A popular benchmark for defining a laser therapy systcm is an output power of less than 100 mW, and low reactive-level laser therapy (LLLT) is commonly regarded as ‘safe’ for irradiating skin. However, with very small spot sizes in the order of 200 μm, the power density at tissue of a 100 mW laser therapy system is in the order of 318 W/cm². If target tissue is painted with black ink or a similar pigment, this power density is quite capable of causing a burn injury. This has obvious implications in the use of such LLLT systems in treating dark-coloured naevi such as naevus cell naevus, or in LLLT on black patients. In order to examine this problem in detail, the authors designed a computer model with a program to calculate and analyze the temperature rise in an irradiated hemispherical block of homogeneous tissue at various powers in the range of 6 mW- 60 mW, and at spot sizes of 200 μm, 400 μm, 1.0 mm and 2.0 mm following 5 seconds irradiation with an 830 nm GaAlAs diode laser, after which the laser was ‘turned off’ The laser was deemed to be applied in the contact pressure mode, thereby compressing superficial blood vessels in the irradiated area so that blood flow cooling could be discounted. At maximum absorption, it was predicted that the 60 mW beam of the GaAlAs diode laser at 830 nm and a 200 μm spot size has the potential for causing thermal injury. The authors would like to stress that this is only a theoretical computer model, with hypothesized constants and a homogeneous target material. However, this model certainly demonstrates the error of applying arbitrary limits as to what constitutes the output power of an LLLT system, and would also appear to limit the application of LLLT at the above parameters on dark-colored naevi or for darker-skinned patients.

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Helium-neon (HeNe) laser radiation is usually utilized in dentistry for diagnostic and therapeutic purposes, principally in Europe. No studies on the ultrastructural effects of HeNe laser irradiation of the periodontal tissues have been reported. This study shows the ultrastructural effects of HeNe laser radiation in mouse periodontium in two different conditions of irradiation. Twenty-four forty days old albino mice were irradiated with a HeNe laser source. They were divided into two groups according to dosage and time (two and six minutes of irradiation. 10.50566J/cm² and 51.51698 J/cm² respectively . Each group was subdivided depending on the time of animal sacrifice (immediately after irradiation or 10 days later, respectively). A further 12 mice served as controls using the same handling procedures and times as the experimental groups, but without radiation. In transmission electron microscopy (T.E.M.) ultrathin sections showed epithelial alterations only in the group irradiated for six minutes, and was more manifested in the sacrificed animals ten days after the irradiation. In the low dose irradiated animals, the bone showed two osteocyte populations according to their response to radiation. The connective tissue also showed two types of fibroblast population. This study showed abnormal cellular effects after HeNe laser irradiation in healthy rat periodontium, being more predominant at higher doses, although also present at doses usually utilized in clinical practice.

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An increasing number of clinical reports on the application of low reactive-level laser therapy (LLLT) in pain attenuation are appearing in the literature, but very few of these reports include a blinding procedure to offset the possible placebo effect of laser therapy, especially with smaller patient populations. The present study describes a protocol set up to remove as much as possible any skewing of the data by the placebo effect. The trial is set up in two (or more) geographically distant institutes under similar environmental conditions. Patients with a variety of pain complaints are selected for the study with similar demographic characteristics in all trial sites, and are each assigned a patient number for trial identification purposes. Treatment parameters are standardized for a single LLLT session using the same laser system at the same parameters (in the present study a GaAlAs diode laser, 830 nm, c/w, 60 mW was used). A computer is programmed to assign real or sham laser treatment randomly to each patient number, every time the number changes as sensed in the computer by the use of the laser therapy system main power switch. The same computer, located distantly from the treatment room, controls the laser system directly to produce real and sham laser therapy, and neither the patient, the therapist nor the computer operator is thus aware to which group the patient has been assigned by the computer, which stores these data to be retrieved after the trial and assessment are complete. A comprehensive record chart is used to record pre- and post therapy subjective and objective evaluations for both individual pain groups and the population as a whole, including any adverse side effects and machine safety, with a series of scores being finally compiled to give an overall efficacy rate. The last stage of the trial involves subjecting the results for the real and sham groups to direct statistical analysis using a combination of χ2 and Fischer’s tests. A value of p= <0.01 is significant with a level of confidence of less than 1%. These data are examined for each pain group and for the population as a whole site by site, and finally similar data for the total population in all the sites is compiled.

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Macrophages are a source of many important mediators of wound repair. Cells of a established macrophage-like cell line (U-937) were exposed in vitro to a 820 nm coherent light source, (Omega Laser Systems) at the following frequencies: 2.28, 18.24, 292.3 and 1000 Hz. The average power output was 50 mW and the irradiation times were such that the energy density to which the cells were exposed was kept constant at 7.2 J/cm². 12 hours later the macrophage-conditioned medium was removed and placed on 3T3 fibroblast monolayers. Fibroblast proliferation was assessed over a five day period. Five days after the addition of the medium conditioned by macrophages exposed to a energy density of 7.2 J/cm², there was a statistically significant increase in fibroblast proliferation in the groups treated with laser at frequencies of 2.28, 18.24 and 292.30 Hz in comparison with the sham-irradiated controls. Treatment at the 1000 Hz frequency was followed by less proliferative activity than in the controls, although this was not statistically significant.

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Open wounds (3 cm x 1 cm) on the anterior surface of teats in four dairy cattle were irradiated using low level laser therapy (LLLT). The laser used was a helium-neon (HeNe) system with an output of 8.5 mW, continuous wave at 632.8 nm. The 16 teats from 4 dairy cattle were divided into 4 groups using Latin Square design and were subjected to daily doses of LLLT : 3.64 J/cm² for 15 min (Group A); 2.42 J/cm² for 10 min (Group B); and 1.21 J/cm² for 5 min (Group C). Group D served as the control. The durations of healing were 18.5 ± 0.5 days for group A; 19 ± 0.7 days for group B; 23 ± 0.7 days for group C; and 24.5 ± 0.5 days for group D, respectively. The rate of wound healing between Groups A and C, A and D, B and C, and B and D were significantly different (P < 0.01). The difference in the hydroxyproline content between normal and healed specimens from Group A was significantly different from that of Group D (P < 0.05). The cosmetic appearance of healed Groups A and B was significantly better than those of Groups C and D.

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We report on a controlled investigation into the accelerated healing of artificial wounds in the Sprague-Dawley rat treated with helium neon (HeNe) laser irradiation over a range of doses up to 60 J/cm². With a treatment schedule of 3 or 5 treatments per week, an acceleration of approximately 27% in healing time and 49% in wound size reduction were seen in wounds of 1.26 cm² in area inflicted on 27 week-old rats at a dose of 25 J/cm² compared with unirradiated control animals. Smaller wounds (0.39 cm²) in younger animals (< 12 weeks old) demonstrated time and wound reduction improvement of approximately 33% and 54% respectively, compared with controls. A statistically significant difference (student’s t-test) was seen in this group of animals treated with 7J/cm² compared with unirradiated control animals. Wound acceleration was seen to be dose-dependent, increasing up to the optimum value, whereafter the stimulatory effect was observed to decrease (maximum dose of 60 J/cm²). Investigations into the treatment schedule revealed saturation after 6 treatments per week. Skin reflection was investigated, and losses of around 74% were observed, requiring higher doses to achieve an effective result. Varying the power density (3.7 - 15.9 mW/cm²) while keeping the dose constant had no statistically significant effect on the result.

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