Impact of different axial wall designs on the fracture strength and stress distribution of ceramic restorations in mandibular first molar.

BACKGROUND: The purpose of this study was to investigate the fracture strength and stress distribution of four ceramic restorations. METHODS: Forty human mandibular first molars were collected and randomized into four groups after establishing the distal defect: full crown group with 4 mm axial wall height (AWH) (FC4); short AWH crown group with 2 mm AWH (SC2); occlusal veneer group with 0 mm AWH (OV0); occlusal distal veneer group with only the distal surface prepared, and 4 mm AWH (OD4). The teeth were prepared according to the groups and the ceramic restorations were completed using celtra duo ceramic blocks. The ceramic thickness of the occlusal surface is about 1.5 mm and the edge is about 1 mm. The failure load values and fracture modes of each group were detected by mechanical test in vitro. According to the groups to establish three-dimensional finite element analysis (FEA) models, a 600 N loading force was applied vertically using a hemispherical indenter with a diameter of 6 mm. and compare the stress distribution under the condition of different restorations. RESULTS: In vitro mechanical tests showed that the failure load values were SC2 (3232.80 ± 708.12 N) > OD4 (2886.90 ± 338.72 N) > VO0 (2133.20 ± 376.15 N) > FC4(1635.40 ± 413.05 N). The failure load values of the short AWH crown and occlusal distal veneer were significantly higher than that of occlusal veneer and full crown (P<0.05). The fracture modes of the full crown and occlusal veneer groups were mainly ceramic fractures and some were restorable tooth fractures. The short AWH crown and occlusal distal veneer groups presented with three fracture modes, the proportion of non-restorable tooth fracture was higher. The results of FEA show that under the spherical loading condition, the stress of ceramic was concentrated in the contact area of the loading head, the maximum von Mises stress values were FC4 (356.2 MPa) > VO0 (214.3 MPa) > OD4 (197.9 MPa) > SC2 (163.1 MPa). The stress of enamel was concentrated in the area where the remaining enamel was thinner, the maximum von Mises stress values was OD4 (246.2 MPa) ≈ FC4 (212.4 MPa) > VO0 (61.8 MPa) ≈ SC2 (45.81 MPa). The stress of dentin is concentrated in the root furcation and the upper third region of the root. However, stress concentration was observed at the tooth cervix in the full crown. CONCLUSION: Under certain conditions, the occlusal distal veneer shows better performance than the full crown.

Low-Temperature Hydrothermal Synthesis of Novel 3D Hybrid Nanostructures on Titanium Surface with Mechano-bactericidal Performance.

Titanium is extensively employed in modern medicines as orthopedic and dental implants, but implant failures frequently occur because of bacterial infections. Herein, three types of 3D nanostructured titanium surfaces with nanowire clusters (NWC), nanowire/sheet clusters (NW/SC) and nanosheet clusters (NSC), were fabricated using the low-temperature hydrothermal synthesis under normal pressure, and assessed for the sterilization against two common human pathogens. The results show that the NWC and NSC surfaces merely display good bactericidal activity against Escherichia coli, whereas the NW/SC surface represents optimal bactericidal efficiency against both Escherichia coli (98.6 ± 1.23%) and Staphylococcus aureus (69.82 ± 2.79%). That is attributed to the hybrid geometric nanostructure of NW/SC, i.e., the pyramidal structures of ∼23 nm in tip diameter formed with tall clustered wires, and the sharper sheets of ∼8 nm in thickness in-between these nanopyramids. This nanostructure displays a unique mechano-bactericidal performance via the synergistic effect of capturing the bacteria cells and penetrating the cell membrane. This study proves that the low-temperature hydrothermal synthesized hybrid mechano-bactericidal titanium surfaces provide a promising solution for the construction of bactericidal biomedical implants.

Cerebellar involvement in patients withprimary Sjögren's syndrome: diagnosis and treatment.

The aim of this study is to describe the clinical features of cerebellar involvement in patients with primary Sjögren's syndrome (pSS). We retrospectively analyzed the manifestations, treatments, and outcomes in patients with pSS-cerebellar complication in Peking Union Medical College Hospital and cases reported in literature. Altogether 13 patients were identified. They were 2 males and 11 females with a mean age at disease onset of 45.2 ± 14.6 years. Nine (69.2%) patients went to the clinic because of ataxia, and pSS was not suspected until accidental screening for autoantibodies. Dysarthria (7, 59.8%), limb tremor (4, 30.8%), and nystagmus (2, 15.4%) were the rest symptoms related to cerebellum. Of the patients, 81.8% (9/11) had abnormal cerebrospinal fluid findings, and 11 patients (84.6%) had cerebellar atrophy in the brain MRI. Dry eyes and dry mouth were detected in 9 (69.2%) and 7 (59.8%) patients, while positive objective xerostomia and ocular test in 82.5% (7/8) and 100% (10/10) of the patients, respectively. Anti-Ro/SSA antibody was positive in 12 (92.3%) and anti-La/SSB in 6 (46.2%) patients. Glucocorticoids were applied in 12 patients (92.3%). Cyclophosphamide (3, 20.1%), mycophenolatemofetil (1, 7.7%), and hydroxychloroquine (4, 30.8%) were chosen as immunosuppressants or anti-inflammatory drug. During a median follow-up of 9 months (range, 1-18 months), 8 (61.5%) patients remained stable, 3 (20.1%) patients were in remission, and 2 (15.4%) patients were in progression. Clinical cerebellar complication secondary to pSS was rare, and sometimes pSS was not suspected until accidental screening for autoantibodies. Because the onset of cerebellar manifestation is often insidious and rapid deteriorates, early diagnosis and empirical aggressive glucocorticoid treatment is warranted.