Tooth Dimensions Do Not Predict Clear Aligner Expansion Efficiency in Study

Measurements of posterior tooth length and crown-root ratio obtained from dental panoramic radiographs do not significantly predict crown-level transverse expansion efficiency during clear aligner therapy, according to a retrospective study published in Scientific Reports. The research evaluated whether specific anatomical variations in tooth morphology correlate with the clinical success of arch expansion in orthodontic patients treated with clear aligners. The investigation aimed to assess the association between dental panoramic radiograph-derived posterior tooth length, crown-root ratio, and transverse expansion efficiency, examining whether individual tooth dimensions account for differences between planned and achieved movements.

The investigation, authored by researcher Saniye Merve Cengiz, evaluated a retrospective cohort of twenty-five patients treated with Invisalign whose therapy involved transverse expansion across both arches. For each patient in the study group, planned expansion values were obtained directly from the ClinCheck digital treatment setup. To evaluate the actual clinical movements achieved during therapy, achieved expansion was measured on pre-treatment and post-treatment digital models using OrthoAnalyzer software. This digital modeling process allowed for direct comparisons between the expansion planned in the ClinCheck setup and the expansion actually achieved in patient dental arches across all evaluated dental regions.

Total tooth length and crown-root ratio values for posterior teeth were obtained from pre-treatment dental panoramic radiographs utilizing ImageJ image analysis software. The research protocol then employed both correlation analyses and multivariable regression analyses to evaluate whether these morphologic variables exhibited any statistically significant relationships with transverse expansion efficiency. These statistical assessments were designed to determine whether dental panoramic radiograph-derived tooth dimensions could reliably predict how efficiently clear aligners deliver transverse expansion at the crown level.

The measurements demonstrated that achieved expansion values were significantly lower than planned values across all evaluated dental regions (p < 0.05). Across the patient cohort, measured transverse expansion efficiency ranged from 80.03% to 91.08%, establishing that clear aligners delivered less transverse expansion than originally programmed in the ClinCheck setup for every dental region examined. Despite the documented variation in expansion efficiency, correlation analyses identified no significant correlations between expansion efficiency and total tooth length (p > 0.05). Similarly, no significant correlation was found between expansion efficiency and the crown-root ratio (p > 0.05).

Multivariable analyses likewise revealed no significant independent effects of the evaluated tooth morphology variables on expansion efficiency. Because dental panoramic radiograph-derived posterior tooth length and crown-root ratio were not significant predictors of crown-level transverse expansion efficiency during clear aligner therapy, the author concluded that transverse expansion outcomes are influenced by factors beyond the specific tooth morphology variables evaluated in the study.

Subject of Research: Tooth morphology and transverse expansion efficiency in clear aligner therapy

Article Title: Association of tooth length and crown-root ratio with transverse expansion efficiency in clear aligner therapy

Article References: Cengiz, S. M. (2026). Association of tooth length and crown-root ratio with transverse expansion efficiency in clear aligner therapy. Scientific Reports. https://doi.org/10.1038/s41598-026-80429-w

Image Credits: AI Generated

DOI: 10.1038/s41598-026-80429-w

Keywords: clear aligner therapy, transverse expansion, expansion efficiency, tooth length, crown-root ratio, Invisalign, ClinCheck, dental panoramic radiograph, OrthoAnalyzer, ImageJ, posterior teeth, digital models, multivariable regression, orthodontic movement, retrospective evaluation, crown-level expansion