Bulk Fill composites: Considerations and keys to success

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6. Know the flow.

Rheology is an important feature of every dental composite, bulk fills included. The viscosity of the material can have a distinct impact on a number of variables, including adaptation, handling, mechanical strength and shrinkage stress. In addition, how the material thins or thickens during shear and application can impact the adaptation, as well as the composite’s ability to shape and sculpt for final anatomy.

While bulk fill composites come in many different viscosities, they’re generally classified as either low or high viscosity – each with their own set of strengths, weaknesses and ideal preparation techniques. High-viscosity bulk fills tend to be strong, thick and packable or shapeable, but have a reputation of poor adaptation and higher stress. On the other hand, low-viscosity bulk fill (or flowable composites), are more fluid and therefore adapt better, but often at the expense of mechanical and wear properties.
Keep in mind that these pros and cons aren’t hard and fast rules – and certain materials properties can be altered with techniques such as using a composite warmer or selecting a different delivery method.

In fact, some bulk fill materials feature delivery systems that take advantage of the material’s thixotropic, or shear thinning, properties. That is, their viscosity temporarily decreases during the shear induced by extrusion and flows into the cavity preparation, for improved adaptation and fewer voids – without compromising mechanical properties. Depending on the material, this viscosity may increase again relatively rapidly to allow for shaping and sculpting of the material. Make sure your material’s viscosity and delivery method are working together to help give you the best result possible.

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