A new way of analyzing tooth movement using universal coordinate system geometry single point superposition in a 3D model

ABSTRACT Introduction: Superposing 3D models is an imminent need. However, current methods rely on marking multiple points on the maxilla and mandible, which could increase point marking and overlapping errors. Objective: This study aimed at developing a method for superimposing 3D models of the maxillary and mandibular arches with Autodesk Inventor® engineering software, using a single universal coordinate system (UCS) point superposition. Methods: A total of 104 STL (stereolithography) models of the maxillary and mandibular arches exported from My iTero® platform were retrospectively selected, in which T0 and T1 were the initial and refinement periods, respectively (n=26 per group). The X, Y, and Z coordinates associated with a single point in each arch were inserted into the models with SlicerCMF® software for model orientation. The arch models with UCS registration were transferred to Autodesk Inventor® for superimposition and to measure tooth movements performed during Invisalign® treatment. Arch expansion, intrusion and rotation were analyzed by two examiners. The statistics were performed using intraclass correlation coefficients (ICC), Dahlberg's formula, and t-test (p<0.05). Results: A reliable method of superimposing 3D digital models using a single UCS point in the maxilla and mandible was developed. ICC showed excellent intra- and inter-examiner correlation (ICC>0.90). A systematic error was not found concerning linear and angular measurements (<1mm and <1.5°, respectively). Digital dental movements could be analyzed, including arch expansion, dental intrusion, and tooth rotation. Conclusions: The developed method was proven reliable and reproducible for superimposing 3D models of the maxillary and mandibular arches by using UCS system.

RESUMO Introdução: A sobreposição de modelos 3D é uma necessidade iminente. No entanto, os métodos atuais dependem da marcação de múltiplos pontos na maxila e na mandíbula, o que pode aumentar a incorporação de erros no processo de sobreposição. Objetivo: O objetivo desse estudo foi desenvolver um método para sobrepor modelos 3D das arcadas superior e inferior utilizando o software de engenharia Autodesk Inventor®, por meio da marcação de um único ponto em cada arcada, usando o sistema de coordenadas universal (UCS). Métodos: No total, 104 modelos STL das arcadas superior e inferior exportados da plataforma My iTero® foram selecionados retrospectivamente, onde T0 foi o período inicial e T1, o de refinamento (n=26 por grupo). As coordenadas X, Y e Z associadas a um único ponto em cada arcada foram inseridas nos modelos usando o software SlicerCMF®. Os modelos com os pontos UCS demarcados foram transferidos para o software Autodesk Inventor® para realizar a sobreposição e medir os movimentos dentários realizados durante o tratamento com Invisalign®. Os movimentos de expansão, intrusão e rotação foram analisados por dois examinadores. A análise estatística foi realizada usando os coeficientes de correlação intra-classe (ICC), fórmula de Dahlberg e teste t (p<0,05). Resultados: Foi desenvolvido um método confiável de sobreposição de modelos digitais 3D usando um único ponto UCS na maxila e mandíbula. O ICC apresentou excelente correlação intra e inter-avaliadores (ICC>0,90). Não foi encontrado erro sistemático nas medidas lineares e angulares (<1mm e <1,5°, respectivamente). Os movimentos dentários puderam ser analisados por meio do método proposto, incluindo expansão da arcada, intrusão e rotação dentária. Conclusão: O método desenvolvido provou ser confiável e reprodutível para sobreposição de modelos 3D das arcadas superior e inferior usando o sistema UCS com marcação de ponto único.

The influence of the model superimposition method on the assessment of accuracy and predictability of setup models.

INTRODUCTION: The aim of this study was to evaluate the influence of different superimposition methods on the accuracy and predictability of conventional and virtual diagnostic setups. MATERIALS AND METHODS: Ten finished cases were used to make a conventional setup and a virtual setup. Second molars were not moved in the two setup situations to allow a reference for superimposition. Conventional and virtual setups were superimposed and compared by second molar registration and the whole surface best fit method (WSBF). Conventional and virtual setups were compared to the posttreatment models with WSBF and palatal rugae best fit (PRBF). Anterior, intermediate, and posterior regions of the dental arches were compared. The paired t-test was used to compare the mean differences between conventional and virtual setups, posttreatment models and both conventional and virtual setups by the WSBF method, and between maxillary posttreatment and virtual setup models using the WSBF and PRBF methods. RESULTS: Conventional and virtual setups differed depending on the two superimposition methods used. Superimposition of the posttreatment models and both setups using WSBF presented no statistically significant differences. There were statistically significant differences between posttreatment and virtual setup models using WSBF and PRBF superimposition methods. CONCLUSIONS: The model superimposition method influenced the assessment of accuracy and predictability of setup models. There were statistically significant differences between the maxillary posttreatment and virtual setup models using the WSBF and the PRBF superimposition methods. It is important to establish stable structures to evaluate the accuracy and predictability of setup models.

Accuracy and reliability of measurements performed using two different software programs on digital models generated using laser and computed tomography plaster model scanners.

OBJECTIVE: The aim of this study was to compare the accuracy and reliability of measurements performed using two different software programs on digital models generated using two types of plaster model scanners (a laser scanner and a computed tomography [CT] scanner). METHODS: Thirty plaster models were scanned with a 3Shape laser scanner and with a Flash CT scanner. Two examiners performed measurements on plaster models by using digital calipers and on digital models by using Ortho Analyzer (3Shape) and Digimodel® (OrthoProof) software programs. Forty-two measurements, including tooth diameter, crown height, overjet, overbite, intercanine and intermolar distances, and sagittal relationship, were obtained. RESULTS: Statistically significant differences were not found between the plaster and digital model measurements (ANOVA); however, some discrepancies were clinically relevant. Plaster and digital model measurements made using the two scanning methods showed high intraclass coefficient correlation values and acceptable 95% limits of agreement in the Bland-Altman analysis. The software used did not influence the accuracy of measurements. CONCLUSIONS: Digital models generated from plaster casts by using laser and CT scanning and measured using two different software programs are accurate, and the measurements are reliable. Therefore, both fabrication methods and software could be used interchangeably.