Dureza Knoop de uma resina composta: influência da fotoativação por luz halógena ou LED, do tempo de armazenagem e do local de medição

Abstract

This study aimed to investigate the influence of the reading location, expended time and light source on the Knoop hardness values of a composite resin. For that purpose, an hybrid composite Filtek Z250 - UD (3M/ESPE) was used. The preparation of 40 Cylindrical samples, 6mm in diameter and 2mm high was carried out in a stainless steel matrix. Samples was fotocured by a quartz tungsten halogen device (QTH) XL 2500 (3M/ESPE) or by a LED (light emitting diode) device Ultrablue Is (DMC) with diferent Power densities (600 and 500mW/cm2 respectively) but standardized energy densities. Samples were stored at 37+1°C for 01h, 24h, 07 days and 30 days in deionized water. Half of the samples of each group were sectioned and Knoop hardness readings were performed at the samples centre, 100μm away from top and from bottom surfaces. In the other half the readings were performed at top and bottom surfaces without sectioning. The results were submitted to variance analysis and the means were compared by Tukey test using the significance level of 5%. Reading location didn’t influenced the Knoop hardness values; The specimens reached highest hardness values 24hours after fotoactivation, except for readings performed in the specimens interior and fotoactivated with LED that reached their highest hardness within 07days and light source didn’t influenced results.