Interdental

Definition of Interdental

The literal definition of interdental is between the teeth. Interdental consonants are produced by putting your tongue between your upper and lower teeth. This creates a narrow gap or space through which air can pass, producing a distinct sound.

Interdental sounds are similar in articulation and sound to both labiodental and dental sounds.

These three places of articulation are similar enough that many languages use them interchangeably.

Fig. 1 - Interdental sounds are produced by bringing the tongue between the upper and lower teeth.

Interdental Sounds

Unlike sounds at other places of articulation, like bilabial and alveolar, interdental sounds are relatively unvaried. The only unique interdental sounds included in the International Phonetic Alphabet (IPA) are the interdental fricatives. Interdental fricatives are usually written as th in English (as in that and whether).

When you produce an interdental fricative, you bring the blade of your tongue to the edges of the upper teeth, leaving a narrow gap. You then force air through the gap, creating a stream of turbulent airflow. Interdental fricatives can be voiced or voiceless.

Other interdental sounds are written as alveolar sounds marked with the advanced diacritic [ ̟ ].

This combination of an alveolar consonant and advanced diacritic represents an alveolar sound that has moved forward in the mouth to the point of becoming interdental.

Interdental Fricatives

As mentioned before, an interdental fricative is a turbulent stream of airflow forced through the narrow opening between the tongue and teeth. The result is a random (or aperiodic) pressure wave, a bit like TV static.

You can see this random fricative noise by looking at a spectrogram.

A spectrogram provides clues about the nature of different speech sounds. Fricatives appear on the spectrogram as "fuzzy" strips of noise.

Produce the sounds [f] as in father, [θ] as in throw, and [s] as in sat to yourself. You might notice that [f] and [θ] sound similar to each other, while [s] sounds very different from both [f] and [θ]. You can see this difference on the spectrogram.

Fig. 2 - The interdental fricative looks similar to other fricatives on a spectrogram, with slight differences in amplitude.¹

On the spectrogram, the voiceless labiodental fricative [f] and the voiceless interdental fricative [θ] both look like fairly consistent fuzzy stripes. The voiceless alveolar fricative [s] looks similar, the major difference being a much darker area at the top of the spectrogram. This represents a very high, loud frequency range characteristic of fricatives like [s].

Interdental Consonants

Interdental consonants can appear in languages as phonemes or as allophones.

As you've seen, the voiced and voiceless interdental fricatives are phonemes in English. These are the only interdental phonemes in English. Even then, English speakers sometimes replace interdental consonants with allophones. Let's look a little closer at allophones now.

Allophones

Not all English speakers produce interdental consonants in the same way. For example, many American English speakers produce them as truly interdental, with the tongue protruding from between the teeth and touching the edges of the upper teeth. Many British English speakers, though, pronounce these consonants with the tip of the tongue touching the back of the upper teeth, producing a dental fricative.²

Different articulations of the same phoneme, as in this example, are called allophones.

This isn't the only example of allophones in interdental consonants. English speakers articulate the interdental fricative phonemes in several ways, such as:

• Alveolar stops [t, d]
• Labiodental fricatives [f, v]
• Dental fricatives [θ̪, ð̪]

Examples of Interdental Consonants

Some examples of interdental sounds in English are:

1. /θ/ - as in "think"
2. /ð/ - as in "this"
3. /s/ - as in "sip"
4. /z/ - as in "zip"
5. /n̪/ - as in "n̪apkin" (this sound is sometimes considered an allophone of /n/ in English)

Interdental sounds can also take the form of advanced alveolar sounds.

• Some speakers of Malayalam, a language spoken in Southern India, produce the interdental nasal [n̟], whereas other speakers produce the dental nasal [n̪]. This was seen in words like /pun̪n̪i/ (which means pig) in research done by Peter Ladefoged and Ian Maddieson.²

• The English word width is usually transcribed as [wɪtθ]. For some speakers, the voiceless alveolar stop [t] assimilates to the position of its neighbor, the voiceless interdental fricative [θ]. The result is the voiceless interdental stop [t̟].

• The speech pattern called a lisp involves replacing the alveolar fricatives [s] and [z] with the interdental fricatives [θ] and [ð]. Just like with [t̟], [d̟], and [n̟], this pattern advances the place of articulation of an alveolar consonant.

In summary, the only phonemic interdental consonants in English are the interdental fricatives [θ] and [ð]. However, alveolar consonants are sometimes articulated interdentally. Interdental plosives and nasals are marked with the advanced diacritic [ ̟ ].