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    How to achieve esthetic results with direct composites

    Why advances in materials and technique are leading to more reliable outcomes.

    Although posterior Class I and Class II restorations comprise the majority of direct restorations performed in the average dental practice, anterior composite restorations demand a higher level of esthetic requirements (shade match and surface finish) as these restorations are often the “showcase” work in our patients’ mouths.

    This article will address several of the material and technique updates that have improved our ability to more simply and reliably achieve esthetic results with direct composites.

    Understanding classifications of composites: a simplified history of filler particles

    The dental composite as we know it today was developed in the 1950s by Ray Bowen. At that time, he mixed a bis-GMA resin with silanated 150-micron ground glass filler particles and camphorquinone, a light activator. The most fundamental change between the resin composite of that time and current resin composites is the filler particle. The first major change occurred in the 1970s when submicron (40 nm diameter) round silica particles fabricated from flame pyrolysis were added to the composite to fill in between the large ground glass fillers.1 This formulation was the beginning of the “hybrid” composite as it contained a hybrid of 40 nm fumed silica and 150-micron ground glass. One way to picture these submicron filler particles is to imagine that if the submicron particles were the size of a golf ball, then the 150-micron ground glass fillers would be about the size of a football field.

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    The next concept in composites was the development of a composite entirely filled with small 40 nm silica particles to take advantage of the polish that can be obtained with small filler particles. To explain this, think of looking out of the window of an airplane. You would not be able to see a divot in the ground the size of a golf ball, but you would definitely notice a football field-sized crater. The same concept applies to filler size when finishing composites.

    Unfortunately, adding a filler load of only 40 nm silica particles that is high enough to achieve favorable mechanical properties results in a composite that is too thick to handle in the clinic. Therefore, these fillers were added to resin in a high concentration, completely cured, then crushed into small particles known as prepolymerized filler particles (PPFs). These PPFs were used as the filler particles in microfilled composites. Although microfills achieve a very high polish, these materials fell out of favor due to their inferior mechanical properties, limiting them mostly to anterior restorations.1

    The next major development in anterior composites was the nano-filled composite. Unlike the micro-filled composites in which submicron fillers were added as PPFs, nanofilled composites have 5-40 nm silica and zirconia particles clumped together and added as “nano-clusters.” These materials are able to achieve both a high polish and favorable mechanical properties.2

    Enhancement of the process of grinding glass fillers has allowed new generations of “hybrid” composites such as micro-hybrid and nano-hybrid composites. These hybrids have smaller and sometimes more homogenously sized ground glass fillers, ranging from a couple microns down to 100 nm.1 In other words, if the original ground glass fillers were the size of a football field, then these glass fillers are closer to the size of a football. They also contain some combination of PPFs, nano-clusters or loose submicron fillers.

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    These categories are all subjective and it is very confusing for the clinician to differentiate materials based on the information given by the manufacturer. In fact, a researcher dissolved out filler particles from commercially available composites and reported that the sizes of the filler particles were unrelated to the category assigned by the manufacturer.3 In general, current generation composites are either hybrids (containing small ground glass fillers and submicron fillers), micro-filled or nano-filled (Fig. 1). As a rule of thumb, the clinician may ask the manufacturer if its composite has any fillers larger than 500 nm. As the wavelength of visible light ranges from 390-700 nm, particles smaller than this may be visually undetectable after polishing. Additionally, the clinician may consult independent research regarding the gloss, gloss retention and roughness achieved by the composite.

    Fig. 1

    Fig. 1

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