Lips measurement
Z-Angle (Merrifield)
Merrifield’s profile line touches the chin and whichever lip sticks out more; the Z-angle is the inner angle it makes with the Frankfort horizontal. Smaller angles mean protrusive lips or a receding chin, larger angles flat lips or a prominent chin.
At a glance
- Ideal
- 75–85°
- Unit
- degrees
- Weight in the overall score
- 4
- Area
- Lips
How it is measured
∠ between the Frankfort horizontal and the profile line from Pog through the more protrusive lip
- Pog Pogonion — The most forward point of the chin.
- Ls Labrale superius (upper lip) — The most forward point of the upper lip.
- Li Labrale inferius (lower lip) — The most forward point of the lower lip.
- Po Tragion (porion) — The top of the tragus — the small flap in front of the ear canal. With orbitale it defines the Frankfort horizontal.
- Or Orbitale — The lowest point of the bony eye-socket rim, just below the lower eyelid.
Ideal range and tiers
Each value falls into a tier (T1 = ideal). Comfortably inside T1 the rating is 10, easing to 9.5 at the edges of the ideal range; beyond it the rating falls with the deviation — fastest in the first tiers outside the ideal — down to 0 at the far end of the worst tier.
| Tier | Range | Rating |
|---|---|---|
| T1 Ideal | 75–85° | 9.5–10 |
| T2 Near ideal | 72–75° or 85–88° | 6.7–9.5 |
| T3 Mild deviation | 69–72° or 88–91° | 4.3–6.7 |
| T4 Moderate deviation | 65–69° or 91–95° | 2.1–4.3 |
| T5 Severe deviation | < 65° or > 95° | 0–2.1 |
Differences between populations
Optional population norms move this range by the difference reported between groups measured the same way:
- East Asian: men −10°, women −9°.
Individual faces vary far more within any group than between groups; these are averages, not targets.
Related measurements
References
- Merrifield LL. The profile line as an aid in critically evaluating facial esthetics. Am J Orthod. 1966;52(11):804–822.
- Hwang HS, Kim WS, McNamara JA Jr. Ethnic differences in the soft tissue profile of Korean and European-American adults with normal occlusions and well-balanced faces. Angle Orthod. 2002;72(1):72–80.