Flowable composite is a resin-based dental material with lower viscosity, allowing it to flow easily into small, intricate areas within a tooth preparation. This fluid characteristic makes it suitable for specific applications in dental practice. Introduced in the 1990s, it expanded options for dental restorations.
Material Characteristics
Flowable composites are engineered from a blend of resin monomers, such as Bis-GMA and TEGDMA, combined with inorganic filler particles and various additives. The resin matrix provides the material’s structural base, while filler particles, typically silica or glass, contribute to its mechanical properties. A defining feature is their lower filler content, generally 37-53% by volume or 56-70% by weight, which directly influences their viscosity. This reduced filler load results in a more fluid consistency compared to traditional composites.
Lower filler content, while providing superior flowability, impacts other material properties. Flowable composites exhibit lower compressive strength and wear resistance compared to traditional composites. They possess a modulus of elasticity similar to natural tooth structure, which helps minimize stress at the tooth-restoration interface. Radiopacity allows the material to be visible on X-rays, aiding in detecting secondary decay or restoration margins. Flowable composites meet or exceed the radiopacity of dentin, due to radiopaque elements in their fillers.
Polymerization shrinkage is an inherent characteristic of resin-based composites, where the material contracts as it hardens. Flowable composites exhibit an average volumetric polymerization shrinkage rate around 5%, which is higher than some traditional composites. However, their lower rigidity helps counteract the stresses created by this shrinkage. Manufacturers continually develop newer formulations to improve mechanical properties and minimize shrinkage while maintaining desirable flow characteristics.
Distinctions from Traditional Composites
Flowable composites differ from traditional, or packable, composite resins primarily in handling characteristics and mechanical properties. Traditional composites have a higher filler load, giving them a thicker, putty-like consistency that can be condensed into a cavity. This higher filler content contributes to greater compressive strength and wear resistance, making them suitable for areas subjected to heavy chewing forces. In contrast, flowable composites, with their lower filler content, exhibit lower viscosity, allowing them to flow easily.
The difference in viscosity directly impacts their adaptability to cavity walls and intricate tooth anatomies. Flowable composites excel at wetting the tooth surface and penetrating small crevices, providing excellent adaptation. Traditional composites, being stiffer, require more force during placement to achieve proper adaptation. While traditional composites offer superior mechanical strength for large, stress-bearing restorations, flowable composites have lower mechanical properties. This means flowable materials are not recommended for high-stress bearing areas unless used as a liner or base.
Clinical Applications
The unique flowable nature of these composites makes them well-suited for various dental procedures. They are commonly used as a cavity liner or base under larger composite restorations. Their ability to flow and adapt intimately to the prepared tooth surface helps seal the dentin, which reduces microleakage and post-operative sensitivity. This creates a smooth interface between the tooth and the overlying restorative material, enhancing restoration longevity.
Flowable composites are also chosen for restoring small Class I fillings, involving pits and fissures on chewing surfaces, and for Class V cervical lesions near the gum line. Their low viscosity allows for precise placement in these small or shallow preparations. They are widely used as pit and fissure sealants, flowing deeply into molar grooves to create a protective barrier against decay. Flowable composites have comparable retention rates as sealants compared to conventional resin-based sealants.
Flowable composites are used for repairing minor defects in existing composite or ceramic restorations. Their ability to seamlessly blend with existing material and good polishability contribute to aesthetic outcomes. They are also employed for cementing ceramic veneers, where their thin consistency allows for even distribution and minimal thickness under the restoration.
The Placement and Curing Procedure
The application of a flowable composite follows a sequence to ensure proper adhesion and hardening. First, the dentist prepares the tooth by removing decay and shaping the cavity. For deeper preparations, a calcium hydroxide liner or glass ionomer base is placed to protect the pulp. The tooth surface is then etched with phosphoric acid gel to create a microscopic roughened surface for better bonding.
After rinsing the etching gel and drying the tooth, a dental bonding agent is applied to the etched surface. This adhesive layer is air-thinned and then light-cured, preparing the tooth for the composite. The flowable composite is then directly injected into the prepared cavity. The dentist dispenses the material along the margins and into any recesses, in layers no deeper than 2-3 mm to ensure thorough curing.
Once the flowable composite is placed and shaped, a specialized blue “curing light” hardens the material through photopolymerization. The light activates photoinitiators within the composite resin, causing it to polymerize and solidify. Curing time varies per layer. Following hardening, the restoration is finished and polished using standard dental burs and polishing instruments to achieve a smooth surface and proper bite.