Biomedical subjects
Publications and source records attributed to A E Kaplan.
We propose a free-space terminator and broadband interferometry based on a coherent blackbody effect in an ultrathin nonreflecting metallic layer in the microwave to infrared domains. A frequency-insensitive device consisting of a metallic layer in a ring (Sagnac) interferometer can be used for autocorrelation measurements of extremely broad EM spectra.
A relativistic field-gradient (ponderomotive) force in a laser standing wave ceases to exist in a familiar form; e.g., the adiabatic Hamiltonian is not separable into kinetic and potential energies for electrons moving in the antinode planes. We show that the force in the direction across the initial motion of an electron reverses its sign and makes the high-field areas attractive for electrons, opposite to a regular ponderomotive force. The reversal occurs at a relativistic-scale incident momentum, and represents the only effect known so far that pins down a distinct borderline between relativistic and nonrelativistic motion.
Conventional glass-ionomer cements (GICs) have a slow maturation time. Reduction in time of maturation may be achieved by acceleration of the setting reaction. One factor that assists this is the reduction in glass particle size producing a larger surface area for reaction. The resulting rapid set and more rapid maturation should potentially lead to less long-term degradation. Biaxial strength measurements were made with respect to time for two GICs of similar compositions but with differing particle size distributions at different time intervals after immersion in both water and artificial saliva. There was little difference between the strength of the two materials over periods up to 12 weeks. A theoretical estimation of the relative surface areas of glasses showed that, despite there being twice the surface area available for reaction for one glass, there was little difference in strengths values between the two materials at any of the times tested here. The similarity in strength values despite this substantial difference suggests that the larger particles may have a greater influence in the cement forming process.
We predict that Coulomb explosion of a nanoscale cluster, which is ionized by high-intensity laser radiation and has a naturally occurring spatial density profile, will invariably produce shock waves. In most typical situations, two shocks, a leading and a trailing one, form a shock shell that eventually encompasses the entire cluster. Being the first example of shock waves on the nanometer scale, this phenomenon promises interesting effects and applications, including high-rate nuclear reactions inside each individual cluster.
AIM: To determine the flow characteristics and subcutaneous tissue reactions to five endodontic sealers. METHODOLOGY: The materials used were Procosol, AH26, Endomethasone, Sealapex and Endion. The sealers were prepared following the manufacturers' instructions, and 0.075 mL of each material was placed on a glass surface, which was then rotated 90 degrees. The samples were stored at 37 degrees C and 95% humidity. The displacement of the sealer was recorded by measuring the difference between its original position and the position recorded at 15 and 60 min. Three samples of each material were used. Two pockets were created in the back of Wistar rats, and one silicone tube, 1 mm in diameter and 1 cm in length, was implanted in each. One was filled with one of the materials under study, and the other empty tube was implanted as a control. Fourteen days after implantation, the animals were sacrificed, and samples of the skin containing the tubes were histologically processed. Histological and histomorphometric evaluations of the tissues adjacent to the open end of the tube were carried out the volume of tissue reaction was measured histomorphometrically according to standard stereological principles. Results were statistically analysed using analysis of variance and Duncan's test. RESULTS: The highest flow values were obtained with Sealapex and AH26. Time significantly affected the flow and the material (P < (1001). Procosol and Endion produced the most severe histological reactions: these were outlined by fibrous tissue; AH26. Endomethasone and Sealapex produced reactions of smaller size and with more moderately defined limits. CONCLUSIONS: The flow did not correlate with the degree of inflammatory response. Procosol and Endion produced the most severe tissue reactions, whereas Endomethasone, Sealapex and AH26 produced only minimum reactions.
Electromagnetic bursts of substantial energy on a nuclear time scale of 10(-21)-10(-22) s [zeptosecond (zs) to sub-zs] can theoretically be generated by a perawatt or multiterawatt laser beam focused on a subwavelength-size solid particle or thin wire. Terawatt laser in a similar setup could be instrumental in reaching the subattosecond domain. The system may also generate a half-cycle pulse magnetic field on astrophysical scale up to approximately 10(6) T.
When evaluating the antimicrobial effect of endodontic sealers it is important to study the variation of pH, since this is one of the properties that may inhibit the microbial growth and influence biocompatibility. The aim of this study was to evaluate the capacity of several endodontic sealers without calcium hydroxide to modify the pH of the solution in which they were immersed. The sealers used were: Endomethasone C-Septodont (EC), Bio Seal-Ogna (BS), Diaket-Espe (D), Procosol-StarDental (P), AH26-Dentsply (AH), Ketac Endo-Espe (KE), AHPlus-Dentsply (AHP), Endion-Voco (E), Endomethasone-Septodont (EM), EZ Fill-Essential Dental Systems (EZ). Samples of each material were placed in tubes with phosphate saline solution (PBS). The pH was determined at 2, 5, 12, 20, 30, 60, and 90 days. A tube with solution alone was taken as control. Statistical analysis of the results was performed by ANOVA. Material, sample, time and material-time interaction elicited statistically significant differences (p < 0.05). The variation of pH produced by immersion of endodontic sealers depends on the composition of the material.
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The aim of this study was to determine the in vitro antimicrobial effect of six endodontic sealers after 2, 20 and 40 days. The sealers studied were Apexit, Endion, AH26, AH-Plus. Procosol and Ketac Endo. The microorganisms used were Candida albicans, Staphylococcus aureus, Streptococcus mutans and Actinomyces israelii. Petri dishes were filled with sterile agar and 0.1-ml wells were prepared and filled with the sealers. The agar plates were stored for 24 h at 37 degrees C. The samples were then removed, immersed in 4.5 ml of culture medium and divided into three groups. The samples in group 1 were stored for 2 days at 37 degrees C whereas the samples of groups 2 and 3 were stored at 4 degrees C for 20 and 40 days respectively. The samples were then removed and discarded, and 0.1 ml of the culture medium was seeded on the agar plates in order to perform colony forming unit counts. Apexit, Endion and AH-Plus produced slight inhibition on Streptococcus mutans at 20 days and on Actinomyces israelii at every time interval. No effect was found on Candida albicans and Staphylococcus aureus. Ketac Endo only produced an antimicrobial effect on Actinomyces israelii at 2 and 40 days. AH26 and Procosol showed antimicrobial effect at 40 days on Candida albicans, at 20 and 40 days on Streptococcus mutans and Staphylococcus aureus, and an effective inhibition on Actinomyces israelii at every time interval. Statistical analysis revealed both sealers and microorganisms to be significant factors affecting results in groups 2 and 3. In conclusion, the sealers evaluated in this study showed different inhibitory effects depending on time span. Overall, sealers containing cugenol and formaldehyde proved to be most effective against the microorganisms at the time intervals studied.
The disintegration of three endodontic cements in water was determined quantitatively and qualitatively. The materials studied were Ketac-Endo (KE), Tubli Seal (TS), and AH26 (AH). Specimens were immersed in water for 48 h (GI), 7 (GII) and 45 days (GIII). The solid residue was then determined. For the qualitative analysis three groups of tubes were filled with the materials and stored in water for the same periods. The exposed surface was photographed. Results expressed as percentage of original mass in the quantitative analysis for loss of mass due to dissolution were: GI = KE 2.39 (0.70); TS 3.56 (0.37); AH 4.94 (2.83); GII = KE 2.84 (0.30); TS 2.50 (0.50); AH 0.66 (0.26); GIII = KE 1.60 (0.84); TS 1.03 (0.42); AH 1.22 (0.54). Tukey's least significant difference (0.05) was 2.94. In the qualitative experiment KE disintegration was far more evident than that suffered by other materials. The quantitative results had no correlation with the qualitative observations probably due to the difference in the moment when the materials were immersed.
The aim of the present study was to analyze different substrates used to determine composite-dentine bond strength. It comprises 3 parts. In the first, results obtained using bovine and human dentin are compared. In the second, bond strength of composite-bovine dentin sections cut at different angles was studied. In the third part, the effect of different storage solutions on bond strength was analysed. Two methods were used to study the capacity of bovine dentin to reproduce "in vivo" conditions as closely as possible: a) bond strength tests. Tensile strength of composite samples mounted on flat dentin surfaces, treated with bonding agents, stored in artificial saliva at 37 degrees C was measured. b) Observation of exposed surfaces by scanning electron microscopy. Results showed that more reliable values were obtained when using bovine dentin stored in distilled water at 4 degrees C sectioned at an angle of 125 degrees to vestibular face and not further than 7 mm from the incisal edge.
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A spectrophotometric method using 6-carboxyfluorescein (CF) was developed to determine intracellular pH in anchorage-dependent monolayers of control cells of rat hepatic origin. Until now, such studies have been carried out with ascites cells in suspension, which lack specific controls for comparative studies. The rat cell line is grown on plastic Leighton tube slides which fit directly into 3 cm spectrophotometer cuvettes. One sample, without CF, serves as a control for the light-scattering properties of the cell monolayers. Steady-state determinations show a decline in intracellular pH from 7.3 to 6.8 ten minutes after the addition of glucose and quercetin. Kinetic determinations show that with the addition of glucose to substrate-free cells the rate of acid formation is -0.02 pH units/min; the addition of quercetin results in a further acceleration of the kinetic rate to -0.10 pH units/min. In both types of analyses, the change in intracellular pH is standardized with nigericin and external buffers, based on the decrease in the maximum absorption of CF at 492 nm. The results demonstrate that even with anchorage-dependent monolayers of a control hepatocyte line which produces very little acid, this spectrophotometric method permits determinations sufficiently sensitive for analysis of intracellular pH.
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