1. Esthetics, environment and the law of lip relation;Ricketts;Am J Orthod,1968
2. A balanced smile—a most important treatment objective;Janzen;Am J Orthod,1977
3. The eight components of a balanced smile;Sabri;J Clin Orthod,2005
4. The gingival smile line;Peck;Angle Orthod,1992
5. Some vertical lineaments of lip position;Peck;Am J Orthod Dentofacial Orthop,1992