The degree of conversion and class II cavity microleakage of different bulk fill composites placed with different restorative techniques

Objectives

The current study aimed to investigate the degree of conversion and microleakage of bulk fill composites placed using different restorative techniques.

Materials and methods

Four types of resin composites were used: Incrementally-placed Filtek Z350 XT (INC), Filtek Bulk Fill Posterior Restorative (B), Filtek Bulk Fill Flowable (F), 3M ESPE, United States, and SonicFill (SON), Kerr, United States. For the degree of conversion (DC) test, five cylindrical samples were prepared for each group (5 mm diameter and 5 mm depth) (n = 5). Five groups, representing different material-technique combinations, were investigated: Group (INC) in which the incremental technique was used for packing Z350 composite (control), Group (B) in which Filtek Bulk Fill Posterior Restorative was placed as a one 5 mm deep increment, Group (FB-1C) in which Filtek Bulk Fill Flowable was used to fill 2 mm in the base of the mold followed by 3 mm Filtek Bulk Fill Posterior Restorative on top of it then both materials were cured simultaneously, Group (FB-2C) in which 2 mm of Filtek Bulk Fill Flowable was placed at the base of the mold and cured then the rest of the mold was filled with Filtek Bulk Fill Posterior Restorative followed by a final cure, and finally Group (SON) in which SonicFill composite was placed as a one 5 mm increment. The DC of both top and bottom surfaces of each sample was measured using Fourier-transform infrared spectroscopy-Attenuated Total Reflectance (FTIR-ATR). Forty-five extracted human premolars were used for the microleakage assessment. One or two class II slot cavities, with standardized dimensions, were prepared in each tooth. Each of the five investigated groups was represented by 11 cavities (n = 11). The cavities were filled using the same composite material-technique combinations used for the DC test. The restored teeth were thermocycled then immersed in 2% methylene blue solution for 24 h at 37 °C. Dye penetration was assessed by examining longitudinal mesio-distal sections through the restored teeth using a stereomicroscope at 25× magnification. The microleakage was scored using predetermined scoring criteria. The results were statistically analyzed.

Results

The (INC) group showed significantly higher DC for the top surface than all bulk fill groups. No significant difference was found between the (INC), (FB-1C) and (FB-2C) groups regarding the DC of the bottom surface and the three groups had the highest DC while the (SON) group had the lowest DC values. Comparing the top and bottom surfaces of each single group, only the (FB-1C) and (FB-2C) groups showed a significant difference. No significant difference was found between the microleakage scores of the five investigated groups.

Conclusions

Conventional incrementally-placed composite has a higher DC compared to all bulk fill types regardless of the technique used for the bulk fill composite. The sonic-activated composite exhibits lower DC of the bottom composite surface than all other bulk fill composites. Regarding the microleakage, bulk fill composites, used with any of their possible techniques, do not perform any inferior compared to incremental composites.