Abstract
ObjectivesThis investigation evaluated the effect of flowable liners beneath a composite restoration applied via different methods on the pattern of shrinkage vectors.MethodsForty 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.ResultsThe 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.ConclusionsThick flowable liner layers had a more pronounced stress-relieving effect than thin layers regardless of the flowable liner type.Clinical relevanceIt is recommended to apply a flowable liner (thin or thick) beneath bulk-fill composites, preferably incrementally.
Highlights
The polymerization reaction of dental resin composites is always accompanied by polymerization shrinkage, which leadsThe application of a flowable liner beneath a composite restoration was introduced when the adhesives were unfilled, i.e., applied in a very thin layer [7, 8]
Thicker layers of flowable liner resulted in smaller shrinkage vectors than thinner layers of flowable liner, except when the covering composite was applied in increments
Our findings show that when a flowable liner was applied, smaller shrinkage vectors were obtained in the flowable liner and the following increment(s) which might be related to the relative elasticity of the intermediate flowable composite layer
Summary
The application of a flowable liner beneath a composite restoration was introduced when the adhesives were unfilled, i.e., applied in a very thin layer [7, 8]. An intermediate flowable liner reduces the polymerization shrinkage stresses at the bonded interface [9, 10]. An intermediate flowable liner below a composite restoration results in an interfacial stress-absorbing layer. In vivo studies have not detected improved composite restoration performance with an intermediate layer of flowable liner [12,13,14,15]. Marginal gaps and other differences at a smaller scale could only be quantified by in vitro experiments
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