Antibacterial, and especially antibiofilm, activity is needed for various composite materials among which dental materials are highly exposed to biofilm formation (Beyth et al., 2010).
Dental materials as well as denture surfaces are often affected by colonization and biofilm formation causing specific diseases. Two main approaches were analyzed, the first one is related to a permanent modification, usually with quaternary ammonium salts while the second approach is related to the temporarily induced antimicrobial/ antibiofilm property by using drug-delivery systems. Various chemical agents (chlor- hexidine, miconazole, natural agents, antibiotics, etc.) were tested, in vitro or in vivo to assure antimicrobial and antibiofilm properties for the most common dental materials including methacrylate-based materials, polydimethylsiloxane, and so on (Wang et al., 2014; Beyth et al., 2010; Sun et al., 2013; Bertolini et al., 2014; Quintas et al., 2015). Among the usual dental materials, ceramics exhibit the lowest adhesive capability due to their inert surface. Based on various papers, zirconia dental ceramics, for instance, manifest lower adherence than metals, or even natural teeth. Some of the most common dental materials and the characteristics of the formed biofilm are presented in Table 7.2. It must be mentioned that based on the literature data, the experimental differences are notable and consequently their comparison is only orientative.
Table 7.2 Materials-biofilm characteristics
The biofilm composition is mainly assured by Streptococcus species (10-26%) as well as Fusobacterium nucleatum (2-5%), Actinomyces naeslundii (2-5%), and Veillonella species (1-3.5%).
Sun et al. (2013) investigated the effect of grafting dental-poly(methyl methacry- late)-based materials with poly(V-vinyl-2-pyrrolidinone). For this purpose, a very widely used dental resin, Lucitone 199, was used according to the manufacturer’s instruction and gradually modified by using 0 (control sample), 5, 10, 15, and 20 wt% V-vinyl-2-pyr- rolidinone-NVP in acetone and diurethane dimethacrylate DUMA (5% of NVP) in the presence of 1 wt% of AIBN as initiator, at room temperature for 30 min. After polymerization, each disc was dried 1 h in air, plasma cleaned 5 min, washed with acetone and distilled water, and air-dried overnight. To achieve constant weight, these samples were stored in a desiccator for 72 h. The modification was done on 13 mm x 3 mm disks. These dental materials were further treated with miconazole and chlorhexidine digluconate as antifungal agents, the loading being realized from 5 wt% aqueous chlorhexidine digluconate solution or from 5 wt% miconazole alcoholic solution, overnight, for a disk: antifungal solution ratio of 1:50. Based on their results, the loading capacity was proved to be proportional with the content of grafted polyV-vinyl-2-pyrrolidone as well as the Candida albicans reduction. The cell viability of the five dental samples (without loaded drug) is not significantly altered by the increasing content of PNVP after 1, 3, or 7 days of incubation. The delivery rate was found slow enough to assure an efficient delivery for over 60 days for miconazole and over 14 days for chlorhexidine digluconate assuring a concentration higher than the minimal inhibitory concentration. The anticandidal efficacy was found to be similar for the two drug-loaded systems. Based on all these data, they found that these systems could be promising drug-delivery systems for chlor- hexidine digluconate (assuring sustained delivery for weeks) and miconazole (assuring sustained delivery for even months for high content of PNVP). The main advantage of these systems is related to the possibility of recharging with the same or with the other drug, the resulted system being able to assure almost the same candidal reduction as the initial samples (presented in Table 7.3) for a long period of time.
The use of quaternary ammonium salts was found to be an efficient, long-lasting antimicrobial agent without negative impact on biocompatibility. Starting from
Table 7.3 Characteristics of drug-loaded PMMA-PNVP dental materials
these premises, Beyth et al. (2010) incorporated 1% wt/wt cross-linked quaternary ammonium polyethylenimine nanoparticles into Filtek Flow commercial available composite resin (47% zirconia/silica average particle size 0.01-6.0 pm; BIS-GMA, TEGDMA). The as-obtained material exhibits good antibacterial activity against a broad range of salivary bacteria. The mixing of commercially available dental materials with low level of cross-linked quaternary ammonium polyethylenimine nanoparticles can assure a prolonged antibacterial activity and thus induce a delay of the onset of secondary caries.
The incorporation of chlorhexidine could be also a solution for assuring antibacterial and antibiofilm activity, but its release is faster. So, usually persist for shorter time especially compared with cross-linked quaternary ammonium salts (Du et al., 2012). Du et al. (2012) showed that the percentage of the vital bacteria strongly decreases even after 4 h of the addition of chlorhexidine, from over 40% to 13- 25% depending on the dental support used (glass-ionomer cement or resin-modified glass-ionomer cements).
Although not as prevalent as quaternary ammonium salts (cationic surfactants), nonionic surfactants such as polypropylene oxide-based surfactants are known as potent antimicrobial agents as well as surface properties altering agents. As proved by Treter et al. (2014), pluronic F127 was easily adsorbed onto the polystyrene surface and was found to be a long-lasting antibiofilm agent, which persists even after 100 successive washing cycles.
Osteomyelitis is one of the most serious complications in orthopedics being usually associated with poor blood circulation in that tissue. Bastari et al. (2014) developed calcium phosphate-poly(lactic-co-glycolic acid) hybrid particles and loaded them with nafcillin and levofloxacin. They found that the presence of CaP can significantly change the delivery rate and even the profile of delivery of the two drugs. Nafcillin is delivered faster delivered from PLGA microparticles, the steady state being obtained faster while the presence of CaP leads to a sustained delivery for about 3 weeks. In the case of levofloxacin, the delivery profile is much complex, the presence of CaP leads to a decrease of the cumulative drug release for up to 4 weeks and after this time, practically the same drug release is recorded regardless the presence of CaP. For both drug-delivery systems, S. aureus biofilm is totally inhibited in the 6 h to 28 days period of time. These systems also exhibit remarkable antibiofilm properties against S. aureus biofilms, being able to reduce the biofilm with about 40% within 1 day and practically destroy this biofilm within 7 days.