Effect of different initial light intensity by the soft-start photoactivation on the bond strength and Knoop hardness of a dental composite

Abstract

This study evaluated the bond strength (push-out method) and Knoop hardness of Z250 composite resin, photoactivated with XL 2500 curing unit, using different protocols: continuous mode (700 mW/cm(2) for 20s) (CO); soft-start (50 mW/cm(2) for 5 s, followed by 700 mW/cm(2) for 15 s) (SS1); soft-start (100 mW/cm(2) for 5 s, followed by 700 mW/cm(2) for 15 s) (SS2); soft-start (150 mW/cm(2) for 5 s, followed by 700 mW/cm(2) for 15s) (SS3); soft-start (200 mW/cm(2) for 5s, followed by 700 mW/cm(2) for 15s) (SS4); soft-start (250 mW/cm(2) for 5 s, followed by 700 mW/cm(2) for 15 s) (SS5); soft-start (300 mW/cm(2) for 5 s, followed by 700 mW/cm(2) for 15 s) (SS6). For the push-out test, the specimens were tested in a universal testing machine at a crosshead speed of 0.5 mm/min. For the hardness test, the specimens were polished for the hardness measurements, using a 50 g load for 15 s. Data were submitted to ANOVA and Tukey's test (alpha=5%). The results of bond strength showed that the SS3 group obtained the highest bond strength when compared to the CO group. There were no significant differences among the other modes in relation to the other groups. Regarding the other results in hardness, there were no significant differences among the groups in the surface region and up to 4 mm depth.

Effect of the photoactivation method on composite resin cure.

“…Corroborating these results, Camargo et al 7 when comparing the hardness after 4 photoactivation methods (stepped, ramped, pulse-delay and continuous conventional) in 4 different thicknesses (0.1, 1, 2 and 4 mm), also observed that at thicknesses of up to 2 mm, all the techniques presented satisfactory polymerization. Statistically significant differences were also observed in a study by Dalli'Magro, 33 in which they observed a decrease in hardness after a 3-mm thickness, in all the groups, when compared with the hardness on the top.…”

“…The soft start technique has low initial intensity in the first few seconds, followed by full intensity. 8 The pulse-delay technique begins with slow polymerization, unleashed after an initial pulse, followed by a waiting period, before final activation with high intensity to complete the polymerization. [9][10] There are few studies evaluating the effectiveness of these techniques on the irradiated opposite surface.…”

Impact of refrigeration on the surface hardness of hybrid and microfilled composite resins

“…These results suggest that the refrigeration allowed a behavior of the composite resin similar to the "soft start polymerization method" because, the low temperature could have proportioned less monomer mobility, decreasing the reaction velocity and providing an extension of the pre-gel phase without decreasing hardness values (20).…”

Characterization of water sorption, solubility and filler particles of light-cured composite resins

“…The characterization and evaluation of resinbased material properties are assessed by flexural strengths, elasticity modulus, degree of conversion, hardness, wear resistance, polishability and other investigations (2,3,(5)(6)(7)(8)(9)(10). Water sorption and solubility are important properties of composite resins and influence their strength, abrasion resistance, volume and color…”