Temperature rise and Knoop hardness promoted by different light-curing units

ABSTRACT

This study characterized the light emitted by a quartz-tungsten-halogen (QTH) and three light-emitting diode (LED) light curing units (LCUs) and investigated the temperature rise and composite hardness promoted by these sources. XL2500 QTH (3M ESPE), Freelight LED (3M ESPE), Ultrablue Is LED (DMC) and Cool Blue Wand LED (Milestone Scientific) were investigated. The irradiance was measured with a power meter, and the light spectral distribution obtained with a spectrometer. Temperature rise was recorded using a thermocouple connected to a digital thermometer during light-activation of Filtek Z250 (3M ESPE) resin composite. Data were submitted to ANOVA and Tukey’s test(α=0.05). Knoop hardness was assessed at different composite depths (20, 1000 and 1980μm), and data submitted to split-plot design two-way ANOVA and Tukey’s test (α=0.05). Correlation between irradiance and temperature rise was investigated by Pearson’s test. All units presented 95% of irradiance between 400-515nm. Temperature rise means (ºC) varied between 1.05±0.16 and 2.74±0.27. The Cool Blue LED presented significantly higher temperature increase thanthe other LCUs, and the QTH promoted significantly higher temperature rise than Ultrablue Is and Freelight LEDs. Significant relationship between irradiance and temperature increase was detected (r=0.867; p<0.001). Hardness means (kg/mm2) varied between 40.1±3.6 and 92.7±6.6. Samples activated by the Freelight LED presented significantly lowerhardness than samples activated by the others units.

RESUMO

Este estudo caracterizou a luz emitida por uma unidade de fotoativação (UF) de lâmpada halógena de quartzo de tungstênio (HQT) e três diodos emissores de luz (LED) e investigou o aumento de temperatura e a dureza do compósito promovida por estas fontes. HQT XL2500 (3M ESPE), LED Freelight (3M ESPE), LED Ultrablue Is (DMC) e LED Cool Blue Wand (Milestone Scientific) foram as UF investigadas. A irradiância (mW/cm2) foi aferida com um medidor de potência e o espectro de luz obtido com um espectrômetro. O aumento de temperatura (ºC) foi registrado utilizando um termopar conectado a um termômetro digital, durante a fotoativação do compósito Filtek Z250 (3M ESPE). Os dadosforam submetidos à ANOVA e teste de Tukey (α=0,05). A dureza Knoop foi avaliada em diferentes profundidades docompósito (20, 1000 e 1980µm) e os dados submetidos à ANOVA de dois critérios, com parcelas subdivididas, e teste de Tukey (α=0,05). A correlação entre irradiância e aumento de temperatura foi investigada pelo teste de Pearson. Todas as UF apresentaram 95% da irradiância concentrada entre 400-515nm. Médias para aumento de temperatura variaram entre 1,05±0,16 e 2,74±0,27. O LED Cool Blue apresentou aumento significativamente maior de temperatura que as demais UFs, e a HQT promoveu aumento significativamente maior de temperatura comparada aos LEDs Ultrablue Is eFreelight. Correlação significativa entre irradiância e elevação de temperatura foi detectada (r=0,867; p<0,001). Médias de dureza (kg/mm2) variaram entre 40,1±3,6 e 92,7±6,6. Amostras ativadas pelo LED Freelight apresentaram dureza significativamente menor que amostras ativadas pelas demais unidades.