Ability of short exposures from laser and quad-wave curing lights to photo-cure bulk-fill resin-based composites

Abstract

This study investigated the ability of a laser, and a 'quad-wave' LCU, to photo-cure paste and flowable bulk-fill resin-based composites (RBCs). Five LCUs and nine exposure conditions were used. The laser LCU (Monet) used for 1s and 3s, the quad-wave LCU (PinkWave) used for 3s in the Boost and 20s in the Standard modes, the the multi-peak LCU (Valo X) used for 5s in the Xtra and 20s in the Standard modes, were compared to the polywave PowerCure used in the 3s mode and for 20s in the Standard mode, and to the mono-peak SmartLite Pro used for 20s. Two paste consistency bulk-fill RBCs: Filtek One Bulk Fill Shade A2 (3M), Tetric PowerFill Shade IVA (Ivoclar Vivadent), and two flowable RBCs: Filtek Bulk Fill Flowable Shade A2 (3M), Tetric PowerFlow Shade IVA (Ivoclar Vivadent) were photo-cured in 4-mm deep x 4-mm diameter metal molds. The light received by these specimens was measured using a spectrometer (Flame-T, Ocean Insight), and the radiant exposure delivered to the top surface of the RBCs was mapped. The immediate degree of conversion (DC) at the bottom, and the 24-hour Vickers Hardness (VH) at the top and bottom of the RBCs were measured and compared. The irradiance received by the 4-mm diameter specimens ranged from 1035mW/cm2 (SmartLite Pro) to 5303mW/cm2 (Monet). The radiant exposures between 350 and 500nm delivered to the top surface of the RBCs ranged from 5.3J/cm2 (Monet in 1s) to 26.4 J/cm2 (Valo X), although the PinkWave delivered 32.1J/cm2 in 20s 350 to 900nm. All four RBCs achieved their maximum DC and VH values at the bottom when photo-cured for 20s. The Monet used for 1s and the PinkWave used for 3s on the Boost setting delivered the lowest radiant exposures between 420 and 500 nm (5.3J/cm2 and 3.5J/cm2 respectively), and they produced the lowest DC and VH values. Despite delivering a high irradiance, the short 1 or 3-s exposures delivered less energy to the RBC than 20-s exposures from LCUs that deliver>1000mW/cm2. There was an excellent linear correlation (r>0.98) between the DC and the VH at the bottom. There was a logarithmic relationship between the DC and the radiant exposure (Pearson's r=0.87-97) and between the VH and the radiant exposure (Pearson's r=0.92-0.96) delivered in the 420-500 nm range.