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.

The effects of two different patterns on the precision of zirconia all-ceramic crowns / 口腔疾病防治

Objective@#The objective of this study was to compare the early clinical effects of zirconia all⁃ceramic crowns using two different impression methods. Zirconia ceramic crowns were produced using digital models based on either a silicone rubber impression perfusion model in vitro or a 3D mouth scanner.@*Methods @#A total of 50 patients with a planned restoration of the first permanent molar with zirconia all⁃ceramic crowns after root canal therapy were se⁃ lected and randomly divided into two groups: a digital impression by intraoral 3D scanning group and a digital impres⁃ sion by extraoral scanning after silicone rubber impression group. Zirconia all⁃ceramic crowns were created by CAD/ CAM in both groups. Marginal adaptation, proximal contact, and occlusal contact were compared between groups. @*Results@#There was no significant difference between the two groups in marginal adaptation (P > 0.05). For proximal con⁃ tact and occlusal contact, no significant differences regarding the number of cases for the criteria of level A and level B were found between two groups (P > 0.05), while the misfit value in level B was smaller in the first group than in the second group (P < 0.05). @*Conclusion@#Zirconia all⁃ceramic crowns with intraoral 3D scanning show excellent early clinical performance.

A standardization model based on image recognition for performance evaluation of an oral scanner

PURPOSE: Accurate information is essential in dentistry. The image information of missing teeth is used in optically based medical equipment in prosthodontic treatment. To evaluate oral scanners, the standardized model was examined from cases of image recognition errors of linear discriminant analysis (LDA), and a model that combines the variables with reference to ISO 12836:2015 was designed. MATERIALS AND METHODS: The basic model was fabricated by applying 4 factors to the tooth profile (chamfer, groove, curve, and square) and the bottom surface. Photo-type and video-type scanners were used to analyze 3D images after image capture. The scans were performed several times according to the prescribed sequence to distinguish the model from the one that did not form, and the results confirmed it to be the best. RESULTS: In the case of the initial basic model, a 3D shape could not be obtained by scanning even if several shots were taken. Subsequently, the recognition rate of the image was improved with every variable factor, and the difference depends on the tooth profile and the pattern of the floor surface. CONCLUSION: Based on the recognition error of the LDA, the recognition rate decreases when the model has a similar pattern. Therefore, to obtain the accurate 3D data, the difference of each class needs to be provided when developing a standardized model.

Application of 3D Surface Scanners in Forensic Science and Medicine ( I ): Digital Storage of Human Skeletons and Development of Appraisal Methods for Incident Scenes / 대한법의학회지

The aim of this project was to use 3D scanning data collected at incident scenes and various evidence to 1) develop surveying methods based on 3D data consisting of overall and detailed scene evidence, captured by long-range and micros-canner, which can be shared by personnel working in different fields such as forensic medicine, video analysis, physical analysis, traffic engineering, and fire investigation; 2) create digital storage for human skeletons and set the foundation for virtual anthropology; and 3) improve the credibility of 3D evidence by virtual remodeling and simulation of incident scenes and evidence to provide a basis for advanced and high-tech scientific investigation. Two complete skeletons of male and female were scanned using 3D micro-scanner. Each bone was successfully reproduced and assembled in virtual space. In addition, recreating evidence scheduled for invasive examination by creating RP (rapid prototype) was possible. These outcomes could play an important role in setting up the new field of virtual anthropology. Case-specific surveying methods were developed through analysis of 3D scanning data collected by long-range surface scanners at the scenes of vehicular accidents, falls, shootings, and violent crimes. A technique and recording method was also developed for detecting forged seals by micro-scanning the pressure exerted on the seal. Appraisal methods developed in this project could be utilized to secure 3D data of human skeletal remains and incident scenes, create a standard for application, and increase objectivity, reproducibility, and accuracy of scanning methods. We plan to develop case-specific 3D data analysis techniques to improve the credibility of analysis at the NFS and to establish a 3D data collection and analysis team.

Preliminary Research for Applying Appraisal Techniques to Evaluate the Cause of Skin Injury / 대한법의학회지

In the field of the forensic medicine, deciding the cause of the injury is very important. Forensic doctors usually use their naked eyes, two dimensional photos, the characteristics and the distribution of the wounds for evaluating the cause of the injuries. After body release, forensic doctors not infrequently met the questions from the law enforcement whether the injuries were matched with the new facts or statements given through the progression of the investigation. In the face of answering this question, the information or evidence about the injury is insufficient. New technologies and instruments are being developed and will be helpful for getting the evidence from the human skin injuries. In this preliminary study, authors try to find the usefulness of appraisal techniques(3D scanner, trace evidence, TMDT, alternative light) that are already used for other purposes in forensic field. These techniques have their own merits for preserving the evidences from the injured skin. But further studies and systemic approaches are essential for more scientifically verified evaluation of the cause of the skin injury.

The effect of variations in the vertical position of the bracket on the crown inclination / 대한치과교정학회지

Precise bracket positioning is essential in modern orthodontics. However, there can be alterations in the vertical position of a bracket due to several reasons. The purpose of this study was to evaluate the effect of variations in the vertical bracket position on the crown inclination in Korean patients with normal occlusion. From a larger group of what was considered to be normal occlusions obtained from the Department of Orthodontics, College of Dentistry, Seoul National University, each of the final 10 subjects (6 males and 4 females, with an average age of 22.3 years) was selected. The dental models of each of the subjects were scanned three-dimensionally by a laser scanner, and measurements drawn from these were made on the scanned dental casts of the subjects were input into the computer program. From this the occlusal plane and the bracket plane were determined. The tooth plane was then constructed to measure the crown inclination on the bracket plane of each tooth. From a practical standpoint, information was obtained on the extent to which the torque of a tooth would be changed as the bracket position was to be moved vertically (in +/-0.5 mm, +/-1.0 mm, +/-1.5 mm) from its ideal position. A one way analysis of the variance (ANOVA) was used to compare each group of the different vertical distances from the bracket plane on a specific tooth. Duncan's multiple comparison test was then performed. There were statistically significant differences in the crown inclination among the groups of different vertical distances for the upper central incisor, upper lateral incisor, upper canine, upper first and second molars, lower first and second premolars, and lower first and second molars (p<0.05). On the upper anterior teeth, upper molars, lower premolars and lower molars, the resultant torque values due to the vertical displacement of the bracket were different depending on the direction of the displacement, occlusal or gingival. This study implies that the torque of these teeth should be handled carefully during the orthodontic treatment. In circumstances in which the bracket must be positioned more gingivally or occlusally due to various reasons, it would be useful to provide the chart of torque alteration of each tooth referred to in this study with its specified bracket prescription.