by Sharon Schindler, DDS, FAGD, LVIF
Restorative materials have undergone a major evolution during my 23 years in practice, particularly during the past decade. For the majority of patients today, tooth colored restorations are the only esthetically acceptable solution for the posterior teeth. Despite the everyday nature of the procedure, placing a direct restoration in the posterior poses several challenges to the clinician, and we must be vigilant during every case. One of the primary challenges dentists face in the posterior, as with any procedure, is using time efficiently.
When a posterior procedure takes extra time, not only is it potentially more costly for the practice, but it can also become uncomfortable for the patient who has to "open wide" longer. Additionally, it is more difficult to keep the area sealed, clear, and dry during a direct posterior procedure versus an anterior procedure.
To help save time, manufacturers have recently started moving toward streamlined bonding systems and other simplified material protocols. But obviously the most important material in the direct restoration is the restorative itself. As I said, restorative materials have undergone a significant evolution in recent years, and there are now a number of classes of material available. The categories and subcategories of these materials can often be confusing, especially in regard to nanotechnology and the various restoratives that claim to use it. Understanding these categories can help dentists choose the best materials for posterior placement.
Dental composite categories can be easily understood by examining their particle sizes:
Macrofills: The first varieties of composites introduced decades ago were "macrofills," which had particles that ranged from 10 μm to 50 μm. Relative to today's materials, these particles were quite large. While this large size contributed to excellent strength for the material, it also made the surface of restorations difficult to polish.
Microfills: The next generation, microfills, were introduced in the late 1970s. Microfills have particle sizes under 100 nm, and their introduction readily addressed the smoothness and polishability problem posed by macrofills. However, in correcting the polishing issue, these materials neglected strength. To create microfills, manufacturers use prepolymerized filled resin particles, which are made when filler is added to resin, polymerized, and then ground down. These particles are designed to increase filler loading, but the ultimate material result is still not strong or wear-resistant enough for posterior use.
Hybrids, microhybrids, and nanohybrids: Between the extremes of the macrofill and microfill categories, today there are hybrid composite materials. These composites have particles in the 10 μm to 50 μm range, as well as particles sized at about 40 nm. Microhybrids and nanohybrids both fall under the larger heading of the hybrid category; particle sizes for these materials range from less than 100 nm to over 1 μm. With this range of particles, these materials have high filler loading, which contributes to added wear resistance and strength.
One problem with hybrids is that their esthetics can suffer over time. This is due to the wear process, during which the resin between particles wears away, leaving the filler particles susceptible to being "plucked" from the restoration's surface. The uneven surface left behind loses its polish retention and reflectivity.
Nanocomposites: One final category of composite, nanocomposite, attempts to address many of the drawbacks of the generations of material that preceded it. While hybrids, microhybrids, and nanohybrids all use particles that are created through milling and grinding (a "top-down" method), nanocomposite particles are synthesized from the bottom up. The patent for this process is held by 3M ESPE, which uses the technology in Filtek™ Supreme Ultra Universal Restorative.
A nanocomposite has a primary particle size of 20 nm, and the particles exhibit a very unique attribute -- they group together to form nanoclusters. These nanoclusters give the material added strength, as they effectively function like larger particles. When they are abraded during wear, individual nanoparticles break away from the clusters, but the resulting void is too small to be seen by the human eye. With these characteristics, nanocomposite restorative material effectively offers strength, wear resistance, and polishability, all crucial attributes in the posterior. We have all seen patients do a "tongue test" over a new restoration, so a material that will polish quickly and smoothly can save the dentist the trouble of having to repolish an area that the patient feels is too grainy.
Beyond particle sizes, there are a number of other factors that dentists should take into consideration when choosing a composite in the posterior:
Incremental strategies: When placing a large posterior restoration, I feel most comfortable using a nanocomposite in the recommended 2 mm increments, as opposed to a bulk fill material. Bulk filling does have time saving advantages, but dentists should carefully examine strength and wear resistance claims for any bulk fill material before use. Additionally, placing material in bulk requires the clinician to adequately cure the material, and if not careful, old lights or a dirty light guide can result in material remaining undercured.
Shade choices: For me, an additional advantage to using a non-bulk fill nanocomposite is that I have a greater range of shades from which to choose. Even in the posterior, a great shade match is important to patients, and dentists should look for materials that give them the best range of options. I find that with my preferred material, I can use a single body shade and still achieve a chameleon-like match to the surrounding teeth. The ability to use a single shade but still deliver excellent matching esthetics is a great timesaver.
Handling and flowability: These characteristics are especially important in the posterior, where maneuverability with instruments can be limited. A composite material should flow easily to the walls and pulpal floor of a preparation. A material that is too tacky can be difficult to work with and add time to the procedure.
Enabling conservative dentistry
My personal goal is to stay as conservative as possible when working anywhere in the mouth, either anterior or posterior. The availability of direct restorative materials that are strong, long lasting, and esthetic gives dentists a great arsenal of tools to perform minimally invasive treatments in the posterior. By examining your options carefully, you can choose the tools that will both save you time and serve your patients best.
Sharon Schindler, DDS, FAGD, LVIF, is the founder of Schindler Dentistry - the Columbus Center for Aesthetic Dentistry in Columbus, Ohio.Her private practice focuses on complex cosmetic and restorative dental care. She is a Fellow of the Academy of General Dentistry, and a Fellow of the Las Vegas Institute for Advanced Dental Studies. She can be reached at schindlerdentistry.com.
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