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

Ana Paula Bonilauri Ferreira,Sérgio Henrique Pezzin,Evelise Machado Souza,Sérgio Vieira,Rodrigo Nunes Rached,Paulo César Soares Júnior

doi:10.1590/1516-1439.267514

Abstract

The aim of this study was to evaluate the effect of different peak wavelengths (450nm, 468nm and 490nm) of experimental LEDs on hardness, elastic modulus, degree of conversion and temperature rise of a microhybrid resin composite – Venus® (Heraeus Kulzer). Hardness and elastic modulus were determined by nanoindentation technique (n=5), degree of conversion was measured by FTIR (n=5) and temperature rise was measured with a thermistor (n=30). Data were submitted to ANOVA and multiple comparisons tests (α=0.05). Mechanical properties and degree of conversion (p<0.001) were superior on the top surfaces of the specimens. 468nm showed the highest mechanical properties values. There was no statistical difference in the degree of conversion (p=0.51) and in temperature rise (p=0.06) among all LEDs. Hardness and elastic modulus were influenced by LED´s wavelength, whereas degree of conversion and temperature rise were not influenced.

Highlights

Composites are expected to reach a high degree of curing for adequate clinical performance[1]
The aim of this study was to evaluate the effect of different peak wavelengths of experimental LED light-curing unit (LCU) on the hardness, elastic modulus, degree of conversion and temperature rise of a composite
The mean values of hardness, elastic modulus and hardness were calculated from the load curves versus penetration by of the ratio between the bottom and top (B/T) surfaces of the Oliver and Pharr method[23]

Summary

Introduction

Composites are expected to reach a high degree of curing for adequate clinical performance[1]. 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]. A suitable photoactivation process is of great importance to emit radiant energy at a specific wavelength[9,10]. Compared to halogen LCUs, LEDs thermal emissions are minimal[8]. This is of great clinical importance since excessive heat can be hazardous to the pulp[13]

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Conclusion