Rods of a visible-light-cured dental composite resin were photo-polymerized and immersed in water at 37 degrees C for 7 days. The residual monomers (TEGDMA and Bis-GMA) trapped in the set composite and those eluted into water were analysed by gas-liquid chromatography. It became evident that minor amounts of the residual monomers dissolved in water, but that most residual monomers remained in the set composite. Extension of the irradiation period contributed to the significant reduction in the residual monomer level and its elution into water.

Seven commercial visible-light-cured (VL) dental composite resins were analytically studied for identification of the photo-initiator consisting of photo-sensitizer and reducing agent. Gas-liquid chromatography (GC) was used for the determination of the dilute components extracted from the composite resin. Mass spectroscopy (GC-MS) was used for confirmation of the qualitative data obtained by GC. The results showed that all composite resins examined included camphorquinone (CQ) as a photo-sensitizer. The concentration of CQ in the resin phase, however, ranged from 0.17 to 1.03% w/w. The composite resin with hybrid-sized filler tended to have a higher concentration of CQ than did the micro-filled composite resin. As for the reducing agent, two out of seven brands contained dimethylaminoethyl methacrylate (DMAEMA), and one included dimethyl-p-toluidine (DMPTI). The mixing ratio between CQ and the amine in these three composite resins also varied. Another four brands did not contain either DMAEMA or DMPTI, and would utilize different reducing agents.

The radiopacity of 12 VL-cured composite resins was determined with reference to an aluminum step-wedge. Two anterior composites were radiolucent while two anterior and one anterior/posterior composites exhibited the radiopacity equal to, or slightly greater than, that of human enamel. Three posterior and one inlay composites possessed the radiopacity equivalent to, or in tiny excess of, that of human enamel. Three posterior composites had the radiopacity, fairly exceeding that of human enamel. Chemical analyses of the filler particles were carried out with SEM/EDX. It became evident that radiopaque fillers contained at least one radiopaque oxide component such as BaO, ZrO2 and Yb2O3 with varying concentrations. In general, the radiopacity of the composite resin was linearly proportional to the amount of the radiopaque oxide in the filler. It was suggested that ZrO2 was radiopacifier equivalent to, or even stronger than, BaO.

New fillers have been prepared for visible-light-cured (VL) dental resin composites with the refractive index adjustable to that of the resin phase. These SiO2 glass powders containing TiO2 up to 20 wt% were formed by heating to 1000 degrees C ground gels made from a mixture of Ti[OCH(CH3)2]4 and Si(OC2H5)4. With increasing TiO2 content, the refractive index of the prepared power increased linearly, while the optical transmittance at 467 nm decreased linearly. The experimentally formulated VL-cured resin composites, consisting of (TEGDMA and Bis-GMA) monomer mixture and TiO2-SiO2 glass filler, had greater transmittance when the refractive index of the filler matched that of the monomer mixture, resulting in a greater degree of monomer conversion upon irradiation with VL.

Four commercial visible light (VL)-cured composite resin veneering materials with a dentine shade were examined for their Knoop hardness and fracture toughness. Composite specimens were classified into three groups. The first group was cured by VL only, the second group was cured by VL and post-cured by VL and the third group was cured by VL and post-cured by heat. It became evident that one composite containing four-functional urethane monomer had both hardness and fracture toughness greater than those of the other three composites containing two-functional urethane monomer. The filler content (vol%) in the composite tended to be linearly proportional to both hardness and fracture toughness. Post-curing by VL and heat were proven to effectively increase both hardness and fracture toughness of once light-cured composites. These results suggest that the clinical performance (e.g. wear resistance and colour stability) of VL-cured composite resin veneering materials might be improved with the aid of post-curing.