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I came to wonder this when studying language (as well as other same theme question posted just few ago). For example the word "fantastic" we use upper teeth and lower lip to produce F sound, instead of using lower teeth and upper lip, which would work as well with a small practice.

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I'd imagine I'm not the only one who just said their saying it to see if you're right. It could be something to do with the bottom teeth being set behind the top ones I suppose, you have to use energy to pull your bottom jaw forward if you're doing it the other way. Really interesting though xD –  Rory M Jun 8 '12 at 11:05
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It definitely feels like an unusual jaw movement to do it with your lower teeth. The jaw is required to laterally move forward rather than longitudinally move, which is a more common movement in terms of other vocalisations and eating. –  Ben Jun 8 '12 at 14:40
    
@RoryM Yeah, I hope nobody was looking a second ago when I was biting my lip and blowing! :) –  Daniel Standage Jun 8 '12 at 21:17
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lol, yes I found that funny experiment. But again more you do it, more natural it comes plus you may become economical with jaw movement. What is the variation of jaw placement on human skulls? Some have a different shape jaw and more in front than others. –  PHPGAE Jun 8 '12 at 21:31
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Nope. Anyhow, here's a PubMed link which should work. ncbi.nlm.nih.gov/pubmed/8035233 –  LanceLafontaine Sep 17 '12 at 0:00
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1 Answer 1

The alternative articulation, called dentolabial, is more difficult to articulate, so it is very rarely used in human language. However, it apparently is common enough in disordered speech to be allocated an ExtIPA diacritic.

The reason labiodentals are easier: Humans normally have a slight overbite.

lower lip near upper teeth

When the jaw and lips are in a "neutral" position, the lower lip is close to or touching the upper teeth, so with a small vertical movement of the jaw (together with tensing the lip) one can articulate a labiodental. Articulating a dentolabial requires moving the jaw a fair distance forward, to go around the upper teeth before reaching the upper lip. As Ben pointed out in the comments, front-back jaw movement is unusual, a less "common movement in terms of other vocalisations and eating".

Furthermore, since labial articulations are directly visible to observers, learners are especially likely to imitate others' exact articulation. Thus even though labiodentals and dentolabials sound similar, everyone in the population of speakers uses the same articulation (rather than having both articulations in free variation).

Perhaps dentolabials would instead be more common if most people were like this:

maxillary hypoplasia

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I wanted to suggest the slight overbite, but had no supporting information. Great answer! –  Daniel Standage Sep 16 '12 at 11:46
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