Most singers don’t realize how tense their jaw is because it feels perfectly natural to them. Jaw tension is developed gradually, slowly over long periods of time. Until you take a “vacation” from that tension, you will never realize how it is impairing your singing. In today’s stressful world, this is something that impacts a huge number of singers, and they don’t even realize it.
Be sure to stretch out your face and jaw muscles. Make a specific point to monitor your jaw when singing (and throughout the day) to be sure it truly is relaxed. Jaw tension is another example of muscle memory, if you are “used” to clenching those muscles, it will take some conscious effort to retrain them.
Here’s the important point: if your jaw is tense, you will not create your best singing tone. Most likely you will not open your mouth as wide or as freely. This will not only result in tone distortion….it will result in pitch problems.