Date Published: January 10, 2019
Publisher: Taylor & Francis
Author(s): Tamer Tüzüner, Aleksandar Dimkov, John W. Nicholson.
Aim: The aim of this article is to review the literature on the use of antimicrobial additives in glass-ionomer dental cements.
Glass-ionomer cements are acid-base materials that are widely used in clinical dentistry . Applications include full restorations, particularly in children, liners and bases, fissure sealants, luting agents and also, to a lesser extent, adhesives for orthodontic brackets bands  and as endodontic sealers .
The first study of the release of organic antibacterial substances appeared in 1991, and used chlorhexidine diacetate . Two concentrations were used (13.3% and 6.65%) with AquaCem (Dentsply), a commercial water-activated luting cement. Results showed that antimicrobial properties improved . Glass-ionomers have some slight antimicrobial properties, even without additive, as a result of their fluoride release [15,16]. This was shown by Seppa et al. , with glass-ionomers against Streptococcus mutans. It has also been shown generally with glass-ionomers against plaque . This is attributed to fluoride release, a feature which may protect teeth from secondary caries .
The effect of organic antibacterial additives on the properties of the cement have been widely studied [22,23,27,39]. Data from various studies are shown in Table 1. These show that additives have two effects, namely slowing down the setting reaction and reducing the mechanical properties of the cement. Similar findings have been reported for both neutral organic additives and for ionic compounds. For example, the organic compounds methanol and 2-hydroxyethyl methacrylate (HEMA) both reduced the speed of the setting reaction and also the compressive strength at 24 h  (see Table 4).
The majority of papers on controlled release from glass-ionomer cements concentrate on a limited range of antimicrobial compounds. However, some other substances have been studied. For example, the combination of casein phosphopeptide/amorphous calcium phosphate with lysozyme, lactoferrin and lactoperoxidase (LLL) added to a glass- ionomer cement was then used to restore extracted third molars in an in vitro study . These teeth were then exposed to a standard strain of S. mutans and results showed that there was a significant reduction in numbers of S. mutans with LLL only at 1 month, though numbers increased by 6 months. The 1 month reduction in bacterial growth was considered clinically desirable, as it would inhibit the progress of caries in newly restored teeth . Unfortunately, no results were reported on how the LLL combination altered setting or strength properties.
Some commercial glass-ionomers are made from strontium-containing glasses where the element strontium effectively replaces calcium in the structure . As such, it is insoluble under neutral conditions but is released from cements under acidic conditions. Strontium has been studied for its antibacterial properties [61,62] and results show that its presence enhances the anti-bacterial activity of glass-ionomer cements to a substantial extent . Details of its mechanism are not known, and the sensitivity of its release to the surrounding pH may limit its usefulness in clinical application.
There have been fewer studies on adding antimicrobial compounds to resin-modified glass-ionomers than to conventional glass-ionomers. An early study used chlorhexidine diacetate (5% concentration) in the resin-modified glass-ionomer Photac-Fil (3M, USA) . Samples were tested for hardness, diametral tensile strength and erosion levels at 24 h and 6 weeks. Chlorhexidine diacetate elution was determined at weekly intervals, and antibacterial properties were measured at 6 weeks only. No differences were found in diametral tensile strengths for specimens containing the additive at either 24 h or 6 weeks. Hardness also did not differ at 24 h, but had become significantly lower for the samples containing chlorhexidine diacetate after 6 weeks. Results from erosion studies showed that the chlorhexidine group lost less material than the additive-free control at 24 h, but significantly more at 6 weeks. Elution levels were highest at 1 week, and substantial antimicrobial effects were recorded against S. mutans. Similar antibacterial properties were found at weeks 2 and 3, but not afterwards.
The majority of antibacterial substances used in glass-ionomer cements are ampiphilic compounds with a reasonable degree of surface activity. This includes both the chlorhexidine species used (diacetate and digluconate) as well as benzalkonium chloride, cetylpyridinium chloride and cetrimide [54,79]. These substances are broad-spectrum antimicrobials that are particularly effective against Gram-positive bacteria. They are used as antiseptics and antimicrobials, including in oral hygiene products such as mouthwashes and lozenges [80,81].
This review has shown that there are potential clinical advantages in adding antimicrobial compounds to glass-ionomer dental cements, either conventional or resin-modified. A limited number of substances have been studied in depth, namely chlorhexidine diacetate, chlorhexidine digluconate, benzalkonium chloride, cetylpyridinium chloride and cetrimide, though others, including natural products and inorganic substances, have also been considered and reported in the literature. Typically such substances reduce the mechanical properties of the cements, though higher loadings have more effect; these additives may also reduce fluoride release. Release is typically a diffusion processes, and at amounts that show effects against bacterial population. Longer-term studies are currently lacking, and further work is necessary to confirm the effectiveness of this approach. The particular organic compounds that have been used as additives do not lead to resistance in the target microorganism S. mutans, so this approach has potential clinical advantages for use in patients.