# Antimicrobials in Dentistry
## 2 Antimicrobials Used in Dentistry
### Antibacterial Monomers in Dental Restorative Systems
#### 2.4.2 Applications of Eugenyl Methacrylate  
Eugenyl Methacrylate in Polyacrylic Acid for Glass-Ionomer Cements  
Glass ionomer cements (GICs) are an important class of dental materials that set by an acid-base reaction of an ion leachable calcium fluoro-aluminosilicate glass powder and a polyalkenoic acid, which is usually either a homopolymer of polyacrylic acid or a copolymer of acrylic and maleic acids in the presence of water [91]. The setting of GIC involves neutralisation of the acid groups available from the water-soluble polymer and the glass powder base. As these cements harden, they are associated with various changes, one of which is an increase in the proportion of tightly bound water within their structure. Therefore, GICs are sensitive to moisture in the early stages of placement and can lose matrix-forming ions in the presence of excessive moisture or desiccation [92]. Different acrylic acid blends and copolymers have been reported not only imbibing anti inflammatory [93] and antibacterial [94] effects, but can also alter the moisture sensitivity of composites [95] such as GICs. The modified GIC with a mixture of acrylic acid and EgMA resulted in the experimental GICs exhibiting physical and mechanical properties in compliance with ISO standard requirements and is not significantly different than the commercial GIC [96]. Furthermore, the eugenyl residue was associated with an increase in the fraction of the volume surrounding the macromolecules, providing more flexible materials. This balance resulted in the experimental GICs having a marked increase in the flexural strength values, whilst maintaining the other mechanical properties over the standard requirements and additionally lowering the net water uptake. An additional advantage of these experimental GICs was the higher pH of the initial mix that was attributed to the lower net amount of \(-\)COOH groups in the copolymer and essentially these being neutralised in the early stages of the reaction and during the maturation process of the ionically crosslinked cement (Figure 4) [97]. The higher pH is expected to reduce irritation of the tooth pulp, when placed near it [98]. Although the incorporation of EgMA molecules in the polyacrylic acid copolymer resulted in a net decrease in the amount of \(-\)COOH groups in the matrix that retain the fluoride ions, there was no difference in the fluoride release between the commercial and experimental GICs. As the pH of the experimental cements was higher than the commercial cement, it was expected to release higher amounts of fluoride in the initial stage, which may improve the anticariogenic effects [99]. Based on these detailed studies, it can be concluded that GICs constituting acrylic copolymers with immobilised eugenol moieties improve physical properties as well as exhibit anticariogenic behaviour. Eugenyl Methacrylate in Resin Composites  
Resin composites were specifically developed for the cementation of endodontic posts and core build-up restorations that would benefit from possessing bactericidal properties; thus, dual cure (chemical and photopolymerisation) resin composites based on EgMA  
Figure 4: Adhesion mechanism between the hydroxyapatite surface and polymeric component of antibacterial glass ionomers formulated with acrylic acid and eugenol-derived copolymer p(AA-co-EgMA) [94]. monomer and Bis-GMA/TEGDMA resin systems were formulated. The addition of EgMA monomer resulted in the enhancement of the viscoelastic properties, the mechanical response of the composites and imparted antibacterial properties to the resin system by virtue of the EgMA residues, specifically against a range of oral bacteria commonly associated with failure of coronal and endodontic restorations. The experimental composites also exhibited outstanding properties in comparison to currently used dental composite materials [100; 101]. The low viscosity of the EgMA monomer functioned as an excellent diluent for the viscous Bis-GMA monomer and enhanced the initial handling viscosity.