Violet-blue light exposure of the skin: is there need for protection?

Advocates of skin protection against blue light express concern about exposure to indoor lighting and electronic screens as well as natural outdoor exposure. However, the nature of adverse effects in skin is unclear and the doses to induce effects are unknown. We aimed to reveal whether there is a scientific basis for promoting skin protection against violet-blue light (400-500 nm, VBL). Based on published literature, we determined the time to reach a threshold dose that induced a biological response in human skin. In the absence of an action spectrum for effects on skin, we used a hand held probe with a defined spectral response and measurements of the unweighted exposure between 400 and 500 nm to estimate the exposure by a selection of artificial light sources and solar light. For comparison, an outdoor threshold erythemally weighted UV dose was set to 1 SED (standard erythema dose). Outdoor, weighted irradiances were obtained using a radiative transfer model. Induction of pigmentation in human skin tissue was the only consistently reported endpoint after VBL exposure of about 65 Jcm-2. This threshold dose was reached in 0.5 to 20 months of exposure to indoor lighting sources. In comparison, specialised medical sources reached this dose in 0.5 min to 45 h. The time outdoors to reach 1 SED was shorter than the time to reach a VBL threshold dose throughout all seasons. Skin protection against VBL is superfluous for exposures to domestic lighting sources or screens and for solar radiation; however, it may be advantageous for patients suffering from photosensitive diseases or taking photosensitising medication.

The dental curing light: A potential health risk.

Powerful blue-light emitting dental curing lights are used in dental offices to photocure resins in the mouth. In addition, many dental personnel use magnification loupes. This study measured the effect of magnification loupes on the "blue light hazard" when the light from a dental curing light was reflected off a human tooth. Loupes with 3.5x magnification (Design for Vision, Carl Zeiss, and Quality Aspirator) and 2.5x magnification (Design for Vision and Quality Aspirator) were placed at the entrance of an integrating sphere connected to a spectrometer (USB 4000, Ocean Optics). A model with human teeth was placed 40 cm away and in line with this sphere. The light guide tip of a broad-spectrum Sapphire Plus (Den-Mat) curing light was positioned at a 45° angle from the facial surface of the central incisor. The spectral radiant power reflected from the teeth was recorded five times with the loupes over the entrance into the sphere. The maximum permissible cumulative exposure times in an 8-hr day were calculated using guidelines set by the ACGIH. It was concluded that at a 40 cm distance, the maximum permissible cumulative daily exposure time to light reflected from the tooth was approximately 11 min without loupes. The weighted blue irradiance values were significantly different for each brand of loupe (Fisher's PLSD p < 0.05) and were up to eight times greater at the pupil than when loupes were not used. However, since the linear dimensions of the resulting images would be 2.5 to 3.5x larger on the retina, the image area was increased by the square of the magnification and the effective blue light hazard was reduced compared to without the loupes. Thus, although using magnification loupes increased the irradiance received at the pupil, the maximum cumulative daily exposure time to reflected light was increased up to 28 min. Further studies are required to determine the ocular hazards of a focused stare when using magnification loupes and the effects of other curing lights used in the dental office.

Detection of leachables and cytotoxicity after exposure to methacrylate- and epoxy-based root canal sealers in vitro.

Root canal sealing materials may have toxic potential in vitro depending on the cell line, cytotoxicity assay, material chemistry, and degree of polymer curing. The aims of the present study were to detect leaching components from epoxy- or methacrylate-based root canal sealers and to investigate the degree of cytotoxicity after exposure to extracts from these materials. Qualitative determination of substances released from the materials was performed by gas- and liquid chromatography/mass spectrometry. Submandibular salivary gland acinar cell death (apoptosis/necrosis) was determined using a fluorescence staining/microscopy technique. The major leachable monomer from the epoxy-based material was bisphenol-A diglycidyl ether (BADGE), whereas leachables from the methacrylate-based materials were mainly triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), hydroxyethyl methacrylate (HEMA), and polyethyleneglycol dimethacrylate (PEGDMA). Exposure to diluted extracts of cured methacrylate-based materials caused a postexposure time-dependent increase in cell death. This effect was not demonstrated as a result of exposure to undiluted extract of cured epoxy-based material. Extracts of all fresh materials induced apoptosis significantly, but at lower dilutions of the epoxy- than the methacrylate-based materials. The degree of leaching, determined from the relative chromatogram peak heights of eluates from the methacrylate-based sealer materials, corresponded with the degree of cell death induced by extracts of these materials.

Methacrylate monomers lower the level of reduced glutathione and increase the in vitro sensitivity of cells to optical radiation.

Induction of cell death by optical radiation in the wavelength range 350-500 nm was significantly increased by commonly used methacrylate monomers, not mediated by absorption of radiation by the methacrylate monomers, but through a mechanism involving rapid reduction in the level of glutathione (GSH).

In vitro photosensitization initiated by camphorquinone and phenyl propanedione in dental polymeric materials.

Documentation is scarce on the photobiological effects of photoinitiators present in dental light curable materials. The aim of this study was to determine cellular effects of the photoinitiators camphorquinone (CQ) and phenyl propanedione (PPD) and to investigate whether these substances produced reactive oxygen species after low and high doses of optical radiation (between 0 and 17J/cm(2)). Rat salivary gland cells in vitro were exposed to visible blue light and/or UVA. Hematoporphyrin (HP), a photosensitizer used in medicine, and the UVA-filter 2-methoxy-4-hydroxy-benzophenone (B-3) were used as reference substances. It was found that PPD produced hydrogen peroxide, but not singlet oxygen, upon light irradiation. CQ produced neither hydrogen peroxide nor singlet oxygen. Cell death by necrosis and apoptosis was induced by irradiation in the presence of CQ, PPD and HP. Doses higher than 6J/cm(2) UVA and blue visible light from a source similar to clinically applied sources, induced apoptosis even in the absence of photosensitizers added. A reciprocity relationship was found between radiant exposure (at constant irradiance) and concentration of photoinitiators. In conclusion, the oral cells under investigation were light sensitive, and the sensitivity increased in presence of photoinitiators. PPD acted by mechanisms that included reactive oxygen species and CQ probably by formation of free radicals.

In vitro efficacy and risk for adverse effects of light-assisted tooth bleaching.

The use of optical radiation in the so-called light-assisted tooth bleaching procedures has been suggested to enhance the oxidizing effect of the bleaching agent, hydrogen peroxide. Documentation is scarce on the potential adverse effects of bleaching products and on optical exposure risks to eyes and skin. The efficacy of seven bleaching products with or without simultaneous use of seven different bleaching lamps was investigated using extracted human teeth. The bleaching effect was determined immediately after treatment and one week later. Tooth surfaces were examined for adverse alterations after bleaching using a scanning electron microscope. Source characteristics of eight lamps intended for tooth bleaching were determined. International guidelines on optical radiation were used to assess eye and skin exposure hazards due to UV and visible light emission from the lamps. Inspection of teeth one week after bleaching showed no difference in efficacy between teeth bleached with or without irradiation for any of the products. Scratches, probably from the cleaning procedure were frequently seen on bleached enamel irrespective of irradiation. Maximum permissible exposure time (t(max)) and threshold limit values were exceeded for about half the bleaching lamps investigated. One lamp exceeded t(max) even for reflected blue light within the treatment time. This lamp also exceeded t(max) values for UV exposure. The lamps were classified as "low risk" and as borderline to "moderate risk" according to a relevant lamp standard.

Evaluation of eye protection filters for use with dental curing and bleaching lamps.

Exposure to intense radiation sources in a dental clinic necessitates the use of eye protective filters to avoid blue-light photochemical retinal hazard. We have investigated the filtering quality and assessed whether the filters protect sufficiently against retinal hazards throughout the workday. Visible light transmittance of 18 protective filters was measured. These products consisted of spectacles, stationary lamp shields, and a hand-held shield intended for use in dental clinics. Nine of the 18 tested filters had adequate filtering capacity according to today's lamp technology and exposure limit values. These filters transmitted less than 0.1% of the radiation at any wavelength between 400 nm and 525 nm. Seven of the nine filters showed transmission values below the detection limit (approximately 10(-3)%) in the wavelength band between 400 nm and 500 nm. Filters of inferior quality may prove inadequate if the use and radiation intensity of the lamps further increase. Lack of protection may also occur if a filter is used to protect against emission from a lamp with properties other than the lamp for which the filter has been intended. It is of major importance that the spectacles/shields accommodate the emission from the lamp source. The suppliers of dental radiation sources should be responsible for information on the need for and proper use of eye protectors. In addition, the filters should be marked according to testing procedures appropriate for the specific use.

Studies on curcumin and curcuminoids. XXIX. Photoinduced cytotoxicity of curcumin in selected aqueous preparations.

Natural curcumin was evaluated as a potential photosensitizer for oral applications. The photocytotoxicity of curcumin on salivary gland acinar cells (SM 10-12) was investigated in five aqueous preparations consisting of 5% DMSO, non-ionic micelles, cyclodextrin, liposomes, or a hydrophilic polymer. The difference in phototoxic effects between natural curcumin and synthetic curcumin was examined. Cytotoxicity in SM 10-12 cells exposed to curcumin in the concentration range 0.4-13.5 microM was investigated by MTT test, a fluorescence-staining microscopic test, and by Western immunoblotting techniques. The potential formation of a photoreaction product, hydrogen peroxide, was evaluated by a fluorescence assay. The light source was a halogen lamp used in the dental clinic, emitting mainly in the blue part of the spectrum. The phototoxic effect on SM 10-12 cells was dependent on curcumin concentration, the light dose and the type of preparation. Natural and synthetic curcumin induced phototoxicity to the same extent. Significant effects on the cells were obtained at low curcumin concentrations (< or =0.5 microM) and at a low light dose (< or =6 J cm(-2)), after 3 h incubation. Neither the activation of caspases-3, -7, -8 or -9, nor the formation of hydrogen peroxide could be detected in cells exposed to curcumin and light. The liposome preparation was the most efficient vehicle for curcumin to induce cell death. The phototoxic effect induced by curcumin is highly dependent on the type of preparation. Curcumin might be a potential photosensitizer in the treatment of oral lesions and cancers provided careful selection of the vehicle.