Ok, I’m new to the forum, excuse me for that please 
Thank you for the advises, is that the only and easiest way to do the animation ? or you think there is another way which is more efficient and less time-consuming (like the slide door animation method for example)
Another thing please, when I import the whole model of the teeth and the bracket into unreal, it opens as a single object and I cant select the teeth seperately, and if I import them separated they become scattered within the scene… I need a way to import the whole group which contains the teeth and brackets , and at the same time be able to control each tooth alone , how is that possible ?
Thanks again for all your efforts