![]() ![]() ![]() With the suggestion that broad-spectrum LED units can be used to cure RBCs that claim a 4-mm or more depth of cure, it is necessary to know how specific regions of LCU emission spectrum have the potential to interact with the RBC photoinitiators, as the thickness of the RBC increases beyond the customary 2-mm.Ī six-inch integrating sphere (Labsphere, North Sutton, NH, USA) connected to a fiberoptic spectrometer (USB 4000, Ocean Optics, Dunedin, Fla, USA) was used to measure the spectral radiant power and the photon count from a polywave ® LED light curing unit (Bluephase G2, Ivoclar Vivadent, Amherst, NY, USA) used on its high power setting for 20 s. Several studies report that, as RBC thickness increases, overall, exponentially fewer photons reach the bottom surface of the RBC, but the effect of a 4-mm thickness of RBC on the transmission of specific wavelengths of light is not well recognized. If the LCU is held stationary, this inhomogeneity can affect the quality of resin polymerization such that a strong, positive correlation exists between beam profile irradiance values and both the hardness and elastic modulus values across the surface, as well as within the depths of a RBC. This is because the spatial positioning of the different LED emitters within the LCU means that not all regions of the emitting surface deliver similar wavelengths, and this affects the uniformity of light output. Although these broad-band LCUs should be more compatible with a wider range of photoinitiators, they may not be the ideal choice for large or bulk-cured RBC restorations. Some manufacturers are now producing light emitting diode (LED) curing lights that contain two or more different wavelengths of LED emitters (broad banded, multi-peak, multi-wave) in order to deliver both the shorter (violet) wavelengths to activate Type I initiators, and longer wavelengths (blue) to activate CQ. The majority of the alternative Type I initiators used in dentistry are more sensitive to light shorter than 420 nm, although the recently introduced benzoylgermanium initiators exhibit good activation potential up to 450 nm. These initiators are considered Type 1 compounds that undergo a unimolecular reaction upon light exposure, and, because they have a greater quantum yield than CQ, they have the potential to increase the depth of cure. Some manufacturers have now added a Norrish Type I monoacylphosphine oxide photoinitiator, Lucirin-TPO or derivatives of dibenzoyl germanium (Ivocerin ® ), to their resins. When exposed to light of the appropriate wavelengths, CQ absorbs a photon to generate a short-lived, excited-state species that complexes with the tertiary amine to promote a sequential electron and proton transfer, which creates the active α-aminoalkyl-initiating radical. The most common photoinitiator used in RBCs is camphorquinone (CQ), which is a Type II photoinitiator having a maximum absorbance close to 468 nm. With the introduction of bulk-filling/bulk-curing RBCs, some manufacturers claim that their RBCs can be adequately photo-cured in up to 6-mm thick increments. Resin-based composites (RBCs) and light curing units (LCUs) have become an essential part of contemporary dentistry to the extent that the process of light curing generates most of the dentist’s income. Clinical relevanceĭespite the increased translucency of bulk curing RBCs, spectral radiant power shorter than 425 nm from a curing light is unlikely to be effective at a depth of 4-mm or more. This attenuation is RBC-dependent with shorter wavelengths (violet) attenuated to a greater extent than longer wavelengths (blue). Increasing RBC thickness results in an exponential decrease in light transmission. Depending on RBC, approximately 100 mW from the Bluephase G2 was transmitted through 0.1-mm of RBC in the ‘violet’ range, falling at most to 11 mW after passing through 2-mm of RBC, and to only 2 mW at 4-mm depth. After passing through 4-mm of RBC, the violet light represented only between 1.2–3.1% of the transmitted light depending on the RBC. ![]() At the light tip, the violet light component represented 15.4% of the light output. ![]() Attenuation was greater for the ‘violet’ than for the ‘blue’ spectral regions. This study measured the transmission of light in the ‘violet’ (350 ≤ λ ≤ 425 nm) and ‘blue’ (425 0.98). ![]()
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