What is the normal seam of upper and lower teeth with retainer?

Within 3 mm. The distance between the upper and lower teeth during normal occlusion is less than 3 mm. At this time, the teeth are arranged neatly and not crowded, and the upper dentition covers less than one third of the lower dentition. Therefore, when the retainer is used for static occlusion, the upper and lower teeth are in a staggered state, and the horizontal distance between the upper and lower teeth is within 3 mm, so that the occlusal function of the teeth can be fully exerted, and then the food can be fully occluded and ground.