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.

Research on a segmentation and evaluation method combining tooth morphology features / Investigación sobre un método de segmentación y evaluación que combina características morfológicas dentales

SUMMARY: To explore a new semi-automatic method to segment the teeth from the three-dimensional volume data which acquired from cone beam computed tomography (CBCT) scanner. Scanned dental cast models are used to evaluate the segmentation accuracy. The CBCT data are loaded to ORS software. Based on gray value, a semi-automatic method was used to segment teeth and then the segmented teeth were saved in STL format data. Smooth the mesh data in the Geomagic Studio software. The upper and lower dental cast models were scanned by a white light scanner and the data was saved in STL format too. After registering the model data to teeth data, the deviation between them was analyzed in the Geomagic Qualify. All teeth could be obtained, the method is simple to use and applied in orthodontic biomechanics. The entire process took less than 30 minutes. The actual measured Root Mean Square (RMS) value is 0.39 mm, less than 0.4 mm. This method can segment teeth from the jaw quickly and reliably with a little user intervention. The method has important significance for dental orthodontics, virtual jaw surgery simulation and other stomatology applications.

RESUMEN: El objetivo de este estudio fue explorar un nuevo método semiautomático para segmentar los dientes a partir de datos de volumen tridimensional adquiridos mediante escáner de tomografía computarizada de haz cónico (CBCT). Los modelos escaneados de moldes dentales se utilizan para evaluar la precisión de la segmentación. Para los datos CBCT se utilizó el software ORS, y basado en el valor gris, se usó un método semiautomático para segmentar los dientes los que posteriormente se guardaron en datos de formato STL. Los datos se ingresaron en el software Geomagic Studio. Los modelo dentales superior e inferior se escanearon con un escáner de luz blanca y la información también se guardó en formato STL. Después del registro y comparación de los datos del modelo y los datos de los dientes, la desviación entre estos se analizó en el programa Geomagic Qualify. Usando este método fue posible obtener de forma fácil todos los dientes y además aplicar en la biomecánica de ortodoncia. El proceso completo demoró menos de 30 minutos. El valor real medido de la raíz cuadrada media fue de 0,39 mm, menos de 0,4 mm. Este método puede segmentar los dientes mandibulares de forma rápida y confiable, con una mínima intervención del usuario. El método tiene una importancia crítica para la ortodoncia, simulaciones virtuales de las cirugías de la mandíbula y otras aplicaciones en estomatología.

A Calibration Method for a Laser Triangulation Scanner Mounted on a Robot Arm for Surface Mapping.

This paper presents and discusses a method to calibrate a specially built laser triangulation sensor to scan and map the surface of hydraulic turbine blades and to assign 3D coordinates to a dedicated robot to repair, by welding in layers, the damage on blades eroded by cavitation pitting and/or cracks produced by cyclic loading. Due to the large nonlinearities present in a camera and laser diodes, large range distances become difficult to measure with high precision. Aiming to improve the precision and accuracy of the range measurement sensor based on laser triangulation, a calibration model is proposed that involves the parameters of the camera, lens, laser positions, and sensor position on the robot arm related to the robot base to find the best accuracy in the distance range of the application. The developed sensor is composed of a CMOS camera and two laser diodes that project light lines onto the blade surface and needs image processing to find the 3D coordinates. The distances vary from 250 to 650 mm and the accuracy obtained within the distance range is below 1 mm. The calibration process needs a previous camera calibration and special calibration boards to calculate the correct distance between the laser diodes and the camera. The sensor position fixed on the robot arm is found by moving the robot to selected positions. The experimental procedures show the success of the calibration scheme.