Kaaren G. Vargas, Marcos A. Vargas and Stephen F. Rosenstiel

 Outline

Fundamentals of Material Selection

The choice of materials is an important consideration when optimizing dental aesthetics. The clinical success of composite resin restorations depends on adhesive systems that provide durable bonding of composite resin to dentin and enamel, effectively sealing restoration margins and preventing postoperative sensitivity and microleakage.1–3

In order to achieve this, a contemporary adhesive system should be used (Figure 39-1). Most of these systems work by demineralizing the dentin-enamel surface with an acid, which is usually either 37% phosphoric or the acid incorporated into the adhesive. If a separate etching acid is used, a primer resin is applied that facilitates the penetration of an adhesive resin into the demineralized dentin and enamel to form a hybridized layer of resin/tooth^2,4 as shown in Figure 39-2. The bonding procedure is often simplified with a single-bottle primer/adhesive. These agents combine the primer resin with the adhesive resin into a single component (bottle).^5,6

The choice of composite resin for aesthetic restorations can be confusing because a variety of products are available with slightly different physical properties.7,8 Basically, the three types of composite resins that can be used are microfilled (those with filler particles averaging 0.04 µm in diameter), hybrid (a blend of different particle sizes, including submicrometer [0.04 µm] and small particle [0.2 to 3 µm]), and nanofilled, containing nanoparticles and clusters as fillers. The particle size difference between microfilled, hybrid, and nanofilled resin composites is readily apparent under magnification (Figure 39-3). Currently, most dental manufacturers are producing microhybrid composite resins with an average particle size of less than 1 µm and nanofilled, which are made of SiO₂, silane-coated SiO₂, and ZrO₂ with a range of 20 to 75 nm. Nanofilled resins have physical properties superior to those of microfills but slightly inferior to hybrids.⁹

The mechanical and physical properties of hybrid composite resins are superior to those of microfilled resins basically because they contain a higher proportion of filler particles. Nevertheless, because of their particle size, microfilled resins can be polished to an enamel-like luster with much more ease and in less time than hybrid resins.

When considering which material to choose for a restoration, it is essential to evaluate the tooth to be restored, the location of the restoration, and the forces to which the restoration will be subjected. Hybrid resins have traditionally been chosen as a universal restorative since they can be used in most clinical situations. Microfilled resins, on the other hand, are primarily indicated when aesthetic restorations are required, such as class V and direct resin veneers, and when the occlusal forces permit. Aesthetically demanding but higher load restorations such as class IV can use a hybrid material as a substrate that is subsequently veneered by a microfilled composite resin.

Regardless of whether a microfilled, nanofilled, or hybrid composite resin is chosen, the use of visible light–curing products is recommended. In addition to the convenience of extended working time and rapid polymerization, these materials also have lower porosity and are less likely to become discolored than the chemically polymerized (spatulated two-paste) systems.

The polymerization of light-activated composite resins is accomplished by using an intense blue light with a peak wavelength of approximately 450-470 nm, which corresponds to the absorption peak of camphoroquinone (CQ), the most popular photoinitiator.10,11 A typical light-curing polymerization unit uses light-emitting diodes (LEDs) to efficiently produce blue light¹² (Figure 39-4, A), although the traditional gun-style units that contain a halogen bulb and cooling fan are still available (see Figure 39-4, B). No matter what light is used, light intensity should be periodically checked (via a radiometer) so that a minimal output of 350 mW/cm² can be maintained. Several modern light-curing units incorporate light meter devices into their bases, so separate radiometers are not needed (Figure 39-5).

Eye protection is important when using the curing lights because direct viewing of the light is detrimental to vision.¹³ Amber filters, which block the intense blue component of the light, are commercially available and can be hand held or worn as eyeglasses (Figure 39-6). In the absence of specific protective devices, one should avoid looking directly at the light.

Fundamentals of Clinical Technique

Shade selection is the first step in achieving an aesthetically pleasing restoration. The teeth to be matched should be cleaned with a rubber prophylaxis cup and flour of pumice. Tooth dehydration should be prevented because it leads to color change. Moistened shade tabs should be held near the tooth to be matched, only in ambient light or indirect sunlight. One should not use the high-intensity operatory light when selecting shades. The proper value (Munsell whiteness) may be better determined by squinting. If shade selection takes more than a few seconds, one may need to resensitize the eyes by staring momentarily at a dark blue or gray object.

Composite resins come in a variety of shades, which are usually keyed to the VITA shade guide (Classical, Lumin Vacuum; Vident, Brea, Calif). Unfortunately, a perfect color match between the composite resins and the VITA guide is very uncommon, and shades among brands are even more variable. In recent years, the range of shades has been increased to match the shades of teeth that have been whitened or bleached. Common names for these shades are bleach shades, superbright shades, or extralight shades.

To overcome some of the shade matching pitfalls, many clinicians allow the patient to choose between two similar shades. Another way to verify the actual shade is to place a small portion of composite resin on the tooth surface, polymerize it, observe the appropriateness of that shade, and then remove it with a hand instrument. It should be noted that one should not etch the tooth before doing this or removal will be difficult. It is also generally best not to combine shades of composite resin by mixing, because porosity may be introduced into the paste.

It is extremely important to maintain an uncontaminated field during the insertion of composite resins. The most reliable way to control moisture is through the use of a well-adapted rubber dam. If not using a rubber dam, one should place cotton rolls and 2 × 2 inch gauze sponges over the tongue to prevent moisture contamination. Another approach to maintaining a dry field is to use a commercially available lip and cheek retractor (Figure 39-7). This plastic device, when used with gauze sponges, provides excellent access and good field control.

The use of a base or liner to protect pulp tissue in deep preparations is generally believed to be beneficial. Many believe that a glass ionomer liner should be used in deep areas of a cavity preparation that is thought to be within 0.5 to 1.0 mm of pulpal tissue (Figure 39-8). The liner provides chemical adherence to tooth structure and slow release of fluoride.

After etching (15 seconds of etch and 5 to 10 seconds of rinse), an appropriate dentin-enamel bonding agent should be placed with a vigorous rubbing action.¹⁴ Next, the photopolymerized composite resin should be inserted in layers no thicker than 2.0 mm, using at least 40 seconds of light exposure per layer. Thin layers and adequate time for light exposure help ensure maximal polymerization and minimize marginal gaps caused by shrinkage.¹⁵ Maximal polymerization provides optimal strength and color stability for the restoration. It is important to cover the light-curing composite resin on the mixing pad so that room light does not initiate the polymerization process. In addition, it may be necessary to reduce the intensity of the operating light.

In an effort to mimic the translucency of enamel and the opacity of dentin, manufacturers have produced materials with a variety of opacities. These materials should be placed in increments in which the more opaque materials replace dentin and the more translucent materials replace enamel to produce restorations with similar optical properties to tooth structure.

Plastic or metal instruments are useful for material placement and contouring. Fine sable or camel hair brushes allow the easy contouring and blending of composite resin into the proper form. To prevent composite resin from adhering to the brushes and instruments, they should be lightly touched to the composite resin with a rapid dabbing motion.

After the polymerization process, the contouring and finishing of the restoration is accomplished with carbide finishing burs, ultrafine diamonds, or />