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At least 1,729 records · Page 96Linked to original sources
PubMed1994

In vivo wear pattern of experimental composite resins containing different filler components.

Using a scanning electron microscope (SEM) and an electron probe surface roughness analyzer (ERA), we conducted the in vivo study of the effect of various filler components on the wear of composite resins. Experimental light-cured composite resins were prepared employing three different filler components; -(1) Silica type, (2) Strontium type, and (3) Barium type. The filler content for all three types was 80 wt%, with the mean particlesize being 2.6 microns in diameter. The resin monomers consisted of 40 wt% Bis-GMA, 40 wt% TEGDMA and 20 wt% UTMA. These materials were placed in 2 mm diameter cylindrical cavities located in the OCA (occlusal contact area) or the CFA (contact free area) of cast crowns temporarily set in a volunteer patient's mouth. The crowns were removed at monthly intervals for longitudinal SEM observation. After two months, worn surfaces were also analyzed by ERA. The result showed that the wear patterns of the composites were characterized by the filler components, especially in the OCA.

Adult↗
PubMed1998

Microstructure and homogeneity of dental porcelain frits.

The microstructure and homogeneity of three commercial dentin and incisal unfired porcelain frits (one conventional and two ultra-low fusing types, fused-to metal were analyzed by X-ray diffractometry, scanning electron microspectroscopy, and wavelength- and energy dispersive X-ray microspectroscopy. The average contents of tetragonal and cubic leucite for the conventional and one of the ultra-low fusing type frits were 20.1-22.6 wt% and 0-2.6 wt%, respectively, whereas those of another of the ultra-low fusing type frits were about 11.5-11.6 wt% and 2.9-4.6 wt%, respectively. The conventional type frits seemed to be admixtures of three kinds of glass frits. One of the ultra-low fusing type frits seemed to be an admixture of four kinds of glass frits. Another ultra-low fusing frits seemed to be only one kind of glass frit dispersed with small size, less than 1 micron, leucite crystals. There were no remarkable differences in microstructure and homogeneity between dentin and incisal porcelain frits in each brand.

Aluminum Silicates↗
PubMed2000

Microfracture mechanisms of composite resins containing prepolymerized particle fillers.

The effect of prepolymerized particle fillers on fracture toughness of four commercial composite resins was studied. The ground surface morphology was examined with a field emission scanning electron microscope. Fracture toughness was determined by using single edge notched specimens. Acoustic Emission (AE), which is the elastic wave due to the release of energy from the localized sources of material, was detected by sensors of a high-sensitivity and low-noise resonance type during the fracture toughness test. Acoustic Emission signals detected were analyzed for parameters such as amplitude and energy. Fracture surfaces were examined with a scanning electron microscope. The fracture toughness values, AE releasing patterns during fracture toughness test, and the fracture surface findings were analyzed to understand the fracture behavior of composite resins containing prepolymerized particle fillers. A microfracture model and fracture mechanisms to increase the fracture toughness of this type of composite resins are proposed.

Acoustics↗
PubMed1999

Behaviour of adult hamsters subjected to hypergravity.

We studied vestibular function in 20 adult hamsters (3 months old) subjected to either prolonged hypergravity (n = 10) or normal gravity (n = 10) for 2 months. Locomotion and swimming of the hypergravity hamsters under light conditions were normal. Equilibrium maintenance was severely disturbed; only 6 of 10 hypergravity hamsters managed to walk on the small tube after 2 months, whereas all 10 controls were able to walk on the tube. The air-righting reflex was severely disturbed; the hypergravity hamsters made 30% correct air-righting responses, while the control hamsters made 88% correct responses. Finally, 5 of 8 hypergravity hamsters had to be saved from drowning when swimming in total darkness. Histological examination of the utricular otoconial layers afterwards, using energy dispersive X-ray element (EDAX) analysis and scanning electron microscopy, did not reveal any differences in calcium content, shape and size distribution of the otoconia between hypergravity hamsters and controls. We suggest that adult hamsters adapt to hypergravity, leading to problems in normal functioning when tested in 1 G, especially in tasks in which sensory input of the vestibular system is important for spatial orientation. These disturbances were more severe in adult hamsters than in young ones, tested in previous experiments. Therefore, we assume that age is a factor for adaptation to altered gravity conditions.

Adaptation, Physiological↗
PubMed1999

A comparison of the preventive effects of lanthanides and fluoride on human experimental root surface carious-like lesions.

OBJECTIVE: To investigate the mechanisms of lanthanides prevention of human root surface carious-like lesions and to compare the effectiveness of lanthanum (La) with that of cerium (Ce) and fluoride (F). Various treatment procedures were also compared. MATERIALS AND METHODS: Acetic buffers containing lanthanum, cerium, and fluoride (500 ppm) were used individually or in combination to treat 48 cementum-dentin samples. The acid-resistant capacity of various treatment procedures was evaluated by means of scanning electron microscope, electron microprobe, and polarizing light microscope analyses. RESULTS: The acid-resistant effects of lanthanide element were comparable to those of fluoride, and their acid-resistant effects were even stronger when combined with fluoride and cerium. These effects are likely due to the formation of La(Ce)HAP, FLa(Ce)HAP, and lanthanum/cerium phosphate compounds. CONCLUSION: Combined F/La(Ce) was more effective in the prevention of root surface caries than were lanthanides alone.

Acetic Acid↗
PubMed1999

Distribution of nanofillers from a simplified-step adhesive in acid-conditioned dentin.

PURPOSE: This in vitro study examined the interfacial ultrastructure of a nanofilled, simplified-step adhesive (Prime & Bond NT, Dentsply), to determine the distribution of nanofillers within the collagen network of the hybrid layer. MATERIALS AND METHODS: Twenty-four dentin discs were divided into two groups and bonded using two recommended conditioning techniques: Group I, NRC (Non-Rinse Conditioner), and Group II, Conditioner 36 (colloidal silica thickened 36% phosphoric acid). Following conditioning, a single coat of adhesive was applied and light-cured. Dentin discs were then bonded to form disc-pairs and processed for TEM examination. Demineralized, ultrathin sections were examined stained or unstained. Non-demineralized sections were used for STEM/EDX analysis of elemental distribution across the resin-dentin interface. In addition, four dentin discs were bonded with a generic adhesive (HEMA/TBBO) for TEM examination of stained collagen and proteoglycans. RESULTS: In unstained sections of both groups, nanofillers from the adhesive layer were congested around patent tubular orifices, but were not found within the interfibrillar spaces of the hybrid layer. EDX analysis of silicon (Si) showed predominant distribution within the adhesive layer and tubular orifices. Phosphorus (P) was present within the hybrid layer and adhesive layer in Group II. CONCLUSION: It is hypothesized that a) aggregation of the nanofillers within the adhesive resulted in filler clusters that are too large to infiltrate the interfibrillar spaces of the hybrid layer; and b) retention of ground substance within the demineralized intertubular collagen matrix may also have prevented the infiltration of the nanofillers.

Acid Etching, Dental↗
PubMed1994

Study on gutta-percha points using scanning electron microscopy and analysis with electron microprobe.

A comparative study of the apical morphology and contour was performed with the scanning electron microscope at 45x, 70x and 300x, while the chemical composition of eight gutta-percha point brands was surveyed with an EDAX 9100 electron microprobe. They were classified according to their apical morphology as conical (25%) and truncate (75%), based on their contour as regular (50%) and irregular (50%) and according to their surface as without defects (50%) and with defects (50%). The analysis of inorganic compounds revealed the presence of varying proportions of Zn, Ba, Si, Mg. Ca, P, Cl and Al, possibly implying that the presence of Ba and Al could interfere with postendodontic repair or at least irritate the periapical area if inadvertently overfilled.

Electron Probe Microanalysis↗
PubMedDate not supplied

In vitro osteoclast resorption of bone substitute biomaterials used for implant site augmentation: a pilot study.

PURPOSE: This observational study examined the resorptive behavior of normal neonatal rabbit osteoclasts grown on slices of bovine cortical bone as compared to samples of commercially available bone substitute biomaterials. It also examined the surface characteristics of these materials. MATERIALS AND METHODS: The 11 materials tested fell into 3 groups: (1) bone-derived, including freeze-dried human rib block, human demineralized freeze-dried bone, and deproteinated bovine bone; (2) synthetic hydroxyapatites (HA); and (3) synthetic non-HA, including coated methacrylates and coated silica glass. After 4 days in culture, 1 group of samples of each material underwent scanning electron microscopy (SEM) to evaluate resorptive pitting versus controls, while another group underwent tartrate-resistant acid phosphatase staining and light microscopy to examine osteoclast numbers and morphology. The 2 bovine-derived HA materials also underwent immunohistochemical staining and surface chemistry analysis. RESULTS: While most of these materials supported osteoclast attachment, some spreading, and survival in culture, only the bone-derived materials, with the exception of sintered deproteinated bovine bone, showed large scalloped-edged resorption pits with trails and exposed collagen when examined by SEM, although not to the same extent as unprocessed natural bone material. The HA materials and the sintered deproteinated bovine bone showed evidence of etching with smaller pits but no evidence of resorptive trail formation. The non-HA materials showed no evidence of pit formation or trails. Under immunohistochemical staining, Bio-Oss appeared to be positive for type I collagen after osteoclast activity on its surface, while Osteograf/N showed no positive staining. Surface chemistry analysis revealed nitrogen present in Bio-Oss specimens (0.17% to 0.47%), while there was no nitrogen detected in the Osteograf/N (0.00%); the percent nitrogen observed in normal bovine bone controls was 6.01% to 9.25%. DISCUSSION: The bone-derived materials supported osteoclast activity on the material surface in a way that facilitated formation of the more complex resorption pits in vitro. Assuming the rate of pit formation observed in vitro mimics that observed in vivo, the quantity and type of osteoclastic remodeling seen on non-bone-derived materials--and perhaps sintered bone-derived materials--would be extremely slow to negligible. Physiologic removal of non-bone-derived bone substitutes in vivo may occur by methods other than osteoclast resorption. CONCLUSIONS: Allogenous and xenogenous bone-derived materials that undergo delayed physiologic resorption may be more appropriately used with a staged surgical approach when used in sites intended to support osseointegrated dental implants. The combination of collagen staining and the presence of nitrogen suggest that there may be residual protein in Bio-Oss.

Acid Phosphatase↗
PubMedDate not supplied

Oxidized titanium screws coated with calcium ions and their performance in rabbit bone.

PURPOSE: The aim was to answer a fundamental question: Do the chemical properties of titanium implants influence osseointegration? MATERIALS AND METHODS: Screw-type implants produced of turned commercially pure (grade 1) titanium (controls) and electrochemically calcium-deposited titanium implants (Ca test implants) were placed in the tibiae and femora of a total of 10 mature New Zealand white rabbits. The macro arc oxidation method was applied for Ca implants. Surface oxides were characterized with different analytic techniques, including x-ray photoelectron spectroscopy, auger electron spectroscopy, scanning electron microscopy, thin-film x-ray diffractometry, and TopScan 3D. The bone response was evaluated by biomechanical tests, histology, and histomorphometry. RESULTS: After a follow-up period of 6 weeks, test Ca implants showed a significant increase in mean peak removal torque (P = .0001) and in the histomorphometric measurement of bone-to-metal contact around the implants (P = .028) in comparison to controls. In addition, more mature mineralized bone was observed adjacent to test Ca implants compared to controls, as evaluated on 10-microm undecalcified, toluidine blue-stained, cut, and ground sections. DISCUSSION: The potential role of surface Ca chemistry to a superior bone response is discussed with specific reference to interaction with Ca(+)-binding proteins and function as binding sites of calcium phosphate mineral. CONCLUSION: The present results suggest that the surface chemical composition of titanium implants is of great importance for the bone response. Ca ion-deposited titanium implants showed fast and strong osseointegration in the rabbit bone model.

Animals↗
PubMedDate not supplied

Functionally gradient bonelike hydroxyapatite coating on a titanium metal substrate created by a discharging method in HBSS without organic molecules.

PURPOSE: This study evaluated the quality of coatings on titanium surfaces prepared by discharging in Hanks' balanced salt solution without organic molecules (HBSS-). MATERIALS AND METHODS: 10 x 10 x 1.0-mm titanium plates were used as cathodes of a coating device developed in the laboratory and immersed in HBSS-. A piece of platinum foil was used as a counterelectrode. Discharging was maintained at 1 A and 10 V (416 mA/cm2) for periods of 90, 270, and 540 seconds. Crystal phases of the coatings were identified by x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). In addition, the surface characterization and Ca/P atomic ratio of the titanium surfaces were determined by x-ray photoelectron spectroscopy (XPS). Furthermore, the surface topography, the thickness of the coatings, and the bonds between coatings and titanium substrates were observed by scanning electron microscopy. RESULTS: The FTIR and XRD studies demonstrated that the deposits on the titanium after 540 seconds of discharging were crystalline hydroxyapatite. In addition, the thickness of the titanium suboxide layer increased during discharging. The XPS studies indicated that after 540 seconds of processing, the mean Ca/P ratio of the coatings on the titanium was 1.71, which is similar to that of human bone. DISCUSSION: In addition, the replacement of sodium ions with calcium ions seemed important for the promotion of crystallization of the coating. Furthermore, the XPS studies demonstrated that the coatings had a gradient function. Scanning electron microscopy showed that adhesion between coatings and the titanium substrate was close. The coatings were approximately 1 microm thick. CONCLUSION: These findings suggest that a very thin crystalline bonelike hydroxyapatite coating with a gradient function could be prepared on a titanium metal substrate in HBSS- by a discharging method.

Adhesiveness↗
PubMed1992

[Qualitative studies of Fahr disease].

We investigated brain tissue from 7 deceased patients with Fahr's disease using X-ray-analysis for the determination of compositional differences between calcareous particles in different areas of brain or between the left and right sides in a brain and differences in composition of concrements in different brains. We found, in all areas of one brain no difference in elementary composition. Differences were found between different brains, two brains showed a high silicon content.

Adolescent↗
PubMed1991

[Principles and application possibilities of cryoultramicrotomy].

This paper reviews the technical aspects of cryoultramicrotomy. The key preparation steps in the technique, namely freezing, sectioning, thawing, and staining are analysed. The application of this method to immunocytochemistry and analytical electron microscopy are discussed with respect to the present possibilities and problems.

Cryoultramicrotomy↗
PubMed1979

The technique of electron probe x-ray analysis and the atomic composition of aurosomes.

Electron probe x-ray analysis is an exciting new method of elemental analysis at the ultrastructural level. This is a relatively non-destructive form of analysis by which elements from Na onwards (i.e. above Z number 10) can be simultaneously detected and displayed as a spectrum. The best spatial resolution that can be achieved is of the order of 20 nm. The sensitivity of detection varies with the elements but about 10-18 g of an element can be detected. With the available computer programs elemental ratios are readily determined without the need of standards. The special appeal of this technique stems from the fact that it is the only way of analyzing minute inclusions in situ within the cell and so correlate morphology with atomic composition. With this method, gold has been demonstrated in aurosomes produced in various sites after the administration of soluble gold salts to experimental animals and man. A more detailed analysis of aurosomes found in the synovial membrane 3 days and 18 months after injection of gold sodium thiomalate into the rabbit knee joint revealed that the aurosome contains gold, phosphorus, and sulphur, and that the atomic ratios of these elements do not alter over the above mentioned time interval.

Animals↗
PubMed1987

Industrial problem solving with microbeam analysis.

The objective of this paper is to provide an overview of the microbeam analytical techniques and to help select the appropriate one to solve complex problems often arising in today's high-tech industries. Case histories are given to show how renowned analytical service laboratories and microbeam experts formulated their strategies to approach a real life problem, what type of conclusions were deduced from the data and, finally, how the problem was solved.

Electron Probe Microanalysis↗