Bulk Fills: Getting a Higher Depth of Cure Than You Might Expect

Bulk-fill composites offer the convenience of thicker layering at four or five millimeters and curing in one step for restorative work. Nevertheless, some dentists do not trust these materials to achieve the proper depth of cure. However, Nanomaterials published a study in May suggesting bulk-fills outperformed conventional composites for depth of cure.

Achieving depth of cure is always essential with restorative dentistry. Composites have less biocompatibility, decreased mechanical properties, and increased residual monomer content when curing is incomplete. Also, the restoration's clinical performance changes esthetically through surface staining and increased risk of marginal leakage. Therefore, the curing technique is critical.¹

To achieve the depth of cure for a resin-based composite, the material requires a specific amount of light energy at the proper wavelength (which matches the wavelength of the photoinitiator in the material). Therefore, dental teams must use the correct diameter for the curing tip, hold the curing tip at the proper distance and angle from the material and cure long enough to deliver this light energy.²

The material you use also contributes to your success in achieving depth of cure—and bulk fills might be the right materials choice for some cases. In 2017, a literature review in The Journal of Adhesive Dentistry suggested that bulk fills were different than conventional composites because of their increased depth of cure, attributed to an increase in the material's translucency. However, the researchers also said bulk fills need more clinical studies that would further examine the benefits of bulk-fill composites.³

What Did the 2022 Study Find?

The researchers for the Nanomaterials study evaluated and compared the depth of cure between bulk fill and conventional composites. They defined depth of cure as "the thickness of resin that can be converted from monomer to polymer under a specific light-curing condition."⁴ The researchers hypothesized that there would be no statistical difference between the compared materials regarding the depth of cure, but they were wrong.⁴

The five materials compared included:⁴

• Filtek™ Bulk Fill Restorative (3M™)
• Tetric® EvoFlow® Bulk Fill (Ivoclar Vivadent)
• G-ænial™ Universal Injectable (GC Europe)
• Filtek Supreme XTE Flowable Restorative (3M)
• G-ænial Flo X (GC Europe)

The researchers discovered that the two bulk fills had a much higher depth of cure than the control materials and the universal injectable. The depth of cure for the bulk fills, Filtek and Tetric EvoFlow had an average of 4.24mm compared to 3.02 for G-ænial Universal Injectable and 2.58 for Filtek Supreme XTE and G-ænial Flo X.⁴

The researchers suggest bulk fills proved suitable for their four-millimeter layers, at least in vitro. Using this technique, dentists can save time and energy by restoring deep and wide posterior cavities. Also, the placement technique is not as operator sensitive as conventional composite. In addition, bulk-fills present a lower risk of contamination during placement, reducing the risk of secondary caries.⁴

The researchers concluded that bulk fills, especially flowable formulations, were an excellent alternative to conventional composites because they featured reduced working time and more straightforward handling. When combined with excellent physical properties, particularly regarding the depth of cure and shrinkage stress, these materials represented an amazing combination of esthetics and longevity. In particular, the researchers thought these materials would be helpful in pediatric dentistry, where lack of compliance and dental anxiety often play a role.⁴

How Manufacturers Increase Depth of Cure in Bulk Fills

Manufacturers have a few ways to increase the depth of cure for these thicker layers of materials. Increasing translucency is one way. By reducing the filler content and expanding the filler size, manufacturers reduce the scatter from the curing light when it hits the material, allowing more of the light to penetrate and cure the material.⁵

However, the same thing that makes bulk fills great for achieving depth of cure can be why clinicians do not want to use them. Too much translucency can mean not enough esthetics.

However, manufacturers have responded by increasing the material's opacity without compromising the depth of cure. For example, 3M Filtek ONE Bulk Fill Restorative material leverages nanofiller technology to influence when the material is translucent and opaque to achieve a more excellent opacity without compromising the depth of cure.

Some manufacturers also add additional photoinitiators to help with the depth of cure. For example, Ivoclar Vivadent's Tetric EvoCeram® Bulk Fill employs its proprietary photoinitiator Ivocerin which allows polymerization in larger increments than camphorquinone and other conventional photoinitiators.⁵

Dual-Cure Bulk Fills help achieve the depth of cure, too. Dual cure refers to composites that combine chemical and light cure polymerization to achieve the depth of cure. For example, Zest Dental Solutions BulkEZ Plus™ and Parkell's HyperFIL® bulk-fills use a dual-cure formulation. The Brazilian Dental Journal found that both of these dual-cure composites improved the depth of cure of bulk-fill restorations in a study published in the fall of 2021.⁶

Bulk fills are materials designed to save time with the composite placement process. But not everyone believes in them.

However, researchers are proving that manufacturers’ enhancements to the materials enable bulk-fill composites to do what the manufacturers claim. As the studies from Nanomaterials and other journals indicate, bulk-fills unique depth of cure performance reduces the risk for some typical dental composite restoration problems associated with uncured materials.⁴

References

1. de Camargo EJ, Moreschi E, Baseggio W, Cury JA, Pascotto RC. Composite depth of cure using four polymerization techniques. J Appl Oral Sci. 2009;17(5):446-450. doi:10.1590/s1678-77572009000500018
2. Dental curing lights. American Dental Association. Updated May 5, 2021. Accessed November 8, 2022. https://www.ada.org/resources/research/science-and-research-institute/oral-health-topics/dental-curing-lights
3. Van Ende A, De Munck J, Lise DP, Van Meerbeek B. Bulk-fill composites: A review of the current literature. J Adhes Dent. 2017;19(2):95-109. Accessed November 9, 2022. doi:10.3290/j.jad.a38141
4. Ludovichetti FS, Lucchi P, Zambon G, et al. Depth of cure, hardness, roughness and filler dimension of bulk-fill flowable, conventional flowable and high-strength universal injectable composites: an in vitro study. Nanomaterials (Basel). 2022;12(12):1951. Published 2022 Jun 7. doi: 10.3390/nano12121951
5. TaughtWell SimplifyEd Youtube page. Accessed November 9, 2022.  https://www.youtube.com/watch?v=hevsfrQeA0w
6. Fraga MAA, Correr-Sobrinho L, Sinhoreti MAC, Carletti TM, Correr AB. Do dual-cure bulk-fill resin composites reduce gaps and improve depth of cure. Braz Dent J. 2021;32(5):77-86. doi:10.1590/0103-6440202104497