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