The six keys to normal occlusion were given by:
ANDREWS SIX KEYS TO NORMAL OCCLUSION
Lawrence F Andrews studied 120 casts of non-orthodontic patients with normal occlusion for four years (1960-1964). He identified 6 key characteristics.
He was of the opinion, that for normal occlusion to exist these six characteristics had to be present. According to Andrews, the 6 keys to normal occlusion contributed individually and collectively to the total scheme of occlusion and, were therefore essential for an orthodontic treatment to be considered successful.
Ref: Textbook of orthodontics Gurkeerat Singh 2nd ed page no 59
Lawrence F. A.
Angle
Lischer
Moyer