4 - Degree of Conversion of Resin-Based Luting Materials Containing Alternative Photoinitiators

Abstract

Evaluate the degree of conversion (DC) of pre-heated composites, light- and dual-cured resin cements containing alternative photoinitiators under lithium disilicate ceramic with different thicknesses light cured using single-peak and dual-peak light curing units (LCUs). Thirty rectangular (12 ×14 mm; n= 5) lithium disilicate ceramic (IPS e.max CAD MT A2) specimens in six different thicknesses (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mm) were cut using a precision saw machine. The spectral irradiance (mW/cm 2 /nm) of a single-peak (SmartLite Pro Cure) and a dual-peak (SmartLite Pro Polycure) LCUs and the light transmittance through the ceramic with different thicknesses were evaluated using a spectrophotometer (MARC Light Collector). LCU beam profile was also evaluated (ZWO ASI). The DC of a pre-heated dental composite (TPT, Tetric Prime T using the CalSet at 68 C), a light-cured resin cement (VLC, Variolink LC) and a dual-cured resin cement (VDC, Variolink DC) was evaluated using FTIR spectroscopy. The luting agents were light cured with no ceramic interposed for 10 s and 40 s and through the ceramics with different thicknesses for 10 s using both LCUs. Statistical analyses were performed according to the different experimental designs with a level of significance of α= 0.05. The single-peak LCU emitted an irradiance of 1335 7 mW/cm2 with 98.4% of the irradiance within the blue spectrum. The dual-peak emitted an irradiance of 1192 4 mW/cm2 with 72.6% of the irradiance within the blue spectrum and 27.4% within the violet spectrum. The ceramic thickness has an exponential effect on the decrease of the light transmitted. VLC had a higher DC when using dual-peak and presented a maximum DC ratio above 80% up to 2 mm of ceramic thickness; VLC DC with single-peak LCU only cured efficiently up to 1 mm of ceramic thickness. There were no significant differences on the VDC DC when light cured with both LCUs at any thickness and VDC cured above the 80% of the maximum DC in all conditions, except for the single-peak LCU with a 3 mm thick ceramic. No differences were found for the TPT using both LCUs and TPT can be efficiently cured through a ceramic with up to 1 mm thickness. Dual-peak LCUs were more efficient than single-peak on curing light- and dual-cured resin cements containing alternative photoinitiators, but there is no difference on the DC of pre-heated composites light cured with single- or dual-peak LCUs.