In the world of singing, "getting stuck" is an all too common frustration. One of the most subtle ways this happens is getting stuck in the first mouth. While it sounds incoherent—after all, sound comes out of the mouth—functional voice training reveals that the singer actually has two mouths.
The mouth we all recognize consists of the lips, teeth, tongue, and jaw. This is where sound technically emanates so others can hear it. However, this mouth is meant for finishing touches and the articulation of consonants. When the sound gets "stuck" here, the pitch and vowel fail to match up. This leads to strained high notes and poor diction because the jaw and tongue are trying to do a job they weren't designed for.
The "real" mouth of the singer is found in the oro-pharynx—the area at the back of the throat above the larynx. When your vocal cords adjust for a pitch, they also define the initial shape of the vowel. This information is carried into the oro-pharynx, which shapes the resonance to match the cord adjustment perfectly.
As you sing higher, the vocal cords vibrate with less mass. To stay in balance, the vowel must "size down" to match that pitch step. When this happens correctly, you experience the sensation of the voice traveling back, up, and over into the head—much like walking up a staircase backwards.
When you utilize the "second mouth" for vowel shaping, the "first mouth" is finally set free. The jaw and tongue no longer have to grip the tone to keep it stable. Instead, they can move flexibly to provide crisp diction and subtle tonal nuances. You won't "hit the roof" of your range; instead, you'll sense a wonderful release as your registration handles the heavy lifting.
Singing with the oro-pharynx isn't something you "force"—it is a result of proper registration. By allowing the vowel to size down as you ascend, you move the work away from the jaw and into the resonant spaces where it belongs. Stop fighting your first mouth and start singing with your real one!