Effects of flowable liners on the shrinkage vectors of bulk-fill composites

Abstract

Objectives This investigation evaluated the effect of flowable liners beneath a composite restoration applied via different methods on the pattern of shrinkage vectors. Methods Forty molars were divided into five groups (n = 8), and cylindrical cavities were prepared and bonded with a self-etch adhesive (AdheSe). Tetric EvoCeram Bulk Fill (TBF) was used as the filling material in all cavities. The flowable liners Tetric EvoFlow Bulk Fill (TEF) and SDR were used to line the cavity floor. In gp1-TBF, the flowable composite was not used. TEF was applied in a thin layer in gp2-fl/TEF + TBF and gp3-fl/TEF + TBFincremental. Two flowable composites with a layer thickness of 2 mm were compared in gp4-fl/TEF + TBF and gp5-fl/SDR + TBF. TEF and SDR were mixed with radiolucent glass beads, while air bubbles inherently present in TBF served as markers. Each material application was scanned twice by micro-computed tomography before and after light curing. Scans were subjected to image segmentation for calculation of the shrinkage vectors. Results The absence of a flowable liner resulted in the greatest shrinkage vectors. A thin flowable liner (gp2-fl/TEF + TBFbulk) resulted in larger overall shrinkage vectors for the whole restoration than a thick flowable liner (gp4-fl/TEF + TBF). A thin flowable liner and incremental application (gp3-fl/TEF + TBFincremental) yielded the smallest shrinkage vectors. SDR yielded slightly smaller shrinkage vectors for the whole restoration than that observed in gp4-fl/TEF + TBF. Conclusions Thick flowable liner layers had a more pronounced stress-relieving effect than thin layers regardless of the flowable liner type. Clinical relevance It is recommended to apply a flowable liner (thin or thick) beneath bulk-fill composites, preferably incrementally.

Assessing Fracture Resistance of Restored Premolars with Novel Composite Materials: An In Vitro Study

“…Shrinkage and voids during restoration in both conventional and bulk-fill composites are the major issues. In a recent study, it was found that by applying a thin or thick layer of flowable liner in an incremental way underneath Tertic EvoCeram bulk-fill restoration could act as a stress reliever [ 36 ]. In another study, Micro-CT was employed to evaluate the internal void in different bulk-fill composite restorations with different types of insertion techniques.…”

A Two-Year Comparative Evaluation of Clinical Performance of a Nanohybrid Composite Resin to a Flowable Composite Resin

“…The use of flowable composite resins has increased dramatically since their introduction in 1995; their main indication was as a base or liner under posterior composite resin restorations. Their fluidity ensures a perfect adaptation to the walls of the cavity, which reduces the risk of air trapping and the formation of voids; this helps to reduce stress at the margin of the restoration [ 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. Their composition consists of a reduction in the number of fillers from 20% to 25% and an increase in the monomeric diluents, which results in a decrease in viscosity and an improvement in fluidity.…”

Eighteen-month clinical performance of preheated nanoceramic resin-based composites in Class I occlusal cavities: A randomized clinical trial

“…using microcomputed tomography concluded that application of a flowable liner of thickness from 0.5 to 2 mm led to favorable shrinkage patterns and better adaptation to cavity walls, thus acting as stress reliever. [ 21 ]…”