OBJECTIVE: To establish a three-dimensional finite element model of a digital wire loop space maintainer for the mandible and primary tooth loss, in order to investigate the stress, deformation, and shear force experienced by patients with the loss of the second primary molar when wearing the wire loop space maintainer. METHODS: Cone beam computed tomography (CBCT) scans were performed on the patients to create a digital model of the mandible with the absence of the second primary molar using Mimics 21.0 software. A digital model integrating the crown's retention and the wire loop structure of the full crown and ring wire loop space maintainer was constructed using pediatric space maintainer design software, utilizing three different materials: cobalt-chromium alloy, polyether ether ketone (PEEK), and titanium alloy. In ANSYS Work Beach 2023 R2 software, vertical loads of 70 N, tilted 45° along the long axis of the tooth loads of 70 N, and a 10 N load on the surface of the wire loop were applied to the occlusal surfaces of models 46 and 84, simulating centric and lateral occlusions during chewing with the wire loop space maintainer in place. The stress states of the wire loop space maintainer and supporting teeth were analyzed. RESULTS: Under various loading conditions, the maximum principal stress of the ring wire loop space maintainer was significantly lower than that of the full crown. Stress contour maps indicated that the peak of the maximum principal stress occurred at the junction of the wire loop and crown structure, indicating that this area was more susceptible to fracture. The ring wire loop space maintainer made from PEEK material exhibited the lowest maximum shear stress on the internal organizational surfaces, with equivalent stresses of 23.18 MPa and 36.35 MPa for models 46 and 84, respectively. Stress contour maps demonstrated that the maximum stress on tooth 46 was located at its mesial, while the maximum stress on tooth 84 was situated near the root area on its distal, in contact with the wire loop space maintainer. CONCLUSION In cases of second primary molar loss, wearing the digital ring wire loop space maintainer can effectively distribute stress, and the ring wire loop space maintainer made from PEEK material reduces the stress experienced by supporting teeth to some extent, demonstrating its superiority in clinical application.
Finite Element Analysis ; Humans ; Tooth, Deciduous ; Cone-Beam Computed Tomography ; Space Maintenance, Orthodontic/methods* ; Imaging, Three-Dimensional ; Orthodontic Wires ; Dental Stress Analysis ; Mandible ; Stress, Mechanical

Objective To observe the efficacy of modified endoscopic sinus surgery(ESS)in treatment of chronic rhinosinusitis with nasal polyps(CRSwNP)complicated by allergic rhinitis(AR).Methods Forty patients with CRSwNP and perennial AR who were scheduled for ESS were divided into study group and control group,with 20 cases in each group.The control group was treated with conventional ESS,while the study group underwent resection of a large part of the middle turbi-nate on the basis of ESS to enhance middle meatal drainage.The postoperative mucosal outcomes,complications,as well as the Visual Analog Scale(VAS),sino-nasal outcome test-20(SNOT-20),and nasal endoscopic Lund-Kennedy scores before surgery,at 3 months after surgery,and at 1 year af-ter surgery were compared between the two groups.Results In the control group,there were 3 cases of local adhesion between the displaced middle turbinate and the lateral nasal wall at 3 months after surgery,and 10 cases of middle turbinate edema at 1 year after surgery,including 4 cases with local polypoid changes in the middle turbinate and polypoid hyperplasia in the ethmoid sinus and frontal re-cess regions.No complications were observed in the study group,and the epithelialization of the surgical area was good.Moreover,the nasal congestion score,olfactory score,and Lund-Kennedy score at 1 year after surgery in the study group were lower than those in the control group,with statistically significant differences(P＜0.05).Conclusion Modified ESS can significantly improve nasal con-gestion and olfactory symptoms in patients with CRSwNP complicated by perennial AR and effective-ly enhance their quality of life.

Objective To investigate the indoor radon concentration and its changing trend in northeastern China. Methods We measured indoor radon levels cumulatively for over three months by solid state nuclear track detection in a total of 261 houses in multi-story or high-rise buildings in Shenyang, Changchun, Harbin, Heihe, and Yichun in northeastern China. The measurement lasted one year in Changchun for seasonal changes. Results The average indoor radon concentration in the five cities was 88 Bq/m³, ranging from 12 to 558 Bq/m³. The indoor radon concentrations were ≤ 100 Bq/m³ in 75.1% of the houses, and ≤ 300 Bq/m³ in 97.7% of the houses. The indoor radon concentration increased with the age of buildings. The indoor radon concentration was highest in winter, and it was higher in summer than in autumn and spring. Conclusion The indoor radon concentration in northeastern China increased compared with the data of 1980s and 1990s. It is highest in the winter heating season, and higher in summer than in spring and autumn. Indoor radon exposure deserves attention.

Objective:To conduct radiation detection and dose assessment in selective internal radiotherapy with 90Y resin microspheres for the purpose of providing a reference for radiological protection. Methods:The dose rates from radiotherapy with 90Y resin microspheres were detected in the process of each operation at different distances from the body surface of patients the levels of dose to the persons concerned were compared with the relevant national regulations and standards. Results:The estimated dose rates were 1.12-454 μSv/h during 90Y resin microspheres dispensing and 2.06-58.2 μSv/h during surgical procedure. The dose rates at 0.5 h after surgery were 22.7-64.1 μSv/h at 5 cm and 0.82-2.55 μSv/h at 1 m from three patient′s body surface. Assuming treating 200 patients a year, the annual individual effective dose to the radiation workers was 0.12-1.03 mSv/year. The annual individual effective dose to the public, comforters and carers of patients was 0.02-0.24 mSv/year after release of a patient. Conclusions:During the treatment, nursing and release of patients, the radiation doses to workers, carers and the public are lower than the individual dose limit given in the GB18871-2002 basic standards for protection against ionizing radiation and for the safety of radiation sources and the management target value set by of the relevant medical institutions.

Objective:To evaluate 90Y activity concentration in renal excretions during the first 48 hours after being treated with 90Y resin microspheres seleceive internal radiation therapy(SIRI) and to provide advice on the management of patient excreta after surgery. Methods:After surgery, urine excreted from 3 patients during 0-24 h and 24-48 h was collected respectively, and the 90Y activity concentration in urine was tested and analyzed. Results:90Y radioctivity in the urine excreted from 3 patients after surgery was (1 266±258)kBq/GBq during 0-24 h and (140±106) kBq/GBq during 24-48 h, respectively, and 90Y activity concentration were (640±113) kBq/L during 0-24 h and (53±12) kBq/L during 24-48 h. Conclusions:90Y radioactivity in patient′s urine excreted at 1 d was about 10 times higher than that at 2 d. After surgery, patients can accelerate the reduction of free 90Y activity by increasing excretion. Urine excreted by the patients during hospitalization should be handled in accordance with the requirements of the national standard HJ 1188-2021 Radiation protection and safety requirements for nuclear medicine.

In this article, a case for random signal interference in resolver (or encoder) of carousel on Varian VitalBeam medical linear accelerator was illustrated. This case was considered as a rare failure of the technology platform (including TrueBeam) by Chinese, European and American technical experts in Varian. In this article, the differences of the carousel in the structure and control system between VitalBeam and traditional accelerator were comparatively analyzed to enable the peers to have a deeper understanding of resolver. The logic and methods to solve the fault were summarized, providing reference experience for analyzing the problems related to carousel. It is found that the interlocking system is imperfect, which provides a factual and technological basis for Varian to optimize the system.

Objective To investigate the suitable methods for reducing the concentration levels of residential radon and its daughters. Methods Three rooms were selected and treated by natural ventilation, air purifier, and sealing/shielding, respectively. The EQF3120 device was used to measure the concentrations of radon and its daughters, and the alpha nuclear trail detector was used to measure indoor radon concentration. The three methods were compared in terms of radon reduction effect. Results After natural ventilation for 2-10 hours, the average reduction rates of the concentrations of radon and attached and unattached radon daughters in the room were 87.7%, 89.8%, and 93.7%, respectively; in the room with air purifier, the concentrations of radon and attached and unattached radon daughters were reduced by 46.3%, 94.5%, and 45.3%, respectively; after sealing and shielding, the concentration of radon was reduced by 74.9% after 1 month and 59.2% after 1 year. Conclusion All three methods have a marked effectin reducing the concentrations of indoor radon and its daughters, and natural ventilation is the most economical and effective method for reducing radon.

Accurate determination of intestinal viability is the key step in the management of acute mesenteric ischemia. For patients with the possibility of intestinal necrosis, the application of laparoscopy for the primary exploration or second look, is significantly less invasive than laparotomy, so to avoid the unnecessary operative trauma for those with negative results. For critical patients, application of bed-side laparoscopy, with the avoidance of risks during transport process, is an effective and safer diagnostic method. And the combination with intraoperative indocyanine green fluorescence angiography may further improve the reliability of exploration so to result in more precise surgical management for these severe situation. So in the era of endovascular management for acute mesenteric ischemia, as an mimmally invasive and precise method for accurate determination of existence or not of intestinal necrosis, laparoscopy is effective in further improving the outcome of these patients.

Objective To explore the source and control of radon in high radon houses in geothermal fields; Methods Radon concentration in indoor and soil was measured by ATD detector in winter and summer; radionuclides in building materials were measured by gamma-ray spectrometry; radionuclides dose rates of building materials were measured by 6150 A D/ 6H X-γ ray detector; and radon reduction technology was applied to one of the houses;Results The average radon concentrations in 32 rooms were （106.4 ± 63.7） Bq/m³ (summer) and （421.3 ± 138.2） Bq/m³ (winter), and the concentrations in 12.5% (summer) and 96.9% (winter) of the rooms exceed 150 Bq/m³. The average radon concentration in soil around buildings was 12890 Bq/m³ (n = 24), which is 1.7 times of the typical soil radon concentration in Beijing (7600 Bq/m³). After soil decompression, the radon concentration in the house could be reduced to less than 100 Bq/m³. The radon reduction rates of active decompression and passive decompression were 94.6% and 71.4%, respectively. Conclusion The effect of soil decompression on reducing radon concentration in the bottom rooms is obvious. Attention should be paid to the radon in residential environment of geothermal field.

The UDRS interlocking fault is a common dose interlocking of Varian high-energy linear accelerator. Due to the complexity of the system, this fault has brought challenges to the engineers for a long time. Hence, an effective solution is urgently required. In this article, the circuit and principle for UFRS interlocking fault for Varian CLINAC-IX linear accelerator were explicitly analyzed and the maintenance methods were summarized. The management methods of such rare fault were shared, aiming to provide reference for subsequent management of similar interlocking faults.