Ultra-fast light-curing resin composite with increased conversion and reduced monomer elution

ObjectivesTo test the null hypotheses that photoactive resin composites containing a Type I photoinitiator would exhibit reduced DC or increased monomer elution at substantially short curing times compared with materials based on a Type 2 ketone/amine system.MethodsTwo experimental resin composites were prepared, using either Lucirin-TPO or camphorquinone/DMAEMA. Specimens were light-cured using appropriate spectral emission that coincided with the absorption properties of each initiator using different irradiation protocols (0.5, 1, 3, 9 s at 500, 1000 and 2000 mW/cm2 for Lucirin-TPO based composites and 20 or 40 s at 1000 mW/cm2 for Lucirin-TPO and camphorquinone-based composites). Degree of conversion (DC) was measured by Raman spectroscopy, propagating radical concentrations were collected by means of electron paramagnetic resonance (EPR) and monomer leaching was characterized using high-performance liquid chromatography (HPLC).ResultsThe null hypotheses were rejected, except for a single irradiation protocol (0.5 s @ 500 mW/cm2). Lucirin-TPO-based composites could cure 20 times faster and release at least 4 times less monomers in comparison to camphorquinone-based composites. At 1000 mW/cm2, and 1 s irradiation time for curing times of 1 s, Lucirin-TPO based composites displayed 10% higher DC. The difference in polymerization efficiency of Lucirin-TPO compared with camphorquinone-based resin composites were explained using EPR; the former showing a significantly greater yield of radicals which varied logarithmically with radiant exposure.SignificanceLucirin-TPO is substantially more efficient at absorbing and converting photon energy when using a curing-light with an appropriate spectral emission and otherwise a limitation noted in several previous publications. At concentrations of 0.0134 mol/L, Lucirin-TPO-based composites require a minimum light intensity of 1000 mW/cm2 and an exposure time of 1 s to provide significantly improved DC and minimal elution compared with a conventional photoinitiator system. The use of a wide range of curing protocols in the current experiment has realized the significant potential of Lucirin-TPO and its impact for clinical applications, in replacement to materials using camphorquinone.