Harmony · Side view · Lips
Lower Lip S-Line Position
The lower lip’s signed distance from a line running from nose-base/tip midpoint to soft-tissue chin.
What is measured
The calculation
Perpendicular lower-lip distance to the S-line × photo scale
Side view / Measurement guide
Follow the measurement
Select a label to focus on its line. Select again to show all measurements.
In these guides, nasion means the nasal root, subnasale the nose base, and pogonion the most forward chin point. Frankfort refers to the direction from the ear-opening landmark to the lower orbital landmark.
Why it matters
This relates the lower lip to the nose–chin framework. Reading it alongside the upper-lip distance helps distinguish the relationship of the two lips to the same reference.
- Negative in FaceIQ: the lip lies in front of the line.
- Positive in FaceIQ: the lip lies behind the line; zero means contact.
Where the idea comes from
FaceIQ adaptation
Steiner’s S-line belongs to soft-tissue profile analysis. FaceIQ approximates its nasal endpoint using the midpoint between the nose base and tip. This construction may differ from tracing the original nasal S-curve. [1]
A worked example
A lower lip 2 estimated mm behind the S-line reads +2 mm. Moving it onto that unchanged line gives zero; 1 mm in front gives −1 mm.
Example values explain the calculation. They are not a target range and are not measurements of the schematic above.
Research & further reading
The sources below explain the history or related evidence. FaceIQ’s score weights and reference ranges are model settings; these papers do not collectively validate the scoring system.
[1] Buschang, Fretty & Campbell · 2011
Can commonly used profile planes be used to evaluate changes in lower lip position?Compared five lip reference lines, including Steiner’s S-line, in 79 orthodontic patients. Moving reference points can make a lip appear to move backward even when it moves forward.