August 2018
Volume 14, Issue 8

Are Nanocomposites Truly Universal?

Marcos Vargas, BDS, DDS, MS | Gaetano Paolone, DDS | K. William “Buddy” Mopper, DDS, MS

Marcos Vargas, BDS, DDS, MS, is a professor in the Department of Family Dentistry at the University of Iowa in Iowa City, Iowa.

Gaetano Paolone, DDS, is an adjunct professor of restorative dentistry at the Università Vita-Salute San Raffaele in Milan, Italy, and maintains a private practice in Rome, Italy.

K. William “Buddy” Mopper, DDS, MS, is the co-founder and chairman of Cosmedent as well as the director of the company’s Center for Esthetic Excellence.

Marcos Vargas, BDS, DDS, MS: My first reaction is to say yes, they can be used universally. Nanofill resin composites can be used in a large variety of situations, from small to medium size restorations in both the anterior and posterior areas, because they offer a good balance of physical properties to support the demands of function and wear. They have excellent esthetic properties that blend well with natural tooth structure, and they are easy to adapt, contour, and polish. However, the polish retention exhibited by nanofills may not be as good as that of the microfills. Polish retention is important because materials with a high polish are less likely to pick up stains and much more difficult for bacteria to attach to. On the other hand, microfills have weaker physical properties when compared to the other composites, which makes them more susceptible to fracture and chipping.

For anterior restorations, some practitioners prefer to use a microhybrid and then cover it with a microfill. They rationalize that while the hybrid material will provide the opacity needed to block the darkness of the mouth and the strength necessary to prevent chipping and fracture, the overlying microfill will provide improved handling and polishability when compared with a nanofill or a hybrid material. Unfortunately, this approach requires a larger inventory, which may make it cost prohibitive for some practices.

Other options available for practitioners include nano- and microhybrid resin composites. These materials have physical and esthetic properties that are similar to nanofills, but some are not as easily manipulated as nanofills because they have the tendency to slump during placement and can be more "sticky." When compared with nano- and microfills, hybrids may also require extra attention during polishing to obtain a high gloss; however, they do retain their gloss over time.

Handling is a very important consideration when choosing a resin composite material. During the last few years, resin composite manufacturers have produced materials with higher viscosities that are less sticky when in contact with instruments. This facilitates manipulation and shaping, but also may impair adaptation to the cavity walls, especially in narrow and deep preparations. In general, nanofills and microfills offer higher viscosities and are less prone to sticking when compared with conventional microhybrids.

A material that can perfectly emulate dentin and enamel has not been created yet. If you are satisfied with your current material, and it gives you predictable results, then you should continue to use it. If you are looking into changing materials, try out a nanofill and make your own conclusions regarding its universality.

Gaetano Paolone, DDS: In recent years, nanotechnology has played an important role in improving the clinical performance of dental resin composites. Nanotechnology involves using chemical and physical methods to produce nanoscale materials that range in size from 0.1 to 100 nm. Nanomaterials include nanoparticles, nanoclusters, nanotubes, nanocrystals, nanofibers, nanowires, nanorods, and other nanostructures. The increasing use of nanomaterials is driven by the idea that they can be used to manipulate the structure of composites to provide further, dramatic improvements in their mechanical, physical, chemical, and optical properties.

Historically, the first composites relied on macrofilled materials (10 to 40 μm), and then the microfilled ones were developed (0.01 to 0.10 μm). The macrofilled composites had nice mechanical properties, but exhibited poor esthetics, whereas the microfilled composites were the opposite. Later, hybrids (15 to 20 μm and 0.01 to 0.05 μm) were released that were able to provide both strong mechanical properties and desirable esthetics. From a clinical standpoint, nanotechnology has improved several aspects of the restorative ability of composites, including the following:

Esthetics. To obtain proper optical properties, especially translucency, scattering must be minimized, which means that the nanoparticles should be as small as possible while the index of refraction should remain as similar as possible to the matrix. This can only be obtained by tailoring the volume fraction of the nanoparticles. Although a material that optically behaves exactly as natural enamel has yet to be obtained, tremendous improvements have been made due to the inclusion and modification of nanoparticles.

Gloss. Surface gloss is another factor that plays an important role in the esthetic appearance of composite resins. Gloss is a desirable characteristic for restorative materials because it mimics the appearance of the natural enamel. Moreover, glossy and smooth surfaces decrease the coefficient of friction and may subsequently reduce the wear rate of restorations. A finer particle size for the composite results in reduced interparticle spacing, greater protection of the resin matrix, and less filler lost. In this manner, nanoparticles can help retain gloss.

Wear resistance. Wear can occur through different processes, including abrasion, adhesion, fatigue, and corrosion. These processes act in various combinations and produce different effects depending upon the properties of the material. Even if improvements in wear resistance have yet to be confirmed, nanofilled resin composites with high filler loadings have been shown to better withstand the processes of polishing and brushing.

Fracture propagation. Including fillers with nanosized dimensions has a favorable impact on mechanical properties. This is a result of the relationship between the different phases (ie, matrix and reinforcement) at the phase boundaries throughout the material and the fact that there are few portions of matrix without fillers.

Remineralization. Some nanocomposites release supersaturating levels of calcium (Ca) and phosphate (PO4) ions that are a requisite for remineralization. This could help in the management of the demineralization and remineralization process that occurs in dental caries.

Considering all of the advantages over other materials, I would say that yes, nanocomposites can be considered universal.

K. William "Buddy" Mopper, DDS, MS: Today,nanofill composites are considered the universal materials for anterior and posterior restorations. My choice for a dentin replacement is either a microhybrid or a nanofill, depending on the restorative need. For me, however, only a microfill composite can really replicate the enamel surface. The very essence of tooth structure is that it is composed of different layers with different material qualities. Each tooth contains both dentin and enamel, and each has very different properties. Consequently, no single material can accurately replicate both enamel and dentin.

If you really want to simulate enamel long-term, you must use a microfill. Microfill composites are the key ingredient for lifelike anterior esthetics. Because of their chemical and physical properties, microfill composites actually reflect light, resulting in a much more natural appearance.

Microfill composites also polish to a much higher and longer lasting shine than nanofill composites, and they hold this level of polish long-term. Highly polished microfill has a refractive and reflective index that more closely simulates enamel than other composite materials.

Because microfill composites are easier to marginate and have superior polishability, they are also more biologically compatible with gingival tissue and more successful at mitigating plaque formation. Biologically, the tissue response to microfill is unsurpassed by any other material, short- or long-term.

Because of its spherical particles and long-lasting polishability, microfill composite is the most wear resistant composite material available. In addition, the translucency of microfill composite allows the effects of selected tints and opaques to shine through the surface, adding to the lifelike appearance of the restoration. When compared with nanofill composites, microfill composites offer better flexibility, and in shallow cervical restorations, they flex more like the natural tooth structure, contributing to better overall retention.

Many clinicians use nanofills as a universal material for all of their anterior and posterior restorations. However, for all the aforementioned reasons, to achieve the best long-term esthetic results when I am dealing with the enamel surface, there is nothing that will replace microfill composite.

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