Age-related changes in the effect of rapid maxillary expansion on the position of labially impacted maxillary canines: A case-control study

Introduction: The early diagnosis and interception of potential maxillary canine impaction is the most desirable approach for correcting their path of eruption. However, there is still a lack of evidence regarding the effect of rapid maxillary expansion (RME) on labially impacted canines. This study aimed to investigate the age-related effect of RME on labially impacted maxillary canines in order to reduce the risk of their impaction in the mixed dentition and to examine the proper timing of interceptive treatment. Methods: All patients aged 7-10 years were treated with an RME appliance using the same protocol. The distance to the occlusal plane, axis to the midline, and distribution in different sectors—depending on the patients' age—were evaluated for maxillary canines before and after treatment on panoramic radiographs in order to detect changes in the position of the impacted canines. These geometric measurements in the impacted canines were also validated by observing the nontreated canines at each age. Results: Significant differences existed between the impacted canines and the erupted canines in all 3 categories in all age groups. RME treatment modulated the position of the impacted canines in all age groups. Interestingly, a statistically significant difference before and after RME in all categories was detected in patients aged <8 years. A discriminant analysis also showed a positive association of RME treatment with the risk of labially impacted canines. The standardized regression coefficients showed that the angulation of the maxillary canine was the most important predictor for impaction. Conclusions: Our findings indicate that RME treatment in the early mixed dentition was effective for managing labially impacted maxillary canines. An age of 7-8 years with early mixed dentition might be the most appropriate timing for therapeutic intervention on the basis of RME treatment for buccal canine impaction.