For a long time I puzzled over the prevalence of buck-teeth among the younger Americans. It is a condition in which the central upper teeth protrude below (and sometimes farther out than) their neighbors. In some cases that condition is grotesque, and it reminds me of a rabbit’s teeth. I was puzzled because buck-teeth are rare among people from poor countries, and also scarce among Americans older than the baby-boom generation. That demographic fact led me to suspect that buck teeth are associated with the dietary or cultural environment of young Americans but I could not think of any specific cause. I am an avid tennis fan, and whenever a young tennis player wins a match and smiles happily in close-up camera shots, I often notice their buck teeth. My puzzlement deepened when I began to notice buck teeth in increasing numbers of players from other countries as well (but, again, only among the younger ones). The growth of teeth is fastest in infants and slows to a stop as we age; so I concluded that the surge of buck teeth phenomenon must relate to some factor of upbringing that is peculiar to affluent modern families. But what were those factors?
I looked up buck teeth online, and the mystery cleared. The condition, it turned out, is a result of malocclusion of jaws: the upper and lower jaws failing to meet properly when the mouth is closed. And malocclusion is promoted by uneven growth of teeth. In proper occlusion the growth of any tooth stops when it is hindered by the neighbors opposite or beside it; in malocclusion a tooth that encounters no opposition in its path continues to grow. The tendency of babies of affluent families to grow up with pacifiers almost constantly in their mouths even while asleep, leaves an empty or soft gap between the upper and lower jaws and the central incisors keep growing into that space. The use of baby pacifiers of course exploded into a fad with the baby-boom generation, a fad that continues till today. A baby constantly sucking the nipple of a feeding bottle (or, for that matter, its thumb) achieves the same malocclusion and buck-toothedness.