Geomagic Studio Research Articles

Abnormal flow pattern of low wall shear stress and high oscillatory shear index in spontaneous vertebral artery dissection with vertebral artery hypoplasia.

Spontaneous vertebral artery dissection (sVAD) might tend to develop in vertebral artery hypoplasia (VAH) with hemodynamic dysfunction and it is crucial to assess hemodynamics in sVAD with VAH to investigate this hypothesis. This retrospective study aimed to quantify hemodynamic parameters in patients with sVAD with VAH. Patients who had suffered ischemic stroke due to an sVAD of VAH were enrolled in this retrospective study. The geometries of 14 patients (28 vessels) were reconstructed using Mimics and Geomagic Studio software from CT angiography (CTA). ANSYS ICEM and ANSYS FLUENT were utilized for mesh generation, set boundary conditions, solve governing equations, and perform numerical simulations. Slices were obtained at the upstream area, dissection or midstream area and downstream area of each VA. The blood flow patterns were visualized through instantaneous streamline and pressure at peak systole and late diastole. The hemodynamic parameters included pressure, velocity, time-averaged blood flow, time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), endothelial cell action potential (ECAP), relative residence time (RRT) and time-averaged nitric oxide production rate (TARNO). Significant focal increased velocity was present in the dissection area of steno-occlusive sVAD with VAH compared to other nondissected areas (0.910 m/s vs. 0.449 vs. 0.566, p < 0.001), while focal slow flow velocity was observed in the dissection area of aneurysmal dilatative sVAD with VAH according to velocity streamlines. Steno-occlusive sVAD with VAH arteries had a lower time-averaged blood flow (0.499 cm3/s vs. 2.268, p < 0.001), lower TAWSS (1.115 Pa vs. 2.437, p = 0.001), higher OSI (0.248 vs. 0.173, p = 0.006), higher ECAP (0.328 Pa-1 vs. 0.094, p = 0.002), higher RRT (3.519 Pa-1 vs. 1.044, p = 0.001) and deceased TARNO (104.014 nM/s vs. 158.195, p < 0.001) than the contralateral VAs. Steno-occlusive sVAD with VAH patients had abnormal blood flow patterns of focal increased velocity, low time-averaged blood flow, low TAWSS, high OSI, high ECAP, high RRT and decreased TARNO. These results provide a good basis for further investigation of sVAD hemodynamics and support the applicability of the CFD method in testing the hemodynamic hypothesis of sVAD. More detailed hemodynamic conditions with different stages of sVAD are warranted in the future.

Visible trephine-based foraminoplasty in PTED leads to asymmetrical stress changes and instability in the surgical and adjacent segments: a finite element analysis

This study aimed to construct a multi-segment lumbar finite element model (FEM) of PTED surgery to analyze the changes in stress and ROM after visible trephine-based foraminoplasty. The CT scans of a 35-year-old healthy male were used to develop a multi-segment lumbar FEM with Mimic, Geomagic Studio, Hypermesh and MSC.Patran. Different foraminoplasty was performed on the model, and these were grouped into normal group (A), the ventral resection group (B), the apex resection group (C), the ventral + apex + isthmus resection group (D), and the SAP + isthmus + lateral recess resection group (E). A vertical load of 500N and a torque of 10N·M were applied to the upper surface of the L3 vertebral body to simulate the biomechanical characteristics under the motion of flexion, extension, lateral bending, and rotation. The von Mises stress maps of the intervertebral f, vertebral body, facet joints, and the ROM of the L3-S1 intervertebral disk were calculated and analyzed. The changes of peak stress on the vertebral body for each group were not significant in the same motion state. Significant stress differences were observed in the L4/5 intervertebral disks, while no obvious stress changes were observed for the L3/4 and L5/S1 intervertebral disks. The stress of the L3/4 and L5/S1 facet joints decreased after L4/5 foraminoplasty, while the stress of L4/5 facet joints displayed an overall increasing trend. Significant asymmetrical stress changes of bilateral facet joints were observed in all three segments, particularly during bilateral rotation movements. The ROM of L3-S1 gradually increased from Group A to Group E, especially during flexion, left lateral bending, and right rotation, with the highest elevation observed for the L45 ROM. Our FEM indicated that enlarged resection and exposure of the articular surface could lead to significant asymmetrical stress changes in the bilateral facet joints and ROM instability of the surgical and adjacent segments. These findings suggested that unnecessary and excessive resection should be avoided in PTED to reduce the incidence of low back pain and the risk of postsurgical degeneration.

Evaluation of the trueness and adaptation of zirconia crowns fabricated with stereolithography.

The aim of this study was to evaluate the accuracy and adaptation of all-ceramic zirconia crowns fabricated by stereolithography (SLA) compared with computer-aided design/computer-aided manufacturing (CAD/CAM) milling technology. Ten all-ceramic zirconia crowns each were fabricated with SLA (experimental group) and CAD/CAM numerical control milling technology (control group). The accuracy (including trueness and precision), and the internal and marginal adaptation of the crowns were measured with the optical impression and silicone rubber film method and the three-dimensional deviation analysis software Geomagic studio, and the results were statistically analyzed. The results indicated no statistical difference in trueness and the occlusal, axial and marginal adaptation between groups (p>0.05), and the precision in the SLA group was better than that in the milling group (p<0.05). Thus, crowns fabricated with SLA meet clinical application requirements.

Hollow screw fixation of type II avulsion fractures of the calcaneal tuberosity using the finite element analysis.

We aimed to establish a model of type II avulsion fractures of the calcaneal tuberosity treated with 2 hollow screws implanted in different directions and to analyze the biomechanical properties of the model using the finite element method. The Dicom data of the calcaneal bone obtained after computed tomography scan were inputted into Mimics 21.0 software and Geomagic Studio software to generate a 3D finite element digital model of the calcaneal bone. The model was then imported into SOLIDWORKS 2020 software. Based on the Beavis theory, the calcaneal bone was cut to build a type II avulsion fracture model of the calcaneal tuberosity; the calcaneal fracture was then simulated by internal fixation using hollow screws. Two screws were used to fix the calcaneal bone from the calcaneal tuberosity in different ways, resulting in 3 different calcaneal models (Model 1 involved 2 screws for fixing the fracture vertically; Model 2 had 2 screws for fixing the fracture cross-wise; and Model 3 had 2 screws for fixing the fracture parallelly). Three internal fixation models were loaded under the same conditions, and lines finite element analysis was then performed to calculate the stress distribution of the generated internal fixation models. Under the same loading conditions, compared with Models 2 and 3, Model 1 exhibited smaller maximum displacement values of the heel bone, maximum equivalent force values of the screws, and more dispersed stresses. Avulsion fractures of the calcaneal tuberosity can be treated using 2 screws to fix the fracture vertically (Model 1), which is more biomechanically relevant.

The Church of Pobeten in the XIV–XV centuries: historical and virtual reconstruction

The purpose of our work is to study the history and virtual reconstruction of the church of Pobeten, an object of historical and cultural heritage of the XIV-XV centuries. The method of analogy, creation of a digital model, photogrammetry, methods of historical informatics were used in the work. Special attention is paid to the history of the church of Pobeten and the work on creating its virtual copy. It describes working with various tools (Agisoft Metashape, Sculptris Alpha, Geomagic Studio and Sketch Up) to create photogrammetric and three-dimensional models of a historical object of the XIV century. The possibilities of using photogrammetry and three-dimensional modeling methods in the synthesis to create a virtual reconstruction of the Pobeten church are considered. The result of the work was the receipt of versatile historical data about the church of Pobeten and a virtual three-dimensional model based on them, which has the ability to edit: it can be supplemented with various elements, as well as integrated into larger works. The scope of application of the work and the results obtained can be historical local lore, preservation of objects of historical heritage, the use of the resulting product in museum installations. An interdisciplinary approach in historical research combined with computer science methods, specifically with three-dimensional computer modeling, provides exceptional opportunities, especially with the growth of information technology development, and is an actual tool of historical research in modern science.

Changing scanning angles on improving finish line trueness of the full crown preparation

Objective: To explore the effect of scanning methods on finish line trueness of the full crown preparation. Methods: The standard full crown preparation model of the right maxillary first molars was prepared by using the maxillary standard resin dentition model. The standard preparation was scanned by imetric scanner and data were used as the true value. CEREC Omnicam and 3Shape TRIOS were used to scan the standard preparation. According to the scanning methods, they were divided into parallel scanning group, occlusal wave scanning group and buccolingual wave scanning group. Each group was scanned repeatedly 6 times. The data were imported into Geomagic Studio 2013 software, and the local finish line image data of the mesial, distal, buccal and lingual regions of the full crown preparation were extracted respectively. Three-dimensional deviation analysis was performed with the reference true value, and the root- mean-square error (RMSE) was the evaluation index of scanning trueness. The statistical method was one-way ANOVA. Results: Parallel scanning group: in general, the RMSE value of complete finish lines of scanner B [(35±6) μm] was significantly lower than that of scanner A [(44±7) μm](P<0.05). After scanner A occlusal wave scanning, the RMSE values of the mesial and distal finish lines [(33±5) and (50±12) μm] were significantly lower than those of parallel scanning group (P<0.05). After buccal and lingual wave scanning, the RMSE values of local finish lines in the mesial, distal, buccal and lingual regions [(37±3), (50±6), (28±6) and (29±8) μm] were significantly lower than those in parallel scanning group [(45±9), (63±7), (38±3) and (40±3) μm] (P<0.05). No significant difference was found in the RMSE values of the mesial, distal, buccal and lingual regions of scanner B between parallel scanning group, occlusal wave scanning group and buccolingual scanning group (P>0.05). Conclusions: The scanning trueness of the full crown preparation finish line obtained by the active triangulation scanning equipment can be improved by changing the scanning method to wave scanning.

A Complete Methodology for Structural Finite Element Analysis of Terracotta Sculptures Based on a 3D Scanned Model: A Case Study on the Terracotta Warriors (China)

ABSTRACT In this paper, the structural mechanical analysis of the Terracotta Warriors, using 3D laser scanning technology and finite element methodology (FEM) is presented. The workflow of the case study mainly includes three steps along with the application of different software. The first step is to capture the point cloud using a 3D laser scanner and the reversed modeling using Geomagic Studio. Next, the model is imported into Hypermesh to accomplish mesh generation. Finally, the meshed model is imported into ABAQUS for analysis. The workflow constitutes an innovation for introducing a mesh generation method that is commonly used in biomechanics by Hypermesh, software that offers benefits such as functional and simple operation. In the analysis, cases such as sculpture at different incline angles to the ground and some particular conditions are included. The results indicate that apart from the ankle, the thigh and hip joints also remain in an adverse position under gravity. Given that the ground for storage and exhibition is not ideally flat, the stress on the whole structure can be reduced by rotating the sculpture at an appropriate angle.

The placement of percutaneous retrograde acetabular posterior column screw based on imaging anatomical study of acetabular posterior column corridor

ObjectiveTo explore the entry point, orientation, and fixation range of retrograde acetabular posterior column screw.MethodThe computed tomography data of 100 normal adult pelvises (50 males and 50 females, respectively) were collected and pelvis three-dimensional (3D) reconstruction was performed by using Mimics software and the 3D model was imported into Geomagic Studio software. The perspective of acetabular posterior column was carried out orienting from ischial tuberosity to iliac fossa in the Mimics software. Virtual screw was inserted perpendicular to the transverse section of acetabular posterior column corridor, and the maximum screw diameter, entry point, orientation, exit point were measured. The screw fixation range, the easy-to-penetrate sites, and intraoperative optimal fluoroscopic views were assessed.ResultsThe acetabular posterior column corridor showed a triangular-prism shape. The virtual screw entry point was located at the midline between the medial and lateral edges of the ischial tuberosity. The distance between the entry point and the distal ischial tuberosity was around 13 mm. The distances between the exit point and the true pelvis rim, and ipsilateral anterior sacroiliac joint line were (19.33 ± 2.60) mm and (23.65 ± 2.42) mm in males, respectively. As for females, those two data were (17.63 ± 2.00) mm and (24.94 ± 2.39) mm, respectively. The maximum diameters of screws were (17.21 ± 1.41) mm in males and (15.54 ± 1.51) mm in females. The angle between the retrograde posterior column screw and the sagittal plane was lateral inclination (10.52 ± 3.04)° in males, and that was lateral inclination (7.72 ± 2.99)° in females. Correspondingly, the angle between the screw and the coronal plane was anterior inclination (15.00 ± 4.92)° in males, and that was anterior inclination (12.94 ± 4.72)° in females. Retrograde acetabular posterior column screw through ischial tuberosity can fix the acetabular posterior column fractures which were not 4 cm above the femoral head center. The easy-to-penetrate sites were located at the transition between the posterior acetabular wall and the ischium, the middle of the acetabulum, and 1 cm below the greater sciatic notch, respectively. The iliac oblique 10°, iliac oblique 60°, and obturator oblique 60° views were the intraoperative optimal fluoroscopic views to assess whether the screw was safely inserted.ConclusionRetrograde acetabular posterior column screw entry point is located at the midline between the medial and lateral edges of the ischial tuberosity, which is 1.3 cm far from the distal ischial tuberosity. The screw direction is about 10° lateral inclination and 15° anterior inclination, which can fix the acetabular posterior column fractures which were not 4 cm above the femoral head center.

Biomechanical analysis of stress around the tilted implants with different cantilever lengths in all-on-4 concept

BackgroundMany clinical studies have reported the high success rate of the All-on-4 concept. In the present study, we aimed to compare the stress distribution with different tilted distal implants and cantilever lengths in an All-on-4 system using the two-dimensional photoelastic method and to establish the All-on-4 implant photoelastic model by computer-aided design (CAD) and rapid prototyping (RP). MethodsThe data of the human edentulous mandible were acquired by computed tomography (CT). Three human edentulous mandible All-on-4 implant models with different distally inclined implant holes were fabricated using Mimic, Geomagic Studio software, and a light solidifying fast shaping machine. Then the final photoelastic models were established through the traditional method. Each of the three models had four NobelSpeedy Replace implants between the interforaminal regions. The two posterior implants were placed 0, 15, and 45 degrees distally before the mental foramen. The four implants were splinted by wrought cobalt-chromium alloy frameworks. Each of the three photoelastic models was submitted to a 150 N vertical load at five points on the framework: the central fossa of the mandibular first molar, and 0 mm, 5 mm, 10 mm, and 15 mm of the cantilever length. The stress produced in the models was photographed with a digital camera, and the highest value of the stressed fringe pattern was recorded.ResultsThe All-on-4 implant photoelastic model established by CAD and RP was highly controllable and easy to modify. The position and inclination of implants were accurate, and the frameworks could be passively emplaced. The stress values were higher around a single tilted implant compared with the distal implant in All-on-4 with the same inclination. The 0-degree distal implant and 45-degree distal implant demonstrated the highest and lowest stress when loading at the central fossa of the mandibular first molar, respectively. With the same inclination of distal implant, the peri-implant bone stress increased as the length of cantilever increased.ConclusionThe method of establishing the All-on-4 implant photoelastic model by CAD and RP was highly controllable, convenient, fast, and accurate. The tilted implants splinted in the fully fixed prosthesis with reduced cantilever lengths did not increase the stress level compared with the vertical distal implants.And this illustrated that the influence of cantilever on stress distribution was greater than the influence of implant inlination.

Clinical study of precision analysis and deviation control of a domestic guide plate-assisted edentulous implant surgery

PurposeTo evaluate the accuracy of a domestic digital implant guide plate to assist edentulous implant surgery, analyze the sources of deviation, and reduce the deviation of the guide plate. MethodsIn total, 14 edentulous patients were selected, and 100 implant sites were measured. The preoperative cone beam computerized tomography (CBCT) data were imported into the software to design and fabricate the guide plate. After implant surgery,the data were imported for 3D reconstruction and alignment model was exported into the Geomagic Studio software for deviation measurement. ResultsAnalysis of the overall accuracy of the domestic guide plate showed deviation of the implant neck center, horizontal direction, implant base center, depth, and angle of 0.83 ± 0.27 mm, 0.39 ± 0.17 mm, 1.11 ± 0.35 mm, 0.45 ± 0.19 mm, and 3.16 ± 1.73°. There were not statistically significant difference (p>0.05) between the tooth/mucosa-supported guide plate and the mucosa-supported, mandibular guide plate and maxillary, vertical implantation and inclined, anterior implant sites and posterior teeth. There was a statistically significant difference (p<0.05) between the use of the modified non-pressure plate tool box and the pressure plate tool box. ConclusionFirst, the domestic implant guide plate can significantly improve the accuracy and efficiency in edentulous implant surgery. Second, the accuracy of the tooth/mucosa-supported guide plate is higher than mucosa-supported guide plate. Third, the accuracy of the new tool box without pressure plate is improved.

Preliminary measurement and analysis of the condylar movement envelope surface parameters in healthy adults

Objective: To measure and analyze parameters of the three-dimensional (3D) model of the condylar movement envelope surface (ES) and provide a reference for the design of the temporomandibular prosthesis. Methods: Thirty-four healthy adults aged (25.4±2.8) years were recruited from the Department of Oral and Maxillofacial Surgery, Peking University School and Hospital of Stomatology as subjects. There were 9 males and 25 females, most of them were university students and others outside the university have received undergraduate education or above. Condylar movement ES were obtained using the previous method on the 3D trajectory of condyle. The simulations of condylar movement were projected according to opening movements, protrusion movements, and lateral movements respectively. The total area of the ES and the area proportions of models formed by above different mandibular movements were measured and calculated. The adults' head and maxillofacial 3D models reconstructed by cone beam CT were registered with ES in Geomagic Studio. The inner and outer poles of the condyle, the corrective sagittal axis of the ES, and the median sagittal plane (MSP) were calibrated in registration models using Geomagic Studio, and the parameters were measured as follows: the anteroposterior and medialateral diameters of the condyle, the anteroposterior diameters and the transverse diameters (anterior, middle and posterior parts) of the ES, the angles between the corrective sagittal axis of the ES and MSP (ES-MSP). Pearson correlation analysis was performed by SPSS 24.0. Results: The total area of the ES was (760±133) mm2, the opening movement part accounted for (63.3±15.2)%, the protrusion movement part accounted for (14.9±9.6)%, the lateral movement part accounted for (21.8±13.3)%. Parameter measurements were as follows: mediolateral diameters of condyle was (19.8±2.3) mm; anteroposterior diameter of the ES was (21.2±3.1) mm, the transverse diameters (anterior, middle and posterior parts) of the ES were (20.6±2.4), (20.4±2.4), (22.0±2.6) mm, respectively; the transverse diameters of the ES were about 2 mm larger than that of the condyle. The angle between the corrective sagittal axis of ES and the MSP was 6.8°±6.2°. The coefficient of variation (CV) in these parameters showed: CV of the transverse diameters (anterior, middle and posterior parts) of the ES and mediolateral diameter of the condyle were 0.98, 0.99, 0.93, respectively (P<0.001). CV of aera of ES and mediolateral diameter of the condyle was 0.64 (P=0.002). CV of aera of ES and anteroposterior diameter of ES was 0.62 (P=0.004). Conclusions: The 3D envelope surface model formed by mandibular opening movements accounted for the largest proportion of the ES. The corrective sagittal axis of the ES was at an angle to the MSP, the transverse diameters (anterior, middle and posterior parts) of the ES were approximately 2 mm larger than the mediolateral diameter of the condyle, the transverse diameters (anterior, middle and posterior parts) of the ES were highly positively correlated with the mediolateral diameter of the condyle.

Evaluation of Articular Morphology and Congruency using a Combination of 3 Dimensional CT Based Bone Segmentation and Joint Surface Mapping

Category: Hindfoot; Ankle; Other Introduction/Purpose: Recently joint congruence has been given a lot of focus in studies evaluating foot and ankle deformities. XR and WBCT scans are the commonly used techniques, however, neither can accurately reflect articular surfaces particularly in joints where only partial bone surfaces are covered by articular cartilage. This study introduced a novel technique using 3D surface mapping and CT bone segmentation to assess articular morphology and congruence of the calcaneocuboid (CC) joint. Methods: A CT scan of a fresh frozen cadaveric foot without trauma history nor deformity was taken and then the calcaneus and cuboid bones were dissected free with all soft tissue removed. Segmentation and reconstruction of the calcaneus and cuboid from the CT scan was performed using Materialise Mimics. Surface mapping and digital reconstructions of the calcaneus and cuboid bones as well as the calcaneocuboid articular surfaces were then obtained using an Artec Space Spider 3D scanner. Both the CT and surface mapping reconstructions were imported into Geomagic Studio 10 where the reconstructed calcaneus via CT was merged with the reconstructed calcaneus via surface mapping. The same procedures were performed with the reconstructions of the cuboid. Then cartilage surfaces from the calcaneocuboid joint of the surface mapping reconstruction were outlined on and compared to the bone surfaces underneath. Results: The articular surfaces of the calcaneocuboid joint were shaped according to the bone contour noting however that on both sides, the articular surface did not fully match the bone surface. On the calcaneal side, the dimension of the bone surface was 357.72 mm2, while the articular surface was 300.92 mm2 (percentage of bone covered by cartilage: 84.12%). On the Cuboid side, the dimension of the bone surface was 372.41 mm2 while the articular surface was 302.60 mm2 (percentage of bone covered by cartilage: 81.25%). When restoring the articulation of the reconstructed calcaneus and cuboid, there was incongruence of the two bone surfaces with the dorsolateral corner of the calcaneus and the plantarmedial corner of the cuboid uncovered by its contralateral bone. The same applied to the articular surfaces but at a smaller uncovering level (Figure 1). Conclusion: Even with 3D CT segmentation and reconstruction of articulating bones, one has no knowledge of the precise articular surface of a joint. 3D surface scanning is a reliable method to study morphology of the cartilage surface of a joint. 3D CT reconstruction combined with 3D surface mapping is a useful tool for studying both the bony surface and the cartilage surface of a joint. This study has implications for treatment of any joint in the foot which appears subluxated on XR or CT scans and where this may represent the normal bone morphology but not true subluxation. Articular congruence study under weightbearing condition is currently under investigation by our research group.

3D Light Scanner Analysis of the Lateral Collateral Ligaments of the Ankle: An Anatomical Study

Category: Basic Sciences/Biologics; Ankle Introduction/Purpose: Recently an anatomical study described a medial connection between the anterior talofibular ligament inferior fascicle (ATFLif), calcaneofibular ligament (CFL) and posterior talofibular ligament (PTFL). Therefore, there is no research evaluating the lateral ligaments and their relationships through a three-dimensional view achieved by a digital marking of their foot prints. The authors hypothesize that a three-dimensional analysis made only by an accurately digital analysis can clarify the lateral collateral ligaments (LCL) connections and their foot prints relations. This work aims to carry out an anatomical study in cadaveric pieces in which the lateral ankle ligaments were dissected and evaluated by a tridimensional scanner that allows a digitally and three-dimensional assessment of their foot prints and connections. Methods: An anatomical study was performed in 11 fresh-frozen ankle specimens. Each ankle was dissected to achieve the amputation of the calcaneus, talus and fibula, keeping the inserts of the footprints of LCL. After that, each bone piece with the insertion remnants of the LCL was submitted to an evaluation by a scanner machine. Surface scans for these bones were collected using a structured light scanner. Each bone piece was set on a 3D automatic turntable to capture a 360° scan and was scanned in two orientations, with 6 scans per orientation. Finally, all the scans were aligned and final fused models were created using the HP DAVID software package and exported to a wavefront 3D object file. The 3D models were imported into Geomagic Studio to calculate surface area of the LCL foot prints. Results: A total of 11 units of each, talus, fibula and calcaneus were dissected from 11 ankles specimens. The ATFL was identified as a two-fascicled ligament and the fibers connecting fibers between the ATFLif and CFL was present in all specimens. In two talus there was only one insertion of the ATFL. After scanning the bones, the authors observed that the foot prints of ATFLif, CFL and PTFL were contiguous at medial side of the fibula, with an average of the surface area of 486,7 mm2. The foot print of the CFL on the calcaneus was located at the junction of a vertical line tangent to the highest point of the posterior subtalar with a horizontal line extending from the sinus tarsi in all specimens. Conclusion: This study demonstrated by a 3D analysis that the LCL of the ankle share the same foot print at medial side on the fibula and are all connected since the foot prints of the ATFL inf, CFL and PTFL were contiguous. In the case of associated proximal lesions of the ATFLif and CFL, ligaments repair with a single suture may be considered. This can be applied in surgical procedures in patients with lateral ankle instability.fig

Treatment effect analysis of curettage for jaw cysts based on volumetric assessment and image registration

The study was conducted to develop a visual and intuitive quantitative evaluation method for maxillary cystic lesions after curettage. Mimics 16.0 and Geomagic Studio 2013 were used to form a precise reconstruction of the cystic lesion morphology of 60 cases; the average reduction rates and 95% confidence interval were calculated. Computed tomography (CT) registration was performed before and after surgery to observe morphology features of the bone regeneration of the cystic area. The average reduction rates (RR) of the cysts after curettage were (43.56 ± 16.79)%, (54.33 ± 17.15)% and (68.53 ± 15.99)% at 3 months, 6 months and 12 months after surgery, respectively. The average monthly reduction rates (MRR) were (12.07 ± 4.35)%, (8.16 ± 2.84)% and (5.35 ± 1.52)% at 3 months, 6 months and 12 months after surgery, respectively. Correlation analysis by comparing with each group showed that the effect of sex and age in the 3-month group and the initial size in the 12-month group on RR and MRR were statistically significant. Within the limitations of the study it seems that the chosen approach for quantitative evaluation of the therapeutic effect of curettage for jaw cystic lesions might facilitate visual and quantitative follow-up of cyst curettage and timely detection of recurrence.

Compressive behaviour of corroded thin-walled circular section steel stub columns

The influences of corrosion on the buckling behaviour and bearing capacity of the circular section steel tubular (CST) stub columns subject to axial compression were investigated experimentally and numerically. Seven CST stub columns with chloride corrosion were investigated. After the accelerated chloride corrosion test on CST stub columns, three methods were used to evaluate the corrosion degree of each specimen. A monotonic axial compression test was then carried out. Based on the test results, the influence of corrosion degree on failure mode, bearing capacity and deformation behaviour were analysed. In addition, the surface morphology of the corroded column was obtained by a 3D Scanner and processed by Geomagic Studio software. Then the reconstructed models were imported into finite element (FE) software ABAQUS. This novel method considering the natural morphology of surface corrosion was verified by comparing the FE solutions to the experimental result. Based on the verified FE model, the deterioration of the mechanical behaviour of corroded compression stub columns under the actual rusty surface was also studied. It was found that the rough surface of the corroded specimens cause non-uniform stress distribution and change buckling mode. Parametric analysis, therefore, was conducted to study the influences of the corrosion degree and steel grade on the yield load. Finally, the proposed design formula is able to predict the axial compression strength of the rusty stub column with reasonable accuracy.

Digital study on the relationship between position of patellar high point and shape of osteotomy surface in Chinese

To measure the position of patellar high point and the shape of the osteotomy surface, and to analyze their relationship, distribution, and gender differences. A total of 127 patients who needed anterior cruciate ligament reconstruction or meniscus repair due to trauma between September 2020 and September 2021 were selected as the research subjects. There were 71 males and 56 females, with an average age of 30.5 years (range, 19-43 years). There were significant differences in height and body weight between male and female patients ( P<0.05), but no significant difference in age and body mass index ( P>0.05). The three-dimensional model of the patella was reconstructed in Mimics software based on the CT images of the knee joint, and then imported into Geomagic Studio software for virtual osteotomy of the patella. The horizontal axis and vertical axis of the osteotomy surface represented the total width (W) and total height (H) of the osteotomy surface, respectively. Then the osteotomy surface was divided into four quadrants with the two axes: inner proximal, inner distal, outer proximal, and outer distal, and the inner width (W1), proximal height (H1), outer width (W2), and distal height (H2) were measured. The midpoint of the patellar ridge was selected as the patellar high point, and the point projected onto the osteotomy surface was defined as the optimal point for patellar prosthesis positioning (OPPP). The distances of OPPP on the horizontal axis (L1) and vertical axis (L2) relative to the center of the osteotomy surface were measured and L1/W1 and L2/H1 were also calculated; the quadrant distribution of OPPP was recorded. The patients were grouped according to gender, and the morphological parameters of the osteotomy surface (W, W1, W2, H, H1, H2) and the parameters related to the position of the OPPP (L1, L2, L1/W1, L2/H1) were analyzed between groups. The width and height of each osteotomy surface of the patella in males were significantly larger than those in females ( P<0.05). As for the relationship between OPPP and osteotomy surface, the L1 of both male and female patients was 1-7 mm, and there was no significant difference in the distribution between the two groups ( χ 2=8.068, P=0.149); L1/W1 in both male and female patients was mainly 1/10-3/10. The L2 of male patients was 0-5 mm, and that of female patients was -1-4 mm; the difference in distribution between the two groups was significant ( χ 2=15.500, P=0.006); L2/H1 in both male and female patients was mainly 0-1/5. The OPPP of male patients was mainly distributed in the inner proximal (98.59%) and outer proximal (1.41%) quadrants, while the female patients were distributed in the inner proximal (91.07%), inner distal (7.14%), and outer proximal (1.79%) quadrants. There was significant difference in the OPPP quadrant distribution between the two groups ( χ 2=5.186, P=0.036). The OPPP points are widely distributed but mainly concentrated on around 1/5 of the medial patella surface and around 1/10 of the superior patella surface. A small portion of females' OPPP were inferior while all males' OPPP were superior to the center of the patella.

Design of Personalized Cervical Fixation Orthosis Based on 3D Printing Technology.

The movement of the cervical spine should be restricted throughout the rehabilitation phase after it has been injured. Cervical orthosis is commonly utilized in clinical settings to guarantee cervical spine stability. However, to date, the investigations are limited to patient-specific cervical fixation orthoses. This study provides a new idea for making personalized orthoses. The CT data of the patient's cervical spine were collected, then mimics were used for reconstructing the skin of the cervical spine, the Geomagic Studio was used for surface fitting, the Inspire Studio was used for structural topology optimization, redundant structures were removed, the resulting orthotics were postprocessed, and finally, it was printed with a 3D printer. No signs of pain or discomfort were observed during the wearing. The cervical spine range of motion in flexion, extension, lateral flexion, and rotation is all less than 8° after using the device. Low cost, quick manufacturing time, high precision, attractive appearance, lightweight structure, waterproof design, and practical customized orthotics for patients are all advantages of 3D printing technology in the field of orthopedics. Many possible benefits of using 3D printing to build new orthotics include unique design, stiffness, weight optimization, and improved biomechanical performance, comfort, and fit. Personalized orthotics may be designed and manufactured utilizing 3D printing technology.

Preliminary study on the method of automatically determining facial landmarks based on three-dimensional face template

Objective: To explore the establishment of an efficient and automatic method to determine anatomical landmarks in three-dimensional (3D) facial data, and to evaluate the effectiveness of this method in determining landmarks. Methods: A total of 30 male patients with tooth defect or dentition defect (with good facial symmetry) who visited the Department of Prosthodontics, Peking University School and Hospital of Stomatology from June to August 2021 were selected, and these participants' age was between 18-45 years. 3D facial data of patients was collected and the size normalization and overlap alignment were performed based on the Procrustes analysis algorithm. A 3D face average model was built in Geomagic Studio 2013 software, and a 3D face template was built through parametric processing. MeshLab 2020 software was used to determine the serial number information of 32 facial anatomical landmarks (10 midline landmarks and 22 bilateral landmarks). Five male patients with no mandibular deviation and 5 with mild mandibular deviation were selected from the Department of Orthodontics or Oral and Maxillofacial Surgery, Peking University School and Hospital of Stomatology from June to August 2021. 3D facial data of patients was collected as test data. Based on the 3D face template and the serial number information of the facial anatomical landmarks, the coordinates of 32 facial anatomical landmarks on the test data were automatically determined with the help of the MeshMonk non-rigid registration algorithm program, as the data for the template method to determine the landmarks. The positions of 32 facial anatomical landmarks on the test data were manually determined by the same attending physician, and the coordinates of the landmarks were recorded as the data for determining landmarks by the expert method. Calculated the distance value of the coordinates of facial anatomical landmarks between the template method and the expert method, as the landmark localization error, and evaluated the effect of the template method in determining the landmarks. Results: For 5 patients with no mandibular deviation, the landmark localization error of all facial anatomical landmarks by template method was (1.65±1.19) mm, the landmark localization error of the midline facial anatomical landmarks was (1.19±0.45) mm, the landmark localization error of bilateral facial anatomical landmarks was (1.85±1.33) mm. For 5 patients with mild mandibular deviation, the landmark localization error of all facial anatomical landmarks by template method was (2.55±2.22) mm, the landmark localization error of the midline facial anatomical landmarks was (1.85±1.13) mm, the landmark localization error of bilateral facial anatomical landmarks was (2.87±2.45) mm. Conclusions: The automatic determination method of facial anatomical landmarks proposed in this study has certain feasibility, and the determination effect of midline facial anatomical landmarks is better than that of bilateral facial anatomical landmarks. The effect of determining facial anatomical landmarks in patients without mandibular deviation is better than that in patients with mild mandibular deviation.

Accuracy analysis of full-arch implant digital impressions when using a geometric feature

Objective: To evaluate the effect of adding a geometric feature on the accuracy of digital impressions obtained by intraoral scanners for implant restoration of edentulous jaw quantitatively. Methods: A dentiform model of the maxilla of completely edentulous arch with 6 implant analogs+scan bodies (No. 1-6) was selected as the reference model. Without geometric feature, the dentiform model was scanned by dental model scanner and repeated for 5 times as true value group. Before and after adding the geometric feature, the same operator used intraoral scanner A (Trios 3) and B (Aoralscan 2) to scan the dentiform model with the same scanning path. Each type of intraoral scanner scanned 10 times and ".stl " datas were obtained. The results were imported into reverse engineering software (Geomagic Studio 2015). The linear distances of center point of upper plane between sacn body 1 to 6 was calculated, denoted as D12, D13, D14, D15 and D16. Trueness was the absolute value subtracted from the measured value of the intraoral scanner groups and true value; precision was the absolute value of pairwise subtraction of the measured values in the intraoral scanner groups.The smaller the value, the better the accuracy or precision.With or without the feature, all scan data were statistically analyzed, and the effect of adding geometric feature on the trueness and precision of the two intraoral scanners were evaluated. Results: As for intraoral scanner A, with the feature in place, significant differences were found in D14, D15, D16 for tureness(t=2.66, 2.75, 2.95, P<0.05); the trueness for D16 decreased from (101.9±47.1) μm to (49.6±30.3) μm. On the other hand, with features on the edentulous area, the precision was significantly increased in D15 and D16 (U=378.00, 672.00, P<0.05); the precision for D15 decreased from 40.8 (45.1) μm to 13.1 (17.0) μm. As for intraoral scanner B, the trueness of D12, D13 and D14 after adding geometric features was significantly better than before (t=3.02, 2.66, U=22.00, P<0.05). With feature on the edentulous area, the trueness for D13 decreased from (116.6±41.2) μm to (70.8±35.5) μm. There was no statistical significance in the trueness of D15 and D16 with or without geometric feature (P>0.05), however, the precision of D15 and D16 after adding geometric feature was significantly better than before (U=702.00, 489.00,P<0.05). The precision of D16 decreased from 112.5 (124.7) μm to 35.9 (85.8) μm. Conclusions: The use of geometric feature in edentulous space improves the trueness and precision of the different principle intraoral scanners tested.

Failure Rate of Orthodontic Mini-screw after Insertion using 3D Printed Guide versus Conventional Free Hand Placement Technique: Split Mouth Randomized Clinical Trial

AIM: The aim of the study is to assess the failure rate after mini-screw insertion using digital three-dimensional printed guide versus free hand placement technique through a well-designed split-mouth randomized clinical trial. METHODS: Forty-two patients with mean age (22.56 ± 3.47 years) indicated for upper first premolars’ extraction (Bimaxillary protrusion and Class II division 1) were included in the study. Their maxillary quadrants were randomized to receive mini-screws as means of anchorage. Pre-operative maxillary cone-beam computed tomography scan with ultra-low-dose protocol was imaged and the maxillary arch was scanned using intra-oral scanner to obtain stereo-lithographic format file for the maxillary arch. Using in vivo and Rapidform Geomagic Studio® _Softwares the mini-screws were planned to be inserted in the buccal inter-radicular space between the upper second premolar and first molar in both right and left sides. For the intervention sides; digital three-dimensional guides were designed and printed for mini-screw insertion. Failure of the mini-screws was assessed till 3 months of loading. RESULTS: There was no statistical significant difference in failure rate of mini-screws in both intervention (7.14%) and control sides (16.6%), with weak and moderate correlation between the root proximity and the mini-screws failure in intervention and control groups respectively. CONCLUSIONS: Using a digital three-dimensional printed guide for mini-screw insertion had no effect on the failure rate of the inserted mini-screws. REGISTRATION: ClinicalTrials.gov Identifier: NCT03653078.