Effect of light curing protocol on degree of conversion of composites

Abstract

Objective. To evaluate the degree of conversion (DC) of two light-cured composites with different protocols of light curing. Materials and methods. One hundred and ninety two specimens (n = 8) were prepared (5 mm  2 mm) according to experimental groups: two composite resins (Filtek Supreme and four seasons); three light curing protocols [20 s with the tip of the light curing unit (LCU) device touching composite surface (C); 20 s with the tip of the LCU at 8 mm distant from composite surface (D); and tip of the LCU at 8 mm distant from composite surface and polymerization time required to obtain a radiant exposure of 16 J/cm 2 (DS)]. Four LCUs (Bluephase 16i, Ultralume LED 5, XL 3000 and Optilux 501C) were used. DC of the bottom and top surface of specimens were measured using a FTIR spectrometer. Data were statistically analyzed by 3-way split splot ANOVA and Tukey's test (alpha = 0.05). Results. The results showed that DC of the top surface was higher than the bottom at all experimental conditions (p < 0.0001). Overall, the curing at 8 mm of distance did not affect conversion rate on the top surface (p > 0.05), but bottom surfaces showed DC reduction (p < 0.05). The highest monomer conversion values were observed for C and DS situations. Conclusion. The distance between the LCU and material surface and radiant exposure can affect the DC. Polymerization at distance should be performed with curing units with higher light power and/or extended exposure time.

Diferencia en la dureza de resinas utilizadas convencionalmente al polimerizarse con diferentes tipos de luz

“…En la tabla 6 se observa el mas alto promedio (90,94) obtenido en el grupo 5 (Filtek® Supreme XT + Optilux® 501 Rampa + incremental) seguido por el grupo 6 (filtek supreme+-bloque+rampa) y 15(filtek Z350+increm+opti501) y el valor mas bajo lo exhibió el grupo19 (Tetric® N Ceram + LED Bluephase® + incremental) corroborando los resultados del primer análisis; en cuanto al análisis de dureza profunda con la prueba ANOVA multifactorial se encontraron diferencias estadísticamente significativas en Discusión Se usó la tonalidad de resina A1 para, permitir una adecuada penetración de la luz y lograr una polimerización más rápida (19). Se mantuvo una distancia constante de 0,5 mm entre la luz y la resina para no generar diferente coeficiente de conversión de polimerización (CCP) y NDV (20); cuando la distancia desde la luz es modificada se afectan las propiedades mecánicas del material, aumenta el monómero residual y puede irritarse el complejo dentinopulpar comprometiendo la longevidad de la restauración (21,22).…”

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

“…The incremental insertion technique (increment no more than 2 mm thick) favors the preservation of the tooth/restoration interface [14] and requires the lightactivation of a subsequent layered increment. It is known that the distance between LCU and material surface and radiant exposure can affect the properties of the material [11] but it is unknown if the successive light-activation of the increments is capable of improving the properties of the material applied in the first increment. The present study was designed to answer this question and aimed the evaluation of the influence of light-activation of successive increments on microhardness and degree of conversion of the top and bottom surface of the first layered increment.…”

“…Although composites are the material of choice for direct restorations and in spite of the improvement that has been submitted since its development, some limitations and disadvantages still exist and are related to the limited depth of cure and the poor distribution of degree of conversion [10,11]. However, during the placement of composite by incremental layering technique, the first layered increment might receive extra energy from the light-activation of the subsequent increment and this process might positively affect the overall polymerization of the first increment.…”

Polymerization efficiency of bulk‐fill dental resin composites with different curing modes

“…These include the composition (monomers, fillers, photoinitiators, silane‐coupling agents), shade, and translucency of the composite and characteristics of the light‐curing unit (LCU), such as the light intensity, thermal emission, wavelength range, diameter of the tip, and curing mode . Other factors, such as the exposure time and distance of the restorative from the tip of the LCU also affect the depth of cure of these materials.…”