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Objectives: To investigate if and why a plasma arc curing (PAC) light tends to undercure methacrylate-based resins or resin composites., Methods: Model dimethacrylate resins, commercial dental adhesives, and commercial resin composites were cured using a PAC light and a halogen light with the similar radiant exposures but different combinations of irradiance and irradiation time. The degree of double bond conversion (DC) was measured with FTIR spectroscopy and analyzed as a function of radiant exposure., Results: The PAC light produced a lower DC than the halogen light for the model resin with the lowest viscosity and for three of the four adhesives. With a high irradiance, the PAC light could cure three of the four composites as thoroughly as its halogen counterpart. When the irradiance was reduced, however, three composites yielded a lower DC., Conclusions: Insufficient cure by PAC lights or any curing lights with very high irradiance is likely to happen when too short an irradiation time is used. It is because under higher irradiance, the lifetime of free radicals is shorter.

Unlabelled: Attempts have been made to improve the mechanical properties and convenience of use of glass-ionomer cement (GIC) by various modifications, in particular by including a free radical-polymerizable component ("resin-modified" GIC, RMGIC). Necessarily, the one replaces part of the other, but the chemistry suggests that the formation of each network separately would inhibit diffusion and thus the other reaction., Objective: To ascertain whether interference occurs between the components of an RMGIC by variation of the irradiation regime., Materials and Methods: Cylindrical specimens (6 mm x 3 mm diameter) of one brand of RMGIC (Shades A3, D2; Fuji II LC, GC; capsules) were prepared in ptfe moulds. After machine-mixing for 10s, each of the three increments was irradiated from the top for various times (0-60s). In addition, extra irradiation from the bottom; from the bottom before, and from the side after, ejection from the mould; the same using two curing lamps; and at various delays after mixing (0-18 h), with four replicates of each. After exposure, or as appropriate, specimens were wrapped tightly in aluminium foil for dry storage in the dark at 37 degrees C for testing at 24h after mixing. Specimens with evident defects were replaced before testing., Results: No increase in strength was found beyond the recommended 20-s irradiation, indeed further exposure reduced the strength. For top-only irradiation, strength rose from the unirradiated value (66+/-9 MPa) to a peak at 20s (215+/-25 MPa), after which it declined steadily. Adding bottom irradiation gave a small decrease in peak value (194+/-36 MPa); adding side irradiation reduced it substantially (113+/-7 MPa). Delay for 2 min gave a marked reduction (155+/-15 MPa), declining to the unirradiated value at 18 h (70+/-15 MPa). No effect due to shade was detected., Significance: Competition between network-forming reactions leads to a sensitive balance between the two, and a critical optimum irradiation: too much may be detrimental, as is delay. The essential compromise involved in such mixed chemistry jeopardizes reliability. It is advisable to follow the duration of exposure prescribed by the manufacturer to achieve optimal performance.

Objective: The aim of this in vitro study was to evaluate the cytotoxicity of resin-modified glass-ionomer lining cements submitted to different curing regimes and applied to an immortalized odontoblast-cell line (MDPC-23)., Methods: Forty round-shaped specimens of each experimental material (Fuji Lining LC and Vitrebond) were prepared. They were light-cured for the manufacturers' recommended time (MRT = 30 s), under-cured (0.5 MRT = 15 s), over-cured (1.5 MRT = 45 s) or allowed to dark cure (0 MRT). Sterilized filter papers soaked with either 5 microL of PBS or HEMA were used as negative and positive control, respectively. After placing the specimens individually in wells of 24-well dishes, odontoblast-like cells MDPC-23 (30,000 cells/cm2) were plated in each well and incubated for 72 h in a humidified incubator at 37 degrees C with 5% CO2 and 95% air. The cytotoxicity was evaluated by the cell metabolism (MTT assay) and cell morphology (SEM)., Results: Fuji Lining LC was less cytotoxic than Vitrebond (p < 0.05) in all the experimental conditions. However, the cytotoxicity of Fuji Lining LC was noticeably increased in the absence of light-curing while the same was not observed for Vitrebond. The length of light-curing (15, 30 or 45 s) did not influence the toxicity of both lining materials when they were applied on the odontoblast-cell line MDPC-23., Significance: The light-activation plays an important role in reducing the cytotoxicity of Fuji Lining LC. Following the manufacturer' recommendation regarding the light-curing regime may prevent toxic effect to the pulp cells.

Objectives: To evaluate the efficiency of the photopolymerization of dental resins it is necessary to know to what extent the light emitted by the light curing units is absorbed by the photoinitiators. On the other hand, the efficiency of the absorbed photons to produce species that launch the polymerization process is also of paramount importance. Therefore, the previously determined PAE (photon absorption efficiency) is used in conjunction with the polymerization quantum yields for the photoinitiators, in order to be able to compare the total process on an equivalent basis. This parameter can be used to identify the best performance for the photochemical process with specific photoinitiators., Methods: The efficiency of LED (Ultrablue IS) and QTH (Optilux 401) lamps were tested comparing their performances with the photoinitiators camphorquinone (CQ); phenylpropanedione (PPD); monoacylphosphine oxide (Lucirin TPO); and bisacylphosphine oxide (Irgacure 819). The extent of photopolymerization per absorbed photon was determined from the polymerization quantum yields obtained by using the photoinitiators to polymerize methyl methacrylate, and afterwards combined with the previously determined PAEs., Results: Although CQ presents a rather low polymerization quantum yield, its photopolymerization efficiency is practically the highest when irradiated with the Ultrablue LED. On the other hand, Lucirin is much more efficient than the other photoinitiators when irradiated with a QTH lamp, due to its high quantum yield and the overlap between its absorption spectrum and the output of the visible lamp light., Significance: Difference in photopolymerization efficiencies arise when combinations of photoinitiators are used, and when LED sources are used in preference to QTH. Mechanistic understanding is essential to optimal initiator formulation.