SDR flow+ in Practice: Where a 4 mm Flowable Base Helps and Where It Doesn't

SDR flow+ is a bulk-fill flowable composite from Dentsply Sirona designed to sit at the base of a posterior cavity and be placed in a single 4 mm increment instead of the usual 2 mm. Rather than a finishing material, it is a stress-relieving base: a polymerization modulator built into the resin backbone slows the gel phase so a thick flowable layer can cure without pulling hard on the cavity walls. For a practice, the appeal is time and control, fewer increments in a deep restoration and less shrinkage stress at the bonded interface. This review covers how SDR flow+ manages that stress, where it performs, where it does not, and what the published evidence supports.

The material belongs to the flowable bulk-fill category that changed how deep posterior cavities are layered, and it sits within the broader comparison of dental composites alongside sculptable and conventional systems. Understanding the chemistry is the key to using it well, because the same modulator that allows a 4 mm base is also the reason it needs a sculptable material over the top.

Material science: how SDR flow+ works

Every composite shrinks as it polymerizes, and the stress that shrinkage sends to the bonded interface is what drives marginal gaps, postoperative sensitivity, and debonding. SDR flow+ addresses this with a modified urethane dimethacrylate that carries a photoactive group inside the polymer chain. That group slows network formation during the gel phase, giving the material more time to flow and relax before it locks up. The result is lower shrinkage stress at a comparable degree of conversion, which is what lets the manufacturer clear it for 4 mm bulk placement rather than the 2 mm limit that governs most composites. Because it is a flowable, it also self-levels and adapts to the cavity floor without the voids that a packable material can trap in a deep box.

Clinical indications for SDR flow+

SDR flow+ is indicated as a dentin-replacement base under a conventional or sculptable bulk-fill composite in Class I and Class II cavities. It is at its best in deep posterior restorations where incremental layering is slow and where shrinkage stress is the main concern, particularly cavities with a high configuration factor and a hard-to-reach floor. It is also useful as a base under Class V and as a liner where a self-leveling first layer improves adaptation. It is not indicated as a standalone occlusal surface, because its wear resistance is not built for direct occlusal contact, and it is not a substitute for a shade-controlled sculptable composite in the esthetic zone.

Step-by-step placement protocol

1. Prepare and isolate. Standard cavity preparation and isolation, then apply and cure the adhesive per its own protocol.
2. Dispense the base. Place SDR flow+ into the base of the cavity in a single increment up to 4 mm and let it self-level.
3. Cure. Light cure for 20 seconds with an output at or above 550 mW per square centimeter, longer for lower-output lights.
4. Add depth if needed. For cavities deeper than 4 mm, place and cure a second increment.
5. Cap the occlusal layer. Place a conventional or sculptable bulk-fill composite over the occlusal 2 mm, contour, and cure.
6. Finish and polish. Finish and polish the capping layer as normal. The base is never the working surface.

Clinical evidence: what the literature shows

According to PubMed, the published evidence points consistently toward lower stress and sound clinical performance. A laboratory comparison of bulk-fill materials measured shrinkage stress and volumetric shrinkage and placed SDR among the lower-stress materials in the group (Attik et al., 2021; PMID 34961643). A micro-CT study of shrinkage vectors reported that a thick flowable liner produced smaller overall shrinkage vectors than a thin one, with SDR yielding slightly smaller vectors than the comparison flowable (Kaisarly et al., 2021; PMID 33506426). Clinically, a 24-month randomized trial of flowable bulk-fill composites in Class III cavities found a 100 percent overall success rate for SDR flow+ and the two comparison materials, with only minor differences in marginal and surface criteria between them (Signore et al., 2024; PMID 38496810). The pattern is clear: a stress-relieving flowable base placed in adequate thickness manages the shrinkage load and holds up in service, provided it is capped and cured correctly.

Handling advantages and limitations

The main advantage is workflow. A single 4 mm increment replaces two or three layers at the base of a deep cavity, the material self-levels without voids, and the lower shrinkage stress is reasonable insurance against postoperative sensitivity. It flows into line angles and around a matrix in ways a packable base cannot.

The limitations follow from the same properties. SDR flow+ is a base, not a surface, so it always needs a sculptable cap over the occlusal 2 mm, and skipping that cap exposes a flowable to occlusion it is not built for. A thick increment is also easy to undercure with a weak or poorly positioned light, so curing time and light output matter more here than with a thin layer. Its shade options are limited, which is a non-issue under a cap but rules it out as a visible surface.

Procurement and inventory considerations

SDR flow+ is a single stock item that serves across most deep posterior work, so it rationalizes inventory rather than adding to it. It comes in compula tips and syringes through the major distributors, and because it is one SKU it is straightforward to compare on price across suppliers before committing to a refill cycle. Shelf life is standard for a light-cured resin, so match order volume to how many deep restorations the practice actually places, since a base used on every deep cavity moves faster than a specialty shade.

SDR flow+ vs alternatives

Against layering a sculptable composite from the floor up, the trade-off is speed and stress control versus surface durability, so the sensible pattern is SDR flow+ as the base with a sculptable cap rather than one or the other. Against other flowable bulk-fills such as Filtek Bulk Fill Flowable or a sculptable bulk-fill like Tetric EvoCeram Bulk Fill placed alone, the evidence shows broadly comparable clinical success, so the choice tends to come down to handling preference, depth of cure with your light, and price. For a practice doing frequent deep Class I and Class II restorations, a stress-relieving base earns its place; for mostly shallow work that a single 2 mm layer already covers, it adds a step without adding much.

Summary

SDR flow+ earns its place by cutting increments and shrinkage stress at the base of deep posterior cavities, and the evidence supports both the lower stress and sound 24-month clinical performance. It is not a universal composite, since it needs a sculptable cap for occlusal wear and offers nothing for anterior esthetics. Used where its mechanism is an advantage, in deep cavities with a demanding configuration factor, it speeds up the restoration and protects the margin without sacrificing the result. For most practices the sensible move is to keep it as the standing base for deep posterior work and reach for a full sculptable layer only when the cavity is shallow enough not to need it.

References

Attik N, Colon P, Gauthier R, et al. Comparison of physical and biological properties of a flowable fiber reinforced and bulk filling composites. Dent Mater. 2021;38(2):e19-e30. PMID: 34961643.DOI: 10.1016/j.dental.2021.12.029

Kaisarly D, Meierhofer D, El Gezawi M, et al. Effects of flowable liners on the shrinkage vectors of bulk-fill composites. Clin Oral Investig. 2021;25(8):4927-4940. PMID: 33506426.DOI: 10.1007/s00784-021-03801-2

Signore A, Solimei L, Arakelyan MG, et al. A 24-month randomized clinical study of flowable bulk-fill resin composites in Class III restorations. J Clin Exp Dent. 2024;16(2):e111-e123. PMID: 38496810.DOI: 10.4317/jced.61153