Interdental consonants

Interdental consonants are produced by placing the blade of the tongue (the top surface just behind the tip of the tongue) against the upper incisors. This differs from a dental consonant in that the tip of the tongue is placed between the upper and lower front teeth, and therefore may articulate with both the upper and lower incisors, while a dental consonant is articulated with the tongue against the back of the upper incisors.

Interdental consonants may be transcribed with both a subscript and a superscript bridge, as, if precision is required, but it is more common to transcribe them as advanced alveolars, for example.

Interdental consonants are rare cross-linguistically. Interdental realisations of otherwise dental or alveolar consonants may occur as idiosyncrasies or as coarticulatory effects of a neighbouring interdental sound. The most commonly occurring interdental consonants are the non-sibilant fricatives (sibilants may be dental, but do not appear as interdentals). Apparently, interdentals do not contrast with dental consonants within any language.

Voiced and voiceless interdental fricatives appear in American English as the initial sounds of words like 'then' and 'thin'. In British English, these consonants are more likely to be dental.

An interdental occurs in some varieties of Italian, and may also occur in some varieties of English, though the distribution and usage of interdental  in English are not clear.

In most Indigenous Australian languages, there is a series of "dental" consonants, written th, nh, and (in some languages) lh. These are always laminal (that is, pronounced by touching with the blade of the tongue), but may be formed in one of three different ways, depending on the language, on the speaker, and on how carefully the speaker pronounces the sound. These are interdental with the tip of the tongue visible between the teeth, as in th in American English; interdental with the tip of the tongue down behind the lower teeth, so that the blade is visible between the teeth; and denti-alveolar, that is, with both the tip and the blade making contact with the back of the upper teeth and alveolar ridge, as in French t, d, n, l.