Correlation Between Facial Forms and Bolton Ratios in Class I and Class II Malocclusions
DOI:
https://doi.org/10.15218/edj.2026.1Keywords:
Facial Forms, Bolton Ratio, Malocclusion, 3D Facial Scanning, Intraoral ScanningAbstract
Background and Objective: Facial morphology and dental arch dimensions coordination are fundamental aspects of orthodontic diagnosis and treatment planning. Tooth-size discrepancies, as quantified by anterior and overall Bolton ratios, may vary with facial form and malocclusion classification. Aim: To evaluate the correlation between facial forms (as measured by facial index) with anterior and overall Bolton ratios in Class I and Class II malocclusion subjects in Erbil city, using three-dimensional facial and intraoral digital scans.
Methods: The cross-sectional study included 128 participants divided by sex (males: 64, females: 64), malocclusion class (Class I: 64, Class II: 64), and facial form based on facial index thresholds (24 euryprosopic, 27 mesoprosopic, 77 leptoprosopic). Facial scans provided measurements of facial height (nasion–gnathion) and bizygomatic width, which were used to calculate the facial index. Digital intraoral scans were used to calculate anterior and overall Bolton ratios. Normality was assessed with the Shapiro–Wilk test. Group differences were analyzed using the Kruskal–Wallis and Mann–Whitney U tests, and associations were evaluated using Spearman correlation.
Results: No correlation was found between facial index and either anterior or overall Bolton ratios (P>0.05). However, anterior Bolton ratios differed significantly among facial form types (P=0.009), with pairwise analysis showing higher values in mesoprosopic forms compared to euryprosopic forms. No significant differences were found between Class I and Class II groups.
Conclusions: These findings indicate that although facial index does not predict anterior or overall Bolton ratios across malocclusion classes, differences in anterior ratios among facial types may still occur. Clinically, this emphasizes that Bolton ratio assessment should always be performed individually, rather than inferred from facial form or malocclusion type, to ensure precise diagnosis and treatment planning.
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