The voiceless bidental fricative is a rare consonantal sound. The only natural language known to use it is the Shapsug dialect of Adyghe, where it appears as a variant of /x/.^[1] People with hypoglossia (abnormally small tongue) may use it for target /s/.

Features

Features of the voiceless bidental fricative:

• Its manner of articulation is fricative, which means it is produced by constricting air flow through a narrow channel at the place of articulation, causing turbulence.
• Its place of articulation is bidental, which means it is articulated with the lower and upper teeth pressed together.
• Its phonation is voiceless, which means it is produced without vibrations of the vocal cords.
• It is an oral consonant, which means air is allowed to escape through the mouth only.
• Because the sound is not produced with airflow over the tongue, the central–lateral dichotomy does not apply.
• The airstream mechanism is pulmonic, which means it is articulated by pushing air solely with the intercostal muscles and diaphragm, as in most sounds.

Occurrence