فصلنامه لیزر در پزشکی
سال هفتم شماره 4 (پیاپی 37، زمستان 1389)

Photodynamic inactivation (PDI) has been investigated to cope with the increasing incidence of multidrug-resistant (MDR) pathogens. PDI employs nontoxic photosensitizers (PSs), which localize in the microbial cells and are activated by a specific wavelength of visible light. The main purpose of this study was to explore the PDI effect of methylene blue (MB) and toluidine blue O (TBO) on Escherichia coli (ATCC 25922) and clinical isolate of multidrug-resistant Escherichia coli.

Effect of PSs concentration (12.5, 25, 50 µg/ml) and laser irradiation time (10, 20, 30 min) on lethal photosensitization was investigated.

Methylene blue (50 µg/ml) photosensitization using red laser light (163.8 J/cm2) was able to achieve reductions of 53.1% and 37.6% in the viable counts of Escherichia coli (ATCC 25922) and clinical isolate of MDR Escherichia coli (using starting concentrations of 104–105 CFU ml-1). TBO at 50 µg/ml, 46.8 Jcm-2, exhibited 0.7 log killing for MDR E. coli and 1.7 log killing for E. coli (ATCC 25922).

In our study, the selected MDR isolate was more resistant to TBO-PDI-mediated killing than its ATCC reference strain. Therefore, the PDI efficacy of TBO may be affected by the antibiotic resistance mechanism that presented in MDR isolate.

Scale and objective of the research: This research analyses the effect of Laser- Lok implant microchannels on the stress distribution in crestal bone of the Laser- Lok implant collar and its surrounding bone interface. The results are compared with the control implant with a standard machined collar to evaluate the effect of the Laser-Lok special microchannels design on the stress distribution in crestal bone. Three- dimensional modeles of the Laser- Lok implant, control implant and the mandible bone is generated for the FEA. On the next step both implants are assembled on the pre-molar mandible bone considering the proper boundary recondition. After meshing and considering the proper elements regarding the mastication forces and normal condition, 100N of axial and oblique loading with 15 and 45 angle is applied to the centre of both Laser- Lok and control implants on similar condition. Results shows that the average crestal bone stress around the Laser- Lok implant is significantly lower than the control. On the whole the Laser- Lok implant shows advantages over control implant in reducing the crestal bone stress. Results indicate that the design of the Laser- Lok implant collar microgrooves influence the reduction of surrounding crestal bone stress and leads to decreasing the crestal bone loss.

Nowadays, mechanical properties of collagenous tissues are improved by physical crosslinking methods like ultraviolet radiation. Collagen as the major structural protein of tissues absorbs far ultraviolet light. There is a tight competition between the two mechanisms of crosslinking and photodegradation during UV irradiation. The occurrence of each depends on the irradiation dose.

In this study, in order to estimate the effect of ultraviolet radiation at 254 nm on collagenous tissue of the renal capsule, mechanical tests including dynamic tensile tests associated with chemical tests i.e. FTIR spectroscopy have been performed.

Samples reach their maximum stiffness until 30 minutes (13.86 J/cm2) irradiation. It means that crosslinking procedure predominates. Increasing the irradiation dose results in photodegradation of the whole tissue. FTIR spectroscopy shows shifting of amide bonds I and II which illustrates the peptide bond destruction in the period of high irradiation.

The nitrogen gas that used in nitrogen laser must be very pure. The gases such oxygen stop action of laser rapidly nearly 23% of air is oxygen and 73% is nitrogen. Because high level of oxygen in air, leasr action in air is not possible realy. Leasr action in air reported at low presseture. The goal in this projet is laser action in air at atmospheric pressture. With make and optimize a TEA N2 Laser, effect of oxygen investigate with accuracy. Result this work produce a TEA Air Laser that act in every pressure in air.

Dental caries is reported to be the most common chronic childhood disease. The prevalence of dental caries has declined due to the worldwide preventive measures adopted, such as water fluoridation and the waste of products containing fluoride. The search for novel methods to improve the binding of fluoride to the enamel is a major research objective in dentistry. One new approach recently introduced into clinical practice is the use of lasers in fluoridation. The laser– fluoridation combination reduces the onset of dental caries and delays its progression in a higher percentage of cases than the ones achieved by separate application of the two methods. Importantly, the use of laser favors the incorporation of the fluoride into the enamel, not only on its surface as calcium fluoride (CaF2) but also within its crystalline structure. Due to the wide range and variable parameters of the available equipments, Considerable uncertainty about which laser device should be used with topical fluoridation to obtain optimal outcomes remains. Because of absorption by the enamel and cracks and/or fissures due to post-fusion recrystallization, some authors consider this treatment to be damaging for the enamel. Damage to pulpal tissue is another concern.. The purpose of this search was to determine some approaches for dentists. Method and materials: The primary search was done with focus on the journals of the American academy of pediatric dentistry. A Medline search was also conducted for publications involving enamel fluoride uptake and retention in using various laser irradiation. The results showed that the difference is significant between the fluoride retention in the lased and unlased groups. The use of laser significantly increased the fluoride retention in lased enamel. This procedure can be considered as an alternative clinical procedure to increase the fluoride content of enamel surface.