Effects of maxillary expansion in mixed dentition with Invisalign First System and Hass: A prospective cohort study

Abstract Objective: This prospective cohort study aimed to compare the dento-skeletal effects of using Invisalign First System with Hass excluding growth factors. Materials and Methods: A total of 51 patients were included in this study: Invisalign First System (First) group (n = 17), Hass group (n = 17), natural growth (NG) group (n = 17), after screening by strict inclusion criteria and propensity score matching (PSM). Research indicators were measured on digital dental casts at baseline (T0) and six-month follow-up (T1), including intercanine width, interpremolar width, second interdeciduous molar width, arch depth, arch perimeter, intercanine alveolar bone width, intermolar alveolar bone width, and molar inclination. Results: In the NG group, there was no statistically significant difference in dento-skeletal indicators. In the First and Hass group, all indicators were significantly increased after treatment. The Hass group showed a greater expansion than First group for intercanine width, first interpremolar width, second interdeciduous molar width and first intermolar mesial width, arch perimeter, intercanine alveolar bone width, intermolar alveolar bone width, and molar inclination (p < 0.05). Whereas, arch depth showed no statistically significant difference between the two groups. Conclusions: 1. Both Hass and First can effectively expand maxillary in mixed dentition. 2. Invisalign First System is a new method of comfortably and effectively acting on maxillary expansion, recommended for patients with aesthetic, arch space management needs and mild to moderate narrowing of the maxillary in mixed dentition. 3. Hass allows a greater expansion, recommended for patients with severe maxillary transverse deficiency. Clinical relevance: The present fndings provide theoretical basis for various clinical treatments regarding maxillary expansion with mixed dentition. Registration number:ChiCTR2200056220, February 1, 2022.