Open embrasures or “black triangles” are usually thought of as a gingival problem, but the papilla is only half of the potential problem, since inadequate contact length can also account for the open embrasure. We must determine whether the open embrasure is the result of inadequate papilla height, or inadequate contact length to understand how to correct the problem.
The easiest place to start is to evaluate the papilla level in the location of the open embrasure and compare it to the adjacent papilla levels. If all the papilla are at the same level, and the adjacent gingival embrasures are closed, you know you have a problem of contact length creating the open embrasure. If the papilla in the site of the open embrasure is apical to the adjacent papillae, then a radiograph should be taken to determine if in fact there is a papilla problem secondary to bone loss.
When you have a patient whose contact between the two centrals doesn't extend far enough apically, it's telling you that the contact length needs to be altered in order to be successful in treatment. Contact length problems have two fundamental etiologies that you need to be aware of.
Root angulation: Anytime the roots of central incisors diverge, the contact is going to get shorter and shorter by nature. You always want to look at root angulation as a potential reason for the short contact. For instance, if you take two central incisors and spread the roots apart, your contact will have no choice but to move all the way up to the incisal edge causing a wide-open gingival embrasure. These problems are very difficult to solve without orthodontic correction to properly align the roots.
Tooth shape: Teeth that are too tapered in their tooth form are always a potential cause of open gingival embrasures. If you have parallel roots, and a very short contact, your patient probably has teeth that aren't rectangular enough to extend the contact up to the papilla. If this is the case, the issue can be addressed either restoratively or sometimes orthodontically.