Bulk-Fill Materials: Simplify Restorations, Reduce Chairtime

While amalgam has a long history of serving the dental industry well, it is a material in steady decline¹ and is no longer the standard material used for bulk-filling posterior restorations. Since its drop-off, dental professionals have been persistently seeking methods and materials that offer a similar ability to quickly and easily complete these restorations, which are performed on a daily basis throughout general restorative practices.

Composite restorations are, of course, a vast improvement over amalgam in terms of esthetics. As manufacturers endeavor to increase the amount of fillers in their resins to improve mechanical and physical properties such as compression strength, flexural strength, elastic modulus, coefficient of thermal expansion, water sorption, and wear resistance, several classification systems of composites have been developed. These systems are based on the particle size, distribution, and quantity of fillers incorporated.² Classifications include hybrid, microhybrid, microfill, and the newer nanofill, as well as bulk fill. The descriptions of these classifications can vary from system to system. Composite is also preferred over amalgam because of its ability to conserve tooth structure, as there is no need for the outline or undercuts to retain the filling. The process involved in incremental layering of composites is technique-sensitive as well as time-consuming due to the many steps and amount of material required.

Newer bulk-fill posterior composite materials are designed to eliminate layering and thereby conserve the clinician’s time as well as simplify the procedure. Most manufacturers recommend their bulk-fill composites for depths up to 4 mm, while some suggest 5 mm is acceptable, as compared to the typical 2-mm increments with conventional composites. Depth of cure for any dental composite, but especially for bulk-fill composites, is a critical issue. A number of factors determine if a material is adequately cured to the depth its manufacturer states.

First of all, an adequate curing light is needed for sufficient polymerization to occur, and reasonable light-curing conditions (approximately 20 J/cm2 when applied very close to the surface of the material) must be met. The three most important characteristics of the light are appropriate wavelength, adequate light output, and exposure time. If the light is not powerful enough and is held too far away from the material (the light should be kept as close to the tooth as possible, as a decrease of power output occurs for each millimeter of distance from the tooth), then the depth of cure will become a moot point. Different photoinitiators besides camphorquinone that absorb visible light at 410 nm are being added to the bulk-fill composites. If the curing light used has an output in the range of 450 nm to 490 nm, the material will not be cured adequately.

Polywave curing lights with different LEDs are being manufactured to cover the wider range of photoinitiators. It is important for the composite manufacturer to state the wavelength of the photoinitiator used in the material. Exposure time is more important than irradiance of the light, as there needs to be adequate exposure for the material to polymerize. Composite restorations cannot be over-cured, however they can be under-cured. Polymerization of resin composites continues at a slow rate after curing and may reach a termination point at almost 24 hours,³ although other studies⁴ show some surface hardness increases up to 1 month later.

Filler content plays a significant role in the depth of cure possible with bulk-fill materials. It is generally true that the higher the filler content, the greater the depth of cure. Increased filler loading reduces the volume of resin matrix for polymerization and intrinsically increases hardness. Due to the amount of filler in a material like SonicFill™ (Kerr Dental, www.kerrdental.com), sonic energy is applied through a special handpiece to increase the flowability and to further ease the packing of the composite. The good degree of conversion may be due to refractive index matching between the resin and filler, which enhances light transmission. Reduction in refractive index differences between resin and filler has improved degree of conversion⁵ and increased depth of cure and also improved color shade matching.⁶

Variations in the depth of cure between bulk-fill resin composites may be ascribed initially to light scattering at particle interfaces⁷ and light absorbance by photoinitiators and any pigments.⁸ Both of these factors reduce the light penetration and thus also the degree of conversion of matrix monomers, which are determined by the light irradiance at depth. Degree of conversion is significantly linked with the values of mechanical properties, biocompatibility, and color stability. Therefore, it may also correlate to the clinical success of the restoration. When more extensive polymerization and cross-linking occurs, greater hardness results.³

If the material can be placed in one increment and does not have to be incrementally placed, this can potentially reduce the amount of voids present in the restoration. In the author’s experience, using bulk-fill materials in clinical practice creates a restoration that is much more translucent then some of the non-bulk-fill materials but is satisfactory to the patient.

The case report highlighted here demonstrates the use of a posterior bulk-fill material that can be light-cured to a depth of 5 mm without layering for Class II restorations and 4 mm for Class I restorations. Because it is a highly filled composite, not a flowable, there was no need for a separate capping layer. The material, which can be dispensed without the need for special equipment, reduced the number of steps to perform the restoration yet still offered excellent adaptation, strength, sculptability, and wear resistance. Without the need for layering, the clinician was able to save time without compromising patient care. Moreover, the chance of contamination between layers was eliminated.

An 18-year-old male patient presented to the author’s practice complaining of sensitivity on the occlusal surface of tooth No. 3, where a clinical examination revealed the presence of decay requiring removal and restoration (Figure 1). The tooth was isolated with a rubber dam (Figure 2), after which the decay was removed using a #557 bur (Figure 3).

The author then selectively etched only the enamel (Figure 4), taking care to keep as much of the etchant off the dentin as possible. A universal adhesive (Scotchbond™ Universal Adhesive, 3M ESPE, www.3MESPE.com) was then applied with a microbrush and scrubbed vigorously for 20 seconds (Figure 5). Although used by the author in a selective-etch technique, this adhesive also can be used in total-etch or no-etch modes. The composite, a bulk-fill posterior restorative in shade A1B (Filtek™ Bulk Fill, 3M ESPE) was then placed into the prepared cavity according to the manufacturer’s capsule procedure kit instructions (Figure 6); alternatively, a routine composite dispensing gun could have also been used. The restoration was then light-cured for a single 20-second cure on the occlusal surface.

Finally, finishing and polishing were completed using first a coarse then a fine spiral finishing wheel (Sof-Lex™ Spiral Finishing and Polishing Wheels, 3M ESPE) (Figure 7 and Figure 8) with the rubber dam in place (Figure 9). The entire procedure was completed in less than 30 minutes, yielding an esthetic and functional restoration (Figure 10) as well as convenience for the patient and the clinician.

Because a majority of restorations are placed in the posterior, having the ability to perform these restorations more quickly and easily without compromising patient care is of great value to the clinician. Incremental technique may be preferred in some clinical situations, such as when the depth of the preparation is greater than 4 mm to 5 mm or when a tooth is being incrementally built using different dentin and enamel composite colors for maximum esthetics. However, the drawbacks of incremental technique include the possibility of trapping voids between layers and the time required to place the restoration. With a reduced number of clinical steps, bulk application technique is simpler and faster.⁹

The posterior restorative used in this case is an example of a newer bulk-fill product that enables this procedure to be completed in a more timely and efficient manner. The product also provided an attractive chameleon effect to blend with the surrounding dentition, and also polished well. Bulk placement composite was selected in this case over a flowable, which, at minimum, would have required placement of a base layer and capping layer—both of which would require etching and light-curing. As described above, this procedure can be quickly completed using a one-step placement technique, inserting up to 4 mm of the bulk-fill posterior restorative into a Class I restoration. The bulk-fill product used is formulated with two methacrylate monomers that act in combination to lower polymerization stress; therefore, its use for bulk placement can be achieved without sacrificing strength or wear resistance. The material’s characteristics also include surface smoothness and gloss retention, and its excellent adaptation and sculptability contributed to its ease of use and fast placement.

In order to sustain practice profitability, it is incumbent for clinicians to look for ways to increase efficiency while also maintaining high-quality care in completing treatments indicated for their patients. Materials that serve this goal help clinicians provide better patient care as well as produce a higher volume of treatments. For everyday practice, in which posterior restorations are performed quite regularly, today’s newer composite resins enable clinicians to follow a predictable, conservative, and reliable chairside protocol for restoring worn and decayed tooth structure with excellent esthetics.

As demonstrated in this case, bulk-fill posterior restoratives offer dentists the ability to place up to 5 mm in one increment while delivering exceptional functionality, including stress relief. By eliminating additional layers and multiple steps, such materials provide dentists with a fast, simplified option for direct posterior restorations. In the case presented, the durable material utilized nanofiller technology that enables high strength, wear resistance, surface smoothness, and gloss retention. The posterior restoration was completed in less than 30 minutes, providing a win-win situation for both clinician and patient.

Robert C. Margeas, DDS
Adjunct Professor, Department of Operative Dentistry, University of Iowa College of Dentistry, Iowa City, Iowa; Private Practice, Des Moines, Iowa

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