Objective: The objective of this retrospective cohort study is to assess and compare the accuracy of three different Invisalign® treatment regimens involving variations of aligner change frequency and type of aligner material in achieving maxillary dental buccal expansion.
Methods: 120 adult patients whose treatment involved maxillary dental expansion with Invisalign® were selected. Three groups, each of 40 patients were identified: SmartTrack® one-week changes (ST1), SmartTrack® two-week changes (ST2) and EX30® two-week changes (EX2). The groups were assessed by comparing actual changes achieved with those prescribed by ClinCheck®. The rates of clinically significant inaccuracies (CSI) seen for buccal expansion (≥ 0.5mm) and buccolingual inclination (≥2°) during expansion were then ascertained.
Results: With respect to expansion, the ST1 group showed the highest rate of CSI at all tooth levels studied while the ST2 group showed the lowest rate of CSI as well as the lowest mean inaccuracy for each tooth level studied. In terms of buccolingual inclination, the ST1 group showed the highest rate of CSI across all tooth levels studied, while the EX2 group showed the lowest rate of CSI at all tooth levels except for the canine level where the ST2 group showed the lowest rate of CSI. A tendency toward overexpression of buccal crown inclination, and underexpression of buccal expansion was seen at all tooth levels.
Conclusions: Two-week aligner change regimens offer improved accuracy compared with one-week aligner changes. SmartTrack® two-week changes were the most accurate for buccal expansion, while EX30® 2-week changes were the most accurate for buccolingual inclination.

Keywords: Aligners, Expansion, Adult treatment, Digital models