Thanks to continued technological tweaking, contemporary composite resins not only can lend strength to teeth, but blend into native tooth structure for what is known as the “chameleon” effect. Mentor explores these developments that have brought direct restorative esthetic dentistry to a whole new level.
Let’s face it: not all of us can get through life without dental fillings. Of all the materials used to fill teeth, amalgam (silver alloy) has been a tried and true favorite. It’s easy to work with and place, and has demonstrated incredible longevity as a direct restorative. But, aside from the fact that mercury is a prime ingredient in amalgam filling material — which gives some patients pause — preparation for amalgam restorations is not what you would call “minimally invasive.”
To place silver fillings, clinicians must carve undercuts and other retentive features into a tooth in order to mechanically lock the material into place. Therefore, quite a bit of tooth structure needs to be removed. That’s because amalgam has zero adhesive characteristics. Perhaps of even greater concern to today’s patients, amalgam fillings can leave dentition with a telltale patchwork of silver, spotlighting evidence of dental foul play. (Was the patient simply too lazy to brush and floss his teeth? Did she overdo it on the candy?)
But with the advent of adhesive dentistry, many of these amalgam shortcomings are resolved. Composite resins do not contain mercury, and when used in conjunction with bonding agents, they are engineered to chemically adhere to tooth structure. So there is no longer the need to cut retentive features into healthy dentition. This supports the concept of minimally invasive dentistry.
Maybe best of all, from the patient’s perspective, is that composite materials are tooth-colored and capable of curing into restorations that can pass for the real deal. Whether used in a large Class II restoration or for directly placed veneers, these materials allow clinicians to leave no trace. They are game changers in regard to esthetics.
“These materials are strong, sculptable, available in lots of shades and translucencies, and they hold up well,” says Besty Bakeman, DDS, a cosmetic dentist based in Grand Rapids, Michigan. “But they’re technique sensitive. You need isolation, and it takes a while to do them well. It’s not like putting amalgam in a tooth. If done well, though, they can deliver beautiful restorations both in posterior and anterior aspects of the mouth. And they’re very conservative of tooth structure.”
Developed in the 1960s, composite resins began as macrofills, which featured large particles. These materials weren’t the best esthetic option, especially for anterior applications. Because of the large particle sizes, they didn’t polish well and were given to “plucking,” or having particles pop out, which left a pitted surface.
It took several generations of composite resin materials, which included microfills, hybrids, and microhybrids, to get us to where we are today. Although, due to low filler content, microfills lack the strength to withstand compressive forces of posterior teeth, are stain resistant and can attain a very high polish. Therefore, they are often used in anterior applications — sometimes as an esthetic layer over another material.
For the most part, one generation of composite after another has suffered from one of two conundrums: Those with large particles offer tremendous strength but are unable to deliver a high polish, and those with small particles can attain a high polish but lack strength. A mix of particle sizes, shapes, and filler density has been found to offer the best recipe for success in providing low polymerization shrinkage, high strength, high polishability and enhanced optical properties. This was particularly the case with the advent of nanomaterials, which feature a mix of extremely small particles.
Composite dental materials are typically composed of a resin matrix — such as bisphenol A-glycidyl methacrylate or urethane dimethacrylate — and inorganic fillers — which can range from silica and glass to ceramics and crystalline quartz. Through numerous generations of composites, filler particles have been dispersed into the matrix in various sizes, shapes and densities to affect viscosity. But fillers also dictate numerous other characteristics, ranging from handling and wearability to strength and esthetics.
Among the most important characteristics composite dental materials should possess is polishability. Certainly, a high polish lends an esthetic boost to any set of teeth. But highly polished composite restorations are far from being just a pretty patch. Polished tooth surfaces provide a poor substrate for bacterial proliferation and staining. They are also kind to opposing and adjacent teeth, minimizing wear of healthy dentition. Therefore, it’s critical to dental health that restorations be polished to a smooth finish.
Currently, nanofilled, and nanohybrid composites are the materials du jour. In fact, Ed McLaren, DDS, director of the University of California Los Angeles Center for Esthetic Dentistry, views the development of nanomaterials as perhaps the most significant innovation with respect to direct restoratives. “When they develop materials that have super small filler and bond them together well, they have better physical properties. They’re stronger, tend to be more wear resistant, and they can be very esthetic,” he explains, but adds, “There has been some rebranding of microfills, but they are not true nanomaterials, where every filler particle is nanosized. That’s the difference.”
Among these newer formulations, nanohybrids, which feature a broader mix of particle sizes than nanofills, are gaining kudos for their esthetic properties, as well as their strength. Offering a wide range of colors, lifelike translucencies and superb polishability, such restoratives allow the creation of fine details and characterizations in anterior applications. These materials are also proving easy to handle and sculpt, while providing low polymerization shrinkage and enhanced physical properties. In fact, they are considered by many to be universal composites in that they can be used throughout the mouth. Given these benefits, nanohybrids may be just the ticket for sales reps whose customers prefer to work with only one product.
Recently joining the product lineup available to clinicians are nanohybrid composites endowed with bioactive properties. These not only are designed to deliver excellent esthetics, but also help protect teeth against caries and foster remineralization, allowing minimally invasive treatment of early-stage caries.
Chroma: Color purity.
Hybrid composites: A resin matrix and various sizes of filler particles.
Hue: Gradations of the primary colors of red, green, blue and yellow.
Nano-sized: Measured in nanometers as nm, in a range of 5 nm to 75 nm.
Because teeth are not monochromatic blocks of white but a mélange of shade gradations, translucencies and characterizations, products such as tints or stains and opaquers can come in handy. Such adjunctive products can facilitate color-matching, helping to create lifelike restorations while hiding unattractive stains. This is where a clinician’s artistic skill really pays off.
“When you have maverick colors such as stains or decalcifications, you absolutely want to have tints and opaquers,” says McLaren. He adds that they’re available in kits, and it’s a good idea to have a couple on hand. But, he warns that they should be used sparingly. “They’re only 50% or so filled, so they’re a weaker composite. So if you use too much, you’ll have a weaker restoration, which can affect longevity or fracture strength.”
But it’s not exactly a slam-dunk to match a restoration material to a patient’s dentition. Everything, including the landscaping outside the window, can impact color matching. And don’t forget that dentists are human and have various levels of visual acuity. Says McLaren, “For the best possible viewing environment, they need to make sure that the tooth isn’t dehydrated, there aren’t strong colors close by, and they’re in a room that has neutral colors with good lighting … similar to daylight.”
Commercially available classic shade guides are available to help dentists pinpoint the correct shades. These shade guides are basically cards with tooth-shaped samples of composite in various shades. Letters and numbers, such as from A1 (the lightest) to D4 (the darkest), help clinicians decipher the correct hue, value and chroma for a particular patient.
McLaren says that most composite systems come with their own shade guides. In the event one doesn’t, he suggests that dentists can easily make their own by making composite tabs and attaching them to a sterilizable piece of plastic. “I would not use a third-party shade guide,” he advises. “I see that as probably the biggest mistake made.”
It is common practice to try in a number of shades in search of the best match. “When matching composite resin restorations, especially for anterior teeth, it’s important to apply different shades and perhaps different manufacturers’ shades to the restoration or tooth that needs to be matched,” says Ronald Goldstein, DDS, a cosmetic dentist and prolific educator, who practices in Atlanta, Georgia. “However, the adjacent teeth should not be allowed to dry because the teeth can become desiccated and appear lighter than the necessary shade to be matched,” he tips. To counter this, Goldstein advises that a good digital photo of the supposed match can also help clinicians see just how close the shade actually is.
For try-ins, McLaren suggests, “Clinicians can take a little piece of composite and put it on the prepped tooth without a bonding agent, and cure it, making sure that it’s hydrated. Within a few seconds, they’ll be 98% sure of the shade. I would see that as by far the most important thing that can be done.”
Goldstein and McLaren, however, both advise against complete reliance on shade guides. This is because batches of composite resin can vary greatly from the advertised shade, depending on the manufacturer. Shade guide colors can also degrade over time or after a few sterilizations.
Fortunately for today’s clinicians, digital shade-taking instruments in the form of handheld spectrometers can be used to scan, measure and analyze color for accurate color reproduction quality. They can create what amounts to a color map of tooth surfaces for almost paint-by-numbers simplicity. Spectrometers measure the level of light energy that’s reflected from the tooth surface to determine value, hue and chroma.
There has long been one major player in this category, though, according to McLaren, other manufacturers are entering the market. Some are reportedly even adding shade-taking technology to their chairside intraoral scanners.
The tips of such devices, protected against contamination by shields, must be placed flat against tooth surfaces to accurately determine the correct shades for either direct or indirect restorations. Otherwise, readings can be off. “Remember,” says McLaren, “a tooth is a curvilinear surface and spectrometers do a lot better with a flat surface. If you let light escape by tilting a degree or two, you’re going to get an incorrect reading.”
Shade-taking devices deliver information about the various shade layers in one tooth. They can even be used to track tooth whitening processes. Information is displayed on a screen and can be stored via complementary software. “My process is to start with a shade guide, and get as close as I can to the right shade,” says McLaren. “Then I put a tiny piece of that composite where it’s supposed to go for dentin layer, and cure it without bonding agents to see if I’m right.” He continues, “I repeat the process for both dentin and enamel layers until I have a match. That’s a lot less time than having to redo a whole restoration — for free. The spectrometer, for me, is really a verification tool to ensure that it’s really the correct shade. All in all, it teaches you to be a better shade taker.”
POINT OF SALE | THE BOLD AND THE BEAUTIFUL
- More than ever, patients are expecting esthetic dental treatments.
- Nanofill and nanohybrid composite materials offer both strength and beauty in today’s restorations.
- Many manufacturers offer shade guides to complement their composite systems.
- Tints and opaquers are important accessories to have on hand to create the best outcomes for patients.
- Digital shade-taking devices offer an extra layer of protection for clinicians concerned about getting it right when it comes to matching restorations to existing dentition.
Goldstein predicts that there will no doubt continue to be significant improvements in direct bonded resins or similar products in areas such as strength, color, permanent adhesion, and in products designed to repair chipped or fractured ceramic restorations. “The current problem,” says Goldstein, “is life expectancy of these repairs, which are usually direct composite to the ceramic. Staining occurs at the margins of the repair, which creates an esthetic problem.”
Says McLaren, “I see improvement in bioactive restorative materials and their use in early intervention in stopping and reversing the decay process, while maintaining the esthetics. We’re just on the precipice of that really.”
Bakeman puts her stock in education. “We have so many wonderful materials available to us. Manufacturers, however, recognize that they can produce a great product, but if the clinician doesn’t know how to best use the material, the outcome often is less than optimal. On the flip side, a product can really shine when we learn its nuances — how to layer various translucencies and opacities and master the skills that enhance our ability to shape, develop finish texture and optimize polish.”
With user-friendly technologies designed to partner with increasingly esthetic composite materials, it appears that manufacturers continue to gain elevation in the direct restorative market. And with more developments on the horizon, the trail ahead looks clear for dentists, who continue to give their patients something to smile about as they leave no trace.
Featured image by WILDACAD/ISTOCK/GETTY IMAGES PLUS
From MENTOR. July 2017;8(7): 18-22.