Sagittal and Vertical Changes After Aligner Versus Acrylic Splint Expansion in Mixed Dentition: A Prospective Trial

The efficacy of acrylic splint expander (Splint) and Invisalign First aligners (First) in increasing transverse width in mixed dentition have been well documented, but little is known about their sagittal and vertical effects. Since sagittal and vertical changes are particularly critical in growing patients, the objective of this study was to assess and compare the sagittal and vertical treatment effects of First and Splint in mixed dentition with transverse maxillary deficiency.

Sixty subjects were included after propensity score matching (PSM) from initial 163 cohort: the Splint group (n = 20), the First group (n = 20), and the Natural Growth (Natural) group (n = 20). Lateral cephalograms were acquired before the initiation of treatment (T0) and at a minimum of one year after treatment (T1). Sixteen cephalometric variables were assessed to detect differences within and between groups from T0 to T1. Intra-group analyses were conducted using paired t-tests, while inter-group comparisons were performed using analysis of variance (ANOVA). Statistical significance was set at P < .05.

In all groups, a significant increase (P < .05) were observed in ANS-Me, N-Me, and S-Go during the T1-T0 period. In the Splint group, ANB and NA-PogA significantly decreased (P < .05), whereas SNB significantly increased (P < .05). In the First group, both overjet and overbite significantly decreased (P < .05), with a greater reduction observed compared to the other two groups (P < .05). No significant differences were found in the remaining variables, either within or between the groups.

Splint therapy improved skeletal relationships, resulting in reduced facial convexity. First therapy produced a pronounced reduction in overjet and overbite primarily through dentoalveolar effects.