Photobiomodulation (PBM) therapy, previously known as low-level laser therapy, was discovered more than 50 years ago, yet there is still no agreement on the parameters and protocols for its clinical application. Some groups have recommended the use of a power density less than 100 mW∕cm 2 and an energy density of 4 to 10 J∕cm 2 at the level of the target tissue. Others recommend as much as 50 J∕cm 2 at the tissue surface. The wide range of parameters that can be applied (wavelength, energy, fluence, power, irradiance, pulse mode, treatment duration, and repetition) in some cases has led to contradictory results. In our review, we attempt to evaluate the range of effective and ineffective parameters in PBM. Studies in vitro with cultured cells or in vivo with different tissues were divided into those with higher numbers of mitochondria (muscle, brain, heart, nerve) or lower numbers of mitochondria (skin, tendon, cartilage). Graphs were plotted of energy density against power density. Although the results showed a high degree of variability, cells/tissues with high numbers of mitochondria tended to respond to lower doses of light than those with lower number of mitochondria. Ineffective studies in cells with high mitochondrial activity appeared to be more often due to over-dosing than to under-dosing.
A positive effect of low-level laser energy on bone regeneration within a certain relationship between dose and output power was found. LLLT stimulates cellular metabolism, increasing protein synthesis and subsequent bone regeneration. A high dose combined with low power or a low dose combined with high power appears to produce a positive effect.
In Paramecium, cilia beating is correlated to intracellular calcium concentration ([Ca ]i) and nitric oxide (NO) synthesis. Recent findings affirm that photobiomodulation (PBM) can transiently increase the [Ca ]i in mammalian cells. In this study, we investigated the effect of both 808 and 980 nm diode laser irradiated with flat-top hand-piece on [Ca ]i and NO production of Paramecium primaurelia, to provide basic information for the development of new therapeutic approaches. In the experiments, the laser power in CW varied (0.1; 0.5; 1; and 1.5 W) to generate the following respective fluences: 6.4; 32; 64; and 96 J cm . The 6.4 J cm did not induce PBM if irradiated by both 808 and 980 nm diode laser. Conversely, the 32 J cm fluence had no effect on Paramecium cells if irradiated by the 808 nm laser, while if irradiated by the 980 nm laser induced increment in swimming speed (suggesting an effect on the [Ca ]i, NO production, similar to the 64 J cm with the 808 nm wavelength). The more evident discordance occurred with the 96 J cm fluence, which had the more efficient effect on PBM among the parameters if irradiated with the 808 nm laser and killed the Paramecium cells if irradiated by the 980 nm laser. Lastly, the 980 nm and 64 or 96 J cm were the only parameters to induce a release of stored calcium.
Thermal capacity, diflusivity, and conductivity were determined for nonmetallic restorative materials. Thermal characteristics were affected by composition, powder-liquid ratio, and water sorption. Diflusivity and conductivity followed the same order of values. The least conductive material investigated was an unfilled acrylic resin. Highest diffusivities and conductivities were exhibited by a resin composite. Values obtained with the composite were about the same as those obtained for a thick mix of unmodified zinc oxide-eugenol cement.Thermal properties of tooth structure and dental restorative materials have been investigated by several authors.'-" Most of the studies involve direct thermal conductivity measurements. Difficulties in obtaining steady-state conditions and in estimating and controlling heat losses have contributed toward large variations in reported values even for the same investigators.7,8 Additional difficulties in correlating results arise from an incomplete definition of compositions and powder-liquid ratios or a lack of identification of commercial brands used. The omissions are particularly obvious with liners and zinc oxide-eugenol cement preparations. To circumvent some of the technological difficulties, Braden' has introduced a simple method of determining diffusivity and has suggested that, under transient thermal conditions of the oral cavity, diffusivity, rather than conductivity, is the more important parameter.1030 conductivity determinations, to measure thermal properties of typical conventional nonmetallic restoratives, and to obtain information on some of the newer materials, such as a polymer-reinforced zinc oxide-eugenol cement and a direct filling resin composite.
Materials and MethodsMaterials used in this study are listed in Table 1. Diffusivity and conductivity were determined for zinc phosphate, silicate, unmodified zinc oxide-eugenol cements; a resinreinforced zinc oxide-eugenol material; an unfilled direct filling acrylic resin; and a direct filling resin composite. Diffusivity was determined by the method described by Braden.' The specimen was a cube with the hot junction of a copper-constantan thermocouple* embedded in its center. Specimen molds were made of silicone rubber held in approximately 5 cm (-2 inch) sections of a 3.18 cm (1 1/4 inch) diameter copper pipe (Fig 1). The materials were mixed for 30 seconds and packed into the molds holding the thermocouples. The open ends of the molds were covered with glass plates. Except for zinc oxide-eugenol cement, the specimens remained in the molds 24 hours at 37 C and a relative humidity of 100%; they were then defiasked and placed in a desiccator at 37 C for seven hours for dry specimen determinations, or in 50 ml distilled water for seven days at 37 C for wet specimen measurements. To ensure complete set, unmodified zinc oxide-eugenol cement specimens were defiasked 48 hours after starting the mix.The surface moisture of the wet specimens was blotted off with tissue paper before test-* Type T insulated 30 gauge (Brown...
Oral mucositis is a painful complication of hematopoietic stem cell transplantation for which photobiomodulation therapy (PBMT) is a safe and effective intervention. Extraoral delivery of PBMT has clinical advantages over intraoral delivery but requires additional dosimetric considerations due to the external tissue layers through which the light must propagate before reaching the oral mucosa. Additionally, to date there has been no dose modeling study, a task essential to developing a justified treatment protocol. We review here some of the complexities surrounding extraoral photobiomodulation therapy and offer that may help guide researchers toward an evidence-based treatment protocol for the prevention of oral mucositis.
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