Bioactive Bulk Composite Satisfies Esthetic Demands While Protecting Against Restoration Failure

Dental fillings have been used in teeth dating back to approximately 8000 BC.¹ References to dental decay can be found in Sumerian texts from 5000 BC.¹ In the early 1700s, the establishment of dentistry as a profession began when Pierre Fauchard, a French surgeon, published his book, The Surgeon Dentist, a Treatise on Teeth. In the book, Fauchard discussed the importance of dental hygiene, proposed the use of dental fillings and dental prostheses, and described how sugar played an important role in dental decay.^1,2

In more modern times, the need for further improvements in dentistry was bolstered as soldiers returned from World War II. This led to the establishment of the National Institute of Dental Research in 1948,¹ which in 1988 became the National Institute for Dental and Craniofacial Research.³

Since then, the basic treatment for dental caries has remained relatively unchanged. Most current restorative materials are inert.⁴ Traditional composite restorations are bonded to tooth structure by different types of adhesives. The weak link in a composite restoration has tended to be at the interface between tooth structure and restorative material, where microgaps trap biofilms leading to secondary decay.^5,6 Manufacturers have aimed toward developing materials with better bond strengths and lower polymerization shrinkage; however, these materials still remain somewhat passive and are often subject to secondary caries. Recently, a new approach has emerged that centers on making these restorative materials active.

Development of Bioactive Materials

The use of direct composite restorations has increased due to the esthetic demands of patients.⁷ Still, composite materials collect plaque and biofilm, which, in turn, produce acids leading to secondary decay.^8,9 Two methods in attempting to curtail secondary decay, particularly at the margins, include suppressing the biofilm and promoting remineralization.⁴ Several "bioactive" restorative materials have been introduced to address these two methods.

The term "bioactive" has prompted different interpretations as to what constitutes a material's bioactivity.¹⁰ In June 2018, the American Dental Association (ADA) published a report in which 318 ACE (ADA Clinical Evaluators) panel leaders discussed the definition of a "bioactive material."¹¹ Most of the respondents, 87%, said that a bioactive material should have the ability to form reparative dentin for pulp capping. Also, 82% of the respondents identified a bioactive material as having the ability to favor tooth remineralization by releasing such ions as calcium, phosphate, and fluoride. Lastly, 56% of the respondents identified bioactivity as having the ability to form hydroxyapatite on its surface to "occlude" a cement gap.

Bioactive materials are not new to dentistry. Calcium hydroxide (Ca(OH)₂) was introduced in the 1920s. It has been shown to promote odontoblast differentiation, aid in the formation of dentin bridges, mineralize coronal pulp, and be antimicrobial by increasing the pH.¹² Although Ca(OH)₂ has been used in dentistry since its introduction, it has limitations. It cannot bond to tooth structure, it is soluble, and if it is not properly sealed it will dissolve, allowing bacterial penetration into the pulpal tissues.¹³ Manufacturers made modifications to address these limitations by incorporating Ca(OH)₂ into a light-curable resin, but subsequent studies found that this alteration limited the release of ions.¹⁴

Another approach in addressing the limitations of Ca(OH)₂ was the development of mineral trioxide aggregate (MTA) in 1993. MTA is composed of tricalcium silicate, dicalcium silicate, and tricalcium aluminate. When MTA is mixed with water, Ca(OH)₂ is produced, triggering the precipitation of hydroxyapatite on the material's surface. MTA can chemically bond to dentin, providing a seal and producing dentinogenic activity.^15,16

During the development of bioactive restoratives, experimental formulations were created in the laboratory that released calcium and phosphate. Researchers found that dental resins which contained calcium phosphate filler could release supersaturating levels of calcium and phosphate ions that remineralized a tooth lesion in vitro. However, the experimental composite was mechanically weak with a flexural strength half that of unfilled resin.¹⁷ Other experimental designs for antimicrobial and/or remineralizing restoratives included the incorporation of a sol-gel-derived silver-doped bioactive glass,¹⁸ the addition of silver sodium hydrogen zirconium phosphate to the composite resin,¹⁹ and the incorporation of quaternary ammonium methacrylate to the resin matrix.²⁰

Today, newer formulations of bioactive restorative materials have been introduced that have been shown to be able to produce layers of hydroxyapatite on their surfaces.^21-23 A study conducted at Uppsala Univeritet in Sweden showed that one such material in particular (Predicta^™ Bioactive Bulk, Parkell, parkell.com) had a fast release of calcium, phosphate, and fluoride up to 7 days with a decrease in release after that time period.²³ The following case report describes the placement of this bioactive bulk composite.

Case Report

A patient presented with a defective class II amalgam restoration in the upper left quadrant and requested a tooth-colored composite restoration (Figure 1). After isolation with a rubber dam the amalgam restoration was removed. A medium-size FenderWedge^® (Directa Dental, directadental.com) was placed interproximally between the maxillary left first molar (No. 14) and second bicuspid (No. 13) to create temporary separation between the two teeth and provide a matrix for the box portion of the class II preparation (Figure 2). In situations where bur damage may occur to the adjacent proximal surface, the FenderWedge may be placed before the removal of the existing restoration. This not only guards against bur damage to the adjacent tooth surface, but it also protects the gingival tissue in deep preparations.

Next, phosphoric acid was applied to the entire cavity preparation. A bonding agent (Universal Adhesive, Parkell) was selected that may be used with self-etch, selective-etch (ie, etching only the enamel), and total-etch methods. All methods provide sufficient bond strength; however, one study showed the highest bond strength was created when the total-etch method was used.²⁴

After etching, the cavity preparation was rinsed and dried. The adhesive was applied to the preparation using a rubbing motion for 20 seconds keeping the surface moist. A second coat of the adhesive was applied for an additional 20 seconds (Figure 3). The second application was applied without air-thinning or light-curing after the first application. Using an air-water syringe, the surface was air-thinned for 10 seconds to evaporate the solvent and remove the dissolved smear layer, as per the manufacturer's instructions. The surfaces were light-cured for 10 seconds. The photopolymerization of this adhesive requires a wavelength between 430 nm and 480 nm at a minimum intensity of 600 mW/cm₂.

Predicta Bioactive Bulk composite is available in two different consistencies, high viscosity and low viscosity. The low-viscosity version, which was used in this case, offers a higher flow rate. A bendable metal-tipped mixing tip, provided by the manufacturer, was used to help facilitate the application of the composite into the deepest portion of the cavity preparation (Figure 4).

Starting in the proximal box portion of the cavity preparation, the bioactive bulk composite was injected to fill the entire cavity preparation (Figure 5). Because the restorative material has dual-cure methods of polymerization, it is advised to wait 1 minute before light-curing the material. Studies have suggested that immediate light activation can interfere with the chemical polymerization of the material by stiffening the polymer chains.^25,26 This is especially true when the depth of the proximal box does not allow close approximation of the light-curing tip, thereby limiting the amount of light for sufficient polymerization.

After the occlusal surface was light-cured, the FenderWedge was removed. The curing light tip was placed on the buccal surface, which was then light-cured. The same step was applied to the lingual surface.

With a series of different finishing burs, the occlusal surface was finished and the occlusion was verified (Figure 6). The occlusal surface was then smoothed with a series of Absolute Polishers^™ (Parkell), and the restoration was polished with Zircon-Brite Polishing Paste (Dental Ventures of America, Inc, dentalventures.com) (Figure 7 and Figure 8).

Conclusion

Secondary decay is the root of composite resin restoration failure. Dental material technology has evolved to produce newer restorative materials that not only satisfy the esthetic demands of patients but now may play an active role in preventing the very cause of failure. Restorative materials that can release calcium, phosphate, and fluoride, creating a precipitate of hydroxyapatite on their surface, no longer are considered inert but become active in the prevention of recurrent marginal failure.

About the Author

Gregg A. Helvey, DDS, MAGD, CDT
Associate Professor, General Dentistry, Virginia Commonwealth University School of Dentistry, Richmond, Virginia; Private Practice, Middelburg, Virginia