Revisiting aetiological models of maxillary canine impaction and its association with non-syndromic hypodontia: a nested case-control study among French orthodontic patients

OBJECTIVES: This study aimed to investigate the association between maxillary canine impaction and non-syndromic hypodontia, and to explore the contribution of specific missing-tooth patterns and craniofacial skeletal characteristics. METHODS: A case-control study was conducted using pretreatment orthodontic records from an initial clinical sample of 4078 patients aged 11-21 years, from whom 251 individuals with maxillary canine impaction (cases) and 753 age- and sex-matched controls were finally included. Dental agenesis was assessed for all patients. Statistical analyses included univariate and multivariable binary logistic regression to evaluate the association between impaction and the presence, severity, and patterns of non-syndromic hypodontia, as well as Chi-squared and Fisher's exact tests to explore associations with impaction characteristics. RESULTS: Hypodontia, when including third molars, showed a weak association with maxillary canine impaction (OR=1.39; 95% CI=1.00-1.93; P=0.050). In multivariable analysis, the association between the number of missing teeth and maxillary canine impaction varied according to skeletal Class II (OR=1.42; 95% CI=1.10-1.84; P=0.007) and skeletal Class III (OR=2.34; 95% CI=1.29-4.93; P=0.012), with no significant effects of tooth-specific agenesis patterns or vertical skeletal relationships. Among affected patients, laterality, impaction position, and the presence of local obstacles were not associated with hypodontia. CONCLUSIONS: The findings suggest that the severity of non-syndromic hypodontia represents a meaningful predictor of maxillary canine impaction when considered in relation to skeletal malocclusion, whereas individual missing-tooth patterns are insufficient to explain this phenomenon and do not support classical aetiological theories of impaction. This trend may help clinicians identify high-risk patients earlier and refine treatment planning.