Evaluation of microtensile bond strength between resin composite and glass ceramic / 北京大学学报(医学版)

OBJECTIVE@#To evaluate the microtensile bond strength of resin composite to glass ceramic, and the effect of surface treatment of resin composite and thermal cycling aging on the microtensile bond strength.@*METHODS@#Rectangular blocks were made with dentin of extracted molars, resin composite or feldspathic glass ceramic respectively. The bonding surfaces of these rectangular blocks were sanded by 600-grit silicon carbide paper before luting. A self-etching resin cement was used as luting agent. The specimens were divided into groups according to the types of substrates of adhesion (dentin/glass ceramic or resin composite/glass ceramic), the way of surface treatments and whether thermal cycling aging ocurred. The dentin blocks were adhered to ceramic blocks as controls (group A1 and A2). The resin composite blocks were adhered to the ceramic blocks as experiment groups. The resin composite surfaces were treated by different ways before luting: no extra surface treatment (group B1 and B2), treated by ethyl methacrylate solution (group C1 and C2) or silane coupling agent (group D1 and D2), coarsened by 360-grit silicon carbide paper (group E1 and E2) or polished by 1 200-grit silicon carbide paper (group F1 and F2). After luting, the microtensile bond strength of the specimens were tested before (group A1-F1) or after (group A2-F2) thermal cycling aging. After microtensile bond strength test, the fracture bonding surfaces of the specimens were observed by a scanning electron microscopy to determine the type of bonding failure. The data were statistically analyzed using one-way analysis of variance.@*RESULTS@#The microtensile bond strength of resin composite to glass ceramic with no extra treatment achieved high bond values before and after thermal cycling [B1 (30.02±3.85) MPa, B2 (26.83±3.14) MPa], which were statistically different from those of the control groups [A1 (20.55±4.51) MPa, A2 (12.94±0.69) MPa, P < 0.05]. The microtensile bond strength between the glass ceramic and resin composite did not increase after different surface treatments of resin composite.@*CONCLUSIONS@#The microtensile bond strength between resin composite and glass ceramic achieved as similar bond strength as that between dentin and glass ceramic and even better. Surface treatment of resin composite via methyl methacrylate solution, silane coupling agent, coarsening, or polishing did not increase the microtensile bond strength effectually.

Genome sequencing and phylogenetic analysis of avian influenza viruses subtype H9N2 / 病毒学报

Samples of chicken, duck, quail, and pigeon were collected from Jiangsu, Anhui, and Hebei in 2009-2011, and sixteen H9N2 subtype isolates of avian influenza virus (AIV) were identified. The eight full-length genes of 16 AIV isolates were amplified by RT-PCR and sequenced. Genome sequence analysis showed that the amino acid motif of cleavage sites in the HA gene was P-S-R/K-S-S-R, which was consistent with the characterization of the LPAIV, and the Leucine (L) at the amino acid position 226 in the HA genes of all isolates indicated the potential of binding with SAalpha, 2-6 receptor. All isolates had a S to N substitution at residue 31 in the M2 gene, which is related to the resistance phenotype of adamantanes. The key molecular features of 16 AIV isolates from different hosts were same. Genome phylogenetic analysis revealed that all 16 H9N2 subtype AIVs originated from F98-like virus as backbone and formed two new genotypes through reassortment with HA gene of Y280-like virus and PB2 and M genes of G1-like virus. Our findings suggest that more attention should be paid to the surveillance of H9N2 influenza virus and its direction of reassortment.