Effect of packing technique and curing time on the marginal sealing and surface hardness of two bulk-fill resin composites

Recent advances in dental resin based restorative materials have given rise to development of composites for bulk placement, to replace the need for incremental layering. Clinical consequences of microleakage are secondary caries, pulp inflammation, marginal discoloration, postoperative sensitivity, and the longevity of filling. Surface hardness is one of the mechanical properties of the restoration that should always be taken into account, particularly when they are faced with large areas of heavy masticatory forces. Accordingly, the current study was conducted to investigate the effect of packing technique and curing time on the marginal sealing and surface hardness of two bulk fill resin composites.
Standardized class II proximal box cavities were prepared on the mesial and distal surface of the selected premolar teeth with the total of 48 cavities. The prepared cavities were randomly divided into 2 main groups, 24 cavities each, according to the placement technique used for cavity restoration either placement of bulkfill single increment of 4 mm depth or incremental placement of two increments of 2 mm each. Each group was subdivided into 2 subgroups, 12 cavities each, according to the bulk fill composite resin used; X-trafil bulkfill composite and Quixfil bulkfill composite. These subgroups were then subdivided into two smaller groups, 6 cavities each, according to the curing times either curing for 10 seconds following the manufacturers’ instructions or curing for 20 seconds.
For all specimens, after bonding procedures, bulk-fill resin composites were manipulated and applied in cavities as the previously assigned methodology, specimens were then immersed in 2% methylene blue dye for 24 hours. Teeth were sectioned and viewed under a binocular stereomicroscope. Readings were recorded.
A total of 80 cylindrical resin composite specimens were prepared. samples were divided into 4 groups according to the type of bulk fill composite (X-tra fil or Quixfil) and irradiation time (10s or 20s). The resin composite was applied in the mold, covered with mylar strips and light cured using LED light curing unit with an intensity of 1200mW/cm2. Vickers Microhardness tester was used with microindentation carried out using a load of 500g. Three readings for each surface were taken and an average reading was calculated. X-trafil bulkfill composite showed significantly lower degree of leakage than Quixfil bulkfill composite. No significant difference in microleakage was shown between different curing times nor different application techniques. X-trafil bulkfill composite showed significantly higher microhardness than Quixfil bulkfill composite Curing for 10 seconds showed significantly higher microhardness. Bulk-fill single increment of 4 mm recorded significantly higher microhardness value. Within the limitations of the current study, we can conclude that 4-mm bulk fill packing of bulkfill composite resin, cured for 10 seconds, had adequate marginal sealing performance. Surface microhardness of bulkfill composite resin packed at 4-mm bulk fill, cured for 10 seconds, is acceptable.