The influence of different digital registration methods on measurement accuracy of clear aligner treatment outcomes

To compare the agreement of three digital model registration methods of different software packages in measuring angular and linear tooth movements obtained with Clear Aligner Treatment Therapy.

Thirty-two maxillary and mandibular intraoral pre-treatment (T1) and progress (T2) scans of patients undergoing clear aligner therapy were randomly selected, converted to STL files and exported to Geomagic, OrthoAnalyzer, and Compare model registration software packages. The amount of tooth movement of all maxillary and mandibular teeth was calculated in six degrees of freedom.

The angular and linear change in tooth position between T1 and T2 was compared using three different digital model registration software packages. Continuous data was expressed as mean and standard deviation. Intra class Correlation Coefficient for agreement between software programs was used. Significance of the obtained results was expressed at p ≤ 0.01. Differences larger than 0.5 mm for linear measurements and 2º for angular measurements were considered clinically relevant. Geomagic and Compare demonstrated excellent consistency in most dimensions (ICC > 0.90), including maxillary tip (ICC = 0.929) and mandibular tip (ICC = 0.912); however, combinations involving OrthoAnalyzer showed the poorest performance in mandibular torque measurements (ICC = 0.484-0.493), with OrthoAnalyzer's mean values (2.72 ± 4.30°) significantly higher than the other two software platforms; in the OG direction, all combinations involving OrthoAnalyzer showed ICC < 0.5, indicating 'poor reliability.

Geomagic and Compare software demonstrated excellent consistency in measuring tooth movements, whereas OrthoAnalyzer consistently showed poor reliability for mandibular torque (ICC < 0.5) and occlusogingival movements (ICC < 0.5). These differences exceeded the clinical thresholds (0.5 mm for translations, 2° for angular changes) and highlight the importance of cautious interpretation when comparing results across platforms.

The use of CAT is exponentially growing in Orthodontics. Studies that compare treatment accuracy by superimposing two digital models, generate values based on a digital registration software. Does the software employed; cause a difference to the values generated, and subsequently our interpretation of accuracy of a given system? This study aims to address this knowledge gap.