@article{nokey,

title = {Stability of transverse changes with clear aligners and hyrax expanders from the mixed to the permanent dentition},

author = {Andrew Tsai and Heeyeon Suh and Sandra Khong Tai and Marta Baird and Heesoo Oh },

doi = {https://doi.org/10.1016/j.ajodo.2026.01.017},

issn = {0889-5406},

year  = {2026},

date = {2026-03-04},

journal = {American Journal of Orthodontics and Dentofacial Orthopedics},

abstract = {This study evaluated the longitudinal stability of transverse changes in patients treated with the Invisalign First system (IFS; Align Technology Inc, Tempe, Ariz) and hyrax expanders during the mixed dentition, followed through the permanent dentition. The objective was to determine whether expansion achieved during the mixed dentition was maintained through the transition to the permanent dentition. This retrospective longitudinal study included 119 patients: 44 patients treated with IFS, 36 patients treated with hyrax, and 39 untreated controls. Arch width changes at the canines, premolars, and first molars were measured on digital study models at 3 time points: pre-phase 1 treatment (T1), post-phase 1 treatment (T2), and pre phase 2 evaluation (T3). Vertical skeletal changes were evaluated in a cephalogram subgroup. Statistical analyses included analysis of variance and linear mixed-effects models. Both IFS and hyrax groups showed greater maxillary arch width increases from T1 to T3 (IFS: 1.8-2.8 mm; hyrax: 2.2-3.7 mm) than controls (0.4-1.2 mm; P <0.0001). At T2, hyrax showed significantly greater interpremolar and intermolar expansion (4.1-4.8 mm) than IFS (1.9-2.8 mm), but more relapse from T2 to T3. The IFS group also showed increased mandibular arch width from T1 to T3 (1.9-2.9 mm) compared with controls (P<0.05). No significant vertical skeletal changes from T1 to T3 were observed. Both IFS and hyrax produced maxillary arch expansion that was maintained throughout the transition from mixed to permanent dentition. The IFS also showed stable mandibular arch expansion, supporting its use for mild crowding or transverse deficiencies without long-term vertical effects.},

keywords = {clear aligners, Hyrax expander, permanent dentition, Transverse},

pubstate = {published},

tppubtype = {article}

}

@article{Torbaty2024,

title = {Vertical and transverse treatment effects of Invisalign First system compared to Hyrax maxillary expanders with fixed appliances in mixed dentition patients},

author = {Parisa Moravedje Torbaty and Heeyeon Suh and Sandra Khong Tai and Marta Baird and Robert Boyd and Heesoo Oh},

url = {https://doi.org/10.2319/121023-818.1},

doi = { 10.2319/121023-818.1},

issn = { 0003-3219},

year  = {2024},

date = {2024-05-17},

urldate = {2024-05-17},

journal = {Angle Orthodontist},

volume = {94},

issue = {5},

abstract = {Objectives: To compare vertical and transverse changes in mixed dentition patients treated with the Invisalign First System (IFS) to those treated with a banded hyrax expander with fixed appliances (Hyrax) and control groups, and to assess the efficiency rate of dental arch expansion with IFS. Materials and Methods: The study included 80 mixed dentition patients, with 40 in each group (IFS and Hyrax) and 40 controls from the American Association of Orthodontists Foundation Craniofacial Growth Legacy Collection. Skeletal and dental vertical dimension changes and arch width changes between pretreatment (T1) and posttreatment (T2) were evaluated. Results: Age at T1, time interval (T1-T2), sex, and Angle class did not significantly differ among the groups. Mandibular plane angle changes showed a similar reduction for the control and IFS groups, with no changes in the Hyrax group. However, the differences among the three groups did not reach statistical significance (P = .06). The Hyrax group showed significantly greater expansion in maxillary intermolar width compared to the IFS group, 4.4 vs 2.5 mm, respectively. The efficiency of maxillary expansion using IFS ranged from 52.3% to 76.87%.

Conclusions: During the mixed dentition stage, no significant changes occurred in vertical dimensions among the control, Hyrax, and IFS groups. Although there was a trend suggesting a greater reduction in mandibular plane angle in the IFS group compared to the Hyrax group, this may not be clinically significant given the less than 1° difference. IFS can be a viable option for addressing mild arch width deficiencies, with a predictable increase in intermolar width of approximately 2.5 mm.},

keywords = {Hyrax expander, Invisalign, Maxillary expansion, Transverse, Vertical},

pubstate = {published},

tppubtype = {article}

}