Effect of build orientation on the manufacturing process and the properties of stereolithographic dental ceramics for crown frameworks

Statement of problemStereolithography (SLA) ceramic crown frameworks are suitable for clinical use, but the impact of SLA build orientation has not been identified.PurposeThe purpose of this in vitro study was to investigate the effect of 3 build orientations on the physical and mechanical properties and the microstructure of SLA alumina dental ceramics.Material and methodsThe physical and mechanical properties and microstructures of 3 different oriented SLA alumina ceramics (ZX, ZY, and XY) were evaluated by visual observation, hydrostatic weighing (n=10/group), Weibull analyses (n=30/group), scanning electron microscopy, 3-point flexural strength (n=30/group), fracture toughness (indentation, single-edge-V-notched-beam) (n=4/group), and Vickers hardness (n=15/group) testing. The hydrostatic weighing, 3-point flexural strength, fracture toughness, and Vickers hardness testing data were statistically analyzed (α=.05).ResultsThe minimum resting period of slurries between the polymerization of 2 layers was shorter for the ZY- and ZX-oriented specimens and increased with the layer surface. The density and Vickers hardness of the SLA-manufactured specimens were similar for all groups (P>.05). The 95% confidence intervals of the Weibull moduli of the ZX- and ZY-oriented specimens were higher than that of the XY-oriented specimens, with no overlap fraction. The ZY-oriented specimens displayed significantly higher 3-point flexural strength (P<.05) and fracture toughness as evaluated by the single-edge-V-notched-beam method than the ZX-oriented specimens (P<.05). They also displayed significantly higher 3-point flexural strength than the XY-oriented specimens (P<.05). The microstructural analysis showed that the texturing was heterogeneous and that the major axis of the large grains of alumina ran parallel to the orientation of the layers.ConclusionsThe ZY orientation produced a reliable dental ceramic by SLA, with the shortest general manufacturing time and the highest mechanical strength when the layers were perpendicular to the test load surface.     

The High Diversity of MRSA Clones Detected in a University Hospital in Istanbul

Background: To characterize the methicillin-resistant Staphylococcus aureus (MRSA) clones present in Istanbul, 102 MRSA isolates collected during a 5-year period at the Istanbul Medical Faculty Hospital were characterized using microarray analysis and phenotypic resistance profiles.Methods: Resistance to methicillin was detected with a cefoxitin disk diffusion assay and confirmed with a MRSA-agar and MRSA detection kit. Antimicrobial susceptibility testing was performed by a disk diffusion assay and interpreted according to the 2012 guidelines of the Antibiogram Committee of the French Society for Microbiology. Decreased susceptibility to glycopeptides was confirmed using the population analysis profile-area under the curve (PAP-AUC) method. The presence of the mecA gene was detected by polymerase chain reaction. Bacterial DNA was extracted according to the manufacturer''s recommended protocol using commercial extraction kits. Strains were extensively characterized using the DNA microarray.Results: Isolates were grouped into six clonal complexes. The most frequently detected clone was the Vienna/Hungarian/Brazilian clone (ST239-MRSA-III), which accounted for 53.9% of the isolates. These isolates were resistant to multiple antibiotics, particularly penicillin, tetracycline, rifampicin, kanamycin, tobramycin, gentamicin, levofloxacin, erythromycin, lincomycin and fosfomycin. Furthermore, three isolates were detected by population analysis profile as heterogeneous vancomycin-intermediate S. aureus (hVISA). The UK-EMRSA-15 clone (ST22-MRSA-IV PVL negative) was detected in 9.8% of the isolates and was mainly susceptible to all anti-staphylococcal antibiotics. Seven isolates (6.9%) were positive for PVL genes and were assigned to the CC80-MRSA-IV clone (European CA-MRSA clone, three isolates), ST8-MRSA-IV clone (USA300 clone, two isolates, one ACME-positive) or ST22-MRSA-IV clone (“Regensburg EMRSA” clone, two isolates). All other clones were detected in one to six isolates and corresponded to well-known clones (e.g., Pediatric clone, Dublin EMRSA clone, WA MRSA-54/63, WA MRSA-1/57).Conclusions: This work highlighted both the high prevalence of ST239-MRSA-III clone and the large diversity of the other MRSA clones detected in a university hospital in Istanbul.     

Intra-tumoral tertiary lymphoid structures are associated with a low risk of early recurrence of hepatocellular carcinoma

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