Effect of light curing tip distance and resin shade on microhardness of a hybrid resin composite

Abstract

Resin composite shades and resin composite polymerization performed with a distanced light tip are factors that can affect polymerization effectiveness. This in vitro study aimed to evaluate the influence of curing tip distance and resin shade on the microhardness of a hybrid resin composite (Z250-3M ESPE). Forty-five resin composite specimens were randomly prepared and divided into nine experimental groups (n = 5): three curing tip distances (2 mm, 4 mm, and 8 mm) and three resin shades (A1, A3.5, and C2). All samples were polymerized with a continuous output at 550 mW/cm(2). After 24 hours, Knoop microhardness measurements were obtained on the top and bottom surfaces of the sample, with a load of 25 grams for 10 seconds. Five indentations were performed on each surface of each sample. Results showed that bottom surface samples light-cured at 2 mm and 4 mm presented significantly higher hardness values than samples light-cured at 8 mm. The resin shade A1 presented higher hardness values and was statistically different from C2. The resin shade A3.5 did not present statistical differences from A1 and C2. For the top surface, there were no statistical differences among the curing tip distances. For all experimental conditions, the top surface showed higher hardness values than the bottom surface. It was concluded that light curing tip distance and resin shade are important factors to be considered for obtaining adequate polymerization.

Wavelength of Experimental LEDS: Hardness, Elastic Modulus, Degree of Conversion and Temperature Rise of a Microhybrid Composite

“…abs C C aliphatic of polymer abs C C aromatic DC abs C C aliphatic of monomer abs C C aromatic (1) Temperature variation was recorded from a thermistor connected to a multimeter. Temperature measurements started immediately after the resin composite (20 ± 0.5 °C) was inserted in a teflon mould, and thereafter it was obtained every 2.5 seconds until it was polymerized for 60 seconds when the final temperature was recorded.…”

“…Composites are expected to reach a high degree of curing for adequate clinical performance 1 . When inadequately polymerized, composites can have their biological, physical and mechanical properties compromised 2,3 .…”

“…When inadequately polymerized, composites can have their biological, physical and mechanical properties compromised 2,3 . As a result, marginal degradation and discoloration 4 , postoperative sensitivity and pulp irritation may occur 1,5 . The efficiency of polymerization depends on several factors, including those related to the material itself in terms of its composition 1,6 , and those related to the light-curing unit (LCU), such as light intensity, spectral distribution, thermal emission and exposure time 7 .…”

“…As a result, marginal degradation and discoloration 4 , postoperative sensitivity and pulp irritation may occur 1,5 . The efficiency of polymerization depends on several factors, including those related to the material itself in terms of its composition 1,6 , and those related to the light-curing unit (LCU), such as light intensity, spectral distribution, thermal emission and exposure time 7 . LED (Light Emitting Diode) LCUs are gradually replacing halogen LCUs because they have a longer lifetime, and the light flux is not compromised with time 4,8 .…”

"Estudo do efeito da distância da ponta de aparelhos fotoativadores na microdureza e no grau de conversão da resina composta usando luz halógena, laser de argônio e LED"

“…Alguns trabalhos mostram haver influência da cor da resina composta na dureza do compósito (AGUIAR et al, 2005;ERSOY et al, 2004;FRIEDMAN;HASSAN, 1984;LELOUP et al, 2002;MANDARINO et al, 1992;RISSI;CABRAL, 2002), apesar de alguns afirmarem que a cor não foi fator determinante na dureza (MARTINS et al, 2002;CAUGHMAN;CURTIS JR, 1994). A cor da resina selecionada foi a A3, uma cor universal.…”