Influence Of Different Frequencies Research Articles

Influence of the frequency of Er:YAG laser on the bond strength of dental enamel.

The present study had the aim of evaluating the influence of different frequencies of the Er:YAG laser on adhesive resistance of enamel and one restorative system. There have been no reports of studies assessing the influence of the pulse frequency variation of the Er:YAG laser on adhesive resistance of the enamel/resin interface. Fifty surfaces of enamel from extracted human third molars were planed and divided into five groups at random. Enamel surface treatment was realized by the Er:YAG laser at 80-mJ power and 1-, 2-, 3-, and 4-Hz pulse frequencies, followed by etching. For the control group, only acid conditioning with 37% phosphoric acid for 15 sec was used. The Single Bond/Filtek Z250 system was chosen for the fabrication of the specimens, which were stored in 100% relative humidity for 24 h, at 37 degrees C. The specimens were submitted to tensile resistance tests using a Universal Testing Machine (50 Kgf and 0.5 mm/min). The mean values in MPa were 1 Hz, 25.58 (+/-6.16); 2 Hz, 25.58 (+/-3.79); 3 Hz, 21.34 (+/-3.78); 4 Hz, 21.17 (+/-3.13); and phosphoric acid only, 22.44 (+/-7.0). Data were submitted to statistical analysis using ANOVA, and there was no significant difference in tensile resistance between the studied groups. The results suggest that the Er:YAG laser, with 80-mJ power associated with acid conditioning at 1-, 2-, 3-, and 4-Hz frequencies, did not present significant improvement in tensile bonding of enamel, as compared to acid conditioning only.

Artificial periodontal defects and frequency of tooth brushing in beagle dogs (II). Clinical findings after a period of healing.

This investigation was designed to determine the influence of different frequencies of tooth brushing on artificial periodontal defects in the beagle dog after a period of healing. In 12 beagle dogs, periodontal defects were created using elastic bands placed in the sulci below the gingival margin after having cut the dento-gingival fibres to the level of the alveolar bone crest. This active phase of creating defects lasted for 6 weeks. After removal of the elastic bands, the created defects were left undisturbed during the remainder of the pre-experimental period (12 weeks). 6 premolars in the lower jaw were used (2P2, 3P3, 4P4). After the pre-experimental period, the 12 dogs were distributed into 3 groups of 4 dogs each. Each group was brushed with a certain frequency, i.e., 7 times, 3 times or once a week. Registrations of plaque index, gingival index and probing depth using a constant force probe were carried out on approximal surfaces. The experiment lasted for 24 weeks. A brushing effect was calculated for each dog to include information on all within-dog and between-dog variations. It was shown in relation to artificially-induced periodontal defects in beagle dogs that after a period of healing, brushing 7 times a week is superior to brushing 3 times a week in establishing and maintaining gingival health.

Artificial periodontal defects and frequency of tooth brushing in beagle dogs (I). Clinical findings after creation of the defects.

This investigation was designed to determine the influence of different frequencies of tooth brushing on artificial periodontal defects in the beagle dog shortly after creation. In 12 beagle dogs, periodontal defects were created using elastic bands placed in the sulci below the gingival margin after having cut the dento-gingival fibres to the level of the alveolar bone. This active phase of creating defects lasted for 6 weeks. 6 premolars in the lower jaw were used (2P2, 3P3, 4P4). After removal of the elastic bands, the 12 dogs were distributed into 3 groups of 4 dogs each. Each group was brushed with a certain frequency, i.e., 7 times, 3 times or once a week. Plaque index, gingival index and probing depth, using a constant force probe, were assessed interproximally. The experiment lasted for 24 weeks. For hypothesis testing, a brushing effect was calculated for each dog. Furthermore, an analysis was performed based on the absolute scores at week 24. From the statistical analysis, it was concluded that in artificially-induced periodontal defects in beagle dogs immediately after creation, brushing 7 times a week is superior to brushing 3 times a week to establish and maintain gingival health.

Seismic response characteristics of marine reflection profiling systems

Summary. Factors influencing the seismic response characteristics of marine profiling systems are reviewed. The single frequency case is used to illustrate the influence of different frequencies on the response, as well as the towing depths of the source and receiver, and the geometry of a linear receiving array. The more realistic case of band-limited source waveforms is considered, using frequency spectra calculated from theoretically derived airgun signals. The results show that the number and shape of sidelobes of the profiling system response, as well as the filtering characteristics for reflections arising from reflectors in the vertical plane perpendicular to the axis of the receiver array are determined by the depths of the source and receiver and the relative amplitudes of the frequencies in the source waveform. These factors, along with the configuration of the hydrophone elements in the receiver array, determine the frequency and amplitude attenuation of reflections in the vertical plane containing the receiver array. The filtering characteristics of the system both in and out of the vertical plane containing the receiver array are discussed, with implications for discriminating between off-axis and in-plane reflections. A plan view of the response of the system is constructed in the time domain for various profiling configurations and sources of different frequency content at a given time. This example shows how useful the resulting pictures are for optimizing acquisition parameters in profiling experiments.

The Influence of Different Frequencies of Laser on the Microbial Production of Alcohol by Saccharomyces cerevisiae

The Influence of Different Frequencies of Laser on the Microbial Production of Alcohol by Saccharomyces cerevisiae