Interdental

From KneeQuickie

Interdental consonants are those articulated with the tip of the tongue protruding between the two sets of teeth; the term is therefore equivalent to laminal dental.

No known language has phonemic interdental consonants; however, in many languages dental consonants, such as /θ/ and /ð/ in English, are optionally pronounced interdentally.

In the IPA and X-Sampa, the recommended way to transcribe interdental fricatives is to add the "dental" diacritic to the symbols for the dental fricatives: /θ̪/, /ð̪/ (X-Sampa /T_d/, /D_d/). An alternative, which would also work for consonants other than fricatives, would be to use the "laminal" diacritic: /θ̻/, /ð̻/ (X-Sampa /T_m/, /D_m/).

Z-Sampa has a diacritic specifically for interdental and bidental sounds, /_t\/. If this diacritic is used with the symbol for any coronal consonant, an interdental is meant. (Note that this allows one to distinguish between the interdental spirants, /T_t\/ and /D_t\/, and the sibilants, /s_t\/ and /z_t\/.)