Developing Bioactive Dental Resins for Restorative Dentistry

Abstract

Despite its reputation as the most widely used restorative dental material currently, resin-based materials have acknowledged shortcomings. As most systematic survival studies of resin composites and dental adhesives indicate, secondary caries is the foremost reason for resin-based restoration failure and life span reduction. In subjects with high caries risk, the microbial community dominated by acidogenic and acid-tolerant bacteria triggers acid-induced deterioration of the bonding interface and/or bulk material and mineral loss around the restorations. In addition, resin-based materials undergo biodegradation in the oral cavity. As a result, the past decades have seen exponential growth in developing restorative dental materials for antimicrobial applications addressing secondary caries prevention and progression. Currently, the main challenge of bioactive resin development is the identification of efficient and safe anticaries agents that are detrimental free to final material properties and show satisfactory long-term performance and favorable clinical translation. This review centers on the continuous efforts to formulate novel bioactive resins employing 1 or multiple agents to enhance the antibiofilm efficacy or achieve multiple functionalities, such as remineralization and antimicrobial activity antidegradation. We present a comprehensive synthesis of the constraints and challenges encountered in the formulation process, the clinical performance-related prerequisites, the materials' intended applicability, and the current advancements in clinical implementation. Moreover, we identify crucial vulnerabilities that arise during the development of dental materials, including particle aggregation, alterations in color, susceptibility to hydrolysis, and loss of physicomechanical core properties of the targeted materials.

Keywords: composite dental resin; dental caries; dentin-bonding agents; nanotechnology; tooth remineralization.

Figure 1.

Clinical image of secondary caries around composite restorations and the vulnerability factors associated with secondary caries.

Figure 2.

Timeline of bioactive restorative materials. (A) In the upper section, the mileposts in developing dental materials commercialized in the market with claimed bioactivity toward secondary caries prevention. In the lower section, the mileposts of the innovative approaches and investigations for developing new bioactive resin-based materials. (B) Some highlighted steps in the design and faced drawbacks in the development of new resin-based formulations proposed to convey bioactivity to dental resin materials, such as resin composites, adhesives, and luting agents.

Figure 3.

Illustrative transmission electron microscopy images of clusters of nanostructures and their respective mechanisms responsible for the antibacterial activities. (A) Titanium dioxide (TiO₂) used as nanotubes (Stürmer et al. 2021), and (B) silver nanoparticles and (C) zinc oxide (ZnO) used as nanoneedles. A variety of metal–oxide nanostructures release metal ions on the surfaces of nanostructures and/or promote nanostructure-induced oxidative stress. (D) Illustration of the structures of ionic liquid–functionalized quantum dots of metal oxides investigated to overcome the drawbacks of agglomeration often presented by several nanostructures.

Figure 4.

Microbiological Experiments. (A) The plaque samples isolated from the subgingival area were used to initiate plaque-derived microcosm biofilms in vitro. (B) A color-coded stack barplot graph shows the average bacterial relative abundance on genus level in both groups of pooled plaque inoculum. Pooled plaque inoculum refers to the bacterial composition used to initiate the plaque-derived biofilms. The pooled colony-forming unit (CFU) control refers to the CFU isolates derived from the control composites. The pooled CFU 5% dimethylaminohexadecyl methacrylate (DMAHDM)–20% nanosized amorphous calcium phosphate (NACP) refers to the CFU isolates derived from the biofilm grown over 5% DMAHDM–20% NACP composites. (C) Schematic illustration for the nonselective and selective agar plates used in the CFU assay to count (D) total microorganisms, (E) Fusobacterium nucleatum, (F) Aggregatibacter actinomycetemcomitans, (G) Porphyromonas gingivalis, and (H) Prevotella intermedia/nigrescens. Values indicated by different letters are statistically different (P < 0.05). Reproduced from Balhaddad et al. (2021).

Figure 5.

Schematic illustration of multimodal or combinatory bioactive materials. These materials can present multiple properties, such as antibacterial, remineralization, and tissue regeneration. The combinatorial approach can also be used to enhance the cited properties.