Presented at the 1977 biennial meeting of the Angle Society, October, 1977.

From the Department of Orthodontics, Univ. of North Carolina.

From the Department of Anatomy, Faculty of Medicine, University of Toronto. This study was made possible by use of material from the Burlington Orthodontic Research Centre, Faculty of Dentistry, which was supported by Grants (No. 605-7-299 and 605-7-733) National Health Grants (Canada) Programme.

From the School of Dental Medicine, University of Pennsylvania, Philadelphia, Pa.

From the Departments of Orthodontics and Occlusion, School of Dental Medicine, Tel Aviv University, Ramat Aviv, Israel.

From the Department of Periodontology and Orthodontics, University of Gothenburg, Gothenburg, Sweden.

This investigation was supported by NIH research grant number DE 02668 from the National Institute of Dental Research and by NIH grant number RR 05333 from the Division of Research Resources.

From the UCLA School of Dentistry, Los Angeles, California.

The Third Edward H. Angle Memorial lecture, read at the biennial meeting of the Angle Society, Lake of the Ozarks, Missouri, October 1077.