# Antimicrobials in Dentistry
## 2 Antimicrobials Used in Dentistry
### Antibacterial Monomers in Dental Restorative Systems
#### 2.4.1 Eugenol and Eugenyl Methacrylate
This, together with the presence of the 4-allyl group and the presence of the hydroxylic group coupled to a delocalised electron system, allows the monomer to maintain the ability to alter the cytoplasmic membrane permeability and the inhibitory capacity of colony growing with a consequent block of ionic pumps as proton and potassium ions [84, 86, 87]. The data also indicated that the disruptive effect on cytoplasmic membranes is maintained after the polymerisation reaction, indicating that EgMA-based materials render bioactive bacteriostatic surfaces that reduce microbial resistance and biofilm formation. Moreover, eugenyl-derivative copolymers showed a clear growing inhibition against _E. coli_ and _S. mutans_, but no halo formation, suggesting that the bacteriostatic effect is caused by immobilised agents. It was observed that the reduction in colonies' growth on the agar zone was only found beneath the polymer samples, indicating that the immobilised molecules showed their activity only against bacteria which came into contact with them, and that the effect does not reach distant areas from the material. Accordingly, dental resins and other restorative materials containing eugenyl derivatives would eventually contribute to the reduction or even the inhibition of bacteria growing at the interface between the materials and the surrounding tissues, possibly inhibiting secondary caries formation between the dentine surface and the restorative material. Antibacterial agents whilst inhibiting bacterial growth should also be minimally cytotoxic to mammalian cells. As is known, low concentrations of eugenol exert anti-inflammatory and local anaesthetic effects on the dental pulp; however, high concentrations can exert some cytotoxic effects [88]. Eugenol and related compounds have been shown to have a high affinity for plasma membranes because of their lipid solubility, which may contribute to cell damage [89]. However, both EgMA monomer and PEgMA polymer were found to be cytocompatible when tested in vitro with human fibroblasts [90]. It should also be noted that the eugenol derivatives are only added in small amounts to high-molecular-weight monomers, with the derivatives being incorporated in a cross-linked network, leading to only traces of any unreacted monomer. The cell morphology and cell-material interaction of fibroblasts with polymeric systems showed cells with normal morphology, well spread and flattened over the materials, indicating the formation of stable adhesive contacts and showing good cytocompatibility of the polymer [84]. All these results open a novel approach to achieve biofunctionalised acrylic systems with potential applications in dentistry, orthopaedic surgery and ophthalmology. The novelty of these systems in comparison with other eugenol-containing materials lies in the covalent anchorage of the eugenol molecule to the macromolecular structure, avoiding its migration to the surrounding tissues and improving its hydrolytic stability, whilst still maintaining the beneficial properties of eugenol [71, 80, 81].