• A Novel Dental Sealant Containing Dimethylaminohexadecyl Methacrylate Suppresses the Cariogenic Pathogenicity of Streptococcus mutans Biofilms

      Ibrahim, M.S.; Balhaddad, A.A.; Weir, M.D.; Oates, T.W.; Xu, H.H.K.; Melo, M.A.S. (MDPI, 2019)
      Cariogenic oral biofilms are strongly linked to dental caries around dental sealants. Quaternary ammonium monomers copolymerized with dental resin systems have been increasingly explored for modulation of biofilm growth. Here, we investigated the effect of dimethylaminohexadecyl methacrylate (DMAHDM) on the cariogenic pathogenicity of Streptococcus mutans (S. mutans) biofilms. DMAHDM at 5 mass% was incorporated into a parental formulation containing 20 mass% nanoparticles of amorphous calcium phosphate (NACP). S. mutans biofilms were grown on the formulations, and biofilm inhibition and virulence properties were assessed. The tolerances to acid stress and hydrogen peroxide stress were also evaluated. Our findings suggest that incorporating 5% DMAHDM into 20% NACP-containing sealants (1) imparts a detrimental biological effect on S. mutans by reducing colony-forming unit counts, metabolic activity and exopolysaccharide synthesis; and (2) reduces overall acid production and tolerance to oxygen stress, two major virulence factors of this microorganism. These results provide a perspective on the value of integrating bioactive restorative materials with traditional caries management approaches in clinical practice. Contact-killing strategies via dental materials aiming to prevent or at least reduce high numbers of cariogenic bacteria may be a promising approach to decrease caries in patients at high risk.
    • Pronounced Effect of Antibacterial Bioactive Dental Composite on Microcosm Biofilms Derived From Patients With Root Carious Lesions

      Balhaddad, A.A.; Ibrahim, M.S.; Garcia, I.M.; Collares, F.M.; Weir, M.D.; Xu, H.H.; Melo, M.A.S. (Frontiers Media S.A., 2020-11-23)
      Resin composites are the material of choice for dental restorative treatment in oral health care. However, the inherent composition of this class of material commonly results in microbial adherence and colonization, which carries the potential risk of recurrent carious lesions around dental restorations. The high risk of resin composites failure complicates the treatment of root caries, defined as the onset of tooth decay over the prone root surface of a tooth. The restorative treatment of root caries among high caries risk individuals, especially for senior patients, is a challenging, painful, and costly. The dysbiotic microbiota colonizes the composite’s surfaces and forms polymicrobial biofilms that are difficult to be dislodged by regular tooth brushing. This study assesses the antibiofilm performance of a surface contact killing antibacterial dental resin composites on the growth of microcosm biofilms using dental plaque sampled from patients with active root carious lesions as an inoculum. The designed formulations contain dimethylaminohexadecyl methacrylate (DMAHDM), a tailored quaternary ammonium monomer with an alkyl chain length of 16, at 3–5 wt.% in a base resin with and without 20 wt.% nanoparticles of amorphous calcium phosphate (NACP). Biofilms were grown on the tested resin composites using a 48 h plaque-derived microcosm biofilm model. Dental plaque collected from active root carious lesions was used as an inoculum to emulate the microbiota present in those lesions. The biofilm growth was assessed via the colony-forming unit (CFU) counts in four culture media, metabolic behavior, lactic acid production, and confocal microscopy. The percentage of reacted double bonds of the formulations was also investigated. The dental resin composites formulated with 3–5 wt.% DMAHDM and 20 wt.% NACP were effective at eradicating surface-attached biofilms from the total microbial load and each relevant cariogenic group: total streptococci, mutans streptococci, and lactobacilli. The metabolic activities and lactic acid production of the plaque-derived microcosm biofilms were reduced by 80–95%, respectively. Fewer viable microorganisms were observed over resin composites containing DMAHDM and NACP. Besides, all the experimental formulations demonstrated an acceptable degree of conversion values. This new strategy fits with ongoing dental caries preventive and minimally invasive approaches by preventing biofilm growth over-restored carious root lesions and improving the lifespan of dental restorations. Copyright Copyright Copyright 2020 Balhaddad, Ibrahim, Garcia, Collares, Weir, Xu and Melo.
    • Tuning nano-amorphous calcium phosphate content in novel rechargeable antibacterial dental sealant

      Ibrahim, M.S.; AlQarni, F.D.; Al-Dulaijan, Y.A. (MDPI AG, 2018)
      Dental sealants with antibacterial and remineralizing properties are promising for caries prevention among children and adolescents. The application of nanotechnology and polymer development have enabled nanoparticles of amorphous calcium phosphate (NACP) and dimethylaminohexadecyl methacrylate (DMAHDM) to emerge as anti-caries strategies via resin-based dental materials. Our objectives in this study were to (1) incorporate different mass fractions of NACP into a parental rechargeable and antibacterial sealant; (2) investigate the effects on mechanical performance, and (3) assess how the variations in NACP concentration would affect the calcium (Ca) and phosphate (PO 4 ) ion release and re-chargeability over time. NACP were synthesized using a spray-drying technique and incorporated at mass fractions of 0, 10, 20 and 30%. Flexural strength, flexural modulus, and flowability were assessed for mechanical and physical performance. Ca and PO 4 ion release were measured over 70 days, and three ion recharging cycles were performed for re-chargeability. The impact of the loading percentage of NACP upon the sealant's performance was evaluated, and the optimized formulation was eventually selected. The experimental sealant at 20% NACP had flexural strength and flexural modulus of 79.5 ± 8.4 MPa and 4.2 ± 0.4 GPa, respectively, while the flexural strength and flexural modulus of a commercial sealant control were 70.7 ± 5.5 MPa (p > 0.05) and 3.3 ± 0.5 GPa (p < 0.05), respectively. A significant reduction in flow was observed in the experimental sealant at 30% NACP (p &lt; 0.05). Increasing the NACP mass fraction increased the ion release. The sealant formulation with NACP at 20% displayed desirable mechanical performance and ideal flow and handling properties, and also showed high levels of long-term Ca and PO 4 ion release and excellent recharge capabilities. The findings provide fundamental data for the development of a new generation of antibacterial and rechargeable Ca and PO 4 dental sealants to promote remineralization and inhibit caries. Copyright 2018 by the author.