Kucera describes the Isakower phenomenon as a regressive experience involving an aggregate of widely varied sensory impressions clustering about the mouth region. He cites clinical material to illustrate his thesis that teething makes a specific contribution to the Isakower phenomenon and a general contribution to the genesis of normal and pathological mental life. The particular significance of dentition derives from the pain experiences it introduces into an oral mode that previously was highly gratifying. Pleasure-yielding acts of the sucking phase produce only further pain and tension. In this way an early and firm link is formed between the satisfaction of libidinal and aggressive drives and painful experience. Teething represents the key situation for the origin of primary masochism: its physiological organic foundation. The ubiquity of the teething experience explains the ubiquity of a basic quantity of erogenous masochism in human behavior.