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  • Title: Influence of extremely high irradiances on the micromechanical properties of a nano hybrid resin based composite.
    Author: Kutuk ZB, Gurgan S, Hickel R, Ilie N.
    Journal: Am J Dent; 2017 Feb; 30(1):9-15. PubMed ID: 29178708.
    Abstract:
    PURPOSE: To investigate in vitro the effect of extremely high irradiance light-emitting diode (LED) light curing units (LCU) with different exposure distances and curing modes on the micromechanical properties of a nano hybrid resin based composite. METHODS: 72 resin based composite (RBC) (Kalore) specimens with 2 mm thickness were cured using two high irradiance LED LCUs (Bluephase 20i and FlashMax P3) at 0 and 7 mm exposure distances. The curing conditions were:a) Bluephase 20i - 10 seconds - High power; b) Bluephase 20i - 15 seconds - High power; c) Bluephase 20i - 5 seconds - Turbo; d) Bluephase 20i - 15 seconds - Soft start; e) FlashMax P3 - 4 mm tip cover - 3 seconds; f) FlashMax P3 - without tip cover - 3 seconds. The incident and transmitted irradiance and radiant exposure were evaluated in real time during curing, with a radiometer (MARC Resin Calibrator). The micromechanical properties (Vickers hardness, HV and indentation modulus, E) were measured with an automatic universal hardness indenter after storing specimens for 24 hours in distilled water. Data were analyzed with one- and two-way ANOVA tests followed by Tukey test and partial eta-square statistics (α= 0.05). RESULTS: For both LCUs, incident irradiance decreased progressively with increased exposure distance, reaching at 7 mm exposure distance less than 50% of the value measured when the LCU was applied directly on specimen's surface. In descending order of strength of their effects, the parameters incident irradiance (HV; η P2 =0.828, E; 0.693), LCU (HV, 0.257, E, 0.043) and exposure distance (HV, 0.031, E, 0.028) were significant factors affecting HV and E (P < 0.05). The localized radiant exposure (the incident and transmitted) as well as the position of HV and E measurements (top-bottom of the specimen) were additional factors affecting significantly only HV (P < 0.05), but not E (P > 0.05). CLINICAL SIGNIFICANCE: Extremely high irradiances were less efficient in adequate curing of the analyzed nano hybrid composite. Using a protection tip, as clinically indicated, reduces the irradiance of FlashMax P3 from 7,681.7 (160.53) mW/cm2; to 3052.5 (71.61) mW/cm2;.
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