Influence of successive light-activation on degree of conversion and knoop hardness of the first layered composite increment

Abstract

Purpose: To evaluate the influence of light-activation of second, third and fourth increments on degree of conversion (DC) and microhardness (KHN) of the top (T) and bottom (B) surface of the first increment. Materials and methods. Forty samples (n = 5) were prepared. In groups 1–4, after each increment light-activation (multiple irradiation), T and B of the first increment were measured in DC and KHN. In groups 5–8, only the first increment was made (single irradiation) and measurements of DC and KHN were taken at 15 min intervals. The light-activation modes were (XL) 500 mW/cm² × 38 s (G1/G5); (S) 1000 mW/cm² × 19 s (G2/G6), (HP) 1400 mW/cm² × 14 s (G3/G7); (PE) 3200 mW/cm² × 6 s (G4/G8). Data for DC and KHN were analyzed separately by using PROC MIXED for repeated measures and Tukey-Kramer test (α = 0.05). Results. For KHN, B showed lower values than T. PE resulted in lower values of KHN in B surface. For single and multiple irradiations, T and B of first measurement showed the lowest KHN and the fourth measurement showed the highest, with significant difference between them. For single irradiation, first and second increments presented similar KHN, different from the third and fourth increment, which did not differ between them. For multiple irradiations, the second light-activation resulted in KHN similar to first, third and fourth increments. For DC, except QTH, T presented higher DC than B. Conclusion. The light-activation of successive increments was not able to influence the KHN and DC of the first increment.