Significant vertical chin lengthening is most successfully achieved by lengthening of the bone. Downfracture of the chin bone with an interpositional graft can easily provide double digits of increased vertical chin length without soft tissue constraint concerns. Calculating how much increased chin lengthen a patient needs is not an exact science although there are several methods to do so which are helpful. But with rare exception under correction is a more likely risk than over correction.
But when the final outcome of vertical bony chin lengthening is inadequate what are the options for secondary chin lengthening? One could always repeat the osteotomy procedure and that would be the best approach if the additional lengthening needed was significant. (6mms or more) If the amount of additional vertical chin lengthening is 5mms or less adding an implant on the end of the bone would be both effective and less traumatic.
Secondary vertical chin lengthening with an implant requires a submental approach for direct access to the inferior border. The type of implant that can be used for direct application to the inferior border can be of various materials. One convenient option is ePTFE sheets which bis easily shaped, placed in layers to the desired thickness and can be secured with microscrews to the bone.
Because of the tightness of the soft tissue chin pad, particularly after vertical bony lengthening, there are limitations as to how much implant can be tolerated on the bottom end of the bone. (soft tissue closure over it) But for a few extra millimeters a secondary implant augmentation can be effective.