Novel Bioactive and Therapeutic Root Canal Sealers with Antibacterial and Remineralization Properties

Abstract

According to the American Dental Association Survey of Dental Services Rendered (published in 2007), 15 million root canal treatment procedures are performed annually. Endodontic therapy relies mainly on biomechanical preparation, chemical irrigation and intracanal medicaments which play an important role in eliminating bacteria in the root canal. Furthermore, adequate obturation is essential to confine any residual bacteria within the root canal and deprive them of nutrients. However, numerous studies have shown that complete elimination of bacteria is not achieved due to the complex anatomy of the root canal system. There are several conventional antibiotic materials available in the market for endodontic use. However, the majority of these antibiotics and antiseptics provide short-term antibacterial effects, and they impose a risk of developing antibacterial resistance. The root canal is a dynamic environment, and antibacterial and antibiofilm materials with long-term effects and nonspecific mechanisms of action are highly desirable in such environments. In addition, the application of acidic solutions to the root canal wall can alter the dentin structure, resulting in a weaker and more brittle dentin. Root canal sealers with bioactive properties come in direct contact with the dentin wall and can play a positive role in bacterial elimination and strengthening of the root structure. The new generation of nanostructured, bioactive, antibacterial and remineralizing additives into polymeric resin-based root canal sealers are discussed in this review. The effects of these novel bioactive additives on the physical and sealing properties, as well as their biocompatibility, are all important factors that are presented in this article.

Keywords: amorphous calcium phosphate; antibacterial; dimethylaminododecyl methacrylate; quaternary ammonium compounds; remineralization; root canal sealer.

Figure 1

Effect of chain length (CL) on dental plaque microcosm biofilm colony-forming units (CFU): (A) Total microorganisms, (B) total streptococci, and (C) mutans streptococci. Two-day biofilms on resins were used for CFU measurements (mean ± sd; n = 6). Note the log scale for the y-axis. The CFU at CL of 16 was 4 log lower than that of SBMP control. In each plot, values with dissimilar letters are significantly different from each other (p < 0.05). Adapted from [50] with permission.

Figure 2

Images of E. faecalis following contact with the novel endodontic sealer and unmodified sealer. (A) E. faecalis following 20 min direct contact with the surface of the novel endodontic sealer. Syncytium like cells and bacterial lysis can be observed. Most of the bacteria show changes in morphology with no visible signs of cell division. (B) Bacteria following 20 min direct contact with a sealing material without QPEI nanoparticles, early biofilm formation with intact membrane and dividing cells can be observed. Bacteria on the surface of the novel sealer and the sealer without nanoparticles after 40 min, (C) and (D) respectively. Adapted from [66].

Figure 3

NACP in dentinal tubules. (A) Representative scanning electron microscopy (SEM) micrograph showing numerous NACP within the resin tags. (B,C) SEM micrographs of NACP particles within the resin tags at higher magnifications. Adapted from [78] with permission.

Figure 4

Calcium (Ca) and phosphate (P) ion release from endodontic sealers PEHB + NACP control and PEHB + NACP + 5DMAHDM + 3MPC. (A,B) Ca ion release, (C,D) P ion release. Ca and P ions concentrations increased with increasing time and decreasing pH. Adapted from [79] with permission.

Figure 5

(A–D) Live/dead staining images of biofilms in dentin blocks. Live bacteria were stained green. Dead bacteria were stained red. Yellow/orange colors represent live and dead bacteria on top of each other. Dentin blocks of (A) bacteria-impregnated dentin control, (B) AH Plus-treated dentin, and (C) 30% NACP-treated dentin were mostly covered with live bacteria. Dentin blocks of (D) 30% NACP + DMAHDM + NAg were mostly covered with compromised bacteria. (E) Colony-forming unit (CFU) counts of bacteria impregnated in dentin Incorporating 5% DMAHDM + 0.15% NAg reduced the CFU counts by 3 orders of magnitude when compared to control groups. Adapted from [27] with permission.