Self-assembly of mono- and bidentate oligoarylene thiols onto polycrystalline Au.

Four thiolated oligoarylene molecules (i) 4-methoxy-terphenyl-4″-methanethiol (MTM), (ii) 4-methoxy-terphenyl-3″,5″-dimethanethiol (MTD), (iii) 4-nitro-terphenyl-4″-methanethiol (NTM), and (iv) 4-nitro-terphenyl-3″,5″-dimethanethiol (NTD) were synthesized and self-assembled as monolayers (SAMs) on polycrystalline Au electrodes of organic field-effect transistors (OFETs). SAMs were characterized by contact angle and AC/DC electrochemical measurements, whereas atomic force microscopy was used for imaging the pentacene films grown on the coated electrodes. The electrical properties of functionalized OFETs, the electrochemical SAMs features and the morphology of pentacene films were correlated to the molecular organization of the thiolated oligoarylenes on Au, as calculated by means of the density functional theory. This multi-methodological approach allows us to associate the systematic replacement of the SAM anchoring head group (viz. methanethiol and dimethanethiol) and/or terminal tail group (viz. nitro-, -NO2, and methoxy, -OCH3) with the change of the electrical features. The dimethanethiol head group endows SAMs with higher resistive features along with higher surface tensions compared with methanethiol. Furthermore, the different number of thiolated heads affects the kinetics of Au passivation as well as the pentacene morphology. On the other hand, the nitro group confers further distinctive properties, such as the positive shift of both threshold and critical voltages of OFETs with respect to the methoxy one. The latter experimental evidence arise from its electron-withdrawing capability, which has been verified by both DFT calculations and DC electrochemical measurements.

Fibre-reinforced composite crowns luted to implant abutments via electroformed primary copings: an in vitro retention study.

AIM: The aim of this study was to investigate the retention values and mode of failure of metal crowns and fibre-reinforced composite crowns. METHODS: Seventy-five implants and the corresponding abutments were used. After the galvanic copings were fabricated, the specimens were distributed into three groups: in group A traditional metal crowns were realized, whereas in groups B and C fibre-reinforced composite crowns were made. In group B the same resin based cement used in group A was employed for luting the fibre-reinforced composite crowns to the galvanic copings, while in group C a dedicated self-adhesive composite cement was used. All galvanic coping/crown assemblies were cemented onto abutments with Panavia 21 cement. Specimens were subjected to a pull-out test; median retentive values and standard deviations were calculated. RESULTS: All samples in the group A showed separation at the abutment-galvanic cap interface. All samples in the group B showed decementation at galvanic cap-crown interface. In 13 samples of the group C the decementation occurred at the abutment-galvanic cap interface and in 12 samples of this group the decementation occurred at the galvanic cap-crown interface. The mean retention value was 659.1 N±162.9 for group A, 304.7 N±101.4 for B and 635.4 N±155.9 for C. Differences between groups A/B and B/C are statistically significant (t-student test, P<0.01), while is not statistically different between groups A/C. CONCLUSION: When a self-adhesive composite cement is used, fibre-reinforced composite single crowns and conventional metal crowns show similar retentive performance.

Probing charge transport in oxidatively damaged DNA sequences under the influence of structural fluctuations.

We present a detailed study of the charge transport characteristics of double-stranded DNA oligomers including the oxidative damage 7,8-dihydro-8-oxoguanine (8-oxoG). The problem is treated by a hybrid methodology combining classical molecular dynamics simulations and semiempirical electronic structure calculations to formulate a coarse-grained charge transport model. The influence of solvent- and DNA-mediated structural fluctuations is encoded in the obtained time series of the electronic charge transfer parameters. Within the Landauer approach to charge transport, we perform a detailed analysis of the conductance and current time series obtained by sampling the electronic structure along the molecular dynamics trajectory, and find that the inclusion of 8-oxoG damages into the DNA sequence can induce a change in the electrical response of the system. However, solvent-induced fluctuations tend to mask the effect, so that a detection of such sequence modifications via electrical transport measurements in a liquid environment seems to be difficult to achieve.

GolP: an atomistic force-field to describe the interaction of proteins with Au(111) surfaces in water.

A classical atomistic force field to describe the interaction of proteins with gold (111) surfaces in explicit water has been devised. The force field is specifically designed to be easily usable in most common bio-oriented molecular dynamics codes, such as GROMACS and NAMD. Its parametrization is based on quantum mechanical (density functional theory [DFT] and second order Möller-Plesset perturbation theory [MP2]) calculations and experimental data on the adsorption of small molecules on gold. In particular, a systematic DFT survey of the interaction between Au(111) and the natural amino acid side chains has been performed to single out chemisorption effects. Van der Waals parameters have been instead fitted to experimental desorption energy data of linear alkanes and were also studied via MP2 calculations. Finally, gold polarization (image charge effects) is taken into account by a recently proposed procedure (Iori, F.; Corni, S. J Comp Chem 2008, 29, 1656). Preliminary validation results of GolP on an independent test set of small molecules show the good performances of the force field.

In vitro retentive strength of metal superstructures cemented to solid abutments.

AIM: The aim of this study was to evaluate the effect of sandblasting on the retentive strength of metal single crowns luted with a resin cement to Straumann implant/abutment assemblies. METHODS: Fifty 4.1 mm-wide Straumann solid screw implants were mounted in self-polymerizing soft resin. Standard 5.5 mm-high, 8 degree tapered solid abutments were placed on each implant and torqued to 35 Ncm. Fifty metal castings were made using prefabricated burn-out caps. Each implant/abutment assembly and its corresponding metal casting was numbered and they were divided into two groups of 25. In the test group, the external surface of the abutments and the cavosurface of the corresponding metal casting were sandblasted. In the control group, neither the implant abutment nor the metal casting underwent sandblasting. Each metal casting was cemented onto its respective implant/abutment assembly using Panavia 21 (Kuraray Europe GmbH, Dusseldorf, Ger-many) resin cement. Specimens were then subjected to a pull-out test using a universal Instron testing machine. The load required to dislodge each crown was recorded and mean values were calculated for each group. Retention values were analyzed using the ANOVA test. RESULTS: The test group showed a higher mean retention value (83.78 kgf+/-19.61) than the control group (44.03 kgf+/-9.45) and the difference was statistically significant. CONCLUSION: Within the limitations of this in vitro study, the results suggest that sandblasting treatment significantly increases mechanical retention of crowns cemented using a resin cement. It is at the clinician's discretion to evaluate whether additional retention is desired in cementing an implant-supported fixed partial denture.

First-principles density-functional theory calculations of electron-transfer rates in azurin dimers.

We have conceived and implemented a new method to calculate transfer integrals between molecular sites, which exploits few quantities derived from density-functional theory electronic structure computations and does not require the knowledge of the exact transition state coordinate. The method uses a complete multielectron scheme, thus including electronic relaxation effects. Moreover, it makes no use of empirical parameters. The computed electronic couplings can then be combined with estimates of the reorganization energy to evaluate electron-transfer rates that are measured in kinetic experiments: the latter are the basis to interpret electron-transfer mechanisms. We have applied our approach to the study of the electron self-exchange reaction of azurin, an electron-transfer protein belonging to the family of cupredoxins. The transfer integral estimates provided by the proposed method have been compared with those resulting from other computational techniques, from empirical models, and with available experimental data.

Hydrogen-induced surface metallization of beta-SiC(100)-(3x2) revisited by density functional theory calculations.

Recent experiments on the silicon terminated (3 x 2)-SiC(100) surface indicated an unexpected metallic character upon hydrogen adsorption. This effect was attributed to the bonding of hydrogen to a row of Si atoms and to the stabilization of a neighboring dangling bond row. Here, on the basis of density-functional calculations, we show that multiple-layer adsorption of H at the reconstructed surface is compatible with a different geometry: in addition to saturating the topmost Si dangling bonds, H atoms are adsorbed at rather unusual sites, i.e., stable bridge positions above third-layer Si dimers. The results thus suggest an alternative interpretation for the electronic structure of the metallic surface.

First-principles theory of correlated transport through nanojunctions.

We report the inclusion of electron-electron correlation in the calculation of transport properties within an ab initio scheme. A key step is the reformulation of Landauer's approach in terms of an effective transmittance for the interacting electron system. We apply this framework to analyze the effect of short-range interactions on Pt atomic wires and discuss the coherent and incoherent correction to the mean-field approach.

Retention of nativelike conformation by proteins embedded in high external electric fields.

In this Communication, we show that proteins embedded in high external electric fields are capable of retaining a nativelike fold pattern. We have tested the metalloprotein azurin, immobilized onto SiO2 substrates in air with proper electrode configuration, by applying static fields up to 10(6)-10(7) Vm. The effects on the conformational properties of protein molecules have been determined by means of intrinsic fluorescence measurements. Experimental results indicate that no significant field-induced conformational alteration occurs. Such results are also discussed and supported by theoretical predictions of the inner protein fields.

Ab initio simulations of homoepitaxial SiC growth.

We present first-principle calculations on the initial stages of SiC homoepitaxial growth on the beta-SiC(111)-(sqrt[3]xsqrt[3]) surface. We show that the nonstoichiometric reconstruction plays a relevant role in favoring the attainment of high-quality films. The motivation is twofold: On one hand, we find that the reconstruction controls the kinetics of adatom incorporation; on the other hand, we observe that the energy gain upon surface stability can induce the reorganization of the deposited material into a crystalline structure, thus revealing that a surface-driven mechanism is able to stabilize defect-free layer deposition on Si-rich surfaces.

Terminal settling velocity and bed-expansion characteristics of biofilm-coated particles.

Fluid dynamic behavior of biofilm-coated particles in ambient water has been investigated. New experimental results are presented and compared with published data. From experimental measurements of the single particle terminal settling velocity the corresponding drag coefficient was found to be larger (by a factor of 1.6) than that for a smooth, rigid sphere at the same Reynolds number. A new simple correlation describing this finding is suggested. For multiparticle systems the Richardson-Zaki equation, derived empirically for rigid particles, provided a satisfactory description of biological beds. Of the two numerical parameters characterizing the expansion law, i. e. the slope n and the extrapolation to voidage equal one ui, the first was found to be similar to that suggested by Richardson and Zaki (1954), whereas ui gave results smaller than the single-particle terminal settling velocity, in contrast with the mentioned work but in agreement with more recently published behavior.

Epithelial odontogenic ghost cell tumour of the mandibular gingiva.

The epithelial odontogenic ghost cell tumour (EOGCT) is considered as a solid 'neoplastic' variant of the calcifying odontogenic cyst and is an uncommon lesion for which various names have been proposed over the years. We describe here an extraosseous case occurring on the edentulous mandibular gingiva in the right bicuspid area of a 70-year-old woman. The lesion was a painless nodule that appeared clinically as a hyperplastic mass, which was considered to be of reactive nature. Radiographic examination showed a localised resorption of the underlying mandibular bone. The tumour was excised; there was no recurrence at a 2-year follow-up examination.

Gingival and mandibular bone necrosis caused by a paraformaldehyde-containing paste.

A paraformaldehyde preparation (Toxavit) was applied to an inflamed and symptomatic pulp of the mandibular right first molar (tooth #46), in a 30-year-old woman. Leakage from the product was responsible for marked necrosis of the gingiva and the alveolar cortical bone, which resulted in loss of the tooth.

An experimental model of biofilm detachment in liquid fluidized bed biological reactors.

Dimensional analysis was applied for the description of biofilm detachment in liquid fluidized bed biological reactors. This technique allowed the identification of the significant parameters influencing detachment mechanisms and suggested suitable experiments for the characterization of involved phenomena. The influence of the significant variables was established on a lab-scale reactor and an empirical model was proposed to correlate experimental results. The detachment rate was strongly dependent on liquid velocity, while the influence of other parameters, such as solid hold-up and liquid shear stress, was found to be less important.

Ectopic third molar in the maxillary sinus. Case report.

Ectopic eruption of teeth can occur in a wide variety of sites. These include the mandibular condyle, coronoid process, palate, nasal cavity and maxillary sinus. While this process is unusual, the detection of a third molar in the maxillary antrum is extremely rare. A case is presented of ectopic eruption of a third molar in the left maxillary sinus of a 35-year-old caucasian male giving rise to local morbidity.

Submandibular sialolithiasis with concurrent sialoadenitis in a child.

Sialolithiasis is a relatively common condition in adults, but it is rarely observed in children. We report a case in a 7-year-old child with a sialolith in the anterior right Wharton's duct resulting in a submandibular sialoadenitis. Under local anesthesia the calculus was removed by means of a sialodochotomy. Post-operative recovery was uneventful and follow-up examinations showed recovery of the function of the affected gland.

Foliate papillitis occurring in a child: a case report.

Foliate papillae may occasionally become irritated, resulting in an hypertrophy of lymphoid tissue. This condition has been described in the literature as foliate papillitis and has been reported to occur in adults. We describe here an unusual case of foliate papillitis in a 9-year-old girl. Clinically the patient presented a pronounced enlargement of one foliate papilla. Furthermore, the lesion had a polypoid morphology and the mass appeared microscopically as aggregates of lymphoid tissue showing a reactive hyperplasia.

Fusion of permanent mandibular molars associated with periodontitis: a case report.

Dental twinning derives from abnormal events during the embryological development of tooth germs. The majority of fused teeth are found in the deciduous dentition, particularly in the anterior region of dental arches. Fusion of posterior teeth is considered a rare event. We report here a true case of posterior fusion between a second and third mandibular molar occurring in a black African woman. The morphology and the position of this abnormal tooth were responsible for a related periodontal problem.