Each facial feature on every subject has its own uniqueness. Capturing the unique character traits in your subject is the key to drawing a realistic portrait. There are several tips and tricks that I've picked up along the way, that I hope you can utilize when drawing mouths.
Pay attention to the corner of the lips
Not every smile is the same and it's easy to get in the routine of simply drawing the perfect "smiley face smile". When drawing mouths the small details that you may overlook, many times prove to be the most important in capturing your subject's character and personality-this includes the corners of lips.
Make sure you pay attention to which way the corners of your subject turn and portray it in your photograph accurately. The small subtleties-like the angle or depth of the corners-can make the biggest difference in expressing the likeness of your subject.
Capturing the philtrum correctly
The philtrum is the part of your face that connects your upper lip to your nose.
Each person's philtrum is unique, in its depth, length, and shape. Capitalizing on this unique aspect of each individual, will allow you to capture yet another important character trait in your subject. When drawing the philtrum make sure you take the opportunity to show the depth and contour of your subjects mouth.
Blending in the edges of Lips
One of the biggest things to remember about drawing lips is to create soft edges where they transcends into, so in the end your mouth doesn't look like the art in a coloring book with dark outlines around the outer edges of the lips.
You can add depth and contour, by making a clear separation between the upper and lower lip with a clean edge to value. This separation is one of the most important concepts to grasp. By creating the soft edges, it will allow your drawing to flow flawlessly between the pigment of the lips and the skin tones of the face.
Separating lips and gums
When your subject has a smile showing the teeth and gums, separating the lips from the gums can have a huge impact on finished realistic look to your drawings.
Just as we add depth on any part of the portrait, we will begin with a clean edge to value, in order to shade and separate the gum away from the upper lip, showing that the gums are set back on a different plane than the lips.
So, separating the dimensions of the lip and the gum, will allow you to add more depth and a 3D, lifelike feel to your portrait.
Edges of teeth
You need to show clear separations between your subject's teeth without drawing 'scary teeth.' By filling in the darker recesses of the mouth first-the gums, without outlining each tooth, will allow us to see the subtle value changes between each tooth.
These subtle value changes between the teeth, instead of a clean, dark pencil line will keep your subject from having dark gaps, separating each tooth.
Even in such a tight space, I'll show you how to use a range of value-so that neither the gums nor the teeth will appear flat. When you are drawing teeth, it is one more place that you can show the contour, dimension, and shape of your subject's face.
Have fun drawing.