favor of the authors' views and arguments for the feasibility and probability of accepting or rejecting the often diverse opinions, while the reader was referred to the already existing literature for factual details. Since 1936, however, factual details ofthe structural biology of the periodon­ tal tissues, i. e. their development, structure, function, and physiology, have been greatly extended and have been internationally accepted. With much less opin­ ionated belief to cope with, this knowledge has formed the solid foundation upon which diagnosis, prevention, and treatment in the fields of clinical perio­ dontology, modem orthodontics, and re- and transplantation procedures of teeth have been built.