Original Article |
Corresponding author: Abbas Bahador ( abahador@sina.tums.ac.ir ) © 2022 Maryam Pourhajibagher, Abbas Bahador.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Pourhajibagher M, Bahador A (2022) Physico-mechanical properties, antimicrobial activities, and anti-biofilm potencies of orthodontic adhesive containing cerium oxide nanoparticles against Streptococcus mutans. Folia Medica 64(2): 252-259. https://doi.org/10.3897/folmed.64.e60418
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Introduction: White spot lesions around orthodontic brackets may lead to the formation of dental caries during and following fixed orthodontic treatment.
Aim: This study aimed to evaluate the physico-mechanical properties and antimicrobial potencies of orthodontic adhesive doped with cerium oxide nanoparticles (CeO2-NPs) against Streptococcus mutans.
Materials and methods: After synthesis and conformation of CeO2-NPs by transmission electron microscope (TEM), shear bond strength (SBS) and adhesive remnant index (ARI) of modified orthodontic adhesive containing different concentrations of CeO2-NPs (0, 1, 2, 5, and 10 wt%) were measured. The antimicrobial effects of modified orthodontic adhesive were evaluated by disk agar diffusion method and biofilm formation inhibition assay.
Results: The pseudo-spherical shapes of CeO2-NPs were observed in TEM micrographs. The physico-mechanical finding showed that 5 wt% CeO2-NPs showed the highest concentration of CeO2-NPs and SBS value (18.21±9.06 MPa, p<0.05) simultaneously with no significant differences in ARI compared with the control group (p>0.05). There was a significant reduction in cell viability of S. mutans with increasing CeO2-NPs concentration. The 3.1 Log10 and 4.6 Log10 reductions were observed in the count of treated S. mutans with 5 and 10 wt% CeO2-NPs, respectively (p<0.05).
Conclusions: Overall, an orthodontic adhesive containing 5 wt% CeO2-NPs had antimicrobial properties against S. mutans without adverse effects on SBS and ARI.
cerium oxide, cariogenic bacteria, orthodontic adhesive, shear bond strength, Streptococcus mutans
The composite resin bonding method in orthodontics is mainly used to attach the bracket to the tooth surface.[
Nanoparticles have high antimicrobial properties due to their small size. In addition to knowing the antimicrobial effects of nanoparticles, their effects on the bond strength between the bracket and the composite or bond strength of orthodontic cement are also important.[
Oral streptococci, especially Streptococcus mutans as the most important member of Viridans streptococci, are known to cause tooth decay and subsequent diseases by synthesizing extracellular polymers and forming biofilms on dental surfaces.[
Recently, the antimicrobial properties of cerium oxide nanoparticles (CeO2-NPs) and their applications in the field of medicine and other sciences have been considered, and the decision to combine these nanoparticles with resin composites used in orthodontics was taken.[
Therefore, this study aimed to investigate the antimicrobial and anti-biofilm properties of orthodontic adhesive doped with CeO2-NPs, as well as maintenance of sufficient shear bond strength (SBS) of orthodontic light-curing composite toward the eradication of S. mutans. Therefore, we tested the hypothesis that CeO2-NPs can act as an antimicrobial and anti-biofilm agent against S. mutans biofilm culture.
CeO2-NPs were synthesized using a modified hydrothermal method.[
For the preparation of modified adhesive containing 1, 2, 5, and 10 wt% CeO2-NPs, 12.5, 25, 62.5, and 125 mg of CeO2-NPs, respectively, were blended into 0.11, 0.22, 0.55, and 1.1 g of Transbond™ XT primer (3M Unitek, Monrovia, CA) as an orthodontic adhesive. The prepared samples were then de-molded, polished, and sterilized according to ISO 11135:1994 for medical devices[
Twenty freshly extracted bovine incisors with intact buccal enamel and with no cracks or any lesions were collected, immersed in 0.5% of chloramine T trihydrate (Sigma Aldrich Chemie GmbH, Taufkirchen, Germany) at 4°C for seven days, and embedded in cold-cure acrylic resin according to ISO/TS 11405:2003. The surfaces of all teeth were cleaned, polished, and rinsed with air-water spray for 10 s and air-dried for 10 s. Thirty-five percent of phosphoric acid gel (Ultra etch; Ultradent Products Inc., South Jordan, UT, USA) was used to etch the buccal surfaces of all teeth. After 20 s, the teeth were rinsed with water for 10 s, and dried with air for 10 s. Then, the etched area of the buccal surface of all teeth was covered with a thin layer of CeO2-NPs at the different concentrations (1, 2, 5, and 10 wt%) and cured with a LED light-curing unit (Demetron, Kerr, Orange, CA, USA). According to the Felemban and Ebrahim study[
ARI score in debonding of stainless-steel brackets from enamel surface was assessed by a stereomicroscope (SMZ800, Nikon, Tokyo, Japan) at ×10 magnification based on the Oliver and Griffiths study.[
S. mutans (ATCC 35668) was cultured in brain heart infusion (BHI) broth (Merck, Darmstadt, Germany) supplemented with 0.1% sucrose and incubated in an aerobic atmosphere with 5% CO2 at 37°C. A 0.5 McFarland standard bacterial suspension (1.5×108 colony forming units (CFUs)/mL) was prepared to examine the antimicrobial efficacy of orthodontic adhesive doped with CeO2-NPs.
Disk-shaped modified orthodontic adhesive patterns were prepared using metal molds 5 mm in diameter and 1 mm thick. Modified orthodontic adhesive disks containing different concentrations of CeO2-NPs were made by the fabrication of CeO2-NPs adhesives section. According to the ISO 11135:1994, prepared disks were then exposed to light cure for 40 s, de-molded, polished, and sterilized.[
Disk agar diffusion test by the Kirby-Bauer method was done to determine the antimicrobial features of orthodontic adhesive by zones of growth inhibition around each of the samples.[
Twenty-five orthodontic adhesive disks with different concentrations of CeO2-NPs were placed in flat-bottomed 48-well microtiter plates containing S. mutans suspension with a concentration of 1.5×108 CFU/mL. To form biofilms on the disks, the microtiter plate was incubated under the aerobic atmosphere with 5% CO2 at 37°C for 72 hours. Afterwards, disks were rinsed in 1 mL of sterile deionized water for 1 min to remove planktonic microbial cells. Orthodontic adhesive disks were then vortexed severely in 1 mL of BHI broth for 30 s. The obtained bacterial suspensions were serially diluted, cultured in mitis salivarius agar (Merck, Darmstadt, Germany), and the microbial colony counts were determined as mentioned in the previous study.[
The microbial experiments were done in triplicate and the data were analysed using one-way analysis of variance (ANOVA). Statistical analysis was performed using SPSS for windows version 23.0 (SPSS Inc., Chicago, IL, USA). P values <0.05 were considered statistically significant.
The data of SBS of orthodontic adhesive doped with different concentrations of CeO2-NPs are presented in Table
The mean of shear bond strength (SBS) of orthodontic adhesive doped with CeO2-NPs
Orthodontic adhesive doped with CeO2-NPs (%) | SBS (MPa) | ||
Minimum | Maximum | Mean ± SD | |
0 | 18.52 | 40.65 | 30.42±11.15 |
1 | 16.26 | 38.12 | 25.02±11.55 |
2 | 13.38 | 30.40 | 20.56±8.81 |
5 | 10.37 | 28.14 | 18.21±9.06 |
10 | 5.28 | 10.14 | 7.75±2.43* |
The frequencies of ARI scores in the test groups are shown in Table
Orthodontic adhesive doped with CeO2-NPs (%) | ARI scores | ||||
0.00 | 1.00 | 2.00 | 3.00 | 4.00 | |
0 | 0 | 2 | 2 | 2 | 3 |
1 | 1 | 2 | 2 | 3 | 3 |
2 | 0 | 2 | 2 | 3 | 3 |
5 | 1 | 2 | 3 | 3 | 3 |
10 | 1 | 3 | 4 | 5 | 2 |
Cell viability of S. mutans according to the percentages of CeO2-NPs incorporated into orthodontics adhesive: A) different concentrations of CeO2-NPs against S. mutans; B) Colonies of treated S. mutans following different concentrations of CeO2-NPs: a. Control (untreated S. mutans); b. 0 wt% CeO2-NPs; c. 1 wt% CeO2-NPs; d. 2 wt% CeO2-NPs; e. 5 wt% CeO2-NPs; f. 10 wt% CeO2-NPs.
The antimicrobial property of orthodontic adhesive disks containing different concentrations of CeO2-NPs was assessed using the release of nanoparticles from the disks. No growth inhibition zone was observed around any of the disks. This indicates that the CeO2-NPs were not able to be released at the plate surface.
As shown in Fig.
Bonding brackets to teeth is one of the common methods in orthodontic treatment.[
Another complex problem in fixed orthodontic treatments is the control of enamel demineralization around the brackets used during treatment. Brackets and various tools used in orthodontic treatments make oral hygiene more difficult and, according to some studies, increase the number of oral bacteria.[
It should be noted that the composites used in orthodontics have a polymer matrix that is involved in the accumulation of aerobic and anaerobic microorganisms. The formation of supragingival biofilm is mainly seen around orthodontic attachments in clinical studies. The main cause of dental caries is S. mutans. S. mutans is a Gram-positive, optional anaerobic coccus that is the oral cavity flora in humans.[
Nanotechnology can be used effectively to maintain oral health. In particular, nanoparticles are useful antimicrobial agents for bonding and orthodontic appliances. They can also be used in dental restorations such as cavities, sealants, and root canals. Its antimicrobial ability reduces plaque around the brackets, which can prevent decay during treatment.[
Due to the problem of decalcification and decay around orthodontic brackets, various research studies have been done on the effect of using antimicrobial and anti-decay materials.[
The relevant literature shows that CeO2-NPs are widely used as a catalyst in industry and as an antioxidant in applied nanomedicine. The antimicrobial mechanism of CeO2-NP action probably occurs via oxidative stress of components in the microbial cell membrane and accumulation of oxygen reactive species in microbial cells.[
Moreover, in this study, the antimicrobial potential of orthodontic adhesive doped with different concentrations of CeO2-NPs was evaluated. Similar to previous studies[
Pelletier et al.[
One of the important aspects of using nanoparticles is their toxicity. Although the evidence is insufficient, nanoparticles do not appear to be more toxic than conventional materials. Due to the wide scope of nanotechnology and the lack of studies on the effects of nanoparticles on SBS of orthodontic adhesives, as well as the physical properties of orthodontic acrylics, further studies are proposed to clarify these aspects. Also, clinical trial studies should be performed to confirm the anti-caries properties of orthodontic adhesive doped with CeO2-NPs.
In overview, this study demonstrated that 5 wt% CeO2-NPs as an orthodontic adhesive with a clinically acceptable score of SBS and ARI had antimicrobial and anti-biofilm activities against S. mutans. However, we acknowledged that further evaluation of these activities of cerium oxide nanoparticles against cariogenic bacteria in multi-species biofilm structure is warranted.
This research was supported by Tehran University of Medical Science.
Disclosure statement
No potential conflict of interest was reported by the authors.