Comparative Cephalometric Norms for Skeletal Class I Adults: A Study of Yemeni and Turkish Cypriot Populations

Background: The shift toward precision orthodontics necessitates population-specific cephalometric databases. Reliance on Eurocentric norms for ethnically diverse populations—particularly underrepresented Middle Eastern groups—represents a significant evidence gap. This study establishes initial normative cephalometric data for Yemeni and Northern Turkish Cypriot (NTC) adults. Methods: This retrospective comparative study analyzed 400 lateral cephalograms from skeletal Class I adults (200 Yemeni and 200 NTC; age 18–40; gender-balanced). Twenty standardized parameters were assessed using VistaDent OC™ software (version 4.2.61, GAC Orthodontic Software solutions, Birmingham, AL, USA). Analyses included *t*-tests, MANOVA, effect size computations (Cohen’s *d*), and variance partitioning. The False Discovery Rate method controlled multiple comparisons. Results: Yemeni adults exhibited a more vertical facial growth pattern (indicated by a lower Jarabak ratio: 60.18 ± 4.50% vs. 65.79 ± 5.20%; *d* = 1.15) and pronounced soft-tissue convexity (N-A-Pog: 5.76 ± 1.20 mm vs. 3.82 ± 1.10 mm; *d* =1.69). NTC adults showed a mild skeletal Class II tendency (ANB: 4.51 ± 1.70° vs. 3.35 ± 1.50°; *d* = 0.72). Ethnicity accounted for 21.3% of craniofacial variance (partial η2 = 0.213). Conclusions: This study provides foundational cephalometric reference data for two underrepresented populations. The significant morphological distinctions quantified here underscore the necessity of developing population-specific norms. These data should be considered as one component within comprehensive, individualized diagnostic frameworks in orthodontics, rather than standalone diagnostic criteria.