All composite materials are a mix of organic resin matrix, filler particles and a coupling agent. The challenges we experience with composites like consistency and stickiness as well as characteristics like polymerization shrinkage, flexural strength and polishability are a result of the type and quantity of filler particles in relationship to the resin matrix. As the proportion of filler particles increase the physical properties of the material improves, but handling properties can be compromised. In a quest to create better composites with optimal physical properties and handling characteristics new advances have been made in filler particle science. As new categories of composites have come on the market some of the older types have continued to find applications and been preferred by some practitioners. With all the different types of composites on the market what should you use when, and do we have a universal material?
The different types of composite materials are grouped based on the characteristic of their filler particles. The original filled composites were macrofills, which contained larger size filler particles. The first microfill composite was available in the early 1970’s with much smaller filler particles. The change created a material with high polishability and low wear. However the size of the particles resulted in a material that is very stiff when filled beyond 35-50%. The low percentage of filler relative to the resin matrix required to allow handling of the material causes increased polymerization shrinkage and low flexural strength and fracture toughness. The next evolution was the creation of hybrid composites which feature micro particles as well as larger aggregate filler particles. The combination of small and large particles allows the material to be filled between 70-80% and still have workable handling. This higher filler percentage results in decreased polymerization shrinkage, increased flexural strength and fracture toughness. One challenge with hybrid composites is they lose their gloss and polish over time.
Microhybrid materials have multiple size filler particles, with the largest of them being smaller than in a traditional hybrid. These materials have improved polish ability over hybrids as well as reduced polymerization shrinkage. Microhybrids are best known for their improved physical properties of strength and fracture toughness. For years practitioners have used a microhybrid as the base of a restoration for it’s strength and low polymerization shrinkage and a top layer of microfill becasue of it’s easy polishability and the duration of this fine finish. The newest types of composites known as nanofills and nanohybrids have reduced the primary particle size from microns to nanometers. Nanohybrids have glass particles in addition to the nanofill particles. The goal was to develop a universal composite that had the strength and physical characteristics of a microhybrid combined with the polishability and esthetics of a microfill. Nanofills and nanohybrids are often referred to as universal composites, as they are designed to be used in both the anterior and posterior. For many practitioners this is true and the acceptable combination of handling and physical properties allow them to have one go to material. Other clinicians still use multiple types of composite based on the clinical situation. So do we have a universal composite? Many clinicians would answer yes, and others still quest for that magic combination of features.