A dental implant crown goes over a metal post which extends out of the implant into the mouth. The dental restoration itself is made of the same materials as a regular dental crown restoration, however, there are significant differences in how the two are designed. The final bite on this restoration should be constructed to avoid side to side shaking of the implant.
A dental implant crown must be designed to encourage up and down biting forces. An dental implant supports up and down biting forces very well but can not deal with shaking forces. It's like a fence post, when you push down on a fence post it resists the pushing but when you shake a fencepost it gets loose. Any biting motions that are from side to side can be harmful. When placed in the back of the mouth, the restoration must be relatively flat so that when the patient chews side to side, it doesn't catch and shake.
The most difficult dental implant crown is most certainly in the front of the mouth in the smile. The primary challenge is the junction between the metal post and the crown. Because of bone loss, many implants are not in ideal positions but the final restorations have to look natural. With a high smile line that shows a lot of teeth and gums, the show of the metal post at the gum line can be quite ugly. Some of this problem can be avoided by having one implant dentist place the implant and do the post and final restoration. When several doctors are involved, the planning can become more erratic.