浓硫酸酸蚀聚醚酮酮的时间对其与牙本质剪切粘接强度的影响

目的研究浓硫酸酸蚀聚醚酮酮(polyether?ketone?ketone,PEKK)不同时间对其与牙本质剪切粘接强度的影响,为临床使用PEKK修复体的粘接操作提供科学依据。方法制备PEKK试件44个,随机平均分为A、B、C、D 4组:A组为对照组,仅用水磨砂纸打磨;B组、C组、D组为实验组,分别用98%浓硫酸酸蚀经打磨试件表面5 s、30 s、60 s。另外,每组随机抽取1个试件用慢速切割机制备出剖面,在扫描电镜下观察其剖面的表面形貌。4组试件与牙本质通过树脂粘接后在37℃蒸馏水浸泡24 h,测量剪切粘接强度后统计分析,通过扫描电子显微镜与体视显微镜检查试件断裂界面,统计粘接失败类型。结果B组PEKK试件酸蚀处理后剖面呈海绵状且孔隙大小均匀,C组、D组可见试件剖面有破坏状孔蚀样结构;剪切粘接强度B组(16.84±1.84)MPa、C组(12.33±1.22)MPa和D组(6.44±1.18)MPa均大于A组(3.99±1.06)MPa(P<0.05),其中B组与牙本质的剪切粘接强度最高(16.84±1.84)MPa。结论采用98%浓硫酸酸蚀PEKK表面5 s处理方法可以使PEKK与牙本质获得较好的剪切粘接强度。     

不同表面处理方式对聚醚醚酮与复合树脂粘接性能的影响

目的研究不同存储条件下6种通用型粘接剂及喷砂条件对聚醚醚酮（PEEK）与复合树脂之间粘接强度和耐久性的影响。 方法将PEEK材料切割成12个边长为2 cm的正方体试件。对其中6个试件进行氧化铝喷砂处理。6种通用型粘接剂为：Tetric N-Bond Universal（TNU）、Single Bond Universal（SBU）、DX.BOND UNI（DXB）、Selective Etch Bond（SEB）、Gluma Bond Universal（GBU）、Prime & Bond Universal（PBU）。实验分为7组,每组包含4个喷砂面和4个未喷砂面。7种表面处理方法分别为：不使用粘接剂（对照组）和6种通用型粘接剂（实验组：TNU组、SBU组、DXB组、SEB组、GBU组、PBU组）。经表面处理后,将流动复合树脂F00注入透明模具并将其无压力置于试件表面后进行光照固化。试件分别在37 ℃恒温水浴24 h或冷热循环3000次后进行剪切粘接强度测试。使用松风EyeSpecial C-Ⅳ口腔专用相机微距模式进行断面拍照并进行断裂模式分析。采用SPSS 23.0软件Three-Way ANOVA（冷热循环、粘接剂与喷砂）与Tukey方法对各组数据进行统计分析（α = 0.05）。 结果24 h水浴条件下,TNU组分别获得不喷砂组（9.92 ± 1.19）MPa与喷砂组（9.97 ± 1.03）MPa最高粘接强度;冷热循环3000次后PBU组分别获得不喷砂组（6.75 ± 0.99）MPa与喷砂组（7.22 ± 1.30）MPa最高粘接强度。三因素分析结果显示：冷热循环（F = 3 045.429,P<0.001）、粘接剂（F = 361.165,P<0.001）与喷砂（F = 80.050,P<0.001）可显著影响粘接强度;冷热循环与粘接剂（F = 155.724,P<0.001）、粘接剂与喷砂（F = 3.535,P = 0.002）、冷热循环与喷砂（F = 9.184,P = 0.003）两两因素间分别具有交互作用;冷热循环、粘接剂与喷砂三因素间具有交互作用（F = 12.392,P<0.001）。 结论（1）喷砂有助于改善通用型粘接剂对复合树脂与PEEK 37 ℃恒温水浴24 h粘接强度;（2）复合树脂与PEEK粘接强度在冷热循环3000次后显著降低;（3）本实验中PBU组粘接耐久性优于其他粘接系统。     

三种脱敏剂对全酸蚀粘结剂牙本质粘结强度和界面形态的影响

目的:研究、比较三种脱敏剂对全酸蚀粘结剂牙本质粘结强度及其粘结界面形态的影响。方法:选择12个无龋损离体人磨牙,磨除牙合面釉质,用600目碳化硅砂纸在流水下预备出有统一玷污层的牙本质粘结面后,随机分为4组,分别用去离子水(对照组)和3种脱敏剂(Hybrid Coat、Gluma、极固宁)进行脱敏处理后,应用Single Bond 2在面粘结4 mm树脂。然后将每个牙垂直于粘结面切割出12个1.0 mm×1.0 mm×4.0 mm的粘结试件,分别在SEM下观察其粘结界面微观形态并进行微拉伸强度(μTBS)测试。结果:HybridCoat组粘结强度最高((14.81±3.87)MPa,随后依次为去离子水组(13.39±4.67)MPa、Gluma组(12.76±2.96)MPa和极固宁组(10.48±4.32)MPa,各组间两两比较,极固宁组明显低于其他3组(P﹤0.05),其他3组间相比均无显著性差异(P﹥0.05);Hybrid Coat组形成的树脂突大部分>35μm,长而密集;Gluma组形成的树脂突长7～35μm;极固宁组形成的树脂突长20～35μm,较稀疏。结论:Hybrid Coat和Gluma对全酸蚀粘结剂牙本质粘结强度无明显影响,而极固宁则明显降低其粘结强度。     

Variability in the Spatial Structure of the Central Loop in Cobra Cytotoxins Revealed by X-ray Analysis and Molecular Modeling

Cobra cytotoxins (CTs) belong to the three-fingered protein family and possess membrane activity. Here, we studied cytotoxin 13 from Naja naja cobra venom (CT13Nn). For the first time, a spatial model of CT13Nn with both “water” and “membrane” conformations of the central loop (loop-2) were determined by X-ray crystallography. The “water” conformation of the loop was frequently observed. It was similar to the structure of loop-2 of numerous CTs, determined by either NMR spectroscopy in aqueous solution, or the X-ray method. The “membrane” conformation is rare one and, to date has only been observed by NMR for a single cytotoxin 1 from N. oxiana (CT1No) in detergent micelle. Both CT13Nn and CT1No are S-type CTs. Membrane-binding of these CTs probably involves an additional step—the conformational transformation of the loop-2. To confirm this suggestion, we conducted molecular dynamics simulations of both CT1No and CT13Nn in the Highly Mimetic Membrane Model of palmitoiloleoylphosphatidylglycerol, starting with their “water” NMR models. We found that the both toxins transform their “water” conformation of loop-2 into the “membrane” one during the insertion process. This supports the hypothesis that the S-type CTs, unlike their P-type counterparts, require conformational adaptation of loop-2 during interaction with lipid membranes.     

试件形状和光滑度对纵折牙牙本质黏接微拉伸强度的影响

目的评价试件形状和牙本质黏接面磨光对纵折牙牙本质黏接微拉伸强度的影响。方法选择新鲜拔除的人完整磨牙及前磨牙15颗,用慢速切割机先去除牙齿咬合面的釉质,再沿牙齿近远中向或颊舌向纵切牙体至釉牙骨质界下,作为纵折裂缝,随机分为3组。A组折裂面用Super-Bond C&B树脂水门汀黏接后,制成哑铃形试件;B组黏接后,制成棒状试件;C组的折裂面用800目碳化硅耐水砂纸湿磨光1min后,再黏接,制成棒状试件。分别测试三组的微拉伸强度。结果A、B、C 3组的微拉伸强度分别为(7．75±2．67)MPa、(21．19±4．90)MPa、(27．56±7．60)MPa。棒状试件组(B组)的微拉伸强度高于哑铃形试件组(A组)(P=-0．0000);磨光组(C组)的微拉伸强度高于非磨光组(B组)(P=0．0088)。结论试件形状和对牙本质黏接面磨光与否对纵折牙的牙本质黏接微拉伸强度有影响。     

表面处理对双固化黏结剂Panavia F黏接强度的影响

目的评价表面处理对双固化黏结剂Panavia F与不同界面黏接强度的影响。方法测定Panavia F与牙本质使用和不使用牙本质处理剂ED primer时的剪切强度,以及Panavia F与钴铬合金、镍铬合金、纯钛、银金钯合金使用和不使用金属表面处理剂Alloy primer时的剪切强度,数据作统计学检验,分析其黏接机制。结果使用ED primer处理后,Panavia F与牙本质的剪切强度从9.1MPa提高到17.6MPa;使用Alloy primer处理后,Panavia F与纯钛的剪切强度从29.0MPa提高到35.9MPa,而与处理后的银金钯合金的剪切强度从21.6MPa提高到30.2MPa。结论Panavia F通过采用ED primer对牙本质的表面处理显著提高对牙本质的黏结强度;Alloy primer可以显著提高纯钛和贵金属与黏结剂的黏结强度,而对钴铬合金和镍铬合金则不明显。     

Delta Variant with P681R Critical Mutation Revealed by Ultra-Large Atomic-Scale Ab Initio Simulation: Implications for the Fundamentals of Biomolecular Interactions

The SARS-CoV-2 Delta variant is emerging as a globally dominant strain. Its rapid spread and high infection rate are attributed to a mutation in the spike protein of SARS-CoV-2 allowing for the virus to invade human cells much faster and with an increased efficiency. In particular, an especially dangerous mutation P681R close to the furin cleavage site has been identified as responsible for increasing the infection rate. Together with the earlier reported mutation D614G in the same domain, it offers an excellent instance to investigate the nature of mutations and how they affect the interatomic interactions in the spike protein. Here, using ultra large-scale ab initio computational modeling, we study the P681R and D614G mutations in the SD2-FP domain, including the effect of double mutation, and compare the results with the wild type. We have recently developed a method of calculating the amino-acid–amino-acid bond pairs (AABP) to quantitatively characterize the details of the interatomic interactions, enabling us to explain the nature of mutation at the atomic resolution. Our most significant finding is that the mutations reduce the AABP value, implying a reduced bonding cohesion between interacting residues and increasing the flexibility of these amino acids to cause the damage. The possibility of using this unique mutation quantifiers in a machine learning protocol could lead to the prediction of emerging mutations.     

Promotion of resin bonding to dental zirconia ceramic using plasma deposition of tetramethylsilane and benzene

The aim of this study was to investigate the effects of plasma‐enhanced deposition of an organosilane and benzene on resin bonding to a dental zirconia ceramic. A total of 70 zirconia specimens, which were polished before sintering, were randomly divided into five groups according to surface treatments before applying a dental adhesive (each group, n = 14): group 1, no previous treatment (control); group 2, plasma deposition with tetramethylsilane (TMS); group 3, plasma deposition with benzene; group 4, sequential plasma deposition with TMS and benzene; and group 5, a zirconia primer (Z‐Prime Plus). A dental adhesive (Scotchbond Multi‐Purpose adhesive) was applied to the surface‐treated zirconia, and resin composite rods were built in to enable shear bond‐strength testing. The sequential deposition of TMS and benzene showed the highest bond strength [22.7 ± 3.7 MPa (mean ± SD)], approximately twice that of Z‐Prime Plus (10.3 ± 3.2 MPa). The plasma deposition with either TMS or benzene also significantly improved bond‐strength values compared with the negative‐control group, and their effects were not statistically different from that of Z‐Prime Plus. Following plasma deposition with TMS, the introduction of silicon–oxygen–zirconium (Si–O–Zr) bonds on the zirconia surface was confirmed via X‐ray photoelectron spectroscopy (XPS) analysis. Transmission electron microscopy and energy dispersive X‐ray spectroscopy showed that a silica‐like layer and a polymerizable carbon‐rich layer were formed through sequential deposition with TMS and benzene.     

Glutaraldehyde collagen cross‐linking stabilizes resin–dentin interfaces and reduces bond degradation

This study evaluated the stability of resin–dentin interfaces treated with glutaraldehyde‐containing agents, and assessed collagen degradation in dentin matrices treated with Gluma. Microtensile bond strength (μTBS) was evaluated 24 h and 6 months after treatment with three desensitizers (Gluma Desensitizer, Gluma Desensitizer Power Gel, and MicroPrime G) and two etch‐and‐rinse adhesives (Comfort Bond & Desensitizer and iBond TE). Demineralized beams of human dentin were treated with water or Gluma, and the degradation of collagen in these beams was assessed by quantification of the dry mass loss and of the amount of hydroxyproline released from hydrolyzed specimens after 1 or 4 wk. All groups demonstrated significant reduction in μTBS after 6 months, except for Gluma Desensitizer and iBond TE groups, which showed decreases of 7.2% and 10.8%, respectively. The most prevalent failure mode was ‘mixed’. Significantly less hydroxyproline was released from Gluma‐treated beams than from control beams after 4 wk. Beams treated with Gluma yielded significantly less dry mass loss than did beams in the control group. Collagen cross‐linking with glutaraldehyde‐containing agents may assist in the stabilization of resin–dentin bonds by reducing the amount of collagen solubilized from dental matrices in the hybrid layer. In turn, this may contribute to the preservation of adhesive interfaces.