The Reliability Of Tooth Image Reconstruction From CT Scans And Impression

Three-dimensional image reconstruction is the fundamental for computer-aided analysis and treatment design. With the development of spiral CT, cone-beam CT, micro CT scan technology, three dimensional image reconstruction from CT scan is becoming the most important method to model establishing for CAD/CAM, body movement animation and biomechanical analysis. Because of the relatively small size and irregular contours of tooth and surrounding bone, digital tooth image reconstruction from CT scan is ineluctably difficult, as well as discrepancy generated. This may consequently affect the further use of the digital image to CAD/CAM, mandibular movement and occlusal contact analysis, and finite element stress analysis.In this study, the reliability of tooth image reconstruction from CT scans was evaluated.Experiment I The accuracy of OKIO-V-100 3D optical digitizerObjectives:The aim of this study to evaluate the dimensional accuracy of OKIO-V-100 3D optical digitizer. Methods:Ball center distance of standard spherite was measured 5 times with 3D optical digitizer and compared with the standard date, the discrepancies were analyzed. Results:The mean discrepancy of ball center distance between ball 1 and 2 were 0.0034±0.0016mm, and 0.0064±0.0048mm for it between ball 2 and 3. Conclusion:OKIO-V-100 3D optical digitizer is precise and reliable for our research.Experiment II The accuracy of tooth surface reconstruction from spiral CT, Micro CT, and cone-beam CT scansObjectives:The aim of this study was to compare the dimensional accuracy of tooth image reconstruction from three kinds of CT scans using three-dimensional superimpositional method. Methods:18 sound extracted human teeth were scanned by 3D optical system, spiral CT, Micro CT, and cone-beam CT scanner. The digital teeth images reconstructed from three kinds of CT scans were superimposed onto the standard image from optical scans respectively. Distribution patterns of shape discrepancy were presented using histogram, as well as showed in different colors on the superimposed images. The ratio of voluminal discrepancy versus the volume of the standard image (RVD/VS) was calculated and analyzed, using the matched-pair t-test and rank sum test. Results: Compared with the standard tooth image, the average RVD/VS of digital teeth images by the Micro CT, cone-beam CT, spiral CT scans were 5.11%,20.73%, 24.60%respectively, and there were statistically significant difference among the three kinds of CT scans (P<0.01). Significant difference were also found among the anterior teeth, bicuspids, and molars (P<0.01). Histogram gave the description about the counts and magnitude of the discrepancies. Marked by difference colors, the superimposed images could give visualized information about the magnitude and distribution patterns of discrepancies. Conclusion:The digital teeth models reconstructed from the spiral CT, Micro CT, cone-beam CT images are inhomogeneous enlarged, compared with the original models.ExperimentⅢThree dimensional accuracy of plaster casts obtained using three impression materialsObjective:The purpose of this investigation was to evaluate the effect of three impression materials on accuracy of reproductions of simian dental arches using a 3-dimensional optical digitizer. Methods:2 simian dental arches were prepared as the master models. Impressions were made for stone casts using three impression materials, including alginate impression materials, C-silicone materials and Impregum-Penta polyether rubber.5 plaster replication models for each master model, as well as for each impression materials were made. The master models and the casts were digitized using a 3-dimensional optical scanner and digitizer. Images of every plaster cast and its original master model were superimposed and obtained the setting cross-section volume of dental crown. The ratios of plaster cast volume change and discrepancy distribution patterns were analyzed. Results: Compared with the volume of the master models, the discrepancies of plaster casts volume were-5.84%,-3.21%,-0.63%for the alginate impression materials, C-silicone materials and Impregum-Penta polyether rubber respectively. The discrepancy between the master models and casts from alginate material was of statistically significance (p<0.05), compared with silicone materials, as well as Impregum-Penta polyether rubber. Maximal deviation of image fitting were located in cervix and gingival areas. Conclusion:Compared with the master model, the volume of all plaster casts from the various kind of impression material become smaller.Impregum-Penta polyether rubber is the most precisely and silicone material is relatively accurate enough for denture model, While the alginate is not. Major error areas are in dental cervical and gingival districts.Experiment IV The preliminary study of dentition surface reconstruction from CT scans and cast scanning imageObjective:The aim of this study was to evaluate the dimensional accuracy of dentition image reconstruction from CT scans and cast scanning image.Methods:A simian dental arch was prepared and digitized as the standard model using OKIO-V-100 3D optical scanner. Impression was made for stone cast using silicone impression material, and the cast was digitized using the optical scanner. Dentition images were also reconstructed from spiral CT and cone-beam CT scans. The dentition images from impression and CT were superimposed onto the standard image. Distribution patterns of dimensional discrepancy were presented using histogram and different colors. The superimposed images were cut using different cross-section. The RVD/VS was analyzed. Results:In the images reconstructed from CT scans, the RVD/VS were more than 40%, compared with the standard image. If the cross-section moved toward gingival direction, RVD/VS declined, while in the image from the cast, RVD/VS increased. Conclusion: Compared with the standard model, the digital dentition images reconstructed from both spiral CT and cone-beam CT are enlarged, and the enlargement is inhomogeneous among different cross-sections. The combination of images from cast scans data and CT scans may be a choice to obtain high quality images of tooth and bone.