Evaluation of effect of polymerization time on curing depth of various bulk fill composites- An in vitro study

ABSTRACT

Objectives: From the time composite has been developed, it has been subjected to various changes in composition like addition of filler and initiators to yield better result. One such modification is the new bulk fill composite. However an acceptable polymerization time to maintain adequate curing depth has to be evaluated. So the aim of this in vitro study was to evaluate the effect of polymerization time on curing depth of four bulk fill flowable composites. Methods: Total of 80 cylindrical specimens were prepared, and divided into 4 groups comprising of 20 specimens in each group. These selected groups were again subdivided into 4 groups comprising of 5 specimens in each group, based on their polymerisation time. The four specimens were Group A SDR flow (DENTSPLY), Group B Tetric N' Flow (Ivoclar Vivadent), Group C Filtek bulk fill (3M) and Group D Venus bulk fill (Heraeus Kulzer).The aluminium mold of 4mm depth and 5mm diameter was filled with composite and top surface was irradiated using Valo LED curing light with polymerisation time of 10, 20, 40, and 60seconds on respective subgroup.The microhardness of top and bottom surfaces were performed using Vickers Hardness tester under the load of 200gram for 15seconds. The depth of cure of each specimen was determined by hardness ratio method using the formula Hardness ratio=VK of bottom surface/VK of top surface.The results were statistically analysed. Results: The study results showed that all the tested bulkfill composites can be cured to an acceptable depth. Tetric N' Flow exhibits maximum curing depth (95.28 ±0.26) at 10sec polymerisation time. Venus bulk fill showed higher depth of cure at 20 and 40sec curing time (96.79±0.39 and 97.56±0.20). SDR flow showed adequate curing depth at 20 and 40sec curing time (92.94±0.49and 93.62±0.22 respectively). Filtek bulk fill has maximum depth of cure at 40sec curing (89.10±0.79). Conclusion: Increasing polymerisation time increases the top as well as bottom micro-hardness of all tested bulk fill composites. Tetric N' Flow maximum curing depth at 10sec curing time. Filtek bulk fill is the material with least depth of cure.