Can surface preparation with CVD diamond tip influence on bonding to dental tissues?

This study evaluated the influence of chemical vapor deposition (CVD) tips surface treatments of enamel and dentin on bonding resistance of two adhesive systems. Thirty embedded samples were divided in 12 groups (n = 10), according to factors: substrate (enamel and dentin), adhesive system [etch-and-rinse (SB) and self-etch]; and the surface treatments (paper discs, impact CVD tips and tangential CVD tip). When CVD tip was used in the impact mode the tip was applied perpendicular to dental surface, while at tangential mode, the tip worked parallel to dental surface. Specimens were tested in tension after 24 h at 0.5 mm/min of cross-head speed. ANOVA results, in MPa showed that in enamel, only adhesive system factor was statistically significant (p = 0.015) under tested conditions, with higher bond strength observed for SB groups. However, in dentin the best bonding performance was obtained in SE groups (p = 0.00). In both tested substrates, results did not show statistically significant difference for factors treatment and its interactions.

Conclusions

It may be concluded that CVD-tip surface treatment, in both tested modes, did not influence on adhesion to enamel and dentin. But, it is important to choose adhesive system according to the tissue available to bonding.     

Zinc-ion implanted and deposited titanium surfaces reduce adhesion of Streptococccus mutans

While titanium (Ti) is a commonly used dental implant material with advantageous biocompatible and mechanical properties, native Ti surfaces do not have the ability to prevent bacterial colonization. The objective of this study was to evaluate the chemical composition and bacterial adhesive properties of zinc (Zn) ion implanted and deposited Ti surfaces (Zn-PIIID-Ti) as potential dental implant materials. Surfaces of pure Ti (cp-Ti) were modified with increasing concentrations of Zn using plasma immersion ion implantation and deposition (PIIID), and elemental surface compositions were characterized by X-ray photoelectron spectrometry (XPS). To evaluate bacterial responses, Streptococcus mutans were seeded onto the modifiedTi surfaces for 48 h and subsequently observed by scanning electron microscopy. Relative numbers of bacteria on each surface were assessed by collecting the adhered bacteria, reculturing and counting colony forming units after 48 h on bacterial grade plates. Ti, oxygen and carbon elements were detected on all surfaces by XPS. Increased Zn signals were detected on Zn-PIIID-Ti surfaces, correlating with an increase of Zn-deposition time. Substantial numbers of S. mutans adhered to cp-Ti samples, whereas bacterial adhesion on Zn-PIIID-Ti surfaces signficantly decreased as the Zn concentration increased (p < 0.01). In conclusion, PIIID can successfully introduce Zn onto a Ti surface, forming a modified surface layer bearing Zn ions that consequently deter adhesion of S. mutans, a common bacterium in the oral environment.     

Vibrational entropy-driven dealloying of Mo(1 0 0) and W(1 0 0) surface alloys

The formation and stability of Cu, Ag and Au-induced c(2 × 2) alloys at the Mo(1 0 0) and W(1 0 0) surfaces have been investigated with low-energy electron microscopy and diffraction. The ordered alloys transform to disordered overlayer structures at elevated temperature. Comparison of the transformation temperatures with energetics obtained from first principles calculations reveals the vibrational entropic contribution to the system free energy that defines alloy thermal stability. Effective Debye temperatures for metal adatoms are determined that exhibit the expected mass and bond strength dependence.     

AFM analysis of bleaching effects on dental enamel microtopography

The purpose of this in vitro study was to test a new methodology to evaluate the effects of 35% hydrogen peroxide agent on the microtopography of sound enamel using an atomic force microscope (AFM). The buccal sound surfaces of three extracted human lower incisors were used, without polishing the surfaces to maintain them with natural morphology. These unpolished surfaces were subjected to bleaching procedure with 35% hydrogen peroxide that consisted of 4 applications of the bleaching agent on enamel surfaces for 10 min each application. Surface images were obtained in a 15 μm × 15 μm area using an AFM. The roughness (Ra and RMS) and the power spectral density (PSD) were obtained before and after the bleaching treatment. As results we could inquire that the PSD analyses were very suitable to identifying the morphological changes on the surfaces, while the Ra and RMS parameters were insufficient to represent the morphological alterations promoted by bleaching procedure on enamel. The morphological wavelength in the range of visible light spectrum (380-750 nm) was analyzed, showing a considerable increase of the PSD with the bleaching treatment.     

Density functional and dynamics study of the dissociative adsorption of hydrogen on Mg (0 0 0 1) surface

A first principles study is performed to investigate the adsorption characteristics of hydrogen on magnesium surface. Substitutional and on-surface adsorption energies are calculated for Mg (0 0 0 1) surface alloyed with the selected elements. To further analyze the hydrogen-magnesium interaction, first principles molecular dynamics method is used which simulates the behavior of H₂ at the surface. Also, charge density differences of substitutionally doped surface configurations were illustrated. Accordingly, Mo and Ni are among the elements yielding lower adsorption energies, which are found to be −9.2626 and −5.2995 eV for substitutionally alloyed surfaces, respectively. In light of the dynamic calculations, Co as an alloying element is found to have a splitting effect on H₂ in 50 fs, where the first hydrogen atom is taken inside the Mg substrate right after the decomposition and the other after 1300 fs. An interesting remark is that, elements which acquire higher chances of adsorption are also seen to be competent at dissociating the hydrogen molecule. Furthermore, charge density distributions support the results of molecular dynamics simulations, by verifying the distinguished effects of most of the 3d and 4d transition metals.     

Ab-initio pseudopotential study of electronic structure and chemisorption of oxygen on aluminium surface

Chemisorption of oxygen atom on aluminium (1 1 1), (1 1 0) and (1 0 0) surfaces is studied using ab-initio plane wave pseudopotential method based on density functional theory (DFT). Oxygen atom chemisorbed on three different high symmetry sites; top, short-bridge and hollow sites on the aluminium surfaces are examined. It has been found that the O-adatom adsorbed at the hollow site on aluminium (1 1 1), (1 1 0) and (1 0 0) plane yield energetically most stable structure. Calculation of chemisorption energies of O-adatom on aluminium surfaces shows that oxygen is most strongly bound to aluminium atoms on Al(1 1 1) plane and the calculated value of the chemisorption energy of O-adatom at the hollow site on Al(1 1 1) surface is 4.8 eV. In this work, the chemisorption energies calculated for O-adatom on Al(1 1 0) and Al(1 0 0) surfaces are reported for the first time. The electronic structures and the electronic charge density distributions of the oxygen chemisorbed aluminium surfaces are also investigated. Calculations show that for aluminium, p orbitals also contribute significantly along with the s orbitals during the bond formation with oxygen atom. Therefore, the possibilities of hybridizations lead to the strong bonding configurations.     

Interaction of CO with atomically well-defined PtxRuy/Ru(0 0 0 1) surface alloys

The interaction of CO with structurally well-defined Pt_xRu_y surface alloys supported on Ru(0 0 0 1) was investigated by thermal desorption spectroscopy and infrared reflection-absorption spectroscopy. The surface composition and the distribution of the surface atoms were controlled by high resolution scanning tunneling microscopy. On these surfaces, which have a nearly random distribution of the two surface species, the adsorption (and desorption) of CO is strongly modified compared to the pure elemental surfaces, by strain effects and electronic ligand effects. CO adsorbs exclusively in a linear configuration on Pt and Ru atoms for all surfaces investigated. The adsorption energy of CO is lowered on the alloy surfaces with respect to both Pt(1 1 1) and Ru(0 0 0 1), similar as for pseudomorphic monolayer Pt films. For both Pt and Ru sites the adsorption strength decreases with increasing Pt concentration.     

The effect of etching time on the CdZnTe surface

The surface quality of CdZnTe plays an important role in the performance of sensors based on this material. In this paper the effect of chemical etching on Cd_0.9Zn_0.1Te sensor performance was examined. Sample surfaces were treated with the same concentration 2% Br-MeOH for different etching times (30 s, 2, 4, 6, 8 min). The surfaces were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and I-V Measurement. These results demonstrate that the best surface quality can be obtained by chemical etching for 30 s. Under these experimental conditions, the surface composition Te/Cd + Zn approaches 1, the roughness is lower than 3 nm, and the leakage current shows a value lower than 10 nA.     

Reactivity of 3-hexyne on oxygen modified Ru(0 0 1) surfaces: Observation of oxametallacycles by RAIRS

The chemical behaviour of 3-hexyne on oxygen modified Ru(0 0 1) surfaces has been analysed under ultrahigh-vacuum, using reflection-absorption infrared spectroscopy (RAIRS). The effects of oxygen coverage, 3-hexyne exposure and adsorption temperature were studied. Two modified Ru(0 0 1) surfaces were prepared: Ru(0 0 1)-(2 × 2)-O and Ru(0 0 1)-(2 × 1)-O that correspond to oxygen coverages (θ_O) of 0.25 and 0.5 ML, respectively. The striking result is the direct bonding to an O atom when the modified surfaces are exposed to a very low dose (0.2 L) of 3-hexyne at low temperature (100 K). For θ_O = 0.25 ML, an unsaturated oxametallacycle [Ru-O-C(C₂H₅)C(C₂H₅)-Ru] is proposed, identified by RAIRS for the first time, through the νCC and νCO modes. Further decomposition at 110 K yields smaller oxygenated intermediates, such as acetyl [μ₃-η²(C,O)-CH₃CO], co-adsorbed with a small amount of carbon monoxide and non-dissociated species. The temperature at which a fraction of molecules undergoes complete C-C and C-H bond breaking is thus much lower than on clean Ru(0 0 1). The ultimate decomposition product observed by RAIRS at 220 K is methylidyne [CH]. Another key observation was that the adsorption temperature is not determinant of the reaction route, contrarily to what occurs on clean Ru(0 0 1): even when 3- hexyne strikes the surface at a rather high temperature (220 K), the multiple bond does not break completely. For θ_O = 0.5 ML, a saturated oxametallacycle [Ru-O-CH(C₂H₅)-CH(C₂H₅)-Ru] is also proposed at 100 K, identified by the ν_asO-C-C (at 1043 cm⁻¹) and ν_sO-C-C (at 897 cm⁻¹) modes, showing that some decomposition with C-H bond breaking occurs. For this oxygen coverage, the reaction temperatures are lower, and the intermediate surface species are less stable.     

The effect of pre-adsorbed atoms on the reactivity of methanol-d4 on Ru(0 0 1): Comparison between hydrogen and oxygen

The influence of pre-adsorbed H and O on the adsorption and decomposition of methanol-d₄ on Ru(0 0 1) surfaces is analysed by RAIRS. It is shown that the reactivity of CD₃OD at 90 K is not determined by the nature of the modifying atom nor by the structure of the pre-adsorbed layer: a low dose of CD₃OD (0.1 L) undergoes O-D bond breaking, yielding CD₃O-, both on Ru(0 0 1)-H (0.5 ? θ_H < 1 ML) and on Ru(0 0 1)-O (0.25 ? θ_O ? 0.6 ML) surfaces. At 90 K, methoxide-d₃ acquires a tilted configuration on all these surfaces, despite the fact that oxygen forms ordered phases whereas hydrogen (adsorbed at this temperature) does not. A fraction of the methoxide-d₃ undergoes C-D bond breaking at 110 K on all the modified surfaces, in a lower extent than on clean Ru(0 0 1). The stabilizing effect is more pronounced on the O modified layers, and is coverage dependent. The chemical nature of the pre-adsorbed atom is determinant of the unreacted methoxide geometry, as only oxygen is capable of inducing a reorientation of this species towards C_3v local symmetry. Confirmation of the adsorption geometries, both at 90 and 110 K, was obtained from the RAIR spectra of the selectively labelled CHD₂OH, adsorbed on the same surfaces. The long-range repulsive interactions between the pre-adsorbed atom and the final decomposition product at 130 K (carbon monoxide) are more evident on the denser O layer (0.6 ML), since this species does not remain on the surface. No partially hydrogenated intermediates were detected on the H modified surfaces, suggesting that, in case exchange reactions occur, they yield only gaseous products. On the contrary, direct evidence for the participation of pre-adsorbed O was supplied by the detection of deuterated formate (DCOO) for θ_O = 0.6 ML.     

Effects of thermo-hygro-mechanical densification on the surface characteristics of trembling aspen and hybrid poplar wood veneers

The effect of thermo-hygro-mechanical (THM) densification temperature on the surface color, roughness, wettability, and chemical composition of trembling aspen (Populus tremuloides) and hybrid poplar (Populus maximowiczii × P. balsamifera) veneers was investigated. Veneers were subjected to four THM densification temperatures (160 °C, 180 °C, 200 °C, and 220 °C). Veneer color darkened with increasing THM densification temperature. Surface roughness decreased between 160 °C and 200 °C. Wettability decreased after THM densification, but no significant difference was found between treated specimens. ATR-FTIR and XPS results confirmed that THM densification caused major chemical changes in veneer surfaces, and more pronounced at temperatures higher than 160 °C.     

Trends in atomic adsorption on titanium carbide and nitride

Extensive density-functional calculations on atomic chemisorption of H, B, C, N, O, F, Al, Si, P, S, and Cl on the polar TiC(1 1 1) and TiN(1 1 1) yield similar adsorption trends for the two surfaces: (i) pyramid-like adsorption-energy trends along the adatom periods; (ii) strongest adsorption for O, C, N, S, and F; (iii) large adsorption variety; (iv) record-high adsorption energy for O (8.4-8.8 eV). However, a stronger adsorption on TiN is found for elements on the left of the periodic table and on TiC for elements on the right. The results support that a concerted-coupling model, proposed for chemisorption on TiC, applies also to TiN.     

Structure and composition of the NiPd(1 1 0) surface

The NiPd(1 1 0) alloy surface was studied using low energy electron diffraction to measure the structure and composition of the first three atomic layers. The surface layer is highly enriched in Pd and has a significantly buckled structure. The second layer is also buckled, with displacements even larger than the surface layer. The second layer also exhibits intralayer segregation (chemical ordering), with alternate close-packed rows of atoms being Ni enriched and Pd enriched. The third layer has a structure and composition close to that of the bulk alloy. These results are compared with results for the other low index faces of NiPd, the extensive literature on NiPt alloy surfaces, and the growing body of theoretical literature for NiPd alloy surfaces.     

Structure analysis of stoichiometric LiNbO3(0 0 0 1) surfaces using low-energy neutral scattering spectroscopy

The atomic structure of LiNbO₃(0 0 0 1) surface was investigated by low-energy neutral scattering spectroscopy (LENS). Poled stoichiometric LiNbO₃ (SLN) samples were prepared for the measurements. The LENS was developed for surface structure and composition analysis particularly of highly insulating materials and was successfully applied to the structure analysis of the SLN(0 0 0 1) surface. The polar angle dependences of intensity of scattered He⁰ from the poled SLN surfaces indicate obvious differences between the negatively and the positively charged surfaces. It is suggested that O atoms cover the surfaces, and the first metal layers underneath the O layer consist of Li and Nb for negatively and positively charged surfaces, respectively, parallel to the applied electric field.     

Calculation of the surface energy of fcc-metals with the empirical electron surface model

The empirical electron surface model (EESM) based on the empirical electron theory and the dangling bond analysis method has been used to establish a database of surface energy for low-index surfaces of fcc-metals such as Al, Mn, Co, Ni, Cu, Pd, Ag, Pt, Au, and Pb. A brief introduction of EESM will be presented in this paper. The calculated results are in agreement with experimental and other theoretical values. Comparison of the experimental results and calculation values shows that the average relative error is less than 10% and these values show a strong anisotropy. As we predicted, the surface energy of the close-packed plane (1 1 1) is the lowest one of all index surfaces. For low-index planes, the order of the surface energies is γ_(1 1 1) < γ_(1 0 0) < γ_(1 1 0) < γ_(2 1 0). It is also found that the dangling bond electron density and the spatial distribution of covalent bonds have a great influence on surface energy of various index surfaces.     

Enhancement of hydrophobicity and tensile strength of muga silk fiber by radiofrequency Ar plasma discharge

The hydrophobicity and tensile strength of muga silk fiber are investigated using radiofrequency (RF) Ar plasma treatment at various RF powers (10-30 W) and treatment times (5-20 min). The Ar plasma is characterized using self-compensated Langmuir and emissive probe. The ion energy is observed to play an important role in determining the tensile strength and hydrophobicity of the plasma treated fibers. The chemical compositions of the fibers are observed to be affected by the increase in RF power rather than treatment time. XPS study reveals that the ions that are impinging on the substrates are mainly responsible for the cleavage of peptide bond and side chain of amino acid groups at the surface of the fibers. The observed properties (tensile strength and hydrophobicity) of the treated fibers are found to be dependent on their variation in atomic concentration and functional composition at the surfaces. All the treated muga fibers exhibit almost similar thermal behavior as compared to the virgin one. At RF power of 10 W and treatment time range of 5-20 min, the treated fibers exhibit properties similar to that of the virgin one. Higher RF power (30 W) and the increase in treatment time deteriorate the properties of the fibers due to incorporation of more surface roughness caused by sufficiently high energetic ion bombardment. The properties of the plasma treated fibers are attempted to correlate with the XPS analysis and their surface morphologies.     

Investigation of dental samples using a 35MHz focussed ultrasound piezocomposite transducer

Dental erosion and decay are increasingly prevalent but as yet there is no quantitative monitoring tool. Such a tool would allow earlier diagnosis and treatment and ultimately the prevention of more serious disease and pain. Despite ultrasound having been demonstrated as a method of probing the internal structures of teeth more than 40 years ago, development of a clinical tool has been slow. The aim of the study reported here was to investigate the use of a novel high frequency ultrasound transducer and validate it using a known dental technique.A tooth extracted for clinical reasons was sectioned to provide a sample that contained an enamel and dentine layer such that the enamel-dentine junction (EDJ) was of a varying depth. The sample was then submerged in water and a B-scan recorded using a custom-designed piezocomposite ultrasound transducer with a centre frequency of 35 MHz and a −6 dB bandwidth of 24 MHz.The transducer has an axial resolution of 180 μm and a spatial resolution of 110 μm, a significant advance on previous work using lower frequencies. The depth of the EDJ was measured from the resulting data set and compared to measurements from the sequential grinding and imaging (SGI) method.The B-scan showed that the EDJ was of varying depth. Subsequently, the EDJ measurements were found to have a correlation of 0.89 (p < 0.01) against the SGI measurements. The results indicate that high frequency ultrasound is capable of measuring enamel thickness to an accuracy of within 10% of the total enamel thickness, whereas currently there is no clinical tool available to measure enamel thickness.     

3D atom probe study of gas adsorption and reaction on alloy catalyst surfaces II: Results on Pt and Pt-Rh

The 3-dimensional atom probe (3DAP) is a unique instrument providing chemical analysis at the atomic scale for a wide range of materials. A dedicated 3DAP has been built specifically for analysing reactions at metal surfaces, called the catalytic atom probe (CAP). This paper presents an overview of results from the CAP on structural and chemical transformations to surface layers of Pt and Pt-17.4 at.%Rh catalysts following exposure to a number of gases typically emitted by vehicle engine exhausts, normally for 15 min at pressures of 10 mbar. Following exposure to the oxidising gases NO on Pt, and NO, O₂ or N₂O on Pt-Rh, both surfaces appear disrupted, while for Pt-Rh, Rh enrichment of the surface atomic layer is noted over the entire specimen apex for exposure temperatures up to 523 K. However, for oxidising exposures at 573-773 K relatively clean, Rh-depleted surfaces are observed on {0 0 1}, {0 1 1} and {0 1 2} crystallographic regions of Pt-Rh. It is suggested that this result is due to surface diffusion of oxide species over the specimen apex, towards the {1 1 1}-orientated areas where the oxides appear to be stabilised. In contrast, CO exposure appears to have little effect on the either the surface structure or composition of the Pt-Rh alloy. Finally, combinations of two gases (NO + CO, O₂ + NO) were also dosed onto Pt-Rh alloys in the same exposure. These revealed that while NO and CO can co-adsorb without interference, CO prevents the build up of oxide layers and reduces the extent of Rh segregation seen under NO exposure alone. On exposing Pt-Rh to NO after an oxygen exposure, heavily oxidised surfaces, Rh segregation and no intact NO molecules were seen, confirming the ability of oxidised Pt-Rh to dissociate nitric oxide.     

Deposition of thick and adherent Teflon-like coating on industrial scale stainless steel shell using pulsed dc and RF PECVD

A unique combination of pulsed dc and radio frequency (RF) discharge deposition was used to deposit thick (∼5 μm) and adherent (2-4 MPa) Teflon-like coatings on a stainless steel (SS) shell of 2 m diameter size, through plasma enhanced chemical vapor deposition (PECVD). The details of deposition on such a big industrial scale component are reported for the first time. In this method, highly adherent thin interface layers were grown on SS shell that was electrically grounded, using pulsed dc discharge, followed by RF discharge deposition to build up the required coating thickness. The fluorocarbon precursor molecules, required for the deposition of Teflon-like coating, are generated indigenously by pyrolyzing the Teflon powder. The deposited coating was studied for its chemical bond state, surface roughness (Ra), morphology, thickness, and adhesive strength. These studies were carried out by using XPS, AFM, SEM, etc. The adhesive strength of the coating was measured by pin-pull test as per ASTM D4541 standard test. The coatings deposited with pulsed dc discharge were observed to have higher adhesive strength when compared with those deposited with RF discharge.     

Effects of anodizing conditions on bond strength of anodically oxidized film to titanium substrate

The bond strength of the oxide film to the titanium substrate and its inherent structural characteristics are very important preconditions for the success of titanium implants. The purpose of this study was to evaluate the micro-morphologies, crystalline structures, and bond strengths of the anodically oxidized films formed on titanium with the variation of electrolytes and applied current densities. In contrast to the specimens produced using sulfuric acid as the electrolyte, those produced using phosphoric acid showed quite different shapes and densities of the pores as the applied current densities were varied. The oxide films anodized in sulfuric acid consisted of anatase and rutile TiO₂, whileTiP₂O₇ was predominantly formed on the Ti surfaces anodized using phosphoric acid as the electrolyte. The oxide films, which did not experience spark deposition showed amorphous shape and their bond strengths were significantly lower than those of the other groups (p < 0.05). Those specimens which experienced initial spark deposition with a low current condition showed the highest bond strengths (34.2 MPa) within each electrolyte sub-set. The growing rates of the oxide film thicknesses in relation to the electric current changes varied according to the type of electrolyte, and the oxide film thickness influenced the bond strength.