Antimicrobial properties of dental cements modified with zein-coated magnesium oxide nanoparticles

Highlights

•Antimicrobial nanoparticles (NPs) are widely used in dental materials to improve their biological properties.
•Magnesium Oxide (MgO) NPs are novel antimicrobial agents.
•Incorporation of MgO NPs in dental cements aids in minimizing bacterial colonization at the restoration margin.
•Zein polymer facilitates the dispersion of MgO NPs and avoid its agglomeration.
•Zein polymer effectively enhances the performance of MgO NPs.

Abstract

The aim of this study was to test the antimicrobial properties of dental cements modified with magnesium oxide (MgO) nanoparticles. Zein-modified MgO nanoparticles (zMgO) in concentrations (0.0, 0.3, 0.5, and 1.0%) were mixed with dental cements (Fuji II, Rely X Temp E, Ionoglass Cem, Es Temp NE, and System P link). Eight discs were fabricated from each zMgO-cement pair for a total of 32 specimens for each cement. Characterization of the dental cements incorporating zMgO was done by X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The antimicrobial properties of the mixtures were tested using direct contact and agar diffusion assays against Streptococcus mutans, Staphylococcus aureus, Enterococcus faecalis, and Candida albicans. Data was analyzed using two-way analysis of variance and LSD post hoc test at 0.05 significance level. XRD spectra showed sharp peaks of zMgO indicating its high crystalline nature, while the amorphous dental cements with zMgO had broad peaks. FESEM analysis showed a uniform distribution of the zMgO nanoparticles in the cement. There were significant inhibition zone values associated with all concentrations of zMgO-cement mixtures tested compared to controls (p < 0.001) with a dose-response recorded only with Fuji II. Optical density values were significantly lower in zMgO groups compared to controls for all microorganisms. The effect was most prominent with Rely X against C. albicans and S. aureus. Dental cements containing zMgO showed significant antimicrobial properties that were dependent on the specific initial cement substrate.

Keywords

Magnesium oxide nanoparticles
Antimicrobial biomaterials
Dental cement
Nanocoatings

1. Introduction

The success of indirect restorations needs a well organized approach to dental cements, restorative materials, and tooth preparation design [1]. Open margins of restorations occur due to defects in the prosthesis or disintegration of dental cements and is usually accompanied by bacterial microleakage leading to recurrent caries [2]. Recurrent caries formed in restoration margins, is a biofilm containing different bacteria such as Streptococcus mutans that produce acids leading to the dissolution of the mineral content of tooth structure [3]. Similarly, Staphylococcus aureus, Enterococcus faecalis, and Candida albicans play major roles in the pathogenesis of some oral diseases [4]. Elimination of bacterial colonization at the restoration margin can interfere with the pathogenesis of dental caries and periodontal disease at tooth-restoration interface [5]. Recurrent decay around dental restorations is still considered a major problem reaching between 50 and 60% of all restorations placed according to some reports [[6][7][8]]. Placing an antimicrobial agent at the restoration margin could potentially decrease microbial load and consequently recurrent caries [9].

Multiple active ingredients were previously added to dental cements in order to prevent bacterial colonization such as nhexametaphosphate microparticles, calcium phosphate, and silver ions [10]. These agents showed improvement in the antimicrobial effect, amount of fluoride delivered, and rate of demineralization, but caused a decrease in the mechanical properties of the cements [11,12]. Maintaining adequate mechanical properties of dental cements is paramount for the long-term service of dental restorations.

The use of nanotechnology in dentistry attained many researchers’ interest in the last few years. Metal oxide nanoparticles have been broadly used in mechanical and biomedical fields [13] since they produce reactive oxygen species that target bacterial metabolism in a variety of mechanisms decreasing the probability of bacterial resistance [14]. However, the promising aspect of nanoparticles like ZnO, AgO and TiO nanoparticles was hindered by biosafety and decrease in materials properties [[15][16][17][18][19]]. However, nanoparticulate MgO is a novel potent antibacterial agent that has been recently incorporated in dental materials to enhance their antibacterial properties. Nonetheless, MgO nanoparticles tend to aggregate and form clusters that can affect its utilization in dental applications [[20][21][22]]. A workaround is required in order to maintain an amorphous phase of the active nanocompound; thus, producing a consistent and prolonged antimicrobial effect.

The addition of zein polymer to the MgO nanoparticle formulation creates a coating that prevents the agglomeration of MgO particles. Zein is a naturally-occurring protein polymer that has a wide range of pharmaceutical applications [23]. The inherent properties of this polymer help it stabilizes particles against aggregation by decreasing the hydrophobic properties of these particles [24]. As reported previously, scanning and transmission electron microscopy images indicated significantly less aggregation of zMgO nanoparticles, while maintaining a nano-sized structure, when compared to pure MgO nanoparticles. Also, there was a 20% more sustained release of the active ingredient detected with zMgO nanoparticles in comparison to pure MgO [[25][26][27]]. Karimi and collaborators have reported that MgO nanowires have good mechanical properties allowing them to be used in dental cements [21,28,29]. Also, Noori and Kareem showed that the addition of MgO nanoparticles to glass ionomer cement enhanced its antimicrobial activity establishing a biocompatible antibacterial dental restorative cement [30]. Similarly, the antibacterial and mechanical properties of denture base materials were tested after the incorporation of MgO nanoparticles showing a significant reduction in the growth of Staphylococcus aureus [31].

Cements are an integral part of the materials utilized in dentistry. They have various applications such as being used as liners, bases, and affixing indirect restorations [28]. The chemistry of these cements is different and can range between glass ionomer-based, resin-based, and oxide-based materials [28]. The addition of antimicrobial agents to dental cements is a viable method to counteract colonization of oral microbes and potentially decreasing the side effect of microleakage. However, this effect could be dependent on the type of the dental cement.

To the authors’ knowledge, the effect of zMgO nanoparticles formulation on oral microbes has not been studied previously. Thus, the main objective of this study was to investigate the antimicrobial properties of common dental cements after incorporating zMgO nanoparticles. The null hypothesis of this study was that there will be no difference between the zMgO cements across the tested dental cements in terms of antimicrobial properties. The significance of this study is that enhancing the antimicrobial activities of dental cements will result in cements with superior biological properties that can enhance the longevity of the restorations and minimize recurrent caries.

2. Materials and methods

2.1. Experimental design

Five dental cements were used for the study from different manufacturers. Four concentrations of zMgO nanoparticles (0.0, 0.3, 0.5, and 1.0%) were mixed with five dental cements. Eight specimens from each cement concentration were…

https://www.sciencedirect.com/science/article/pii/S2452199X21002978

Nano grade magnesium oxide
Nano grade magnesium oxide

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