Formulate recommendations for light curing resin-based cements through indirect restorative materials (IRM).
Method:
Energy delivery of Valo® Cordless (Ultradent, South Jordan, USA) as function of distance was determined (MARC; Resin Calibrator, BlueLight Analytics, Halifax, Canada). 0.5-mm thick of Variolink Veneer (Ivoclar-Vivadent) were light-cured through 1-mm thick e.maxCAD/A1/LT (A) or 0.61-mm thick e.maxPRESS/B1/LT (B) using Valo®. The irradiance delivered to the cement through A and B were 370 and 580mW/cm2 (MARC). Curing times were 2.5 to 60s at intervals of 5-10s. The energy (E) irradiated from the bottom of cement layer during curing was also measured. The Vickers Hardness (VH) of the bottom surface was measured immediately after irradiation and 10d later to establish the minimum energy required to reach maximum surface hardness.
Result:
Valo® exhibits a linear reduction of light energy with distance at 1-4mm. Non-linear regression (SAS 9.4) of VH against E by VH=α[1-exp(-β·E)] shows that hardness reaches 22.6±1.3Kg/mm2 and 23.0±1.5Kg/mm2 for A and B measured immediately, and 30.2±3.4Kg/mm2 and 30.3±2.1Kg/mm2 for A and B measured 10d later. The postcuring VH was statistically significantly higher (P<0.001). Irradiation energy measured at the bottom surface of cement was 5-6J/cm2, which is equivalent to 11-13J/cm2 delivered to the cement surface. Previous study has established that shades and translucency affect light transmission which further decreases exponentially with increase of IRM thickness. Calculations based on the energy-distance relationship of light curing unit (LCU) with 1500mW/CM2 and energy attenuation by 1mm IRM (A1-HT to A3) yields light curing times of 10-30s for properly immediate cuing resin cement.
Conclusion:
Knowing energy required for curing a resin-cement, energy-distance relationship of LCU and energy absorption relative to the IRM thickness, it is possible to calculate minimum light curing time (ideal conditions) for a given LCU and restorative material.
Materials were graciously provided by Ivoclar-Vivadent and Ultradent