhdr I'm gathering that you want a chapter about modeling a mouth cavity?