Interdental consonants are produced by placing the tip of the tongue between the upper and lower front teeth.
That differs from typical dental consonants, which are articulated with the tongue against the back of the upper incisors.
Voiced and voiceless interdental fricatives [ð̟, θ̟] appear in American English as the initial sounds of words like 'then' and 'thin'.
Interdental approximants [ð̞] are found in about a dozen Philippine languages, including Kagayanen (Manobo branch), Karaga Mandaya (Mansakan branch), Kalagan (Mansakan branch), Southern Catanduanes Bicolano, and several varieties of Kalinga,[1] as well as in the Bauchi languages of Nigeria.
They are always laminal (pronounced by touching with the blade of the tongue) but may be formed in one of three different ways, depending on the language, the speaker, and how carefully the speaker pronounces the sound.