Excellent Results with Today’s Resin-Based Composites
A review of the advances making placement more predictable
Over the past 2 decades, dentistry has seen the increased use of resin-based composites, as their reliability, predictability, quality, and characteristics have improved. Over time, clinicians have found amalgam-restored teeth to be more susceptible to internal and external fractures than teeth restored with composite alone. In addition, composite restorations allow for a minimally invasive approach, in which only the carious dentin is removed. This type of preparation design diminishes the need for macro-mechanical retention that is required for amalgam restorations.
In the past 30 years, patients have become more concerned with the esthetics of restorations, which has led to the widespread, gradual replacement of amalgam in posterior teeth. Additionally, the mercury found in amalgam has potential adverse health effects that are worrisome for many patients. Together, these factors have led to the increased use of composite over amalgam in general practice.
In the early 1990s, Bowen questioned composite adhesion to cavity walls and stated that polymerization shrinkage and pulp irritation were problems of resin-based composite restorations.1 The lifespan of posterior composites was reported to be 3 to 10 years at that time. Nevertheless, there was still a shift in the late 1990s away from use of amalgam restorations in posterior teeth in favor of composite. Improvements in posterior composite technology and adhesion may have been largely driven by patient demand for esthetic, tooth-colored restorations.
Changes in composite composition, including increased filler content, smaller particle size, improving adhesion of filler to organic matrix, and the introduction of low-molecular-weight monomers, greatly improved qualities such as esthetics and handling.2 The five different types of resin-based composites on the market today are:
• Microfills—the advantages of microfills include a low modulus of elasticity and high polishability. Disadvantages include low fracture toughness and higher marginal breakdown.
• Hybrids—these materials have better clinical properties than microfills, but they do not maintain a high polish.
• Microhybrids—due to a smaller particle size, these have high polishability similar to microfills, higher strength, and improved wear resistance.
• Packables—these are indicated for stress-bearing areas and ideal for Class II restorations. However, they are not superior to hybrids.
• Flowables—these improve the marginal adaptation of posterior composites, but they are more prone to polymerization shrinkage.
Polymerization Shrinkage
Although all composites demonstrate some degree of polymerization shrinkage from light curing, proper technique can make a big difference in the ultimate success or failure of a restoration. There are varying techniques, but the most common is careful wedge-shaped incremental application in oblique layers, which helps to minimize contraction of each layer from opposing walls.2
Adhesive Systems
Just as resin-based composites have evolved and improved over the years, so has adhesive dentistry. These advances have helped make composite resin more reliable. Although a complete review of adhesive systems is beyond the scope of this article, an overview is presented here.
Bonding systems are categorized based on their components and grouped into generations as new ones emerge. The primary categories are fourth and fifth generations, also known as “total-etch” or “etch and rinse,” and sixth and seventh generations, or “self-etch.” The fifth and sixth generations are most widely used because they are effective and relatively simple, with each containing two steps.2
Total-etch systems etch the enamel and dentin with 30% to 40% phosphoric acid. This removes the smear layer and demineralizes the dentin tubules. The primer and adhesive, contained in one bottle, are applied and penetrate the micropores of etched enamel, forming the hybrid layer.
Self-etch systems are less technique sensitive and save time. The acid and primer are combined in one step, and the adhesive is the second step.2 The smear layer is not removed. The self-etching primer, invented by Watanabe and Nakabayashi, consists of an aqueous solution of 20% phenyl-P in 30% HEMA for bonding to enamel and dentin at the same time.3
Selective-etch systems are a combination of total-etch and self-etch, where only the enamel is etched with the phosphoric acid for 15 seconds, rinsed, and dried. The dentin can be prepared with the self-etch system, which has been found to reduce sensitivity that could be caused by over-etching dentin with phosphoric acid. The selective-etch technique allows for better bond strength to enamel while minimizing pulpal sensitivity.4
As with all dental procedures, attention to detail is critical when placing composite restorations, especially with moisture and hemostatic control. Hemostatic agents, used on dentin and enamel to aid with excessive gingival bleeding, have been found to contaminate dental surfaces, leading to decreased bond strength. These agents tend to greatly affect the bond strength of self-etching adhesive over that of etch-and-rinse systems. Research reveals that rinsing dental surfaces to be restored with ethylenediaminetetraacetic acid for 60 seconds and rinsing with water restored the bond strength of self-etch adhesives to dentin. An equally effective method is to use phosphoric acid for 15 seconds followed by a water rinse.5
Curing Options
Composite resins used as a core build-up after a root canal or prior to a crown preparation are available in self-cure, light-cure, and dual-cure formulations. Each composition has its advantages and disadvantages.
Self-cured composites require a longer setting time that is difficult to control. Traditional light-cured materials need to be placed and cured in increments, which takes a considerable amount of time, particularly when compared to a bulk-fill technique. The limitations of the curing light and technique mean there is a risk of not properly polymerizing the material. This disadvantage has been associated with inferior mechanical properties, postoperative sensitivity, microleakage, recurrent caries, and pulpal irritation from the leftover monomers.6
Dual-cured resin-based composites overcome some of the disadvantages of self- and light-cured composites. These materials combine an oxidation-reduction initiator system as well as photo-initiators. A chemical reaction allows for polymerization in the deeper portions of the restoration that cannot receive sufficient light while the top layers will polymerize mainly with photoactivation, allowing initial stability of the restoration.6 There are many dual-cured core build-up materials available, including Clearfil™ DC Core Automix (Kuraray, www.kuraraynoritake.com), Core-X flow (DENTSPLY, www.dentsply.com), Luxacore Z-Dual (DMG, www.dmg-dental.com), and MultiCore® Flow (Ivoclar Vivadent, www.ivoclarvivadent.us).
New Composite Placement and Polishing Techniques
The advent of sectional matrix systems revolutionized composite placement, especially in the posterior. Dental clinicians have experienced improved form, function, and esthetics. These matrices help create ideal anatomical contours as well as interproximal contact. Examples include Composi-Tight® 3D XR (Garrison Dental), Triodent™ V3 (Ultradent, www.ultradent.com), and Palodent® Plus (DENTSPLY).
Bioclear (www.bioclearmatrix.com) is a new matrix system for anterior and posterior Class II restorations. The anterior matrix is used without a wedge; the matrix seal is achieved by the papilla. This matrix system allows for improved esthetics for the treatment of peg laterals, reshaping undersized teeth commonly occurring after orthodontic treatment, diastema closures, complex black triangles, and deep Class III and IV anterior composites.7
Bioclear founder Dr. David Clark also developed a three-step polishing technique for creating an infinity edge and lifelike appearance with composite resins. The first step is finishing the composite restoration with a diamond finishing flame bur. Then, the Shofu Brownie (www.shofu.com) is used for margination and to create mamelon grooves. It does not cut enamel. If using an electric handpiece, set it to 12,000 rpm. Then use course pumice with a disposable cup, going in all directions to give a matte finish. Lastly, use the D-Fine shape and shine polisher (Clinician’s Choice, www.clinicianschoice.com). These diamond-impregnated polishers allow the clinician to shape, contour, and polish cured composite material in a single step. They feature 45-micron diamond particles that can conservatively contour composite when additional pressure is applied. During polishing, these diamond particles continuously break down, creating submicrons. This process results in a high luster, unrivaled finish on all hybrid and nanofilled composite materials.7
References
1. Bowen RL, Marjenhoff WA. Dental composites/glass ionomers: the materials. Adv Dent Res. 1992; 6:44-49.
2. Bardwell DN, Deliperi S. An alternative method to reduce polymerization shrinkage in direct posterior composite restorations. J Am Dent Assoc. 2002;133(10):1387-1398.
3. Ferrari M, Kugel G. The science of bonding: from first to sixth generation. J Am Dent Assoc. 2000;131(1): 20s-25s.
4. Radz GM. Posterior composites and universal bonding agent applications in the modern dental practice. Dentaltown. 2015;63-66.
5. Bernades KO, Hilgert LA, Riberio AD, et al. The influence of hemostatic agents on dentin and enamel surfaces and dental bonding. J Am Dent Assoc. 2014;145(11):1120-1127.
6. Taubock T, Oberlin H, Buchalla W, et al. Comparing the effectiveness of self-curing and light-curing in polymerization of dual-cured core buildup materials. J Am Dent Assoc. 2011;142(8):950-956.
7. Clark D. Articles. Bioclear website. www.bioclearmatrix.com/resources/articles. Accessed October 15, 2015.
