Population-specific Craniofacial and Airway Norms Using McNamara Analysis: A Cross-sectional Study in Shimla Hills Cohort

Introduction Cephalometric norms are often population-specific due to ethnic and environmental influences. The Shimla Hills region of Himachal Pradesh, India, represents a distinct population influenced by high-altitude and cold climatic conditions, which are known to affect craniofacial morphology. This study aimed to establish McNamara cephalometric norms for this population and evaluate their deviation from Caucasian standards. Materials and Methods Digital lateral cephalograms of 200 adult subjects (18-29 years) native to the Shimla region, with Class I occlusion, were analyzed. Skeletal, dental, and airway parameters were measured and compared with Caucasian norms and regional Indian data. Results The Shimla population exhibited a distinct craniofacial pattern. Maxillary and mandibular positions were significantly more retrusive compared to Caucasians. Mandibular length (Co-Gn) was significantly shorter, mirroring South Indian trends more closely than Maratha (Central India) or Caucasian standards. Vertical analysis showed reduced anterior facial height but a steeper mandibular plane angle. Pharyngeal airway dimensions were significantly narrower when compared to Caucasians. Sexual dimorphism was evident, with males generally exhibiting a proportionately larger skeletal framework and females showing slightly more dental proclination. Conclusion McNamara’s Caucasian norms are not directly applicable to the Shimla population. The established population-specific norms reflect a unique phenotype of bimaxillary retrusion and reduced airway space, emphasizing the need for individualized diagnostic standards in orthodontic and orthognathic planning for this region.