The predictability of arch expansion with the Invisalign First system in children with mixed dentition: a retrospective study

This study aimed to quantify the predictability of arch expansion in children with early mixed dentition treated with the Invisalign First® system and evaluate the clinical factors for the predictability of arch expansion. Pretreatment, predicted and posttreatment digital models from Invisalign's ClinCheck® software were obtained for 90 children with mean (standard deviation) age of 8.42 (0.93) who planned arch expansion. Arch width measurements were collected using Invisalign's arch width table. The predictability of expansion was calculated by comparing the amount of expansion achieved with the predicted expansion. Linear regression analysis was used to evaluate clinical factors associated with predictability of expansion. The predictability of the expansion of the maxillary teeth was as follows: 71.1% primary canines (n = 55), 67.5% first primary molars (n = 46), 65.2% second primary molars (n = 79), and 53.4% first permanent molars (n = 90); the predictability of the expansion of the mandibular teeth was 81.1% primary canines (n = 31), 81.2% first primary molars (n = 51), 77.8% second primary molars (n = 80), and 69.4% first permanent molars (n = 90). The predictability of arch expansion was significantly higher in the mandibular arch compared to the maxillary arch and significantly lower in the permanent first molar than in the other primary teeth. Predictability decreased significantly as the amount of predicted expansion per aligner increased in the upper and lower permanent first molars, primary second molars, and upper primary canines. Predictability significantly increased when buccal or palatal attachments were placed on the bilateral side compared to cases without attachment at the upper permanent first and primary second molars. The predictability of arch expansion using the Invisalign First® system varies according to arch and tooth type. The amount of predicted expansion per aligner and the number of attachments to the maxillary teeth are potential clinical factors that can affect the predictability of expansion.