# Antimicrobials in Dentistry
## 2 Antimicrobials Used in Dentistry
### Antibacterial Monomers in Dental Restorative Systems
#### 2.4.2 Applications of Eugenyl Methacrylate
This effect is desirable as it can facilitate injection into the root canal system through the delivery devices [102]. It also reduced the polymerisation shrinkage stress within the material during early setting [103], and the stress relief via resin flow relaxation decreases the possibility of gap formation [104] and marginal leakage [105], which consequently can enhance the longevity of the restorations. The experimental resin composites with EgMA also exhibited significantly higher depth of cure and lower polymerisation exotherm compared to commercial composites. The reduction in exothermic polymerisation constitutes an additional advantage preventing thermal damage of the adjacent root dentine whilst curing occurs within the endodontic cavity. The addition of EgMA into the composite formulations also increased both flexural and compressive strengths. This confirms the effect of EgMA, which allows for both crosslinking and forming branched structures. The crosslinked network leads to strengthening whilst an increase in ductility is observed due to the branching [106]. Water sorption and solubility of polymeric composites are also of importance for dental applications since the physical and mechanical properties of resin composite materials may be significantly altered by fluid uptake in the oral environment, which also leads to the harbouring of bacteria within these composites that eventually leads to discolouration and failure. The water sorption and diffusion coefficient values of the EgMA resin composites were significantly reduced with increasing content of EgMA due to the hydrophobicity and ability to form slightly crosslinked structures. The increasing surface contact angle and decrease in surface free energy of the EgMA resin composites were expected due to the presence of the aromatic ring in the structure of EgMA. As the antibacterial activity of the experimental composites is derived from the pendent eugenyl residue, the ability of these composites to reduce or inhibit bacterial growth is highly dependent on the direct contact between eugenyl residues of the composite surface and the bacteria [107; 108; 109]. It was noted that the greater hydrophobic character of EgMA-containing composites improved the total interaction energy with the bacteria and resulted in a higher accessibility to the eugenyl moieties responsible for the bacteriostatic activity. The antibacterial activity of the EgMA-containing resin composites determined against _E. faecalis, S.mutans_ and _P. acnes_ showed surface-inhibition properties using the agar diffusion test [101]. The lack of inhibition zones around the composite discs containing EgMA confirmed their non-releasing behaviour, as the inhibition zones were formed by the diffusion of antimicrobial material, indicating that the antibacterial activity of the composites is not through the release of agents to the medium but is instead associated with surface contact. Secondly, the surface antibacterial activity test against the adherence and growth of _E. faecalis, S. mutans_ and _P. acnes_ was performed. There was a significant reduction in the number of colony-forming units (CFUs) of the bacteria tested, indicating that the chemically bound monomer has the capability to reduce or inhibit the colonisation of these bacteria that come into contact with the composite surface. Therefore, incorporation of EgMA monomers as immobilised bactericidal moieties within polymerisable formulations provides a novel approach to develop resin composite materials with intrinsically antibacterial activity against common coronal and endodontic oral bacteria.