The difference between registered natural head position and estimated natural head position in three dimensions

Area of Science:

• Dentistry
• Orthodontics
• Medical Imaging

Background:

• Accurate assessment of skeletal deformities is crucial in orthognathic surgery.
• Natural Head Position (NHP) is a key reference for evaluating facial posture and skeletal relationships.
• Three-dimensional (3D) stereophotogrammetry offers advanced imaging for facial analysis.

Purpose of the Study:

• To evaluate the intra-rater and inter-rater reliability of clinicians estimating NHP from 3D facial images.
• To compare clinician-estimated NHP (ENHP) with automatically re-oriented NHP (RNHP).
• To assess the impact of ENHP on the perceived severity of Class III skeletal deformities.

Main Methods:

• 15 pre-surgical Class III orthognathic patients' 3D facial images were captured.
• Images were automatically re-oriented to NHP (RNHP) using stereophotogrammetry and custom software.
• Six clinicians performed ENHP estimations, with re-estimations after 2 weeks; differences in yaw, roll, pitch, and chin position were measured.

Main Results:

• Intra-rater reliability (ICC: 0.55–0.77) was moderate for roll, yaw, pitch, and chin position.
• Inter-rater reliability (ICC: 0.38–0.58) ranged from poor to moderate.
• Clinicians tended to estimate NHP with a posterior chin tilt (6.3±5.2mm), reducing perceived anterior-posterior skeletal deformity.

Conclusions:

• Clinician reliability in estimating NHP from 3D facial images is moderate for single raters but inconsistent between raters.
• Systematic bias in chin positioning by clinicians can alter the perceived severity of skeletal deformities.
• Standardized NHP determination methods are needed for reliable 3D facial analysis in orthognathic surgery.