This in vitro study aimed to characterize the surface morphology and composition of toothbrushed titanium casting and thereby to elucidate interactions between the metal and abrasive material in ...dentifrice.
Specimens were cast from CP Ti ingots and then mirror-finished. Two fluoride-free toothpastes containing crystalline CaHPO
4·2H
2O and amorphous SiO
2 particles as abrasive were slurried with distilled water (15
g/30
mL). While toothbrushes were reciprocated at 120
strokes/min for 350,400 strokes, the specimens were brushed with the respective slurries under a load of 2.45
N. The brushed and non-brushed surfaces were characterized by means of SPM, EPMA, and XPS. SPM data were analyzed using one-way ANOVA, followed by post hoc Tukey test (
p<0.01).
Irrespective of toothpastes, toothbrushing had a significant influence on surface roughness. The CaHPO
4·2H
2O-containing paste produced much rougher surface than the SiO
2-containing paste. Both the surfaces were chemically altered due to reactions with the respective abrasive materials. Abrading chips had dimensions of micron to submicron order. A number of chips were attached to abrasive particles.
The alterations of surface morphology and composition may affect biological responses of titanium in the oral environment. Dentifrice with lower abrasivity might be advisable for daily oral hygiene practice of patients with dental titanium devices.
This investigation was concerned with the effect of 3 superstructure materials on the strain around an implant under static and nonimpact dynamic loading.
Five highly filled composite resin-veneered ...crown analogs, 5 autopolymerized acrylic resin-veneered crown analogs, and 5 gold-alloy full cast crown analogs were prepared. The resin veneers were applied to gold-alloy frameworks. These crown analogs were prepared to fit an ITI implant-abutment assembly, which was screwed into a block of acrylic resin to simulate implantation in bone. The crown analogs were successively placed on the abutment, and a lateral load of 100 N was applied to the superstructure by a lever-type testing machine. Strains were recorded under static and dynamic loading by a 2mm-long strain gauge bonded to the surface of the bone simulant tangential to the implant. The dynamic load simulated masticatory cycles (75 strokes/min).
Although the strain values differed significantly between the static and dynamic loading (P < .05), there was no significant difference among the superstructure materials under either loading condition (P > .05).
These findings are in agreement with in vivo measurements, thus suggesting that cyclic rather than impact loading should be used in the investigation of occlusal material behavior under functional loading.
Under static and nonimpact dynamic loading, the 3 superstructure materials tested (highly filled composite resin, acrylic resin, and gold alloy) had the same influence on the strain transmitted to a bone simulant that surrounded a single implant.
In this paper, we have proposed a new method that gives quantitative distributions of metallic elements in a tissue section by electron probe microanalyser equipped with wavelength dispersive ...spectrometers. Its principal merit is the clear expression of element distribution with micrometer resolution in typically prepared section samples for routine histopathological diagnosis. By analysing thin standard films containing metallic atoms of interest, it was confirmed that the detection limit is about 1 x 10(6) atoms microm-2. This value corresponds to 100 microg g(-1) (dry weight) in case of tissue section of 2 microm thickness. Furthermore, for copper, iron and aluminium, the exact linear relationship between the amount of metallic atoms and the characteristic X-ray intensity was established in the range up to 15 x 10(6) atoms microm(-2). The element maps of tissue sections from patients with Wilson's disease proved that the copper levels in analysed areas were not homogeneous and indicated abnormal accumulation in some portions. These results confirmed the usefulness of this method for histopathological diagnosis.
The Laser Interferometer Gravitational-Wave Observatory has performed a third science run with much improved sensitivities of all three interferometers. We present an analysis of approximately 200 ...hours of data acquired during this run, used to search for a stochastic background of gravitational radiation. We place upper bounds on the energy density stored as gravitational radiation for three different spectral power laws. For the flat spectrum, our limit of omega0 < 8.4 x 10(-4) in the 69-156 Hz band is approximately 10(5) times lower than the previous result in this frequency range.
Viral movement through plasmodesmata in host plants depends on the interaction between virus‐encoded movement protein (MP) and host proteins. To search for MP‐interacting protein (MIP), far‐western ...screening of a tobacco cDNA library was carried out using a recombinant MP of tomato mosaic virus (ToMV) as a probe. One of the positive cDNA clones, designated MIP204, was highly homologous to a class of transcriptional coactivators commonly referred to as multiprotein bridging factor 1 (MBF1). ToMV MP could also bind to the Arabidopsis homologues of MBF1. The recombinant MIP204 bound to MPs of ToMV and a crucifer tobamovirus CTMV‐W, but not of cucumber mosaic virus. MPs of ToMV and the related virus may interact with MBF1‐like proteins to modulate host gene expression.
Fatigue failure in a removable partial denture framework includes fracture of the occlusal rest at the rest-minor connector angle.
This in vitro study evaluated the fatigue resistance of 0.8-mm–thick ...occlusal rests cast with Co-Cr and Ag-Pd-Cu-Au alloys.
The specimen consisted of occlusal rest (0.8 × 2.0 × 10 mm), vertical minor connector (0.9 × 2.0 × 5.0 mm), and denture base connector (1.5 × 5.0 × 25 mm). Twenty-five specimens each were cast with Co-Cr and Ag-Pd-Cu-Au alloys. From each group, 5 specimens were subjected to a load-deflection test conducted to determine the amount of deflection to be used in fatigue test. The fatigue test was performed such that the occlusal rest component was deflected by displacing the denture base component in a tissueward direction. Predetermined denture base displacement values of 0.25 and 0.49 mm for Co-Cr and Ag-Pd-Cu-Au specimens, respectively, were repeated at a rate of 500 cycles/min by use of a displacement-controlled fatigue testing machine, until occlusal rest failure occurred or a preset limit of 2 million cycles was achieved. The survival rates of the occlusal rests were calculated assuming a chewing cycle of 2 × 10
5 per year. Scanning electron microscopy (SEM) photographs were made to examine the fracture surfaces and to identify casting defects. The relationship between fatigue cycles and number of casting defects was determined by Spearman rank correlation analysis (
P<.01).
All 20 Co-Cr specimens outran the preset limit, whereas 18 Ag-Pd-Cu-Au specimens fractured. After 3 years of simulated clinical use, only 50% of the Ag-Pd-Cu-Au occlusal rests survived. Statistical analysis showed that the fatigue cycles and number of casting defects were inversely related (
P<.01). Fatigue crack initiation occurred at the inner-curvature surface of the rest-minor connector angle. The typical Ag-Pd-Cu Au fatigue fracture surface consisted of smooth propagation and dimpled and smooth final fracture areas.
This study suggests that cast Co-Cr rests are more rigid and fatigue resistant than Ag-Pd-Cu-Au rests. The fatigue resistance of 0.8-mm–thick occlusal rests may be adequate if cast with Co-Cr alloy. An increased number of casting defects may hasten the fatigue failure of occlusal rests.
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