Arch width changes following first premolar extractions: a comparison between invisalign and fixed appliances

Arch width (AW) affects space availability and shifts the anchorage balance in extraction cases. This study aimed to investigate whether AW differs between patients treated with clear aligners (CAs) and those treated with conventional fixed appliances (FAs) following the extraction of four first premolars.

This retrospective study included 60 Class I patients who underwent extraction of four first premolars and were treated with either CAs (Invisalign, Align Technology) or FAs (MBT prescription, 0.022-inch slot). The CAs group consisted of 3 males and 27 females (mean age, 24.53 ± 4.58 years), and the FAs group included 4 males and 26 females (mean age, 22.60 ± 3.92 years). In the CAs group, patients were instructed to change the aligners every 10 days and to wear them for at least 22 h per day. Digital dental casts and lateral cephalometric radiographs were obtained at the beginning (T1) and completion (T2) of treatment. Maxillary and mandibular intercanine, interpremolar, and intermolar widths were measured. Paired t-tests were used for intragroup comparisons, and independent t-tests were used for intergroup comparisons. Statistical significance was set at P <.05.

Maxillary and mandibular incisors in the CAs group exhibited significantly greater retroclination than those in the FAs group (P <.05). No significant intergroup differences in AW were identified before treatment (P >.05). However, post-treatment measurements demonstrated significantly greater AW in the CAs group at the cusp level of the maxillary and mandibular canines (P <.05). Both groups exhibited statistically significant reductions in maxillary and mandibular interpremolar widths (P <.05), with a more pronounced decrease in the FAs group (P <.05). In the CAs group, intermolar AW remained stable (P >.05), whereas the FAs group showed a significant post-treatment reduction (P <.05). Moreover, following treatment, the achieved AW exceeded the ClinCheck-predicted values at the gingival level of both maxillary and mandibular molars (P <.05).

In extraction cases, patients treated with CAs demonstrated a larger AW and greater lingual inclination of the anterior teeth than those treated with FAs.

The relatively wider dental arches observed in the CAs group may have implications for space management during treatment. Additionally, the combination of a larger AW and greater incisor retroclination could impose excessive mechanical demands on the flexible aligner trays. Therefore, careful case selection is essential when considering extraction-based treatment with CAs.