In our smile design process, we have learned from Dr. Dawson how to develop incisal embrasures. And also from Dr. Dawson and the American Academy of Cosmetic Dentistry, how to develop the apparent contact zone between teeth.
So between two centrals it should be 50%, a central and lateral, 40%, and a lateral and a canine, 30%.
There are times, though, where, depending on the restorative interfaces, say, for example, two implants, we cannot create an apparent contact zone that falls in those parameters. And if we want to keep the incisal embrasures developed, as Dr. Dawson's taught us, we need to have a long contact zone.