Composite Restorations: Wheels of Progress Continue to Turn
Composite resin restorations remain an everyday challenge in clinical practice. Developments in this area of dentistry, including bulk-fill techniques, curing light advancements, and biocompatibility features, continue to evolve, with durability and predictability being primary goals.
Presently, more than two-thirds of direct restorations placed in the United States are of the composite resin variety.1 Although dentists have been placing composite resin restorations since the late 1950s,2 they remain technique-sensitive and an everyday challenge in clinical practice. Composite resin restorations are more time-consuming than previous amalgam restorations, and their long-term success is multifactorial. These factors include: operator technique, cavity preparation size and depth, adhesion materials, liners, matrix systems, fill techniques, choice of light source, light ergonomics, and light-curing time. The current trends in this wide-ranging area of dentistry are evolving, with the end-goal being the creation of a more durable, predictable composite restoration.
Bulk Vs. Incremental Fill Techniques
While not a new concept, bulk-fill restorative resins have recently had a resurgence in popularity. It has been suggested that not only is bulk-fill technique more efficient, but it may also eliminate voids that might be created by incrementally placing composite. Another benefit, according to some manufacturers, is low volumetric shrinkage.3 This does not mean there is less stress at the adhesive interface. The inherent properties of different composite resins such as modulus of elasticity, type of filler and monomer, rate of polymerization, gel point, conversion degree, and choice of initiator all have an effect on stress.4 Increased stress affects the marginal quality of the restoration and causes potential cracking and debonding. This, in turn, leads to clinical failure causing leakage, recurrent caries, and, ultimately, pulpal damage.
Bulk-fill restorations are typically designed to be placed in 4-mm to 5-mm depths.5 Adequately curing composites to this depth is highly contingent on not only operator technique but also the intensity, spectral range, irradiation time, and type of bonding light (eg, light-emitting diode [LED], halogen, or plasma arc) used for polymerization. To help ensure depth of cure and allow the light source to transmit deeper into the restoration, the bulk-fill materials are commonly more translucent than incrementally placed composites.5
Incremental techniques are still the predominant method of composite placement used today. It is commonly accepted that the incremental approach delivers a more predictable depth of cure since the increments are usually 2 mm or less. It has also been commonly accepted that incremental filling provides the least stressful pull on the buccal and lingual cusps, however not all of the research confirms this.6
Matrix Bands
Achieving proper interproximal contact for composite restorations has improved for Class II cavity preparations. The new sectional matrices are often Teflon® coated to prevent the composite from sticking. The bitine rings hold the sectional matrices and may be stacked to provide support for larger restorations that extend both mesially and distally.7
Curing Lights
Currently, as alluded to earlier, there are three main types of lights utilized in dental practices: LED, plasma arc, and halogen. Although halogen lights emit a broad spectrum of light and cure all composite resins, LED lights have become very popular due to their portability and low cost and have surpassed the other two for use in private practice. LED lights deliver a narrow spectrum of blue light and are best in activating resin with camphorquinone (CQ). CQ is activated at around the wavelength of 468 mm.8 Newer LED lights have two light-emitting diodes and a broader spectrum of light, and activate alternative photoinitiators within composite resin. The alternative photoinitiators are sensitive to wavelengths less than 410 nm. Thus, it is important to know the LED wavelength range that is being delivered. Manufacturers may choose alternative photoinitiators because CQ is chromogenic and may cause color changes in the cured composite. Ideally, manufacturers should list the photoinitiator but often do not for proprietary reasons.
8 This can lead to an undercured composite resin, which will result in failure of the restoration.
Dentists should perform routine evaluation of their operatory curing light with a radiometer designed for the specific type of light. While these radiometers are adequate to measure overall output, they are not highly accurate.8 The caution here is that the amount of energy is most likely much less than the reading on the radiometer. Prior to measuring the curing light, the tip should be meticulously cleaned. If a sterilization sleeve is used, it, too, should be used for measurement. The seam of the sleeve should be off the face of the tip.8 The manufacturer’s instructions of the composite should be checked to confirm the recommended curing time. Darker color composite resin will require longer curing times.
A recent development involves a light-curing simulator called MARC® (Managing Accurate Resin Curing). Developed by Dr. Richard Price of Dalhousie University in Halifax, Canada, this is a patient simulator (dental mannequin) that can be attached to a patient chair. Inside the head of the mannequin is a laboratory-grade fiber-optic spectroradiometer. MARC measures the irradiance, radiant exposure, and wavelengths delivered to simulated restorations under clinical conditions.9 Studies show with training and proper use this tool delivers more energy to the restoration.9,10 The training includes four “CORE” factors: curing light, operator technique, restoration characteristics, and energy requirement (Table 1).9
Bioactive Capability
Bioactive capability in composite is a potential feature that dentistry visited a number of years ago but with low acceptance. Manufacturers are presently researching this possibility again, with the intention of creating a restorative material that will interact with the oral environment to remineralize, better integrate, and possibly rebuild tooth structure.
Composites typically have silica-based fillers. In order to remineralize the tooth, calcium phosphate–based fillers need to be added. Remineralization occurs with the leaching of the calcium and phosphate ions. However, the undesirable effect of these fillers is that, by increasing the opacity, they change the optical quality of the composite. Technically, this challenge may be corrected by using nano-fillers that are de-agglomerated.11
Going forward, a concern that needs to be addressed is that the actual process of bioactivity may lend itself to the reduction of some of the mechanical properties in the composite.11 More research is needed in the restorative area, but bioactive properties in preventive materials has been quite successful.
The Future of Composites
Future goals for composite restorations include simplifying technique, facilitating speed of placement, and improving predictability of the success of the restoration long term. Studies have shown that the average composite lasts 5.7 years.8
The bulk-fill approach certainly satisfies a simpler, faster approach to composite placement. Clinicians must be careful to not be cavalier with placement, the curing, or finishing procedures. Each step is still critical to the long-term success of the restoration.
Ideally, the new composites will also have low shrinkage and low stress, which should afford a greater lifespan of the restoration. Bioactive and antimicrobial restorations would be desirable as a built-in feature, thereby eliminating the need for any additional steps.
Lastly, a true universal adhesive would be an attractive addition to the dental armamentarium. Providing simplification, this adhesive would ideally be used for a myriad of materials ranging from dentin, enamel, and both light- and self-cure composite cements, to various ceramics. Not be confused with 7th generation “all in one” adhesive systems, which do not have a broad application, there is no standard definition for a universal adhesive at this time. Reduction of product inventory and storage would be an added bonus for the dental practice.12
References
1. Christensen GJ. Should resin-based composite dominate restorative dentistry today? J Am Dent Assoc. 2010;141(12):1490-1493.
2. Buonocore MG. A simple method of increasing the adhesion of acrylic filing to enamel surfaces. J Dent Res. 1955;34(6):849-853.
3. Christensen GJ. Advantages and challenges of bulk fill resins. Clinician’s Report. 2012;5(1):1-6.
4. Ferracane JL, Alex G, Margeas RC. Are bulk-fill composites a good idea? Inside Dentistry. 2014;10(10):42-44.
5. Margeas R. Composite restorations: assembling the armamentarium. Compend Contin Educ Dent. 2014;35(6)426-427.
6. Versiuis A, Douglas WH, Cross M, et al. Does an incremental filling technique reduce polymerization shrinkage stresses? J Dent Res. 1996;75(3):871-878.
7. Alex G. Direct posterior composite restorations and adhesives. Paper presented at: Yankee Dental Congress; January 31, 2015; Boston, MA.
8. Price R. Avoiding pitfalls when choosing a curing light. Presented at: First Annual International Symposium on Light Sources in Dentistry; October 11, 2012; Halifax, Canada. https://www.youtube.com/watch?v=TpDQPJxL4lA. Accessed April 16, 2015.
9. Effective use of dental curing lights: a guide for the dental practitioner. ADA Professional Product Review. 2013;8(2):2-12.
10. Seth S, Lee CJ, Price RB, Alshaafi M. Effectiveness of using Marc-PS to teach light curing to dental students. J Dent Res. 2013;92(spec iss A):2520.
11. Alex G, Kugel G, Margeas, RC, et al. Current thinking on composites and adhesion. Inside Dentistry. 2013;9(8):39-49.
12. Alex G. Universal adhesives: the next evolution in adhesive dentistry? Compend Contin Educ Dent. 2015;36(1):15-28.
About the Author
Rena Vakay, DDS
Clinical Instructor
Kois Center
Seattle, WA
Accredited Member
American Academy of Cosmetic Dentistry
Dr. Vakay has served on the Board of Directors of AACD and is past-President of local chapter. She also served as Chairman and on the Board of Directors of Association of Contemporary Dental Education
Private Practice
Centreville, Virginia
TABLE 1
CORE Training Factors Associated with MARC Light-Curing Simulator
1. Curing light
Operator must know specific curing light irradiance values and spectral emission range. Exposure time can then be accurately produced.
2. Operator technique
Since light does not turn corners, light placement is critical to complete curing of composite resin. When operator looks away from the light to avoid retinal damage, the light is often shifted, thereby delivering less energy to the restoration.
3. Restorations characteristics
The curing light must have excellent access to the restoration; the tip should be as close to a 90-degree angle to the resin surface as possible.
4. Energy requirement
Operator must know the energy requirement and wavelengths for the specific material and shade. The difference in curing time can be dramatic—up to 7 times different from one shade to another.
