Frontal jaw angle

The sides of the lower face can descend almost vertically or turn inward towards a narrower chin. The measured lines follow this transition from each jaw corner to the corresponding side of the front chin contour. More inward slope increases the angle between them.

The slope depends on how much width is lost and how far the lines descend. A wide jaw leading to a narrow chin over a short distance creates an abrupt taper. The same change in width spread over more height creates straighter-looking sides and a smaller angle. This is a frontal construction; the gonial angle seen in profile follows a different part of the jaw.

Moving the jaw corners farther apart makes the lines travel farther inward to reach the same chin. Narrowing the chin has a similar effect while leaving the corners in place. Both increase the angle, but one adds breadth at the sides and the other creates a finer ending below the mouth.

The vertical distance matters even when both widths stay fixed. Bringing the chin-side points closer to the level of the corners makes the transition steeper and raises the angle. Extending that distance lowers it. A smaller result can therefore belong to a long, narrow jaw as well as a broad, square one.

Several dimensions can change together without changing the slope. Wider corners paired with a wider chin may preserve the angle, as may a longer descent paired with a larger difference in width. Faces with matching angles can still differ substantially in the size of the lower face.

A high angle with broad jaw corners and a narrow chin describes a lower face that is wide at the sides and strongly tapered at the front. With narrower corners, a similar angle belongs to a finer lower face. Bigonial and chin-width ratios help locate this difference instead of treating every pronounced taper as the same shape.

At a low angle, broad corners and a broad chin can form a rectangular outline. When both are narrow, nearly parallel sides can instead create a long, slender shape. Lower-face height helps distinguish these arrangements, although the relevant distance runs between the marked jaw and chin points rather than across the entire lower third.

The neck affects how clearly these sides can be seen. A narrower neck leaves more separation beneath the jaw, while a broad neck may make the outline more continuous. Facial hair and soft-tissue curvature can also change the visible edge without changing the slope between its endpoints.

Mandibular growth changes the widths and heights that form the lower face. The taper develops through their combined proportions, so it may change as the chin gains height or the jaw corners broaden. Ferrario's growth study and Velemínská's work on facial size describe some of the wider changes accompanying this development.

The photographed outline follows skin and muscle over the bone. A rounded jaw edge and a sharply defined edge can share the same endpoints, even though their contours differ between them. When comparing photographs over time, check whether the landmarks still mark equivalent parts of the outline.

The 85–95° reference belongs to the two directed lines shown in the figure. Some jaw-angle measurements instead use a single point at the chin or measure the jaw in profile. A similar number under one of those definitions can describe different geometry, so the endpoints and angle direction need to match before values are compared.

The female-jaw experiment cited below varied jaw width and height, while Mogilski and Welling varied jaw prominence alongside other facial features. Neither isolated this exact angle.

Inspect each side separately before relying on the combined angle. Unequal corner heights or a chin shifted to one side can create different slopes while leaving the total angle similar. Accurately placed points should follow that difference rather than be moved to make the sides match.

Use a frontal photograph with the jaw relaxed and the chin contour visible. Turning the head changes the apparent widths, while tilting it can shorten or lengthen the descent seen in the image.