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Biomedical subjects

I Nicander

Publications and source records attributed to I Nicander.

15 recordsLinked to original sources
PubMed1999

Electrical bioimpedance related to structural differences and reactions in skin and oral mucosa.

Electrical bioimpedance can reflect structural and chemical changes of the skin and the oral mucosa in the beta-dispersion frequency range. From our measured multifrequency data set, four physically distinct indices have been formulated to distinguish the electrical properties for different anatomical locations and to detect different reactions and conditions of the skin and the oral mucosa. In comparison with the skin, the differences for various anatomical regions were greater in the oral cavity, which showed as well a different impedance pattern after irritant responses. We conclude that the impedance technique is able to classify and quantify different responses and conditions, preferably by using contralateral reference sites, or following a site in time; however, mapping of baseline properties facilitates the use of the method even if a large part of the skin or the oral mucosa is involved. The method has the potential of becoming a diagnostic decision support tool.

Adult↗
PubMed1999

Inter- and intra-individual differences in human stratum corneum lipid content related to physical parameters of skin barrier function in vivo.

For a full understanding of the properties of the human skin barrier, physical macroscopic parameters of barrier function must be correlated to the structural organization of the barrier on a molecular level. This study was undertaken to relate differences in the relative composition of the three main lipid classes of human stratum corneum, i.e., free fatty acids, cholesterol, and ceramides, to differences in transepidermal water loss, stratum corneum electrical impedance, and corneometer value. A new high performance liquid chromatography/light scattering detection-based analysis method recently developed was used for collection of quantitative lipid data in conjunction with gas chromatography/mass spectrometry/flame ionization detection measurements on the free fatty acid fraction. After subtraction of contaminating lipid fractions we have estimated the molar ratio of the human skin barrier lipid composition to be, respectively, 15% cholesterol esters, 16% saturated long chain free fatty acids, 32% cholesterol, and 37% ceramides. The inter-individual difference in the relative amount of free fatty acids, cholesterol, and ceramides, respectively, can be >100% in the individual case. It was found that the relative amount of ceramides to cholesterol is larger in the wrist area, paralleled by a higher transepidermal water loss and corneometer value as well as different skin electrical impedance values as compared with the upper forearm area. We conclude that the site-dependent differences in the stratum corneum lipid composition are small compared with the large inter-individual variation. Interestingly, in the individual case, no correlation was registered between relative ceramide content and barrier properties.

Adolescent↗
PubMed1998

A new HPLC-based method for the quantitative analysis of inner stratum corneum lipids with special reference to the free fatty acid fraction.

The inner stratum corneum is likely to represent the location of the intact skin barrier, unperturbed by degradation processes. In our studies of the physical skin barrier a new high-performance liquid chromatography (HPLC)-based method was developed for the quantitative analysis of lipids of the inner stratum corneum. All main lipid classes were separated and quantitated by HPLC/light scattering detection (LSD) and the free fatty acid fraction was further analysed by gas-liquid chromatography (GLC). Mass spectrometry (MS) was used for peak identification and flame ionization detection (FID) for quantitation. Special attention was paid to the free fatty acid fraction since unsaturated free fatty acids may exert a key function in the regulation of the skin barrier properties by shifting the physical equilibrium of the multilamellar lipid bilayer system towards a noncrystalline state. Our results indicated that the endogenous free fatty acid fraction of the stratum corneum barrier lipids in essence exclusively consisted of saturated long-chain free fatty acids. This fraction was characterized as a very stable population (low interindividual peak variation) dominated by saturated lignoceric acid (C24:0, 39 molar%) and hexacosanoic acid (C26:0, 23 molar%). In addition, trace amounts of very long-chain (C32-C36) saturated and monounsaturated free fatty acids were detected in human forearm inner stratum corneum. Our analysis method gives highly accurate and precise quantitative information on the relative composition of all major lipid species present in the skin barrier. Such data will eventually permit skin barrier model systems to be created which will allow a more detailed analysis of the physical nature of the human skin barrier.

2-Propanol↗
PubMed1998

Electrical impedance of nodular basal cell carcinoma: a pilot study.

BACKGROUND: Previously, we have explored the use of measurements of electrical impedance and devised 4 physically distinct indices named magnitude index (MIX), phase index, real part index and imaginary part index (IMIX) from the impedance data. Our results indicated that these indices could characterize contact reactions. OBJECTIVE: The goal of the present study was to use the electrical impedance method for the preoperative assessment of nodular basal cell carcinoma (BCC). METHODS: We included 11 patients with a total of 12 nodular BCC, diagnosed clinically and histologically. The noninvasive measurements were performed by transepidermal water loss (TEWL) and electrical impedance. For reference, normal looking contralateral or ipsilateral skin was used. RESULTS: Compared to controls, the mean TEWL of BCC was increased, but this finding was not statistically significant. The electrical impedance measurements of BCC tissue revealed statistically significant changes of the impedance indices MIX and IMIX (p </=0.001). CONCLUSION: The results suggest that the measurement of electrical impedance might become useful for investigations of BCC.

Aged↗
PubMed1997

Information in full and reduced data sets of electrical impedance spectra from various skin conditions, compared using a holographic neural network.

Information relating to patho-physiological events in living tissues, including skin, should be found in the beta-dispersion frequency range of the electrical impedance. For intact skin, the alpha-dispersion is strongly influenced by the condition of the stratum corneum, particularly its hydration. For intact skin, these dispersions are not well separated: in a Nyquist plot, most of the relatively small beta-dispersion will be hidden behind the upper-frequency end of the alpha-dispersion arc. In the study, information obtained with a set of four indices, claimed to extract most of the information in the pertinent frequency interval, is compared with the full information measured at 31 frequencies, between 1 kHz and 1 MHz, for irritant and allergic contact reactions and nodular basal cell carcinomas, using a holographic neural network that appears to be useful for model-independent evaluation of the consequences of data-reduction procedures. Cole parameters should be avoided in the beta-range for intact skin. The indices are well supported, as long as differences from a reference site are used, and it seems that they can serve as the basis for differential diagnostics even as absolute values, although more information may be extracted from the complete spectrum.

Diagnosis, Differential↗
PubMed1997

Electrical impedance. A method to evaluate subtle changes of the human oral mucosa.

In a previous study, we mapped the differences in electrical impedance between various anatomical locations in the oral mucosa. We now explore the ability of the impedance technique to detect mild reactions in the buccal mucosa induced by the irritant sodium lauryl sulphate. This substance was applied for 15 min at a concentration of 2% to the mucosa of 26 healthy subjects. A contralateral site was used as a control. Responses were evaluated by measuring electrical impedance before exposure and after removal of the irritant, and also by visual inspection and histology. Magnitude and phase of impedance were determined in the frequency range 1 kHz to 1 MHz at 5 depth settings, and 4 physically distinct indices were calculated from the impedance data. The results showed the response to be at its maximum 5 min after removal of the test chamber, for all indices. These changes were statistically significant, whereas visual and histological alterations were slight or negligible. We conclude that the electrical impedance technique is capable of detecting mucosal changes in the invisible or barely visible range, and that the mucosal response to sodium lauryl sulphate is well characterised by the 4 indices.

Adult↗
PubMed1997

Electric impedance measurements at six different anatomic locations of macroscopically normal human oral mucosa.

We have used an electric impedance technique to explore the properties of the oral mucosa at various sites in the normal mouth. Investigations were performed on 26 healthy non-smoking subjects at 12 test areas, representing a range of mucosal types. Electric impedance spectra were measured in the frequency range 1 kHz to 1 MHz at five depth penetration settings of the instrument, and four indices were calculated for each depth. Statistically significant differences in the indices were found between most of these locations but not between contralateral sites at a similar position. The differences between some areas were considerably greater, and the differences between contralateral sites were smaller, than those encountered in the skin. Our results suggest that the choice of site for investigation of the oral cavity is more critical than with experimentation on the skin and that cognizance of this fact makes the oral cavity readily available for studies by the impedance method.

Adult↗
PubMed1996

Influence of paste temperature at curing on conversion rate and bending strength of light-cured dental composites.

Pastes of three dental composites were tempered to 20 degrees C, 37 degrees C and 60 degrees C. Test specimens (22 x 2 x 2 mm) were cured by light and stored in deionized water. Three-point bending strength was measured after 1 h and after 24 h. Degree of conversion on the surface exposed to the curing light and the opposite surfaces at the bottom of the mould was analysed by Fourier transform infrared (FTIR) after 1 h. After 1 h, specimens produced using the pastes cured at 60 degrees C showed significantly higher bending strength than the specimens produced using pastes cured at 20 degrees C and 37 degrees C. However, after 24 h the composites pretempered at the lower temperatures had developed the same level of bending strength as the composites cured at 60 degrees C. An increase in the degree of conversion with increased paste temperature was found in all materials after 1 h.

Acrylic Resins↗
PubMed1996

An electrical impedance technique for assessment of wheals.

In previous studies of the electrical impedance of the skin, we introduced a set of physical indices which could be used to distinguish between the cutaneous effects produced by different irritants and allergic contact reactions. In this study, wheals were induced in 10 allergic patients by performing prick tests on the forearm with the relevant allergen and histamine, respectively. Normal skin was used for control. The wheals were evaluated by visual scoring, laser Doppler, and electrical impedance. As expected, there was a close agreement between the visual and laser Doppler readings. Compared to the controls, there were significant changes in the electrical impedance of the wheals, especially in the index related to the phase angle. The changes in the indices were found to follow a particular pattern, which diverged from those obtained in contact skin reactions of both allergic and irritant type. Our results indicate that, by the application of the impedance technique, it will be possible to characterize objectively and quantify the wheal reaction. The results also suggest that cutaneous reactions of completely different causes, such as allergic skin reactions of the late and immediate type, and irritant contact reactions, may be distinguished on the basis of their effects on the electrical impedance of the skin.

Adolescent↗
PubMed1996

Factors influencing shear strength of incrementally cured composite resins.

Factors influencing the shear strength of incremental curing of three different composite resins were examined. The first increment was cured under different surface conditions, in air, or under a coverglass. A separate experiment studied the effect of curing in nitrogen atmosphere. There was no difference in the shear strength of the specimens if the first increment was created in air or under a coverglass. One material (Heliomolar RO) showed higher shear strength when cured in increments and one when bulk-cured (Herculite XR). Curing increments in a nitrogen atmosphere increased the shear strength for two of the three materials tested (P50 and Heliomolar). The results showed that the bond strength between the increments of composites was influenced by the surface properties of the composites themselves after they had been cured under the different conditions; it was also affected by the inherent chemical and physical properties of the materials utilized.

Acrylic Resins↗
PubMed1996

Correlation of impedance response patterns to histological findings in irritant skin reactions induced by various surfactants.

We have explored the use of measurements of electrical impedance to discriminate between the effects of different irritant substances upon the skin, and have studied the relationships between impedance and histopathological change. Three compounds with different chemical profiles were tested on volunteers: sodium lauryl sulphate, benzalkonium chloride and nonanoic acid. The concentrations selected were such that each irritant produced responses of a similar order, as judged by visual scores. The magnitude and phase of electrical impedance were measured and, for comparison, also the transepidermal water loss. Four physically distinct aspects (indices) were devised from the impedance data, and the values obtained were statistically analysed. The three irritants produced different effects, giving distinctive impedance patterns. These were also found to be reflected by three different types of histopathological skin response. Our results suggest that the indices can be used to classify irritant contact reactions, which it is difficult or impossible to achieve by other non-invasive techniques.

Adult↗
PubMed1995

Electrical impedance measured to five skin depths in mild irritant dermatitis induced by sodium lauryl sulphate.

The non-invasive electrical impedance technique used in this study reflects structural changes in a tissue, and provides an estimate of the level of oedema by a simple impedance index. Sodium lauryl sulphate (SLS), dissolved in water at concentrations of 0.1, 0.5 and 2.0%, was applied for 24 h in 12 mm Finn chambers on both volar forearms of 12 healthy volunteers. An unoccluded area was used as a reference site. Readings from all sites were taken before the application of the irritant, and 24 h after its removal. After the last reading, a 3-mm punch biopsy was taken from each test site for histological examination. The results obtained from electrical impedance measurements at five different skin depths were correlated with those obtained from histological examination, visual scoring and transepidermal water loss (TEWL). For all of the methods used the responses were proportional to the concentration of the irritant. Statistically significant changes of electrical impedance were found for all depths and concentrations, except for 0.1% SLS at the most superficial depth. The histological changes were focused in the epidermis, and mainly consisted of oedema. Alterations in the thickness of the epidermis due to oedema were used as a quantitative parameter for correlation with the assessment of irritation using the electrical impedance technique. For the detection of irritant reactions, TEWL and electrical impedance are more sensitive than visual scoring, and selection of the optimum depth penetration further increases the sensitivity of the electrical impedance measurement.

Adult↗
PubMed1994

Electrical impedance compared with other non-invasive bioengineering techniques and visual scoring for detection of irritation in human skin.

A new, non-invasive device, which enables local measurements of electrical impedance to a controlled depth, has been used to evaluate the degree of irritation in human skin. The results have been compared with those obtained using other non-invasive techniques, i.e. with transepidermal water loss (TEWL), electrical capacitance moist measurement (ECM), laser-Doppler flowmetry (LDF), and visual scoring. Sodium lauryl sulphate solutions (0.1-5.0%), and a blank, were applied in Finn Chambers for 24 h on the volar forearm of 10 healthy volunteers. Values were recorded before application of the test chambers, and at 1 h, 24 h, 1 week and 2 weeks after removal. Thus, both the degree of initial damage and the healing process were monitored. There was close agreement among values obtained using electrical impedance, TEWL and visual readings. Results obtained using ECM and LDF were not consistent with the other three methods. In evaluating irritation of the skin, the practical situation may influence the choice of bioengineering tools. In most circumstances, a combination of methods would be preferable.

Adult↗
PubMedDate not supplied

Microhardness and porosity of Class 2 light-cured composite restorations cured with a transparent cone attached to the light-curing wand.

A new technique for curing class 2 composite fillings was investigated with respect to microhardness and porosity in the cervical part of the restorations. The technique is based on a plastic transparent cone that is attached to the curing wand. Before polymerizing the cervical portion, the cone is pressed down into the material in the direction of the floor of the approximal box. When the light is activated, it concentrates in the tip of the cone, from where it is distributed into the composite material. In order to compare this technique with conventional curing, standardized class 2 cavity preparations were made in brass blocks. Four different composite materials were used for 20 restorations each: Heliomolar, Herculite XR, Occlusin, and P-50. Ten restorations of each material were cured using the conventional technique (in two portions), and in the remaining 10 restorations the cervical portion was cured with the transparent cone. The irradiation time was 60 seconds in all instances. The Vickers hardness of the cervical approximal surfaces was measured after one and 24 hours. The surfaces were photographed in a stereomicroscope, and the numbers of porosities were counted on black-and-white prints.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylic Resins↗