Guidance of shrinkage vectors vs irradiation at reduced intensity for improving marginal seal of class V resin-based composite restorations in vitro.

This study evaluated the influence of radiation intensity on polymerization of a resin-based composite (RBC) and compared the influence of guidance of shrinkage vectors vs irradiation at reduced light intensity on the marginal seal of Class V RBC restorations in vitro. The degree of cure was studied indirectly by measuring the Vickers hardness (1.96 N, 30 seconds) at the bottom of disc-shaped specimens 2 mm in height at different periods of time after light irradiation. After one hour, irradiation using a high-intensity curing light (Heliolux GTE, Vivadent, 600 mW/cm2) [HICL] from close distance for 20 seconds, 40 seconds or 60 seconds or a low-intensity curing light (Vivalux, 250 mW/cm2) [LICL] from close distance for 60 seconds produced higher hardness values compared to 20 seconds or 40 seconds using the LICL or using the HICL from a distance of 10 mm. After three and 24 hours, higher hardness was observed for all irradiation protocols. After 24 hours, only specimens irradiated by the HICL for 20 seconds or 40 seconds from 10 mm distance featured significantly lower hardness compared to the remaining curing modes. The influence of different irradiation strategies on marginal seal of Class V RBC restorations was evaluated in vitro using dye penetration after water storage (60 days, 37 degrees C) and thermocycling (2500 cycles 5 degrees-55 degrees C). The HICL produced more dye penetration than the LICL. Placing the light tip directly over or 10 mm above the center of the cavity ("standard irradiation, ["distance irradiation"]") resulted in similar penetration values. In contrast, positioning the light tip apical to the cervical margin and moving it slowly to the center of the cavity ("cervical start irradiation") compromised the marginal seal.