Composite Resins

Gerald E. Denehy, DDS, MS

Composite resins are the most widely used esthetic material in dentistry. Their evolution, however, has been controversial and contradictory. In the past, composite resins were viewed as provisional materials that held little promise of longevity; even now, they are often shunned in favor of porcelain as a long-term material for solving anterior esthetic problems. Although they were condemned for use in posterior restorations in their early days, many dentists now favor them as a permanent replacement for amalgam. Composite resins appear to be simple to use; yet if long-term esthetic success and longevity are to be achieved, they require more discipline than that of most other direct restorative materials. While composite resins provide reasonable results for most dentists, they can offer superior long-lasting esthetics for the skilled operator who is willing to devote time and effort into placing them.

Composite resin systems have been available to dentists for more than 40 years. Early materials were self-polymerized, large-particle restorative systems with very limited shade and opacity selection. When the acid-etch technique was applied to early composite resin systems, it was primarily for retention in Class IV restorations and often supplemented with pins. Restorations placed in the first few years showed the results of these limitations, demonstrating discoloration from the amines, wear from the large inorganic filler particles, and staining at enamel margins and around pins from limited etching.

Research advances occurred in the next several decades and had a very positive influence on composite resins. Light polymerization, first from ultraviolet and then blue wavelength, provided the dentist with the ability to control setting times and sculpt the restoration to contour during placement, significantly minimizing finishing procedures. Inorganic filler particle size was greatly reduced, which resulted in less wear, and microfilled resins were introduced. A greater variety of shades and opacities became available, resulting in improved esthetic results.

Physical properties were further improved by combining microfilled resin particles with the larger particle sizes, resulting in hybrid resins. Although still limited to enamel, acid etching was routinely used, eliminating the use of pins and reducing microleakage. These changes provided a much wider and more successful range of use, which included both anterior and posterior applications. As more advances in bonding technology occurred, dentin bonding became possible, further expanding the range of applications.

The resins of today offer the dentist various options. Particle sizes range from micron to nano, and resins are available in widely diverse particle combinations. Handling properties can be selected to fit many different desires and techniques. Most resin systems are keyed to the VITA Shadeguide® (Vident, Bad Sackingen, Germany), offering a wide range of shades and opacities similar to those used by a laboratory technician. A trend toward a more simplistic approach by reducing the number of shades and limiting opacities to one or two choices has been apparent in some recent products. Although these materials often compromise absolute shade matching, they provide many dentists with the simplicity that they desire to maintain low restoration placement time and patient costs. For the dentist who enjoys the challenge of creating the ideal shade-matched restoration, however, selection of a material that provides different opacities and a wide choice of shades will provide the best polychromatic blending of the tooth restoration.

Problems persist with composite resins, including polymerization shrinkage and the inability to bulk place material in thicknesses greater than 2 mm. Although some recently introduced products offer lower shrinkage and increased light curing, further improvements are needed.

Handling characteristics of composite resins are important when placing and contouring the material. Although the microfilled resins can be easily free-hand sculpted, the hybrids and microhybrid systems exhibit somewhat sticky or slumping characteristics. Recently introduced nanofilled systems produce many of the positive characteristics of the microfilled resins, including polish and handling, along with the better physical properties of the microhybrid systems.

Improved matrix systems have facilitated the placement of the composite resin material in both anterior and posterior teeth. These systems include quick-set impression material matrices for anterior restorations, which allow the dentist to place the material in the correct layering sequence and reproduce missing contours. They also include the use of contoured sectional matrix bands and their corresponding tooth contoured rings, which, in Class II restorations, result in tightly adapted margins and properly contoured tight contacts. Heating devices have been developed to ensure better adaption and to decrease polymerization time by lowering the viscosity of resins placed in cavity preparations. Polishing materials and sequencing have improved to the point at which most newer resins can be polished relatively quickly. Unfortunately, this polish still diminishes slowly with many systems.

Many factors can limit the longevity expected from the current composite resin restoration. Patient teeth maintenance varies tremendously from person to person. The ingestion of staining materials, oral habits, and alcohol-related fluids can influence the long-term success of composite resin restorations. The patient has the responsibility to periodically have the restorations checked for possible staining and chipping. Many times, the dentist can do minor touch-up on the restorations, resulting in extended longevity.

The restorative dentist, however, has the greatest effect on longevity. Success with composite resin restorations requires a disciplined technique. Simplification and speed are emphasized with most of the newer materials and equipment. Although these factors are desirable in a dental office, taken to an excess, they may result in decreased quality in restorations.

Although composite resin restorations may last 20 years or longer, each restoration will vary. In general, patients should normally expect 8 to 10 years or more of quality service from an anterior direct resin restoration and even longer with posterior restorations.

Direct composite resin systems provide ultraconservative, long-lasting, low-cost solutions to many dental esthetic problems. These certainly include simple restorations, such as Class III and Class V restorations. They also should encompass Class IV restorations, diastema closures, realignment cases, and veneering of stains. Often, however, dentists may not offer the option of this range of choices but instead use porcelain restorations. The reasons may be a lack of confidence in the material, lack of training, or the desire to promote more income-producing dentistry.

For a dentist to use direct resins, training is required for producing the desired result in a time frame while ensuring adequate reimbursement. Many dental schools have only recently begun training their students, and some have yet to do so. However, many quality continuing education hands-on courses are available at major dental meetings and private teaching clinics to expand a clinician’s skills in direct resins.

In the future, positive changes for resins are expected. Some of these improvements will involve departure from the resin matrices seen with traditional systems. Polymerization shrinkage will continue to be reduced. Research is in process to produce self-adhesive restorative composite resin systems that will successfully bond in a hydrophilic environment. Long-term polish retention will be addressed. By simplifying placement procedures, many of the variables in techniques that may lead to failure will be eliminated, leading to increased longevity.

Ultimately, the esthetic success of the final restoration will still depend on the skills of the restorative dentist. Form and contour are as important as correct shade matching. Without this knowledge and the ability to provide it, the restoration will be an esthetic failure. As with any quality restorative material, a discipline is required to ensure the ultimate success.

Composite resin systems are one of the best esthetic services that a dentist can offer patients. With ongoing research and upcoming advances, resins’ future will be even brighter.

About the Author
Gerald E. Denehy, DDS, MS
Professor and Department Head,
Department of Operative Dentistry,
University of Iowa College of Dentistry,
Iowa City, Iowa