Systems and methods are disclosed for forming a pontic in a pontic-housing pocket of one or more polymeric shell appliances having teeth-receiving cavities. Cavities in the polymeric shell appliances corresponding to the location of a missing or extracted tooth may include a pontic-housing pocket. The pocket may be filled with a composite resin or acrylic material that hardens and presents with a similar visual appearance to a tooth, thereby presenting the illusion that there is no missing tooth. The pontic-hardening pocket may have a single opening of sufficient size for receiving a syringe for injecting the pontic material. After the material hardens and the pontic is formed, it is locked into the pocket, as it cannot fit through the single opening. As the space of a missing tooth is widened or narrowed by the alignment treatment, successive shell appliances may have pontics of successively larger or smaller size.