# Skeletal and dentoalveolar effects on the midpalatal suture and maxillary arch assessed by occlusal radiographs and three-dimensional digital models in patients treated with invisalign palatal expander and rapid palatal expander: a pilot study

## TL;DR

This pilot study compares the Invisalign Palatal Expander and Rapid Palatal Expander for maxillary expansion, finding similar skeletal effects but more controlled results with the Invisalign device.

## Contribution

The study introduces the Invisalign Palatal Expander as a valid, controlled alternative to conventional rapid palatal expansion in mixed dentition.

## Key findings

- Both IPE and RPE achieved midpalatal suture opening and comparable skeletal effects.
- RPE showed greater arch depth and canine width changes after normalization.
- IPE provided more controlled and predictable results with similar side effects.

## Abstract

Maxillary transverse deficiency (MTD) is a common craniofacial condition associated with posterior crossbite, dental crowding, and compromised respiratory function. This study aimed to evaluate whether the Invisalign Palatal Expander (IPE) can induce midpalatal suture opening and occlusal changes, and to compare these outcomes with those obtained using conventional rapid palatal expansion (RPE).

Thirty subjects (14 females, 16 males; aged 6–18 years) with mixed dentition were enrolled and divided into two groups: 15 treated with IPE and 15 with RPE. Radiographic images and digital dental models were analyzed before (T0) and after treatment (T1) to assess skeletal and occlusal changes, including midpalatal suture opening and transverse arch dimensions. Molar tipping and palatal depth were also measured. Patient-reported side effects during the first month of treatment were evaluated using a questionnaire addressing bulkiness, tongue impression, dysphonia, dysphagia, and gag reflex, scored on a 1–5 scale. Inclusion criteria comprised mixed dentition, erupted first molars, deciduous fourth/fifth teeth or erupting premolars, and complete diagnostic records. Exclusion criteria included previous orthodontic treatment, craniofacial anomalies, extraction therapy, allergies, hereditary angioedema, or active caries.

No significant differences were found between groups in the number of activations, radiographic outcomes, or theoretical expansion, indicating comparable skeletal effects. Midpalatal suture opening was achieved in all patients. Baseline occlusal conditions were similar between groups. After normalization for the number of activations, statistically significant differences were observed for arch depth, canine gingival width, canine dental width, and arch perimeter, all of which were greater in the RPE group (p < 0.05). No significant differences were found in intermolar angle or palatal depth changes. Questionnaire analysis revealed no significant differences in reported side effects between groups.

The Invisalign Palatal Expander effectively produced transverse maxillary expansion with midpalatal suture opening, yielding skeletal and occlusal outcomes comparable to those of the Hyrax expander. Although the amount of expansion was slightly lower, the IPE demonstrated more controlled and predictable results, supporting its use as a valid alternative in mixed dentition and as a step toward fully digital orthodontic protocols.