Efeito das fontes de luz mono e multiwave com diferentes diâmetros de ponta e métodos de fotoativação na dureza Knoop de facetas em resinas compostas

Abstract

To evaluate the effect of mono and multiwave light-curing units (LCU) with different tip diameter and light exposure protocols on the Knoop hardness of resin composites with different photoinitiators used for direct veneers. Central incisor-shaped specimens with 12 mm of incisal-cervical length and 9 mm of mesial-distal width, and 1.5 mm thick were made using 2 resin composites with different photoinitiators: TN, Tetric N-Ceram (Ivoclar Vivadent) - and VI, Vittra APS (FGM) shade A2E; light-cured with 4 LCU: 2 multiwave - GV, Grand VALO (Ultradent) and EN, Emitter Now Duo (Schuster); and 2 monowave - RX, Radii Xpert (SDI) and EL, Elipar Deep Cure (3M Oral Care); in 2 localized light exposure (LEP): for the 40 s centered over the specimen and double light exposure shifting 3 mm from the center of the specimen to cervical and to incisal (20 s each), totaling 16 groups (n=10). Knoop hardness (KH, N/mm2) was measured at the top and bottom of the specimen in the central, cervical, incisal, mesial, and distal regions. The LCUs were characterized in: active tip diameter (mm), power (mW), and beam profile with and without specimen interposition (mW/cm²). Data were analyzed by ANOVA in 3 factors and the Tukey test (α = 0.05). Mono and multiwave LCUs do not interfere on the Knoop hardness of resin composite TN and VI. The KH values of VI and TN resin composite specimens were significantly influenced by the LCU (P <.001), by the location of the measurement (P <.001), and also by the face of the specimen (P <.001).The KH values at the top were significantly higher than at the bottom when localized light exposure was used, especially at the periphery of the specimen. All LCUs do not achieve 80% of maximum hardness to the bottom of the cervical region to localized light exposure. VG resulted in better performance with localized light exposure. The double light exposure minimized the differences among the LCU and also among the locations of the resin composite veneer. All LCUs showed homogeneous light distribution Photoactivation covering the entire restoration proved to be essential to achieving adequate resin composite Knoop hardness. LCUs with larger active tip diameter resulted in better light distribution generating higher resin composite Knoop hardness in the margins of the resin composite veneers.