Periodontal disease (PD) is one of the most important oral afflictions and is one that contributes to the global burden of chronic disease. Because PD is highly prevalent worldwide it represents a major public health problem in numerous countries. Like severe dental caries, PD is a major cause of tooth loss, which directly affects people’s quality of life by lowering their functional capacity and self-esteem and deteriorating social relationships [1
]. Clinically speaking, PD is defined as an inflammatory condition of the gingiva and supporting tooth structures. Gingivitis and periodontitis are the most common forms [2
The most common commercial products used to treat PD are oral rinses. However, not even extensive oral rinsing with antibacterial solutions reaches deep into subgingival tissues, while the high dosages of antibiotics required to achieve therapeutic levels in the periodontal pocket can result in unpleasant or even toxic adverse effects [3
Various drug delivery systems for periodontal applications have been developed, including acrylic strips, fibres, films, injectable system gels, intra-pocket strips, vesicular systems, and microparticle and nanoparticle systems [5
The drug candidate chosen for this study was chlorhexidine (CHX) base, which is widely used in clinical dental practice as an antiseptic oral rinse due to its activity against a wide range of microbial species. The CHX base (1,1’-hexamethylene-bis-5-(4-chlorophenyl) biguanide) is a symmetric molecule with two ionisable guanidine moieties in the form of a solid white crystal (m.p. 132 °C, MW
505.5). The water solubility of the CHX base at 20 °C is 0.008% (w/v
). The chemical structure of the CHX base is depicted in Figure 1
. Its pKa values are 2.2 and 10.3, which render it dicationic over the entire range of physiological pH values [9
]. This base is an antimicrobial agent often used in dentistry as an antiplaque agent but it has also demonstrated good activity against a wide range of oral bacteria. The CHX base is a drug of choice for treating periodontal disease because it prevents the development of an oral environment conducive to periodontal diseases [12
Currently, 0.2% CHX aqueous solutions have been shown to be moderately effective in treating PD. Thus, there is growing interest in developing novel delivery systems that maintain the concentration of CHX for long periods to help reduce the incidence of these diseases [14
]. Several nanocarriers or nanomaterials, such as liposomes, lipid, metal and polymeric nanoparticles, nanocrystals, dendrimers, and nanofibers, have been proposed as treatment options for PD [15
]. They all use nanocarriers (e.g., organic nanoparticles) as drug delivery devices and have often been recommended as a means of meeting the specific requirements of the oral mucosa and enhancing conventional therapies by avoiding dilution effects while increasing the infiltration and adherence of the nanoformulations [11
Cellulose derivatives (cellulose ethers and esters) have played a strong supporting role during the development of sustained, controlled-release oral dosages as (1) coatings capable of responding to changes in the physiological environment, (2) semi-permeable membranes, and (3) hydrophobic matrices that lower the dissolution rate of the active drug embedded in the matrix. Cellulose acetate phthalate (CAP) was one of the earliest and most effective polymers used for pH-controlled release. Its use continues today [17
] because it resists prolonged contact with strongly acidic gastric fluid but dissolves in a mildly acidic or neutral intestinal environment [19
]. This polymer does not form a gel in the presence of water but forms pH-sensitive and semi-permeable microporous systems. These properties make CAP a suitable excipient for developing new drug delivery systems that are now recognized as promising strategies for prolonging residence time and improving the specific localization of systems. Hence, they can reduce dosage frequency in controlled release formulations [20
An alternative antibacterial approach involves antibiotic synergists. In antimicrobial therapy, synergism is used to describe the supra-additive activity of antibiotics when used in combination with other compounds. Eugenol (4-allyl-2-methoxyphenol) was selected as the model substance to form the oily core of the nanocapsule (NC) formulations prepared by the emulsification-diffusion method in order to potentiate the drug’s antimicrobial action and realize the synergistic, analgesic, and anti-inflammatory effect of the eugenol. This substance is the principle chemical component of clove oil derived from E. aromatic
and has long been known for its analgesic, local anaesthetic, anti-inflammatory, and antibacterial effects [21
]. Used in the form of a paste or mixture as a dental cement, filler, and restorative material, it belongs to the class of essential oils that are Generally Recognized as Safe (GRAS) by the U.S. Food and Drug Administration (FDA). Eugenol acts primarily by disrupting the cytoplasmic membrane [27
] but its biological effects vary greatly depending on concentration. Eugenol may have a beneficial effect at concentrations ranging from 10−8
M to 10−5
M (prostaglandin synthesis, nerve activity, and white blood cell chemotaxis inhibition) but can be cytotoxic at concentrations >10−3
M (cell death, cell growth, and respiratory inhibition) [29
]. Today, the development of innovative drug delivery systems focuses on designing multiple options, blocking the adverse effects of drugs, and reducing dosage intervals.
Oral fluid can be considered the protective medium for all tissues of the oral cavity. It acts as a buffer by maintaining a pH between 5.75 and 7.05. This fluid is composed mainly of water (99.5%), organic compounds (0.3%), and inorganic and trace elements (0.2%) [30
]. By contrast, the periodontal microenvironment is more anaerobic and perfused by a plasma filtrate called gingival crevice fluid. The growth of microorganisms in this microenvironment has been shown to cause periodontal disease. Because the site of bacterial infection is usually inaccessible to agents present in the oral cavity, antimicrobial agents administered there tend to be ineffective. Therefore, a local antibiotic agent loaded in an intra-pocket delivery system promotes a high drug concentration in the gingival crevice fluid that reduces adverse effects and provides such advantages as improving drug efficacy and patient compliance [31
Nanometer-sized systems have the potential to infiltrate easily into the periodontal pocket and remain in the damaged tissue where they release the drug in a controlled manner [32
]. PDs usually involve diverse, complex mechanisms that require various molecules to achieve effective treatments. Because the bacteria that cause periodontal tissue inflammation and destruction are present in every stage of PD, treatment requires antimicrobials, antioxidants, antiresorptives, and anti-inflammatory drugs. At present, some commercial products for treating PD include mouthwashes that are applied daily, systemic antibiotics, and systems for the local delivery of bioactive agents [33
The aim of the present study was to develop two nanoparticle systems—nanospheres and nanocapsules—loaded with CHX base as novel formulations to improve treatment of PD by (1) enabling the maintenance of therapeutic drug levels over long periods, (2) preventing relapses, (3) decreasing the amount of drug needed to achieve the therapeutic effect, and (4) reducing treatment time. These factors should also result in greater patient acceptance.
The emulsification-diffusion technique used in this work allowed the preparation of two systems—CHX-CAP-NSphs and CHX-CAP-NCs—that can be applied as local drug delivery systems in the oral cavity. More specifically, they can infiltrate, or be administered into, the periodontal pocket. The NCs showed the best entrapment efficiency at 84.30%. DSC showed that introducing CHX into CHX-CAP-NC systems decreases the glass transition temperature of the polymer. The CHX release test showed that the CHX-CAP-NSphs and CHX-CAP-NCs adjusted to the Higuchi and Korsmeyer-Peppas models and so correspond to Fickian diffusion that is dependent on time in the case of NSphs, and non-Fickian diffusion (anomalous transport) in that of the NCs, perhaps because eugenol oil acts as a polymer plasticizer. Both processes involve diffusion-erosion processes. These results indicate that CHX-CAP-NSphs and CHX-CAP-NCs could be of great help in treating periodontal disease because they affect a larger surface area and have both controlled release and potential tissue infiltration. In addition, eugenol could potentiate the antibacterial effect of CHX and exert a synergistic effect that takes advantage of its analgesic and anti-inflammatory properties.
Applying CHX-CAP-NCs reduced the dentobacterial plaque index by 65.78%, in contrast to a commercial mouthwash, which reduced this index by only 25.8%. Therefore, we can suggest that nanoparticulate systems allow much greater infiltration into the subgingival tissue (periodontal pocket) because they cover a greater surface area and so reduce both the therapeutic dosage and treatment time.