To evaluate the reliability and between-method agreement of a freely available orthodontic model analysis software (FusionAnalyser) against a commercial platform (OrthoAnalyzer™) and conventional digital calliper measurements on plaster casts.

In this retrospective cross-sectional study, pre-treatment records of 40 patients collected between 2022 and 2025 were analysed by two examiners, each performing measurements twice at least 15 days apart. Mesiodistal tooth widths, Bolton ratios, and arch space deficiency were measured by all three methods. Intra- and inter-rater reliability were assessed using intraclass correlation coefficients and Dahlberg errors; between-method agreement was assessed with Friedman and Wilcoxon signed-rank tests, and Bland–Altman analyses with predefined clinical thresholds (±0.50 mm for tooth widths, ±1.50 percentage points for Bolton ratios, ±1.00 mm for arch space deficiency).

Of 52 records screened, 40 met the eligibility criteria and were included. ICC values across all methods and both examiners ranged from 0.74 (95% CI 0.56–0.86) to 0.996 (95% CI 0.993–0.998). Between-method differences in mesiodistal tooth widths were small (mostly 0.10–0.30 mm) and remained within the ±0.50 mm threshold. Limits of agreement for the anterior Bolton ratio exceeded ±1.50 percentage points across all comparisons. For mandibular arch space deficiency, 100% of FusionAnalyser-versus-calliper differences fell within ±1.00 mm (mean difference 0.20 mm, 95% CI 0.12–0.29); agreement in the maxillary arch was marginally lower but clinically acceptable.

The free orthodontic software produced tooth-width and arch space deficiency measurements clinically comparable to those of the commercial platform and within clinically acceptable agreement limits of plaster-cast calliper measurements. Bolton ratio agreement was less interchangeable due to the cumulative aggregation of small per-tooth errors. These findings support the adoption of freely available orthodontics-specific software, particularly where commercial licensing is a barrier.