Tooth width measurement using the Lythos digital scanner

Abstract

Introduction: Digital models have become more widely accepted for orthodontic diagnostic purposes. Intraoral scanners have the advantage of eliminating the need for conventional impressions. The aim of the present study was to assess the reliability and reproducibility of the Lythos intraoral scanner and to determine if a significant advantage is delivered over stone model and caliper measurements in tooth width and Bolton ratio accuracy. Methods: The study comprised 30 typodont models for which conventional alginate impressions and digital scans were obtained to generate stone and digital models, respectively. Mesiodistal tooth width measurements and Bolton ratios were obtained with either calipers and stone models or with Digicast (Ormco Lythos digital model software, Ormco, CA, USA) software using digital models. Pearson’s correlation coefficients tested intra-examiner reliability. Interclass correlation coefficients were used to assess agreement between examiners (reproducibility). The differences in the mean tooth width measurements and Bolton ratios from the typodont values and either the digital or conventional method were used to assess validity by applying two tailed t-tests. Results: The measurements obtained from the Lythos and stone models had near perfect intra-examiner agreement (Pearson ≥ 0.98). The inter-examiner reproducibility for tooth widths, anterior Bolton and overall Bolton ratio was high and similar for both methods (Lythos scanner Interclass correlation coefficient (ICC) above 0.89, stone models ICC above 0.92). Stone model measurements were statistically twice as accurate as those derived from the digital system (0.032 mm versus 0.074 mm). There were no significant differences in accuracy between the methods for Bolton calculations. Clinically, there was no difference between the methods for tooth width measurements and Bolton calculations. Conclusions: The Lythos system is as reliable and reproducible as conventional calipers and stone models in tooth width measurements and Bolton calculations. The caliper method presents a statistically more valid tooth width measurement technique but the clinical significance of this is questionable.