Occlusal fissures, in human as well as other mammalian molars and premolars, are normal structural characteristics. They result from early retardation of amelogenesis in predetermined areas between the cusps, and from relatively pronounced development of enamel in the immediate periphery of these areas. There is no justification for the common assumption that fissures are defects or faulty formations, since fissures occur regularly and normally in perfectly formed molars and bicuspids in prehistoric men, and in recent primitive as well as civilized races. High incidence of caries in fissures in modern man does not prove that fissures are ” defects.”
Reference: J. Am. Den. Assoc., 22, 1131, 1935.