The marginal fit of lithium disilicate crowns: Press vs. CAD/CAM Abstract: This study aimed to compare the vertical marginal gap of teeth restored with lithium disilicate crowns fabricated using CAD/CAM or by pressed ceramic approach. Twenty mandibular third molar teeth were collected after surgical extractions and prepared to receive full veneer crowns. Teeth were optically scanned and lithium disilicate blocks were used to fabricate crowns using CAD/CAM technique. Polyvinyl siloxane impressions of the prepared teeth were made and monolithic pressed lithium disilicate crowns were fabricated. The marginal gap was measured using optical microscope at 200× magnification (Keyence VHX-5000, Japan). Statistical analysis was performed using Wilcoxon test. The lithium disilicate pressed crowns had significantly smaller (p = 0.006) marginal gaps (38 ± 12 µm) than the lithium disilicate CAD/CAM crowns (45 ± 12 µm). This research indicates that lithium disilicate crowns fabricated with the press technique have measurably smaller marginal gaps compared with those fabricated with CAD/CAM technique within in vitro environments. The marginal gaps achieved by the crowns across all groups were within a clinically acceptable range.

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Amorphous silicon carbide (a-SiC) films are promising solution for functional coatings intended for harsh environment due to their superior combination of physical and chemical properties and high temperature stability. However, the structural applications are limited by its brittleness. The possible solution may be an introduction of nitrogen atoms into the SiC structure. The effect of structure and composition on tribo-mechanical properties of magnetron-sputtered a-SiCxNy thin films with various nitrogen content (0–40 at.%) and C/Si close to one deposited on silicon substrates were evaluated before and after exposure to high temperatures up to 1100 °C in air and vacuum. IR transmission spectroscopy revealed formation of multiple C-N bonds for the films with N content higher than 30 at.%. Improvement of the organization in the carbon phase with the increase of nitrogen content in the a-SiCN films was detected by Raman spectroscopy. Nanoindentation and scratch test point out on the beneficial effect of the nitrogen doping on the tribo-mechanical performance of a-SiCxNy coatings, especially for the annealed coatings. The improved fracture resistance of the SiCN films stems from the formation of triple C≡N bonds for the as deposited films and also by suppression of SiC clusters crystallization by incorporation of nitrogen atoms for annealed films. This together with higher susceptibility to oxidation of a-SiCN films impart them higher scratch and wear resistance in comparison to SiC films before as well as after the thermal exposure. The best tribo-mechanical performance in term of high hardness and sufficient level of ductility were observed for the a-Si0.32C0.32N0.36 film. The enhanced performance is preserved after the thermal exposure in air (up to 1100 °C) and vacuum (up to 900 °C) atmosphere. Annealing in oxidizing atmosphere has a beneficial effect in terms of tribological properties. Harder films with lower nitrogen content suffer from higher brittleness. FIB-SEM identified film-confined cracking as the initial failure event in SiC, while it was through-interface cracking for SiCN at higher loads. This points out on the higher fracture resistance of the SiCN films where higher strains are necessary for crack formation

Desorption nanoelectrospray (nanoDESI) was described in 2007 and it represents a miniaturized version of desorption electrospray without the assistance of the nebulizing gas. Compared to DESI, a nanoelectrospray tip (2 ± 1 μm I.D.) generates primary charged droplets of smaller sizes and lower spray liquid flow rates. This is the first report on utilization of nanoDESI for mass spectrometry imaging (MSI). Its new coupling with a Q-TOF instrument allowed faster mass spectra acquisition (4 Hz) essential for MSI of fine surface details. To evaluate nanoDESI potential for mass spectrometry imaging, etched glass substrates with Rhodamine B patterns of different dimensions were prepared. The Rhodamine B lines were analysed in 1D scanning mode and their width was determined experimentally by nanoDESI measurement. The experimental data revealed that the lateral resolution of nanoDESI is close to 30 μm along the x-axis (orthogonal to the inlet). 2D scanning mode confirmed good resolution along both axes as dye squares with dimensions about 60 μm × 60 μm were easily distinguished. The low flow rate of the spray liquid reduced undesirable analyte washing effects, which allowed repeated scanning analysis of the surface. The presented results demonstrate the applicability of nanoDESI for high surface resolution mass spectrometry imaging.

OBJECTIVES: The objective of this study was to observe and to measure the impact of corundum sandblasting on the thickness of the Immediate dentin sealing layer. METHODS: 20 recently extracted molars were collected and divided randomly into two groups. A standardized preparation was performed on each tooth and the Optibond FL dentin bonding agent (Kerr, Orange, USA) was applied on the prepared surface according to the manufacturer 's instructions. The surface was then partially sandblasted. RONDOfl ex plus 360 (KaVo, Bieberach an der Riss, Germany) and Airsonic Mini-Sandblaster (Hager&Werken, Duisburg, Germany) were used. Microscope observations were made. RESULTS: The arithmetic mean of the Optibond FL dentin bonding agent fi lm thickness was 48.72 μm (Group 1=45.55 μm and Group 2 = 51.88 μm). The dentin bonding agent layer thickness was reduced to the average value of 17,12 μm by RONDOfl ex plus 360 sandblasting (Group 1). The zero value was recorded in 16 % of the locations. The Airsonic Mini-Sandblaster sandblasting changed the average thickness of the dentin bonding agent layer to 13.25 μm with 31 % of zero values (Group 2). CONCLUSION: The results of this research lead to a refl ection on modifi cations of the immediate dentin sealing procedure (Tab. 4, Fig. 3, Ref. 28).

Statement of problem It has been shown that selective etching improves the bond strength of some self-adhesive resin cements to enamel. The same has yet to be determined with dentin pre-treatment. Purpose To evaluate the tensile bond strength of two self-adhesive resin cements after two dentin surface pre-treatments, and also to analyze the cement/dentin interface. Material and Methods One hundred and twelve human third molars were extracted. The teeth were distributed into seven groups (n = 16). Maxcem Elite Chroma (MAX) (Kerr, Scafati, Italy) and Relyx U200 (RLX) (3M ESPE, Neuss, Germany) were used without pre-treatment or with two dentin pre-treatments (polyacrylic acid or phosphoric acid). A conventional etch-and-rinse (EAR) luting cement, NX3 Nexus (NX3) (Kerr, Scafati, Italy), was used as an external control group. Before testing, all specimens were stored in distilled water for 24 hours. Three specimens from each group were prepared for scanning electron microscopy observation (SEM). A tensile bond strength test (TBS) was performed for the remaining samples. The data were statistically analyzed using the Kruskal–Wallis test and Pairwise comparisons using the Wilcoxon rank sum test. Results MAX without pre-treatment and with phosphoric acid etching attained statistically similar bond strengths to NX3 (P > 0.05). There was a statistical difference (P = 0.00488) between RLX without pre-treatment (5.62 MPa) and NX3 (10.88 MPa). Phosphoric acid pre-treatment increases the bond strength values of RLX to a strength that is comparable to NX3 (P > 0.05). The lowest tensile bond strength (TBS) was attained after the application of polyacrylic acid with MAX (1.98 MPa). No statistical differences were found between the RLX bond strength values after polyacrylic acid treatment and RLX without pre-treatment or NX3 (P > 0.05). SEM observations disclosed an enhanced potential of the self-adhesive cements to infiltrate into dentin tubules and form resin tags when applied after phosphoric acid pre-treatment. The failure mode was dominantly adhesive. Conclusions On dentin, the self-adhesive resin cement MAX might be an effective alternative to conventional resin cement. Etching the dentin with phosphoric acid does not have a negative effect on the bond strength of MAX to dentin. On the other hand, phosphoric acid improved the bond strength of RLX when compared to EAR cement.

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Selective laser melting (SLM) is a technology of layer-by-layer additive manufacturing using a laser. This technology allows one to get complex-shaped, three-dimensional (3D) specimens directly from metal powder. In this technology, various metal powders are used, including different steels. Stainless steel 1.4404 (CL20ES) and maraging steel 1.2709 (CL50WS) have been investigated. The surface of samples manufactured from CL20ES and CL50WS powders by SLM (with and without combination sandblasting and annealing) was studied by conversion X-ray Mössbauer spectroscopy (CXMS) and conversion electron Mössbauer spectroscopy (CEMS). The surface morphology, elemental composition, and structure were examined by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD). Samples with sandblasted (corundum powder) and non-sandblasted surfaces were annealed at 540 °C (CL50WS) or 550 °C (CL20ES) for 6 h in air. Oxidation processes on surfaces of samples manufactured from both initial powders were observed after post-process annealing by CEMS and CXMS, as well as confirmed by XRD. The transformation of the austenitic to ferritic phase was observed in a sandblasted and annealed CL20ES sample by CEMS and XRD.