Can commonly used profile planes be used to evaluate changes in lower lip position?

Area of Science:

• Orthodontics
• Cephalometric analysis
• Dental aesthetics

Background:

• Accurate assessment of lower lip horizontal changes is crucial in orthodontic treatment planning and evaluation.
• Several cephalometric profile planes are commonly employed to estimate these changes, but their validity requires scrutiny.

Purpose of the Study:

• To evaluate the accuracy of five commonly used profile planes (Rickett's E-line, Steiner's S1-line, Burstone's B-line, Sushner's S2-line, and Holdaway's H-line) in measuring horizontal lower lip (labrale inferiorus) displacement during orthodontic treatment.

Main Methods:

• Pre- and post-treatment lateral cephalograms from 79 orthodontic patients (mean age 12.4 years) were analyzed.
• Lower lip changes were measured relative to the five specified profile planes and a stable, independent reference plane (sella-based SN-7°).
• Statistical analysis compared measurements from the profile planes against actual lip movement and assessed sex and treatment modality differences.

Main Results:

• The lower lip actually moved anteriorly (2.35 ± 3.35 mm), while the five profile planes indicated a posterior (retrusive) movement.
• Profile planes showed no significant sex differences, contradicting actual measurements where males had greater changes.
• Actual lip movement differed between nonextraction and extraction treatments, a distinction not captured by the profile planes.
• Intercorrelations among the five profile planes were high (0.81–0.97), but correlations with actual labrale inferiorus changes were weak (r < .35).

Conclusions:

• The five evaluated profile planes do not accurately reflect actual horizontal lower lip changes during orthodontic treatment.
• These cephalometric planes demonstrate poor validity for measuring lip position alterations and should be reconsidered for clinical use in assessing treatment outcomes.