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Interdental consonants are produced by placing the tip of the tongue between the upper and lower front teeth. That differs from dental consonants, which are articulated with the tongue against the back of the upper incisors. No language is known to contrast interdental and dental consonants.
Interdental consonants may be transcribed with the extIPA subscript, plus superscript bridge, as in ⟨n̪͆ t̪͆ d̪͆ θ̪͆ ð̪͆ r̪͆ ɹ̪͆ l̪͆ ɬ̪͆ ɮ̪͆⟩, if precision is required, but it is more common to transcribe them as advanced alveolars, as in ⟨n̟ t̟ d̟ θ̟ ð̟ r̟ ɹ̟ l̟ ɬ̟ ɮ̟⟩.
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. Apparently, interdentals do not contrast with dental consonants in any language.
Voiced and voiceless interdental fricatives appear in American English as the initial sounds of words like 'then' and 'thin'. In British English, the consonants are more likely to be dental.