What Is A Composite?
Resin composites consist of four parts:
The organic polymer matrix usually consists of dimethacrylate. The inorganic filler particle can be finely ground quartz or glass, or other materials. These provide a number of characteristics, including reinforcing the matrix, allowing for translucency, and controlling the amount of shrinkage when cured. The coupling agent is known as silane, and its responsibility is to form a bond between the organic and inorganic phases of the composite. The initiator-accelerator system is what allows for the hardening of the composite when a light is placed on it – this is due to a chemical known as camphorquinone that absorbs light (ideally at 465nm) which triggers the reaction.
As the composite is subjected to light, a reaction known as polymerization occurs. This is important – during polymerization, a reduction of volume of the composite occurs, and shrinkage results. Shrinkage is a big deal when understanding and respecting our dental materials, and it can allow for small leaks into the preparation if the materials are not used properly. There are a few ways manufactures have limited this polymerization shrinkage in their materials, including using pre-polymerized resins, maximizing the amount of filler, and using methacrylate that has a high molecular mass. These are important details about the characteristics regarding composites that will help us understand the differing properties of bulk flow and traditional composites¹.
How Do We Measure The Effectiveness Of Composites?
There are numerous ways to measure the physical properties of composites, and although we touched on polymerization shrinkage above, we can dive into a few of those properties now.
What’s The Big Deal About Bulk-Fill, Anyway?
Now that we understand a bit about how composites are characterized, let’s talk a bit about the background of bulk-fill composites. Bulk-fill composites are a type of resin-based composite that claim to be light-curable in increments of 4-10 mm. Normally, traditional composites only allow a depth of cure maximum of 2 mm thickness. The reason traditional composites can only be cured at depths of 2 mm is due to polymerization shrinkage – the shrinkage increases as the thickness increases (remember, we want polymerization shrinkage to be low so there is a tight seal between our restoration and preparation). Bulk-flow composites have claimed to not adversely affect polymerization shrinkage while allowing for larger depths of curing². In this post, we are going to explore the studies that compare polymerization shrinkages, as well as strengths and other properties, between bulk-fill composites and traditional composites.
So What Does The Research Say?
If you’ve made it this far into the post, you know that dental materials have a lot of jargon and can be a bit confusing. Let’s try and sift through some of the details and find out which material has the advantage over the other.
The mechanical properties of the bulk-fill composites were mostly lower compared with the conventional high viscosity material, and, at best, comparable to the conventional flowable composite.Physico-mechanical characteristics of commercially available bulk-fill composites, Leprince et al, 2014
¹Sakaguchi, R., Powers, J. (2012). Craig’s Restorative Dental Materials, 13th Edition. [VitalSource Bookshelf 9.4.0]. Retrieved from vbk://978-0-323-08108-5
²Balkaya, H., Arslan, S., & Pala, K. (2019). A randomized, prospective clinical study evaluating effectiveness of a bulk-fill composite resin, a conventional composite resin and a reinforced glass ionomer in Class II cavities: one-year results. Journal of applied oral science : revista FOB, 27, e20180678. https://doi.org/10.1590/1678-7757-2018-0678
³Chesterman, J., Jowett, A., Gallacher, A. et al. Bulk-fill resin-based composite restorative materials: a review. Br Dent J 222, 337–344 (2017). https://doi.org/10.1038/sj.bdj.2017.214
⁴Nagi, S. M., Moharam, L. M., & Zaazou, M. H. (2015). Effect of resin thickness, and curing time on the micro-hardness of bulk-fill resin composites. Journal of clinical and experimental dentistry, 7(5), e600–e604. https://doi.org/10.4317/jced.52536
⁵El-Damanhoury, H., & Platt, J. (2014). Polymerization shrinkage stress kinetics and related properties of bulk-fill resin composites. Operative dentistry, 39(4), 374–382. https://doi.org/10.2341/13-017-L
⁶Nascimento, A. S., Rodrigues, J., Torres, R., Santos, K. O., Fook, M., Albuquerque, M. S., Lima, E. A., Filgueira, P., Santos, J., Oliveira, L., & Braz, R. (2019). Physicomechanical and thermal analysis of bulk-fill and conventional composites. Brazilian oral research, 33, e008. https://doi.org/10.1590/1807-3107bor-2019.vol33.0008
⁷Leprince, J. G., Palin, W. M., Vanacker, J., Sabbagh, J., Devaux, J., & Leloup, G. (2014). Physico-mechanical characteristics of commercially available bulk-fill composites. Journal of dentistry, 42(8), 993–1000. https://doi.org/10.1016/j.jdent.2014.05.009
The medical advice given in this blog should only be utilized by a medical professional who has received a medical degree. I am not responsible for the medical advice given in this blog and each case should be reviewed extensively with sources outside my blog. This blog is for education purposes only and is not meant as a substitute for an academic institution.