In Ricketts esthetic plane, lower lip rests:
1 mm anterior to plane
On the plane
2 mm posterior to plane
1 mm posterior to plane
Ricketts’ E line:
R. M. Ricketts suggested using an esthetic (E) plane to evaluate the relationship between the nose, lips and chin. Ricketts’ E line is drawn from the tip of the nose to the soft tissue chin. A quick method to look at one profile is to imagine a line tangent from the lower chin to the nose tip. Cephalometrically, Ricketts’ E line is drawn from the tip of the nose to the soft tissue chin. Normal values suggest that the upper lip is 4 mm behind the E line, while the lower lip lies 2 mm behind this reference line. It is important to mention that, this reference line is influenced a great deal by the growth of the nose and also varies with age and sex. Ricketts recommended that lip position should be analyzed using the nose–chin line as a reference point. These values are for Caucasians and clearly cannot be applied to all races.
Ref: Orthodontics: Diagnosis and Management of Malocclusion and Dentofacial Deformities, 3e, Om P. Kharbanda pdf no 1097