Low Power Red Laser Research Articles

Low-power red laser and blue LED modulate telomere maintenance and length in human breast cancer cells.

Cancer cells have the ability to undergo an unlimited number of cell divisions, which gives them immortality. Thus, the cancer cell can extend the length of its telomeres, allowing these cells to divide unlimitedly and avoid entering the state of senescence or cellular apoptosis. One of the main effects of photobiomodulation (PBM) is the increase in the production of adenosine triphosphate (ATP) and free radicals, mainly reactive oxygen species (ROS). Existent data indicates that high levels of ROS can cause shortening and dysfunctional telomeres. Therefore, a better understanding of the effects induced by PBM on cancer cell telomere maintenance is needed. This work aimed to evaluate the effects of low-power red laser (658nm) and blue LED (470nm) on the TRF1 and TRF2 mRNA levels and telomere length in human breast cancer cells. MCF-7 and MDA-MB-231 cells were irradiated with a low-power red laser (69J cm-2, 0.77W/cm-2) and blue LED (482J cm-2, 5.35W/cm-2), alone or in combination, and the relative mRNA levels of the genes and telomere length were assessed by quantitative reverse transcription polymerase chain reaction. The results suggested that exposure to certain red laser and blue LED fluences decreased the TRF1 and TRF2 mRNA levels in both human breast cancer cells. Telomere length was increased in MCF-7 cells after exposure to red laser and blue LED. However, telomere length in MDA-MB-231 was shortened after exposure to red laser and blue LED at fluences evaluated. Our research suggests that photobiomodulation induced by red laser and low-power blue LED could alter telomere maintenance and length.

Effects of low‑power red laser and blue LED on mRNA levels from DNA repair genes in human breast cancer cells.

Photobiomodulation (PBM) induced by non-ionizing radiations emitted from low-power lasers and light-emitting diodes (LEDs) has been used for various therapeutic purposes due to its molecular, cellular, and systemic effects. At the molecular level, experimental data have suggested that PBM modulates base excision repair (BER), which is responsible for restoring DNA damage. There is a relationship between the misfunction of the BER DNA repair pathway and the development of tumors, including breast cancer. However, the effects of PBM on cancer cells have been controversial. Breast cancer (BC) is the main public health problem in the world and is the most diagnosed type of cancer among women worldwide. Therefore, the evaluation of new strategies, such as PBM, could increase knowledge about BC and improve therapies against BC. Thus, this work aims to evaluate the effects of low-power red laser (658nm) and blue LED (470nm) on the mRNA levels from BER genes in human breast cancer cells. MCF-7 and MDA-MB-231 cells were irradiated with a low-power red laser (69Jcm-2, 0.77 W cm-2) and blue LED (482Jcm-2, 5.35 W cm-2), alone or in combination, and the relative mRNA levels of theAPTX,PolB, andPCNAgenes were assessed by reverse transcription-quantitative polymerase chain reaction. The results suggested that exposure to low-power red laser and blue LED decreased the mRNA levels fromAPTX,PolB, andPCNAgenes in human breast cancer cells. Our research shows that photobiomodulation induced by low-power red laser and blue LED decreases the mRNA levels of repair genes from the base excision repair pathway in MCF-7 and MDA-MB-231 cells.

Low-power red laser and blue LED on circadian gene mRNA levels in human breast cancer cells

Low-power blue light-emitting diode (LED) and red laser have been used for therapeutic proposals based on photobiomodulation (PBM). This effect is trigged after absorption of radiation by photoacceptors, which lead to molecular, cellular and systemic responses. Cryptochromes are involved in circadian cycle control, and associated with development and progression of tumors. Despite such proteins are able to absorb violet-blue lights, there are few data on their participation in PBM. Thus, this work aims to evaluate the effects of radiations emitted by low-power blue LED (470 nm) and red laser (658 nm) on mRNA levels from cryptochromes genes as well as those from involved in their regulation in human breast cancer cells. The MCF-7 and MDA-MB-231 cells were exposed to low-power blue LED (470 nm, 640 J cm−2) and red laser (660 nm, 9 J cm−2), and relative mRNA levels from CRY1, CRY2, PER2, BMAL1 and CLOCK genes were evaluated by reverse transcription-quantitative polymerase chain reaction. The results suggested that exposure to low-power blue LED and red laser do not alter the mRNA levels from cryptochromes genes, and those involved in their regulation, in MCF-7 and MDA-MB-231 human breast cancer cells.

Effects of photobiomodulation by low-power lasers and LEDs on the viability, migration, and invasion of breast cancer cells.

Among the malignant tumors, breast cancer is the most commonly diagnosed worldwide, being the most prevalent in women. Photobiomodulation has been used for wound healing, swelling and pain reduction, and muscle repair. The application of photobiomodulation in cancer patients has been controversial. Therefore, a better understanding of radiation-induced effects involved in photobiomodulation on cancer cells is needed. Thus, this study aimed to investigate the effects of exposure to low-power lasers and LEDs on cell viability, migration, and invasion in human breast cancer cells. MCF-7 and MDA-MB-231 cells were irradiated with a low-power red laser (23, 46, and 69J/cm2, 0.77 W/cm2) and blue LED (160, 321, and 482J/cm2, 5.35 W/cm2), alone or in combination. Cell viability was assessed using the WST-1 assay, cell migration was evaluated using the wound healing assay, and cell invasion was performed using the Matrigel transwell assay. Viability and migration were not altered in MCF-7 and MDA-MB-231 cultures after exposure to low-power red laser and blue LED. However, there was a decrease in cell invasion from the cultures of the two cell lines evaluated. The results suggest that photobiomodulation induced by low-power red laser and blue LED does not alter cell viability and migration but decreases cell invasion in human breast cancer cells.

Low-Power Red Laser Treatment for Anisometropic Myopia Control in Children: A Contralateral Comparison Study.

There are some uncertainties about the effect of low-power red laser treatment on myopia control for anisometropic myopia in children. To evaluate the effect and safety of low-power red laser treatment on refractive development for anisometropic myopia in children, a contralateral comparison study was conducted. The more myopic eye of child with anisometropic myopia was treated with low-power red laser treatment (LRL group), the other eye received no treatment other than the wearing of single-focus spectacles (SFS) (SFS Group). The LRL treatment was given at home under parental guidance for 3 minutes each time, twice daily with a minimal interval of 4 hours, 7 days per week, using an equipment that produces red laser of 650 nm wavelength at an illuminance range of roughly 1200-1800 lux and an energy of 0.60 mw for a 4-mm pupil (class I classification). Among 51 included children, 44 (86.27%) completed the 3-months study, consisting of 15 girls (34.1%) and 29 boys (65.9%). After 3-months axial length (AL) and spherical equivalent refraction (SER) progression were -0.08 mm [95% CI (confidence interval), 0.11 to 0.06 mm] and +0.23 diopter (D) (95% CI, 0.13-0.33 D) for LRL group and +0.08 mm (95% CI, 0.05-0.11 mm) and -0.07 D (95% CI, -0.16-0.03 D) for SFS group. AL and SER progression between the groups varied by 0.17 mm (95% CI, 0.13-0.20 mm) and -0.30 D (95% CI, -0.42 to -0.18 D). There was no visible structural damage on optical coherence tomography (OCT) scans. AL growth, myopia progression, and anisometropia of the binoculars can all be slowed down by LRL treatment. Compared to SER progression, axial elongation is more accurate and simpler to monitor. LRL treatment unrecorded functional and structural damage of binoculus.

Laser Therapy Stimulation at Red Low-level on Some Human Blood Cells

The purpose of this study is to see how low-power red laser helium-neon and diode lasers with wavelengths of 632.8 nm and 650 nm, respectively, affect some human blood sample factors like viscosity HCT, Platelets PLT, White blood cells WBC, white blood lymphocytes LYM, neutrophilic white blood cells NEUT, red blood cells RBC, and Erythrocyte Sedimentation Rate ESR. Blood samples were collected from healthy people and placed in EDTA-contained tubes, blood tests were performed on control samples in a blood analyzer, and the samples were divided into two parts and split into two equal tubes to be irradiated with diode and helium-neon lasers for 15 minutes. Using a blood analyzer, measurements were taken immediately after irradiation. The results of this analysis indicated a decrease in the number of white blood cells (WBC), red blood cells (RBC), and blood viscosity (HCT), as well as a significant rise in the number of neutrophils (NEUT) and platelets (PLT) and increase in the Erythrocyte Sedimentation Rate ESR after exposure to both helium-neon and diode lasers. This suggests that It is possible to make recommendations, a low-power laser could be used to stimulate blood cells so a laser could be used to treat blood viscosity. Because of the increasing concentrations of free intracellular Calcium ions and the action of laser on the plasma composition, it is acceptable to suggest that laser irradiation can lower the number of white blood cells (WBC), red blood cells (RBC), and the reason of that is because of a mechanical change in the blood such as a change in the pores of the surfaces and their fixation.

Effects of photobiomodulation by low power lasers on the in vitro proliferation and aggressiveness of breast cancer cells

Through the metastatic process, cancer cells spread through the body by migrating and invading via the extracellular matrix. Photobiomodulation therapy (PBMT) on oncologic patients is controversial as it could stimulate cell proliferation and aggravate the metastatic process. Thus, this study aimed to investigate PBMT induced by low power red and infrared lasers on cell proliferation, migration and invasion and on mRNA levels from Rat sarcoma virus (RAS) oncogenes in MDA-MB-231 breast cancer cells. MDA-MB-231 cells were irradiated with low power red and infrared lasers at 25 and 50 J cm−2, cell proliferation was evaluated using water-soluble tetrazolium salt assay, cell migration was evaluated using wound healing assay, cell invasion was performed using Matrigel transwell assay and real-time quantitative polymerase chain reaction was performed to evaluate mRNA of RAS oncogenes. Exposure to low power infrared laser could increase MDA-MB-231 cell proliferation at 25 J cm−2. Neuroblastoma RAS oncogene (NRAS) mRNA relative levels reduced when irradiating with low power infrared at 25 J cm−2 and for low power red laser at 50 J cm−2. Kirsten rat sarcoma viral oncogene (KRAS) mRNA relative levels were not modified. Cell migration and invasion after exposure to low power red and infrared lasers at both fluences evaluated did not change. These results show that PBMT could modify MDA-MB-231 cell proliferation and NRAS mRNA relative levels, but no effects were found on KRAS mRNA relative levels, cell migration and invasion in both red and infrared lasers. Therefore, the screening for therapies should be tested by searching for safe conditions and herein the PBMT using red lasers altered the proliferation ratio and changed the aggressiveness phenotype of breast cancer cells.

Low Power Laser Therapy: A Strategy to Promote the Osteogenic Differentiation of Deciduous Dental Pulp Stem Cells from Cleft Lip and Palate Patients.

Dental pulp stem cells (DPSCs) can undergo several types of differentiation, including osteogenic differentiation. One osteogenesis-inducing factor that has been previously described is in vitro low-power laser irradiation of cells. Laser irradiation promotes the acceleration of bone matrix mineralization of the cell strain. However, no consensus exists regarding the dose and treatment time. We used DPSC strains from cleft lip and palate patients because new bone tissue engineering strategies have used DPSCs in preclinical and clinical trials for the rehabilitation of alveolar bone clefts. Optimizing bone tissue engineering techniques for cleft and lip palate patients by applying low-power laser therapy (LPLT) to DPSCs obtained from these patients can help improve current strategies to quickly close large alveolar clefts. The aim of this study was to investigate the effects of LPLT at different energy densities in DPSC strains obtained from cleft lip and palate patients during in vitro osteogenic differentiation. Ten DPSC strains were obtained from cleft lip and palate patients and then used in the following study groups: group 1: control, the strains underwent osteogenic differentiation for 21 days; and groups 2, 3, and 4: the strains were irradiated each day with a low-power red laser (660 nm) (5, 10, and 20 J) during 21 days of osteogenic differentiation. Using Bonferroni's test, a statistically significant difference in the mean values was found between the irradiated groups (2, 3, and 4) and the control group (p < 0.001). However, no significant difference in osteogenic potential was found among the irradiated groups. Our findings showed that the osteogenic potential of DPSCs increases with red laser irradiation at 5, 10, and 20 J, and this treatment could be considered a new approach for preconditioning these cells to be used in bone tissue engineering.

Abstract B18: A label-free, high content, moderate throughput analytical platform for quantitative kinetic analysis of cell behavior upon drug activation in cell-culture models based on the Kolmogorov-Smirnov test

Abstract Our objective is to develop multi-functional nanotechnology-based anti-tumor drug delivery systems for improving efficacy of treatments and reducing undesirable side effects. The essential part of this process is the development of un-biased quantitative analytical techniques. We are reporting a successful validation of a very high content, medium throughput system in multi-well plates. We employed a newly developed holographic imaging cytometry system HoloMonitor® M4 for label-free time-lapse cellular analysis (Phase Holographic Imaging, Sweden), typically at 5 minute intervals for 48–72 hours. A low power red laser is split into sample and reference beams to obtain holograms of cells. The holograms are unwrapped by proprietary software into quantitative dark field images, with very precise calculation of the cell optical thickness. These images are segmented, and a vast variety of features are extracted for cellular events. In our evaluations we found that cell optical thickness, volume and area have high correlation with features used in traditional fluorescent DNA-stained analysis. We obtain full cell cycle profiles, including the separation of mitotic cells, cells undergoing mitotic dysfunction, and apoptotic cells—all in label-free environment. We recently developed a novel 4D image display of evaluated fields of view: X position, Y position, cell thickness coded as brightness over time in the Z direction. In these images, the history of the viewing area over time is displayed, and salient features such as cell proliferation, cell thickness, and cell motility, contact inhibition, and cell death are discernable. As an example, a combinatorial liposomal formulation containing paclitaxel and a P-gp inhibitor tariquidar was compared to free paclitaxel in SKOV3 TR (taxol resistant) cells seeded in Petri dishes. TR cells treated with free paclitaxel presented increased mitoses, while TR cells treated with the combinatorial preparation exhibited a complete abrogation of mitotic division. Cells were frozen in mitosis due to the polymerization of tubulin, the mechanism of paclitaxel toxicity. In this study Hela cells were seeded in a 6-well plate and allowed to acclimate overnight. Free doxorubicin (DOX) was added to 5 wells at concentrations ranging from 1.6 nM to 1 uM in 5-fold increments. Three fields (0.56 mm2) in each well were imaged for 48 hours at 5 min. intervals. We developed a modified version of the Kolmogorov-Smirnov 2-sample test to analyze the data. The classic test takes control and test frequency distributions (histograms), and converts them to probability functions. The maximum vertical displacement between the two is reported as the D-value, which quantifies the amount of difference between the two. In our version, we obtain histograms of the D-values. We set up our analysis so the X-axis is time, and the feature is any of the reported metrics from the HoloMonitorM4 software. Our results are briefly summarized in the following table indicating where the sample is greater than the control (+), less than the control (-), and a transition (/). Dox Con......(1.6 nM).(8 nM).....(40 nM)..(200 nM)..(1 uM) Cell Count.........(+).......(-)........(---).......(---).......(---) Area..................(-)......(+)....(+++++)..(++/-)...(++/-) Max. Thick.........(+)....(++)...(+++++)...(-/+)......(-/+) Volume.............(+)......(+)....(+++++)...(++)......(++) Perimeter........ (+/-)...(+/-).......(++)....(--/++)...(-/++) Roughness.........(-).......(-).......(++/-)....(++/-)......(--) The results are consistent with the known effects of Dox. At low concentration, unrepaired DNA strand breaks start to accumulate and cause slight increases in the volume and thickness of the cells. At mid-concentration the DNA repair process is overwhelmed, proliferation is halted, and vast changes in cellular morphology are evident. At the higher concentration, changes in morphology correspond with cell death followed by eventual deterioration. Citation Format: Ed Luther, Livia Mendes, Daniel Costa, Jiayi Pan, Elena Holden, Vladimir Torchilin. A label-free, high content, moderate throughput analytical platform for quantitative kinetic analysis of cell behavior upon drug activation in cell-culture models based on the Kolmogorov-Smirnov test. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr B18.

Investigation of the mechanical properties of collagen fibrils under the influence of low power red laser irradiation

The low level red laser has been increasingly used for medical applications over the last decade. Despite the recorded positive effects of low level red laser in various medical treatments, the exact collagen—red light interaction mechanism still remains unknown. Hence, in this paper, thin collagen films were irradiated using red low power laser in order to investigate the effects of red light on collagen nanoscale features and mechanical properties. The results demonstrated that the red light did not induce statistically significant changes on nanoscale collagen topography features. The topography of the alternating sequence of overlapping and gap regions (D-band periodicity) and the surface roughness were not affected. However, significant changes on the mechanical properties of the collagen fibrils were recorded. In particular, the red light induced major changes in the mechanical heterogeneity of the fibrils due to the D-band periodicity. The above results provide new information about the red light-collagen interaction mechanism and are a step forward towards to the clarification of the impact of red light on collagen nanoscale features.

Abstract LB-A22: Comparison of the effect of pharmaceutical compounds on tumor cells in 2D and 3D in vitro models using label-free, quantitative 4 dimensional holographic imaging

Abstract Introduction Development of in vitro models for the evaluation of drugs represents a useful approach as in vivo studies may be costly and time consuming. Ideal models should take into account the effects of the cellular microenvironment, which includes the extra-cellular matrix, stroma and neighboring cells. Phase Holographic Imaging The Holomonitor®M4 (Phase Holographic Imaging, Lund, Sweden) is an incubator-adapted time-lapse holographic imaging cytometry system that enables quantitative, label-free analysis of living cells. A low-power red laser creates an interference pattern (hologram) which is reconstructed by software into images. Software modules are available for cellular segmentation, calculating quantitative features (optical thickness and volume), and individual cell tracking. Cells were plated in Petri dishes and imaged in 5 minute intervals for 2 to 3 days. The field of view with a 20X objective is 538 μm2 with an effective depth of field in the mm range, allowing monitoring elongated cubes of the tumor microenvironment. We export 2D projections of the holograms into Image J. We then produce 4-dimensional plots of the tumor microenvironment (X and Y position, cell thickness coded as brightness, and time in the Z direction). 2D models of non-motile adherent cells. When untreated HeLa cells are seeded at low density, colonies manifest as inverted cones increasing in diameter as the cell number increases. Mitotic cells appear as short duration bright spots due to rounding of the cells and increase in optical thickness. Treatment with colchicine at concentrations sufficient to block the completion of mitosis caused the brightness of the tracks is persistent. When treated with doxorubicin (dox) at concentrations sufficient to induce apoptosis, cell tracks briefly become bright, but then decrease in diameter and brightness as the cells gradually disintegrate. 2D models of motile cells. HT1080 fibroblasts present two distinct morphological types, an amoeboid form that move via extensions of lamellipodia from a leading edge that adhere to a substrate and a mesenchymal form, where small protrusions termed lobopodia propel cells by attaching to ECM components. In untreated samples, cells are predominately in the amoeboid form, with the cell tracks moving upward. Low concentrations of dox (50nM) abolish cell proliferation, and a shuttling motion is seen, caused by dysfunctional lamellipodia attachment to the substrate prior to eventual cell death. 3D models of motile cells. We plated HT1080 cells on the dishes, treated them with compounds, and then overlaid the cells with 1 mg/ml collagen type 1. With 50 nM dox there is a high degree of proliferation and vastly increased planar motion. In videos it can be seen that cells are following pathways created by other cells, consistent with cells burrowing through the ECM. Conclusion We developed a novel 4-D holographic imaging method using the Holomonitor HM4 and Image J. Here, we present methods for comparing traditional 2D and 3D in vitro models. Our example of HT1080 cells treated with dox clearly shows the superiority of the 3D model, an important step in developing assays that better emulate multi-dimensional biological processes and offer the possibility of evaluating effects of drugs at lower cost and experimental complexity than those of in vivo assays. Citation Format: Ed Luther, Giuseppina Salzano, Shravan K. Sriraman, Daniel Costa, Vladimir P. Torchilin. Comparison of the effect of pharmaceutical compounds on tumor cells in 2D and 3D in vitro models using label-free, quantitative 4 dimensional holographic imaging. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr LB-A22.

Comparison of the effect of low level laser therapy with alvogyl on the management of alveolar osteitis

BackgroundThis study investigated the efficacy of low level laser therapy (LLLT) for managing alveolar osteitis (AO).Material and MethodsSixty patients with alveolar osteitis of mandibular third molars were randomly divided into three groups. In group 1, socket irrigation was followed by alvogyl placement, and the treatment was repeated 48 hours later. In group 2, socket was irradiated with a low power red laser for 3 consecutive days (200 mW, 30 seconds on each of the buccal and lingual surfaces and 30 seconds at the middle of the socket, 6 J per area). The subjects in group 3 underwent treatment with a low power infrared laser with the same parameters as group 2. A visual analogue scale (VAS) was used to record the degree of pain at the morning (T0, before intervention) and at 6 (T1) and 12 (T2) hours later for 3 days.ResultsPain was significantly lower in the alvogyl group than the other groups at T1 and T2 points on day 1 and at T0 and T1 points on day 2 (p<0.05). At T2 point on day 2 and on day 3, VAS became significantly lower in the red laser group compared to the other groups (p<0.05). The infrared laser was not more efficacious than the other groups at any of the treatment intervals, but it reduced VAS to an acceptable level.ConclusionsLLLT displayed good results in this study for treatment of alveolar osteitis and should be further investigated as an alternative to alvogyl for AO management. Key words: Low level laser, low power laser, therapy, alvogyl, dry socket, alveolar osteitis, mandibular third molar.

A randomized clinical trial of the effect of low-level laser therapy before composite placement on postoperative sensitivity in class V restorations.

This study aimed to investigate the efficacy of low-level laser irradiation when applied just before placement of resin composite on reducing postoperative sensitivity of class V lesions. In this randomized clinical trial, 31 patients with 62 class V cavities were included (two teeth in each participant). The teeth were randomly assigned into laser and placebo groups. After cavity preparation, the teeth in the experimental group were subjected to irradiation from a low-power red laser (630 nm, 28 mW, continuous wave, 60 s, 1.68 J), which was applied for 1 min on the axial wall of the cavity. In the control group, the same procedure was performed but with laser simulation. Then, a self-etch adhesive was applied and the cavities were restored with a microhybrid resin composite. Before treatment and on days 1, 14, and 30 after treatment, tooth sensitivity to a cold stimulus was recorded using a visual analogue scale. Data were analyzed by Friedman and Wilcoxon signed-rank tests (p < 0.05). Pain scores after restorative procedures were significantly lower in the laser group compared to the placebo application (p < 0.05). Although both groups experienced a significant improvement in pain and discomfort throughout the follow-up periods (p < 0.001), the changes in visual analogue scale (VAS) scores between baseline and each follow-up examination were significantly greater in the laser than the placebo group (p < 0.05). Low-level laser therapy (LLLT) before placement of resin composite could be suggested as a suitable approach to reduce postoperative sensitivity in class V restorations.

Comparative evaluation of the effect of Er:YAG laser and low level laser irradiation combined with CPP-ACPF cream on treatment of enamel caries.

Objectives: This study investigated the effectiveness of low power red and infrared lasers and that of Er:YAG laser, in association with CPP-ACPF cream, on remineralization of white spot lesions. Study Design: Fifty intact premolars were immersed in a demineralization solution for 10 weeks to induce caries like lesions and then were divided into five groups. In group 1, the teeth were covered with a CPP-ACPF cream for 3 minutes and then irradiated with a low power red laser (660 nm, 200 mW) for 1 minute through the cream. In group 2, the treatment was the same as that in group 1, but an infrared laser (810 nm, 200 mW) was employed. The specimens in group 3 were irradiated with an Er:YAG laser (100 mJ, 10 Hz) combined with CPP-ACPF. In group 4, the CPP-ACPF cream was applied for 4 minutes and group 5 was submitted to neither laser nor CPP-ACPF. The micro Vickers hardness was compared at 20, 60 and 100 µ from the enamel surface among the groups. Results: The highest microhardness was observed in the low power red and Er:YAG laser groups and the lowest one belonged to the CPP-ACPF alone and control groups. However, no significant difference was found in microhardness of the experimental groups at any of the evaluation depths (p>0.05). Conclusions: With the laser parameters used in this study, neither the combined application of Er:YAG laser with CPP-ACPF nor the combination of low power lasers with CPP-ACPF provided a significant increase in remineralization of enamel caries. Key words:Low level laser, Er:YAG, laser, enamel caries, CPP-ACP, microhardness, white spot lesion.

Laser-guided intraoral radiography: A future focus.

Over the past few decades, rapid changes have taken place in the fields of science and technology. Simultaneously, great progress has been made in research work on laser applications. Today, laser use ranges from simple applications such as recording prices of groceries to complex applications such as measuring distance to the moon and laser-guided warfare.1 In the field of dentistry, the research and development of laser technology was initiated in the 1960s; since then, it has made significant progress, and today, this technology is being used for a wide variety of clinical applications ranging from surgical (biopsy and frenectomy) to endodontics and conservative dentistry (root canal treatment, tooth whitening, vitality checking, cavity preparations, and reduction of dentinal and hypersensitivity) and from periodontics (gingivectomy and gingivoplasty) to oral medicine (treatment of aphthous and herpetic ulcers).1,2,3 Perhaps the only specialty of dentistry that has not made optimum use of lasers is oral radiology. Although laser-guided positioning of a patient is routinely performed in panoramic radiography, its application in intraoral radiography has not been researched sufficiently.4,5 However, recently, pioneering research work has been carried out in the field of laser-guided collimation in dental radiographic training.5,6 In 2006, Chau et al. designed and fabricated a custommade collimator with four red laser diodes on each corner of the rim of an aluminum alloy cubic housing.5 In their study, 18 dental hygiene students were randomized into test and control groups. The laser group used a rectangular collimator with the laser device, while the non-laser group used a conventional rectangular collimator. Each group attended nine intraoral radiography training sessions. All radiographs were assessed and classified into three categories - Excellent, Acceptable, and Repeat - by a masked academic staff member. Reasons for repeats were recorded. Statistical comparisons between the two groups were made. They found that a total of 2334 radiographs were taken, and cone-cuts were more common on bitewings than on periapicals. The laser group produced fewer cone-cuts than the non-laser group. The laser group produced more excellent radiographs with fewer repeats than the non-laser group, but there was no significant difference. Similarly, in 2010, Zamani et al. devised a laser-guided indicator, which was made of two low-power red laser diodes and was capable of generating two perpendicular rays forming a cross (+) in the center of the tube, which indicated a central ray.6 In their study, a total of 18 students were divided into two groups of nine. In the first group, the periapical technique was taught without the use of the laser-guided indicator, while in the second group, the laser-guided indicator was applied in training the students. All students took radiographs from the phantom. In total, 216 radiographs were taken, and technical errors and the quality of these radiographs were evaluated. The researchers found that the radiographs taken by students showed significant differences in cone cutting (p value=0.014), overlapping (p value=0.018), and elongation (p value<0.001) between the two study groups. In the subjective review of radiography quality, the difference was also significant (p value<0.001). The results of the above studies strongly indicated that a laser-guided indicator/collimator could be used as an effective training aid for easier learning of central ray adjustment and reduction of technical errors by dental students. We firmly believe that laser-guided collimators/indicators should be taken up as research topics for inventing more such teaching aids. With this background in mind, we developed a laser guide device using a single laser-guided device that could be capped to the intraoral unit so as to make the student aware of the accurate extraoral landmark prior to the radiographic procedure (Fig. 1). The device has been named Laxmi-Kanth Aiming Device (LKAID) after Dr. Laxmikanth Chatra, Professor and Head, Department of Oral Medicine and Radiology, Yenepoya Dental College, Yenepoya University. The device is in its initial trial stages, and the outcomes will be discussed in detail in future articles. Fig. 1 A photograph shows the Laxmi-Kanth Aiming Device (LKAID) capped to an intraoral unit for demonstrating an extraoral landmark for maxillary central incisors.

Effects of low-power red laser on dentine–pulp interface after cavity preparation. An ultrastructural study

Objective Studies on the influence of low-power red laser on the repair of dental structures are very scarce. This study investigated the effects of the laser therapy on the ultrastructure of the dentine–pulp interface after conservative class I cavity preparation. Design Two female volunteers with 8 premolars indicated for extraction for orthodontic reasons were recruited. Class I cavities were prepared and the teeth were randomly divided into two groups. The first group received treatment with a GaA1As laser, λ = 660 nm, power of 30 mW and energy dose of 2 J/cm 2, directly and perpendicularly into the cavity in a single visit. After the irradiation, the cavities were filled with composite resin. The second group received the same treatment, except by the laser therapy. Results Twenty-eight days post-preparation, the teeth were extracted and processed for transmission electron microscopy analysis. Two sound teeth, without cavity preparation, were also studied. The irradiated group presented odontoblast process in higher contact with the extracellular matrix and the collagen fibrils appeared more aggregated and organised than those of control group. These results were also observed in the healthy teeth. Conclusion These findings suggest that laser irradiation accelerates the recovery of the dental structures involved in the cavity preparation at the predentine region.

Photoactivation of Vascular iNOS and Elevation of cGMP In Vivo: Possible Mechanism for Photovasorelaxation and Inhibition of Restenosis in an Atherosclerotic Rabbit Model¶

Recently, intravascular low-power red laser light (LPRLL) therapy has been proposed for the prevention of postangioplasty restenosis due to the observed inhibition of experimental neointimal formation. The objective of this study was to determine the impact of endoluminal LPRLL on vascular levels of inducible nitric oxide synthase (iNOS) and cyclic guanosine monophosphate (cGMP) to help define the mechanism of this effect. Eight atherosclerotic male adult New Zealand White rabbits weighing 4–6 kg were used in these studies. The iliac arteries were treated in separate zones with: (1) balloon inflation only; (2) laser illumination only; and (3) balloon inflation + laser illumination. An uninjured zone of the iliac artery served as a control. Laser irradiation (630 nm) was delivered to the vessel wall via a Cold™ laser Illuminator (Cook, Inc., Bloomington, IN), with a 3 mm–diameter balloon. Experiments demonstrated that vascular cGMP levels obtained immediately following treatment in the balloon only group was the lowest (0.29 ± 0.05 pmol/mg protein) and significantly lower compared with the uninjured controls (1.01 ± 0.07 pmol/mg protein) (P < 0.001). In the laser only treated group cGMP levels were significantly increased (2.87 ± 0.12 pmol/mg protein) compared with the uninjured control (P < 0.001) and the balloon only group (P < 0.001). Vascular cGMP levels in the balloon + laser group (2.09 ± 0.07 pmol/mg protein) was also increased compared to the balloon only (P < 0.001) and control (P < 0.001) groups. Qualitative analysis of Western blot demonstrated that laser illumination induces iNOS. In contrast balloon dilatation did not induce iNOS. Balloon + laser treatment, however, tended to restore the expression of iNOS. Our study demonstrated that intravascular low dose laser irradiation induces iNOS and elevates vascular cGMP in an in vivo atherosclerotic rabbit model.

Effects of low power red laser on induced-dental caries in rats

Objective The purpose of this study was to investigate the effects of low power red laser associated with acidulated phosphate fluoride on the development of induced-dental caries in rats. Design Dental caries were induced in molars of 40 rats divided into five groups: control group (CG), the teeth were not submitted to any treatment; laser group (LG), teeth were irradiated with a low power red laser (LPRL), power of 30 mW and dose of 5 J/cm 2; fluoride group (FG), teeth were treated with topical acidulated phosphate fluoride (APF) 1.23% applied for 4 min; laser + fluoride group (LFG), teeth were irradiated with LPRL followed by APF; fluoride + laser group (FLG), teeth were treated with APF followed by LPRL. The animals were killed after 48 days, and the first and second molars were extracted to analyze the caries lesion area, microhardness, and calcium and phosphorus ratio. Results There were no statistical differences among FG, LFG, and FLG regarding to caries area and microhardness, although the caries area were smaller in LFG. Ca/P ratio did not show significant differences among all groups. Conclusions Although LPRL before APF application appeared to diminish the caries progression, LPRL did not present any additional benefit compared with acidulated phosphate fluoride on the prevention of induced-dental caries in rats.

Free-Space Optical communication using visible light

The possibility of visible red light laser being used as signal light source for Free-Space Optical (FSO) communication is proposed. Based on analysis of transmission in atmospheric channel concerning 650 nm laser beam, performance of wireless laser communication link utilizing a low power red laser diode was evaluated. The proposed system can achieve a maximum range of 300 m at data rate 100 Mb/s theoretically. An experimental short-range link at data rate 10 Mb/s covering 300 m has been implemented in our university. It is feasible to enhance the system performance such as link range and data rate by increasing transmitting power and decreasing laser beam divergence angle or through other approaches.

Bactericidal effect of malachite green and red laser on Actinobacillus actinomycetemcomitans

The aim of this study was to investigate the ability of malachite green (MG) combined with a low-power red laser to kill Actinobacillus actinomycetemcomitans and to investigate MG photodegradation after photodynamic therapy (PDT) by optical absorption spectroscopy. The etiology of periodontal disease is that microorganisms form a bacterial biofilm on the surface of the teeth. It is an infectious disease and A. actinomycetemcomitans is considered an important agent in biofilm ecology. Instead of using antibiotics, PDT is an alternative approach to eradicate bacteria. Cultures of A. actinomycetemcomitans were exposed to a 30 mW diode red laser, in the presence or absence of MG. A group of cultures was treated in dark conditions in the presence of MG (0.01% w/v) for 5 min. In the presence of MG, two exposure times for laser irradiation were used: t = 3 min (energy dose = 5.4 J/cm 2), and t = 5 min (energy dose = 9 J/cm 2). The samples were diluted and bacterial colonies were counted and converted into colony forming units. Absorption spectra of the bacterial suspensions, MG, MG-stained bacterial suspensions, and photosensitized bacterial suspensions were obtained. A. actinomycetemcomitans can be photoinactivated by a red laser in the presence of MG. Significant differences were observed between the two energy doses used ( p < 0.05). Red laser alone and MG alone were not able to kill bacteria. Optical absorption showed that MG is photobleached after irradiation. These results indicate that A. actinomycetemcomitans can be photosensitized by red laser combined with MG and that the dye is photodegraded following irradiation.