The sounds of the World's Languages. I have always called these dentilabials, using the terminology that the lower articulator comes first. I don't think they occur in normal speech, but they are known in pathological speech. John Davis Please let me know if anyone tells you of any languages with labiodental fricatives involving the bottom teeth with the upper lip. My own impression is that such an articulation would be awkward to the point of not occuring, either in fricatives or in glides.
Reasons are as follows.
In case of labiodental fricatives like f,v active articulator is lower lip moving towards upper teeth line . It is not that upper teeth line moves towards lower lips. Upper teeth line is a passive articulator. Both the teeth lines are passive articulators. Not only that even upper lip is a passive articulator and if the upper lip is used as active articulator oral cavity will be totaly closed and sound cannot be audible one.