What I did has been to copy and paste the teeth and the gums from the original blender file to the blender file that I'm using and an odd thing is happened : the yellow color of the teeth and its brillance is lost,as well as the reddish color of the gums. Do you know the reason ? thanks.
Go to the render context of the properties editor. Set render engine to cycles. Scroll down to Color Management panel and expand it. Were it says view transform change from filmic to RAW. Change look to none. Change exposure to 1. Change gamma to 1.1.