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

Abstract

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.

Investigation of the effect of different application techniques on microhardness in bulk-fill composite resins

“…The incremental technique has long been accepted as the gold standard for inserting composite resin into the cavity to reduce shrinkage stress. (28). Sarret (29) and Campodonico et al (30) noticed that reducing the layering and using the bulk technique may result in successful applications.…”

“…Winkler et al (31) reported that the layering technique does not have an advantage over the bulk technique when approximal stresses are taken into consideration. It is important for the longevity that the composite resin restorations are polymerized sufficiently (27) to give the polymerization reaction a sufficient hardness level (28). In this study, teflon molds that absorb much less light and allow the light emitted from the light device to pass deeper were used during the preparation of the samples, and the microhardness values were measured after the specimens were kept in distilled water for 24 hours.…”