Efficiency and predictability of Invisalign® G8 features in maxillary posterior arch expansion

Objectives: In 2021, Invisalign® G8 introduced SmartForce Aligner Activation and Optimized Expansion Support Attachments that claimed to improve posterior arch expansion. The aim of the study is to determine the efficiency and predictability of the Invisalign® G8 protocol in relation to maxillary arch expansion. Methods: 220 participants treated with Invisalign® were retrospectively selected, comprising of 110 treated before the introduction of the G8 protocol (pre-G8 group) and 110 treated with the G8 protocol (post-G8 group). The study focused on the expansion of the maxillary first molars, second premolars, and first premolars. All participants were scanned at the start of treatment and after the first series of aligners. Four maxillary digital models—initial ClinCheck®, predicted ClinCheck®, pre-treatment scanned models, and post-treatment scanned models—were superimposed to assess buccolingual displacement and angulation of each tooth. Inter-premolar and inter-molar widths were measured. Independent sample t-tests or Mann-Whitney U tests were used to compare the differences. Results: Both the pre-G8 and post-G8 groups showed similar linear predictability for the first premolars and molars. However, the post-G8 group demonstrated improved predictability in the left second premolar, with an average mean difference of 0.23 mm (P < 0.05). The post-G8 group had better angular predictability for the left first molar, second premolar, and first premolar, with average mean differences of 1.75˚, 2.09˚, and 1.18˚ respectively (P < 0.01). In terms of efficiency, the post-G8 group achieved greater expansion on average in the right second premolar (0.34 mm) and demonstrated better torque control in the right first molar, left first molar, and left first premolar, with reduced buccal tipping of 1.58˚, 1.51˚, and 1.80˚ respectively (P < 0.001). The pre-G8 group showed greater torque control only in the left second premolar (-1.85˚, P <0.01). The first premolar and second premolar inter-tooth widths were, on average, 0.25 mm and 0.52 mm greater in the post-G8 group respectively (P < 0.01). Conclusions: The Invisalign® G8 protocol demonstrated trends towards improved predictability and efficiency in linear and angular measurements for certain teeth. Due to variability among individual patients, caution should be taken when interpreting the clinical significance of these findings.